Evaluation and Verification of Aerosol Diluters: …...Exhaust Measurement and Inhalation Toxicology Testing of Emerging Diesel Fuel study group members – Naomi Zimmerman, Krystal

Evaluation and Verification of Aerosol Diluters:

Accuracy and Particle Loss

by

Terry Hoon Suk Jung

A thesis submitted in conformity with the requirements

for the degree of Master of Applied Science and Engineering

Graduate Department of Mechanical and Industrial Engineering

University of Toronto

© Copyright by Terry Hoon Suk Jung 2014

ii

Evaluation and Verification of Aerosol Diluters: Accuracy and Particle Loss

Terry Hoon Suk Jung

Master of Applied Science and Engineering 2014

Department of Mechanical and Industrial Engineering

University of Toronto

Abstract

The aerosol diluter characteristics of three different systems, the single-stage and the two-

stage TSI 379020A rotary disk thermodiluters and Dekati FPS-4000 ejector diluter, were tested

using gases and particles over a range of dilution ratios. The upstream and downstream gas and

particle concentrations of the diluters were measured in real-time to compute the actual dilution

ratio achieved by the three systems. Dilution ratios from approximately 15 to 100 were found to

fall within the expected operating error margin of ± 10% for CO2 and CH4. Dilution ratios covering

a similar range were also achieved to within ± 10% for particles with diameters from 9.3 to 200

nm. However, when engine exhaust was sampled, significant loss of particles smaller than 29.4

nm occurred during the dilution process. As the dilution ratio increased, the deviation from the

expected value increased due to an increase in measurement uncertainty.

iii

Acknowledgements

First and foremost I would like to thank Professor Wallace and Professor Evans for their

insightful guidance and support through this process. I would also like to extend my thanks to all

of the laboratory mates and staff in the Engine Research and Development Laboratory and

Southern Ontario Center for Atmospheric Aerosol Research, with a special thanks to The

Exhaust Measurement and Inhalation Toxicology Testing of Emerging Diesel Fuel study group

members – Naomi Zimmerman, Krystal Godri-Pollitt, Cheol-Heon Jeong and Josephine Cooper.

Finally, I would like to give my profound thanks to my parents, grandparents and brother

for their never ending support of all my pursuit in life. Without their support and encouragement,

this work may have never been completed.

iv

Table of Contents

Abstract ………………………………………………………………………………………….. ii

Acknowledgements ……………………………………………………………………………... iii

Table of Contents ………………………………………………………………………………... iv

List of Figures ………………………………………………………………………………….. viii

List of Tables …………………………………………………………………………………….. xi

List of Acronyms ……………………………………………………………………………….. xii

List of Symbols ………………………………………………………………………………… xiv

Chapter 1 Introduction ………………………………………………………………………... 1

1.1 Introduction …………………………………………………………………………... 1

1.2 What is an Aerosol? …………………………………………………………………... 2

1.3 Properties of Aerosol …………………………………………………………………. 3

1.3.1 Dynamics of Single Aerosol Particle …………………………………………… 4

1.3.2 Dynamics of Aerosol Populations ………………………………………………. 6

1.4 Why Study Automotive Aerosol? …………………………………………………….. 7

1.5 Other Related Concern: Visibility Degradation ………………………………………. 7

1.6 What is Aerosol Dilution? …………………………………………………………….. 8

1.7 Literature Review …………………………………………………………………… 12

1.7.1 Nucleation of Nanoparticles …………………………………………………... 12

1.7.2 Influence of Dilution Condition ……………………………………………….. 14

1.7.3 Ultrafine Diesel Exhaust Particles …………………………………………….. 16

1.7.4 Emission Regulations …………………………………………………………. 18

1.7.5 Diesel Engine Improvements ………………………………………………….. 18

v

1.7.6 Emission Control Technologies Improvements ……………………………….. 20

1.7.7 Summary ….…………………………………………………………………… 21

1.8 Objectives …………………………………………………………………………… 21

Chapter 2 Aerosol Diluter Review …………………………………………………………... 23

2.1 Introduction …………………………………………………………………………. 23

2.2 Description of Diluters ………………………………………………………………. 23

2.2.1 TSI 379020A Rotary Disk Thermodiluter ……………………………………... 23

2.1.2 Dekati FPS-4000 Ejector Diluter ……………………………………………… 25

2.3 Aerosol Diluter Systematic Comparison …………………………………………….. 27

2.4 Known Problems of Aerosol Diluters ……………………………………………….. 29

Chapter 3 Description of Test Instrumentation ……………………………………………… 32

3.1 Introduction …………………………………………………………………………. 32

3.2 Gas Concentration Measurement ……………………………………………………. 32

3.2.1 Heated Flame Ionization Detector …………………………………………….. 32

3.2.2 Non-dispersive Infrared Gas Analyzer ………………………………………… 34

3.3 Particle Number Measurement ……………………………………………………… 36

3.3.1 EEPS/FMPS …………………………………………………………………... 36

3.4 Soot Generator ………………………………………………………………………. 40

Chapter 4 Evaluation of Dilution in the Diluter Systems using the Gas Phase Species …….. 42

4.1 Introduction …………………………………………………………………………. 42

4.2 Dilution Evaluation Apparatus ……………………………………………………… 42

4.3 Dilution Evaluation Methods ………………………………………………………... 45

4.4 Sampling Time Parameters ………………………………………………………….. 48

4.5 Leakage Check ……………………………………………………………………… 48

4.6 Calculation Methods ………………………………………………………………… 49

vi

4.7 Results ………………………………………………………………………………. 50

4.7.1 Single-Stage TSI 379020A Rotary Disk Thermodiluter ……………………….. 50

4.7.2 Two-Stage TSI 379020A Rotary Disk Thermodiluter …………………………. 53


4.8 Error Analysis and Discussion of Results …………………………………………… 57

Chapter 5 Particle Loss in Aerosol Diluters …………………………………………………. 64

5.1 Introduction …………………………………………………………………………. 64

5.2 Particle Loss Measurement Apparatus ………………………………………………. 64

5.2.1 Diesel Emission Test Apparatus ……………………………………………….. 65

5.2.2 Soot Generator Test Apparatus ………………………………………………... 68

5.3 Particle Loss Measurement Methods ………………………………………………... 70

5.4 Sampling Time Parameters ………………………………………………………….. 72

5.5 Leakage Check ……………………………………………………………………… 72

5.6 Calculation Methods ………………………………………………………………… 73

5.7 Results ………………………………………………………………………………. 74

5.7.1 Single-Stage TSI 379020A Rotary Disk Thermodiluter ……………………….. 74

5.7.2 Two-Stage TSI 379020A Rotary Disk Thermodiluter …………………………. 84


5.8 Investigation of Heating and Thermal Conditioning Elements ……………………… 98

5.8.1 TSI 379020A Rotary Disk Thermodiluter ……………………………………... 99

5.8.2 Dekati FPS-4000 Ejector Diluter …………………………………………….. 103

5.9 Error Analysis and Discussion of Results ………………………………………….. 104

Chapter 6 Conclusions and Recommendations …………………………………………….. 110

6.1 Conclusions ………………………………………………………………………... 110

6.2 Recommendations …………………………………………………………………. 111

Appendices ……………………………………………………………………………………. 114

vii

Appendix A Preliminary Experiment Result for Single-Stage TSI 379020A

using Methane Gas ……………………………………………………….. 114

Appendix B Derivation of Uncertainty Analysis Equations …………………………… 116

References …………………………………………………………………………………….. 118

viii

List of Figures

Figure 1-1 Photomicrograph of Diesel Particulates: Cluster (Upper Left), Chain

(Upper Right), and Collection from Filter (Heywood, 1988) ………………….. 3

Figure 1-2 General Aerosol Dilution Process ………………………………………………… 9

Figure 2-1 Principle of Dilution Method for TSI 379020A (TSI, 2009) …………………….. 24

Figure 2-2 TSI 379020A Single and Two-Stage Layout (TSI, 2009) ………………………... 25

Figure 2-3 Principle of Dilution Method for Dekati FPS-4000 (Dekati, 2010) ……………... 27

Figure 3-1 Flame Ionization Detection Technology

(Rosemount Analytical NGA 2000 Manual) ………………………………….. 33

Figure 3-2 Non-dispersive Infrared Detector Technology (LI-COR, 2009) …………………. 36

Figure 3-3 Differential Mobility Analyzer Technology (TSI, 2004) ………………………… 37

Figure 3-4 EEPS Concentration Range (TSI, 2012) …………………………………………. 39

Figure 3-5 FMPS Concentration Range (TSI, 2004) ………………………………………… 39

Figure 3-6 Soot Generator Technology (Jing, 2009) ………………………………………… 40

Figure 3-7 Quenching Gas Flow Rate Dependent Soot Particle Size Distribution ………….. 41

Figure 4-1 Dilution Evaluation Apparatus for the TSI 379020A (Left)

and the Dekati FPS-4000 (Right) ……………………………………………... 43

Figure 4-2 Diluted CO2 Concentration Measurement at Various Dilution Ratios

for the Single-Stage TSI Diluter ………………………………………………. 51

Figure 4-3 Experimental Dilution Ratios for the Single-Stage TSI Diluter …………………. 52

Figure 4-4 Diluted CO2 Concentration Measurement at Various Dilution Ratios

for the Two-Stage TSI Diluter ………………………………………………… 53

Figure 4-5 Experimental Dilution Ratios for the Two-Stage TSI Diluter …………………… 54

Figure 4-6 Diluted CH4 Concentration Measurement at Various Dilution Ratios

for the Dekati Diluter ………………………………………………………….. 55

Figure 4-7 Experimental Dilution Ratios for the Dekati Diluter …………………………….. 57

Figure 5-1 Diesel Exhaust Particle Loss Test Apparatus for Diluters ……………………….. 66

Figure 5-2 Soot Generator Particle Loss Test Apparatus for Diluters ……………………….. 69

ix

Figure 5-3 EEPS/FMPS Equivalency Correction Factor (Zimmermann et al, 2013) ……….. 71

Figure 5-4 Engine Exhaust Particle Distribution at Various Dilution Ratio


Figure 5-5 Engine Exhaust Experiment Percent Particle Penetration


Figure 5-6 Engine Exhaust Experimental Dilution Ratios


Figure 5-7 Soot Generator Particle Distribution at Various Dilution Ratio


Figure 5-8 Soot Generator Experiment Average Percent Particle Penetration


Figure 5-9 Soot Generator Experimental Dilution Ratios









for the Two-Stage TSI Diluter ……………………………………………….... 88









x









Figure 5-22 Engine Exhaust Dilution Ratios Corresponding to

the Primary Dilution Air Temperature

for the Single and Two-stage TSI Diluters …………………………………….. 99

Figure 5-23 Engine Exhaust Percent Particle Penetration Corresponding to

the Evaporation Tube Heater Temperature

for the Two-Stage TSI Diluter ……………………………………………….. 100









for the Dekati Diluter ………………………………………………………… 103



for the Dekati Diluter ………………………………………………………… 104

Figure A-1 Diluted CH4 Concentration Measurement at Various Dilution Ratios

For the Single-stage TSI Diluter ……………………………………………... 115

xi

List of Tables

Table 2-1 Aerosol Diluters Specification Summary Table (TSI, 2009; Dekati, 2010) ………. 28

Table 2-2 Percent Particle Penetration Values for Varying Particle Sizes for the Diluters …... 30

Table 4-1 Table of Uncertainty Analysis for TSI Diluter Experimental Apparatus …………. 61

Table 4-2 Table of Uncertainty Analysis for Dekati Diluter Experimental Apparatus ………. 62

Table 5-1 Summary of Average Percent Dilution Ratio Difference

and Highest Deviation Point for the Single-Stage TSI Diluter ………………... 84


and Highest Deviation Point for the Two-Stage TSI Diluter ………………….. 91


and Highest Deviation Point for the Dekati Diluter …………………………… 98

Table 5-4 Table of Uncertainty Analysis for Experimental Apparatus ……………………... 107

xii

List of Acronyms

BTE Brake Thermal Efficiency

DHT Dilution Air Heating Temperature

DMA Differential Mobility Analyzer

DOC Diesel Oxidation Catalyst

DPF Diesel Particulate Filter

DPM Diesel Particulate Matter

DR Dilution Ratio

EEPS Engine Exhaust Particle Sizer

EGR Exhaust Gas Recirculation

EHT Evaporation Heater Temperature

EMITTED Exhaust Measurement and Inhalation Toxicology Testing of

Emerging Diesel Fuels

FMPS Fast Mobility Particle Sizer

GSA Gaseous Sulfuric Acid

HC Hydrocarbon

HDD Heavy-Duty Diesel

HEI Health Effects Institute

HFID Heated Flame Ionization Detector

LDD Light-Duty Diesel

LNT Lean NOx Trap

NDIR Non-Dispersive Infrared

NMP Nucleation Mode Particle

NTE Not-to-Exceed

OXICAT Oxidation Catalyst

PDR Particle Dilution Ratio

PDT Primary Dilution Temperature

PM Particulate Matter

xiii

PMP Particulate Measurement Program

PRDR Primary Dilution Ratio

PRH Primary Dilution Relative Humidity

RR Relative Risk

RT Residence Time

SCR Selective Catalytic Redcution

SI Spark-Ignition

SVI Sulfur VI

VDR Volumetric Dilution Ratio

xiv

List of Symbols

∝ Related to

ρ Density

≈ Approximately equal to

~ Approximately

�� Potentiometer dial number of the primary and secondary flow settings

for TSI 379020A diluter

�� Diameter of particles

�� Dilution ratio of sample �� Average dilution ratio of sample �� Rate of carbon atom input

� Electrical current

�� Ionization rate of hydrocarbon

∑�� Sum of mass of particles �� Concentration of sample �� Average concentration of sample ∑�� Sum of concentration of particles

� �� Loss/Conversion rate of particle number

� Particle penetration value

�� Particle number

�� Volumetric flow of sample �� Volumetric flow rate of sample �� Variance of the average measured value of sample � ! Standard deviation for any function R

[$%&] Total hydrocarbon concentration

( Volume

1

Chapter 1

Introduction

1.1 Introduction

Diesel and gasoline fuel combustion is a major source of atmospheric air contaminants.

Further, a range of adverse human health effects are associated with particulate matter (PM) from

engine emissions. Numerous studies report that long term human exposure to PM results in

increased risk of cardiac ischemia and arrhythmias, increased blood pressure, decreased heart rate

variability, and increased circulating markers of thrombosis and inflammation (Froines, 2005).

Ultrafine particles are categorized as the particles smaller than 100 nm in diameter. Inhalation and

exposure to ultrafine particles, especially to the volatile fraction of such particles, is hypothesized

to induce acute cardiopulmonary responses and compromise cardiorespiratory status. Existing

regulations cover particles > 2.5 µm in diameter (PM2.5). Compared to the PM2.5 standard, the

mass of these ultrafine particles is relatively small and yet they are more effective in transporting

hazardous substances absorbed on their surface due to their high surface area to mass ratio

compared to larger particles (Stoeger, 2006; Oberdörster, 2000).

Studies of air pollution exposure and mortality suggest that the cardiopulmonary mortality

is associated with living near a high traffic density area. People living within 100 m of a freeway

or 50 m of a major urban road had their cardiopulmonary mortality relative risk (RR) value

increased to 1.95 (Hoek et al, 2002). The RR value is a ratio of the probability of the event

occurring in the exposed people compared to non-exposed. Hence the RR value of 1.95 indicates

that people living near a high traffic density area have 1.95 times higher risk of cardiopulmonary

2

mortality. In addition, wheezing in school children living within 150 m of a main road increases

RR to 1.08 (Venn et al, 2001).

Awareness of the potential risk of ultrafine particles leading to adverse effects is increasing.

Studies pertaining to ultrafine particles are valuable in order to characterize the effectiveness of

current automotive combustion and emission control technologies, and to address adverse health

related concerns.

1.2 What is an Aerosol?

An aerosol is a gaseous suspension of fine and liquid particles. It can be a typical cloud in

the sky or undesired air pollutions such as automotive exhaust and smog. Under typical

atmospheric conditions, the sizes of aerosol particles measured vary with different contributing

factors for specific size ranges. For instance, human activities, including combustion processes,

contribute primarily to the submicron size range. The aerosol from primary natural sources, such

as sea salt and soil dust, is concentrated in the size range larger than 1.0 µm diameter. Also, the

mode in the volume distribution that occurs in the 0.1 to 1.0 µm diameter range results from the

growth of particles by gas-phase chemical reactions with condensable products (gas-to-particle

conversion). Regardless of where the aerosol comes from, exposure to these particles is

unavoidable. Therefore the surrounding atmospheric particles are studied to understand and define

what is breathed in.

The particles in diesel engine exhaust are referred to as the organic and inorganic species

that can exist in both liquid, such as hydrocarbons, water, and sulfuric acid, and solid, such as

elemental carbon and ash. Also some droplets of liquid content can exist, which can provide

coating for the solid particles. Representative images of diesel particulates are shown in Figure 1-

3

1, which includes photomicrographs of diesel particulates in a cluster, in a chain, and a selection

collected from a filter.

Figure 1-1

Photomicrographs of Diesel Particulates: Cluster (Upper Left), Chain (Upper Right), and

Collection from Filter (Heywood, 1988)

1.3 Properties of Aerosol

The study of aerosol physico-chemical properties is crucial in explaining why certain

particles behave in a particular way and how they are formed. The particles can undergo various

chemical or physical processes as they move from one place to another. Such knowledge aids in

4

determining the fate of the pre-existing and emitted particles in the atmosphere. The overview of

aerosol properties in this section is based on the textbook by Senifeld and Pandis (2006).

1.3.1 Dynamics of Single Aerosol Particle

The mean free path of a gas molecule can be defined as the average distance travelled

between collisions with other gas molecules, The mean free path of an aerosol particle is difficult

to define because the aerosol particles collide only very infrequently with other particles. In a case

where the collision actually occurs, it is usually assumed that the two particles adhere to each other.

The aerosol particles have large size and mass relative to gas molecules. Thus, they experience a

large number of collisions per unit time with the surrounding gas molecules and are not influenced

significantly by any one collision. Consequently, the motion of an aerosol particle can be seen as

continuous in nature.

In the elementary kinetic theory of gases, transport properties such as viscosity, thermal

conductivity, and molecular diffusivity are related to the mean free path by the flux of gas

molecules across planes separated by a distance. Therefore, the diffusional mean free path is

defined in terms of the molecular diffusivity of the vapor and its mean speed.

The most important concept that explains the dynamics of aerosol particles is Brownian

motion. Brownian motion refers to the particles suspended in a fluid undergoing irregular random

motion due to bombardment by surrounding fluid molecules. It can be described as a diffusion

process. A particle of sufficiently large size, approximately 100 µm, would experience only the

drag force and its motion would be unaffected by the molecular bombardment. However, if the

diameter of the particle is continually reduced, the fluctuations in its motion due to molecular

bombardment become increasingly noticeable and Brownian motion becomes dominant. As the

5

particle gets smaller, the force associated with Brownian motion must be considered in addition to

gravitational and drag forces. To further explain, Brownian diffusion is comparable to gravitational

settling in terms of the distance that a particle travels in both cases (Seinfeld and Pandis, 2006):

1. Over a period of 1 s, a 1 µm radius particle diffuses a distance of 4 µm, while it falls

about 200 µm under gravity.

2. Under the same time period, a 0.1 µm radius particle diffuses a distance of 20 µm

compared to a distance of 4 µm due to gravity.

The temperature of a Brownian particle suspended in a fluid is the same as that of the fluid,

but the kinetic energy of its motion must be determined from the kinetic energy of the molecules

of the fluid. The transfer of kinetic energy to the Brownian particle must be accompanied by a

local cooling of the fluid. Thus, small random fluctuations in temperature about the equilibrium

temperature always exist.

Phoretic effects produce a directional preference in the Brownian diffusion of aerosol

particles due to a difference in momentum imparted to a particle by molecules coming from

different directions. The directional preference depends on the local gradient of molecular

momentum caused by a difference in energy, or velocity, or by differences in mass. Phoretic effects

in the Brownian diffusion can be categorized into three types. Thermopheresis is the particle

motion caused by the higher energy molecules on one side of the particle due to a macroscopic

temperature gradient. This result causes the aerosol particles to diffuse away from warmer regions

toward cooler regions. Photophoresis results when incident radiation heats one side of the particle

more than the other, leading to differences in the energies of gas molecules adjacent to the surface

of the particle. Diffusiophoresis occurs in the presence of a gradient of vapor molecules that are

6

either lighter or heavier than air molecules due to a balance in the directional fluxes between the

two molecules.

1.3.2 Dynamics of Aerosol Populations

The aerosol particles suspended in a fluid may come into contact because of their Brownian

motion. They evolve in size by coagulation and gas-to-particle conversion or condensation. It has

been found that 0.01 µm to 1.0 µm particles grow principally by gas-to-particle conversion, the

process by which vapor molecules diffuse to the surface of a particle and subsequently are

incorporated into the particle. The rate-controlling step in condensation may be a result of one or

a combination of these three mechanisms (Seinfeld and Pandis, 2006):

1. The rate of diffusion of the vapor molecule to the surface of the particle (diffusion-

controlled growth).

2. The rate of a surface reaction involving the absorbed vapor molecule and the particle

surface (surface reaction-controlled growth).

3. The rate of a reaction involving the dissolved species occurring uniformly throughout

the volume of the particle (volume reaction-controlled growth).

The understanding of Brownian motion and condensation mechanisms allow us to describe

how the aerosol particles will behave when subjected to varying conditions. The aerosol particles

found in the atmosphere can be very small, which makes them difficult to trace and analyze. As

such, when studying these particles, it is important to recognize the governing principles to further

identify why a certain phenomenon has occurred.

7

1.4 Why Study Automotive Aerosol?

The exhaust particles emitted from diesel and spark-ignition (SI) engines are of concern to

engine builders for their influence on engine performance and wear. Not only that, but the focus

has been shifted towards the health and environmental impacts that these engine-emitted particles

induce, more so for diesel than SI engines.

The inhalation of air is a natural process to provide oxygen throughout the body. Thus,

breathing of the surrounding atmospheric air is inevitable. Studies have shown that PM can induce

health related problems, not to mention that pollutants can cause serious environmental issues.

Thus it is important to characterize aerosol in automotive emissions to help avert adverse effects,

whether on health or the environment.

1.5 Other Related Concern: Visibility Degradation

One concern arising from automotive aerosol emissions is visibility reduction. The

prevailing visibility is defined as the greatest distance in a given direction for which it is just

possible to see and identify an object. Absorption and light scattering are the two effects that

aerosol particles have on visible radiation which causes the visibility reduction. Light scattering is

usually the more important phenomenon responsible for visibility impairment. Visibility is reduced

due to significant scattering of light into the line of sight, which decreases the contrast between the

object and the background sky. The scattering by PM of sizes comparable to the wavelength of

visible light is responsible for visibility reduction. Particles in the range of 0.1 to 1 µm in radius

are the most effective per unit mass. The scattering coefficient is directly dependent on the

atmospheric aerosol concentration in this range. Scattering by particles causes 60 to 95 percent of

visibility reduction. The chemical species sulfates, nitrates, and organics are the main contributors

8

to the light-scattering coefficient. Sulfate, SO42- is often the most important scattering material,

followed by organic carbon.

In many cases, light absorption by black carbon particles is a significant contributor to

visibility reduction. Black carbon is more effective than non-absorbing aerosol particles in

attenuating light. Absorption by soot particles causes 5 to 40 percent of visibility reduction. Soot

is about three times more efficient than SO42-, NO3

-, or organics in terms of visibility reduction per

unit mass of airborne particles (Seinfeld and Pandis, 2006).

1.6 What is Aerosol Dilution?

Before the composition and concentration of the raw PM from an engine can be studied,

the exhaust must be diluted by a known factor in order to cool the exhaust and reduce the

concentrations to values within the ranges of the instruments available. The PM concentration

released from engine exhaust is orders of magnitude higher than the mixture (of air and exhaust)

found in the atmosphere. The process of dilution is a simple act to reduce this raw amount by a

known ratio in order to obtain a condition more representative of the air we breathe. In certain

cases, dilution is performed to reduce the concentration below the maximum detection capacities

of the particle analyzers. In automotive studies, a dilution process is essential in all parts of

emissions experiments. Therefore, it is crucial to identify the operating behavior of the dilution

system prior to carrying out an extensive experimental matrix. In a general dilution process, the

number of particles per unit volume in the given raw sample stream is reduced by introducing a

particle-free air flow.

The generalized premise of a dilution process is described in Figure 1-2. The volumetric

flowrate from the upstream, Qupstream (volume/unit time), with concentration Nupstream (particle

9

number/unit volume) is mixed with the dilution flowrate, Qdilution, with concentration Ndilution at a

certain ratio. During the dilution phase, associated size dependent particle loss,

�� ,�� (particle number/unit time) occurs at some rate where PN denotes the particle

number. The outflow from the process, Qdownstream, with concentration Ndownstream is the diluted

sample with a defined dilution ratio (DR).

Figure 1-2

General Aerosol Dilution Process

Assuming constant pressure and temperature and density, the conservation of particle

number and the volumetric flow rate equations of the flow in Figure 1-2 are described as (Collins,

2010)

�� ,�� ,�� , ��

�� ,�� ,�� Equation 1-1

�� Equation 1-2

10

Using the assumption that the dilution flow is particle-free, ��,�� 0, and

neglecting the effect of coagulation, evaporation and associated losses such as wall deposition and

diffusion, �� , �� ,�� 0, the appropriate DR can be described as

!�� "#$%&'()�*+,-$&'() �

."#$%&'()/.*01"%0+-."#%&'() Equation 1-3

This equation is defined as the volumetric DR of the process since it is dependent only on the

volumetric flow with zero particle loss – other terms are assumed negligible.

Similarly, the particle size dependent DR, defined as the particle DR, can be generalized

as

!�� ,�� "#$%&'(),$02'3*#-*�*+,-$&'(),$02'3*#-* Equation 1-4

However in case where a loss is present such that �� ,�� ≠ 0 but all other

assumptions remain valid, �� , �� ,�� 0, then Equation 1-1 can be

rewritten as

1 �� ,�� ,�� ,�� ,�� 6�� 7

Equation 1-5

Using the previous Equations 1-3 and 1-4, the above expression can be simplified to

11

1 �� ,�� ,�� !��,�� !�� ,�� 8��

Equation 1-6

where 8�� is defined as the (diluter) penetration number (Collins, 2010). The

particle penetration number quantifies the fraction of particles lost during the dilution process. In

this expression, unity is defined as the condition where there are no particle losses present in the

system. This is referred to as an “ideal dilution”, meaning that a particle DR equal to that of the

volumetric DR has occurred in all particle size distributions. It should be noted that such a

condition is most unlikely to occur in a typical operating condition. Frequently, the value of P will

be lower or greater than unity. The case where the value of P falls below unity describes a system

in which particle loss is present, where the DRparticle is greater than the DRvol. In contrast, when the

value of P rise above unity, the system is generating particles when DRparticle is less than the DRvol.

Apparent particle generation in the system might occur due to condensation on particles in a certain

particle size range during the dilution process. The resulting particle growth would cause a shift of

size distribution causing a reduction of particle number in smaller size bins and an increase in

larger size bins.

It is important to note that such particle generation or loss present within the dilution

system can result in a skewed outcome when measuring the concentration of the raw exhaust. In

emission testing and aftertreatment technology development, it is crucial to discern the mode

particle size. Consequently, a thorough investigation of the operating diluter is necessary to avoid

any misrepresentation of the data.

12

1.7 Literature Review

The chemical and physical properties of diesel particulate matter (DPM) can vary for

different fuels and emission control technologies. Many studies have characterized the influences

of biodiesel fuel and the aftertreatment systems, but further investigation is still required. Such

technologies include the diesel particulate filter (DPF) for removal of PM or soot from the diesel

emissions and selective catalytic reduction (SCR) systems for converting NOx into diatomic

nitrogen and water. In all of these research areas, it should be noted that an appropriate aerosol

dilution technology is necessary to make accurate measurements of system performance. Thus, in

order to provide context for PM measurement requirements, the underlying relevant research

papers from the literature are reviewed to provide an overview of the current state of these

technologies.

This review provides an overview of the basic characteristics of nucleation of nanoparticles,

the influence of dilution condition on particle number measurement, the investigation of ultrafine

diesel exhaust particles, diesel emission regulations, and the improvements in diesel emission

control strategies. Unless stated otherwise, the literature reviewed in this section relates to diesel

engines (Note that gasoline direct injection engines also produce particles).

1.7.1 Nucleation of Nanoparticles

Kittelson (1998) describes diesel exhaust particles as consisting mainly of highly

agglomerated solid carbonaceous material and volatile organic and sulfur compounds. The

particles are classified into different modes depending on the particle diameter: accumulation and

nuclei mode. Most particle mass exists in the accumulation mode range from 50 -500 nm in

diameter. In contrast only 5-20% of the particle mass is contributed by the nuclei mode, D < 50

13

nm. However, more than 90% of the total particles by number, exist in this mode.

Studies by many institutes and research centers have raised concerns about the increase of

nanoparticle emissions from new diesel engine technologies (Kittelson 2001, Heikkilä et al. 2009,

Park et al. 2009). Although the newly developed engine reduce particle mass emissions, the

number emissions of these nanoparticles sharply increases. Kittelson (1998) postulated that

particle formation by future engines would rely on the relative amount of condensable species and

solid surface area on which the vapor species can condense or absorb. Furthermore, the primary

composition of these nanoparticles must be characterized, because if these particles are volatile,

they may have different health impacts than solid particles.

The nanoparticle number emissions from diesel engines are mostly found in the nucleation

mode. Exhaust gas cooling and dilution in the atmosphere induces nucleation, which leads to the

formation of these nanoparticles. Concerns about nanoparticles have been raised because of their

adverse human health effects. There have been numerous studies done to explain the nanoparticle

nucleation mechanism.

Some authors suspect ion-induced nucleation as the mechanism describing the formation

of nucleation mode particles (NMPs) (Yu et al., 2001, 2002, 2004; Ma et al., 2008). However,

Collings et al. (1988) and Moon (1984) found that particles in the nucleation mode had little or no

charge. Jung et al. (2005) confirmed that diesel NMPs carry little or no electrical charge and

concluded that ion-induced nucleation is not the primary mechanism for the nucleation. Ma et al.

(2008) also concluded that an ion trap prior to dilution did not significantly influence nucleation

mode formation due to the low ion concentration. Conversely, Yu (2001) proposed that the

charging occurred from the attachment of chemi-ions, produced from the combustion process

14

under high temperature conditions. Yu (2001) claimed that the ion induced nucleation theory

agrees well with measurements in terms of total nanoparticle concentration. This claim was further

supported by Yu et al. (2004) through measurement of ion concentrations in diesel exhaust.

Conclusions arising from studies pertaining to particle nucleation, as suggested, are still

unclear. Many studies seem to contradict or support the other findings but there are no definite

conclusions as to how these particles nucleate. Thus, particles and their physicochemical

mechanisms are a subject of increased interest for many researchers.

1.7.2 Influence of Dilution Conditions

Many studies have focused on the measurement of engine-out emissions and the influence

of the various schemes for reducing emissions. In many cases, the sampling and dilution systems

are not clearly defined. Consequently, extreme difficulties are encountered in interpretation of

measurement results because the concentration of ultrafine and nanoparticles are strongly

influenced by dilution. Thus, variations in the measured concentration of such particles are evident

between the different dilution systems.

The typical diesel-emitted emissions are conducted in either two standard test setups:

engine dynamometer and chassis dynamometer setups. The dynamometer is a device for

measuring force, torque and power of an engine. In an engine dynamometer layout, the engine is

removed from the vehicle and direct emissions from the engine can be studied. A chassis

dynamometer is used to simulate road loading conditions and the tailpipe emissions of a fully

functional vehicle can be studied. In most cases reviewed here, light-duty diesel emissions were

studied using an engine dynamometer setup and heavy-duty diesel emissions were studied using a

chassis dynamometer. This is in contrast to the regulatory emissions tests, where light duty vehicles

15

are tested on a chassis dynamometer and heavy duty engines are tested on an engine dynamometer.

Numerous studies have been conducted measuring the NMPs under real-world dilution

conditions in the vehicle exhaust plume (Kittelson 2002; Vogt et al. 2003). Mohr et al (2003)

proposed that the repeatable measurements could only be achieved through a dilution scheme that

does not favor formation of NMPs and is not sensitive to small changes of dilution parameters.

However, Mathis et al. (2004) proposed that the accumulation-mode particles and NMPs should

not be disregarded for a comprehensive characterization of particulate emission. Hence, strict

requirements and conditions should be suggested for the exhaust dilution process. The main

influential dilution parameters, which have been investigated in several studies (Kittelson 1998;

Abdul-Khalek et al., 1999; Shi et al., 1999; Khalek et al., 2000; Mathis 2002; Ntziachristos et al.,

2004a), are primary dilution temperature (PDT), primary dilution ratio (PRDR), residence time

(RT), and primary dilution relative humidity (PRH).

Abdul-Khalek et al. (1999) concluded that the accumulation mode was stable and was not

influenced by the dilution conditions. On the other hand, the nuclei mode was highly sensitive to

PDT and PRH (Mathis et al., 2004). They concluded that a decrease in PDT or an increase in PRH

initiated the formation of NMPs and consequently increased the number concentration of NMPs.

Lowering of the PDT favored the formation and growth of NMPs due to possible higher partial

vapor pressures and the reaction of volatile compounds during nucleation. Abdul-Khalek et al.

(1999) found that at low PRDR and low PDT, the influence of the RT is the strongest and the

nucleation mode concentration was at highest; vice versa at the opposite conditions. Additionally,

Collings et al. (2000) proposed that the total number of NMPs produced is extremely non-linear

and highly sensitive to PDT. However, when the concentration of accumulation mode is

16

sufficiently large, the formation of NMPs can be suppressed, and the total number of NMP

concentration cannot be associated to the influence of dilution condition (Kittelson 1998; Mohr et

al., 2001).

From the result of Mathis et al. (2004), it was determined that a PRDR between 20 and 30

produced the highest NMPs number concentration. A number reduction and decreasing NMP size

was observed at a PRDR above 30 due to the reduction in partial vapor pressures. A number

reduction was observed at a PRDR below 20 due to coagulation. Size growth was induced from

condensation of organic compounds on NMPs and acid catalyzed particle-phase heterogeneous

reactions. In addition, the highest NMP volume concentration was found at a low PRDR because

of the size growth.

Abdul-Khalek et al. (1999) indicated that the increase in PRH at constant DT led to an

increase in number concentrations by 30%. Mathis et al. (2004) however, found that the increase

in PRH resulted in a shift of the particle number size distribution toward larger diameter and a

decrease in the particle number concentration, due to coagulation of NMPs and possible interaction

between particles.

Aside from the sampling parameters indicated, a significant effect of engine cooling from

the local airstream speed around the vehicle was observed. With increased airstream speed,

nucleation mode was decreased (Mathis et al., 2004). Lastly, the utilization of ultra low sulfur fuel

resulted in a 70% decrease in number emissions (Abdul-Khalek et al., 1999).

1.7.3 Ultrafine Diesel Exhaust Particles

Commonly, an oxidation catalyst (OXICAT) is used to treat engine exhaust (aftertreatment)

17

to control DPM emissions of the diesel engine. Although the OXICAT reduces the concentration

of accumulation mode particles to undetectable levels, it increases emissions of ultrafine particles

in the nucleation mode (Kittelson et al., 2006). Gaseous sulfuric acid (GSA) is the most important

nucleating gas present in modern diesel vehicle exhaust. The presence of GSA triggers the

formation of new aerosol particles and growth by condensation and coagulation (Arnold et al.,

2006).

The sulfur VI (SVI) emission increases with increasing fuel sulfur mass fraction and

fraction F (fraction of fuel-sulfur conversion to SVI) of SO2 converted to SO3. Subsequently, F

increases in an OXICAT with high exhaust temperatures, through conversion of SO2 to SO3 and

H2SO4 (Arnold et al., 2006; Grose et al., 2006). Additionally, the absence of soot induces the build

up of a larger GSA super-saturation, which tends to ultimately increase GSA nucleation leading to

the formation of fresh nanoparticles. The atmospheric residence time of these nanoparticles

increases with increasing particle diameter and decreases with increasing larger particle

concentration (Arnold et al., 2006).

The results of Grose et al. (2006) showed that the diesel particles behaved in a manner

similar to ammonium bisulfate. But their observation indicated that a fraction of pure sulfuric acid

particles became neutralized by presumed ammonia contamination of the apparatus. Nonetheless,

12 nm particles all behaved like the neutralized sulfate and no additive volatile particles were found

in comparison to 12 nm sulfuric acid. Thus the observed results confirmed that the diesel exhaust

particles were neutralized to some extent, and the main composition of the particles was sulfuric

acid.

Lastly, the review of Sakurai et al. (2003) and Cooper et al. (1989) indicated that the

18

OXICAT effectively oxidized the high molecular weight semi-volatile organics (e.g. hydrocarbons;

HCs) and induced the conversion of SO2 to sulfate. Herner et al. (2007) confirmed that the removal

of gas phase HCs by the OXICAT reduced the formation of HC NMPs, or prevented the growth of

sulfate 1 nm particles to detectable size. It was predicted that the unexpected nucleation events

could have occurred due to storage or release of materials in the constant volume sampling system.

The conclusion was drawn that even with the use of ultra low sulfur diesel fuel to enhance the

formation of a nucleation mode, considerable amount of sulfates were in existent. The growth of

nucleated 1 nm sulfate particles to a detectable size was indicated as a function of availability of

additional condensates, notably HCs. Therefore, the existence of the ultrafine particles in the

nucleation mode from the diesel exhaust should be recognized and regulated for further reference.

1.7.4 Emission Regulations

In 2007, the finalization of the light-duty diesel (LDD) Euro 5 and 6 emissions standards

occurred in Europe. Euro 5 regulates NOx emission control measures to 180 mg/km and PM to 5

mg/km; and Euro 6 regulates NOx to 80 mg/km and PM to 4.5 mg/km with a particle number

standard of 6 × 1011/km that are determined using the UN/ECE Particulate Measurement Program

(PMP). The European Commission proposed Euro VI heavy-duty diesel (HDD) standards of 400

mg/kW-hr NOx and PM standards of 10 mg/kW-hr as measured on the European steady state and

transient cycles. In addition to criteria pollutant standards, the first standards on CO2 emission

limits at 130 g/km were proposed.

1.7.5 Diesel Engine Improvements

In general, the diesel engine developers are responding to the change in regulations by

using advanced fuel injection technologies, better exhaust gas recirculation (EGR) control as well

19

as EGR cooling, advanced and two-stage turbocharging, variable valve actuation, close loop

combustion control, and advanced model-based control for LDD (Johnson, 2007; 2008). It was

reported that the Euro 5 regulations could be satisfied with DPF without NOx aftertreatment. In

contrast, NOx aftertreatment is needed to meet Euro 6. However, Akmadza (2007) reported that

going from a Euro 5 calibration to a Euro 6 calibration results in a nominal 7% fuel penalty by

using NOx aftertreatment. It was pointed out that the choice between additional engine

technologies and NOx aftertreatment would need to balance costs and fuel economy benefits

(Johnson, 2008).

HDD engine developments are primarily aimed at improved fuel economy, reliability cost,

and durability. Hence, advancements are conservative and incremental. HDD engine researches

are more focused on traditional diesel combustion but some advanced combustion strategies have

emerged to meet the US 2010 Not-to-Exceed (NTE) in-use emissions limits (Johnson, 2007; 2008).

The incremental technologies of the research engines showed 10% fuel saving with significant

reductions in NOx (Dellmeyer et al., 2007). These engines showed brake thermal efficiency (BTE)

of 47%, and the potential to hit 53% BTE by 2013 (Shanton, 2007). Where BTE refers to the

efficiency of an engine in converting the heat from a fuel to the mechanical energy.

Dreisback (2007) examined the non-road engine technologies to attain the interim Tier 4

and final Tier 4 emission levels. The EGR and DPF were capable of hitting the interim levels, but

to meet the final level further development was needed. These developments include 2-stage

turbocharging; increasing EGR, cooling, and control; high-pressure flexible fuel injection; and

premixed or low temperature combustion strategies. Nishimura (2007) and Signer (2007) however,

proposed only DPFs as the non-road DPM reduction technology solution.

20

1.7.6 Emission Control Technologies Improvements

For the purpose of PM control, DPF technology was reported to be in a state of

optimization and cost reduction (Johnson 2007; 2008). Although SiC has been the main filter

material for LDD, the advancement in technology enabled utilization of alternative materials, such

as cordierite (Pidria et al., 2006; Craig et al., 2005; Maramatsu et al., 2006). Fischer et al. (2006)

showed that the fuel penalties due to DPF regeneration are minimized due to much lower thermal

conductivity for the cordierite. Moreover, the new DPF regeneration strategies pertaining to

control, in-cylinder injection, the fundamentals of how soot interacts with the catalyst, and the

impact of DPF pore structure were examined (Ootalke et al., 2007; Parks et al., 2007). Lastly, a

new DPF substrate material, aluminum titanate, was also studied (Ingram-Ogunwami et al., 2007).

Improvements in NOx control were focusing on SCR for diverse applications. SCR

efficiencies reached up to 90% with better mixing and control (Johnson, 2007). Low temperature

deNOx efficiency was addressed with better understanding on limitations. Solid urea and gaseous

ammonia storage in magnesium dichloride were suggested as substitutes for liquid urea (Mueller,

2007; Johanssen, 2007). Moreover, the suggested solution to meet LDD requirements of nominally

65% reduction was to use a lean NOx trap (LNT). A LNT refers to a NOx absorber which is

designed to reduce the oxides in the lean burn (combustion with excess in air) engine. Newly

developed SCR catalysts are emerging with improved durability and better ammonia slip

conversions, such that the aged LNTs are effective up to 60-70 % deNOx efficiency (Hu et al.,

2006). Also, the combination of LNT and SCR systems have been reported to convert NOx on the

LNT to ammonia during the rich regeneration, which in turn is stored on the SCR catalysis for

additional NOx removal during the lean treatment (Lambert et al., 2005). The LNT durability and

21

performance was enhanced with a sulfur trap (Yoshida et al., 2007). In addition, lean NOx catalysts

were significantly improved with a double layer concept utilizing ammonia generated in a NOx

absorber material (Satoh et al., 2006; Wada et al., 2007; Morta et al., 2007).

Finally, studies on diesel oxidation catalysts (DOCs) showed that the hydrocarbon

emissions from a low temperature combustion engine are difficult to treat potentially due to the

class of HC generated (Knafl et al., 2007). Noack et al. (2007) and Katare et al. (2007) also

proposed that NO2 was not formed at temperatures below the light-off temperature of HC and the

CO. NO2 was consumed as long as HC and CO were present in the exhaust. In addition, Punke et

al. (2006) reported a method of incorporating the DOC function onto the DPF.

1.7.7 Summary

Building upon these reviews, the important parameters that should be noted for the

measurement and collection of PM emissions data can be determined. Such parameters include:

the particle measurements relating the effects of dilution conditions; the particle size distribution

of diesel particulates; and the expected particle concentrations and the particulate composition.

Knowing the basics along with these parameters will further help to understand the behavior of the

diesel emissions. Better understanding will lead to improvements in diesel emission control

strategies. Finally, the literature review documented above will support generalizing observations

made through the study and will be used to derive conclusions or validate the collected data.

1.8 Objectives

At this point, the importance of a dilution system in emission testing and aftertreatment

technology development is clear. Investigating the dilution system behavior in terms of loss is then

22

necessary to prevent misrepresentation of the sample measurement. Thus, the primary goal of this

thesis was to verify the validity of the dilution systems – mainly to identify the portion of

concentration and particle loss during the dilution process. In order to quantify such loss during

the dilution process, experiments were conducted with base gases and particles. As indicated by

the Equation 1-6, the loss within the dilution system (or penetration number) can be described in

terms of the volumetric and particle dilution ratios. Therefore the body of work done to investigate

the behavior of diluters for both gases and particles was crucial. The secondary objective was to

validate the functionality of the dilution system features, such as heating and thermal conditioning.

From this portion of work, conclusions could be derived regarding the optimal configuration for

operating under typical exhaust testing conditions.

23

Chapter 2

Aerosol Diluter Review

2.1 Introduction

As discussed in Chapter 1, an aerosol diluter is used to lower the concentration of the

engine exhaust to simulate near-atmospheric conditions and to reduce the concentration below the

maximum detection capacities of the particle analyzers. In a general dilution process, a particle-

free air flow is introduced into a given raw sample stream to reduce the number of particles per

unit volume. Validation and analysis of the dilution system is essential in all parts of engine

emission studies. Particle loss from dilution may result in under estimation of the emitted particle

number in certain size bins. Thus, any conclusions drawn from tests where unknown loss occur

can be very misleading.

2.2 Description of Diluters

Two types of diluters will be considered in this thesis: a rotary disk diluter and an ejector

diluter. The systems reviewed and compared are single-stage and two-stage TSI 379020A rotary

disk thermodiluters and a Dekati FPS-4000 ejector diluter.

2.2.1 TSI 379020A Rotary Disk Thermodiluter

The TSI 379020A is a rotating disk type diluter. A schematic is shown in Figure 2-1. The

diluter construction consists of a rotating disk having 10 small cavities placed in a dilution block

with heating elements. A portion of the raw sample is pumped in at approximately 1.0 lpm and is

captured by the cavities of the rotating disk and mixed with HEPA-filtered, particle-free dilution

24

air in the measurement channel. The dilution air flow is controlled by an internal pump over a

dilution factor range of 0 – 10. This dilution air can be heated up to 150 °C along with the diluter

block, which allows the removal of condensed volatile materials. The dilution ratio is a linear

function of the disk rotation frequency and the dilution air flow rate as shown in Equation 2-1.

DR � <��=��>��?��@<�AB��?� C� ��D<��E��?��B�� Equation 2-1

The flow rate of diluted sample available for measurement ranges from 0.5 – 5 lpm.

Figure 2-1

Principle of Dilution Method for TSI 379020A (TSI, 2009)

Additional features of the two-stage TSI 379020A include a thermal conditioner and an

internal air supply to the built-in single stage as shown in Figure 2-2. The supply air to the primary

dilution is controlled to 1.5 lpm. The thermal conditioner consists of an evaporation tube, which

allows the elimination of the condensed nanodroplets and prevents volatile particle formation. The

temperature of this tube can be adjusted up to 400 °C but is normally operated at 300°C, as

25

recommended by the TSI manual. Secondary dilution is achieved in a mixing assembly through

adjustment of a calibrated dilution airflow over a range from 0 – 15 lpm, which corresponds to a

dilution factor range of 1 – 11. The flow rate of the diluted sample exiting the system and available

for measurement, ranges up to 16.5 lpm.

Figure 2-2

TSI 379020A Single and Two-Stage Layout (TSI, 2009)

2.2.2 Dekati FPS-4000 Ejector Diluter

The Dekati FPS-4000 is an ejector type diluter. There are two stages to the operation of

the Dekati FPS-4000 as shown in Figure 2-3. In the primary stage, the filtered, particle-free dilution

air flows into the inner tube of the probe through perforated walls. Introduction of the dilution air

through entire length of the tube minimizes particle loss. In addition, primary dilution air and the

probe itself can be heated for the purpose of evaporating the condensed volatile material. In the

second stage, the primary diluted sample is drawn through the nozzle. The nozzle causes a high

26

velocity flow and the resulting pressure drop creates suction inside the tube. The DRs for both

stages are governed by the diluter dimensions, the dilution airflow, the sample temperature, and

the pressure drop in the sample input and the ejector nozzle. These parameters are pre-calibrated

by the manufacturer, controlled, and monitored by the control unit in real-time to calculate the

spontaneous DR within the system. With proper venting, the diluted sample exiting the second

stage is always at ambient pressure regardless of the initial condition.

Dilution air is provided to the Dekati as compressed air at a minimum pressure of 6 bar

and a maximum pressure of 9 bar. The compressed air must have a particle concentration of less

than 100 particle/cc and a very low relative humidity such that the air is non-condensing at -40 oC.

An internal pressure regulator maintains a constant pressure of 4.5 bar to the FPS valve unit.

Dilution air flow to both stages is controlled by the FPS valve unit. Pressurized filtered air is

supplied to the valve units, which has eight magnetic valves, each of which is connected to a

critical flow orifice. Valves 1 and 2 are used to control the ejector diluter (secondary dilution) air

flow, while valves 3, 4, 5, 6, 7, and 8 control the primary dilution air flow. Each critical orifice has

a different size. Opening and closing various combinations of the 8 magnetic valves produces

various dilution ratios. If the dilution air into the primary stage is greater than what is drawn with

the ejector, the dilution ratio becomes infinite – indicated by the sign NaN on the display. When

this occurs, the primary dilution air flow rate should be lowered.

27

Figure 2-3

Principle of Dilution Method for Dekati FPS-4000 (Dekati, 2010)

2.3 Aerosol Diluter Systematic Comparison

The specifications and capabilities of the two aerosol diluter types, shown in Table 2-1

below, are significantly different from one another. As such, each diluter has distinct technical

advantages that makes it suitable for different experimental conditions. Note that these

specifications are directly sourced from their manufacturers, TSI and Dekati.

The TSI 379020A rotary disk thermodiluters are designed with more focus on simplicity

and robustness. For instance, the adjustment of DR can be done without the use of tools or

recalibration. The rotating cavity disk can be easily accessed and maintained. The engineered

coatings on the disks allow great reduction in wear and improve lifetime. In addition, replaceable

28

disks are readily available for added convenience and to reduce maintenance downtime. As such,

these advantages make the TSI 379020A diluters to be more suitable for uses in simple engine

exhaust emission studies where the accurate measurement of concentration with numerous

repeated sessions is critical.

TSI Model 379020A Dekati FPS-4000

Raw sample temp. 0 – 200 ºC 0 – 600 ºC

Raw sample press. (abs) 900 – 1100 mbar 750 – 2000 mbar

Sample flow Approx. 1 lpm 0 – 10 lpm1

Primary dilution air flow 0.5 – 5 lpm 2 – 40 lpm

Secondary dilution air flow 0 – 15 lpm2 40 – 140 lpm

Diluted sample flow Up to 16.5 lpm 60 – 160 lpm

Dilution ratio 1:15 – 1:30003 1:20 – 1:2004

Primary dilution ratio 10-cavity disk: 1:15 – 1:300

8-cavity disk: 1:150 – 1:3000

1:3 – 1:20

Secondary dilution ratio 1:1 – 1:11 1:7 – 1:15

Dilution temp. OFF, 80, 120, or 150 ºC 0 – 350 ºC

Evaporation tube temp.5 Ambient to 400 ºC

1 Measurement at 1.013 bar and 20 ºC

2 With accuracy of 3% of set value +0.1 lpm

3 Dilution accuracy within ±10% range using the calibrated factors supplied with each disk

4 Dilution ratios displayed within ±10% of reading

5 Temp. measurement within ±2 ºC and temp. control within ±3 ºC accuracy

Table 2-1

Aerosol Diluters Specification Summary Table (TSI, 2009; Dekati, 2010)

29

The Dekati FPS-4000 ejector diluter is designed with an emphasis on the ability to create

a wide variety of dilution conditions. Using the Dekati diluter, conducting a study of the particle

dynamics is more manageable than with the TSI diluters. For instance, volatile vapors can be

handled in three ways: preventing condensation with heated dilution; preventing condensation and

possibly capturing some of the vapor in absorbing material with a Dekati thermodenuder; and

facilitating nucleation of vapors with cooled dilution and a residence time chamber. As such, both

heated and cooled dilution can be performed. The residence time within the system is nominally

less than 0.5 seconds, but can be altered by simply installing a longer residence time chamber. In

addition, the particles sampled through the Dekati diluter travel on a straight path with no bends

or moving parts, making it more traceable. These advantages make the Dekati diluter to be more

suitable for uses in nucleation and particle dynamic studies where dilution condition variability

and controlling mechanisms are vital.

2.4 Known Problems of Aerosol Diluters

A previous study of loss in diluters was conducted as part of the European PMP (PMP

report GRPE-PMP-25-5, 2010). The report presented percent particle penetration (Refer to

Equation 1-6) values for various particle sizes, and these are reproduced and shown in Table 2-2.

As shown, the Dekati diluter has a higher percent penetration over the different size bins,

meaning that particle losses within the Dekati diluter are less than those within the TSI diluters.

One thing to note is that the 68% particle penetration value of the TSI 379020A at the 30 nm size

bin is low, indicating that particle numbers in the 30 nm range will be understated in particle

measurements made using the TSI 379020A.

30

P (30 nm) P (50 nm) P (100 nm)

TSI 379020A 68% 88% 95%

Dekati FPS-4000 (heated) 96% 98% 100%

Dekati FPS-4000 (not heated) 100% 99% 100%

Table 2-2

Percent Particle Penetration Values for Varying Particle Sizes for the Diluters

In addition to the percent particle penetration values at different particle sizes, the PMP

report indicated some problems with regards to the concentration measurements made using all of

these diluters.

The PMP report indicated that there has been overestimation of particle number

concentrations measured using the TSI 379020A diluters. The measurement error was caused by

the production of wear particles from the diamond-like carbon rotating disk of the primary diluter.

In response, the manufacturer has developed an alternative coating to prevent this. However, to

the extent that the disk coating deteriorates, it could contribute to the overestimation of the particle

number emissions values.

For the Dekati diluter, the report states that there has been underestimation of the measured

particle number concentrations caused by particle loss inside the thermodenuder evaporating tube

due to evaporation of condensed species.

Any particle loss within the aerosol diluters contribute to over and underestimation of the

measured particle number concentrations, so that an analysis based on the inaccurate measurement

will not be correct and could be misleading. Therefore, verification of diluter characteristics and

31

performance is very important.

In addition, the manufacturers specify that the dilution ratio presented by these diluters will

be within ±10% of the reading. Therefore, to use these diluters with confidence, further

investigation of dilution accuracy is necessary.

32

Chapter 3

Description of Test Instrumentation

3.1 Introduction

Investigations of particle loss in aerosol diluters were done on both vapor and particle

phases. In order to collect quantifiable data to signify the dilution efficiency of the system, effective

methods of measuring concentration of designated gases and particle numbers as a function of

particle size are necessary. However, working with particles can be problematic under various

circumstances, especially for smaller particles (< 30 nm). Smaller particles are subject to

coagulation, surface growth and agglomeration into bigger particle; and bigger particles can

evaporate into smaller ones. Therefore, a means to produce stable solid particles of all sizes is

required to evaluate particle loss through the diluters.

3.2 Gas Concentration Measurement

Verification of actual DRs was done by measuring the dilution of a known tracer gas

passing through the diluter. Two different gases, each at a specified concentration and balanced

with nitrogen were used as tracer gases: methane at 6500 ppm (nominal) and carbon dioxide at

2.15% (nominal). The concentration of methane was measured using a heated flame ionization

detector (HFID) and that of carbon dioxide with a non-dispersive infrared (NDIR) gas analyzer.

3.2.1 Heated Flame Ionization Detector

Measurement of methane concentration was done using a California Analytical Model 600

HFID. The HFID is a very sensitive gas detector for hydrocarbons. In principle, a regulated flow

33

of sample gas (1.5 – 3.0 lpm) is introduced into a hydrogen flame sustained by a flow of hydrogen

fuel gas (40% H2/60% He at 120 cc/min) and zero air (< 1 ppm C at 220 cc/min) in the burner as

shown in Figure 3-1.

Figure 3-1

Flame Ionization Detection Technology (Rosemount Analytical NGA 2000 Manual)

As the sample passes through the burning flame, the hydrocarbon components in the sample

undergo a complex ionization as they are burnt. The burning hydrocarbons produce electrons and

positive and negative ions. The negative ions are collected by the polarized electrodes, which are

biased with a high DC voltage (+ 90 V). Collection of the negative ions causes a current to flow

through an electronic measuring circuit. The ionization current in the measuring circuit is

proportional to the rate of the ionization, which in turn is proportional to the rate at which the

carbon atoms enter the burner. Therefore, the number of carbon atom entering corresponds to the

concentration of hydrocarbon within the sample gas, as shown in Equation 3-1:

34

F ∝ �HI�� =0-

�� [KLM] Equation 3-1

where I is the current through an electronic measuring circuit; IH is the ionization of hydrocarbon;

and Cin is the carbon atom entering the burner.

The CH4 or THC (total hydrocarbon) measurement capacity that can be detected by the

Model 600 HFID ranges from 0 – 3 ppm to 3% carbon (30,000 ppm). Therefore, the 6500 ppm

(nominal) concentration of methane in the tracer gas, falls within the measurement range of the

HFID. The repeatability of the instrument is indicated to be better than 0.5% of full scale – meaning

the measurement error is expected to be always less than 150 ppm (0.5% of 3% carbon). Similarly,

the linearity between the ranges is expected to be better than 0.5% of full scale. The amount of

deviation throughout the instrument’s range is to be less than 150 ppm. The response time of the

Model 600 HFID can be adjusted from 1.0 second to 60 seconds. By default, the response time

was always set to 1.0 second in order to simulate real-time measurement of concentration for better

accuracy.

3.2.2 Non-dispersive Infrared Gas Analyzer

The measure of carbon dioxide concentration was done using the LI-COR LI-820 CO2 gas

analyzer. The NDIR gas analyzer is a simple spectroscopic instrument used to measure CO/CO2

contents in a sample gas. As shown in Figure 3-2, the infrared (IR) source is directed through a 14

cm gold plated optical path, also known as the sample chamber, towards an optical detector. When

a sample flows through the sample chamber, exposure to the IR beam induces absorption at a

specific frequency for each constituent gas. Each element of gas introduced to the IR light absorbs

different wavelengths of light due to differences in their chemical properties. For instance, CO2

35

molecules will absorb IR light at a wavelength of approximately 4.26 µm. The term “non-

dispersive” is used because the wavelength passing through the sampling chamber is not pre-

filtered until a short way before the detector, meaning that the wavelength absorbed by the gas is

allowed to propagate without disturbance or change in shape. This non-dispersive exposed sample

is then passed through 3.95 and 4.26 µm optical filters to eliminate any light other than the

wavelengths that can be absorbed by the CO2 molecules. The 3.95 µm optical filter is used to

measure the reference wavelength for higher measurement accuracy. The electro-optical detector

then measures the amount of IR absorbed by the sample and computes the concentration.

As shown below, the LI-820 is constructed with a gold plated reflector and optical path to

maximize energy transmission. The sample passing through the sample chamber is kept close to

constant conditions by the controlling mechanisms; thermally by a heating element; barometrically

by a pressure transducer; and mechanical shock and vibration protected by the foam enclosure.

The CO2 measurement capacity of this system ranges from 0 – 2% carbon (20,000 ppm), where

the maximum threshold was around 2.5% carbon. Therefore sampling a carbon dioxide gas

concentration below 2.5% is accepted for measurement, in particular the mix containing 2.15%

(nominal) of carbon dioxide that was used as a tracer gas and calibration. The repeatability of the

instrument is indicated to be better than 3% of reading – meaning the measurement error is

expected to be within ± 3% of the current measurement. For instance, when a measurement

displays 2,000 ppm, the expected margin of error is ± 60 ppm. The response time of the LI-820 is

at 1.0 second to simulate real-time measurement of concentration for improved accuracy.

36

Figure 3-2

Non-dispersive Infrared Detector Technology (LI-COR, 2009)

3.3 Particle Number Measurement

The complexity of the particle phase condition arises from the unexpected behavior of

particles in different size bins. When investigating dilution efficiency under the particle condition,

loss due to coagulation, evaporation, condensation, and other possible variables must be

considered. As such, a dependable means to accurately measure particles with a widespread size

distribution is required. The engine exhaust particle sizer (EEPS) and fast mobility particle sizer

(FMPS) each provide such a reliable method for proper measurement.

3.3.1 EEPS/FMPS

The EEPS and FMPS are spectrometers that are used to measure the size distribution of

particles in the range from 5.6 to 560 nm. The core operating principle is identical in the two

instruments. However, the naming of the instruments reflects characteristics that differentiate them.

37

The EEPS provides faster time resolution that is more beneficial in engine exhaust studies.

Figure 3-3

Differential Mobility Analyzer Technology (TSI, 2004)

Measurement of particle size distribution was performed using one or both of the TSI

EEPS spectrometer 3090 and TSI FMPS spectrometer 3091, depending on the specific experiment

being conducted. Collectively, these two instruments are known as the differential mobility

analyzers (DMA). The DMA utilizes an electric field to classify and analyze charged aerosol

particles of different sizes in a gas phase. When aerosol particles of a specified sample are drawn

continuously into the system, they are positively charged to a predictable level by a corona charger,

as illustrated in Figure 3-3.

These charged particles are introduced to and transported down a high voltage electrode

column by the HEPA-filtered sheath air. The electrode column is also charged with a positive

38

voltage, which causes the charged particles to be repelled outwards according to their electrical

mobility. It is important to note that the electrical mobility of a particle depends on its size. Larger

particles with larger surface area will have lower electrical mobility and smaller particles will have

higher electrical mobility. Therefore, smaller particles are repelled further outwards and larger ones

less so. These charged particles then strike the appropriate highly sensitive electrometers and

transfer their charges. Figure 3-3 shows that the smaller diameter particles will strike an

electrometer near the top (E1) whereas the larger diameter particles strike one at the bottom (EN).

The counts of transferred charges from the particle to the respective electrometers are then

computed to result in a particle number at appropriate size bins simultaneously.

As previously mentioned, both the EEPS and FMPS are capable of measuring particles in

the range from 5.6 to 560 nm. The resolution for particle size distributions is 16 channels per

decade, meaning there are 32 size bins measured between 5.6 and 560 nm. The size bins indicated

by the analyzers are the average of a local range of similar particle sizes. For example, the size bin

of 6.98 nm include particle sizes from 6.51 to 7.52 nm. The maximum and minimum concentration

measurements for the two instruments are not identical however. As shown in Figures 3-4 and 3-

5, the maximum and minimum concentration measurement at various averaging times (or response

times) for the EEPS is an order of magnitude higher than for the FMPS. However, for better

comparison and relation to one another, the averaging time was set to 1.0 seconds for both

instruments. When direct comparison between the concentrations measured by both instruments

was necessary, the appropriate correction factor was applied Details of the correction procedure

are provided in Chapter 5.

39

Figure 3-4

EEPS Concentration Range (TSI, 2012)

Figure 3-5

FMPS Concentration Range (TSI, 2004)

40

3.4 Soot Generator

In the particle phase dilution study, having a particle-generating source capable of

producing a constant size distribution over time is crucial. A diesel engine is a great source for

producing particles having a widespread size range. However, the ultrafine particles produced are

significantly subjected to the particle coagulation, evaporation, or condensation (gas-to-particle

conversion) mechanisms that can change the distribution Thus, a means to produce stable small

solid particles is necessary to avoid such particle conversion mechanisms. The soot generator

provides the capacity of producing suitable particles in sufficient concentration.

Figure 3-6

Soot Generator Technology (Jing, 2009)

The desired particles were produced using the Jing miniCAST MOD6203 soot generator.

It consists of an isolated flame chamber where a stable flame enables the production of a particle

stream. As shown in Figure 3-6, a co-flow diffusion flame generates soot particles due to

hydrocarbon pyrolysis in the diffusion flame core. Pyrolysis is a process where thermochemical

decomposition of a vapor phase organic compound occurs at elevated temperatures in the absence

41

of oxygen. It is a process where the solid residue is produced from the result of burning organic

material.

The miniCAST uses propane gas supplied at 43.5 psi as the fuel source to produce soot

particles. The fuel flow rate is constant and the generated particle size distribution is adjusted by

varying the quenching gas flow rate. Nitrogen gas, supplied at 43.5 psi, is used as a quench gas

The flow rate of nitrogen is adjusted to prevent further combustion processes from occurring at

various stages of burning and to stabilize the soot particles. The quenching process inhibits particle

condensation at ambient air conditions. As shown in Figure 3-7, increasing the flow rate of the

quenching gas shifts the size distribution towards the ultrafine region. With a higher quenching

flow rate, the mode size of generated particles becomes smaller. For instance, the particles

concentrated around 20 nm diameter can be produced at 80 sccm (Standard Cubic Centimeter per

Minute, cm3/min) of nitrogen flow.

Figure 3-7

Quenching Gas Flow Rate Dependent Soot Particle Size Distribution

dN

/dlo

gD

p (

#/c

m3)

42

Chapter 4

Evaluation of Dilution Accuracy Using Gas Phase Species

4.1 Introduction

The performance of an aerosol diluter is significantly affected by any loss of sample within

the dilution process. The actual dilution ratio delivered by the diluter must be known accurately.

This portion of the work will focus on evaluating the dilution accuracy in the aerosol diluters using

gas phase species as tracers. This investigation will quantify the difference between the actual

dilution ratio delivered and the user selected (theoretical) dilution ratio performed by the diluter

system, neglecting the effect of particle loss such as coagulation, evaporation and condensation.

Particle loss will be investigated in Chapter 5. The diluters tested were the single-stage and two-

stage TSI 379020A rotary disk thermodiluters, and the Dekati FPS-4000 ejector diluter.

4.2 Dilution Evaluation Apparatus

Figure 4-1 shows the apparatus used for the dilution evaluation measurement of the

diluters investigated. A specified gas mixture with a known concentration was used as the input

source for the diluter. The downstream concentration level was monitored continuously with an

appropriate analyzer (i.e a HFID for a hydrocarbon containing gas mixture or an NDIR instrument

for a CO2 containing mixture).

Varied experimental layouts were used to verify the volumetric dilution condition for the

different types of diluters. Substantial loss of gas phase organic compounds can occur in rotary

disk thermodiluters according to the TSI 379020A manual (TSI, 2009) due to the presence of an

43

evaporation tube in the flow path. This loss was verified in a series of preliminary experiments

(described in Appendix A). Consequently, a hydrocarbon mixture, such as methane, is unsuitable

as the input source to test diluter performance. Thus, to evaluate these TSI diluter measurements,

a mixture of 2.15% (nominal) carbon dioxide balanced in nitrogen was used as the tracer gas. The

ejector diluter, on the other hand, did not scavenge volatile compounds. As such, a mixture of 6500

ppm (nominal) of methane balanced in nitrogen was used as the upstream sample.

Figure 4-1

Dilution Evaluation Apparatus for the TSI 379020A (Left) and the Dekati FPS-4000 (Right)

As shown in Figure 4-1, an excess flow airway was placed before the diluters to ensure

near atmospheric pressure at the sample inlet point. Since the volumetric DRs are subjected to

fluctuation due to pressure change, a “positive flow” to the ambient is required to relieve any

44

pressure above atmosphere.

The pressure has a significant effect on the behavior of the dilution process in the diluters.

As shown in figure 2-3, the Dekati diluter consists of an ejector pump. The pressure drop across

the inlet and the outlet points determines the flow rate through the ejector pump. Hence, the

accumulation of pressure at the inlet of the ejector pump causes an undesirably high flow rate and

affects the DR. Although the effect of such a pressure build up is less in the TSI diluters, inaccurate

dilution can still occur. The higher flow rate caused by the pressure can increase the pump

controlled flow rate. Therefore a mitigating strategy for relieving such pressure build up was

necessary.

The flow rate at the sampling point for the Dekati diluter varied from 0-10 lpm depending

on the DR, so constant monitoring for the presence of excess flow was crucial. The excess flow

was vented to the atmosphere through the 1/2” diameter Teflon tubing to accommodate the large

flows. For the TSI diluters, the undiluted sample is pulled in at a rate of approximately 1.0 lpm,

thus there was a sufficiently greater flow of inlet gas (> 1.0 lpm) and 1/4” diameter Teflon tubing

was adequate.

A bypass line was installed for the Dekati test apparatus to provide an option for

monitoring the upstream concentration level. As mentioned before, the Dekati diluter sampling

flow rate varies significantly depending on the set DR. For the case in which the sample flow rate

becomes greater than the source, an undesired dilution occurs at the excess flow tee – by drawing

in atmospheric air from the ventilation. Observing the upstream concentration of the Dekati

provided secondary insurance to avoid such “negative flow” from happening. Sudden changes in

the input sample concentration could be used to indicate that such “negative flow” had occurred.

45

A modification was made to the commercial single-stage TSI 379020A for this test

apparatus. The original single-stage TSI 379020A drew dilution air from an open rear port, covered

inside the aluminum rear panel with small ventilation openings. Evidently, the system was

circulating a mix of atmospheric and dusty air from the internal component as the dilution air. Thus

inconsistent concentrations of unfiltered air from these sources were injected in the dilution

process. To compensate for this, the rear port was extended outwards through the aluminum panel

using quick-disconnecting tube couplings and 1/4’’ flexible polyvinyl chloride tubing. This new

inlet was supplied with a “positive flow” of 5.0 zero grade air (CO2 ≤ 1 ppm) at the excess airway.

Again, the “positive flow” was important to avoid any pressure induced variations. The two-stage

TSI 379020A has the single-stage unit imbedded within system in addition to the secondary

dilution unit. The secondary dilution component generates the HEPA-filtered, particle-free primary

dilution air for both stages with a calibrated and controlled flow of 1.5 lpm (TSI, 2009).

A TSI flowmeter was installed downstream of the TSI 379020A diluters to monitor the

diluted output flow rate. The dilution in the TSI diluters was governed by the output flow of the

diluted sample. Variance in the dilution ratio occurred when the flow rate of the diluted output was

changed. The NDIR analyzer, downstream of the flowmeter, had an internal pump, which allowed

a relatively constant flow rate to enter the instrument. This pump was used to provide a flow rate

of approximately 1.4 lpm and monitored with an external flowmeter to avoid any fluctuation in

DR during the tests.

4.3 Dilution Evaluation Methods

In order to properly characterize dilution, it is crucial to calibrate the analyzers using gas

concentrations covering the desired range prior to the installation of diluters. The calibration gas

46

concentrations must be within 80% of the measurement range capacity of the analyzers. This

precursor step ensures higher accuracy at both the high and low concentrations being measured.

Thus, the calibration gas cylinders were also used as the sample gas in the appropriate range of the

analyzers.

Once the analyzers were calibrated with the sample gases, the downstream concentration

measurements were done on varying DRs. The DRs were adjusted according to the system being

tested, ranging from the lowest possible DR to a DR of approximately 100 in increments of 10 ±

5. This range covered the dilutions most often used in engine emission testing. A DR higher than

100 may dilute the concentration of minor exhaust constituent to a level below the detection limit

of analyzers. As such, the investigation focused on the DRs up to approximately 100. However,

the diluters are capable of performing dilution at higher DRs.

For the two-stage TSI 379020A, the primary dilution potentiometer was kept constant at

100% while the secondary dilution potentiometer was adjusted. This isolated the effect of the

primary from the secondary dilution for analysis. Behavior of the primary dilution was verified by

testing the single-stage TSI 379020A. It should be noted that a higher DR is possible if the primary

dilution potentiometer is adjusted. Furthermore, any heating features associated with the diluters

were disabled during the experiment as the sample gases were balanced in nitrogen with minimal

or no volatile materials and heating was therefore not needed.

When operating the single-stage TSI 379020A, it is important to note that the supplied

zero dilution air was always at “positive excess flow” as mentioned before. It was observed that

the DR range coverage was greatly altered when the supplied air quantity was insufficient or

pressure buildup occurred at the inlet. This had no impact for the two-stage diluter as the air was

47

supplied through an internal air generator at a controlled flow rate of 1.5 lpm.

Determining the relative theoretical DR when operating with the two-stage TSI 379020A

was found to be problematic. The DR given by the conventional TSI method (calculation

spreadsheet provided by TSI) deviated more than 20% from the measured value. To correct this

issue, it was necessary to measure both the sample outlet flow and the excess flow from the diluter.

The summation of these flows was used to back-calculate for the corrected DR, which gave better

results with ±10% error margin at 99.7% confidence level. More on this is covered in section 4.6.

In addition, the particle-free air generated internally by the two-stage diluter also

contained undesired supplementary CO2 from the room which resulted in a misrepresentation of

the concentration measured downstream. To compensate for this, quantification of the zero

condition at various DRs was necessary prior to each experiment. It was established that the

internal generator was producing approximately 471.4 ppm of CO2 consistently regardless of the

DR variations. Therefore 471.4 ppm was subtracted from the successive measured mean

downstream concentration for the two-stage diluter. It should be noted that the approximate

concentration level of CO2 found in the atmosphere is approximately 398.58 ppm (Mauna Loa

Observatory: NOAA-ESRL, 2013). However, the concentration measured in the two-stage TSI

diluter was higher than this average level. This phenomenon occurred because the experiment was

conducted in a closed environment filled with potential CO2 sources. These sources include various

instruments running and the number of people present. Therefore, it is important to conduct a zero

condition testing prior to the experiment in order to specify the CO2 concentration level specific

to the current environment.

48

4.4 Sampling Time Parameters

The sample time is defined as the allocated length of time the data is logged for a specified

experimental condition. The sample time used in the diluter evaluation was 180 seconds. During

the sampling period, the analyzers were recording data at an averaging time of 1 second. The

averaging time of the analyzers corresponds to the time interval between the two consecutive

recorded data points. Hence a sample time of 180 seconds with an averaging time of 1 second

resulted in 180 data for each condition. This sample size ensured a large enough population for a

more precise evaluation. In between the varying sample conditions, sufficient time was allowed

for the measured concentration to settle down so as to adjust for the change in the dilution air flows.

It was experimentally determined that approximately 60 seconds of stabilization time was

necessary to measure a comparatively consistent value. In response to this finding, the inter-sample

time was set to 120 seconds during which the DR was effectively changed and stabilized.

4.5 Leakage Check

Another important preparatory step before the actual measurements was inspecting for

any source of leakage in the experimental setup. When measuring the concentration of carbon

dioxide and methane, it was absolutely necessary to verify that there was no source of leakage

occurring in the sampling lines. A small leak allowing atmospheric carbon dioxide or methane to

enter the system under negative pressure could considerably skew the results. Similarly, when the

system was under positive pressure, the sample gas could leak out to the atmosphere causing the

concentration level to decrease. Thus the system was checked thoroughly using the soapy water

leak test. Soapy water was applied to all junctions and lengthy lines while the gas flowed through

the apparatus. Any bubble formation on the applied surface indicated that there was a leak and the

49

appropriate part was replaced prior to initializing the test matrix. To guarantee that there was no

leak in the system, the zero air was flowed into the apparatus and measured by the analyzers. The

system was considered leak tight if the concentration determined by the appropriate analyzer was

less than 1 ppm.

4.6 Calculation Methods

Equation 1-3 described the general calculation method for the volumetric DR. All of the

data collected during the sampling period was averaged over the sample population of 180. Thus,

the average concentration was used to calculate the mean experimental volumetric DR as follows:

!OOOO�� P"#$%&'()�*+,-$%&'() Equation 4-1

where �P is the average gas concentration measured by the analyzer in ppm.

As mentioned in section 4.3, back-calculation was necessary to correct for the inherent

deviation of the theoretical DR value given by the TSI spreadsheet. The conventional method

calculates the appropriate DR as follows:

!�� ,QRH � =*[email protected]@<�$'X+-*<�#&0)(&Y Equation 4-2

�Z �� 1.5 @ � �� 0.3(^_`) Equation 4-3

�Z �� Z�� Z b� (^_`) Equation 4-4

where M��A = 1543 is the constant coefficient specific to the ten cavities disk supplied with the

diluter; �� is the potentiometer dial number of the primary and secondary flow settings; and �Z � is the average flow to the specific outlet of the diluter. Therefore, �Z�� and �Z b� were

50

measured for each specified DR and recorded. Using Equations 4-3 and 4-4, the corrected

� �� was computed. With ��D being kept constant at 100%, the corrected

!�� ,QRH was calculated using Equation 4-2.

4.7 Results

In each case, the diluter performance was studied using the concentration measured

upstream and downstream to calculate the experimental DRs. The recorded values were then

compared with the theoretical values given by the diluter setting. A mentioned previously, the

heating elements were disabled for the duration of the experiments.

4.7.1 Single-Stage TSI 379020A Rotary Disk Thermodiluter

As shown in Figure 4-2, the downstream CO2 concentration was measured by the NDIR

analyzer. The resulting concentration showed that the measured values were within 4.0% of the

theoretical values with exception of an 11.1% deviation at a DR of 45. The uncertainty graphed

for each point was at the 99.7% confidence interval (3 sigma). These y-axis error bars correspond

to the precision of the measured values over 180 points. The results show that greater fluctuation

occurs at DRs below 30 and the fluctuations became visibly smaller as the DR value increased.

Overall, the concentration values were very consistent at a stabilized condition with 99.7%

confidence.

51

Figure 4-2

Diluted CO2 Concentration Measurement at Various Dilution Ratios for the Single-Stage

TSI Diluter

The measured concentration trend line was graphed and compared with the theoretical line.

A power function best describes the experimental results since Equation 4-2 shows that the

downstream concentration is inversely proportional to the DR for a fixed upstream concentration.

The coefficient of the determination, R2, indicates that the equation y = 21352x-1 matched the data

well (R2 = 0.997). There is a discrepancy between this empirical model and the theoretical model.

The constant term (i.e. 21352), if the dilution processes were performed ideally, should correspond

to the initial tracer gas concentration (21500 ppm). The difference in this constant term suggests

that there may have been a leak in the system or imprecision in measured values. These issues will

be discussed later in section 4.8.

The prediction of measurement outcome was made based on this function over the

y = 21352x-1

R² = 0.997

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200

CO

2C

once

ntr

ation [ppm

]

Dilution Ratio

Measured Conc. Theoretical Conc. Power (Measured Conc.)

52

measured DRs up to DR = 106. Comparison of this projection to the hypothesized line illustrates

that the probability of the system operating within 4.0% of the theoretical DR is very likely.

Figure 4-3

Experimental Dilution Ratios for the Single-Stage TSI Diluter

Based on the concentration measurement results, the corresponding DR was calculated as

shown in Figure 4-3. Direct comparison of the measured outcome to the theoretical trend indicated

that the values were generally within 3.9%. The highest deviation of 10.2% occurred again at a

DR of 45. The standard deviation of the result showed that, unlike the concentration result, greater

fluctuation generally occurred at a higher DR. The reason for this was because at higher DRs the

fluctuation in the measured downstream concentration was relatively larger than at lower DRs,

regardless of consistency (i.e. a change of 5 ppm at 2000 ppm is minuscule compared to the same

change at 200 ppm). However, the overall regression of the measured DRs fit the theoretical DR

well. Thus the actual DR can be expected to deviate by less than 3.9% from theoretical DR over

0

20

40

60

80

100

120

0 20 40 60 80 100 120

Mea

sure

d D

ilution R

atio

Theoretical Dilution Ratio

Measured/Theoretical Theoretical/Theoretical

53

the DR range of 12 to 106.

4.7.2 Two-Stage TSI 379020A Rotary Disk Thermodiluter

The CO2 concentrations downstream of the diluter, measured with the NDIR analyzer are

shown in Figure 4-4. The measured concentration values are within 7.9% of the theoretical values,

with exception a difference of 21.3% at a DR of 15. The standard deviations calculated over the

range were small. This suggested that the measured values remained very consistent at the

stabilized condition with 99.7% confidence.

Figure 4-4

Diluted CO2 Concentration Measurement at Various Dilution Ratios for the Two-Stage TSI

Diluter

A trend line was fitted to the measured concentration data and compared with the

theoretical line. As before, a power function is used to best describe the experimental result. The

0

200

400

600

800

1000

1200

1400

1600

1800

0 50 100 150 200

CO

2C

once

ntr

ation [ppm

]

Dilution Ratio


54

coefficient of the determination indicated that the equation y = 22587x-1 described the data well

(R2 = 0.988). A prediction of measurement outcome was made based on this function over the

measured DRs up to DR = 110. Comparing this projection to the theoretical line showed that the

likelihood of the system operating within 7.9% of the theoretical DR was very high. Again, there

is some discrepancy in the constant term (22587), where the theoretical model corresponds to y =

21500 x-1. This issue will be discussed in section 4.8.

Figure 4-5

Experimental Dilution Ratios for the Two-Stage TSI Diluter

The DR calculated from the concentration measurement results are shown in Figure 4-5.

Direct comparison of the measured outcome to the theoretical trend indicated that the measured

values were generally lower by 7.1%. The highest deviation, 17.5%, occurred again at a DR of 15.

The standard deviation of the result showed that the fluctuations became more significant with the

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

Mea

sure

d D

ilution R

atio



55

higher DR due to the difficulty of measuring the lower concentration at the outlet with high DRs.

Regardless of these variations, the regression of the measured DRs matched the theoretical DR

within an acceptable range (≤ 10%). Therefore the two-stage TSI 379020A is expected to deviate

by less than 3.9% from the theoretical DR over the DR range of 22 to 110.


Figure 4-6

Diluted CH4 Concentration Measurement at Various Dilution Ratios for the Dekati Diluter

The methane concentrations measured downstream of the diluter by the HFID analyzer

are shown in Figure 4-6. The measured values were within 6.2% of the theoretical values, with

exception of a difference of 14.9% at a DR of 125. The results indicate that the increase in deviation

was directly proportional to the increase in DR. The graph showed a divergence of measured

concentration from the ideal values as the DR values got higher. The y-axis error bars computed

0

100

200

300

400

500

600

0 50 100 150 200

CH

4C

once

ntr

ation [ppm

]

Dilution Ratio


56

over the range were narrow, suggesting that the measured values were very consistent at a


As before, a power function trend line was fitted to the measured concentration data and

compared with the theoretical line. The function fit describing the experimental outcome was

closely in line with the theoretical line. The coefficient of the determination indicated that the

equation y = 6608x-1 fit the data well (R2 = 0.993). Once again, the power law constant would be

expected to be the 6500 ppm concentration of the methane test mixture. The discrepancies between

the fitted power function constant (6608) and the theoretical value 6500 is believed to be due to

measurement imprecision (see section 4.8).

The measurement result was predicted based on the power function over the measured

DRs up to DR = 125. Comparison of this projection to the hypothesized line illustrates that it is

very likely that the system will operate within 6.2% of the theoretical DR.

Relative DRs based on the concentration measurements are shown in Figure 4-7. The

direct comparison of the computed result to the theoretical trend indicated that the values were

generally higher by 6.3%. The highest deviation of 17.3% occurred again at a DR of 125. At this

point, a DR = 125, the system was not operating within the manufacturer’s stated range of ≤ 10%

due to a sudden change in test conditions. Such changes were caused by the unstable (fluctuation)

pressure at the inlet point. The standard deviation of the result showed that the divergence became

more significant as DR increased. With the exception of DR = 125, the regression of the measured

DRs fit the theoretical values within the margin of tolerance. Therefore, the performance of the

Dekati FPS-4000 was found to adequate in that it deviated by less than 6.3% from the theoretical

DR over the DR range of 13 to 107.

57

Figure 4-7

Experimental Dilution Ratios for the Dekati Diluter

4.8 Error Analysis and Discussion of Results

All three diluters were expected to perform the dilution process with an actual DR ±10%

of the theoretical dilution ratio. As the result indicated, the diluters tested generally performed

within this tolerance, with minimal outliers. The volumetric dilution ratios of the single-stage TSI

diluter indicated a 3.9% deviation over the dilution ratio range of 12 to 106. The two-stage TSI

diluter operated within 7.1% deviation over the DR range of 22 to 110. The Dekati diluter had less

than 6.3% of deviation over the DR range of 13 to 107.

As was described by Equation 1-3, the volumetric dilution ratios are dependent only on

the volumetric flow. Thus it can be speculated that the expected DR variance within the tested

diluters are contributed from the measurement precision, the consistency of the operating

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140

Mea

sure

d D

ilution R

atio



58

conditions, and the dilution accuracy.

Through leakage testing and numerous secondary procedures, such as monitoring of the

upstream concentration for the Dekati, the consistency of the testing conditions were ensured.

From the literature review, it was stated that the primary dilution temperature, residence time and

relative humidity of the primary dilution air could have influence on the dilution conditions.

However, the experiments were performed under a closed environment where the effects of such

factors are minimal. Thus, any variance contributed from such factors was presumably negligible.

Therefore, the measurement precision and the dilution accuracy were considered as the major

contributing factors to the variance from the expected DR values.

The precision and accuracy of the dilution and measurement instruments were very

important in investigating performance, since small inaccuracies in the data could significantly

affect the result.

To investigate the source of inaccuracies from the test apparatus, an error analysis was

performed on the instruments. The purpose of this analysis was to determine to what extent

measurement error contributed to the discrepancies between the measured DRs and the theoretical

DRs computed.

The uncertainties associated from the gas analyzers are solely dependent on the

measurement precision and accuracies. Therefore the equation for a volumetric DR, Equation 4-2,

is used to determine the uncertainties in the analyzers/particle sizers. This expression can be related

to the general form found in Appendix B as shown below, where k and d terms are simply unity:

!OOOO�� eP"#$%&'()eP*+,-$%&'() ≈ R � k ghi ≈ R � g

i Equation 4-5

59

Then the expression for the percent uncertainty for the analyzers can be re-expressed as

�&B�j � �kg �

j � �li �j Equation 4-6

where mg and mi are the variances of the average measured downstream and upstream gas

concentrations n and o.

For example, at DR = 12 for the single-stage TSI diluter: mg � 171, n � 20,877 ppm,

mi � 29.3 , and o � 1872 ppm. These values are experimentally measured using the NDIR

analyzer. Computing these values into the Equation 4-6, the percent uncertainties value for DR

=12 can be calculated.

�m�!�j � t 171

20877uj � t29.31872u

j → m�! � 0.018

Using the data collected for the other DRs, the appropriate percent uncertainties values

can be computed for the concentration measurement analyzers, the NDIR and the HFID.

Similarly, the uncertainties in the DRs contributed from the flowmeter used to set the TSI

DRs can be derived. The uncertainties associated with the flowmeter are dependent on the two

measured parameters: the sample flow rate and the excess flow rate, as shown in Appendix B.

Rearranging the expression, the resulting function can be related to the general form found in

Equation 4-5 as shown below, where M��A and ��D are constants:

!�� ,QRH � M��A @ 0.83 @ (�Z�� Z b� � 0.3)1.5 @ ��D ≈ R′ � k(Xy � Yy)

Equation 4-7

60

Re-expressing this equation in terms of &{By gives

�&{By�j � � |/hygy/hy mgy�

j � � |/gygy/hy mhy�j Equation 4-8

where mgy and mhy are the manufacturer’s specified accuracy (±2% of the current reading) of the

sample and the excess flow rate readings n′ and d′. For example, at DR = 15 for the two-stage TSI diluter: mgy � 0.019, n′ � 0.93 lpm,

mhy � 0.015, and d′ � 0.76 lpm. These values are experimentally measured using the flowmeter.

Substituting these values into Equation 4-8, the percent uncertainties value for the DR =15 case

can be calculated.

�m�y!′�j � t 1 � 0.76

0.93 � 0.76 ∙ 0.019uj � t 1 � 0.93

0.93 � 0.76 ∙ 0.015uj → m�! � 0.026

Using the data collected for the other DRs, the appropriate percent uncertainties values

can be computed for the flowmeter measurements.

Table 4-1 shows the uncertainties for the instruments used in the TSI diluter experiments

at various range of DRs measured. The analysis indicates that the NDIR has relatively low

uncertainties at lower DRs of 1.8%/1.3% (single /two-stage TSI diluters). The uncertainty values

of the diluters, however, increased as the DRs became higher. The uncertainties associated with

the NDIR for the single-stage TSI rose to 9.2% at DR of 106, and to 5.3% at DR of 110 for the

two-stage TSI. This phenomenon was observed in the previous experimental results, where the

higher DRs deviated more from the expected than the lower DRs.

61

Instrument Percent Uncertainties

Diluters

DR

NDIR

Flowmeter

Single-stage

TSI

12 1.8 2.0

53 3.8 2.0

106 9.2 2.0

Two-stage TSI

15 1.3 2.6

55 3.0 5.9

110 5.3 10.3

Table 4-1

Table of Uncertainty Analysis for TSI Diluter Experimental Apparatus

Similarly, the uncertainties from the flowmeters also increased along with the DR

increment. At lower DRs, the percent uncertainties for the single and two-stage TSI were 2% and

2.6% respectively. One thing to note is that the flowmeter measurement for the single-stage TSI

diluter remained relatively constant throughout the change in DRs (~1.4 lpm). Thus the

uncertainties contributing to the DR value of the single-stage TSI was minimal regardless of the

DR increase. The excess flow rate measured for the two-stage TSI diluter, however, increased

along with DR values, resulting in significantly higher uncertainties at DR = 110 (10.3%).

Direct comparison of the uncertainties associated from the NDIR and the flowmeter

suggests that as the DR increases, the imprecision of the flowmeter becomes the major contributing

factor. At DR = 110, the uncertainties from the flowmeter are twice the uncertainties from the

NDIR. Therefore, accurate measurement of flow is crucial at higher DR to set an accurate DR

value.

62

Likewise, the uncertainties for the instruments used in the Dekati diluter experiment at

various range of DRs measured as shown in Table 4-2. Again, the uncertainty values of the HFID

increased along with the DR increment. At a low DR of 13, the uncertainty value was 1.7%, where

at a higher DR of 125, it rose to 4.7%.

These analyses suggest that the major factor contributing to discrepancies in the

experimental and theoretical DRs measurements are indeed from the precision of the instruments.

It should also be noted that the uncertainties contributed from the flowmeter become more

significant with higher flow rates at higher DRs.

Instrument Percent

Uncertainties

Diluters

DR

HFID

Dekati

13 1.7

56 3.7

125 4.7

Table 4-2

Table of Uncertainty Analysis for Dekati Diluter Experimental Apparatus

As previously indicated in the result sections, there were some discrepancies in power law

constants between the empirical and the theoretical models. The difference in these constant terms

for the TSI single-stage, TSI two-stage, and Dekati diluters were found to be 0.7%, 5.1%, and 1.7%

respectively. These percent differences are well within the expected uncertainties due to the

imprecision in measurement apparatuses. Thus, the discrepancies in power law constants can be

believed to be due to the measurement imprecision quantified in the calculations above.

63

In addition, the result indicated that there were some cases where the dilution ratio

deviated more than the expected error margin. The uncertainty analysis on such a case is

represented by the values of the two-stage TSI. Compared to the single-stage TSI test setup, the

uncertainty on the diluter increased and the others remained constant. This indicates that such

outliers are caused solely by the effect of dilution conditions changing within the diluter. The

primary reason for the cause of change in dilution condition is believed to be a sudden fluctuation

in input pressure. A stabilized pressure at the sample inlet is very difficult to maintain. However,

an extended inter-sample time to allow for a longer adjustment period for a dilution ratio change

can alleviate the effect of the pressure change. Therefore, for future experiments it is suggested to

implement a longer inter-sample time of 5 min for stabilization purposes.

This chapter has examined the accuracy of the dilution ratio actually achieved by the

various diluters. With this knowledge in hand, it is now possible to quantify particle loss in the

diluters, which is the topic of Chapter 5.

64

Chapter 5

Particle Loss in Aerosol Diluters

5.1 Introduction

The results of Chapter 4 show that the actual dilution ratio achieved by all of the diluters

can be expected to be within ±10% of the user set dilution ratio. With dilution ratio accuracy

established, this chapter will focus on the particle phase loss within the aerosol diluters. The effect

of particle loss, neglected in the vapor phase such as coagulation, evaporation, condensation, and

other diffusion loss, will be discussed. The influence of these effects on different particle sizes is

investigated to further characterize the systematic behavior of the diluters. In addition, the

operating features such as heating and thermal conditioning are explored. Again, the diluters tested

were the single-stage and two-stage TSI 379020A rotary disk thermodiluters, and the Dekati FPS-

4000 ejector diluter.

5.2 Particle Loss Measurement Apparatus

Due to the complexity of particle dynamics of the engine-emitted emission particles, the

particle loss measurement experiments were conducted in two phases with varying particle sources:

the exhaust emitted from the diesel engine and the soot particles generated from the Jing

miniCAST MOD6203 soot generator. The ultrafine particles produced from the diesel engine may

undergo coagulation, evaporation, or condensation mechanisms due to their significant organic

carbon content. Thus, particles below the 29.4 nm size range were significantly lost during the

dilution process (As indicated by the results in section 5.7). Hence accurate measurements of

particle distribution were extremely difficult. Therefore, the soot generator was used as a means to

65

produce stable small solid particles to minimize such particle conversion mechanisms.

5.2.1 Diesel Emission Test Apparatus

Figure 5-1 shows the apparatus used for the particle loss measurement of the diluters

investigated utilizing the diesel exhaust. The sample particles were generated from a Tier 1 direct

injection, turbocharged, water-cooled, Cummins diesel engine operating in stabilized condition at

mode 9 of the ISO 8178 engine test procedure (1400 rpm, 25% load). The upstream and

downstream concentration levels were monitored continuously with the EEPS and the FMPS.

As discussed in Chapter 1, the direct emission from the engine was sampled using an

engine dynamometer setup, where the engine is isolated from the vehicle body. The engine out-

emission is directed through the 3” thermally insulated stainless steel exhaust pipe to a sampling

canister with an 11.5” diameter. This canister is used as a placement holder for diesel aftertreatment

systems such as a DPF or DOC. The engine exhaust then can be sampled at various points along

the canister through a 1/2” outlet port – i.e. pre-treated and post-treated emissions can be examined.

After the diesel exhaust is treated by the aftertreatment system, the number of particles in all size

ranges is greatly reduced. The particle numbers in certain size ranges may fall below the detection

limit of the particle sizer. Thus for the purpose of verifying the particle loss within the diluter

system, the exhaust upstream of the aftertreatment system was used due to the higher particle

number available in all size bins.

66

Figure 5-1

Diesel Exhaust Particle Loss Test Apparatus for Diluters

As illustrated in Figure 5-1, the raw exhaust from the diesel engine was pre-diluted with

HEPA-filtered, particle-free, dry air to dilute the raw exhaust down to the appropriate concentration

level. This step was necessary since the upper particle number limit of the EEPS is lower than the

untreated concentration from the engine exhaust. The flow rate of the dilution air was gradually

increased until the monitored mode particle concentration fell below the detection capacity of the

particle sizer (approximately 108 #/cm3). It should be noted that the dilution ratio of this pre-

dilution process does not have to be known since the concentration upstream and downstream of

the diluters are collected simultaneously. Therefore, regardless of the dilution ratio used in the pre-

dilution phase, the sample upstream concentration can be related to the sample downstream

concentration.

67

A pre-dilution also helps to decrease the inlet sample temperature. This is essential for the

proper functioning of the EEPS. The temperature of the raw exhaust from the operating engine at

1400 rpm is approximately 140 °C. This temperature is well beyond the range of accepted inlet

sample temperature of the particle sizer: 10 to 52 °C. Thus, by introducing the dilution air at room

temperature (approximately 24 °C), the sample temperature can be reduced to the acceptable range.

Dilution with ambient temperature air also forces condensation of volatiles, ensuring a large

concentration of very small particles.

A vent line to the atmosphere was installed before the diluters to avoid any pressure

accumulation at the sampling point. The presence of any pressure buildup has a direct effect on

the dilution ratio as discussed in the previous chapter.

A post-dilution was also performed before the downstream measurement. The reason for

this additional dilution process was due to the difference between the flow rates of the diluters and

the FMPS. The FMPS samples at 9.15 lpm, whereas the TSI diluters provide ~ 1.425 lpm and the

Dekati diluter operates at various flow rates depending on the dilution ratio chosen. Thus the flow

rates from the outlet of the diluters are well below the inlet flow required by the FMPS. Directly

connecting the FMPS to the outlet of the diluters will cause pressure fluctuations and as discussed

before, will cause significant change in the dilution conditions. Therefore, a post-dilution was done

with HEPA-filtered, particle-free air to provide make-up flow for the FMPS.

A flowmeter was installed before the connection between the FMPS and the diluter to

measure the post-dilution ratio achieved. It was necessary to quantify this dilution ratio as opposed

to the pre-dilution process in order to identify the diluted concentration at the diluter output –

which was the true downstream concentration of the diluter.

68

5.2.2 Soot Generator Test Apparatus

Figure 5-2 shows the apparatus used for the particle loss measurement of the diluters

investigated utilizing stable ultrafine particles produced by the soot generator. As discussed in

Chapter 3, the particle size distribution generated from the soot generator can be varied using

different flow rates of the quenching gas, nitrogen. To produce particles below 29.4 nm, the

quenching flow rate was gradually increased until the mode particle size fell within the range of

8.06 and 22.1 nm. A quenching flow rate of approximately 60 sccm produced such a particle

distribution and this could be varied through the fuel gas condition (i.e. proportions of fuel and N2

and pressure). Fuel pressure can also have an effect in producing a different particle size

distribution.

The diffusion flame in the soot generator is very sensitive to the pressure at the outlet. The

flame will extinguish in the presence of a pressure build-up at this point. Therefore, to produce a

stable flame, a 1/2” vent line to the atmosphere was used to relieve any buildup pressure. There

was a flow pipe reduction from 1/2" to 1/4" between the soot generator and the diluter. Hence, a

second vent line to atmosphere was necessary to relieve the pressure at the diluter inlet. As

discussed in Chapter 4, a “positive flow” to the atmosphere was always ensured during the

experiment to ensure a precise dilution process.

69

Figure 5-2

Soot Generator Particle Loss Test Apparatus for Diluters

Unlike the engine exhaust particle loss test apparatus, producing constant particle

concentration over the various size bins was difficult for the soot generator particle loss test

apparatus due to unstable flame conditions. The placement of the EEPS upstream of the diluter

extinguished the flame by creating too much pressure from the sampling flow rate. Hence, the

measurements of the particle concentrations upstream of the diluter were made prior to the

experiment. Once the flame was stabilized, the particle size distribution produced from the soot

generator was very consistent. Hence the distribution change over time was minimal and it was

safe to assume that the upstream measurement made prior to the experiment was valid. These

measurements will be presented in section 5.7.

For the reasons discussed in the previous section, the diluter output was further diluted

and a flowmeter was installed to allow appropriate measurement of the true downstream flow rate.

70

5.3 Particle Loss Measurement Methods

For the measurement of diluter particle loss, it was crucial to stabilize the engine speed

and the soot generator flame prior to the measurement. At an unstable condition these sources will

produce particle distributions with fluctuations in the mode particle size. The engine or the soot

generator should be allowed to pre-run for 30 minutes before the experiment. This preliminary

step ensured higher precision with less fluctuation in the size distribution.

Once the particle producing sources are stabilized, simultaneous measurement was done

on the upstream and downstream concentration for varying DRs, except that when the soot

generator was used, the upstream concentration was measured prior to that downstream. For the

soot generator, the DRs were adjusted ranging from the lowest possible DR to a DR of

approximately 100 in increments of 10 ± 5. When testing with the engine exhaust, three specific

DRs (8, 15, 26 for the single-stage TSI; 50, 72, 100 for the two-stage TSI; 9, 12, 14 for the Dekati)

were verified. These DRs were chosen in accordance to the range of DR used in the Exhaust

Measurement and Inhalation Toxicology Testing of Emerging Diesel Fuels (EMITTED) study. The

EMITTED study characterizes the diesel engine exhaust emission at various points along the

aftertreatment systems and evaluates the effect of these control technologies. The single-stage TSI

diluter is used to dilute the post-treated emissions at lower DRs.; the two-stage TSI diluter is used

to dilute the pre-treated emission at higher DRs; and the Dekati diluter for the filter collection of

exhaust at lower DRs. A wider range was tested through the soot generator experiment, from

lowest to the highest DR possible without affecting the state of the flame.

It should be noted that the same operating procedures and conditions were followed as

discussed in the dilution evaluation measurement methods section (Chapter 4) when operating the

71

diluters. Any heating features associated with the diluters were disabled during the experiment

(primary air and evaporation tube temperature at room temperature ~ 24 °C). The heating and

thermal conditioning features were investigated separately in section 5.8.

When measuring the same source simultaneously there were discrepancies between the

measurements by the EEPS and the FMPS. The particle concentrations measured at varying size

bins were not identical to one another. Since the two particle sizers were reading different number

concentrations under the same condition due to the systematic behavior difference, equivalency

testing was performed. Such testing was essential for the DR analysis, as the disagreement between

the two instruments will result in a misrepresentation of the particle loss.

Figure 5-3

EEPS/FMPS Equivalency Correction Factor (Zimmerman et al, 2013)

As shown in Figure 5-3, appropriate correction factors were derived for the individual

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

5 50

EEPS/F

MPS -

Cle

aned

Colu

mn

Diameter (nm)

40 10 15 20 25 30 35 45 100 150 200 250

72

particle size bins from 9.31 to 220.7 nm. The difference between the two instruments at the varying

particle size bins was up to 30%, thus indicating that if the DR analysis is performed with raw data,

the result of particle loss within the system will be exaggerated by a factor of 1.3. Therefore, to

appropriately equate the readings from the two instruments, these correction factors were applied

to the individual size bins of the FMPS.

5.4 Sampling Time Parameters

The sample time used in the particle loss measurements was 10 minutes. During the

sampling period, the analyzers were recording the data at the averaging time of 1 second. The

averaging time of the analyzers corresponded to the time interval between the two consecutive

recorded data. Hence a sample time of 10 minutes with an averaging time of 1 second resulted in

600 data points for each condition. This sample size ensured a large enough population for a better

averaging value.

After changing the test conditions (i.e. DR), adequate time was required for the measured

concentration to settle down to adjust for the change in the dilution air flows. It was observed

experimentally that approximately 180 seconds of stabilization time was necessary to measure a

comparatively consistent value. In response to this finding, a period of up to 180 seconds was

allowed before taking data under a new test condition.

5.5 Leakage Check

Another important preparatory step before the actual tests was inspecting for any source

of leakage in the experimental setup. When measuring the concentration or particle size

distribution, it was absolutely necessary that there was no source of leakage occurring in the

73

sampling lines. A small leak that allowed atmospheric particles to enter the system could

considerably skew the results. Similarly, operating the system under positive pressure could allow

particles to leak out to the atmosphere causing the number concentration to decrease. Thus, the

system was checked thoroughly using the soapy water leak test. Soapy water was applied to all

junctions and lengthy lines while particles were flowed into the apparatus. Any bubble formation

on the applied surface indicated that there was a leak and the appropriate part was replaced prior

to initializing the test matrix. To guarantee that there was certainly no leak in the system, zero air

was flowed into the apparatus and measured by the particle sizers. The system was considered leak

tight if the particle number concentration determined by the particle sizers were below the

detection limit.

5.6 Calculation Methods

Equation 1-4 described the general calculation method for the particle DR. But, all of the

data collected during the sampling period was averaged over the sample population of 600. Thus,

the average concentration is used to calculate the mean experimental particle DR as follows:

!OOOO�� ( �� ) � eP"#$%&'()( �#

�$02')eP*+,-$%&'()( �#

�$02') Equation 5-1

where �̅ is the average particle concentration in individual particle size bin measured by the sizers

in #/cm3.

The same method for correcting theoretical DR for the TSI two-stage diluter described in

Chapter 4 was used. Using Equations 4-4 and 4-5, the corrected � �� was computed. With

��D being kept constant at 100%, the corrected !�� ,QRH was calculated using the

Equation 4-3.

74

In the particle loss test apparatus, additional post-dilution was performed in order to

compensate for the detection capacity of the particle sizers. As such, a correction factor had to be

applied to the measured downstream particle size bins to compute the appropriate particle

concentration. For this correction, the post-dilution process was assumed to be a volumetric phase

and any particle loss was assumed to be negligible. With this assumption, Equation 1-3 was used

to calculate the correction factor. Since the upstream concentration of the post-dilution process

was desired, the equation was rewritten as

�� ."#$%&'()/.*01"%0+-."#$%&'() @ �� Equation 5-2

where the term ."#$%&'()/.*01"%0+-

."#$%&'() � M is the determined correction factor. This correction factor

was then applied to the individual particle size bins. The computed concentration from this

correction was used as the downstream concentration for further analysis.

5.7 Results

In each case, the particle loss within the diluter system was studied using the concentration

measured upstream and downstream to calculate the experimental DRs. The recorded value was

then compared with the theoretical values given by the diluter setting.

5.7.1 Single-Stage TSI 379020A Rotary Disk Thermodiluter

As shown in Figure 5-4, the upstream and downstream engine exhaust particle

distributions at various DRs were measured by the appropriate particle sizers (i.e. an EEPS for the

upstream concentration and an FMPS for the downstream concentration). The resulting

concentrations showed that the measured downstream distributions at the three DRs tested, 8, 15,

75

and 26 were following a similar trend to the undiluted (raw exhaust) concentration. The undiluted

concentration was measured simultaneously for each DR. Because these were very similar, only

the undiluted concentration measurement at DR = 8 is presented in Figure 5-4. From the direct

comparison of undiluted and diluted data for DR = 8, it can be seen that the shape of two

distributions is indeed similar. The mode particle size for each distribution was found to be around

93.1 nm for DR = 8 but it was shifted to 60.4 nm for DR = 15 and 26. This, however, did not

suggest that the dilution behavior had changed because the simultaneous measurement of the

upstream concentration indicated a similar trend as the data graphed for DR = 15 and 26.

Figure 5-4

Engine Exhaust Particle Distribution at Various Dilution Ratio for the Single-Stage TSI

Diluter

It should be noted that the standard deviation graphed for each point was at the 99.7%

confidence level. These y-axis error bars correspond to the precision of measured values over 600

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)

Undiluted DR = 8 DR = 15 DR = 26

40 10 15 20 25 30 35 45 100 150 200 250

76

points. The result indicated that a greater fluctuation in particle counts occurred for smaller

particles. For particle size bins above 29.4 nm, the error bars were very small. This indicated that

the values were very consistent at a stabilized condition with 99.7% confidence. However below

a particle size of 29.4 nm, particles were being significantly lost after the dilution process. The

increased standard deviation for these particles were a direct result of the undiluted concentration

measurement, where the existence of such variation was evident. Hence, the fluctuation in the

undiluted gas concentrations were reflected on the diluted concentration measurements.

Figure 5-5

Engine Exhaust Experimental Percent Particle Penetration for the Single-Stage TSI Diluter

Figure 5-5 shows the percent particle penetration values corresponding to the measured

concentrations. The resulting values suggested that a significant portion of particles smaller than

29.4 nm were indeed being lost. In fact, the low particle penetration for these small particles may

have been due to a combination of particle loss and particle growth. The percent particle

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

PDR = 8 PDR = 15 PDR = 26

40 10 15 20 25 30 35 45 100 150 200 250

77

penetration values above 100% for size bins 29.4 to 52.3 nm suggested that volatile components

in these smaller particles, such as organic carbon, were evaporating and condensing onto the larger

29.4 to 52.3 nm particles. The overall average percent particle penetration for the DRs tested were

98.5%, with lowest penetration at 191.1 nm with 90.8%.

Particle penetration values greater than 100% indicate that mass was gained during the

dilution process. In order to evaluate the extent to which the disappearing small particles contribute

to the increase in numbers (and consequently their mass) of the larger size particles, a mass balance

was performed between the particle size bins below 29.4 nm and the size bins that have particle

penetration values above 100%. If, during the dilution process, the mass of all particles in the

smaller size bins that have disappeared is the only contributor to the increase in mass of the larger

size bins that show penetration values above 100%, the two masses should be equal to one another.

The bins for particle sizes less than 29.4 nm include 9.31, 10.8, 12.4, 14.3, 16.5, 19.1, 22.1, and

25.5 nm diameters while those bins that have particle penetration numbers greater than 100%

include bins with 29.4, 34, 39.2, 45.3, and 52.3 nm diameters. The mass balance relation can be

expressed as:

∑ (`�� `� �)j�.��.W| � ∑ (`� � �`�� )�j.Wj�.� Equation 5-3

where: ∑`� represents the sum of the mass of particles in each bin � , the subscript �ℎ��

represents the theoretical particle mass and the subscript `��m represents the particle mass

calculated from the measured particle numbers in the bin. Here, theoretical means the value

calculated by applying the volumetric dilution ratio to the undiluted particle number concentration

in that bin. There is a mass loss on the left hand side of the equation, where the measured

concentration values are much less than the expected (theoretical) values. There is a gain of mass

78

on the right hand side where the measured concentration exceeds the expected value.

Particle mass can be computed from the number of particles, but the measurement

provides concentration, particles/unit volume of diluted engine exhaust. In order to make use of

the concentration measurements, equation 5-3 can be expressed on a per unit volume basis as:

∑ �� j�.��.W| � ∑ ��

�� j.Wj�.� Equation 5-4

Particle mass per unit volume can be calculated from the concentration �� , particle

diameter �� and density �:

�� ∙ ��W ��#j �W�� ∙ � Equation 5-5

Substituting equation 5-5 into equation 5-4 for �� gives:

∑ ��,�� ,� �� ∙ ��W ��#j �W�� ∙ ��j�.��.|

� ∑ ��,� �� ,�� ∙ ��W ��#j �W�� ∙ ��j.Wj�.� Equation 5-6

The equations above assume a common density for all particles. The particles less than

29.4 nm in diameter were assumed to be liquid and to have the density (ρ= 0.770 g/cm3) of cetane,

a surrogate for diesel fuel.

Performing the mass balance for DR = 8, the theoretical mass of all particles below 29.4

nm that were lost in dilution was 4 @ 10�|� g/cm3 (mass of cetane/volume of air) and the mass

of all particles gained in the size bins where particle penetration exceeded 100% was 5.7 @ 10�|W

g/cm3. The particles below 29.4 contributed only 7% of the added mass of particles in the bins

79

where greater than above 100% penetration occurred. Hence, it can be hypothesized that the

evaporation and condensation of volatile components in the smaller particles onto the larger 29.4

to 52.3 nm particles are a minor contributor to the increase in particle penetration value. The major

contributor to the particle growth is unclear. However, diesel exhaust contains many organic and

inorganic species that are in the gas phase at normal exhaust system temperature. As the gas

temperature falls during the dilution process these species could condense or adsorb on existing

particles, resulting in growth. Small particles have a larger surface to volume ratio than larger

particles, which means that growth by surface addition would have a much larger effect on particle

mass for small particles.

Based on the concentration measurement results, the corresponding DRs were calculated

for each individual particle size bin as shown in Figure 5-6. Direct comparison of the outcomes

(PDR, particle DR) to the theoretical trend (VDR, volumetric DR) indicated that the values were

generally within 6.6% at DR = 8, 6.6% at DR = 15 and 3.8% at DR = 26 for all size bins above

29.4 nm. The highest deviation of 9.7% occurred at a particle size of 220.7 nm for DR = 8, 11.6%

at a particle size of 191.1 nm for DR = 15, and 9.3% at a particle size of 191.1 nm for DR = 26.

The standard deviation of the result showed that, again, greater fluctuation occurred at lower

particle sizes where a significant portion of the particles was being lost. However, disregarding the

particle concentration measured below 29.4 nm, the overall regression of the measured DRs fit the

theoretical volumetric DR well. Thus, from the engine exhaust studies, the particle loss within the

single-stage TSI 379020A was minimal, and this unit can be expected to dilute to within 6.6% of

the theoretical value for particles larger than 29.4 nm.

The compounds in diesel exhaust are in both the vapor and solid phases, and therefore the

80

particles are subjected to coagulation, condensation and evaporation. Thus, larger particles can

shrink due to hydrocarbon condensation onto smaller particles, which can cause them to grow to

a larger size. Therefore to accurately verify particle loss in the smaller particle ranges, the soot

generator was used as the source instead of the engine exhaust.

Figure 5-6

Engine Exhaust Experimental Dilution Ratios for the Single-Stage TSI Diluter

The appropriate particle sizers measured the upstream and downstream soot generator

particle distributions at various DRs as illustrated in Figure 5-7. The resulting concentrations

showed that the measured downstream distributions at various DRs are very similar in shape. The

mode particle size for each distribution was found to be around 10.8 nm for all DRs tested with

the soot generator. Direct comparison of the undiluted distribution to the diluted distribution

indicates that the general trend of the particle distribution is consistent regardless of the change in

DR. The standard deviations calculated over the ranges were also noticeably small for both

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

5 50

Dilution R

atio

Particle Size (nm)

PDR = 8 VDR = 8 PDR = 15

VDR = 15 PDR = 26 VDR = 26

40 10 15 20 25 30 35 45 100 150 200 250

81

undiluted and diluted conditions. This indicates that the measured values were very consistent at a


Figure 5-7

Soot Generator Particle Distribution at Various Dilution Ratio for the Single-Stage TSI

Diluter

Figure 5-8 shows the average percent particle penetration values corresponding to the

measured concentrations for all the DRs tested with the soot generator. The resulting values

indicate a relatively consistent percent particle penetration over the particle size bins. The percent

particle penetration values above 100% for size bins 16.5 to 29.5 nm were likely due to the

measurement precision of the instruments used in the experiment. As will be discussed in section

5.8, these instruments have certain associated uncertainties that lead to imprecision in

measurement (< 5.9%). However, the average percent particle penetration for the DRs tested were


1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)


DR = 40 DR = 50 DR = 60 DR = 70

DR = 80 DR = 90 DR = 100

40 10 15 20 25 30 35 45

82

Figure 5-8

Soot Generator Experimental Average Percent Particle Penetration for the Single-Stage

TSI Diluter

The DRs calculated from the particle concentrations measurement results are shown in

Figure 5-9. Comparing individual measured PDR values to the theoretical trend indicated that the

computed PDR values for individual size bins at various DRs were generally within ± 6.0%. The

average percent DR difference (between particle and set volumetric DRs) and the highest

deviations for the various DR conditions are summarized in Table 5-1. From the result, it can be

seen that the highest deviation points occur at various particle size bins with no specific size

preference. These repeated outcomes suggest that the single-stage TSI diluter can suffer particle

loss in any particle size bin. However, the particle loss within the single-stage TSI 379020A is

generally small, less than 12.8% over the DR range of 12 to 100.

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etart

ion (%

)

Particle Size (nm)

Average of Tested PDRs

40 10 15 20 25 30 35 45

83

Figure 5-9

Soot Generator Experimental Dilution Ratios for the Single-Stage TSI Diluter

0

10

20

30

40

50

60

5 50

Dilution R

atio

Particle Size (nm)

PDR = 12 VDR = 12 PDR = 20 VDR = 20

PDR = 30 VDR = 30 PDR = 40 VDR = 40

PDR = 50 VDR = 50

40

50

60

70

80

90

100

110

120

5 50

Dilution R

atio

Particle Size (nm)

PDR = 60 VDR = 60 PDR = 70 VDR = 70

PDR = 80 VDR = 80 PDR = 90 VDR = 90

PDR = 100 VDR = 100

40 10 15 20 25 30 35 45

40 10 15 20 25 30 35 45

84

DR

DR Difference (%)

Highest Deviation Point

Particle Size (nm) DR Difference (%)

12 12.8 39.2 16.1

20 4.6 34 8.3

30 3.5 34 6.3

40 6.5 25.5 9.7

50 6.3 22.1 10.8

60 5.7 22.1 11.5

70 5.9 16.5 11.4

80 4.3 6.04 10.6

90 5.6 12.4 9.8

100 6.0 9.31 11.6

Table 5-1

Summary of Average Percent Dilution Ratio Difference and Highest Deviation Point for the

Single-Stage TSI Diluter

It should be noted that the trends of the PDR values over the range of particle size bins at

various DRs are relatively similar to one another. Such behavior suggests that the systematic

operation of the single-stage TSI diluter is consistent with high repeatability.

5.7.2 Two-Stage TSI 379020A Rotary Disk Thermodiluter

The particle concentrations downstream and upstream of the diluter, measured with the

particle sizers are shown in Figure 5-10. Comparison of the measured downstream distributions to

the upstream distribution at three DRs of 50, 72, and 100 showed similar trends. The shape of the

undiluted size distribution plotted corresponds to that of the upstream measurement at DR = 50.

85

From the direct comparison of these two data sets, it can be seen that the shape of two distributions

are indeed similar. The mode particle size for each distribution was found to be around 69.8 nm

for all DRs tested. This suggested that the engine was producing a consistent concentration of

particles distributed over the entire size range.

Again, the results indicated that the greatest fluctuation in particle counts occurred in the

lower particle size ranges. Particles smaller than 29.4 nm were being lost through the dilution

process and the standard deviation was increased. For ranges above 29.4 the deviations over the

ranges were noticeably smaller, suggesting greater consistency at a stabilized condition with 99.7%

confidence.

Figure 5-10

Engine Exhaust Particle Distribution at Various Dilution Ratio for the Two-Stage TSI

Diluter


1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)


40 10 15 20 25 30 35 45 100 150 200 250

86

concentrations. Again, the resulting values indicated that a significant portion of particles were

being lost below a particle size of 29.4 nm. The percent particle penetration values were above

100% for size bins 29.4 to 52.3 nm suggesting condensation of hydrocarbons into larger particles

in those particle size bins. However, the average percent particle penetration for the DRs tested

were 98.8%, with lowest penetration at 165.5 nm with 91.1% at DR = 50, 91.2% at 165.5 nm for

DR = 72, and 96.6% at 107.5 nm for DR = 100.

Figure 5-11

Engine Exhaust Experimental Percent Particle Penetration for the Two-Stage TSI Diluter

Once again, a mass balance for DR = 50 was performed. The lost mass per unit volume of

diluted exhaust gas of all particles below 29.4 nm was 3.4 @ 10�|� g/cm3. The mass per unit

volume of diluted exhaust gas gained by all particle sizes where the particle penetration was above

100% was 2.3 @ 10�|� g/cm3. Thus, the particles smaller than 29.4nm that disappeared during

dilution only contributed 14.5% of the mass gained by the particles having a particle penetration

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

PDR = 50 PDR = 72 PDR = 100

40 10 15 20 25 30 35 45 100 150 200 250

87

value above 100%. Therefore, similar to the TSI single-stage diluter, the volatile components that

have evaporated and condensed onto the larger 29.4 to 52.3 nm particles are a minor contributor

to the particle growth in these size bins.

Figure 5-12

Engine Exhaust Experimental Dilution Ratios for the Two-Stage TSI Diluter

The DRs corresponding to each individual particle size bin calculated from the

concentration measurements are shown in Figure 5-12. Direct comparison of the PDRs to the

theoretical VDRs indicated that the values were generally within 3.0% at DR = 50, 1.9% at DR =

72 and 4.3% at DR = 100 for all size bins above 29.4 nm. The highest deviation of 7.2% occurred

at a particle size of 34 nm for DR = 50, 6.7% at a particle size of 39.2 nm for DR = 72, and 10.9%

at a particle size of 34 nm for DR = 100. The standard deviation of the result showed that greater

fluctuation occurred at a lower DR where a significant portion of the particles was being lost.

However, disregarding the particle concentrations measured below 29.4 nm, the overall regression

1.E+01

1.E+02

1.E+03

1.E+04

5 50

Dilution R

atio

Particle Size (nm)

PDR = 50 VDR = 50 PDR = 72

VDR = 72 PDR = 100 VDR = 100

40 10 15 20 25 30 35 45 100 150 200 250

88

of the measured PDRs fit the theoretical VDRs well. Thus, from the engine exhaust studies, the

particle loss within the two-stage TSI 379020A was minimal. The expected DR deviation was less

than 4.3% from the theoretical DR over the particle size bins above 29.4 nm.

Figure 5-13

Soot Generator Particle Distribution at Various Dilution Ratio for the Two-Stage TSI

Diluter

The appropriate particle sizers measured the upstream and downstream soot generator

particle distributions at various DRs as illustrated in Figure 5-13. The resulting concentrations

showed that the measured downstream distributions at various DRs are very similar in shape. The

mode particle size for each distribution was found to be around 10.8 nm for all DRs tested with

the soot generator. Direct comparison of the undiluted distribution to the diluted distributions

indicated that the general trend of the particle distribution was consistent regardless of the change

in DR. The standard deviations calculated over the ranges were also noticeably small for both

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)


DR = 45 DR = 56 DR = 64 DR = 74

DR = 85 DR = 98 DR = 113

40 10 15 20 25 30 35 45

89

undiluted and diluted conditions. This suggests that the measured values were very consistent at a

stabilized condition with 99.7% confidence. For DR = 113, however, the standard deviation

increased. The reason for this increase in error bar was due to fluctuation in pressure causing the

flame to become unstable.

Figure 5-14

Soot Generator Experimental Average Percent Particle Penetration for the Two-Stage TSI

Diluter



indicated a relatively consistent percent particle penetration over all particle size bins. The percent


measurement precision of the instruments used in the experiment. However, the average percent

particle penetration for the DRs tested were 99.4%, with lowest penetration at 29.4 nm with 94.2%.

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)


40 10 15 20 25 30 35 45

90

Figure 5-15

Soot Generator Experimental Dilution Ratios for the Two-Stage TSI Diluter

The DRs calculated from the particle concentrations measurement results were shown in

Figure 5-15. Comparing individual PDR values to the theoretical volumetric DR trend indicated

10

20

30

40

50

60

70

5 50

Dilution R

atio

Particle Size (nm)

PDR = 16 VDR = 16 PDR = 24 VDR = 24

PDR = 35 VDR = 35 PDR = 45 VDR = 45

PDR = 56 VDR = 56

50

70

90

110

130

5 50

Dilution R

atio

Particle Size (nm)

PDR = 64 VDR = 64 PDR = 74 VDR = 74

PDR = 85 VDR = 85 PDR = 98 VDR = 98

PDR = 113 VDR = 113

40 10 15 20 25 30 35 45

40 10 15 20 25 30 35 45

91

that the computed DR values for individual size bins at various DRs were generally within ± 3.9%.

The average percent DR difference and the highest deviations for the various DR conditions are

summarized in Table 5-2. From the result, it can be seen that the highest deviation points occurred

in various particle size bins. This suggested that the two-stage TSI diluter can suffer particle loss

in any particle size bin. However, the particle loss within the two-stage TSI 379020A is expected

to be small, less than 5.7% over the DR range of 16 to 100.

DR

DR Difference (%)



16 2.7 45.3 7.0

24 2.7 45.3 7.0

35 5.7 34 10.3

45 3.5 34 6.7

56 3.7 34 8.3

64 3.7 6.98 7.8

74 3.2 6.04 7.2

85 3.9 29.4 8.1

98 4.8 45.3 9.9

113 5.0 45.3 10.8

Table 5-2


Two-Stage TSI Diluter

A similar pattern of particle dilutions over the ranges of size bins suggest that the

systematic operation of the two-stage TSI diluter is consistent with high repeatability. The standard

92

deviation of the individual particle dilutions were also less than 10% suggesting that the system is

operating within the accepted error margin.


Figure 5-16

Engine Exhaust Particle Distribution at Various Dilution Ratio for the Dekati Diluter

The particle concentrations downstream and upstream of the diluter, measured with the

particle sizers are shown in Figure 5-16. The comparison of the measured downstream distributions

to the upstream distribution at three DRs of 9, 12, and 14 showed a similar trend. The undiluted

distribution plotted corresponds to the upstream measurement at DR = 9. From direct comparison

of these two data sets, it can be seen that the shape of the two distributions are indeed similar. The

mode particle size for each distribution was found to be around 69.8 nm for all DRs tested. This

suggested that the engine was producing a consistent concentration of particles distributed over

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)


40 10 15 20 25 30 35 45 100 150 200 250

93

the entire particle size range.

The result indicated that the greater fluctuation in particle counts occurred at lower particle

size ranges. For particle size bins below 29.4 nm, the particles were being significantly lost after

the dilution process and the standard deviation is increased. For ranges above 29.4 nm, the

deviations over the ranges were noticeably small, suggesting great consistency at a stabilized

condition with 99.7% confidence.

Figure 5-17

Engine Exhaust Experimental Percent Particle Penetration for the Dekati Diluter

Figure 5-17 shows the percent particle penetration value corresponds to the measured

concentrations. Again, the resulting values indicated that a significant portion of particles were

being lost below a particle size of 29.4 nm. The percent particle penetration values were above

100% for size bins 29.4 to 52.3 nm suggesting condensation of hydrocarbons into larger particles

in those particle size bins. However, the average percent particle penetration for the DR tested was

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

PDR = 9 PDR = 12 PDR = 14

40 10 15 20 25 30 35 45 100 150 200 250

94


The mass balance comparison shows that at DR = 9, the lost mass of all particles smaller

than 29.4 nm was 2.9 @ 10�|� g/cm3 and the mass gain of all particles having greater than 100%

particle penetration was 3.9 @ 10�|W g/cm3. Thus, the particles smaller than 29.4 nm only

contributed 7.6% of the mass gained by the particles having a particle penetration above 100%.

Therefore, similar to both TSI diluters, the volatile components that evaporated and condensed

onto the larger 29.4 to 52.3 nm particles are a minor contributor to the particle growth in these size

bins.

Figure 5-18

Engine Exhaust Experimental Dilution Ratios for the Dekati Diluter

Relative DRs based on the concentration measurements corresponding to each individual

particle size bin are shown in Figure 5-18. Direct comparison of the PDRs to the theoretical VDRs

1

10

100

1000

5 50

Dilution R

atio

Particle Size (nm)

PDR = 9 VDR = 9 PDR = 12

VDR = 12 PDR = 14 VDR = 14

40 10 15 20 25 30 35 45 100 150 200 250

95

indicated that the values were generally within 5.7% at DR = 9, 7.3% at DR = 12 and 9.6% at DR

= 14 for all size bins above 29.4 nm. The highest deviation of 14.1% occurred at a particle size of

34 nm for DR = 9, 18.2% at a particle size of 34 nm for DR = 12, and 14.6% at a particle size of

39.2 nm for DR = 14. The standard deviation of the result showed that greater fluctuation occurred

at a lower DR where a significant portion of the particles was being lost. However, disregarding

the particle concentration measured below 29.4 nm, the overall regression of the measured PDRs

fit the theoretical VDRs well. Thus, from the engine exhaust studies, the particle loss within the

Dekati FPS-400 was relatively small. The measured DR was expected to deviate less than 9.6% of

theoretical DR over the particle size bins above 29.4 nm.

Figure 5-19

Soot Generator Particle Distribution at Various Dilution Ratios for the Dekati Diluter

Figure 5-19 shows the upstream and downstream soot generator particle distributions at

various DRs measured using the appropriate particle sizers. The resulting concentrations showed

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

5 50

dN

/dlo

g D

p (#/c

m3)

Particle Size (nm)


DR = 44 DR = 55 DR = 66

40 10 15 20 25 30 35 45

96

that the measured downstream distributions at various DRs are very similar in shape. The mode

particle size for each distribution was found to be around 10.8 nm for all DRs tested. The direct

comparisons of the undiluted distribution to the diluted distributions indicate that the general trend

of the particle distribution is consistent regardless of the change in DR. The standard deviations

calculated over the ranges were also noticeably small for both undiluted and diluted conditions.

This suggests that the measured values are very consistent at a stabilized condition with 99.7%

confidence. For DR = 44, however, the standard deviation increased. The reason for this increase

in error was due to fluctuations in pressure causing the flame to become unstable.

Figure 5-20

Soot Generator Experimental Average Percent Particle Penetration for the Dekati Diluter



indicate a relatively consistent percent particle penetration over the particle size bins. The percent

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)


40 10 15 20 25 30 35 45

97


measurement precision of the instruments used in the experiment. However, the average percent

particle penetration for the DRs tested were ~100 % (99.9 %), with lowest penetration at 6.04 nm

with 93.6%.

The DRs calculated from the particle concentrations measurement results are shown in

Figure 5-21. Comparing individual PDR values to the theoretical VDR indicated that the computed

DR values for individual size bins at various DRs were generally within ± 5.1%. The average

percent DR difference and the highest deviations for the various DR conditions are summarized in

Table 5-3. The highest particle loss at various size bins suggest that the Dekati FPS-4000 diluter

can suffer particle loss in any particle size bin. The particle loss within the Dekati FPS-4000 is

expected to be small, less than 6.4% over the DR range of 12 to 66.

Figure 5-21

Soot Generator Experimental Dilution Ratios for the Dekati Diluter

0

10

20

30

40

50

60

70

80

5 50

Dilution R

atio

Particle Size (nm)

PDR = 12 VDR = 12 PDR = 23 VDR = 23

PDR = 35 VDR = 35 PDR = 44 VDR = 44

PDR = 55 VDR = 55 PDR = 66 VDR = 66

40 10 15 20 25 30 35 45

98

DR

DR Difference (%)



12 4.5 19.1 7.8

23 4.5 25.5 8.4

35 6.2 14.3 8.2

44 6.4 25.5 9.7

55 4.3 6.04 6.6

66 4.8 6.04 9.2

Table 5-3


Dekati Diluter

A relatively similar pattern of the particle dilutions over the ranges of size bins suggest

that the systematic condition of the Dekati diluter is consistent with high repeatability. The

standard deviation of the individual particle dilutions were also less than 10% suggesting that the

system is operating within the accepted error margin.

5.8 Investigation of Heating and Thermal Conditioning Elements

As mentioned before, the diluters investigated have the capacity to heat the dilution air to

a higher temperature for removal of condensed volatile materials from the sample. In addition, the

two-stage TSI 379020A has a thermal conditioner that allows the elimination of condensed

nanodroplets and volatile particle formation. In the previous experiments, any heating features

associated with the diluters were disabled (primary air and evaporation tube temperatures were

room temperature ~ 24 °C). In this section, the effect of these operating features will be quantified

99

in regards to the particle dilution ratio using the engine exhaust – a known source with a volatile

fraction.

5.8.1 TSI 379020A Rotary Disk Thermodiluter

Figure 5-22

Engine Exhaust Dilution Ratios Corresponding to the Primary Dilution Air Temperature

for Single-stage TSI Diluters

Figure 5-22 illustrates the engine exhaust particle DRs corresponding to the primary

dilution air heating temperature (DHT) for the single-stage TSI diluters above 29.4 nm size bin.

The size bins below 29.4 nm were neglected due to significant loss of particles as noted in section

5.7. The result indicated that as the primary dilution air temperature was increased, the particle

DRs along the recorded size bins converged towards the theoretical dilution ratio. At DR = 5

without heating, the highest deviation was 30% from the theoretical value. These data suggest that

3

4

5

6

7

8

9

10

20 200

Dilution R

atio

Particle Size (nm)

DHT = Off VDR = 5 DHT = 80 °C

VDR = 7 DHT = 150 °C VDR = 8

160 40 60 80 100 120 140 180

100

heating is required to get good agreement for particle sizes below 124.1 nm. However, at 150 °C

or DR = 8, the highest deviation was greatly reduced to 4.4%. One thing to note about this result

is that the dilution settings were kept constant except the temperature. Thus, the increase in dilution

temperature also increases the dilution ratio because the density changes. Therefore the dilution

ratio without heating was at 5 but with the increase in temperature up to 150 °C, the dilution ratio

rose to 8.

Figure 5-23

Engine Exhaust Percent Particle Penetration Corresponding to the Primary Dilution Air

Temperature for the Single-stage TSI Diluters


concentrations for all the primary dilution air temperature tested with the engine exhaust. The

resulting values indicate that, when the heating element is disabled, condensation causes growth

in the particle range 29.4 to 60.4 nm, where the particle penetration values exceed 100% (discussed

0

20

40

60

80

100

120

140

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

DHT = Off DHT = 80 °C DHT = 150 °C

40 10 15 20 25 30 35 45 100 150 200 250

101

in section 5.7). However, at 150 °C, there is an evident improvement in particle penetration below

29.4 nm and a relatively consistent percent particle penetration over all particle size bins above

29.4 nm (98.2 %). The particle condensation was thus minimized with the primary dilution air

heating.

Figure 5-24

Engine Exhaust Dilution Ratios Corresponding to the Evaporation Tube Heater

Temperature for the Two-Stage TSI Diluter

The effect of evaporation heater temperature (EHT) on the dilution ratio above 29.4 nm is

shown in Figure 5-23. The result suggests that there are no significant effects on particle dilution

ratio corresponding to the evaporation heater temperature. The overall deviation percentage at

300 °C (or On) was comparable to the percentage at Off, 6.6% to 6.3%. This suggests that there

was no significant formation of nanodroplets or volatile particles during the dilution process. Thus

the evaporation heater temperature had no influence towards the particle DRs.

60

65

70

75

80

85

90

95

100

20 200

Dilution R

atio

Particle Size (nm)

ETH = On ETH = Off VDR = 72

160 40 60 80 100 120 140 180

102

Figure 5-25

Engine Exhaust Percent Particle Penetration Corresponding to the Evaporation Tube

Heater Temperature for the Two-Stage TSI Diluter


concentrations for evaporation tube heater temperature tested with the engine exhaust. The overall

average percent particle penetration values above 29.4 nm size bin of heating temperature at 300 °C

(or On) and at room temperature (or Off: ~ 24 °C) were 98.8% and 99% respectively. As discussed,

there was no significant effects on particle dilution ratio corresponding to the evaporation heater

temperature. However, it is suggested to have the evaporation tube heater at 300 °C to actively

prevent formation of undesired particles and droplets

0

20

40

60

80

100

120

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

ETH = On ETH = Off

40 10 15 20 25 30 35 45 100 150 200 250

103


Figure 5-26

Engine Exhaust Dilution Ratios Corresponding to the Primary Dilution Air Temperature

for the Dekati Diluter

Figure 5-26 illustrates the particle DRs corresponding to the primary dilution air

temperature for the Dekati diluter. It should be noted that the size bins below 29.4 nm were

excluded to make the effect of dilution air heating more visible. The result indicated that as the

primary dilution air temperature was increased, the particle DRs along the recorded size bins

diverged from the theoretical dilution ratio. At DR = 14 without heating (DHT = Off), the highest

deviation neglecting the first point was 19.6% from the theoretical value. However at 300 °C, the

highest deviation was greatly increased to 45.3%. Similar to the TSI experiment, the dilution

settings were kept constant except the temperature. As the DHT increases, the particles in size bins

39.2 to 93.1 nm seems to deviate more from the theoretical.

10

15

20

25

30

35

30 300

Dilution R

atio

Particle Size (nm)

DHT = Off VDR = 14 DHT = 80 °C

VDR = 15 DHT = 150 °C VDR = 15

DHT = 300 °C VDR = 16

240 60 90 120 150 180 210 270

104

Figure 5-27

Engine Exhaust Percent Particle Penetration Corresponding to the Primary Dilution Air

Temperature for the Dekati Diluter


concentrations for all the primary dilution air temperature tested with the engine exhaust. Overall

percent particle penetration values for temperatures above 80 °C (83.3%) is comparably lower than

when the temperature was at ~ 24 °C (90.3%). However, the convergences of points at higher

temperatures are visible in the result, suggesting that volatile fractions may have been successfully

removed at temperatures above 80 °C.

5.9 Error Analysis and Discussion of Results

The expected margin of tolerance for the operating diluters was below 10% for particle

loss. All three diluters are expected to perform the dilution process with an actual DR ±10% of the

0

20

40

60

80

100

5 50

Part

icle

Pen

etra

tion (%

)

Particle Size (nm)

DHT = Off DHT = 80 °C DHT = 150 °C DHT = 300 °C

40 10 15 20 25 30 35 45 100 150 200 250

105

theoretical (user set) DR. As the results indicate, the particle loss within the diluters tested were

often below such an error margin, with minimal outliers, for particles larger than 29 nm. The

overall particle DRs of the single-stage TSI diluter indicated 6.0% discrepancies between the

measured and the user set DRs over the dilution ratio range of 12 to 100. The two-stage TSI diluter

operated within 3.9% over the DR range of 16 to 110. The Dekati diluter had less than 5.1% over

the DR range of 12 to 66. The overall averaged particle penetration value also suggested high

percent of particle penetration through all size bins. The single-stage TSI diluter operated at 98.8%

penetration value, the two-stage TSI diluter at 99.4%, and the Dekati diluter at ~100%.

As observed from the engine exhaust experiment, the particles below 29.4 nm are greatly

influenced by evaporation. The presence of such effects is indicated by the constantly higher

overall particle DRs. Under the engine exhaust experiment condition; the overall particle DR

(excluding the size bins below 29.4 nm) deviation was 6.6% for the single-stage TSI diluter, 4.3%

for the two-stage TSI diluter, and 9.6% for the Dekati diluter compared to the values stated above

(also indicated by low particle penetration below 29.4 nm). The divergence of the overall particle

dilution ratio suggests that the particles below 29.4 nm evaporated and condensed onto the larger

particles above that range. Particle growth contributes to the decrease in the downstream particle

concentrations for these smaller particles. Thus referring to the general formulation of the DR,

Equation 1-4, the computed DR values will be higher than the expected values. Such cases are

evident in the previous results where a significant portion of the particles was lost in those size

bins and the resulting DRs were magnitudes higher.

However, such effects are absent in the soot generator experiments. The solid particles

generated from the soot generator are more stable and gas-to-particle conversions can be avoided.

106

The result from this experiment, however, also indicated some particles loss, resulting in deviation

from the theoretical values.

As discussed previously, through leakage testing the consistencies of the testing conditions

were ensured. From the literature review, it was stated that the primary dilution temperature,

residence time and the relative humidity of primary dilution air could have an influence on the

dilution conditions. However, the experiment was performed under a closed environment where

the effects of such factors are minimal. Thus, the loss contributed from such changes in dilution

conditions can be neglected. Therefore, the measurement precision and the dilution accuracy are

considered as the major contributing factors to the DR discrepancies between the measured and

the expected.

The precision and accuracy of the dilution and measurement instruments are very

important in investigating particle loss. As previously mentioned, the misrepresentation of the data

can significantly affect the result.

To investigate the source of loss from the test apparatus, an error analysis was performed

on the instruments at various range of DRs measured for the mode particle size bin (10.8 nm) using

Equations 4-9 and 4-11 as shown in Table 5-4.

As shown in Table 5-4, individual uncertainties for the instruments used in the experiment

at various range of DRs measured were calculated. The analysis indicates that the uncertainties of

the particle sizers increased along with the increase in the DR. At lower DRs, the uncertainties

were 5.4%/3.1% for the single/two-stage TSI and 3.0% for the Dekati diluter. At higher DRs, the

uncertainties associated with the particle sizer for the Single-stage TSI rose to 5.9% at DR of 100,

and to 7.3% at DR of 113 for the two-stage TSI, and to 7.2% at DR of 66 for the Dekati diluter. As

107

mentioned before, a similar phenomenon was observed in the experimental results, where the

higher DRs deviated more from the expected than the lower DRs.

Instrument Percent Uncertainties

Diluters

DR

Particle Sizers

Flowmeter

Single-stage

TSI

12 5.4 2.0

50 5.8 2.0

100 5.9 2.0

Two-stage TSI

16 3.1 2.5

56 3.3 5.8

113 7.3 10.3

Dekati

12 3.0 2.0

35 3.5 2.0

66 7.2 2.0

Table 5-4

Table of Uncertainty Analysis for Experimental Apparatus

Likewise, the uncertainties from the flowmeters also increased along with the DR

increment. At lower DRs, the percent uncertainties for the single-stage TSI and Dekati diluters

were 2% and 2.6% for the two-stage TSI diluter. The flowmeter measurement for the single-stage

TSI and the Dekati diluter remained relatively constant throughout the change in DRs. Thus the

uncertainties contributing to the DR value of the single-stage TSI and the Dekati was minimal

regardless of the DR increase. The flow rate measured for the two-stage TSI diluter, however,

increased along with DR values, resulting in significantly higher uncertainties at DR = 113 (10.3%).

108

This analysis suggests that the major factor contributing to discrepancies in the experimental and

theoretical DRs measurements are, once again, from the precision and accuracy of the instruments.

It should also be noted that the uncertainties contributed from the flowmeter used with the TSI

diluters become more significant with higher flow rates at higher DRs.

The result indicated that there were some cases where the dilution ratio deviated more

than the expected error margin. As discussed previously, such outliers are caused most likely by

the effect of dilution condition change within the diluter. The primary reason for the cause of

change in dilution condition can be speculated to be a sudden fluctuation in input pressure.

Stabilization of the pressure at the sample inlet is very difficult to maintain. However, with

extended inter-sample time allowing for a longer adjustment period for the dilution ratio change

can alleviate the pressure change. Therefore, for future experiments using a longer inter-sample

time of 10 min (600 seconds) is recommended for stabilization purposes. Such a lengthy time is

especially required for the engine exhaust experiment because the compositions and effects of

diesel particles are more unpredictable than the particles generated by the soot generator.

Based on the various findings about the operating features of the diluters, a few

suggestions can be made to improve the sampling condition for the future engine emission studies.

When using the TSI 379020A rotary diluters, the primary diluter air temperature should

be set to 150 °C for better convergence of particle dilutions over the measured size bins. Use of

this higher temperature is found to be effective in reducing the overall DR deviation value by

approximately 25.6%. This suggests that the heated primary diluter air will effectively remove the

condensed volatile material from the engine exhaust. As mentioned previously, the study showed

that the evaporation heater temperature had no significant effect towards the particle loss or

109

dilution ratio. However, the purpose of the thermal conditioner is to prevent formation of

nanodroplets and volatile particles. Therefore it is suggested to keep the thermal conditioner

temperature at 300 °C consistently as a precautionary measure to reduce the formation of particles

from condensate and volatile fractions.

The qualitative observation of the dilution ratio change in response to an increase in the

primary dilution air temperature for the Dekati diluter suggested that with increase in the primary

dilution air temperature, the DR deviation value increased in size bins 39.2 to 93.1 nm. However,

the result indicated convergence of points at higher temperature for the individual size bins,

suggesting that the sampled exhaust is rich in volatile material and large portion of particles was

removed. Therefore, for the purpose of removing the volatile fraction from the engine emissions,

the heater should be kept at 80 – 150 °C.

110

Chapter 6

Conclusions and Recommendations

6.1 Conclusions

The results confirmed the ability of all three diluters tested to dilute a particle laden flow

without significant particle loss when the particles are solid carbon. Tests with a soot generator

showed average percent particle penetration values of 98.1% and 99.4% for the single and two-

stage TSI 379020A diluters respectively, and nearly 100% for the Dekati diluter.

As previously discussed in Chapter 2, the percent particle penetration value of the TSI

379020A at the 30 nm size bin was significantly lower, 68%, according to the European PMP

report (PMP report GRPE-PMP-25-5, 2010). The European PMP test was conducted using diesel

engine exhaust as the sample. The findings of this work also showed similar percent penetration

to the PMP test for engine exhaust particles below 29.4 nm. However, the result obtained with the

soot generator indicated ~ 100 % penetration of particles smaller than 29.4 nm for the single-stage

and 94.2% for the two-stage diluters.

The different response to particles produced by the engine and by the soot generator

suggests that when the particle laden flow contains significant amount of liquid droplets (e.g.

engine exhaust), there can be a substantial loss of very small particles (< 29.4 nm diameter). This

loss is accompanied by an increase in number of particle in the size ranges 29.4 to 52.3 nm,

suggesting that the liquid particles agglomerate, coagulate, or condense on larger particles.

Sample flow through all of the diluters depends on the pressure difference between the

111

sample inlet and the diluter outlet. Consequently the performance of all three diluters was affected

by the actual pressure difference encountered in use. The two TSI 3709020A diluters were not as

sensitive to pressure difference as the Dekati FPS-4000 diluter because they have a controlled

sample pump. However, the theoretical (user set) DR given by the system was deviating ±20%

from the measured DR. Use of a supplemental flowmeter to measure the TSI diluter sample flow

and excess flow and then using these to compute the corrected DR was found to improve the DR

accuracy from ±10% to ±5%.

The Dekati FPS-4000 diluter uses an air ejector to pump the sample flow and is therefore

extremely sensitive to the pressure difference between the sample point and the diluter outlet

(generally at atmospheric pressure). Great care must be taken in use of the Dekati FPS-4000 diluter

to ensure that the pressure difference encountered in a test (i.e. engine exhaust system pressure and

the diluter outlet pressure) are within the operating range of the Dekati diluter. In this work, the

Dekati FPS-4000 performed well (~100% percent penetration value) because precautions were

taken to ensure minimal pressure difference across the diluter.

The different characteristics exhibited by the two diluter designs (TSI 379020A and Dekati

FPS-4000) suggest that there are specific applications for which each diluter is best suited. The

TSI 379020A diluters are more suitable for uses in simple engine exhaust emission studies where

the accurate measurement of concentration with numerous repeated sessions is critical. The Dekati

FPS-400 diluter is more suitable for use in nucleation and particle dynamic studies where dilution

condition variability and controlling mechanisms are vital.

6.2 Recommendations

Prior to operating the diluters discussed in this thesis (the single and two-stage TSI

112

379020A rotary thermodiluters and the Dekati FPS-4000 ejector diluter), there are a few

preparatory steps that must be followed in order to achieve satisfactory results.

For best results, the actual volumetric dilution ratio obtained in use should be continuously

monitored by the use of a tracer gas. This is especially true for the Dekati diluter due to its extreme

sensitivity to sample inlet (engine exhaust) and diluter outlet pressures. Carbon dioxide, a product

of combustion of all hydrocarbon fuels and therefore present in engine exhaust in large

concentrations, is the obvious choice to use as a tracer gas since it is a highly superheated vapor in

the exhaust as well as non-reactive. It is therefore unchanged by any physical or chemical processes

that might occur in the diluter. The carbon dioxide concentration in engine exhaust is routinely

measured by exhaust emissions analyzers. However, the low concentration of carbon dioxide after

dilution requires the use of a different CO2 analyzer designed for the appropriate concentration

range, since the exhaust emissions CO2 analyzer is not accurate at low concentrations. Quantifying

the actual volumetric dilution ratio through use of a CO2 tracer will ensure accurate operation of

the diluters.

For high dilution ratios, the diluted concentration can approach the concentration of

carbon dioxide in the ambient air. Since ambient air is used for dilution, the local background

CO2 concentration must be measured and taken into account in calculating the measured dilution

ratio. For example, the particle-free aerosol generated internally from room air by the two-stage

diluter also introduced undesired supplementary 471.4 ppm of CO2 from the room. Therefore,

471.4 ppm was subtracted from the successive measured mean downstream concentration for the

two-stage diluter. The reason for the discrepancy between the atmospheric CO2 level (398.58 ppm)

and this measured concentration was because the experiment was conducted in a closed

113

environment filled with potential CO2 sources including people and instruments. Therefore, it is

important to measure the CO2 concentration level specific to the local environment prior to

conducting any experiments.

The primary diluter air temperature of the TSI 379020A diluters should be set to 150 °C

for better convergence of particle dilutions over the measured size bins. This temperature was

found to be effective in reducing the overall DR deviation value by approximately 25.6%. It is also

suggested to keep the thermal conditioner temperature at 300 °C consistently to reduce the

formation of condensate and volatile fraction particles.

Although the deviation of the measured DR increased with a primary dilution air

temperature increase, the heater should be kept in the range 80 – 150 °C. The result indicated

convergence of points at higher temperature for the individual size bins, suggesting that the

sampled exhaust was rich in volatile material and large portion of particles was removed.

The results showed that the diluters tested in this thesis are expected to perform dilution

within ±10% of the theoretical dilution ratio in both volumetric and particle phases as stated by

the manufacturer. However, outliers are present when pressure fluctuations or a change in dilution

conditions occur. To maintain relatively consistent dilution condition for improved dilution

precision and accuracy, it is suggested that a longer inter-sample time of 10 min be implemented

for stabilization purpose for the future experiments.

Due to concern about its pressure sensitivity, further study of the Dekati FPS-4000 diluter

under engine sampling conditions is warranted to identify the limits of its exhaust pressure

capability.

114

Appendices

Appendix A

Preliminary Experiment Result for Single-Stage TSI 379020A using

Methane Gas

According to the TSI 379020A manual (TSI, 2011), substantial loss of gas phase organic

compounds can occur in rotary disk thermodiluters, where the cause of such losses are unclear. In

order to verify that such phenomenon indeed occurs, the preliminary experiment, discussed in

Chapter 4, was conducted using a mixture of 1200 ppm (nominal) of methane balanced in nitrogen

as the upstream sample. The experiment layout used in this test followed the one illustrated in

Figure 4-1 (left for TSI 379020A).

With known concentration of the gas mixture at upstream, the downstream concentration

was measured using the FHID analyzer. The result of the concentration measurements is shown in

Figure B-1.

The measured concentrations were well below the theoretical concentration at various

DRs measured, with the exception of the first two points. It should be noted that even the first two

points fail to fall within the expected error margin of ± 10%. The results indicate that the increase

in deviation was directly proportional to the increase in DR. The graph showed a divergence of

measured concentration from the ideal values as the DR values got higher. At higher DR values,

the TSI 379020A diluter was over-diluting the mixture of methane gas to a point where almost

entire volume of gas was lost (~ 0.4 ppm).

115

Figure A-1

Diluted CH4 Concentration Measurement at Various Dilution Ratios for the single-stage

TSI Diluter

Thus, it was verified that the substantial loss of gas phase organic compounds occur in

rotary disk thermodiluters. Therefore, to evaluate these TSI diluter measurements, a mixture of

2.15% (nominal) carbon dioxide balanced in nitrogen was used as the sampling gas.

0

10

20

30

40

50

60

70

80

90

100

10 20 30 40 50 60 70 80 90 100

CH

4C

once

ntr

ation [ppm

]

Dilution Ratio

Measured DR Theoretical DR

116

Appendix B

Derivation of Uncertainty Analysis Equations

The discussion of uncertainty that follows is based on the method presented in Theories

of Engineering Experimentation (Schenck, 1974). The term s2 is defined as the deviation envelope

that encloses 95 percent of all the readings, also known as the criterion of “twenty-to-one odds”.

This means that this value is the numerical expression for the size of an envelope that has twenty-

to-one odds of containing the true value, or simply as standard deviation. The m�j (also known as

standard deviation) for any function R of measured variables X, Y, Z, etc. can be expressed as

m�j � ��B�g�hj , … mgj � ��B�h�g

j , … mhj � ��B�i�hj , … mij �⋯ Equation B-1

where mg, mh,mi, etc., are the variance for the measured variables X, Y, Z, etc…(Schenck, 1974).

With the assumption that the measured variables are independent of one another and the function

R is of the general form

R � k ghi , Equation B-2

then the Equation B-1 can be re-expressed as

m�j � �� hi�j mgj � �� gi�

j mhj � �� ghi��j mij Equation B-3

Dividing this equation by R2, it can be simplified to

�&B�j � �kg �

j � � h �j � �li �

j Equation B-4

The terms kg ,

h , and

li represent percentage error of the individual measurements. Unless

117

stated otherwise, this term will be referred to as the “uncertainty” of the measured variable. Then

the term &B represents the percent error of the result.

118

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