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New Catalytic Stripper System for the Measurement of Solid Particle Mass, Number, and Size Emissions from Internal
Combustion Engines
Imad A. Khalek, Ph.D. Southwest Research Institute ®
Department of Emissions Research, 6220 Culebra Road San Antonio, Texas, 78238, [email protected]
7th ETH Conference on Combustion Generated Particles, Zurich, Switzerland, August 18-20, 2003
Particulate matter (PM) emitted from combustion sources, particularly diesel engines, is typically composed of volatile and solid material. The solid material ("soot") consists mainly of carbon and a small amount of inorganic ash. The volatile material consists of unburned and partially burned fuel and lubricating oil, and sulfur compounds. Dry soot particles are formed in the combustion chamber of an engine while most of the volatile material enters the particle phase from the gas phase as the exhaust cools. Hence, particulate matter is a combined measure of solid and volatile particles. It is important to be able to distinguish between the two components because the mechanism of their formation and control are different. Such information can also be useful for researchers investigating the effect of particulate emissions on human health.
A catalytic stripper system referred to in this work as the solid particle
measurement system (SPMS), Patent Pending, was designed to allow for the measurement of real time solid particle mass, size, and number in the size range from 10 nm to 500 nm. The SPMS consists of a heated mini oxidation catalyst and a micro-dilution system to cool the heated sample by dilution and prevent particle thermophoretic deposition downstream of the oxidation catalyst. The SPMS is equipped with two 47 mm filter holders for the measurement of solid particle mass and total (volatile plus solid) particle mass. Similarly, the SPMS is also equipped with sample ports for total and solid particle size and number measurements.
The SPMS is a stand-alone system on a moving laboratory cart. All that is needed is an electric power outlet. Vacuum and compressed air sources are available on-board. The SPMS is also equipped with a Labview data acquisition system and a laptop computer for data processing and data analysis.
The SPMS was characterized with sodium chloride, ammonium sulfate, and engine oil particles. The SPMS removed more than 99 percent of engine oil without generating sulfuric acid particles. The SPMS had better than 99 percent penetration of sodium chloride solid particles.
The SPMS was applied to measure particle number and size distributions
from a 1998 DDC Series 60 heavy-duty on-highway diesel engine operating at high
and low engine load. The total particle number-weighted size distribution was bimodal in nature with a nuclei mode at about 20 nm and an accumulation mode at about 50 nm. The solid particle number-weighted size distribution in the accumulation mode was similar to that of total, suggesting that the majority of accumulation mode particles for this engine are solid in nature. For the nuclei mode, a significant reduction in particle number was obtained downstream of the SPMS, suggesting that the majority of particles in the nuclei mode are volatile and were removed by the catalyst used in the SPMS.
The SPMS also revealed, however, that under most engine operating conditions the solid fraction, the ratio of solid to total particle number in the sub 20 nm diameter range increased and exceeded 100 percent for particles between 9nm and 11 nm in diameter. By the definition of the solid fraction, it is not surprising to have a solid fraction over 100 percent. The following example explains how that can be possible. Suppose 50 percent of one hundred 10 nm solid particles present in the exhaust grew by the absorption of volatile material to a size above 10 nm. For the total size distribution, one would measure 50 particles with size 10 nm and 50 particles above 10 nm. If one applies the SPMS, one would measure a 100 solid particles for 10 nm particles. The solid fraction for 10 nm particles will then be 200 percent. This new findings suggest the presence of a solid core in the sub 20 nm particle size range that may go down to below 9 nm, the lower detection limit of the instrument used on this program. The nature of this solid core may be solid carbon or possibly metallic ash from the engine lubricating oil. Such information is extremely important to the health authorities trying to understand the effect of particles on human health.
The application of the SPMS in future work is expected to generate significant information as to the composition and characteristics of particulate emissions from combustion sources. Coupled with a Nano-SMPS or similar devices that can measure particle size and number down to 3 nm, the use of the SPMS is expected to provide significant information as to the generation and growth of even the smallest of particles.
1
New Catalytic Stripper System for the measurement of Solid Particle mass, Number
and Size
Imad A. Khalek, Southwest Research Institute, San Antonio, Texas
7th ETH Conference on Combustion Generated Particles, Zurich, Switzerland, August 18-20, 2003
Acknowledgments
• This work was funded by SwRI Committee for Internal Research and Development.
2
Note
• The new catalytic stripper system will be referred to as the solid particle measurement system (SPMS) throughout this presentation
Outline
• What is the SPMS?• Characterization with Laboratory Aerosol• Application on A Heavy-Duty Diesel
Engine• Conclusions
3
SPMS Development Objectives
• To Develop a Stand-Alone Laboratory Instrument that Facilitates the Measurement of Solid Exhaust Particle Mass (Filter and Non-Filter based), Number, Size, and Other Physical PM Characteristics Using Different Real Time Instruments
• To Minimize Solid Particle Losses and Achieve Near a 100 Percent Penetration of Solid Particles
• To Maximize the Removal of Volatile to Near 100 percent• To Prevent the Potential Formation of Sulfuric Acid Particles• To be Capable of Measuring Total PM (Solid and Volatile) So Volatile
PM can be Determined• To be Used Either with Diluted or Undiluted Exhaust Stream
SPMS Principle of Operation
Temperature Probe
TemperatureController
Heater
Cool CleanCompressed Air
OxidationCatalyst
Temperature Probe
Raw or Dilute Exhaust
To Particle Measurement System
DilutionTunnel
4
Example of Gas Diffusion and Flow Optimization In Catalyst Square Channel
0.0001%
0.0010%
0.0100%
0.1000%
1.0000%
10.0000%
100.0000%
0 200 400 600 800
Temperature, K
Mol
ecul
ar P
enet
ratio
n, %
C10H22 C19H40 C40H82
Region of Interest
0.025 slpm
0.0001%
0.0010%
0.0100%
0.1000%
1.0000%
10.0000%
100.0000%
0 200 400 600 800
Temperature, KM
olec
ular
Pen
etra
tion,
%
C10H22 C19H40 C40H82
Region of Interest
0.10 slpm
Example of Particle Penetration and Flow Optimization In Catalyst Square Channel
65%
70%
75%
80%
85%
90%
95%
100%
10 100 1000Particle Size, nm
Parti
cle
Pene
tratio
n, %
293 K 393 K 493 K 573 K623 K 673 K
Mass Mean Diameter Region
0.025 slpm
Number Mean Diameter Region
65%
70%
75%
80%
85%
90%
95%
100%
10 100 1000Particle Size, nm
Parti
cle
Pene
tratio
n, %
293 K 393 K 493 K 573 K623 K 673 K
Mass Mean Diameter Region
0.10 slpm
Number Mean Diameter Region
5
Example of Dilution Ratio and Temperature Requirement at the Exit of Catalyst at
Temperature of 300 oC
-400
-300
-200
-100
0
100
200
0 10 20 30 40Dilution Ratio
Dilu
tion
Air
Tem
pera
ture
, °C
MT: 25 °C MT: 47 °C MT: 75 °C MT: 100 °C
Practical Dilution Range for PM Filter Measurement
Cutting The Appropriate Size Catalyst from The Stock Catalyst
6
Partial View of the SPMS
SampleInlet
Clean AirInlet(Optional)
ParticleNumber andSize SamplePorts
VortexTube
DieselOxidationCatalyst
ParticleMass FilterHolderLocation
CSS Outlet ParticleNumber and SizePorts
Total FlowOut LaminarFlow Element
CompressedAir In LaminarFlow Element
Total FlowTube
MicroDilutionSystem
Stand-Alone SPMS
7
SPMS Characterization with Laboratory Aerosol (Nominal Flow and Dilution Ratio)
Unheated CSSFlow
ConditionsTotal Flow
(slpm)Air Flow(slpm)
Sample Flow(slpm)
Dilution Ratio
1 65.2 49.4 15.8 4.122 73.9 49.2 24.7 2.993 80.4 49.2 30.2 2.57
Heated CSS (300 ////C)1 70.7 49.7 21.0 3.362 64.3 49.2 15.1 4.253 60.0 50.0 10.0 6.00
SPMS Performance with NaClParticles at 300 oC
0
0.2
0.4
0.6
0.8
1
1.2
1.4
10 100 1000Particle S ize, nm
Parti
cle
Size
-Spe
cific
Pen
etra
tion
(PSS
P)
F low 1 - N ew Flow 2-N ew Flow 3 -N ew T heory
8
SPMS Performance With Engine Oil Droplets
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1 10 100 1000
Particle Size, nm
Parti
cle
Num
ber C
once
ntra
tion,
Par
t./cm
³
NC S-200 °C S-250 °CS-300 °C S-350 °C S-400 °C
Flow 11.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000Particle Size, nm
Parti
cle
Volu
me
Con
cent
ratio
n,nm
³/cm
³NC S-200 °C S-250 °CS-300 °C S-350 °C S-400 °C
Flow 1
Engine Oil Droplet Residue
Engine Oil Droplet Residue
SPMS Performance with Ammonium Sulfate Particles
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1 10 100 1000Particle Size, nm
Parti
cle
Num
ber C
once
ntra
tion
Part.
/cm
³
NC S-200 °C S-250 °CS-300 °C S-350 °C S-400 °C
Flow 11.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000Particle Size, nm
Parti
cle
Volu
me
Con
cent
ratio
n,nm
³/cm
³
NC S-200 °C S-250 °CS-300 °C S-350 °C S-400 °C
Flow 1
9
Particle Penetration for Engine Oil Droplets Based on Number and Volume
0.1%
1.0%
10.0%
100.0%
0 50 100 150 200 250 300 350 400 450
CSS Inlet Temperature, °C
Tota
l Par
ticle
Pen
etra
tion,
%
Flow 1- N Flow 2-N Flow 3-N Flow 1-V Flow 2-V Flow 3-V
Particle Number
Particle Volume
Engine Test Matrix
Mode Speed, rpmLoad, % of Loadat Rated Speed
Number ofRepeats
1 1800 65 6
2 900 25 6
3 1800 35 6
4 600 0 6
1998 DDC Series 60 Heavy-Duty Diesel Engine
10
Total and Solid Particle Size Distributions Using SPMS (Heavy-Duty Diesel Engine Operating at
High Load, Rated Speed, Mode 1)
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000Particle Size, nm
Part
icle
Con
cent
ratio
n (P
art/c
m³ a
nd n
m³/c
m³)
Total Number Solid Number Total Volume Solid Volume Solid Fraction, %
Number Reduction : 93 %
Volume Reduction : 34 %
Total and Solid Particle Size Distributions Using SPMS (Heavy-Duty Diesel Engine Operating Near
Low Idle, Mode 4)
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1.00E+11
1 10 100 1000Particle Size, nm
Part
icle
Con
cent
ratio
n (P
art/c
m³ a
nd n
m³/c
m³)
Total Number Solid Number Total Volume Solid Volume Solid Fraction, %
Number Reduction : 86 %
Volume Reduction : 42 %
11
Summary
• A Stand-Alone SPMS was developed for Solid and Total Particle Mass, Number, and Size.
• Solid Particle Losses were at minimum level and no correction is need in the size range from 10 nm to 300 nm.
• The SPMS removed more than 99 percent of oil droplets• No apparent formation of sulfuric acid particles• Engine Emissions Data revealed that some of the volatile droplets
contain a solid core. It is possible to attribute such core to Ash derived from the lube oil.
• This instrument Can be a very useful for Assessing Solid ,Volatile, and Total Particles in Real Time.
• More Detail Description and Analysis of the SPMS will be available in future publications
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