Investigation of solid particle number

measurement: existence and nature of sub 23

nm particles under PMP methodology

Zhongqing Zheng, Kent C. Johnson, Thomas D. Durbin, and Heejung Jung

College of Engineering, Center for Environmental Research and Technology

(CE-CERT) University of California, Riverside

Shaohua Hu and Tao Huai

California Air Resources Board (CARB)

David B. Kittelson

Department of Mechanical Engineering University of Minnesota

Typical diesel particle size distribution Currently, diesel PM is regulated on a mass basis

Background

• Current gravimetric method

– Difficulty quantifying particle mass emissions accurately

• Particle number method

– The European Particle measurement program (PMP)

– The PMP measures solid particles bigger than 23 nm

• Findings of previous PMP work

– Sub 23 nm particles appearing-to-be solid present below PMP

Existence of sub 23 nm particles

1.E+08

1.E+09

1.E+10

1.E+11

1.E+12

1.E+13

1.E+14

1.E+15

1.E+16

OnRoad

Hills

OnRoad

Flat

ETC

URBAN AB

ETC

URBAN BA

ETC

CRUISE

West

ETC

CRUISE

East

ARB

CREEP CD

ARB

CREEP ED

UDDS

ABCD

UDDS

EDCB

Pa

rtic

les

Co

un

t (#

/mi)

MD 3790 MD 3025 MD 3760 MEL 3025 MEL 3760 CVS 3022

EURO 5/6 # Standard 8E11 #/mi (light duty)

What is the nature of these sub 23 nm particles downstream the PMP?

PMP schematic

Objective Investigate the nature of the sub 23 nm particles

downstream the PMP

Method Compare the PMP system with another volatile particle

remover – Catalytic Stripper (CS)

Catalytic Stripper (CS) schematic

Cooling

coil

Wall temperature 300 °C

S-trap

Sulfur trap Oxicat

Oxidation

catalyst

BaO + SO3 BaSO4

Test conditions

Base CE-CERT HD Chassis dynamometer

Vehicle Freightliner class 8

Engine Caterpillar C-15 (14.6L)

Fuel ULSD

Lubricating oil SAE 15W-40

DPF JM CRT

Vehicle weight 65,000 lb

Truck mileage 41442 miles

Cycles (a) 56 mph cruise at 74% engine load;

(b) 56 mph cruise at 26% engine load.

Experimental setup

CVS

CPC

3772

CPC

3776

CPC

3025A

nano-

SMPS

to vacuum

needle

valve

vent

rotameter

heated

line

fast-

SMPS

catalytic

stripper (CS) ejector venturi

CPC

3772_CS

compressed air

vent

ball

valve

PMP system

AVL particle counter

(APC)

CPC 3790_APC

chopper

diluter

EEPS

CPC

3022A_CVS

cyclone particle cut point 2.5 µm

Alternate between the APC and CS

CS

Results

CVS particle size distribution

74% engine load 26% engine load

Time (s) Time (s)

Dp

(nm

)

Dp

(nm

)

dN/dlogDp (#/cc) dN/dlogDp (#/cc)

Integrated particle number emissions

1.0E+10

1.0E+11

1.0E+12

1.0E+13

1.0E+14

26% engine load 74% engine load

Par

ticl

e n

um

ber

em

issi

on

(#

/ k

Wh

)

Testing Cycles

Euro VI HD limit 6 x 1011 #/kWh

(proposed for WHSC)

3022A at CVS (7 nm)

3790 under APC (23 nm)

3772 under CS (11 nm)

CPC concentrations-74% load

(23 nm)

(11 nm) (11 nm)

APC showed higher

concentration than

the CS

CPC concentrations-74% load

(23 nm)

(11 nm) (11 nm)

(3 nm) (2.5 nm)

CPCs with smaller

cut off diameters

showed higher

concentration than

CPCs with higher

cut off diameters

CPC concentrations-26% load

Similar trend

observed at 26%

load

CPC concentrations-26% load

Difference between

CPC 3025A and

3776 indicates:

Particles are

formed due to re-

nucleation of semi-

volatiles

downstream the

PMP

APC ET temperature oscillation

Conclusion • Particle number emissions for both the PMP and CS were higher

than the Euro VI HD limit at the 74% engine load and lower at the

26% engine load.

• Particle number concentrations between 3 and 10 nm downstream

the APC were ~ 2 and 7 times higher than the number

concentrations of particles above 10 nm at the 74 and 26% engine

load, respectively

• Most of the sub 10 nm particles downstream the PMP were formed

in the ET of the PMP, because:

– CPC 3025A had higher concentration than CPC 3776;

– Particle concentration of those sub 10 nm particles oscillated in relation

with the oscillation of the PMP ET temperature.

• The CS showed much less of a tendency to form particles

downstream than the APC.

Acknowledgements

• CARB For funding and instruments

Drs. Alberto Ayala and Jorn Herner for encouraging this study

• AVL LIST GmbH Inc. Providing an AVL particle counter and technical support

Drs. Barouch Giechaskiel and Richard Frazee, and many other people

• UCR/CE-CERT Mr. Donald Pacocha, Mr. Joe Valdez, Mr. Edward O’ Neil, and Zhihua Liu of

Contributions in conducting the chassis dynamometer test

Drs. Akua Asa-Awuku, David Cocker, and Paul Ziemann

• University of Minnesota Dr. Jacob Swanson for advice