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, Ikhalek@Swri.org

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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