# Presentation: 299351

## POLARIZED LIGHT SCATTERING MEASUREMENTS FOR SIZING DIESEL PARTICULATES

- A.J. Hunt, I.G. Shepherd,
-  M.S. Quinby-Hunt
- Lawrence Berkeley National Laboratory
- Petroleum Environmental Research Forum
- Berkeley, CA
- March 10, 1999

## OBJECTIVES

- Develop a method to characterize diesel exhaust soot from polarized light scattering
- Develop a _*real-time*_ light scattering instrument to measure diesel particulate size
- Study the effect on particulate characteristics of
- Running conditions
- Fuel composition
- Post-combustion factors (humidity, dilution, etc.)

## RELEVANCE TO DOE-OTT CIDI OBJECTIVES

- PM emissions are technical barriers to all but one CIDI R&D task
- Accurate real time measurements of PM are essential for
- engine development and monitoring
- evaluation of aftertreatment technologies
- Emissions Compliance
- Current measurement methods are inadequate (e.g., smoke meter, filter methods, impactors

## RELEVANCE TO DIESEL DEVELOPMENT, TESTING, AND USE

- Accurate real time measurements of PM are essential for
- engine development and monitoring
- evaluation of aftertreatment technologies
- Emissions Compliance
- Current measurement methods are inadequate (e.g., smoke meter, filter methods, impactors) or slow (e.g. mobility analyzers)

## APPROACH

- A existing light scattering instrument used to measure diesel exhaust streams *in situ* :
- angle-dependent scattering intensity
- angle-dependent polarization transformations
- determine size distribution and optical properties (n, k)   (refractive and absorptive) properties of soot by comparing experimental data with modeled scattering
- Model soot scattering as:
- spheres - Mie scattering theory to fit data
- agglomerates -represent clusters as coupled dipoles

## Polarized Light Scattering

**4 x 4 Mueller Matrix**

- 

- I

- M

- I

- Q

- U

- V

**Total Intensity**

**Scatterer, represented **
**         ****by Mueller matrix,**

**Incident beam**

**Scattering **
**Angle**

**Scattered**
**      ****Beam**

**Circular Polarization**

**± ****45****°**

**0°,90° Polarization**

## Mueller Matrix Formalism

- Stokes Vector - describes polarized light

**All elements except S****11**** normalized by S****11**

## PROJECT ACCOMPLISHMENTS

-  Characterized Diesel Exhaust Particulates
- Size
- Morphology
- Optical Properties
-  Background for Scatterometer Development
- Performed complete scattering measurements on Diesel soot
- Modeled scattering from loose aggregates of primary soot ‘spherules’ by Mie and coupled dipole approaches
- Identified light scattering/polarization signatures
- Designed built and tested scatterometer to measure  particle size in real time

## Scattering Results for Two EnginesCummins B5.9 175  MAN turbo-diesel and Acme Motori - ADX 300

## Time Response(Acme Motori - ADX 300 Diesel)

## INTERPRETING SCATTERING DATA

- Mie scattering theory - spherical particles
- Calculates angle dependent polarized scattering given size and optical properties of particles
- Levenburg-Marquardt optimization
- Matches observed scattering with Mie calculations varying:
- Log normal, Gaussian, power law distributions
- Real and imaginary indices of refraction
- Fits four matrix elements simultaneously
- Determines particle size distribution and their complex refractive index (“composition”)

## Comparison: Mie Theory & Experiment(Small Diesel)

- -0.1

- 0.0

- 0.1

- 0.2

- 0.3

- S

- 34

- /S

- 11

- Full Load

- No Load

- Rayleigh

## Particle Size Distribution from Mie FittingAcme Motori -ADX 300

## Number and Mass based Size Distributions, Cummins Diesel

## Effects of Oxygenated FuelPreliminary Results

## DIESEL PARTICLE SCATTEROMETER(DPS)

- Three simultaneous matrix elements sufficient
-  0f, 1f, & 2f with single detection polarization
- Laser Wavelength (450 - 900 nm)
- Detector system design
-  Number - 12
- Type - compact programmable photomultiplier
- Placement - 20o intervals
- Multiplexed into 16 bit A/D converter
- Software implementation of lock-in detection
- Time response (1 -10 Hz)

## DPS  DESIGN

- Laser

- Polarization modulator

- Detection volume

- Detectors (12)

- Polarizer

- Baffle

- Base plate & optical bench

## Fractal-Like Soot Particle(if S22 1 use correction or coupled dipole calculation)

## MODELING OF DIESEL SOOT PARTICLES AND SCATTERING

- Particle generated by random walk procedure
- Size (characterized by radius of gyration) is specified by number of primary soot particles
- Fractal dimension calculated (compactness)
- Coupled dipole calculation in parallel on Cray T3E (using up to 512 processors)
- Sizing by Levenburg-Marquardt optimization technique using look-up tables

## COLLABORATIONS

- Joint development project with ORNL (Engineering Technology Division)
- Combined measurement program with UCB Engine Laboratory (Prof. Dibble)
- Software development with Prof. Patricia Hull of Tennessee state University
- Working with researchers in the environmental program at LBNL on diesel particulate characterization

## Future Plans

- Complete calibration of 2 scatterometers for particle size measurements at 1-10 Hz rates (ORNL & LBNL)
- Compare scatterometer results with Scanning Mobility Particle Sizer and Electrical Aerosol Analyzer (>50nm)
- Characterize exhaust from several fuels in OAAT fuel matrix
- Explore shorter wavelengths for enhanced sensitivity
- Continue coupled-dipole modeling for sizing non-spherical diesel particles with the scatterometer
- Evaluate commercial potential of scatterometer