POLARIZED LIGHT SCATTERING MEASUREMENTS FOR SIZING DIESEL PARTICULATES

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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

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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.)

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RELEVANCE TO DOE-OTT CIDI OBJECTIVES

• PM emissions are technical barriers to all but
  one CIDI RD 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

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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)

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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

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Polarized Light Scattering

Scatterer, represented by Mueller
matrix,
M
Scattering Angle
q
I
Incident beam
Scattered Beam
Total Intensity
I
Q
0,90 Polarization
4 x 4 Mueller Matrix
U
45
V
Circular Polarization
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Mueller Matrix Formalism
Stokes Vector - describes polarized light
All elements except S11 normalized by S11
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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

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Scattering Results for Two EnginesCummins B5.9
175 MAN turbo-diesel and Acme Motori - ADX 300
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Time Response(Acme Motori - ADX 300 Diesel)
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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)

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Comparison Mie Theory Experiment(Small Diesel)
0.3
Full Load
0.2
S
/S
0.1
34
11
0.0
Rayleigh
No Load
-0.1
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Particle Size Distribution from Mie FittingAcme
Motori -ADX 300
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Number and Mass based Size Distributions, Cummins
Diesel
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Effects of Oxygenated FuelPreliminary Results
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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)

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DPS DESIGN
Detectors (12)
Detection volume
Polarizer
Baffle
Laser
Base plate optical bench
Polarization modulator
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Fractal-Like Soot Particle(if S22 ¹ 1 use
correction or coupled dipole calculation)

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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

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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

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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 (gt50nm)
• 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