In situ optical sensing of diesel exhaust particulates using a polychromatic LED source

R. A. Aspey*, K. J. Brazier

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


A novel optical probe for in situ monitoring of diesel exhaust particulates has been developed and is demonstrated. The probe uses a transmissive configuration to interrogate a particulate stream using polychromatic (white) light from an electroluminescent LED, the probe being mounted transversely to the exhaust flow in the tailpipe. Consequently the effects of scattering and absorption are measured on the transmission spectrum. The optical signal is relayed via an optical fibre bundle to a remote detection and data logging unit. Photodetector signals representing red, green and blue spectral information are monitored using detectors having overlapping spectral responsivities. Data collection is by red-green-blue (RGB) tristimulus detection and spectral analysis uses the hue-lightness-saturation (HLS) algorithms. It is shown that changes in spectral width may be used to represent particulate bursts (scattering) via the saturation parameter with a compensation algorithm being used to compensate for shifts in the operating point due to contamination of the optics. As polychromatic light is used it is demonstrated that variation in the mean particle size may be represented in terms of the ratios of polydisperse extinction for adjacent spectral bands. The potential advantages of chromatic sensing for signal processing in terms of reduced susceptibility to vapour content and optical contamination is demonstrated by comparison with an intensity based sensor.

Original languageEnglish (US)
Pages (from-to)751-758
Number of pages8
JournalMeasurement Science and Technology
Issue number6
StatePublished - Jun 2003
Externally publishedYes


  • Chromatic modulation
  • Diesel
  • LED
  • Mie
  • Particulates
  • Polychromatic
  • Rayleigh
  • Scattering

ASJC Scopus subject areas

  • Instrumentation
  • Engineering (miscellaneous)
  • Applied Mathematics


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