A Critique of Laser-Induced Incandescence for the Measurement of Soot PDF Download

Author: Gregory J. Smallwood
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Languages : en
Pages :

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Book Description
The health and environmental risks due to airborne nanoparticles are important issuesfacing the citizens and governments of the industrialized countries. To assess andmitigate these risks, increasingly stringent regulations are being enacted to reduce theparticulate emissions from the combustion of hydrocarbon fuels, which primarilyconsist of soot. Improvements to the understanding of the formation of sootnanoparticles and their impact on the health and the environment are required. Thisnecessitates advances in the state of quantitative measurement of soot. Laser-induced incandescence (LII) is an optical diagnostic technique for themeasurement of concentration and primary particle diameter of soot with highselectivity. Limitations with conventional LII were identified and a significantlyenhanced technique, autocompensating LII (AC-LII), was developed employing time-resolved two-colour pyrometry, low fluence, and an absolute intensity calibration toaddress these limitations. AC-LII was shown to measure the soot particle temperatureand automatically compensate for variations in the measurement environment thataffected the peak soot particle temperature. With low fluence, AC-LII was shown toavoid soot sublimation, which impacted the measurements of concentration and sizewith high fluences. AC-LII was applied to flames and to combustion-generated emissions. At low ambienttemperatures it was discovered that the measured concentration varied with fluence. Tomitigate this issue, it was recommended that AC-LII be performed at a moderate fluencenear the sublimation threshold. In order to assess the impact of distributions of the sootprimary particle diameter and of aggregate size, analysis coupling experiments with astate-of-the-art numerical model of the heat transfer was performed. The results showedthat AC-LII signal evaluation should begin immediately after an initial anomalouscooling period but before distribution effects become dominant. The sensitivity of AC-LII was optimized and applied to measure atmospheric blackcarbon concentrations. Comparison to other instruments demonstrated that AC-LII hassignificant advantages for the measurement of soot, and represents a major advancementin techniques for nanoparticle characterization.