Measurement of in-cylinder soot particles and their distribution in an optical HSDI diesel engine using time resolved laser induced incandescence (TR-LII)

Soot particles generated during combustion process in a single cylinder optical diesel engine were measured using time-resolved laser induced incandescence technique (TR-LII). Experimentally measured LII data were fitted with theoretically simulated LII data to determine the count median particle diameter and the geometric width of the particle size distribution. TR-LII signals were acquired simultaneously at two different wavelengths for crank angles in the range from 48.4 degrees to 111.4 degrees after top dead centre (aTDC) and for various engine operating conditions. Particle size was found to be dependent on the engine load but no significant change in particle sizes were observed for different fuel injection timings. The average size of the primary particles measured over different crank angles were larger at higher engine loads compared to lower engine loads. A general trend of the soot particle diameter decreasing with crank angle was observed due to oxidation, but towards the end of the expansion stroke a marginal increase in size was noted. For all operating conditions the width of the particle size distribution was found to decrease with crank angle until 61.4 aTDC, and thereafter it increases to reach a well defined size distribution for a given fuel injection quantity despite the differences in the injection timing. The soot particles are randomly transported by the complex fluid motion present within the combustion chamber leading to strong cycle to cycle fluctuations of the measured time resolved LII data. The in-cylinder soot volume fraction derived from TR-LII data revealed that for different fuel injection timings, a relatively higher amount of soot was produced for shorter ignition delay compared to larger ignition delays. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.