Time-resolved laser-induced incandescence was used to estimate primary particle size distributions inside the combustion chamber of a heavy-duty diesel engine as a function of the crank angle, for two different engine loads at two different probe locations. Assuming a log-normal particle size distribution, an increase of the mean primary particle size was seen during the first stages of the combustion cycle, followed by a decrease later on during the combustion process. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.