Abstract:

Laser-induced incandescence with time-resolved detection (TR-LII) at two wavelengths was established and applied to the combustion chamber of a single-cylinder two-stroke Diesel engine. The optical system was calibrated by a black-body radiation source. TR-LII signals for different crank angles and varying engine operation conditions were measured. By fitting calcd. TR-LII cooling curves to the measured signals, it was possible to det. the mean primary particle diam. and the geometric std. deviation of the in-cylinder particles for an assumed lognormal size distribution. At the beginning of the combustion process the resulting particle sizes increased with increasing crank angle (CA) according to particle formation. This was followed by a subsequent redn. of the particle sizes at later crank angles due to particle oxidn. In all examd. cases the mean particle sizes increase with increasing engine load. For validation purposes, soot samples from the exhaust gas were taken onto transmission electron microscopy (TEM) grids for different engine operating conditions and were analyzed by TEM. For the obtained loose agglomerated particle structures, the particle sizes at late crank angles measured by TR-LII are in excellent agreement with the TEM-detd. mean primary particle sizes in the exhaust gas. Finally, soot vol. fractions were detd. from the max. TR-LII signals via calibration by in-cylinder laser-extinction measurements.