Coagulation and combustion of soot particles in diesel engines

Abstract

Coagulation and combustion of soot particles formed in a diesel engine have been studied on two direct-injection diesef engines. Coagulation was studied by collecting samples of soot in the engine exhaust with a thermal precipitator and examining them by electron and optical microscopy. A coagulation constant which can be used to predict with a fair degree of accuracy the diameter of soot coagulates in the engine exhaust was derived. Soot combustion was studied by generating soot in two cylinders of a four-cylinder engine and recycling it in another cylinder where the soot-containing exhaust gases were subjected to a temperature cycle by undergoing compression. A soot combustion constant was derived which can be used to predict the rate of soot combustion under known oxygen partial pressure. The results of soot coagulation and combustion studies were applied to calculate for a diesel engine the importance of the combustion of soot during the expansion part of the cycle which follows the main burning period during the cycle.