Soot particle evolution and transport in a direct injection diesel engine

Abstract

Particle-based in-cylinder soot distribution study is becoming more important as the rules and regulations pertaining to particulate emission of diesel-powered vehicles have been increasingly more stringent. This paper focuses on the investigation of soot size evolution and its distribution and transport inside an engine cylinder. The overall process of soot formation includes soot nucleation, surface growth, oxidation, coagulation and agglomeration. The present study considers only soot surface growth, oxidation and coagulation to predict the in-cylinder soot particle size. The soot surface growth model was based on Hiroyasu’s soot formation model while soot oxidation was referred to Nagle & Strickland-Constable’s soot oxidation model. Coagulation rate was defined using Smoluchowski’s equation with constant proposed by Wersborg. From this study, it is demonstrated that soot particles with relatively larger size are gathered in the centre of the cylinder while smaller soot particles are found to be in the region near the wall. Soot number density is considerably high at the start of combustion and reduces sharply afterward while the soot particle size shows the opposite trend. Soot formation rate was found to be dominant at earlier crank angle and is overcome by soot oxidation and coagulation processes that caused lower soot number density but higher soot particle size.