Simulation Of The Soot Oxidation In Direct-injection Diesel Engines

The mechanism of soot oxidation relates with soot nanostructure, types of oxidants and reaction conditions. The widely used soot oxidation model is based on experimental oxidation data of high temperature graphite which are obtained from laminar flame reactor or shock tube. Soot oxidation in cylinder has important influences on formation mechanism of diesel soot and particle emissions. As the simulation of diesel soot oxidation, especially in-cylinder soot, is required more and more accurately, soot oxidation model need to be improved urgently. Due to the complexity of operating conditions of diesel engine, researches on in-cylinder soot oxidation of diesel engines are very few. So this dissertation does researches on process of in-cylinder soot oxidation of diesel engine in high temperature gas phase and explores the post-injection technology way to low in-cylinder soot concentration.Based on the experimental measurements, soot particle size distributions and soot nanostructure parameters via engine crank angle are obtained. The phases of soot formation and oxidation are determined. Using soot particle size distributions of post-combustion period in which soot formation stops, experimental in-cylinder soot oxidation rates of diesel engine in high temperature gas phase are calculated with a new method. Then experimental soot oxidation rates are predicted by widely used soot oxidation model and the results are compared with experimental data. Based on experimental soot nanostructure parameters and influences of nanostructures on soot oxidation, a method to improve now available soot oxidation model is presented.The formation and evolution of in-cylinder soot of diesel engine are analyzed with numerical simulation software. The influences of dwell angles and mass of post-injection on formation of post-injection premixed mixture, cylinder induced turbulence, soot vortex crushing are studied. And then the technique of speeding up post-combustion, raising temperature of post-combustion period and promoting soot oxidation is explored.