Study Of Combustion Process And Heat Release Mechanism On Diesel Engine Under Low Excess Air Coefficient Condition

Due to the development of science and technology, diesel engine has made considerable progress in performance in recent years and fuel economy, the power per litre has even reached the level of gasoline engine.But when it is used in the inlet flow limited condition, especially in the vast plateau environment of our country, the turbocharger efficiency and air inflow is decreased, and the excess air coefficient is lower, due to the thin air. The process of flow, spray atomization and heat release in the engine is changed, causing the power is decreased seriously.In this paper, I established and validated a three-dimensional simulation model for a highly intensified engine. By means of comparation under different excess air coefficient conditions, the study of the process in cylinder was carried out. The cylinder is divided into three parts, and two boundaries between them are defined for statistical purpose, based on the shape of cylinder. Then the variation of mass flow between the three areas, amount and diameter of the fuel droplets, fuel evaporation rate and so on under low excess air coefficient condition were studied quantificationally.The mixture in cylinder is not uniform, the density in different area is different and changing quickly. So it was divided into different parts by equivalence ratio zones for study. Characteristic parameters of fuel-air mixing velocity and uniformity were founded, and then the fuel-air mixing mechanism under low excess air coefficient condition was studied. By means of comparation under different excess air coefficient conditions, characteristics of mixture distribution in cylinder, different equivalence ratio zones of mixture and mixture in cylinder and the parts of it were analyzed.Heat release characteristic is affected seriously by mixing process, and it determines the performance of the engine directly. By means of comparation of heat release rate in the three-dimensional space of cylinder, characteristics of heat release in cylinder and the parts of it, heat release in different equivalence ratio zones of mixture under different excess air coefficient conditions, heat release mechanism under low excess air coefficient condition were mastered.