The Analysis Of Influencing Factors Of Transient Performance Of Diesel Engine

With energy problem and environment problem increasingly prominent,the emission regulations become also more and more strict.And energy conservation and emissions reduction of internal combustion engine is one of the major problems that the internal combustion engine workers facing.Compared with gasoline engine,one of the biggest features of the diesel engine is the high thermal efficiency.Automotive diesel engine is usually work under transient conditions,and the performance shown under steady state condition will be deteriorated during the transient conditions.Therefore,the research on the transient conditions of diesel engine is paid more and more attention by domestic and foreign scholars.Due to the variability of the transient conditions of the diesel engine,the different stages of the phase(small load stage,medium load stage and heavy load stage)show different characteristics.It is helpful to make full use of the characteristics of each stage to provide guidance for the development of better transient performance control strategy.The in-depth analysis of transient process in stages is helpful to make full use of the characteristics of each stage and provide guidance for developing better transient performance control strategies.The performance deterioration of diesel engine under transient conditions is caused by the lag of cylinder thermodynamic state,and heat is accumulated ceaselessly under transient process.This paper takes into account making the use of the advantages of large air-fuel ratio and low emissions on small load stage,to ensure in the case of that emissions and the economy do not deteriorate and increase the cylinder heat atmosphere of diesel engine,so as to ease the transient process of large load cylinder heat state lag to improve the transient performance of diesel engines.This paper,with CA6 DL heavy-duty turbocharged diesel engine as the research object,set up the three-dimensional numerical platform,and studied the impact of boundary conditions on the transient performance of diesel engine: on the one hand,the laws of macroscopic parameters of diesel engine under different boundary conditions are discussed,on the other hand,the influence of boundary conditions on the cylinder microscopic field and the thermal atmosphere of diesel engine was further studied.1?In the small load condition of transient process,compared to the original machine steady state condition,diesel engine transient conditions sauter mean diameter(SMD)is larger and evaporation rate lower;The internal pressure of the diesel engine is obviously lower than the steady state value,and the average temperature in the cylinder is higher than the steady state value;The combustion phases CA10,CA50 and CA90 are slightly delayed,and the combustion duration is prolonged;However,due to the difference between the steady state combustion phases and the transient combustion phases within 1oCA,the difference in heat release rate is small;NOx and soot emissions are reduced compared with the original machine steady-state condition;The diesel engine transient conditions indicated thermal efficiency is lower than the original machine steady state,indicating fuel consumption higher.2?The effect of the injection timing on the combustion phase is large.In the small load condition of transient process,with the early injection timing,the cylinder pressure peak value,the average temperature peak value and the heat release rate peak value are advance,indicating that the injection timing in advance,burning closer to the compression top dead center and burning heat release more concentrated;And the effect of fuel injection timing on the transient conditions CA10 and CA50 of diesel engine is greater than that on combustion duration;In the small load condition of transient process,the early injection timing,the cylinder high temperature cell ratio peak increases and the phase is advanced,so NOx emission increased significantly;Increasing the injection pressure and the early injection timing can increase the flow velocity in the cylinder of the diesel engine,increase the high temperature area and accelerate the combustion rate,which is beneficial to the rapid promotion of the hot atmosphere in the cylinder and can effectively reduce the fuel consumption rate.3?In the small load condition of transient process,the effect of intake air temperature on the cylinder pressure is small,which has a great influence on the heat release rate.The influence of the air inlet density and EGR rate on the cylinder pressure of diesel engine is relatively large,and the effect of heat release rate is relatively small.When EGR rate is less than 20%,EGR rate has little effect on cylinder pressure and heat release rate.Reducing the intake air temperature and EGR rate,increasing the air inlet density can increase the total driving energy of the diesel engine transient process 25% load condition,and improve the oil and gas mixing process,reducing the remaining fuel rate,the degree of improvement of oil and gas mixing : the air inlet density > EGR rate> intake air temperature.Increasing the intake air temperature and the air inlet density,decreasing the EGR rate can improve the cylinder thermal atmosphere of the diesel engine during the transient process.Increasing the intake air temperature and the EGR rate,reducing the air inlet density will cause to a lower indicate thermal efficiency of the diesel engine,indicating an increase in fuel consumption rate.There is no direct correspondence between the cylinder thermal atmosphere and the economic performance of the diesel engine.