Analysis On Exergy Flow Characteristics Of Automotive Diesel Engine

With large output torque,wide range of power and good fuel economy,diesel engine is widely used in automotive.In recent years,due to the increasingly strict law,regulation and the pressure brought by competition with all kinds of new energy power,the energy efficiency of the diesel engine has become one of the main research targeting in the field of internal combustion engine.In order to consider the quantity and quality of energy,it has become a very important topic to carry out research on thermal balance and exergic balance.To perform exergy analysis on the working process of diesel engine,this paper designed and established a test platform for the energy analysis of diesel engine,and realized the characteristic analysis of exergy distribution such as effective work,exhaust exergy,heat transfer exergy,and exergy loss.Meanwhile,the influence of different boundary condition parameters(EGR rate,injection parameter and cooling parameter)on exergic flow distribution of diesel engine was studied,and the sensitivity of boundary condition parameters was analyzed.According to the experimental results,the optimization directiones of exergic efficiency were proposed.The main content of this paper is divided into two parts.In the first part,the distribution of exergic flow of a diesel engine was mainly studied in the test.The test results show that:1.Under the change of load,the effective work,exhaust exergy,heat transfer exergy and exergy loss increased with the increase of load,in which the exhaust exergy and exergy loss increased at a faster rate when the load was large,while the heat transfer exergy increased at a slower rate when the load was large.In terms of proportion,exergic efficiency and exhaust exergic proportion increased with the increase of load;on the contrary,exergic proportion of heat transfer and exergic loss decreased with the increase of load,which was mainly caused by the increase of the equivalent ratio with the increase of the circulating oil supply during the rise of load and the deterioration of combustion.By comparing load characteristics of exergic flow distribution under A(1517r/min),B(1921r/min),C(2307r/min)and nominal speed(2600r/min),the trend of load characteristics of diesel engines at different speeds is relatively consistent.2.In the subsystem of diesel engine,the energy recovered by the exhaust gas turbine and the energy taken away by the cooling in the intake air are positively related to the load.In terms of the proportion,with the increase of load,the turbine energy proportion presented a convex rise,while the intercooler energy proportion presented a concave rise.At the nominal speed,the highest exhaust exergy utilization rate of low and medium load was 33.57%.3.At the designated point(2600r/min,100% load),the effective power of the diesel engine for the vehicle is 112.01 kw,the exhaust exergy is 51.03 kw,the heat transfer exergy is 25.25 kw,the heat transfer exergy is 120.91 kw,the exergy efficiency is 36.23%,the exhaust exergy accounts for 16.5%,the heat transfer exergy accounts for 8.17%,and the exergy loss accounts for 39.1%.In the second part,the influence of different boundary condition parameters on exergic flow distribution of diesel engine was studied and the sensitivity of boundary condition parameters was analyzed.The main conclusions are as follows:1.When the EGR rate increases from 0% to 20%,exergic efficiency decreases,exhaust exergy increases,heat transfer exergy decreases,and exergic loss increases,because a small amount of EGR can shorten the ignition delay period and reduce the temperature in the cylinder.When the fuel injection pressure increased from 130 MPa to 160 Mpa,the exergy efficiency increased,the exhaust exergy proportion decreased,the heat transfer exergy proportion increased,and the exergy loss was basically unchanged.It was because of the influence of the fuel injection pressure on the atomization degree that the exergy flow distribution changed under different loads.When the inlet temperature increases from 30? to 70?,exergy efficiency decreases,exhaust exergy proportion increases,heat transfer exergy proportion increases,exergy loss proportion decreases,which is due to the increase of the average temperature in the cylinder and the shortening of the ignition delay period.When the coolant temperature increased from 50? to 90?,the exergy efficiency increased,the exhaust exergy proportion increased,the heat transfer exergy proportion decreased,and the exergy loss was basically unchanged.2.Under the parameters of different boundary conditions,the injection parameters have a high sensitivity to exhaust exergy and heat transfer exergy proportion,while the intake temperature has a good sensitivity to exergy efficiency,exhaust exergy proportion and heat transfer exergy proportion,and the coolant temperature has a good sensitivity to exergy efficiency and heat transfer exergy proportion.According to exergic distribution sensitivity,three optimization schemes were put forward: using two-stage successive supercharging equipment,formulating the control strategy of oil injection parameters,optimizing cooling coefficient,etc.