Analysis Of Characteristic Parameters Of Combustion Process On Diesel Engine

Nowadays，the energy crisis and the more strict emissions regulations cause theattention of people. Because of high thermal efficiency of diesel engines, people focus on itmore than before. But the high NOx and particulate matter (PM) emission of traditionaldiesel engines become a serious problem which should be solved. Optimizing thecombustion is a fundamental method to achieve machine purification of NOx and PM.Theapplication of combustion feedback controlling technology on the engine offers the effectivemethod for the realization of optimization of combustion.To realize the controlling of dieselcombustion process, firstly, we need to analyze the impact of combustion boundarycondition on the combustion process. Next step is selecting the sensitive parameters of thecombustion characteristics as the feedback signal. Therefore, based on the characteristicparameters of combustion process, the research of the influence of boundary conditions onthe combustion process is the early foundation to realize combustion feedback controlling.In this research, we define CA6DL diesel engine as the research object and1650r/minwith50%load as test conditions. Study the laws of common rail pressure and fuel injectiontiming affect characteristic parameters of cylinder combustion. We define CA4DC dieselengine as another object. The test conditions is2425r/min and25%load,50%load,75%load and transient operating conditions. Studying the laws of EGR rate affects characteristicparameters of cylinder combustion. The results show that:1. The heat release rate is sensitive to the change of common rail pressureranging.When the common rail pressure increases, peak of heat release rate increase from150.1J/°CA to228.1J/°CA and its peak phase from26°CA move forward to18°CA. Thereason is improving injection rate, shortenning the fuel injection pulse width and improvingthe degree of fuel atomization.The phase of peak heat release rate is sensitive to the changeof fuel injection timing.When the fuel injection timing move forward, the phase of peak heatrelease rate from27°CA move forward to19°CA.2. The combustion characteristic parameters CA50move forward significantly when the injection pressure increasing and injection timing moving forward. And then establish themapping relations among the CA50, the effective thermal efficiency and smoke. When theinjection pressure is134MPa, CA50is18°CA.When the injection timing is-3.1°CA ATDC,the CA50is19°CA. The study found that, thermal efficiency increases and smoke lowerwhen the CA50moves forward. With the CA50moves afterwards to a certain range(ΔCA50is higher than5°CA), the inflection point of smoke curve appears and it deterioratesseriously. So, it is necessary to control the changing of CA50in the combustion process. Inorder to prevent the deterioration of the smoke，it has to make ΔCA50less than5°CA.3. This paper studies how the EGR impacts CA50in the steady-state conditions andtransient operating conditions. In the low and middle load of steady-state conditions,CA50moves backward with the EGR rate increasing. Because the temperature is lower in cylinder,the inert gas in the exhaust gas lead to the ignition delay of growth.In large load, CA50isconstant when the EGR changes. The reason is initial high temperature in cylinder lead tothe burning speed up.In the transient operating conditions from10%load to90%load, transient EGRovershoot will lead smoke to a sharp deterioration.When the transient EGR rate is higherthan the EGR rate in stable conditions, the ΔEGR has a linear relationship with ΔCA50.Lower the transient EGR valve opening degree of the control strategy to reduce theovershoot amplitude of the EGR rate. ΔCA50maximum is lower than4°CA, and the smokepeak is5.3%, a decline of43.7%compared with the original machine transientprocess.Controlling of EGR can reduce the overshooting amplitude of EGR in the transientprocess. Achieve to make the CA50process forward, and lead the smoke emission lower.