The Research On Simplified Numerical Model For Heat-work Conversion Process Of Gasoline Engine

In the original development process of engine,the choice of optimization for design and operating parameters can be only realized according to experience or bench test due to lack of enough understanding for internal relationships and change trend among engine performance,design and operating parameters.However,before completing the entity development of internal combustion engine,the bench test cannot be carried out.For this reason,the development for a new type of engine often experiences more than one round of design modification and test validation.In order to improve the efficiency and accuracy of new engine at the conceptual design stage,on the basis of tested data of three advanced turbocharged gasoline direct injection engines and by the utilization of numerical development software based on the Excel VBA platform,the minimum combustion duration was proposed and the common rules and effects of combustion characteristic parameters on engine performance as well as inner relationships and effects of combustion characteristic parameters were studied in this paper.The research results in this paper indicate that:1)The differences between 80% minimum combustion duration and 10%~90% combustion duration are mainly affected by load.Moreover,when the load is lower,the differences are larger,which also means more space of optimization for combustion process.2)The combustion quality parameter increases slowly with the ascent of load.Apart from the low-speed condition,the values are in the range from 1.8 to 2.4.However,the combustion quality parameter under the low-speed condition is always more than 2 with serious deviations and its value is mainly in the range from 3 to 7 at the low load to high load.3)50% combustion position,peak cylinder pressure position and combustion quality parameter are all positive correlations with ignition timing.With the retard of ignition timing,the above three parameters begin to move backward or increase slowly and when the ignition timing is still retarded at the late stage,the parameters are moving backward or increase fast.On the contrary,10%~90% combustion duration is negatively correlated with the ignition timing.With the retarding of ignition timing,10%~90% combustion duration decreases fast and then gradually tends to be stable.In addition,50% combustion position determines the peak cylinder pressure position and there is a standard linear relationship between them.Peak cylinder pressure position lags behind 50% combustion position and lag phase is about 5 °CA~7°CA.4)As far as influence factors of high-pressure cycle thermal efficiency are concerned,the impacts of load are very higher than those of engine speed.With the delay of ignition timing,high-pressure cycle thermal efficiency firstly increases slowly to the stable value which is also the maximum interval,and then decreases rapidly.The ignition timing must be controlled appropriately to ensure good high-pressure cycle efficiency.The above research results provide data for boundary condition evaluation at the numeric simulation stage under the engine conceptual design process,choice for key design parameters and optimization for operating parameters,and also theory basis for optimization of engine heat-work conversion process,which improves the efficiency and accuracy of new engine at the conceptual design stage.