Study On Phenomenological Fast Prediction Combustion Model Of Direct Injection Diesel Engine

In recent years,with the increasing use of electronic sensors and actuators on diesel engines,the requirements for calibration,control and response speed of diesel engines are also increasing.The traditional quasi-dimensional multi-zone combustion model has low computational efficiency due to the large number of divided regions and cannot meet the requirements of rapid and real-time in actual engineering requirements.Therefore,this paper analyzes the combustion process,simplifies the zoning and establishes a rapid prediction model for direct injection diesel engine combustion.Firstly,considering the high injection pressure and strengthening degree of modern diesel engines,the gas jet theory is used as the theoretical basis of the combustion model.The factors affecting the combustion and its sub-processes in the diesel engine are analyzed,and the combustion process is divided into three stages including premixed combustion,diffusion combustion in fuel injection and diffusion combustion after fuel injection to calculate the heat release rate;comprehensively balancing the calculation efficiency and model accuracy,the cylinder is separated into spray unburned zone,spray burned zone and air zone to calculate temperature distribution and emissions.In order to verify that the prediction accuracy of the model is comparable to the traditional quasi-dimensional multi-zone model and the calculation efficiency is higher,at the rated speed,the 90%load condition of a multi-cylinder diesel engine is calibrated and the other load conditions are compared and validated.The errors of medium and high load cylinder pressure and heat release rate are equivalent to the traditional quasi-dimensional multi-zone model.The error of emission prediction value is lager than that of the traditional quasi-dimensional multi-zone model,reaching to 13.7%.The calculation speed is greatly improved,more than five times the traditional quasi-dimensional multi-zone model in the same computer.Finally,the application scope of the model is further tested.On the single-cylinder diesel engine,the parameters of speed,load,injection timing and fuel injection pressure were used as factor variables to verify predictability of the model for low and medium speeds,different loads,different injection timings and different injection pressures.The prediction ability is also tested for medium and high speed and different loads in the multi-cylinder diesel engine.Among them,the error of explosion pressure and average pressure are less than 5%.In most working conditions,the crank angle error of CA10 is less than 0.5°CA,and the crank angle error of CA90 is less than 5°CA.The calculation error of NO_x is within 10%,and the calculation of each working condition can be completed in a few seconds on a general configuration computer.The results show that this phenomenological combustion model can quickly and accurately predict the combustion of direct injection diesel engines under high load conditions.