Study On The Fuel Film Dynamic Effects And Air Fuel Ratio Control For Gasoline Under Transient Conditions

For intake manifold multi-point fuel injection (MPI) of gasoline engine, the dynamic effect of fuel film is the main reason to excursion of transient A/F ratio control. In order to improve the engine combustion and fuel economy, increase the specific output power, and reduce the exhaust emission, the transient A/F ratio should be accurately controlled based on the dynamic effect study of the transient fuel film.Gasoline engine with intake manifold MPI system was studied in this thesis, and in order to analyze the dynamic effect of the fuel film, spray impingement and evaporation characteristics of fuel injection were simulated. The simulation was studied under different injection parameters with varying intake manifold wall setup and intake air conditions. Among all the parameters, the formation and concentration of fuel film and spatial distribution of liquid fuel particles were more influenced by injection angle, intake air speed and the wall temperature of intake manifold.As can be demonstrated by the simulation result, the gradual deposit of suspended fuel particles was another important fuel film source besides the direct spray impingement. The fuel film accumulation and evaporation of a single injection would laste for a long-time process,which was the basic reason to fuel film transmission delay.The fuel film model was established and model parameter was identified by least square method and Charpy deviation function. As indicated by the comparison result, the divergence degree of simulation by Charpy deviation function was better than that by least square method.On the basis of model parameter identification, a fuel film compensation model was set up and simulated in Matlab/Simulink, and a pulse width predication model of fuel injection based on BP neural network was designed along with intake air and fuel film models. Results of calibration experiment and model simulation indicated that the pulse width predication model was relatively accurate. A/F ratio simulation was studied with BP neural network model, and the maximum deviation of A/F prediction was less than that of the original model, which means the model established can be used to effectively control the transient A/F ratio of gasoline engine.