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Fuel consumption, emissions and output power are some of the very important factors for automotive engine design. Since the combustion efficiency depends on the quality of the air-fuel mixture and mixture quality depends on the fuel injection parameters, the investigation of spray features is an overall goal in direct injection engines. In this paper, simulation of GDI spray is carried out in a constant volume chamber contains nitrogen in four different injection pressure using the AVL Fire software. The results are validated against the Istituto Motori-CNR experimental data. The log-normal probability distribution as an initial droplet diameter and Huh-Gosman model as secondary breakup were used. Then the combustion of EF7 Engine with direct injection was studied and wall film thickness was compared at different injection pressures and injector angles. Also, the effects of wall temperature and single-stage and two-stage fuel injection with different ratios of injected fuel mass were evaluated on the wall film. Since the fuel can be injected into the combustion chamber in both intake and compression stroke according to engine operating conditions in gasoline direct injection engines, the simulation was done for open cycle engine.

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The main aim of this paper is the numerical investigation of air-fuel mixture formation and spray and combustion characteristics of EF7 engine equipped with spray-guided direct injection system. For this purpose, first, a six-hole injector is simulated in three different injection pressures and to validate the fuel injection characteristics, the results are validated against the Istituto Motori-CNR experimental data. Then, the injector position is selected near the spark plug and by changing of injector angle relative to the axis of combustion chamber, the appropriate angle for optimization mixture formation is obtained. Then, the effect of injection pressure, start of first and second injection as well as the effect of two-stage fuel injection with different proportions of fuel mass at primary and secondary injection are studied on the mixture formation, wall film and engine emissions. The results showed that the injector angle is extremely effective on the mixture formation, pressure and the amount of unburned hydrocarbons due to its direct impact on wall film mass. Also, in the two-stage injection, relatively homogeneous lean mixture compared to the stratified mixture results better combustion at part load condition.