Optimization Design Of Combustion System Of Four Stroke GDI Engine Using CFD Model

The application of gasoline direct injection in cylinder has brought new feature to developmentof automobile engine. Comprising with the carburetor type or port fuel injection, in-cylinder directinjection technology has many advantages, for example: good cold starting, strong Antiknockperformance, good fuel economy and fast load response.In the internal combustion engine fuel, the flash point of kerosene is high, so it is relatively safeand easy to store and transport. The research on kerosene fuel internal combustion engines is of greatsignificance, when it has special requirements for fuel safety, engine volume and weight. Whendomestic and foreign research institutions study kerosene ignition engine, the first problem is to solvethe atomization problem of kerosene which has bad atomization and volatilization. Then the designsof combustion chamber and the inlet of in-cylinder direct injection combustion system are carried out,the relative arrangement of spark plug and injector nozzle and optimization matching of injection timehave great influence on the mixture concentration distribution in the cylinder, which affect the coldstart and knock limit power of heavy load of spark ignition kerosene engines.The paper is based on a particular horizontally-opposed four cylinder engine with two valves andwedge chamber for the structure characteristics. The main work is simulating the mixture formationprocess with hollow cone fuel sprays and low pressure air auxiliary injection technology. Firstly，theCFD dynamic grid technology has been researched, which guarantees the grid quality when the valvesand piston of engine are moving. Secondly, it is the analysis of coupling of fuel injector andcombustion chamber when dividing of grid. Finally, the effect factors of evaporation of the fueldroplet in cylinder are analyzed, to prepare for further spray simulation.Based on the simulation of four stroke engines, this paper analyses and evaluates the flow field incylinder and spray model of the prototype machine, especially cold start. The results show that enginespeed and fuel injection time have a great influence on the composition of mixture. According to theresult of calculation, the paper puts forward improvement scheme of the combustion chamber, inlet,injector and spark plug position arrangement, and simulates and evaluates the improved combustionchamber system. Research shows that inlet radius of curvature has little effect on the mixture, butcombustion chamber shape, injector placement and injection time have a great influence on mixture.In order to validate the correctness of the calculation, this paper researches the couplingcalculation of the air assisted fuel injector and combustion chamber, comparing with the high-speed photography oil beam shape of air assisted fuel injector constant volume experiment. The results showthat spray simulation results of auxiliary air injector consistent with experimental results.