Research On Simulation For Mixture Formation Of Air-assisted In-cylinder Direct Injection Gasoline Engine

Compared with conventional port fuel injection gasoline engine, GDI engine has its own advantages of higher volumetric efficiency, compression ratio, thermal efficiency, response performance and GDI is considered as the most effective fuel-saving measures. It is the effective mean for the current energy crisis and the most stringent emission regulations. In this paper, we study intake port flow characteristics and analysis and optimization the mixture formation of air-assisted direct injection gasoline engine through three-dimensional numerical simulation.First, the geometry and computational grid of the intake port and combustion chamber was established for a direct injection gasoline engine. Through the steady calculation of the intake port and combustion chamber, we get airway flow distribution performance and roll forming process, and the calculation results and experimental results have good consistency.Transient calculation was carried on the mixture formation process and spray calibration was completed with the constant volume combustion. On this basis, adjusting the injection timing and injection angle to optimize the mixture quality , and the following results are obtained:1,Analysis of the air movement in cylinder of different plane: in the y-z plane can format a wide range of strong tumble sport in cylinder before ignition, but in x-z plane the roll gradually offsets.2,At different injection timing the mixture formation is different. The earlier staring injection(SOI=410°CA), the fuel evaporate more sufficient and the mixture time longer. Thus the mixture concentration before ignition is relatively uniform. For the injection direction towards to the intake valve, the fuel mainly distribute around the intake valve region.3,Adjusting the injection angle along the cylinder axis, the simulation results show that a small dip gets a more uniform mixture and too large dip results the fuel depositing on the piston which leading to carbon deposition and UBHC emissions increasing.