Study On Cold-Start Emission Characteristic Of GDI Engine

The injection pump feed pressure of modern direct-injection gasoline engine has reached 5~12Mpa so that atomization quality can be improved. Furthermore the formation of evaporation mixture of gasoline which mainly rely on spray fog in cylinder and the movement of air appropriate colliding with the cylinder wall can form the ideal fuel-air mixture distribution. That is an effective solution to gasoline cold start and warm-up emission.In this paper, by calibration software INCA where the original single injection control strategy was changed to the secondary injection control strategy through flexible control of the first injection timing, the second injection timing and their injection ratio, combined with the tumble characteristics optimizing fuel-air mixture distribution the emission of noxious gas can be improved in the process of cold start of direct-injection gasoline engine.Firstly, direct-injection gasoline engine with 4G15 was selected for the study, In the process of the engine cold start by fluid dynamics software (CFD) the flow characteristics of the inlet and compression stroke in cylinder was simulated in order to acquire more detailed data about fluid field and how combustion process of cold start impacted on the tumble combustion system in cylinder was analyzed.Using CFD-FIRE have simulated the variation of air-fuel ratio distribution which ensue from single injection strategy and secondary injection strategy from fuel injection to the ignition in the process of cold start and have analyzed the effect of the strategies to air-fuel ratio distribution. Then by compared with the strategies, the impact on combustion characters was analyzed.Finally single injection strategy and secondary injection strategy were studied by engine bench test. It was discussed that the impact of the first injection timing, the second injection timing and their injection ratio during cold start on emission. The results show that secondary injection strategy which is superior to the single injection strategy can improve combustion and reduce HC and other harmful emissions during cold start.