Improving the partial-load performance and emission of GDI engine by combining injection strategy and exhaust variable valve timing technology

The combustion and emission characteristics of a gasoline direct injection engine were investigated at different injection strategies combining with the exhaust variable valve timing (EVVT) technology. The results indicated that at 1400 rpm, fuel injection quantity was 11.5 mg/cycle, and the optimization of fuel injection timing and EVVT opening degree (injection timing = 290 degrees CA bTDC, EVVT = 40 degrees CA) can reduce the break specific fuel consumption (BSFC) by up to 6.12% compared to the basic engine (injection timing = 260 degrees CA bTDC, EVVT = 0 degrees CA). When the EVVT opening was 30 degrees CA and the injection timing is 270 degrees CA bTDC, the engine emissions and performance can obtain a trade-off effect, while the BSFC and the emissions all have a significant decrease. This is because EVVT can significantly increase the residual gas in the cylinder, which changed the thermodynamic and chemical properties of the charge, thereby reducing pumping losses, improving thermal efficiency and emission performances. Advancing the injection timing to 280 degrees CA bTDC was beneficial to improve engine performance, but it will cause wall-wetting phenomenon to greatly increase particulate emissions. Increasing the EVVT opening degree can effectively offset this problem. The use of split injection was beneficial to increase the flame speed and augment the tolerance of engine to the dilution of residual exhaust gas.

Automated summary

By optimizing the injection strategy and exhaust variable valve timing, it is possible to reduce the fuel consumption and emissions of a gasoline direct injection engine, while improving its performance.