Browse Publications Technical Papers 2018-32-0014
2018-10-30

Effect of injection timing on mixture preparation in a small gasoline direct-injection engine 2018-32-0014

Gasoline direct-injection (GDI) engine has evolved as a solution to meet current demands of automotive industry. Benefits of a GDI engine includes higher fuel economy, good response, and lower cold start emissions. But it suffers from problems like combustion instabilities, misfires, and fuel wall impingement. This study focusses on implementing the gasoline direct-injection technology in a small bore engine where problems mentioned above are more predominant. Effects of fuel injection on in-cylinder flow, turbulence, mixture distribution and wall impingement are analyzed. Results showed that air motion inside the engine cylinder is influenced by direct-injection of fuel, with considerable variation in turbulent kinetic energy at the time of injection. Due to charge cooling effect, the mixture density was increased by about 10.8 % and trapped mass by about 9.5 %. A significant drop (about 100 0C) in mean in-cylinder temperature was observed with direct-injection of fuel compared to the case without injection, with further variation based on injection timing. Fuel distribution near the spark plug, and fuel impingement on in-cylinder surfaces were carefully evaluated. An early injection timing of 80 crank angle degree after intake top dead center was found to give the best fuel distribution and minimum wall impingement. In-cylinder turbulence at spark timing was also found to be higher for above-mentioned injection timing. Overall, the increased turbulence and trapped mass, and decrease in in-cylinder temperature indicated the potential of increasing the thermal efficiency and power density in a GDI engine.

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