In-cylinder Combustion Visualization of a Direct-injection Spark-ignition Engine with Different Operating Conditions and Fuels

A direct-injection and spark-ignition single-cylinder engine with optical access to the cylinder was used for the combustion visualization study. Gasoline and ethanol-gasoline blended fuels were used in this investigation. Experiments were conducted to investigate the effects of fuel injection pressure, injection timing and the number of injections on the in-cylinder combustion process. Two types of direct fuel injectors were used; (i) high-pressure production injector with fuel pressures of 5 and 10 MPa, and (ii) low-pressure production-intent injector with fuel pressure of 3 MPa. Experiments were performed at 1500 rpm engine speed with partial load. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording. Visualization results show that the flame growth is faster with the increment of fuel injection pressure. The mass fraction burned curves, calculated from the averaged in-cylinder pressure data, show that the burn duration is shorter for the higher fuel injection pressure. It is observed that with the advancement of the injection timing, the flame size increased faster than that of retarded injection timing. Comparing different fuels, it was found that the flame growth is much faster for ethanol-gasoline blended fuels than for gasoline.