The Effect of Fuel Injection Pressure on Spray and Combustion Characteristics in a Gasoline Direct-Injection Engine

A single-cylinder gasoline direct-injection engine was used for fuel spray and combustion visualizations with optical access to the combustion chamber. Experiments were conducted to investigate the effect of fuel injection pressure on spray and combustion characteristics inside the engine cylinder. A multi-hole high-pressure production injector was used with fuel pressures of 5 and 10 MPa. A Mie scattering technique was used to image the liquid phase of the fuel dispersion. The obtained spray images were then used to study the macroscopic spray characteristics such as spray structure, spray tip penetration and spray angle. Combustion visualization tests were performed to evaluate the effect of fuel injection pressure on combustion characteristics. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording. Results showed that higher fuel injection pressure led to faster spray tip penetration and an increased spray area for better fuel-air mixing. The results of combustion visualization showed faster flame growth with the increment of fuel injection pressure. The profiles of mass fraction burned confirmed that the burn duration is shorter for higher fuel injection pressure.