Effects of spray patterns on the mixture formation process in multi-hole-type direct injection spark ignition (DISI) gasoline engines

The direct injection concept is a prominent issue in spark ignition engines owing to direct injection's high fuel efficiency. However, proper fuel-air mixing technology is necessary to restrict exhaust emissions. Mixture preparation requires an understanding of the complex phenomena and physics regarding direct injection spark ignition (DISI) gasoline engines. Multihole-type DISI gasoline injectors can be used to generate various spray patterns. In this study, five types of spray patterns were considered for mixture preparation simulation: reference-type, circle-type, triangle-type, T-type, and Y-type patterns. Mass flow rate and initial droplet size were assumed to be the same for each nozzle. Also, cavitation for each nozzle was considered to be equal. Numerical analysis was carried out for wide open throttle conditions with a fixed engine speed (1500 rpm). Injection timing was set to BTDC 360 degrees, BTDC 315 degrees, and BTDC 270 degrees. The spray model and motoring pressure were validated before mixture preparation analysis. The BTDC 360 degree injection case was characterized by instant vaporization, whereas the BTDC 315 degree injection case was characterized by a fuel injection-dominant case, and the BTDC 270 degree injection case was characterized by a spray-flow interaction-dominant case. T-type and Y-type spray patterns showed faster evaporation than reference-type, circle-type, and triangle-type spray patterns.