Liquid/Vapor penetration and plume-plume interaction of vaporizing iso-octane and ethanol SIDI sprays

Spark-ignition direct-injection (SIDI) engines operating in a stratified, lean-burn regime offer improved engine effi-ciency; however, seemingly random fluctuations in stratified combustion that result in partial-burn or misfire prevent widespread implementation. Eliminating these poor combustion events requires a detailed understanding of engine flow, fuel delivery, and ignition, but knowing the dominant cause is difficult because they occur simultaneously in an engine. In this study, the variability in fuel-air mixture linked to fuel injection hardware was addressed by experimentation in a near-quiescent pressure vessel at high-temperature and high-pressure conditions representative of late, stratified-charge injection. An 8-hole SIDI spray was interrogated using high-speed schlieren and Mie-scatter imaging from multiple, simultaneous views to acquire the vapor and liquid envelopes of the spray. 3D plume analyses combined with jet spreading angle measurements showed the sprays were attracted towards the injector axis during injection. The decreasing plume angles affected the mixing field at the end of injection, resulting in a single, central plume. Long-working distance microscopy imaging showed that droplets at the end of injection were attracted to the injector axis. These droplets persisted farther downstream in the case of ethanol. Despite the merging of plumes, which could increase total momentum and penetration, single orifice models show greater penetration than that of plumes in the multi-hole injector, leading to the conclusion that multi-hole interactions decrease penetration at these particular operating conditions.