Effect of temperature on fuel adhesion under spray-wall impingement condition

•Fuel adhesion evaporates from the periphery to the impingement regime.•High ambient temperature promotes the uniformity in thickness of fuel adhesion.•Secondary breakup droplets redepositing on the wall is the reason for fuel adhesion increasing.•Different mechanisms are purposed for fuel adhesion formation. In direct-injection spark-ignition (DISI) engines, spray-wall impingement affects the formation of the air–fuel mixture as well as combustion and exhaust emissions. In this study, the characteristics of fuel adhesion injected by a mini-sac gasoline injector with a single hole were investigated under the evaporation and non-evaporation conditions. The fuel spray was observed using Mie scattering, and fuel adhesion was measured using the refractive index matching (RIM) method under high injection and ambient pressures. The results showed that when evaporation occurs, the thin fuel adhesion evaporates quickly, whereas the thicker adhesion barely evaporates in a short period of time, resulting in a more uniform fuel adhesion on the wall. The maximum adhesion thickness continues to increase even after the end of injection, likely because of the re-deposition of the splashing droplets. Various mechanisms are purposed to explain the spray-wall interaction: fuel droplets primarily impinge on the wall forming primary impingement region, followed by the re-depositing droplets which form secondary impingement region.