Fuel adhesion characteristics under non-evaporation and evaporation conditions: Part 2 – Effect of ambient pressure

Abstract

The formation of the fuel adhesion on the wall is demonstrated as the major cause for the efficiency loss and particle number (PN) emission increase in direct-injection spark-ignition (DISI) engines, making it difficult to meet the regulation of the future standards. In this study, experiments were performed in a constant high-pressure chamber to clarify the characteristics of impinging spray injected by a mini-sac gasoline injector with a single hole. The fuel spray and adhesion were measured by Mie scattering and Refractive Index Matching (RIM) methods, respectively. The effects of ambient pressure on the spray-wall interaction under room and high temperature conditions were checked. The results showed that the increased ambient pressure decreases the spray tip penetration but increases the impinging spray height by strong air-fuel entrainment under both room and high temperature conditions. However, for fuel adhesion, under room temperature, the ambient pressure promotes better atomization by stronger air drag force, resulting in more fuel adhesion on the wall. Moreover, the increased ambient pressure decelerates the droplets, leading to the transition of droplets behavior from “splashing” to “spread” or even “stick”, thus increasing the fuel adhesion on the wall. While, when evaporation occurs, apart from these reasons above, higher ambient pressure suppresses the fuel evaporation, leading to more fuel adhesion on the wall.