Effect of surface roughness on spread and evaporation of liquid film formed by fuel spray impingement on wall

In this study, the spreading and evaporation of a fuel film on a wall with various surface roughness Ra was investigated. Iso-octane was used as the test liquid fuel and injected from a multi-hole injector for a DISI (Direct Injection Spark Ignition) engine. Under atmospheric pressure and room temperature (25℃), the injected spray impinged on an aluminium wall, resulting in the formation of a fuel film. Wall surface temperature was controlled by an electric heater (from 25℃ to 120℃). The behavior of the fuel film over time was recorded by a high-speed camera. As a result, it was found that fuel film area after spray impingement became smaller with an increase of surface roughness Ra. For less than approximately Ra = 1 ~ 2 μm, the fuel film area on the hot wall was larger than that on the non-hot wall. For more than approximately Ra = 1 ~ 2 μm, the fuel film area on the non-hot wall was larger than that under hot wall (110℃ and 120℃) condition. Regarding the evaporation time of fuel film, it decreased with an increase of surface roughness Ra under a constant roughness ratio r. However, beyond a certain Ra, the evaporation time remained constant. In addition, at higher wall temperatures, the evaporation time became constant even at lower Ra.