Experimental Investigation of Fuel Film Characteristics after Spray Impacting on Ultra-cold Surface

In extremely cold environments, the phenomenon of spray impacting on surfaces is unavoidable and the fuel film attached to the surface is one of the crucial factors influencing emission, stability, and cold-start performance in internal combustion engines. However, there is currently a lack of research on the effects of spray impacting on ultra-cold surfaces. In this study, researchers investigated the effect of surface temperature on impinging spray and fuel film area with different values of injection pressure, injection duration, and surface roughness visually using backlight and scattering methods. The penetration and diameter of the impinging spray were not affected by the low surface temperature due to the ample momentum, whereas the height was slightly decreased at the ultra-cold surface. The fuel film area significantly decreased with the lower surface temperature and the shorter injection duration. An empirical correlation for the fuel film area was established for reflecting the relationship between the fuel film area and the low surface temperature or injection conditions. The decrease in fuel film area was more noticeable on the surface with lower temperature and higher surface roughness (Ra=17.69μm). Nevertheless, the longer injection duration weakened this decreasing trend. With the increasing number of injections, the fuel film area rose while the area on the ultra-cold surface, increased more slowly because of the higher viscosity and thickness of the previous residual film.