Effect of Lube Oil Film Thickness on Spray/Wall Impingement with Diesel, M20 and E20 Fuels

Spray impacting on a lube oil film with a finite thickness is a common phenomenon in IC engines and plays a critical role in the fuel-air mixture process and combustion. With the use of early injection strategy to achieve HCCI combustion mode in diesel engines, this phenomenon becomes more and more prominent. In addition, oxygenated fuels such as methanol and ethanol are regarded as alternative fuel and additives to improve the overall performance of HCCI engine. Therefore, a better understanding about the role of lube oil film thickness in methanol-diesel and ethanol-diesel blended fuels spray/wall impingement is helpful for accumulating experimental data to establish a more accurate spray/wall impingement model and optimize the combustion in HCCI engines. In this paper, the effect of lube oil film thickness on the characteristics of spray/wall impingement of different fuels are investigated in a constant volume bomb test system. Fuels include diesel, methanol (20v%)-diesel (80v%) blended fuels(M20),ethanol(20v%)-diesel(80v%) blended fuels(E20). With the novel measurement methods, the information about film thickness and adhered fuel ratio was obtained. In general, the results demonstrate that the initial lube oil film influence the wall film distribution after impingement. With the increase of initial lube oil film thickness, the diffusion and merge interaction between spray droplets and oil film become obvious which intensify the phenomenon of the dilution of oil film. But due to the low-density and high-volatile property of M20 and E20 fuels compared to diesel, the level of diffusion and merge interaction between alcohol-diesel blended fuels spray and lube oil film is lower than that of diesel which means using alcohol-diesel blended fuels can mitigate the problem of lube oil dilution and local rich mixture during spray/wall impingement process.