The Impact of Fuel Blends and Ambient Conditions on the Heating and Evaporation of Diesel and Biodiesel Fuel Droplets

This work presents recent approaches to the modelling of heating and evaporation of automotive fuel droplets with application to diesel-biodiesel fuel blends in conditions representative of internal combustion engines. The evolutions of droplet radii and surface temperatures for diesel-biodiesel fuel blends have been predicted using the Discrete Component model (DCM). These blends include up to 112 components (98 diesel hydrocarbons and up to 14 biodiesel components of waste cooking oil and soybean methyl esters). The effects of ambient conditions (ambient pressure and temperature, and radiative temperature) on multi-component fuel droplet heating and evaporation are investigated. Ambient pressures and temperatures, and radiative temperatures in the ranges 20-60 bar, 700-950 K, and 1000-2000k, respectively, are considered. Transient diffusion of 98 hydrocarbons and up to 14 methyl esters, temperature gradient, and recirculation inside droplets, are accounted for using the DCM. In contrast to previous studies, it is shown that droplet evaporation time and surface temperature predicted for 100% biodiesel (B100) are not always close to those predicted for pure diesel fuel (B0), but are dependent on the biodiesel fuel type and ambient conditions. Finally, the impact of radiation on opaque droplet lifetimes is shown to be significant, leading to about 19.4% and 23.3% faster evaporation for B0 and B100, respectively, compared to the case where radiation is ignored.