It is widely known that direct application of biomass fuels oil to DI diesel engines increases the carbon deposit in the engine. To minimize this effect, biomass fuel is subjected to transesterification process. Nevertheless, it is still desirable to use biomass fuel without transesterification. As diesel engine combustion and emissions are strongly dependent on spray characteristics and mixture formation, this study tries to clarify the spray characteristics of rape-seed oil (SVO) including spray structure, spray development, fuel evaporation, and droplets atomization.
Optical observation reveals that rape-seed oil (SVO) spray forms a stick-like structure without branching structure at spray boundary and has heterogeneous density distribution in a liquid column at spray centerline. SVO spray hardly penetrates at exceedingly initial stage of injection, in particular at low injection pressure. Combination of high injection pressure and high ambient temperature lengthens spray penetration and produces branching structure and fine droplets. Macro-scale characteristics of SVO spray can be improved by applying reduction of nozzle sac-volume and scaling of nozzle hole-diameter accompanied with high injection pressure. However, it is hard to improve stick-like structure and heterogeneous density distribution of SVO spray under low injection pressure and low ambient temperature.
