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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.

It is well known that indirect injection (IDI) diesel engines have better exhaust performance but lower fuel economy than direct-injection (DI) diesel engines. In recent years, fuel efficiency has been strongly demanded to reduce global warming. Therefore, the IDI engine is required to reduce fuel consumption. According to past research, fuel injection control can be one of the means to improve fuel efficiency in the IDI system. This paper tried to apply two-stage fuel injection as one of the fuel injection control methods to improve fuel efficiency while suppressing exhaust emissions. Particularly, since it is considered necessary to reduce the amount of injection during the ignition delay period in the sub-chamber with the IDI type, two-stage injection with a small amount of pilot injection was applied.

High boosting technology is commonly applied to diesel engines in recent years. Amid this trend, the study of spray behavior at ignition delay period still plays an important role in diesel combustion. This study focuses on the effect of ambient condition on diesel spray. The study investigates both macro-scale and micro-scale dynamic behaviors of diesel spray affected by ambient density and temperature at early stage of injection. A study via dual nano-spark shadowgraph method and rapid compression machine has been carried out to simulate real diesel engine combustion and to further understand the dynamics behavior of droplet evaporation and size distribution at early stage of mixture formation in the chamber. The micro-scale images captured reveal a shape variation of branch-like structures formed at the spray boundary. The evaporation of droplets is also captured clearly in macro- and micro scale photographs under the condition of high temperature ambient.

This study tries to reduce SOF (Soluble Organic Fraction) emissions at low load by improving spray characteristics of rape-seed oil and avoiding wall-impingement of the spray to the piston wall in a real direct-injection diesel engine applying rape-seed oil directly. High swirling air motion and squish flow caused by the piston configurations are taken as measures. Further, flat bottom shape of the piston is applied. Results show that emissions can be improved by the support of air motions. High swirl with toroidal piston is effective to reduce SOF emissions. Re-entrant piston with flat bottom shape offers the best emission performance. Raising gas temperature is also effective to reduce SOF emissions at low load.