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Selected as an alternative diesel fuel based on consideration regarding the relationship between the fuel molecular structure and exhaust emission and criteria as alternative fuels, Dimethylacetal (DMA) was evaluated in both a direct injection (DI) diesel and a Direct Fuel Injection Impingement Diffusion Combustion Diesel (OSKA-D) engines. Since DMA with a 1% commercial-type cetane improver has 53 for the cetane number, no ignition-assist divice such as a spark plug is needed, unlike methanol. According to the DI diesel engine test, the NOx emission for DMA was almost equal to that for hydrocarbon diesel fuel, but smoke for DMA was much lower than that for diesel fuel. The OSKA-D engine test showed that NOx emission for DMA was much lower than that for diesel fuel and smoke emission for DMA was zero under all engine conditions.

The effect of fuel properties on the performance of a new type of diesel engine with fuel jet impingement was investigated in comparison with the performance of a DI diesel engine. The new engine has a unique mixture formation process, but the details have not been well investigated. Therefore, the combustion processes of the engine was observed with a transparent piston engine and a high-speed camera system. Observations of the combustion process showed that after impingement, the fuel diffused almost symmeterically into the shape of a disk. Ignition usually started near the cavity wall and extented toward the center of the combustion chamber. The flame appeared to extend from the inside cavity radius to the outside cavity radius because of the strong squish flow. The fuel consisted of petroleum derived samples with a wide range of cetane number and viscosity. High cetane number resulted in reduced NOx mass emission from both engines, but an increased amount of smoke was emitted.

The effect of the fuel properties on diesel exhaust emissions was investigated using a commercial DI diesel and a prototype diesel engine with fuel jet impingement(OSKA--DH). The new type of diesel engine has a unique concept for the mixture formation process and is regarded as a clean diesel engine. Four types of fuels were prepared to investigated the effect of fuel properties such as cetane number, composition, oxygen content in fuel and oxygenate type on exhaust emissions for both of the engines. The decrease in cetane number caused an increase in NOx and a decrease in PM for the DI diesel engine because of the long ignition delay. However, in case of the OSKA-DH engine, a decrease in cetane number seldom caused an increase in PM emission. Although NOx and PM from aromatic fuel were higher than those from paraffinic fuel, the fuel effect for the OSKA-DH engine was smaller than that for the DI diesel engine.