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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 new idea incorporates an impinging part in the central piston cavity. A relatively low injection pressure, lower than that of a conventional IDI Diesel engine, and a single hole fuel nozzle are used. The fuel spray is injected against the impinging part, spreads and forms a fuel-air mixture. Since a comparatively rich fuel-air mixture always stays around the impinging part and ignition is accomplished near the center of the mixture, steady, instantaneous and high-speed combustion is possible. As the fuel-air mixture is formed mostly in the cavity, there is little fuel in the squish area. Therefore, it is possible to prevent end-gas knocking, and in spite of the use of spark ignition, to employ a higher compression ratio than that of the conventional premixed SI engine. Experiments with a single cylinder prototype (4-stroke cycle) engine with gasoline fuel showed that the maximum BMEP was 1.0 MPa and the maximum brake thermal efficiency was 37.7 % (217 g/kW.h).