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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.

Smoke emission from single-cylinder DI and IDI diesel engines was shown to strongly depend on oxygen content in fuel regardless of oxygenate molecular structure. Thus, with cetane improver and oxygenate used in combination in a proportion determined from blending properties and potential cost for modern heavy-duty DI diesel engines were assessed. The combined use of nitrate type cetane improver with glycol ether type oxygenate reduced particulate, HC, and CO emission but not that of NOx. Particulate reduction depended on oxygenate content. Oxygenate at less than 5% with cetane improver seldom worsened volume-based fuel economy compared with the base hydrocarbon fuel.