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In order to determine the main factors causing the mileage-related increase in formaldehyde emission from methanol-fueled vehicles, mileage was accumulated on three types of vehicle, each of which had a different air-fuel calibration system. From exhaust emission data obtained during and after the mileage accumulation, it was found that lean burn operation resulted in by far the highest formaldehyde emission increase. An investigation into the reason for the rise in engine-out formaldehyde emission revealed that deposits in the combustion chamber emanating from the lubricating oil promotes formaldehyde formation. Furthermore it was learnt that an increase in engine-out NOx emissions promotes partial oxidation of unburned methanol in the catalyst, leading to a significant increase in catalyst-out formaldehyde emission.

Fischer-Tropsch Diesel (FTD) fuel is expected to be a promising clean diesel fuel in the future because of its characteristics of zero sulfur, zero aromatics and a high cetane number. However, the optimum fuel properties for diesel engines have not been realized. In this study, the effects of cetane number and distillation characteristics on engine-out PM emissions from a conventional direct injection diesel engine were investigated by using paraffinic fuels which were made to simulate FTD fuel. From the results of the vehicle exhaust emissions test and engine dynamometer test, it was found that the narrow distillation characteristics (which eliminates heavy hydrocarbon fraction) could reduce the soluble organic fraction (SOF) in PM emissions, and the excess high cetane number characteristic promoted the formation of insoluble organic fraction (ISOF).