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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.

When adapted for use in automotive engines, CNG and LPG are considered environmentally friendly compared to gasoline or diesel fuel. However, when these gaseous fuels are used, wear of the valve seat insert and valve face increases if materials meant for use with gasoline are adopted. In comparison to a gasoline engine, the oxide membrane that is formed on the sliding surfaces of the valve face and valve seat insert is limited. As a consequence, adhesion occurs and increased wear of these components is the result. Based on analysis materials that are more compatible with these gaseous fuels were developed.