Methanol as a Fuel for Spark Ignition Engines: A Review and Analysis

Abstract

A review and analysis of recent literature data on the use of methanol as an alternative fuel for internal combustion engines have been performed. The properties of methanol have been analysed from the point of view of its application to spark ignition (SI) and compression ignition (CI) engines. From this analysis it may be concluded that fewer modifications to the engine are expected when methanol is used in SI engines than in CI engines. Neat methanol is the most suitable, because all the positive properties of methanol as a fuel can be utilized. In the case of SI engines, only minor modifications of the fuel system and/or addition of ignition improver to the fuel are required. Use of methanol-gasoline blends of up to 15 per cent methanol (by volume) and diesel oil-methanol blends of up to 20 per cent methanol require only minor engine modifications. However, miscibility of methanol and conventional fuels is poor; in order to avoid fuel separation, mixtures of these fuels require fuel additives. Methanol engines burn cleaner and more efficiently, but have higher emissions of aldehydes, which increase with increasing mileage of the vehicle. In the presence of an oxidation catalyst unburned methanol can be converted to formaldehyde and simultaneously nitrous oxide to nitrogen dioxide. The advantage of engine fuelling with reformed methanol (CO + H2) is shown. The reasons for better efficiency, performance and less emissions (except of aldehydes) of methanol-fuelled SI engines in comparison with gasoline- and diesel oil-fuelled engines respectively have been analysed. Technical aspects of using methanol as an automotive fuel that have not yet been satisfactorily solved are pointed out. The feasibility of the widespread use of methanol as a transportation fuel for SI engines is discussed from technical, economic and ecological points of view. The need for further research and development work on problems related to methanol as a fuel for SI engines is also discussed.