Fuel Vaporization Improves Fuel Economy of Alcohol-Burning SI Engines

Fuel vaporization and combustion of the thereby achieved homogeneous mixtures improve the overall efficiency of SI engines in comparison to operation with liquid fuels. The improvements result from a recovery of waste heat and the thus achieved greater usable energy of the fuel, which is increased by the heat of vaporization over the lower calorific value of the liquid fuel, and from the fact that very lean mixtures can be burnt without misfiring. The favorable fuel economy of the air/fuel-vapor mixture-aspirating engine is explained with the aid of engine cycle computation which also enables comparison of different combustion processes. Consideration of common substances shows that methanol is the fuel best suited for this type of SI engine.