The Effects of Fuel Evaporation on the Octane Number of Methanol-Gasoline Blended Fuels

A procedure is described to estimate the influence of end-gas temperature on Octane Number. Blending methanol with gasoline is known to cause a disproportionate increase in Research Octane Number, and this is found to correlate well with the evaporative cooling characteristics of these blends. The Motor Octane Number test eliminates evaporative effects, and the difference between the two test methods is evaluated in terms of evaporative cooling. It is concluded that the high heat of vaporization of methanol is largely responsible for the excellent RON performance of methanol-gasoline blended fuels.