Theoretical Limits of Performance and Economy for Methanol, Ethanol and Gasoline Blends in Automotive Engines

摘要

This report addresses the theoretical upper limits of indicated Otto cycle engine performance and economy with pure methanol and ethanol fuels. The ideal adiabatic constant volume Otto cycle was used to determine the limits. Parameters varied were compression ratio, fuel-air ratio, exhaust residual, intake temperature, intake pressure, and exhaust back pressure. Explored in this study in addition to the two pure alcohols were 15% blends by volume with iso-octane and results are compared to the characteristics produced by four pure hydrocarbon fuels. These were benzene, C sub 6 H sub 6 ; ethylene, C sub 2 H sub 4 ; iso-octane, C sub 8 H sub 18 ; and methane, CH sub 4 . Results show all fuels had similar peak efficiencies with maximum differences of about 3%. Consequently, any experimental results to the contrary must reflect factors other than the thermodynamics of the cycle. Numerous ideal Otto cycle characteristics for the various fuels are presented in graphical form. (ERA citation 07:004642)