In the present study, the turbulent flame propagation process and combustion in an
automobile SI engine fuelled with gasoline, ethanol and various gasoline–ethanol blends
have been investigated by means of a quasi-dimensional SI engine combustion model.
Comparisons performed between the results obtained from the presented model and those given by several literatures confirm that this model has an ability of accurately computing SI engine combustion.
Blending ethanol with gasoline up to 25% by volume positively affects the geometric
properties of flame and the mass burning rate, leading to faster burning. It also produces higher cylinder pressures and temperatures compared with gasoline. As a result, the mean indicated work, and therefore engine output power and thermal efficiency, may also increase.
Higher combustion temperatures can result in higher dissociation rates. Hence, NO
concentrations may increase when gasoline–ethanol blends are used in SI engines. Rising pressure and temperature can cause damages on engine structural components such as piston, cylinder and valves. In this case, engine components should be manufactured to resist higher pressure and temperature.
These results have been obtained theoretically. Therefore, some shortcomings of ethanol could not be considered here. In an engine operating under real conditions, the improvements obtained here are somewhat offset by the unfavorable properties of ethanol, such as water contamination and volatility problems, leading to phase separation problem in the blended fuels. If such effects are examined in an actual engine, more sensitive results would be obtained.
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