Octane number stratified mixture preparation by gasoline–ethanol dual injection in SI engines

Abstract

High octane number is one of the attractive properties of ethanol. Appropriate distribution of ethanol vapor concentrations in combustion chamber at the end of the compression process could suppress engine knock phenomena and hence improve performance and reduce pollutants emission of spark ignition engines fueled with gasoline–ethanol. This paper presents numerical simulation results of a new concept of octane number stratified charge mixture via dual injection of ethanol and gasoline. The principle of the concept is the optimization of fuel vapor concentrations distribution in combustion chamber to ensure high ethanol concentrations in zone risk of knock. Two dual-injection schemas have been studied: (1) port inject of gasoline and direct injection of ethanol and (2) separate port injection of gasoline and ethanol through two opposite intake manifolds. In the first case, direct injection of ethanol in axial direction did not result in ethanol concentration stratification. Stratification occurred when direct injection of ethanol in radial direction started later than port injection of gasoline. In the second case, significant stratification of ethanol concentrations occurred when ethanol injection started earlier than gasoline injection. In the combustion chamber, high ethanol concentration was found near the ethanol injection inlet port, whereas high equivalence ratio was found in the opposite side. Thus, the location of the spark plug in the opposite side of ethanol injector is optimal for improving anti-knock performance of engine fueled with ethanol gasoline at a given fuel ratio.