Abstract
Abstract
The basic characteristics of direct injection (DI) combustion fuelled with compressed natural gas (CNG) and gasoline was studied using a rapid compression machine. The characteristics of stratified combustion and emission of natural gas and gasoline direct injection at the optimum injection settings over a wide range of equivalence ratios were investigated. The results showed that, similar to premixed combustion, natural gas stratified combustion was of shorter duration than gasoline DI combustion. In contrast to this, the heat release pattern for gasoline DI combustion was similar to that of diesel combustion, which seems to have both a premixed phase and a diffusion phase. This phenomenon tends to be more obvious at a lower overall equivalence ratio, which suggests that fuel and charge stratification have a great influence on DI stratified charge combustion. Thus, this faster burn for natural gas promotes extremely lean combustion and a higher pressure rise. However, natural gas DI stratified combustion produces more hydrocarbons (HC) than gasoline DI stratified combustion at a low overall equivalence ratio. Combustion effciency is at the same level for the two fuels, and natural gas DI combustion was shown to have a slightly leaner combustion capability than gasoline DI combustion, which suggests the better feasibility of natural gas stratified combustion.
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