Effects of Octane Number on Stratified Charge Combustion in a Direct Injection Gasoline Engine

The effects of octane number on stratified charge combustion were investigated with single cylinder direct injection gasoline engine. Two tests were conducted. First, combustion characteristics of stratified charge combustion were studied by changing fuel octane number. Second, auto-ignition characteristics of stratified charge combustion were compared with that of homogeneous charge combustion by changing fuel component. Three types of fuels were used to change octane number and fuel component. They were single-component fuel, multi-component fuel and refinery feedstock, Unique combustion characteristics concerning octane number was found on stratified charge combustion. The increase of indicated thermal efficiency and decrease of unburned hydrocarbon were observed as octane number decreased. The difference of octane number influence between stratified charge combustion and homogeneous charge combustion was discussed.