EFFECTS OF INTAKE AIR-TEMPERATURE AND RESIDUAL-GAS CONCENTRATION ON CYCLE-TO-CYCLE COMBUSTION VARIATION IN A 2-STROKE CYCLE SI ENGINE EQUIPPED WITH AN AIR-ASSISTED FUEL-INJECTION SYSTEM

Irregular combustion is the major disadvantage of two-stroke cycle S. I. engines under low load conditions. This study was intended to find the cause of the irregular combustion and to suggest ways to deal with this problem. The effects of intake air temperature, skip firing and fuel-injection timing on the cycle-to-cycle combustion variations in a two-stroke low-pressure air-assisted fuel injection S. I. engine were investigated. The cylinder pressures of successive engine cycles were recorded for statistical analysis. The intake air temperature was changed from 35 to 70 degrees C. The residual gas concentration was changed by skip firing strategy, with skip 0, skip 4, skip 5 and skip 6. The air-injection timing which determines the fuel-air mixture injection timing into the cylinder was controlled by an electronic control unit. The items of injection timing were changed from 180 to 230 deg-ATDC. Results showed that the effects of intake air temperature, residual gas concentration variation and air-injection timing on combustion variations were significant. Raising the intake air temperature, reducing the residual gas content and adjusting the air-injection timing have greatly decreased cycle-to-cycle combustion variations and unburnt HC emission. The optimal values of coefficient of variation of indicated mean effective pressures (COVlmep) exist under the effects of the above parameters.