EFFECTS OF TRAPPED RESIDUAL CONCENTRATION AND SURFACE-TEMPERATURE ON THE COMBUSTION PROCESS OF A 2-STROKE CYCLE SPARK-IGNITION ENGINE WITH AN AIR-ASSISTED FUEL-INJECTION SYSTEM

Poor combustion is one of the drawbacks of two-stroke cycle engines op erated at light load condition. Dilution with residuals is the most li kely cause for this phenomenon. The main objective of this study was t o reduce the residuals within the cylinder in order to improve the com bustion performance and hydrocarbon (HC) emission. Experiments were co nducted on a 124 cm3 two-stroke cycle engine with a low-pressure air-a ssisted fuel injection system at idling condition. The main areas of i nvestigation were the effects of trapped residual concentration, air i njection pressure and surface temperature on combustion and HC emissio n. The trapped residuals were reduced using a skip firing strategy wit h skip numbers of 0, 1, 2, 3, 4 and 5. The air injection pressure was varied in the range of 50-300 kPa and the surface temperature was chan ged from 120 to 180-degrees-C. The in-cylinder gases, cylinder pressur e and HC emission were measured simultaneously. Results showed that th e skip firing had a significant improvement in the concentration of ox ygen as well as the residuals trapped in the cylinder. A suitable comb ination of skip firing and surface temperature control could be a pote ntial measure to improve the combustion and the HC emission at light l oad. Meanwhile, it also illustrated that the air injection pressure ex erted no significant influence on the results.