Effects of Trapped Residual Concentration and Surface Temperature on the Combustion Process of a Two-Stroke Cycle Spark Ignition Engine with an Air-Assisted Fuel Injection System

Abstract

Poor combustion is one of the drawbacks of two-stroke cycle engines operated at light load condition. Dilution with residuals is the most likely cause for this phenomenon. The main objective of this study was to reduce the residuals within the cylinder in order to improve the combustion performance and hydrocarbon (HC) emission. Experiments were conducted on a 124 cm3 two-stroke cycle engine with a low-pressure air-assisted fuel injection system at idling condition. The main areas of investigation were the effects of trapped residual concentration, air injection pressure and surface temperature on combustion and HC emission. The trapped residuals were reduced using a skip firing strategy with 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 changed from 120 to 180°C. The in-cylinder gases, cylinder pressure and HC emission were measured simultaneously. Results showed that the skip firing had a significant improvement in the concentration of oxygen as well as the residuals trapped in the cylinder. A suitable combination of skip firing and surface temperature control could be a potential measure to improve the combustion and the HC emission at light load. Meanwhile, it also illustrated that the air injection pressure exerted no significant influence on the results.