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To investigate the mixture distributions in an LPG engine with Liquid phase port injection for heavy duty vehicles, an optical single cylinder engine, which is optically accessible both in side and bottom view, and laser diagnostic system were incorporated to apply PLIF (planar laser induced fluorescence) technique. Acetone was used as a dopant in LPG fuel, which was excited by KrF excimer laser (248nm), and its fluorescence images were acquired with ICCD camera. The effects of fuel injection timing, swirl intensity and excess air ratio were investigated. For the case of open valve injection, favorable stratification of fuel, both in axial and radial direction, was clearly observed compared to the closed valve injection, where reverse stratification in axial direction was observed. At the Ricardo swirl ratio of 3.4, it was apparent that excessive axial stratification of fuel got dominant, which would lead to poor engine performances.

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean burn operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean burn performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using a UV intensified high-speed CCD camera. Concepts of flame area speed, in addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics.

Exhaust gas recirculation (EGR) and lean burn utilize the diluents into the engine cylinder to control combustion leading to enhanced fuel economy and reduced emissions. However, the occurrence of excessive cyclic variation with high diluent rates, brings about an undesirable combustion instability within the engine cylinder resulting in the deterioration of both engine performance and emissions. Proper stratification of mixture and diluents could improve the combustion stability under high diluent environment. EGR stratification within the cylinder was made by adopting a fast-response solenoid valve in the midst of EGR line and controlling its timing and duty. With EGR in both homogeneous mode and stratified mode, in-cylinder pressure and emissions were measured. The thermodynamic heat release analysis showed that the burning duration was decreased in case of stratified EGR. It was found that the stratification of EGR hardly affected the emissions.