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LPG (Liquefied Petroleum Gas), which has a higher content of hydrogen than gasoline, has been attracting worldwide attention for its various advantages. These advantages include low emissions of greenhouse gases and, as a result, LPG has little influence, direct or indirect, on the ozone layer. The electronic feedback-mixing system of a conventional LPG engine, however, has certain disadvantages to a gasoline engine with respect to output, air to fuel ratio control, charging efficiency and fuel economy. For these reasons, the majority of current bi-fuel vehicles in Europe employ a LPI system that injects LPG in liquid state that attempts to make up for the shortcomings of the feedback mixing system. The mono-fuel vehicle recently developed by HMC performs with the same output level, torque and fuel economy as conventional gasoline engines by employing the world's first liquid-state-injection system for exclusive use of LPG.

Four ports which have slightly different shapes have been applied to 3-valve MPI SI engine to develop Axially Stratified Lean Combustion engine. The purpose of port modification test was to investigate the effects of swirl ratio and direction on engine performance and emissions. In the engine test injection characteristics, i.e. timing, flow rate, direction as well as port design significantly effected on the engine combustion. Especially, it was observed that injection timing was the most important factor for combustion stability, but its effect on performance has some differences in accordance with the port designs. To verify the relationship between port shape and injection timing, in-cylinder gas was sampled by high speed gas sampling device varing injection timing through whole intake and compression,. strokes at spark plug position and analyzed by gas chromatography.