Development of a Direct Injection High Flexibility Cng/Lpg Spark Ignition Engine

Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meeting the ever-tightening emissions regulations. This paper explores the use of propane and methane gas fuels in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and a centrally located DI injector. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. DI of fuel reduces the embedded air displacement effects of gaseous fuels and lowers the charge temperature. Injection timings and compression ratio are optimized for best performances at Wide Open Throttle (WOT) conditions when configured to achieve homogeneous charge at stoichiometry or run lean jet controlled stratified. Effects of fuel properties on gas exchange, mixture formation, in-cylinder charge cooling, wall-jet interactions, and turbulent combustion evolution and knock occurrence are taken into account. Results are presented in terms of brake mean effective pressure, specific fuel consumption, specific CO₂ production and efficiency. This paper is a contribution to the development of a high flexibility gas fuel SI engine for the Australian market.