Charge dilution effects in a direct-injection gasoline engine with advanced spark ignition and valvetrain systems

Abstract

Current legislative trends and customer demand drive the need for clean and efficient vehicles. Homogenous lean combustion is widely recognised within the industry as the viable mean of pushing efficiency of gasoline engines to the territory which was previously reserved for higher compression diesel engines. Diluted mixtures are thermodynamically very attractive, however they present challenges related to limited ignitability and often require assistance to realise their theoretical potential. Such assistance can be related to either enhanced flow motion inside the cylinder or a higher energy ignition system. Experimental work was carried using the single cylinder engine test facility which was designed and commissioned in partnership with the project sponsor – Jaguar Land Rover. The aim was set on understanding the limitations of a current combustion system, and implementing advanced technology packages in the proof of concept studies to increase engine tolerance towards diluted mixtures. An advanced valvetrain system with capabilities of continuously variable valve lift was used to assess effects of deactivating one of the intake valves. It was found that increased TKE at ignition led to significant improvements in combustion stability and shorter burn durations, however the benefits were largely offset by heat transfer penalty. Heat transfer effects were quantified at various speeds and loads to provide comprehensive understanding of implementing the valve deactivation strategy. An optimisation study followed based on the findings and staggered lift was used on one of the valves. By utilising advanced, optimised valvetrain strategies dilution tolerance was significantly increased and indicated thermal efficiency of the engine surpassed 40%. Prototype high energy ignition systems from two suppliers were also tested with the use of very high sampling rate data acquisition system built for the purpose of this work. It was found that significant benefits in dilution tolerance could be achieved, especially when combining the valvetrain and ignition systems potential.