Naturally aspirated and boosted controlled auto-ignition combustion with positive valve overlap in a four-stroke gasoline engine

Extensive engine experiments were carried out on controlled auto-ignition combustion, also known as homogeneous charge compression ignition, in a four-stroke gasoline engine, by internally recycling burned gases through positive valve overlap, variable compression ratio, intake temperature control and boosting. The operational range of controlled auto-ignition combustion was determined for a range of compression ratios and intake air temperatures at wide-open throttle conditions. This was followed by further engine experiments with boosted intake and external exhaust gas recirculation in order to evaluate their effect on the operational range of controlled auto-ignition combustion and the engine's performance and emissions. It has been found that the controlled auto-ignition operational region could be extended to the higher load region by boosting and running with leaner mixtures, whilst the use of external exhaust gas recirculation allowed the engine to operate controlled auto-ignition combustion optimized in the region between naturally aspirated and lean boosted controlled auto-ignition operational regions. The highest fuel conversion efficiency was obtained when the exhaust heat could be utilized to supply the intake air heating.