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A new combustion concept, called spark-ignited compression ignition (SI-CI) combustion, is proposed for expanding the operation range of homogeneous charge compression ignition (HCCI) combustion. The authors previously showed that raising the mixture temperature before compression so as to induce auto-ignition near top dead center reduces the quantity of trapped gas, resulting in a lower maximum indicated mean effective pressure (IMEP). With the newly proposed combustion concept, auto-ignition of a homogeneous lean mixture is accomplished by the additional compression resulting from SI combustion of a small quantity of stratified mixture instead of raising the intake air temperature. This SI-CI combustion process reduced the necessary increase in intake air temperature compared with conventional HCCI combustion. A higher maximum IMEP was achieved with SI-CI combustion than with conventional HCCI combustion, as was planned.

A fundamental examination was made of gasoline-fueled homogeneous charge compression ignition (HCCI) combustion under various compression ratios, intake temperatures and intake gas compositions. The results revealed the basic combustion characteristics, and the ignition timing and combustion duration were found for every set of conditions. Suitable intake air temperatures were also determined for every operating condition. Internal residual gas was used to raise the mixture temperature in the cylinder. The region of maximum engine speed was expanded without heating the intake air. Minimum and maximum indicated mean effective pressures (IMEP) were found in several engine speed regions under several residual gas rates. Based on the results, a comprehensive interpretation is given of conventional HCCI combustion in 2- and 4-stroke gasoline engines.