Despite a real progress since their introduction in early sixties by NSU, Wankel engines are still lagging behind their equivalent reciprocating counterparts as far as fuel economy and emissions are concerned. Fuel stratification during combustion promises further progresses, but a similar move is expected for reciprocating units.
A type of stratified combustion system, which was called hybrid fuel energy conversion system, is outlined in the text. One special characteristic of such a system is the dilution of the already burned gases by the air which does not participate in combustion, when engine is operating at partial loads.
The hybrid system features a deep recess in the rotor housing which has the function of a prechamber. The resultant geometry produces a significant recirculation of unburned gases, late in the expansion process of the leading chamber to the trailing chamber performing compression, with a major impact on engine thermodynamic cycle.
The objective of this paper is to analyze the fundamental consequences of the high pressure recirculation of unburned gases on engine operation.