A computational study of high efficiency Wankel rotary engines using a passive pre-chamber

Wankel rotary engines are renowned as compact machines with high power-to-weight ratios, which make them suitable for use as range extenders for battery electric vehicles or as propulsion systems for unmanned aerial vehicles. However, their overall efficiency and emissions still need significant improvement to make them compliant to make them stringent regulations and comparable with classical reciprocating 4-stroke engines. With the aim of improving these shortcomings, this work focuses on the application of a passive pre-chamber in order to enhance the combustion phase and the overall efficiency and emissions of such engines. The study was conducted using CFD methods by implementing numerical models of the commercial AIE 225CS rotary engine in CONVERGE, configured with port fuel injection and fully-premixed gasoline combustion. The engine was extensively tested in a previous project while different CFD models were validated against experimental data in previous studies by the same authors. In the present work different pre-chamber configurations were investigated, characterized by different chamber volumes and number of nozzles with different orientations within the main combustion chamber. Some configurations were implemented with volumes and nozzles section in order to comply with the sizing theory of Gussak while others had a volume directly comparable with that of the two spark park plug recesses of the original engine which could be considered very wide-nozzle pre-chambers themselves. In addition, different the effect of spark advance was investigated to capture the development of the flame and jets and the resulting effects on the indicated pressure cycle. Heat losses were demonstrated to be a critical aspect for the different configurations of engine but in some an absolute increase of 4% on the indicated efficiency was recorded. Such potential opens an important new path in the development of this type of engine, especially in view of the more-beneficial utilisation of decarbonised and innovative future fuels.