Further Investigations into the Benefits and Challenges of Eliminating Port Overlap in Wankel Rotary Engines

In a previous study it was shown that a production vehicle employing a Wankel rotary engine, the Mazda RX-8, was easily capable of meeting much more modern hydrocarbon emissions than it had been certified for. It was contended that this was mainly due to its provision of zero port overlap through its adoption of side intake and exhaust ports. In that earlier work a preliminary investigation was conducted to gauge the impact of adopting a zero overlap approach in a peripherally-ported Wankel engine, with a significant reduction in performance and fuel economy being found. The present work builds on those initial studies by taking the engine from the vehicle and testing it on an engine dynamometer. The results show that the best fuel consumption of the engine is entirely in line with that of several proposed dedicated range extender engines, supporting the contention that the Wankel engine is an excellent candidate for that role. Also, continued 1-D modelling of the zero overlap peripherally-ported engine has shown that a potential route to regain lost performance and better fuel economy is to turbocompound the engine. While compounding using turbomachinery provides one direction for further work, a new concept is proposed which uses the conventional three-flank Wankel rotor in its two-lobe housing to provide a positive displacement compounder to enable zero overlap anywhere in the device. This will allow the potential to configure large unobstructive ports with unimpeded timing. This novel concept is discussed in the paper.