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In this paper we discuss a rotary implementation of the High Efficiency Hybrid Cycle (HEHC) engine. HEHC is a thermodynamic cycle which borrows elements of Diesel, Otto and Atkinson cycles, characterized by 1) compression of air only (e.g. Diesel), 2) constant volume heat addition (e.g. Otto), and 3) expansion to atmospheric pressure (e.g. Atkinson). The engine consists of a compressor, an isolated combustion chamber, and an expander. Both compressor and expander consist of a simple design with two main parts: a rotor and an oscillating rocker. Compared to conventional internal combustion engines, in which all processes happen within the same space but at different times, in this engine, all processes are occurring simultaneously but in different chambers, allowing for independent optimization of each process. The result is an engine which may offer up to 57% peak efficiency, and above 50% sustained efficiency across typical driving loads.

The X engine is a non-Wankel rotary engine that allies high power density and high efficiency by running a high-pressure Atkinson cycle at high speeds. The X engine overcomes the gas leakage issue of the Wankel engine by using two axially-loaded face seals that directly interface with three stationary radially-loaded apex seals per rotor. The direct-interfacing of the apex and face seals eliminates the need for corner seals of the typical Wankel engine, significantly reducing rotary engine blowby. This paper demonstrates the sealing performance that can be achieved by this new type of seal configuration for a rotary engine based on dynamics models and experiments. The dynamics models calculate the displacement and deformation of the face and apex seals for every crank angle using a time implicit solver. The gas leakage is then calculated from the position of the seals and pressure in the chambers and integrated over a rotor revolution.

This paper describes the development of small rotary internal combustion engines developed to operate on the High Efficiency Hybrid Cycle (HEHC). The cycle, which combines high compression ratio (CR), constant-volume (isochoric) combustion, and overexpansion, has a theoretical efficiency of 75% using air-standard assumptions and first-law analysis. This innovative rotary engine architecture shows a potential indicated efficiency of 60% and brake efficiency of >50%. As this engine does not have poppet valves and the gas is fully expanded before the exhaust stroke starts, the engine has potential to be quiet. Similar to the Wankel rotary engine, the ‘X’ engine has only two primary moving parts - a shaft and rotor, resulting in compact size and offering low-vibration operation. Unlike the Wankel, however, the X engine is uniquely configured to adopt the HEHC cycle and its associated efficiency and low-noise benefits.