Search Results

This paper presents initial progress in the development of LiquidPiston’s ‘X4’, a 30 kW heavy-fueled rotary compression ignition engine prototype. The X4 is the newest version of the unique rotary ‘X’ engine architecture. This development is partially funded by the Defense Advanced Research Projects Agency (DARPA), with broad dual-use civilian / military applications including UAVs, generators, and for propulsion. The 30 kW size may be of significant interest in the automotive application as a range extender for Electric Vehicles. The final performance objectives of the program are aggressive: 45% brake thermal efficiency; > 1 hp / lb power-to-weight; and the engine is targeted to fit within a 10”x10”x10” box weighing <40lbs. A first prototype engine “core” has been designed, analyzed, prototypes, and completed its initial testing.

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.