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Sikorsky names LiquidPiston winner of 7th Entrepreneurial Challenge

Sikorsky, a Lockheed Martin company, named LiquidPiston, developer of engines based on its High Efficiency Hybrid Cycle (HEHC) (earlier post), as the winner of the 7th Entrepreneurial Challenge. The Entrepreneurial Challenge, driven by Sikorsky Innovations, the technology development organization of Sikorsky, is designed to accelerate innovators and disruptive technology concepts with applications for the vertical flight market.

LiquidPiston specializes in development of compact, powerful, quiet, efficient, low-vibration, scalable, multi-fuel capable rotary combustion engines, based on the HEHC. LiquidPiston received a $25,000 cash prize along with an opportunity to explore opportunities for LiquidPiston’s technology with the Sikorsky product line.

HEHC is an improved thermodynamic cycle optimized for fuel efficiency that combines features of four existing cycles: high compression ratio (Diesel); constant volume (isochoric) combustion (Otto); over-expansion to atmospheric pressure (Atkinson); and internal cooling with air or water (Rankine).

The cycle has a theoretical efficiency of 75% using air-standard assumptions and first-law analysis. The rotary engine architecture shows a potential indicated efficiency of 60% and brake efficiency of >50%. As the engine does not have poppet valves and the gas is fully expanded before the exhaust stroke starts, the engine also has potential to be quiet.


  • Daniele Littera, et al. (2015) “Development of the XMv3 High Efficiency Cycloidal Engine”, SAE Technical Paper 2015-32-0719


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