LiquidPiston’s X Engine is a non-Wankel rotary embodiment of the HEHC. Expected realized brake efficiency for the X engine is 58% (peak) and 50% at partial load; power density is targeted to be around 2 hp/lb.
HEHC is an improved thermodynamic cycle optimized for fuel efficiency that combines features of four existing cycles:
- High air compression ratio (Diesel)
- Constant volume combustion (Otto)
- Over-expansion to atmospheric pressure (Atkinson)
- Internal cooling with air or water (Rankine)
The combination of high compression ratio, true constant volume combustion, expansion into a larger volume than intake, and (optionally) water turning to high pressure steam cumulatively add to the efficiency of the engine.