LiquidPiston’s X Engine is an innovative High Efficiency Hybrid Cycle (HEHC)

LiquidPiston’s X Engine is a non-Wankel rotary embodiment of the company’s innovative High Efficiency Hybrid Cycle (HEHC). The X Engine has few parts and three combustion events per rotor revolution, resulting in tremendous power density.

Credit: Inventor Alexander Shkolnik

"Except for ancillary parts such as injectors, fuel pumps, and oil pumps, there are no other moving parts," according to a statement by LiquidPiston.

The president and co-founder, Dr. Alexander Shkolnik, said the team had plans to further optimize the engine for increased power (greater than 5 horsepower) and efficiency, and lower operational noise.

According to the company release, "When mature, the engine is expected to weigh 3 pounds, produce over 5 horsepower at up to 15,000 RPM, and be over 30 percent smaller and lighter than comparable four-stroke piston engines."

While it is a rotary engine, the company points out that the X Engine is not a Wankel engine, as it has "a fundamentally different thermodynamic cycle, architecture and operation."

Shkolnik co-authored a paper, "Development of a Small Rotary SI/CI Combustion Engine," which described 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 percent using air-standard assumptions and first-law analysis."

This image shows the size difference between a standard diesel engine and the X engine.

Credit: LiquidPiston

Similar to the Wankel rotary engine, the 'X' engine has only two primary moving parts, they said, but unlike the Wankel, "the X engine is uniquely configured to adopt the HEHC cycle and its associated efficiency and low-noise benefits."

"The result is an engine which is compact, lightweight, low-vibration, quiet, and fuel-efficient."

LiquidPiston adopted the saying "Think Outside the Cylinder" as their philosophy, on the premise that by rethinking the engine, starting with basic scientific principles (e.g., thermodynamics), engines can be significantly improved on all parameters.

The company is upbeat that the X Mini may enable new applications not possible with current engine technology; early next year, they will host an open call for ideas about new applications with a cash prize for the most innovative submission.