The LiquidPiston engine is a rotary engine

Rotary engine

The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

, which operates on the High Efficiency Hybrid Cycle. This cycle consists of compressing air (with no fuel) to a very high ratio, as is typical in the Diesel cycle

Diesel cycle

The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897. It is assumed to have constant pressure during the first part of the "combustion" phase...

. The air is then isolated in a constant volume chamber. Fuel is injected, and allowed to combust fully under constant volume conditions, which is how Otto cycle

Otto cycle

An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines....

 combustion is modeled. Finally, the combustion products are expanded to atmospheric pressure, utilizing Atkinson cycle

Atkinson cycle

The Atkinson cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density, and is used in some modern hybrid electric applications.-Design:...

.