What is a LiquidPiston Engine?

In this brief article we are going to discuss the LiquidPiston Rotary engine. We will look at how it is designed, how it works and the novel features of the engine that makes it more efficient.

What is a LiquidPiston Engine?

LiquidPiston is a MIT based startup that has come up with a novel rotary engine that is smaller and more efficient than a regular internal combustion engine.While the technology is still in development stage, the LiquidPiston is a promising prospect in engine technology.

How does it differ from regular engines?

Conventional internal combustion engines of reciprocatory type use a piston in the engine cylinder.The piston is a moving component whose purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a connecting rod. A liquid piston engine is one where in a rotary cycle is employed to carry out combustion. Although rotary technology is not new in automobile engine technology, the Liquidpiston Engine is a new innovation that is more efficient,smaller, lighter and quieter. 

The LiquidPiston X engine runs on the company’s  patented HEHC cycle which is different from the regular Wankel cycle used in rotary engines of Mazda RX-8.

The design of the LiquidPiston Engine:

The construction of LiquidPiston is  simpler and involves fewer parts than the typical IC engine.It uses a simple and efficient architecture having fewer moving parts.It contains a rotor and an eccentric shaft other than the regular ancillary parts such as the fuel pumps, injectors etc. The LiquidPiston engine is claimed to be simple to design and construct. While it shares most of its components with a regular rotary engine, LiquidPiston is different in working. Some of the striking features of this engine is as follows:


A hollow crankshaft funnels fuel and air into the engine.It thus eliminates the need of a separate intake mechanism such as poppet valves.It thus saves weight and increases efficiency.


A peanut shaped rotor is the heart of the LiquidPiston rotary engine.It contains a ridge shaped hole in the centre that mates with a gear and delivers power to the crankshaft. As it rotates it forms the chambers of inlet, combustion and exhaust.


The housing of the engine is made up of a solid aluminium block cut into an epitrochoid shape.It also contains the cooling fins of the engine. The shape of the housing is unconventional and resembles the rotor of traditional wankel engines.Three profiles are cut for providing an intake chamber, combustion chamber and exhaust chamber.

Exhaust Cover

An exhaust cover with three ports is used rease the exhaust gases from the housing chamber.

How does a LiquidPiston Engine work?

The Liquidpiston uses the High Efficiency Hybrid Cycle which is patented by the company is fundamentally different from the cycles used in reciprocating Petrol or Diesel Engines. It is claimed to have greater efficiency (upto 30 percent).

The High Efficiency Hybrid Cycle:

The LiquidPiston Rotary Engine uses a novel thermodynamic cycle called the HEHC cycle which combines various elements of the Otto Cycle, Diesel Cycle, Rakine Cycle and the Atkinson Cycle.Compression of air happens  (Diesel), Heat addition in constant volume(Otto). Expansion to atmospheric pressure(Atkinson).

The engine consists of a compressor,an isolated combustion chamber, and an expander.

Bothe compressor and expander consist of a simple design with two main parts:a rotor and an oscillating rocker.Compared to conventional internal combustion engines, in which all processes happen within the same space but at different times, in this engine, all processes
are occurring simultaneously but in different chambers, allowing for independent optimization of each process.

The Benefits of LiquidPiston Engine:

The LiquidPiston engines are uniquely configured to adopt the  HEHC cycle and its associated efficiency and low-noise benefits. LiquidPiston’s X Engine improves virtually all parameters – efficiency, weight, size, vibration, and noise.

1.Lightweight and Compact

The LiquidPiston engines are about 30% smaller than gasoline(petrol) engines and 75% smaller than diesel engines.They also have a high power to weight ratio.

2.Low Noise

The LiquidPiston engines do not use poppet valves and their exhaust turbulence is minimum.Thus they operate with less noise than conventional engines.

3.Low Vibration

Because of very few moving parts compared to a regular reciprocatory engine, LiquidPiston engines are less prone to vibration.

4.High Efficiency

The fuel efficiency obtained by a LiquidPiston engine is much higher than conventional engines.They consume about 20% less petrol and 50% less diesel.

5.Multifuel Capable

The LiquidPiston engine can be modelled to run on petrol, diesel,natural gas,JP-8. Unlike conventional engines no major design change is required for this purpose.


LiquidPiston engine is a nascent technology which is still being developed.However, it has found applicability in a plethora of areas that require low power. They are being used in  lawnmowers, go-karts, small aircrafts, mopeds,range extenders, handheld power equipment etc. However there is ongoing research on its scalability to higher power and torque requirements.


Liquidpiston Engine is a potential disruptor in powerplant technology. It uses the best features of other thermodynamic cycles to evolve a newly patented High Enfficiency Hybrid Cycle that is efficient, silent and light. While the technology is still developing and is used on a limited scale, it is only a matter of time before the model is scaled to bigger applications.

Frequently Asked Questions (FAQs):LiquidPiston Engines

1.How different is a LiquidPiston Engine from a regular IC Engine?

LiquidPiston Engines are based on an entirely different thermodynamic cycle vis-a-vis reciprocatory engines.

2.Are LiquidPiston Engines better than conventional IC engines for the environment?  

LiquidPiston Engines are known to have better fuel consumption and efficiency.Thus they contribute less amount of pollutants and thus are less harsh on the environment.

3.Is the LiquidPiston engine technology available in cars?

Currently, the LiquidPiston is developed on a small scale.However,the company believes that the engine can be scaled to cars in the near future.


Nabours, S., Shkolnik, N., Nelms, R., Gnanam, G. et al., “High Efficiency Hybrid Cycle Engine,” SAE Technical Paper 2010-01-1110, 2010, https://doi.org/10.4271/2010-01-1110.

Alexander Shkolnik, Daniele Littera, Mark Nickerson, and Nikolay Shkolnik et al., SAE Technical Paper 2014-32-0104, 2014, doi:10.4271/2014-32-0104.