Alternative experimental engines

Other experimental engines are under development. However, none of them combines all the advantages of the Libralato engine.

Liquidpiston Engine

Liquidpiston Engine

Novel design with separated expansion chamber
Very high thermal loading on combustion chamber device which will make sealing a significant problem
Friction losses very high
Cooling of the expander may also be an issue

RAD Max Engine

RAD Max

Novel rotary 12-vane positive displacement device that produces 48 pump actions every revolution
Excessive number of moving parts needed
Excessive number of sliding components
Force translation performed by sliding components

Lontra Engine

Lontra Engine

Novel design based on two separate cylinders with a ceramic coated conduit joining them
Two cylinder design is not very compact - lower power to weight ratio
Conduit is vulnerable to vibration and could fracture; so the design is not so appropriate for vehicle applications
Company targeting different markets for compressors and gensets

REVETEC Engine

REVETEC Engine

Novel 4-stroke design uses two counter rotating tri lobular cams and rollers to produce the reciprocating motion normally generated by a crankshaft and connecting rod
Independently verified to achieve 38.5% efficiency (BSFC 212g/kWh @ BMEP 4.5 bar, 2000 rpm, lean-air ratio 15.2: 1)
Claimed to be the most efficient gasoline engine in the world
Engine does not represent substantial size/ weight/ cost savings
Tri lobular cams and roller assembly subject to wear and maintenance issues

Ox2 Engine

Ox2 Engine

The Ox2 engine is a circular engine block containing 8 cylinders which exert their force on a bevel shaped cam. While a camshaft rotates on a 4-stroke engine, the entire engine block rotates on the Ox2 engine
Pistons are connected by rings (called "plates") that move via rollers along a fixed cam (track)
At higher rpm (1,000<) the centrifugal force lifting the pistons from the track increases, therefore the size and power of the engine is limited

Star Rotor Engine

Star Rotor Engine

The Star Rotor engine is based on a recuperated Brayton cycle gerotor, which has separate compressor and expander units. This is predicted to have exceptionally high efficiency (up to 50% at full load) because:

  • The recuperator captures thermal energy from the expander exhaust and recycles it into the engine
  • The rotors do not touch thereby reducing friction
  • Speed control is accomplished without throttling losses
  • Fuel combustion is complete thus reducing the amount of fuel required to operate
  • Spraying atomized liquid water into the compressor allows nearly isothermal compression, reducing compression work significantly


This engine shares many of the advantages of the Libralato engine and even possibly exceeds them through the use of a Brayton cycle approach
However at full load, the engine consumes 2 gallons of water for every gallon of gasoline. This extra requirement limits the application of the engine in an automotive context

Anyoon Rotary Engine

Anyoon Rotary Engine

The Anyoon rotary engine is a novel concept with some of the advantages of the Libralato engine and the Star Rotor engine:

  • Like the Libralato engine it uses a greater expansion volume than the compression volume
  • Like the Star Rotor engine it uses injected water to cool the combustion chamber


Sealing is a major problem for this design and very expensive diamond like composite materials are being investigated to counter the problem
Stoppers held by rollers in a track of parabolic spirals, are subject to fatigue, seal wear and maintenance issues
Use of injected water limits the application of the engine in an automotive context

Lotus Range Extender Engine

Lotus Range Extender Engine (series hybrid)

Three cylinder 1.2L, 56 kg gasoline engine optimized between two power generation points: 15kW @ 1,500 rpm and 35 kW @ 3,500 rpm
Innovative architecture comprising an aluminium monoblock, integrating the cylinder block, cylinder head and exhaust manifold in one casting
This engine is not powerful enough to power a mid sized vehicle at more than about 85 mph / 140 kph
Engine efficiency is estimated to be significantly less than the Libralato engine, in the region of 240 g/kWh

Hefley Engine

Hefley Engine

The Hefley engine is a variable displacement engine with opposed pistons acting on a central cam, similar to the REVETEC engine
The design is not space efficient
Potential fatigue issues on the central connecting shaft
The usefulness of variable displacement for different fuels is questionable

Scuderi Engine

Scuderi Engine

The Scuderi engine is a split cycle engine which divides the four strokes of a conventional combustion cycle over two paired cylinders, with one intake/compression cylinder and one power/exhaust cylinder
The design is not space efficient
The design involves extremely high pressures which require extremely low tolerances and high manufacturing costs

GO Engine

GO Engine

The Go engine is a conventional engine which incorporates eccentric bearings with a planetary gear. This allows variable compression ratios and use of Atkinson cycle greater expansion volume compared to compression volume
The engine does not offer significant advantages in terms of size, weight, vibration, noise, cost etc

Moller Engine

Moller Engine

The Moller engine is a Wankel type engine with improved combustion surface coating and incoming fuel-air charge cooling. This allows it to avoid the disadvantages of the oil cooling system used by Mazda
The Moller engine achieves a similar power to weight ratio as the Libralato engine, but is less efficient at about 255g/kWh BSFC

OPOC Engine

OPOC Engine

The OPOC engine is an opposed piston opposed cylinder turbo charged diesel engine
The OPOC engine achieves similar efficiency as the Libralato engine, (c.40%) but is not a compact shape and still must balance the large reciprocating masses of the pistons