“Automotive transport is ripe for transformation. We need to accelerate the commercialisation of vehicles with diversified primary energy sources, high efficiency and compatibility with a sustainable, renewable energy future.”

"Plugged In: The End of the Oil Age” by WWF
(Dr. G. Kendall, 2008)

Libralato Engine Total efficiency gain = 10-15%

5.5% combustion efficiency gain 50% less NOx and PM 50% less noise 50% less vibration 30% less volume 30% less weight
Figure 1. Overall advantages of Libralato engine over conventional 4 stroke design

A reciprocating engine requires linear pistons to turn a crankshaft, with associated connecting rods, valves and camshaft. During the four phases of the engine cycle (air intake, compression, combustion, exhaust) the crankshaft turns twice, with only one power phase due to combustion. The Libralato engine has only four moving parts which perform the four phases in every revolution of the engine. Therefore more work per cycle is extracted and this work does not need to be converted from linear motion to rotary motion. The engine has a unique, asymmetrical compression and expansion geometry which could deliver a step change in thermal efficiency. The engine’s unique, integral exhaust gas recirculation could deliver a step change in cleanness. The main advantages of the engine are:

1. Exceptionally simple design leading to lower production and maintenance costs
2. Higher power to weight ratio and compact shape
3. Greater mechanical efficiency and power per revolution and low vibration due to rotary design
4. Greater thermal efficiency due to asymmetrical expansion and combustion volumes (~Atkinson cycle)
5. Lower emissions due to recirculation of exhaust gas, integral to engine cycle
6. Silent and low temperature exhaust gases due to low exhaust pressure
7. Good sealing and thermal dispersion characteristics, avoids problems of Wankel engines
8. Adaptable for alternative fuels such as biofuels (and hydrogen - no valve overlap)

The engine consists of two interlaced circular chambers of slightly different diameters. Inside these chambers revolve two rotors about separate centres. The rotors do not rely on casing contact for their location as in Wankel engines. Sealing of the rotors against the chamber walls is excellent because of the large rotor sealing surfaces and their circular orbits. The engine does not require high manufacturing tolerances and wear of the rotors is not a mechanical constraint.

Induction air enters at the centre of the engine and compression/expansion occurs at the periphery producing uniform heat flow characteristics as air circulates around the two sides of the engine. The two rotors are connected together by a connection rod that has a quasi-circular orbit. The three components, Rotor 1, Rotor 2 and the connecting cam form the total internal mechanism of the engine as can be seen in figure 3. The Exhaust port is located on the outer lower side of the engine block.

The engine does not have a traditional Otto or Diesel cycle. There are two compression phases.

The first compression phase, which has a low compression ratio, controls the later scavenge of the exhaust gases. The fresh air utilised to expel the exhaust gases is recirculated for the subsequent combustion cycle. In the second compression phase, the air is compressed at a higher compression ratio where the fuel is added. It is this fuel/air mixture that ignites to form the expansion phase. The inlet phase is in part contributed to by the scavenged gases. This all provides for an extremely efficient handling of the gases, with a significant reduction of exhaust emissions and excellent fuel economy.

Unlike most rotary engine designs the Libralato engine possesses a true combustion chamber. This is fundamental to the design and has important implications. Ideally a combustion chamber should provide the optimum conditions for the combustion of the air/fuel mixture. In a conventional engine the combustion chamber also houses the valves and its shape is governed to a large extent by their inclusion. The combustion chamber on the Libralato engine is free from valves and can be shaped to provide turbulent compression of the air and optimum mixing of the injected fuel. Long flame paths and excessive heat conducting surfaces associated with the Wankel engine are avoided. Significant increases in torque are obtained with the Libralato engine whilst the rotor driving faces are within the confines of the combustion chamber, being held in place by ball bearings.