The fuel efficiency in the conventional reciprocal engines is very poor still. This efficiency supposes in the 4-stroke cycle engine (currently, the most efficient marketed engine) less to 25% of the total energy produced in the combustion. But, to obtain this yield it is necessary equip this engine with a complex and expensive valves train, which limits its elasticity and consumes a part of the useful output power. The reciprocal motion of the pistons, (that must be accelerated and decelerated until completely stopping 2 times in each return of crankshaft), is another reason that diminishes the output power.
The rotary engine (Wankel) was designed to suppress the previous disadvantages. In the basic configuration this engine is equipped with a rotor and a stator. The rotor function is almost similar to the piston. The movement is rotary (in fact almost rotating), reason why does not make mass reversion. 
In the stator are located two distributed passive ports for the intake and the exhaust, that replace the valves. Theoretically the rotary engines would offer a performance very superior to the conventional reciprocal piston engines, but actually is demonstrated that it is not thus. This is occasioned mainly by the following causes: 

•  The thermodynamic efficiency in the Wankel engine is harmed by the unfavourable surface / volume ratio of its combustion chamber, that being long and narrows obstruct the combustion process.

•  Although the intake and the exhaust are made without valves, the rotor shape prevents to optimise the intake / exhaust interaction (overlap), being harmed the volumetric efficiency about 25%. This provokes furthermore unstable operation on low rotations regime and high pollutants emissions. To prevent low volumetric efficiency some Wankel engines must be aided with turbochargers.

• The torque is little elastic still.

• The engine sealed is not as satisfactory yet as in the conventional engines; being left the compression ratio enough limited still.
  
  
  

The Hybrid Engine conjugates the advantages of the conventional pistons engine with those of the rotary engine, eliminating the main disadvantages of both. It consists of a 4-stroke engine of positive displacement devised with rotating and reciprocal technology, reason why it have the advantages of the rotary engines in relation with its packaging size, power density and operation simplicity, and the proven reliability and fuel efficiency of the reciprocal pistons engines. The main advantages are as follows: 

• The volumetric efficiency is even greater to the conventional reciprocal pistons engines. Due to the fact that the intake and exhaust ports can have equal section that the cylinders, the "breathing" capacity is very great.

• This novel engine does not incorporate valves train or parts under reversion, allowing to simplify its manufacture and increase the output power simultaneously. Neither need for heavy flywheel (the rotor operates also as inertial flywheel).

• The number of parts is fewer about 30% to the equivalent conventional engine. The moving parts are reduced about 70%.

• The volume occupied and the overall weight is reduced in more than 50%.

• The operation without valves reduces the nitrogen oxide (NOx) emissions.

• The theoretical volume/power ratio and weight/power ratio must be widely superior to the conventional engine. 
  

The mechanical simplicity makes this engine very reliable. The technical level required for its manufacture is relatively low, because it does not have parts of difficult mechanization or particular technological processes. Its final price must be very less to the conventional engine of the same power. Its maintenance also is simple, being able to be made by non-specialized workers. Because of these characteristics this engine is very appropriate as power plant for the future hybrid vehicles and light aircrafts.

Antonio Sánchez.. Málaga (Spain).