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Summary on Rotary Engines

 
     
 

 

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Rotary Engine

A rotary engine is a type of internal combustion engine that makes use of a rotor, instead of a regular piston. That is to say, rotary engines have specially designed combustion chambers containing triangular rotors (rotating part), which help burn fuel within the combustion chamber to produce torque or “driving force”.

History and development
Felix Wankel, a West German engineer developed the first practical triangular rotor and subsequently, the first rotary engine, called the Wankel engine, during the early 1950’s. He, along with a few colleagues, worked out the basic principles 
of such an engine. This design was however rejected by automobile manufacturers, on the basis of its low mileage, short operating life and dirty exhaust. Engineers eventually solved the problem and the engine gained popularity on account of its simplicity and low cost.

   

Several automobile manufacturers from Japan, West Germany and the United States started using these engines on a large scale. However, by the 80’s, the engine’s original problems forced manufacturers to reduce their development efforts.

How it works
The rotary engine consists of two important parts, namely, its specially designed chamber and its triangular rotor. The movement of the rotor is such that its tips are always in contact with the walls of the chamber, so that at any instant, the chamber is always divided into three regions. A different part of the combustion process takes place in each of the three areas of the combustion chamber. It may be noted that a single rotary engine may comprise a number of rotors, each with its own combustion chamber.

A Rotary Engine
A Rotary Engine

 

Similar to the principle involved in a four stroke cycle, a rotary engine goes through four steps in order to complete one combustion cycle. The following steps are involved in each cycle.

  • Intake
    The first step involves the movement of a combustible mixture of air and gasoline into the first area of the combustion chamber. In other words, fresh air mixed with fuel is drawn into the engine as one tip of the rotor passes through a particular point, through the intake opening.

  • Compression
    The rotor then begins to compress the fuel-air mixture when the next tip of the rotor passes the intake opening.

  • Expansion
    One or two spark plugs then ignite this mixture. This burning mixture of gases undergoes expansion and it causes the rotor to move around the output shaft.

  • Exhaust
    The burned gases leave the chamber through an exhaust port after the rotor tip passes through it, thereby uncovering the port. 

This completes an entire combustion cycle and the entire process is repeated all over again.  

A rotary engine operates continuously. Each full rotation of the rotor is associated with three full combustion cycles. That is to say, a single revolution of the rotor produces three power strokes or the output shaft connected to the rotor makes three revolutions for a single revolution of the rotor. 

A single rotor engine produces one power stroke per rotation of the rotor. On the other hand, a regular piston engine produces one stroke when the piston moves up or down once. A dual rotor engine is therefore an equivalent power-producing engine as that of a four-cylinder piston engine.

How is it different from a piston engine
A rotary engine has fewer parts than a piston engine of the same power. It uses lower-octane gasoline, burns less efficiently and is more polluting.  

The noise and vibration produced by a rotary engine is opposite to that of a piston engine. At high speed, it operates smoothly and more quietly than a piston engine. At low speed, it is noisier and tends to vibrate more.  

When introduced, the rotary engine was smaller and lighter than a piston engine of equal power. This drawback was, however, overcome in the 1980’s where comparably smaller, lighter and more efficient piston engines were developed.

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