Rotary engine is a type of internal-combustion engine that uses a rotor (rotating part) instead of a piston. A West German engineer, Felix Wankel, developed the first practical rotary engine, called the Wankel engine, during the 1950’s. It has a triangular rotor design.
A rotary engine differs from a piston engine in several ways. For example, a rotary engine has fewer parts than a piston engine of the same power. A rotary engine also uses lower-octane gasoline. However, lower-octane gasoline burns less efficiently, and thus rotary engines use more fuel and emit more exhaust pollutants. The noise and vibration produced by a rotary engine tend to be opposite to those of a piston engine. At high speed, a rotary engine operates more quietly and smoothly than a piston engine. But at low speed, a rotary engine makes more noise and vibrates more. When it was introduced, the rotary engine was smaller and weighed less than a piston engine of equal power. But by the early 1980’s, manufacturers produced comparably small and lightweight piston engines that were more efficient than rotary engines.
How a rotary engine works.
The most important parts of a rotary engine are its triangular rotor and specially shaped chamber. The rotor moves so that its tips always touch the walls of the chamber and divide the chamber into three areas. A different part of the combustion process takes place in each of the three areas of the chamber. A rotary engine may have several rotors, each with its own chamber.
A rotary engine, like a piston engine that operates on a four-stroke cycle, goes through four steps to complete one combustion cycle: (1) intake, (2) compression, (3) expansion or power, and (4) exhaust. During the intake step, a combustible mixture of air and gasoline enters the chamber. Then the mixture is compressed. One or two spark plugs then ignite the mixture. The burning produces expanding gases that move the rotor. The exhaust step pushes the burned gases from the engine.
In a piston engine, each piston must move back and forth twice and stop four times to complete the cycle. A rotary engine operates continuously. It completes three combustion cycles with each full rotation of its rotor. Each revolution of the rotor produces three power strokes. The output shaft connected to the rotor makes three revolutions each time the rotor turns once. As a result, a single-rotor engine produces one power stroke per turn of its output shaft. A piston engine produces one power stroke every other time a piston moves down its cylinder. A dual-rotor engine therefore generates the same number of power strokes as a four-cylinder piston engine.
History.
Felix Wankel developed the basic principles of the rotary engine during the early 1950’s. By 1958, Wankel and researchers at a West German engine plant had worked out the engine’s design. Automobile manufacturers rejected the engine at first because of its poor fuel economy, short operating life, and dirty exhaust. But after engineers began to solve some of these problems, the rotary engine’s simplicity and low cost attracted interest. Several automakers in Japan, West Germany, and the United States sought to develop efficient rotary engines. But many of the engine’s original problems proved difficult to overcome. Today, few manufacturers produce automobiles with rotary engines.
See also Gasoline engine .
