Bob McCarthy, age 16, of Annapolis, Md., for his question:
HOW DOES A WANKEL ENGINE WORK?
A Wankel engine is a gasoline engine that has a rotor instead of a piston. It is sometimes called a rotary engine. It operates more quietly and smoothly than a piston engine because it does not involve the reciprocating or back and forth motion of pistons.
The most important parts of a Wankel engine are its triangular rotor and specially shaped chamber. The rotor moves so that its tips always touch the walls of the chamber and divided the chamber into three areas.
Different engine operations take place in each of the three areas. A Wankel engine may have several rotors, each with its own chamber.
A Wankel engine, like a four stroke piston engine, goes through four steps to complete one cycle of operation: intake, compression, expansion of power and exhaust.
During the intake step, a cumbustible mixture of air and gasoline enters the chamber. This mixture is compressed into a smaller volume. One or two spark plugs then ignite the compressed 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 fourth twice and stop four times to complete the cycle. The Wankel rotor turns only once in its chamber to complete the cycle and it never stops moving. The steps in the cycle occur at the same time in different areas of the chamber. Thus, a Wankel rotor produces three power strokes each time it rotates.
The shaft connected to the rotor makes three revolutions for each turn of the rotor. As a result, the Wankel engine produces one power stroke per turn of its shaft. A piston engine, on the other hand, produces one power stroke every other time a piston moves down its cylinder. As as result, a small Wankel engine may generate the same power as a larger piston engine.
The engine is named for its inventor, a German engineer named Felix Wankel.
Felix Wankel developed the basic principles of his rotary engine during the early 1950s. By 1958, he and a team of researchers had worked out the present design of the engine.
At first manufacturers rejected the Wankel engine because of its poor fuel economy, short operating life and dirty exhaust. But after engineers began to solve these problems, the Wankel engine's simplicity and low cost caught the attention of manufacturers. During the mid 1960, a number of companies in Germany, Japan and the United States started to develop the engine for widespread use.
At the present time, Wankel engines are made in a wide variety of sizes. These engines power automobile and other vehicles including boats, motorcycles, propeller airplanes and snowmobiles.
A Wankel engine operates more economically than piston engines for a number of reasons including the fact that it uses a lower octane gasoline.
Many environmental experts believe that the Wankel engine can help reduce air pollution from automobiles because control devices remove pollutants from the exhaust of a Wankel engine more easily than from the exhaust of a piston engine.