Vocabulary Practice

1. What is a gas turbine engine?

2. What is a turboprop engine?

3. What is a turbojet engine?

4. What is the purpose of a blower?

5. What is the characteristic of a fanjet which has given it its name?

6. What is the characteristic of a pulsejet which has given it its name?

7. What is the characteristic of a ramjet which has given it its name?

Gas Turbines

The idea of an internal combustion engine to drive a turbine, rather than pistons, evolved on paper as long ago as 1791 but it needed modern technology to make such an engine possible. The problem was that the blades of a turbine could not withstand the great heat resulting from the combustion in such an engine. Now new alloys or mixtures of metals, as well as some ceramics and crystals that do not fail or disintegrate at high degrees of heat, have been developed.

In a basic gas turbine engine air is taken in and compressed until it becomes extremely hot. The compressed air is then mixed with fuel, usually kerosene, which ignites. The expanding gases caused by the combustion cause the turbine to turn. The turbine then turns a shaft which performs the actual work. In a turboprop engine for aircraft that shaft turns a propeller.

Experiments to adapt gas turbines for other forms of transportation have not been entirely successful. A major drawback, especially in view of today's energy crisis, is the necessity for large amounts of fuel; the combustion is continuous in gas turbines rather than intermittent as in piston engines.

The first successful turbojet engine was designed by Frank Whittle, an English officer in the Royal Air Force. Jets were in use as military aircraft before the end of World War II but they did not come into commercial use until the 1950s. They have enormously increased the speed, range, and size of modern airplanes. Some types of turbojets can propel a plane at speeds faster than sound. The use of engines at supersonic speeds is one of the more controversial subjects of our time.

In a turbojet engine air is taken in by a blower that operates on a shaft from a turbine; the waste gases are expelled from the rear of the engine at an extremely high rate of speed. The plane is driven forward by a practical illustration of Newton's Third Law of Motion: for every action there is an equal and opposite reaction; therefore the thrust of the gases backward pushes the plane forward.

The type of turbojet in common commercial use is the fanjet. The intake blower is in effect a highly sophisticated version of the everyday electric fan. Two other types, used for military aircraft, are the pulsejet and the ramjet. The pulsejet, used by the German V-l bombs to attack London during World War II, has lateral intake valves that produce a pulsing or vibrating movement; air pressure opens the valves, the explosions of fuel close them and push against them to provide forward propulsion; no turbine is necessary in this type of engine. In the ramjet, air is rammed or forced into the intake at such pressure that no blower or turbine is necessary, only a means of injecting the fuel.

Discussion

1. Why did a turbine engine become possible only in modern times?

2. How does a basic gas turbine engine work?

3. What does the shaft in a turboprop engine turn?

4. Why have experiments to use gas turbines for forms of transportation in addition to airplanes not been successful?

5. Who designed the first successful jet engine? When did it come into commercial use?

6. What have jets done to air transportation?

7. How does a turbojet engine work? How do the jet engines make the plane move forward?

8. What kind of turbojet is in common commercial use? Describe its blower.

9. How does a pulsejet work?

10. Why isn't a blower or turbine necessary in a ramjet?

Engines That do not Use Petroleum as Fuel

Special Terms

Petrochemical Products: Products made from petroleum by chemical processes, including some kinds of plastics.

Nuclear Fission: The splitting or fission of the nucleus, the central part of an atom; a result of the fission is energy.

Nuclear Fusion: The joining or fusion of the nuclei of different atoms; a result of the process is release of a great deal of energy.

Hot-air Engine: An engine using heated air to push down a piston; also known as the Stirling engine.

Rotary Engine: An internal combustion engine producing rotary in­stead of reciprocating motion; the best known type is called the Wankel engine after its inventor.

Rotor: A machine component which revolves, thereby producing rotary motion.