Text: What Is a Gas Turbine Engine?

When you go to an airport and see the commercial jets there, you can't help but notice the huge engines that power them. Most commercial jets are powered by turbofan engines, and turbofans are one example of a general class of engines called gas turbine engines.

A gas turbine engine uses a pressurized gas to spin a turbine and compressor. Inside the engine, fuel is ignited to increase the gas’s temperature and pressure. This causes the gas to act on the turbine at a higher velocity. Gas turbine engines are used to power many aircraft and helicopters, boats and have recently been used in some battle tanks.

A turbine uses the energy of a flowing fluid to rotate a wheel. The concept of a turbine has existed for many years; windmills and water wheels are simple examples. Moving air passes over a windmill’s slanted blades, causing the wheel to spin. Turbines can also be used with steam, as in the case of many power plants. The turbine in a gas turbine engine, however, uses highly pressurized air to rotate.

Norwegian engineer Aegidius Elling was granted a patent for a gas turbine in 1884. His first turbine model that produced more power than it consumed was unveiled in 1903. Elling’s design locked a spinning air compressor to the turbine, a feature widely used today. He believed that if more heat-resistant materials could be found, the gas turbine engine could be used to power airplanes.

The main parts of a gas turbine engine are the compressor, the combustion area and the turbine. Air enters the compressor at normal pressure and then gets compressed. In the combustion area, some type of fuel is burned to increase the temperature and energy content of the air. The high-temperature, high-pressure gas is then forced to exit the engine, turning the turbine on its way out. A solid shaft connects the compressor and turbine—the rotation of the turbine is used to spin the compressor, which makes the engine as a whole more efficient.

The shaft that connects the compressor to the turbine may or may not be used to power additional devices. In a jet engine, the method of obtaining thrust is expelling the exhaust gas at a high velocity, which causes the aircraft to be pushed forward. In vehicles that are not powered by thrust, the spinning shaft can be used to do mechanical work.

A gas turbine engine has several advantages over the type of engine found in most automobiles. First of all, it has a better power-to-weight ratio. Gas turbine engines are also smaller than their automobile counterparts for a given amount of power. These reasons explain why many helicopters and airplanes use this type of engine.

Exercise 9. Translate the sentences with the adjectives in the comparative form. Remember! To compare things we use: much - намного; far - гораздо; a little – немного.

1. The more efficient the compressor, the higher the pressure generated for a given work input.

2. The more efficiently the turbine uses the expanding gas, the greater the output of the work for a given pressure drop in the gas.

3. Because the turbojet engine is a heat engine, the higher the temperature of combustion the greater is the expansion of the gases.

4. Although the turbo-rocket engine is smaller and lighter than the turbo/ramjet, it has higher fuel consumption.

5. The centrifugal flow compressor is usually more robust than the axial compressor and is also easier to develop and manufacture.

6. The axial flow compressor consumes far more air than a centrifugal com­pressor of the same frontal area and can be designed to attain much higher pres­sure ratios.

7. The more the pressure ratio of a compressor is increased the more difficult it becomes to ensure that it will operate efficiently over the full speed range.

8. Engines operating at higher turbine inlet temperatures are thermally more efficient and have an improved power to weight ratio.

9. Bypass engines have a better propulsive efficiency and thus can have a smaller turbine for a given thrust.