Gas Turbines Trivia Quiz

Answer: Brayton Cycle

The Rankine Cycle describes the operation of a steam engine, in which the operating fluid is continuously flowing water/steam. The Otto Cycle describes the operation of a four-stroke gasoline engine, where the operating fluid is a trapped volume of gas such as air.

The Ericsson Cycle describes the operation of a largely theoretical external combustion engine, which uses a continuously flowing stream of gas as the operating fluid. The Brayton Cycle describes the compression, heat addition (or combustion), and expansion of a continuously flowing stream of gas as it passes through a gas turbine engine.

Answer: Isentropic (constant entropy)

In the ideal Brayton Cycle both the compressor and the turbine are assumed to operate isentropically (i.e. they do not change the amount of entropy of the gas). Gas pressure, temperature, and enthalpy (heat content) all increase as the gas is compressed. Of course, since no real compression process is isentropic, the ideal Brayton Cycle is only an approximation of the operation of a real engine.

Answer: Isobarically (at constant pressure)

In the ideal Brayton Cycle, heat addition is assumed to occur at a constant pressure. Unlike the ideal cycle's isentropic compression and expansion, this portion of the cycle more closely matches what happens in a real gas turbine.

Answer: Rotors

Stators are the stationary blades located between the rotating stages of the compressor. An impeller is the spinning portion of a centrifugal compressor. The only gas turbines found with a propeller are turboshafts (on helicopters) or turboprops (on airplanes), which spin the propeller through a series of shafts and gears.

The propeller does not participate in the thermodynamics of the gas turbine portion of the engine.

Answer: Centrifugal

The MiG-15's engine was essentially a reverse-engineered Rolls-Royce Nene centrifugal-flow jet engine. Modern jet fighters and airliners use axial-flow compressors, which have a smaller frontal area than centrifugal-flow compressors and are capable of higher compression ratios. The F-86 Saber, the MiG's primary opponent, was equipped with an axial-flow compressor.
Many turboprop aircraft still use centrifugal compressors due to their relatively small size.

Answer: It can use a variety of fuels

Gas turbine engines are relatively inefficient while idling, are generally more expensive to produce than piston engines, and are not as responsive as piston engines. However, Gas turbines are more flexible than gasoline or Diesel engines when it comes to the kind of fuels they can consume.

The Abrams' gas turbine engine can burn gasoline, Diesel, kerosene, and jet fuel. When conditions on the battlefield may limit what fuel types are available, it can be beneficial to be able to burn several different types. Additionally, a gas turbine typically has a higher power to weight ratio than a piston engine.

Answer: Turbofan

In a turbofan the bypassing air contributes to the thrust of the engine. In typical jet fighter turbofans only a fraction of the air entering the engine is bypassed. In the turbofans of modern airliners the majority of the incoming air is bypassed. Land based gas turbines, in which thrust is not a desired attribute, do not bypass any of the incoming air.

Answer: A nuclear reactor took the place of a combustor

Modified jet engines were used for the HTRE-1, HTRE-2, and HTRE-3 experiments in which a relatively small nuclear reactor took the place of the traditional fuel-burning combustor. The engines were never used to power an aircraft although they achieved nearly full thrust during ground tests.

More recently interest has been shown in a land-based gas turbine which utilizes nuclear power for the heat addition phase of the gas turbine cycle. Preheating of air prior to entering the compressor would not increase the efficiency of a gas turbine.

However, gas turbines with regeneration will heat air exiting the compressor using otherwise wasted exhaust heat. This does result in an increase of efficiency.

Answer: Hydrogen

Von Ohain's first gas turbines had difficulty with combustion stability, resulting in combustion occurring after the fuel had already passed through the turbine. The higher flame speed of hydrogen gas solved the problem until improved combustors utilizing gasoline could be installed.

Answer: It has a triple spool design

Standard turbofans used on airliners have a double spool design. This means that the engine has a low pressure compressor followed by a high pressure compressor and a high pressure turbine followed by a low pressure turbine. Concentric shafts connect the low pressure compressor to the low pressure turbine and the high pressure compressor to the high pressure turbine respectively.

A triple spool design includes an intermediate pressure compressor and an intermediate pressure turbine.