The working fluid of a gas turbine engine is

• A. Gasoline
• B. Kerosene
• C. Air
• D. Water

Answer: (C)

In a gas turbine, the engine operates on the Brayton cycle, where a working fluid is compressed, heated, expanded, and exhausted to produce work. The common working fluid in this cycle is air from the atmosphere. It is drawn in, compressed to a high pressure, mixed with fuel and combusted to raise temperature, and then expanded through the turbine to drive the compressor and generate power. Air is ideal for this role because it remains gaseous at the cycle temperatures, is readily available, and its properties allow efficient compression and high-temperature expansion. The other substances listed are fuels or liquids: gasoline and kerosene provide the energy through combustion, while water would not serve well as the primary working fluid in a typical gas turbine due to phase changes and material considerations.