FAA Powerplant Written Practice Test

What method is used to cool the combustion liner walls in a gas turbine engine?

1. By direct water injection

2. Through oil circulation

3. By secondary air flowing through the combustion chamber

4. Through ambient air intake

The correct answer is: By secondary air flowing through the combustion chamber

The correct method for cooling the combustion liner walls in a gas turbine engine is through secondary air flowing through the combustion chamber. In gas turbines, high-temperature combustion gases are produced, and to prevent overheating and damage to the combustion liner, cooling is essential. Secondary air, which is bypassed from the compressor on its way to the combustion chamber, is directed around the combustion liner and through various cooling passages. This air absorbs heat from the combustion liners, maintaining structural integrity and performance under extreme thermal conditions. The flow of this cooling air can also help maintain a suitable temperature gradient, which is crucial for prolonged operation. This method is especially effective as it utilizes air already present in the system, ensuring that cooling is efficient and assists with the overall aerodynamics and thermal management of the engine.