FAA Powerplant Written Practice Test

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

1. By fuel injection

2. By external air cooling

3. By secondary air flowing through the combustion chamber

4. By refrigeration units

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

In a gas turbine engine, the primary method of cooling the combustion liner walls is achieved by utilizing secondary air that flows through the combustion chamber. This secondary air is drawn from the engine's compressor and is directed toward the combustion liner. As it circulates, this air absorbs heat from the combustion process, thereby maintaining the structural integrity of the liner and preventing overheating. The design of gas turbine engines incorporates this cooling approach because it optimizes the efficiency of the engine while protecting critical components. The secondary air helps maintain the temperature of the combustion liner within acceptable limits, thus enhancing the longevity and reliability of the engine. While fuel injection plays a vital role in the combustion process, it does not serve the purpose of cooling the combustion liner. External air cooling could hypothetically be used, but it is not practical for the design of gas turbine engines, which primarily rely on the internal flow of secondary air. Refrigeration units are not relevant in this context, as they are not a standard component in turbine engine operation.