FAA Powerplant Written Practice Test

What is the primary function of the diffuser section in a turbine engine?

1. To increase air pressure and decrease its velocity

2. To cool the combustion gases

3. To compress the incoming air

4. To mix fuel and air

The correct answer is: To increase air pressure and decrease its velocity

The primary function of the diffuser section in a turbine engine is to increase air pressure and decrease its velocity. This process occurs after the air has been accelerated through the engine's inlet and compressor sections. As the air moves into the diffuser, there is a gradual increase in cross-sectional area, which allows the kinetic energy of the high-speed airflow to convert into static pressure. In an effective diffuser, as the air slows down, its pressure increases, which is essential for maintaining optimal operation of the engine. This high-pressure air then moves into the combustion chamber where it mixes with fuel for combustion. The increase in pressure ensures that the turbine has an adequate fuel-air mixture to produce thrust efficiently. The other options, while related to various functions of a turbine engine, do not accurately describe the primary purpose of the diffuser section. The cooling of combustion gases is typically handled in areas further downstream, the compression of incoming air occurs within the compressor section, and the mixing of fuel and air happens in the combustion chamber rather than in the diffuser. Thus, the correct answer aligns perfectly with the engineering principles of how air management within a turbine engine operates.