A gas turbine diffuser, also known as a diffuser duct, is a crucial component in a gas turbine engine that helps increase the efficiency of the engine's air compression process. Its primary function is to slow down and expand the high-velocity, compressed air exiting the compressor section before it enters the combustion chamber. This expansion and deceleration of the airflow are vital for several reasons:

1. Pressure Recovery: The diffuser helps to recover static pressure in the airflow. The high-speed air exiting the compressor contains kinetic energy, and the diffuser's diverging shape converts this kinetic energy back into static pressure, which is useful for combustion.

2. Temperature Reduction: The rapid compression of air in the compressor can raise its temperature significantly. Slowing down the air in the diffuser reduces its temperature, which is essential to prevent overheating in the combustion chamber.

3. Combustion Stability: Slower, lower-temperature air is easier to mix with fuel and ensures more stable and efficient combustion.

The design of the gas turbine diffuser is carefully engineered to achieve these goals. It typically consists of a diverging duct with carefully contoured surfaces to minimize flow separation, pressure losses, and turbulence. This design helps maximize pressure recovery and improve the overall performance and efficiency of the gas turbine engine.

In summary, a gas turbine diffuser is a critical component that prepares the compressed air from the compressor for efficient and stable combustion in the gas turbine engine. It plays a vital role in improving pressure recovery, reducing air temperature, and enhancing combustion efficiency.