Question

In a subsonic jet engine, what is the primary thermodynamic purpose of the diffuser located after the compressor?

• A. To decrease the static temperature of the air
• B. To act as a heat exchanger for the incoming fuel
• C. To increase static pressure by decreasing flow velocity
• D. To increase Mach number to ensure rapid fuel mixing

Hint:

For a subsonic diffuser, \[ \boxed{ V\downarrow,\qquad P\uparrow. } \] Its primary purpose is pressure recovery before combustion.

Answer 1

The Correct Option is C

Step 1: Recall the function of a diffuser. A diffuser is designed to reduce the velocity of the incoming flow. As the velocity decreases, \[ \boxed{ \text{kinetic energy is converted into pressure energy.} } \]

Step 2: Identify the thermodynamic purpose. For subsonic flow, \[ V\downarrow \Longrightarrow P\uparrow. \] Thus, the diffuser increases the static pressure before the combustion chamber, improving combustion efficiency. Therefore, \[ \boxed{\text{To increase static pressure by decreasing flow velocity}} \] is the correct answer. Thus, \[ \boxed{(C)} \] is the correct answer.