Jet propulsion diffusers: The diverging inlet duct in a jet propulsion unit acts as a diffuser to convert incoming air kinetic energy into static pressure energy.

Introduction / Context:
Air-breathing propulsion systems use inlet diffusers to condition the flow for the compressor or combustor. An efficient inlet recovers dynamic pressure (ram pressure) by diffusing the flow and raising static pressure.

Given Data / Assumptions:

• Diverging inlet duct shape (area increasing in the flow direction).
• Subsonic inlet operation for typical turbojets and turbofans.
• Goal: deliver higher static pressure and lower Mach number to the compressor face.

Concept / Approach:
For subsonic flow, a diffuser converts velocity head into static pressure. The continuity and momentum relations show that expanding area slows the flow. The Bernoulli relation for adiabatic, low-loss subsonic diffusion indicates an increase in static pressure at the expense of kinetic energy.

Step-by-Step Solution:

Verification / Alternative check:
Inlet pressure recovery coefficients quantify performance; well-designed subsonic diffusers show static pressure rise and total pressure losses kept minimal.

Why Other Options Are Wrong:

• False: Contradicts diffuser function in subsonic inlets.
• True, but only at zero speed: At zero speed there is little kinetic energy to recover; the diffuser benefit is evident at finite flight speed.
• False, it converts pressure to velocity: That is the role of a nozzle, not a diffuser.

Common Pitfalls:
Confusing supersonic inlets (which need shocks and area variations) with subsonic diffusers; the basic energy conversion is the same but controlled differently.

Final Answer:
True