The inlet duct of a jet engine at subsonic speeds is designed to convert which energy form?

• A. Kinetic Energy to Pressure Energy
• B. Pressure Energy to Kinetic Energy
• C. Enthalpy to Entropy
• D. Temperature to Velocity

Answer: (A)

The main idea is that the inlet diffuser slows the airflow to raise its static pressure. In subsonic flow, the air carries kinetic energy as it moves. As the air is decelerated in the diffuser, that kinetic energy is converted into static pressure energy, increasing the pressure at the engine face. In an ideal diffuser, the total pressure stays nearly the same while velocity decreases, so static pressure rises to improve compressor charging.

So the inlet’s job is to transform kinetic energy (related to the air’s motion) into pressure energy (static pressure). The other options describe different energy transfers that aren’t what a subsonic diffuser accomplishes: accelerating the flow would require converting pressure to kinetic energy; changing enthalpy into entropy implies irreversible losses not used for pressure recovery; and converting temperature to velocity isn’t the primary energy exchange in diffuser operation.