The diffuser in a jet engine is designed to be divergent to convert kinetic energy to pressure energy. What is the effect at the compressor face?

• A. Increased velocity
• B. Increased static pressure
• C. Decreased temperature
• D. Decreased mass flow

Answer: (B)

A diffuser’s job is to slow the flow by making the duct divergent, converting the flow’s kinetic energy into pressure energy. As the air enters the compressor face, its velocity decreases while the static pressure increases. In an adiabatic diffuser, the total (stagnation) temperature stays the same, so the loss in velocity shows up as higher static pressure (and a small rise in static temperature, not a drop). The mass flow through the diffuser in steady operation remains essentially the same. So the effect at the compressor face is an increase in static pressure.