Definition
Stationary vanes arranged radially (like spokes of a wheel) at the outlet of a centrifugal compressor that slow the high-velocity air leaving the impeller and convert that velocity into a rise in pressure before the air enters the combustion section.
Plain English
A ring of fixed blades that sits just outside the spinning compressor wheel. The fast-moving air thrown off the wheel hits these blades, slows down, and gets squeezed into higher pressure before it reaches the burner.
Context Anchor
Seen in turboprop engine descriptions, especially where the airflow path through a split-shaft or free turbine engine is being explained.
Derivation
Radial comes from the Latin radius, meaning 'spoke of a wheel' — the diffusers are arranged in that spoke-like pattern around the compressor outlet. Diffuser comes from the Latin diffundere, 'to spread out.' The vanes spread the airflow outward and slow it, which is exactly what raises its pressure.
Why Pilots Care
Proper diffuser function directly affects compressor efficiency, engine power output, and resistance to surge or stall.
Analogy
Think of putting your thumb over a garden hose. The water slows where your thumb restricts it, but the pressure behind that point goes up. The diffuser does the same thing to the air leaving the compressor — slows it, raises its pressure.
Intuition Check
Do not think of a diffuser as something that simply scatters air randomly. In an engine, a diffuser slows and guides air in a controlled way so pressure increases.
Example Sentence 1
Air leaving the centrifugal impeller passes through the radial diffusers, which slow it down and raise its pressure before it enters the combustion chamber.
Example Sentence 2
Damage to the radial diffusers can reduce engine performance by disrupting smooth airflow after the impeller.