Definition
A component in the engine's fuel system that delivers metered fuel into the combustion area in a finely atomized spray pattern, allowing it to mix with air and burn efficiently. In a piston engine, fuel nozzles are located at each cylinder intake port; in a turbine engine, they discharge fuel into the combustion chamber.
Plain English
The small jet that sprays fuel into the engine in a fine mist so it burns evenly. There is one at each cylinder on a piston engine, and several inside the combustion chamber on a jet engine.
Context Anchor
Seen in engine-system discussions and abnormal engine indications, especially when rough running, unusual exhaust temperature, or uneven cylinder performance may point to a blocked, dirty, or leaking nozzle.
Derivation
From Latin focus (hearth, fire) for 'fuel,' and 'nozzle' from a diminutive of 'nose' — meaning a small spout or projecting tip. So a fuel nozzle is literally a 'small spout for fire,' which fits its job of squirting fuel into the burning area.
Why Pilots Care
A clogged, worn, or misaligned fuel nozzle can cause uneven combustion, leading to rough engine operation, elevated temperatures on affected cylinders, power loss, or in turbines the risk of flameout.
Intuition Check
Do not confuse a fuel nozzle with the fueling hose nozzle used to fill the airplane. In this context, it is an engine component that sprays fuel inside the engine system.
Example Sentence 1
The mechanic cleaned the fuel nozzles after the pilot reported one cylinder running noticeably hotter than the others.
Example Sentence 2
During the post-maintenance run-up, the mechanic verified that all fuel nozzles were delivering an even spray before returning the aircraft to service.