Definition
A fuel nozzle in a gas turbine engine that sprays fuel into the combustion chamber through a single fixed orifice. Because it has only one fuel passage, the spray pattern and atomization quality vary with fuel pressure, producing a good spray at high engine speeds but a poor, less efficient spray at low engine speeds.
Plain English
A turbine engine fuel sprayer with just one opening. It works well when fuel pressure is high but doesn't spray as cleanly when pressure is low.
Context Anchor
Seen in turbine-engine fuel system descriptions, combustion section discussions, and maintenance troubleshooting for fuel spray problems.
Derivation
Simplex comes from the Latin simplex, meaning 'single' or 'one-fold.' The name reflects the nozzle's single fuel passage, in contrast to a duplex nozzle, which has two.
Why Pilots Care
The simplex design's weakness at low pressure is why most modern turbine engines use duplex nozzles instead. Knowing the difference helps when reading engine system descriptions and troubleshooting fuel atomization issues that affect starting and low-power operation.
Analogy
Think of a garden hose with a single fixed nozzle. Turn the water up high and you get a fine mist; turn it low and you get a weak dribble. A simplex nozzle behaves the same way with fuel.
Intuition Check
Simplex does not mean the nozzle is unimportant or easy to ignore. Here it means the nozzle uses a single fuel passage and outlet arrangement.
Example Sentence 1
The older turbine engine used simplex fuel nozzles, which sprayed well at cruise power but atomized poorly during idle.
Example Sentence 2
The engine manual called for simplex nozzles on this particular fuel-injected model.