Definition
A fuel delivery system in which fuel is sprayed under pressure directly into each engine cylinder, rather than being mixed with air in a carburetor or injected into the intake port upstream of the cylinder. A fuel pump, fuel/air control unit, fuel manifold, and individual discharge nozzles at each cylinder meter and deliver the fuel precisely to each combustion chamber.
Plain English
Instead of mixing fuel and air in one place and sending the mixture to all cylinders, the engine sprays fuel straight into each cylinder. Every cylinder gets its own fuel line and its own nozzle.
Context Anchor
Seen in discussions of aircraft piston engines, especially when comparing fuel-injected engines with carbureted engines.
Derivation
"Direct" comes from the Latin directus, meaning "straight" or "without intermediate steps." Here it signals that fuel goes straight into the cylinder itself, with no mixing chamber or intake-port stop along the way.
Why Pilots Care
Gives better fuel efficiency, eliminates carburetor icing risk, and keeps the mixture accurate at changing altitudes.
Analogy
Like giving medicine straight into the bloodstream rather than mixing it into a drink first.
Intuition Check
Direct does not mean the pilot pours fuel in manually or that the system is simple. Here, direct means the fuel is delivered at the cylinders instead of being mixed upstream in one carburetor.
Example Sentence 1
Because the aircraft has direct fuel injection, the pilot followed the hot-start procedure in the POH rather than the normal start checklist.
Example Sentence 2
Mechanics checked the direct fuel injection nozzles for proper spray pattern before the annual inspection.