Dieseling
Engine run-on in gasoline engines and air rifles.
Dieseling, also known as engine run-on, is a condition in which a spark-ignited gasoline engine continues to run briefly after being switched off, drawing fuel and igniting it without a spark. The term derives from the similarity to diesel engine operation, where combustion is initiated by compression heat rather than a spark. In automobiles, dieseling typically produces sputtering before the engine gradually stops.
Quick Facts
- Common in
- carbureted engines with many miles
- Remedy
- electric solenoid in carburetor fuel supply circuit
Facts from the source article.
Potential causes
Several factors can lead to dieseling. Built-up carbon in the ignition chamber may glow red after the engine is off, providing a heat source to ignite unburnt fuel; this can occur when the engine runs very rich, depositing unspent fuel and particles on pistons and valves. Rough metal regions within the piston chamber can also glow red and cause the same problem. An improperly rated spark plug that retains heat may contribute. A carburetor that does not completely close can allow extra fuel and oxygen into the warm piston chamber. Hot vaporized oil gases from the engine crankcase can supply fuel for dieseling. Incorrect timing, an engine running too hot or too lean, an idle speed that is too fast, or inlet valves that do not seal fully can also cause run-on after ignition is turned off.
In air rifles
In air rifles, dieseling refers to the deliberate or accidental burning of oils or similar flammable hydrocarbons when the rifle is discharged. A spring or ram-powered air rifle compresses air rapidly in the chamber behind the projectile; if the air contains flammable contaminants, the temperature rise from compression may ignite the mixture, adding energy to the system and increasing pellet velocity. While generally unwanted due to adverse effects on accuracy and potential damage to the rifle or sight, dieseling is sometimes deliberately engineered by oiling the rear hollow base of the pellet or chamber to boost power, usually as a stunt or experiment, as the tiny amounts of oil make consistency impractical.
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