The Diesel Engine Cycle differs from the Otto 4 Stroke Cycle often found in cars. In cars fuel and air are mixed which creates controlled explosions in the combustion chambers. Diesel Engines differ in that they work primarily on the concept of high temperature compressed air being ignited with diesel fuel.

Diesel Engine Runaway: Runaway occurs when a Diesel engine fuel injectors become jammed and constantly supply the engine with diesel, valves become stuck open and the engine begins to burn anything combustible. When this happens the engine begins to rev beyond its red line capabilities and runs at very high RPMs. The Engine is effectively feeding itself and there is no way to stop it.

Jammed Fuel Injectors: Although this condition is rare one of the most common causes for Diesel Engine Runaway is a set of faulty fuel injectors. The injectors essentially "spritz" a small amount of diesel per stroke. When they jam, they are in effect "dumping" diesel fuel into the chambers which causes the ignition to happen more frequently and more violently thus speeding up the engine.

Blown Turbochargers: Turbochargers are essentially small turbines operating at high RPMs. When these devices fail what frequently happens is one if the Turbo fan blades ruptures and metal shavings break off into the turbocharger and are subsequently sucked into the engine. Metal shavings inside of the engine combustion chambers could cause an Injector to fail as well as other damage, this is the second known cause of Diesel Engine Runaway.

Correction: The only way to stop a Diesel Engine with this rare defect is to cut of its air supply. This is usually done by spraying a CO2 Fire Extinguisher into the Air Intake. This will choke off the air supply to the engine and with no fuel air mixture the engine will stop. The other less safe method would be to jam towels and shirts into the air intake as well.

Other than this there is no way to stop Diesel Engine Runaway from catastrophic engine failure. The only thing that can be done is to wait until all of the fuel, oil etc that has made its way into the engine to burn out. The low ignition point of Diesel means that its less volatile and will burn just about anything combustible