Hi guys,
Just curious.. What does it mean when the engine runs away?
When operating as designed, the injection pump supplies the fuel and the engine has a provision to be shut down via some type of fuel shutoff.
Over time or because of a defect, oil seals can begin to leak and allow engine oil into the intake area of the engine. A common culprit are the axle seals on a turbocharger. The pressure differential across the seal on a running engine literally "sucks" more oil out. Because a diesel engine will run quite happily when burning engine oil as fuel, the revs will go up. This increases the pressure differential and even more engine oil gets sucked into the intake and burnt as fuel. The rpms climb.
The engine will continue to accelerate until either the crankcase oil is gone or some parts decide to leave their pre-arranged position and exit the block. Conventional safety equipment, such as rpm governors or shutoffs will be useless, because the engine is finding its own fuel source and the shutoffs usually target the diesel fuel system only.
The only reliable way of shutting down a runaway diesel is to shut off the air. A flap in the air intake (fitted on some engines as a safety add-on) or a phone book (oh, there is a story...) or a plank of wood or....will be sucked tight over the intake opening and the engine starves of air.
Before anybody mentions it - no, you can not use your hand over the intake. You will get hurt, probably badly. Even on a TDI Volkswagen.
Runaways are scary when they happen; the rpm can climb so quickly that destruction occurs before you can do anything. I have in my ear the scream of a marine diesel that I never thought could revv that high, ever.