Home |
Search |
Today's Posts |
#9
|
|||
|
|||
Emergency diesel shutdown
"Gould 0738" wrote in message ... A paragraph in a book I've been sent to review seems to be in error. Either that, or I'm not properly intuitice about this situation. The paragraph poses a mulitple choice question. "What is the best way to shut down a runaway diesel engine?" One choice is a throw-away. "Cut off the electrical supply." Bzzzt! "Thanks for playing, and we do have some lovely parting gifts for you........" The other two choices: 1. Cut off the fuel supply 2. Cut off the air supply I immediately thought, "the fuel supply. You shut down a diesel by cutting off the fuel." According to the author, the correct answer is supposed to be "Cut off the air supply." The author recommends "discharging a fire extinguisher into the air intake." Well, first off it would need to be the correct type of fire extinguisher. Some extinguishers are charged with halon (which is no longer legal to mfg in the US but is imported or recycled from other extinguishers) and a diesel will run like crazy on halon. And, I'm aware of emergency shut downs that have been accomplished with CO2 extinguishers, etc. I just thought those were cases where it was impractical to cut off the fuel supply. Wouldn't putting a postive stop to the fuel supply from the injector pump be a more certain solution? "Some" air might get sucked into the air intake along with the fire suppressant, maybe enough to allow the engine to cough past the extinguisher discharge and keep running. But, the engine absolutely will not run without fuel. Shutting off the fuel very far upstream wouldn't be a good choice, as an engine can run quite a while on the fuel in lines, filters, etc. Somebody care to agree, disagree, or show me why my preference for fuel shut down would be wrong? The early Detroit Diesel 8V71 engines were notorious for the fuel injector control racks sticking, usually in the in the full fuel position. The normal "off control" just moved fuel command to the governor (the governor actually moves the racks) to the "no fuel" position so this clearly is not going to work. GM fixed this by putting an air door in the intake manifold. This door is located in the odd looking 90 degree bend going into the blower. When you pulled the red emergency stop T-handle on the dash, this door drops and cuts off the air supply to the engine. The air door shaft is spring loaded and e-stop just releases it - it has no facility to pull the door back into position. After this you had to manually reset this door by gaining access to the engine (usually jacking the cab) and flipping the little lever on the intake manifold. This also work in the case of old engines that will run on oil that leaks past the ring. When you shut them off they just keep limping along. This is a reliable indication that it is time to rebuild the engine. Usually by then the exhaust smoke is pretty blue, but the engine seems to work fairly well otherwise. Given the huge number of these engines installed in marine applications I can see the need for the question. BTW: I never heard a GM rep say this, but as a idea of an external valve for shutoff in normal engine operation, the injector pumps use the fuel for lube and run at some high pressures and close tolerances. Between possible priming problems and potential wear, I don't think that shutting off the fuel to the engine is a good idea. Mark Browne |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
4.3L Diesel conversion | General | |||
Diesel refit for existing Crysler 318 with V-drive? | General | |||
TBO Model 210HP 3208 Cat Diesel?? | General |