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Emergency diesel shutdown
On 07 Dec 2003 14:56:08 GMT, (Gould 0738) wrote:
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
Cut off the air supply. Rags in the intake work well.
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.
I'm curious as to why a diesel will run like crazy on halon. If it
supports combustion as an oxidizer, it wouldn't make a very good fire
extinguisher.
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.
A positive stop to the fuel supply from the injector pump is how a
diesel is normally shut down. A problem with turbocharged diesels is
that if a seal breaks allowing lubricating oil to get into the intake,
the engine can run on that until there isn't anymore. So stopping the
air supply is the only solution in that case.
Steve
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