"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