(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?




http://www.tomorrowsbestseller.com/w...State/book.asp

When a diesel engine has run away one of two things has probably
happened. You may have an injection pump failure and the pump is
jammed in the wide open position. In this case the engine will
normally only run up to as high as the governor is set at. The engine
can be shut down by shutting off the fuel supply.

Or, the worst case, on old engines, the piston rings are leaking oil
up into the cylinders and the oil is being burned instead of the fuel.
Shutting off the fuel supply will not shut the engine down and the
engine will continue to accelerate until it runs out of oil and the
engine binds up, or it "comes apart". The only way to shut the engine
down is to cut off the air supply. A few plastic bags over the intake
might work, but don't be surprised if they just get sucked in. I had a
car diesel run away like this. The car just began to accelerate on
it's own and was blowing all kinds of smoke. I had a manual
transmission and stalled it out by keeping it in gear and hitting the
brakes until it stalled. It burned up about half the engine oil in
about 30 seconds.
On a boat it takes "some big ones" to jump down into the engine room
with this screaming engine and try to shut it down. And it's over
pretty quick. Some older boats had air shut down's on them that will
do the trick.