Diesel Generator Overspeed 2

[clientsarealwaysrite]

Hi Folks,

I recently was asked by a client to investigate a catastrophic overspeed failure on a Dorman V12 diesel engine. The unit provides standby power for a UPS system. The claim is that the fuel rack stuck then went to full fuel, resulting in the engine over-revving, to the point that pistons met valves and seized. Cost for new camshaft etc £50K. The overspeed switch is mounted on the suction side of the turbo blower and was proved to be operational after the rebuild.
The question is why ? Why did the overspeed not stop it, the governor not shut the fuel off etc.
Has anyone ever experienced this before and has anyone any other ideas as to why the engine should overspeed in this manner?

thanks

 

[waross]

Actually gasoline will lighten the fuel and reduce the power. Adding used lube oil to the fuel will increase the SG and give a little more power or better mileage. Unfortunately the newer engines have much finer orifices in the injectors and finer filters to match. If you use the old trick of adding used lube oil to the fuel you spend more time and money replacing clogged fuel filters than you ever save on fuel.
Now I remember one 4-71 where the crew used gasoline to clean the oil bath air filters and put the filters back on the engine before the residual gasoline had evaporated. The owner was frantically trying to shut the engine down with the governor override and I had to push my way past him to pull the linkage on the air flap to shut it down. I did get it choked off before any damage was done. It was gaining speed but the gasoline was pre-igniting so bad that it wasn't accelerating that fast.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dicer]

I had a case of a D353 engine wanting to go overspeed, the governor would not do a thing and it was working perfectly. It would have blown if I would not have had a compression release lever to pull. It was a stuck pump follower that caused it. There would only be 3 ways to stop this kinda engine in this case. 1 Compression release 2 shut off fuel
3 block air intake.
So yes this sort of thing can happen.
If you don't want it happening again, the only for sure cure is a fuel shut off system, that is completly separate from the engine and governor system.
My question what kinda fuel injection equipment on it?

 

[GregLocock]

No, fuel shutoff doesn't work in the commonest cause of runaway I've seen. You have to remove air.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ivymike]

right, a guillotine-style ASO (air shutoff) valve is the thing to have. You can check 'em out anywhere a diesel is used in a potentially flammable atmosphere.

 

[786392]

Another Catastrophe not to forget Was
'BP Amoco North America Texas Refinery Tragedy'
Back in March 2005
Report available at

http://www.csb.gov

has overspeed(run-ways of a Diesel pickup engine)in flammable atmosphere discussed as possible cause.

Best Regards
Qalander(Chem)

 

[dicer]

The old solenoid fuel shutoff that cummins has used from the old days, seems to work just fine. I agree air is probably the best, but also the most difficult to do.

 

[waross]

Many engines do not have an emergency shutdown. However in any situation where there is a probability of a second fuel source, the fuel shut-off doesn't cut it.

Bill
--------------------
"Why not the best?"
Jimmy Carter