Another Diesel Generator Question

You didn't supply enough data to be certain, but I will take a stab at it anyway.

By "huge diesel engine" and your title about it being for a generator, I would guess that this is a "skid package" (turn key...). By that and the assumed size, I would guess that it has some brains (e.g. PLC) as part of the package. The brains are there to keep people like operators from taking a machine with a lot of mechanical, and electrical energy, and just going BAM! COME TO A SCREECHING HALT. This is NEVER a good idea to do with ANY form of energy.

Part Deux: The PLC code is not written properly to handle that sort of abuse (it should be). Contact the OEM's tech support and explain the situation. If they are worth their weight in dung, they will either have heard about this problem and be working on a fix, or they will check the problem out once you have explained it. That could save them and you a lot of grief.

Steve S. and I are coming to your facility with folding chairs, binoculars, telephoto video cam, ear plugs and popcorn . . . . this is great stuff. Andy, Dell . . . want in on this?

What do you call big? 1000 kW ? 3000 kW ? Big to me is 5 MW and above. Big to Pwr2thepeople is 150 MW and above.

Suggestion to end 20 rounds of Q/A: Don't post questions about equipment without make, model, year, size, rated speed and if it is a control system question then decribe the control system logic.

Sorry there Petro, this one was only 800 kw, it is a v-12 Cummins engine I think, but for my field here the biggest we have is 2 MW. To me she's big ( I think I will need to get around more and see the other monsters that are out there)

There are 2 Cummins V-12 models, a 600 kW +/- old unit (VTA 1710) and an KTA 2300 (Now called a KTA 38 I think . . . for 38 liters) maybe about 1 ~ 1.2 MW or so, both with PT fuel systems and a fuel shutoff solenoid valve right on top of the PT fuel pump discharge. This stops the fuel NOW when de-energised. RIGHT NOW! Running on after ramping up with a shutdown during ramp up may be burning off a touch of unburned fuel injected (but this would only be a few seconds, not 10 -15 seconds of running on) at a slow RPM, or a control issue where partial voltage is still available at the shutoff solenoid cracking it open a bit.

I ounce turned off the fuel accidentally to a unit, it was on a ship that had three diesels with only two being used to generate power to the drive, I was able to re-establish supply before the engine stopped, and it had only slowed down a bit before I realised. It is not unusual for the fuel system to have surge bottles in the system, these have a small supply of diesel that it can run on before becoming staved. I'm not sure that this is the answer, you will need to check.

Regards JD.

When gasoline engines do this, it's called "dieseling". It sounds like the control system turns off the fuel pump, but doesn't shut the valves. I suspect that the intake vacuum was sufficient to drag a small flow of fuel into the cylinders, allowing continued combustion. If the fuel system has shutoffs for the individual cylinders, it's possible that one of the shutoffs leaks by when cold. A full startup would warm the fuel line and prevent the leakby.

It's possible that your control system has a minimum speed setting before a normal shutdown is allowed to occur. If so, some portion of the shutdown sequence may have been blocked for safety reasons. It's very likely that the manufacturer has encountered this issue before. I suggest you contact them for guidance regarding your particular system.

Well we are expected to recieve back that unit next week. I intend to investigate this problem further. Surely I will post the results.

BTW: Mr PetroPower, you are very welcome to my facility any day ! There are alot of interesting stuff that happens to Generators in the Rental Business......

Historically, for diesels built before about 1960, the way you shut them off was to open the throttle all the way and then slam it to the closed position. (Any one whose driven a 1946 D4 Cat would have experience operating this way). As I undertand it the reason is due to the diesel engines' use of compression instead of ignition to run. By bring the engine up to full speed and then shutting of the fuel forces it torapidly consume the available fuel in the cylinders. If you don't burn off the fuel quickly it is basically allowing the engine to idle to a stop. Won't really hurt it but takes a long time.

Check turbo lube oil seals. when cold there may be oil leakage allowing the engine to run on this oil not fuel.

Also if a high hour engine, intake valve seals may drop oil until engine is warm or intake system is up on boost from turbo to make the seals active.

I have seen this on other diesel engines.

If it would have been an EMD, there could be even more things to look at.

Keep us posted.

Log.

This has brought to mind a situation, that happened on ferry, of a company I worked for. There was a situation where they could not stop the main engine, even when the fuel was shut off, this I believe I came about by over heated sump oil, there was enough vapourised oil drawn from the sump scavenge to keep the engine running.

Regards JD.

The reason ( most likely) for extended engine run is the solenoid cut off system is leaking. Check the fuel PT pump, also check whether somebody has fiddled with the manual override knob, which basically overrides the cut-off. At crawling speeds the fuel required to sustain the engine is quite low and hence it continues even after the main shut off valve is closed till all the fuel between the shutoff valve and the fuel pump is sucked up by the engine. Good luck !!

You are correct, however the most likely reason for a diesel engine to "run on", is a leaking injector. I have come across this on numerous occasions. If the engine has not been timed/tuned correctly it can also lead to "no fuel" being "some fuel". This will also cause "run on".

Another though has just come to mind, some diesel engines do not immediately shut down, they have a built in timer to allow the engine to cool before shutting down completely, this is common I believe with some cars? not sure of my facts, you will need to check.

Regards JD.

Additionally, to the possibility of some "leakage" of DC to the run solenoid on the PT pump (check that the DC is removed from the SD solenoid, you can place a temporary jumper wire in place, start the unit then shut the unit via the control equiptment & remove the jumper) = No DC, is to check the fuel return line for restriction or pressure. Some cummins units will continue to run ~ 600-800 rpm'ish after the DC is removed from the solenoid. The return line can be removed and placed into a container for the testing purposes.