Diesel engine overspeed

A place to exchanges questions and ideas of a technical / procedural nature. Go ahead, try to stomp us !
Pengze
Mechanic
Posts: 60
Joined: Tue Sep 23, 2008 8:57 pm

Diesel engine overspeed

Postby Pengze » Wed Aug 29, 2012 8:47 pm

What are the causes for diesel combustion engine suddenly running overspeed ?

User avatar
JK
Enduring Contributor
Posts: 2697
Joined: Tue Sep 04, 2007 2:29 am
Currently located: East Coast, Canada

Re: Diesel engine overspeed

Postby JK » Thu Aug 30, 2012 4:18 am

fuel pumps put together incorrectly or mis-calibrated.
We had a fuel pump on a common rail engine lose a nut internally and jam the rack open. We lost the engine with a crankshaft failure.
governor issues-such as unshielded wiring to electronic governor. I have seen an unloaded diesel generator follow the loaded engines as they ramped up in load, because of unshielded wiring and stray signals. It is scary as hell to see a 16 cylinder engine dance while you are standing beside it.
sudden loss of load.

User avatar
Big Pete
Engineering Mentor
Posts: 817
Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

Re: Diesel engine overspeed

Postby Big Pete » Thu Aug 30, 2012 11:18 am

I recently saw two main engines overspeed. An Agency called me up while I was on leave and asked me to join a ship in Drydock, apparently the Chief quit without notice.
The yard had removed and refitted the main engine governors and fuel pumps, they had all gone to specialists for overhaul.
When the engines were started they ran straight up to overspeed and shut them selves down. They were medium speed Weichmans (now part of Wartsilla).
I found the fuel pump stand outs were all set to "10" when the engine was stopped. No indication anywhere in the manuals or test bed data what the correct settings were. After an evening spent phoning every contact number I could find, I found out that the racks should have been set to "Zero" when the engine was stopped.
It looked as if the governors came back first and the splined shafts were fitted to them slightly out of position, when the fuel pumps came back they were just connected up to the governor output shafts without anyone checking the correct position.
As they say, "it is what it is".

Another cause can be the ship running into a "gas cloud" from leaking hydrocarbons which are drawn into the air intakes and provide extra fuel over and above what the governor is supplying.

BP
It is always better to ask a stupid question than to do a stupid thing.

Pengze
Mechanic
Posts: 60
Joined: Tue Sep 23, 2008 8:57 pm

Re: Diesel engine overspeed

Postby Pengze » Thu Aug 30, 2012 9:09 pm

To provide you here with more details:-
1. This overspeed happens to our high speed diesel genset. The genset had been running for the last 24 hours without any abnormal parameter.

2. It happens all of a sudden and causing severe damages to the engine block, conn rod, crankshaft, bearings, etc.

3. The alarm status history printout recorded the sequence as "Safety system common failure" followed by "Overspeed" within approx. 1 second.
Therefore, I am wondering whether this "Safety system common failure" is the cause for engine "Overspeed". Pls explain if this is so. I am doubtful about this.

4. From my point of view, let's assume that the "Safety system common failure" malfunction, it should not cause "Overspeed". This will only cause the engine unable to stop if any safety parameters happen like failure of lube oil pressure / temperature, jacketwater temperature too high, overspeed and so on.

5. Another scenario would be, if presumed that " Safety system common failure" exists due to the card's internal fault or transmitter sensor faults, and all engine running parameters are normal., the engine will still operate normally until we shut down as normal practice. Then afterwards to check and rectify the " Safety system / devices defects".

Please correct me if I am wrong.

User avatar
JK
Enduring Contributor
Posts: 2697
Joined: Tue Sep 04, 2007 2:29 am
Currently located: East Coast, Canada

Re: Diesel engine overspeed

Postby JK » Fri Aug 31, 2012 2:17 am

Strange.
I would think that on the failure of the safety system, there would be an alarm and maybe the start up of secondary pumps to prevent the loss of cooling and lubrication in a fail safe mode. There shouldn't have been an overspeed IMO.
I assume it was on load at the time of the failure. Is there any indication of when the breaker opened? Could the breaker have tripped at the same time leaving the engine with no load when it was running at high power output?

BP, you are lucky the engines shut down. We had an engine destroy itself in 90 seconds when the fuel pumps were incorrectly installed. The only way to shut it down was to turn the fuel valve off. It wouldn't shut down on any of the trips.

User avatar
Big Pete
Engineering Mentor
Posts: 817
Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

Re: Diesel engine overspeed

Postby Big Pete » Fri Aug 31, 2012 11:08 am

Are the engines fitted with Electronic Governors??
If that is so maybe a governor failure is indicated by " Safety System Common Failure". It could be that the alarm is caused if the actuator does not respond correctly to the governor commands.
I have often found that the description of an alarm on the printout is misleading when you investigate the faults that actually cause that message to come up.
On many modern Gen set installations, a non urgent alarm will cause the standyby gen set to "auto start" & "autosynch" to reduce load on the set that is in "alarm" and in readiness for the alarm to become a "shutdown".

Good luck.

BP
It is always better to ask a stupid question than to do a stupid thing.

User avatar
JollyJack
Fleet Engineer
Posts: 1128
Joined: Wed Mar 24, 2010 3:57 am
Currently located: Eastern Canada

Re: Diesel engine overspeed

Postby JollyJack » Fri Aug 31, 2012 6:11 pm

Another good example of why electronics should be used only for playing games and the temporary storage of data. Computers should NEVER be allowed anywhere near marine machinery. Reliable overspeed devices are mechanical and operate on centrifugal force. Electronics cannot be trusted. Your "safety system failure" was in allowing a geek to dictate how your overspeed protection device works.
Discourage incest, ban country "music".

User avatar
JK
Enduring Contributor
Posts: 2697
Joined: Tue Sep 04, 2007 2:29 am
Currently located: East Coast, Canada

Re: Diesel engine overspeed

Postby JK » Sat Sep 01, 2012 12:40 am

Another thing to check from the maintenance history, is how often the mechanical overspeed trip was tested and what speed it was set to.
It should have tripped before the engine destroyed itself. You should check it on the other engines as well. The operating protocol of the safety system should tell you what the proper sequence of events should have been....if it was supplied.


JollyJack, I recently read about a ship so automated it can be run by a handfull of people. What a nightmare that will be.

User avatar
JollyJack
Fleet Engineer
Posts: 1128
Joined: Wed Mar 24, 2010 3:57 am
Currently located: Eastern Canada

Re: Diesel engine overspeed

Postby JollyJack » Sat Sep 01, 2012 6:28 pm

I have sailed on such ships. (2 bulkers, 1 tanker) Crew of 7, Capt, 2 mates, 2 Engineers, 2 ABs. 6 hour watches (the computerised UMS system didn't work), no cook (you need a crew of 10 to justify a cook), usually 1 man bridge watch when the ABs worked on deck. The "Deadman" alarm was held back with a broomstick so the buzzer didn't wake the Mate on watch. (Mates are very busy on coastal tankers, loading and discharging cargo.)

As you can imagine, not much maintenance was done. I believe one ship was 15 years old when she was eventually scrapped, they couldn't find a buyer for her and passing the 15 year survey would cost far too much.

Incidentally, that company had a ship on which the UMS system did work. She carried one Engineer only.
Discourage incest, ban country "music".

jimmys
Officer of the Watch
Posts: 127
Joined: Tue Nov 16, 2010 4:09 am
Currently located: Glasgow Scotland

Re: Diesel engine overspeed

Postby jimmys » Tue Sep 04, 2012 1:38 am

Check on the UPS (uninterruptable power source) for the electronics. Its a relay and a battery which prevents interuption to the power source for the governing chip. The relay can be faulty and the battery can be poor. Faults can cause these type of failures. You would normally replace the whole UPS.
If there is an interruption the system thinks the engine has stopped, the switch is at run and she tries to start while running, racks go to 100% as for a normal start, but on a running engine. Can cause a lot of damage. Difficult to fault find thats why we change the UPS.

regards

User avatar
JollyJack
Fleet Engineer
Posts: 1128
Joined: Wed Mar 24, 2010 3:57 am
Currently located: Eastern Canada

Re: Diesel engine overspeed

Postby JollyJack » Tue Sep 04, 2012 3:50 am

One more arguement for discarding electronic controls and relying on a purely mechanical device.
Discourage incest, ban country "music".

User avatar
JK
Enduring Contributor
Posts: 2697
Joined: Tue Sep 04, 2007 2:29 am
Currently located: East Coast, Canada

Re: Diesel engine overspeed

Postby JK » Tue Sep 04, 2012 4:19 am

you will never see it JollyJack.
I have seen a running ship service engine have the starter try to engage on a generator automation glitch caused by the tach pickup, never realized that the racks could also go to full. I think the sparks flying across the platform from the grinding bendix caught most of my attention.

jimmys
Officer of the Watch
Posts: 127
Joined: Tue Nov 16, 2010 4:09 am
Currently located: Glasgow Scotland

Re: Diesel engine overspeed

Postby jimmys » Tue Sep 04, 2012 5:53 am

What makes me think this could be the problem is the timescale. A power interruption can be 25 milliseconds and it can cause problems. Your system will not pick up faults if it is out. When it comes back on this is when you get the chip failure, the stored alarm is overspeed.
If she senses no speed (governor) or stopped she wants to start. On auto start the system thinks engine is stationary and calls for a start. On start racks go to 100% and start engages, the engines runs up and shoves the starter out. The governor takes over and pulls the racks back to idle. The engine can tolerate this 100% racks only for the start. It cant come on at any other time. If it does you a certain to get damage.
Checks along these lines are needed. Were you starting any heavy plant at the time, maybe switchboard voltage drops?? start it off.

regards

User avatar
The Dieselduck
Administrator
Posts: 2747
Joined: Sun Jul 22, 2007 1:41 pm
Currently located: Nanaimo, British Columbia, Canada (West Coast of Canada)

Re: Diesel engine overspeed

Postby The Dieselduck » Fri Sep 07, 2012 8:48 am

In my experience, overspeed are generally caused by stupidity or a mechanical fuel control failure, usually a nut or bolts that falls off. I've made it a point to myself on smaller machines to do a careful once over of the machine's governor mounts, linkages, wiring etc, as part of the oil change routine - 250-350 hrs. I have not experienced electronic failures causing overspeeds, although I am a fan of the idea of having a mechanical overspeed system on all engines - hopefully it is simple to operate, allowing for routine, worry free testing.

My most recent experience with overspeed, resulting in a 150 kW generator overspeeding, damaging the alternator, was the result of a lack of proper equipment, and subsequent lack of training to work around first issue. The engineer on duty was using what was shown to him to be the normal way to shut down a detroit diesel, which was by overpowering the governor linkage to shut down fuel. In a rush to do something else, things, of course, went awry, and he increased fuel. The funny thing with overspeeds, it does not take long to create damage. This incident was compounded by a lack of overspeed protection.

The generators now have overspeed protection, but more importantly, have a simple electro-mechanical way of shutting down - on off switch, hopefully preventing human meddling with the mechanical fuel control mechanism.

I hear new ships will run with one engineer and one dog. The engineer to feed the dog, and the dog to make sure the engineer doesn't touch anything.
Martin Leduc
Certified Marine Engineer and Webmaster
Martin's Marine Engineering Page
http://www.dieselduck.net

User avatar
Big Pete
Engineering Mentor
Posts: 817
Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

Re: Diesel engine overspeed

Postby Big Pete » Sat Sep 08, 2012 1:41 pm

One of the problems with overspeds is if the are operated by the governor, they are dependant on the governor and fuel pump linkages all being correctly adjusted. On several ships I have found these to be incorrectly adjusted after removing the governor / fuel pumps for overhaul. I have also found fuel pumps refitted out of line with the racks, causing them to "Bind".
Some engines using seperate cylinders and pistons for each fuel pump to move it to minimum delivery, others shut off the combustion air to achieve an emergency stop.
It must make sense to have an overspeed sensor (whether electrical or mechanical) that is completely independant of the governor and an Emergency/ overspeed shut down system that is completely independant of the normal fuel pump control.

Years ago a British coastal company called Crescent Shipping lost a small cargo ship. They had decided that they didn't need to carry an Engineer at all. The main engine was a B&W Alpha, medium speed. In bad weather the engine started overspeeding as the prop came out of the water and the mechanical overspeed trip operated. Nobody onboard realised why the engine had stopped and they were unable to restart it. ( you had to push a little button on the overspeed unit at the Port forward end of the engine to reset the trip) Consequently the ship went onto the Beach. But the company had saved an Engineers wages, so it was agreat commercial success.

BP
It is always better to ask a stupid question than to do a stupid thing.


Return to “The Workshop”

Who is online

Users browsing this forum: No registered users and 2 guests