pv fiassco

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adreno1981
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pv fiassco

Postby adreno1981 » Mon Jul 13, 2009 10:45 pm

hey fellas ,

pv.jpg
pv.jpg (27.33 KiB) Viewed 3838 times



this pv diagram belongs to one of the units of a main engine , and this engine has been running like this since 4-5 years.guess what all has been done , changing of piston , exh valve overhaul , fuel injectors overhaul , but to no use.the indicator drive of this unit was overhauled in dry dock and put back.much observations were carried out in regards to this unit,including the timing check , exhaust temperatures n so on...unit remains the same.the diagram is not exactly similar ,but the one towards tdc is exactly similar , yeah, at constant volume , the pressure drop takes place...any comments buddies..till then...
adios..
adreno

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ArkSeaJumper
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Re: pv fiassco

Postby ArkSeaJumper » Wed Jul 15, 2009 11:37 pm

I think I would go back to the indicator drive, has a draw card been taken?

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Big Pete
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Re: pv fiassco

Postby Big Pete » Wed Jul 29, 2009 2:12 am

Hi,

This may be a stupid question, but have you tried changing or overhauling the indicator cock itself?
Big Pete.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: pv fiassco

Postby JK » Wed Jul 29, 2009 4:50 am

I edited the original photo to make it more viewable.

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Dieseldame
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Re: pv fiassco

Postby Dieseldame » Wed Jul 29, 2009 8:31 am

What model of make/model of engine are we talking about here?

Any chance there could be a small crack in the cylinder liner/ block or head? Also, you mentioned overhauling the exh valve, what about the intake valve?

DD

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Big Pete
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Re: pv fiassco

Postby Big Pete » Thu Jul 30, 2009 5:35 am

Hi again,

Further to my earlier post I have had problems in the past with totally spurious cards caused by blockages or leakages of the indicator cock, or leakages on the screw thread on the cock connection to the indicator machine.

If everything has been overhauled, all the fuel rack standouts on the engine are within +/- 1mm, injection timing is same as testbed, and there is no large variation in exhaust temperature, the exhaust sounds smooth when you stand by the funnel and there is no surging of the turbocharger, I don't think you have a problem with the engine. I would also check turbo RPM and charge air pressure from the Test Bed trials to see if they correspond to the fuel rack standout. though they can be hard to compare if you have a fixed pitch prop.

The problem is most likely with the cards you are taking. If you are getting good cards from the other cylinders, the indicator machine is OK and so is the method used.
The only variables left that are specific to one unit are the drive mechanism, which you say you have already overhauled and the indicator cock.
Q.E.D. as they used to say.

With regard to cracks:-
I had a cracked fuel injector on a MAN engine many years ago, this showed up as an intermittent water flow at the return hopper, there was no loss of water from the system, but when the engine fired, exhaust gas got pushed into the cooling space.

I also joined a ship with 2 medium speed MaK engines, and found that every time the load on the engine was increased to about 60% we lost cooling water pressure. We were not losing cooling water and no significant quantities of water appeared when we blew the engine over on air prior to starting.

Eventually I ran the engines steadily just below the the point at which we lost cooling pressure and manually increased the fuel rack standouts on one cylinder at a time until we lost cooling pressure or the cylinder was on full power.
Having determined which cylinders were causing the problem we changed the cylinder heads. This cured the problem. We hydraulically pressure tested the heads immediatly after they came off the engine (still hot) and found small cracks in the combustion face. However, when the heads were sent to a workshop ashore (cold) they could not find any leaks. However, after changing about 4 heads we were able to run both engines at full load. So eventually we had a success.
I suspect someone, in the past had run the engines dry and not recorded it.

Peter

It is possible that if exhaust gas is dissolving in the cooling water it may turn the water acid so chemical testing of the ph may indicate this is the problem. But I did not find the cooling water acid when I had problems.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: pv fiassco

Postby JK » Thu Jul 30, 2009 4:21 pm

I suspect someone, in the past had run the engines dry and not recorded it

Or maybe drained the engine immediately after shut down to repair something?

Excellent posts Big Pete, I wish you had been at my elbow while I was studying!!

astat101
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Re: pv fiassco

Postby astat101 » Tue Dec 01, 2015 12:34 am

Hi, Just a note on turning water to acid... if the air has sulphur content it is possible that as the air cools, condensation forms and before you know it you have sulphurinc acid. I work for a company called Vestas aircoil who design and manufacture charge air coolers and aware that this has been an issue in the past.

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Merlyn
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Re: pv fiassco

Postby Merlyn » Tue Dec 01, 2015 4:24 am

We used to sniff the freshwater coolant with a four or five gas exhaust analyser machine and see straight away any excessive HCs present in the coolant system indicating a cracked head problem present.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Big Pete
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Re: pv fiassco

Postby Big Pete » Wed Dec 02, 2015 12:08 am

I see this has resurfaced after a year and a half, but no feed back from Adreno 1981.
Please guys, if you ask a question, please give us feed back, as to what the eventual diagnosis/ findings are.
"Close the Loop" in control terms.
BP
It is always better to ask a stupid question than to do a stupid thing.

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Merlyn
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Re: pv fiassco

Postby Merlyn » Wed Dec 02, 2015 1:06 am

I endorse that BP 100% , I am still awaiting the push rod outcome, could it be something different or not? Can there be something out there that none of us have yet encountered? Perhaps we will never know and it remains one of life's mysteries.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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D Winsor
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Re: pv fiassco

Postby D Winsor » Wed Dec 02, 2015 6:28 am

Agreed a little feedback from adreno1981 would be nice in this case.
I would like to know what type of indicator is being used, is the indicator strictly dedicated to that cylinder or is the same indicator used for all cylinders and if the indicator is mechanical or electronic?
Where adreno1981 referred to a single exhaust valve makes me think that the engine is either a B&W or Sulzer RTA which have 2 injectors per cylinder. If this were the case and where because of the difference in length of the fuel line between the primary and secondary injector, the secondary injector only fires at near maximum power and usually injects later in the stroke. I suspect that the issue could be in the rack setting for the fuel pump causing too much fuel to be injected by the secondary injector. I've seen fuel racks adjusted in order to supply more fuel, when after the injector was pulled found to be clean and testing OK was thought not to be getting sufficient fuel to fire. An issue with the primary injector would prevent the secondary injector from firing because there would be insufficient pressure in the system to open the injector. By forcing the secondary injector to inject more fuel than is required, this could be an explanation for the sudden rise in peak pressure at constant volume phase of the stroke. I've also seen the injection pressure setting on the secondary injector deliberately set lower than recommended in order to make the injector fire
Troubleshooting 101 "Don't over think it - K.I.S.S. it"


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