Diesel generator - Pcomp high

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SanMarino
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Diesel generator - Pcomp high

Post by SanMarino »

Good day to all!

I have been lurking around here for a some time and learned so much from you guys. Just wanna hear some thoughts about my problem recently about our aux diesel engine (Hyundai Himsen 7H25/33).

I replaced fuel injectors(new atomizers, adjusted opening pressure according manual) and adjusted valve clearance. After a week I took performance tests and found out that pcomp is almost the same as pmax for all units. Pcomp were high reaching almost the same as pmax. After this, i tried to adjust again valve clearances and made sure it was correct also recalibrated the opening pressure of fuel injectors. Took again performance test after that and i had normal result for some units and the other were still with high PComp. After a week i took again performance test and all of them were back again to high pcomp. And also smoke from the funnel was fine at first but after a few days it produced darker smoke.

It could be the valve clearance because i made it when the engine was not in cold condition and messed up the timing of the valves causing to have high comp pressure? but i have done this with other engines and everything was fine. Im thinking also about the fuel injectors opening pressure dropped again causing to have ignition during compression(Atomizers were were not original from maker). Or it could be the device i used to take the performance test , but it seems good cause i get normal results for other engines.

Will appreciate all your response.
Big Pete
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Re: Diesel generator - Pcomp high

Post by Big Pete »

I don't think the tappet clearances would have much effect. I have sailed with engines where the maker sent out a service bulletin to increase the valve clearances by 50 % because it made the engine run quieter. If you had too little valve clearance the valves wdould not close and you would have low pressure. The fuel pressure before the pump rises so quickly that wrong pressure settings on the injectors will not effect the timing.
Is the engine developing full power and does it stop normally or does it tend to keep running?
Possible fuel timing issue, oil leaking from the injector cooling or elsewhere and burning in the cylinder?
Are the fuel rack and governor output readings the same on all the engines for the same power output? How about the exhaust temps?

Good luck and keep us informed.
BP
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JK
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Re: Diesel generator - Pcomp high

Post by JK »

We have found with fuel valves to go with the manufacturer and not knock offs. This may be your problem. What you think may be the same, may not be.
SanMarino
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Re: Diesel generator - Pcomp high

Post by SanMarino »

Hello, thank you for the inputs!

Based on BP's suggestions, the fuel racks have diferences +-3 to 5 mm from average, we adjusted it based from the exhaust gases and keep little deviation from each other. I tried to increased the opening pressure from 400 bars(which was from the recent service letter sent by maker) to 450bars( which was the original setting before they sent the recent service letter). But i think the thing that solved my problem was I tried to reset the racks all to zero by setting the governor load limit to zero then adjusted the linkages to let them have the same readings of racks.after starting, we got big deviations from exhaust gases ( -+30 to 50deg) then I took a performance test, the result was successful. We got normal pcomp now. And then i adjusted the racks based on the performance test i got.

Seems we got this problem from adjusting the fuel racks just to get good exhaust gas temperature without making sure if our sensors give the real readings and thus causing unbalanced distribution of load on each cylinder.

Thank you guys for the help!
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Re: Diesel generator - Pcomp high

Post by Big Pete »

Good News,

Most engine makers nowadays don't care what the individual exhaust temps are, the individual fuel rack settings and timings should be exactly as per makers manual and never changed, on a turbocharged engine small variations in exhaust temperatures, say 50 degrees between cylinders, have no importance unless the maximum permitted exhaust temperature is exceeded, in which case the injector probably needs changing or an exhaust valve is leaking.

BP
It is always better to ask a stupid question than to do a stupid thing.
popeye62
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Re: Diesel generator - Pcomp high

Post by popeye62 »

This is an interesting one because a Pcomp that is high has nothing to do with timing* or fuel. An overspeed could cause a high Pcomp but not in this case. When you take performance measurements the conditions are the same as the previous for spotting trends especially the load. It is not clear where you are getting the Pcomp from; reading it off your electronic draw card diagram (the top of the curve just before the dip at injection) or you are pulling each pump rack to zero and taking a straight pressure measurement. If the latter then it is likely that the fuel is not off regardless of the pump index and you think you are measuring Pcomp when you are measuring something between Pcomp and Pmax.
NB if this engine is fitted with dual valve timing (DVT) on the inlet and uses Miller timing I am presuming that this has been considered. Having said that, these would only reduce Pcomp not increase it unless* measurements were taken with Miller timing on then off.
As mentioned never adjust exh. temps they are an indicator not a controller, they are telling you something is wrong and a 50 degree deviation is an alarm state and in some engines a shutdown. Always use OEM parts.
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Re: Diesel generator - Pcomp high

Post by ThasleemH »

Hi all,
i have some queries regarding the same issue , but mine is little different from SanMarino's.
when i took performance of a auxiliary engine (Man B&W holeby 6L28/32H), i noticed that the pcomp and pmax values are almost same in all units .
previous engineer who handed over had done pressure test of all the injectiors in his time , found some were opening below manufacture specified pressure .
hence changed injectors with o'hauled ones(old nozzle , new spring , pressure tested to 320bar no leaks and atomization was satisfactory ).

performace taken with a MARIDIS MarPrime equipment .
Switchboard


generator total load cap:1250KW

Switchboard

KW voltage amps freq
806 447 1115 60.2


Cylinder Data
  • Cyl. No. MIP (bar) P.Comp.(bar) pmax(bar) Ind.Power (kW) % pump index Exh (°C) HT
    1 15.2 93.4 94.9 179.6 35.0 306.0 73.0
    2 12.6 100.5 101.1 148.9 35.0 303.0 73.0
    3 14.6 97.7 101.4 172.7 36.0 357.0 73.0
    4 14.4 98.2 100.6 170.6 32.0 342.0 73.0
    5 14.8 97.4 99.4 175.5 36.0 332.0 73.0
    6 13.5 100.0 100.5 160.0 35.0 335.0 73.0
    mean 14.2 97.9 99.6 167.9 34.8 329.2 73.0
what all could be reason for this type or performance reading?
kindly advise how to do setting on racks as discussed above in detail. with a UG8 dial type woodward governor.
currently all units are around rack index 3 when engine is stopped .
Attachments
AE1_MAN_6L28-32H_2023_0905_0349_SumReport.docx
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popeye62
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Re: Diesel generator - Pcomp high

Post by popeye62 »

Hello ThasleemH. For a moment there I thought we were going to be rich, you are producing 806kW without adding any heat, unfortunately, I then saw your SFOC which seems high at over 220 g/kWh. Your figures don't seem possible, I would expect at least 20b over Pcomp at this load (65%). Have you noticed any change in fuel consumption? All of the figures seem reasonable with the exception of the Pmax figures. T/C looks efficient. Is there anything wrong with engine performance-wise? Is the current normal for that load? Even your power factor is good. Any excess/discoloured smoke? I think the Pcomp figure is accurate but the Pmax is not. Have you tried taking a straight max pressure reading off the cock with a Heine or similar (MARIDIS MarPeak)? I would try loading it up (>85%) and take another set of readings. I don't know MARIDIS; is it on-line or off-line i.e. is it always connected or do you have to go and attach something to the cock manually? Is this genny running in parallel with another and does the other have similar load (kW) and current (I)?
ThasleemH
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Re: Diesel generator - Pcomp high

Post by ThasleemH »

Thanks for the quick reply .
I have to manually time it to check the consumption
Like there are no individual flowmeter to check the consumption .
Yes exhaust is little smoky . Not that dark. It comes in bursts
Yes they are running parallel , I had put the switchboard on manual and transferred some load to this generator to take the performance .load remains more or less the same but vary as some loads cut in ( such as main air compressor ) .
Maridis have to be connected to indicator cock , just like a dial type pmax indicator .
About the Amps, I have to confirm with electrical officer onboard or take a same capacity genei to same load and check , whether they are drawing same current.
I have one equipment used for main engine , which has got a stylus and drum , where you draw card paper and draw out the string. May be I'll give it a try .
popeye62
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Re: Diesel generator - Pcomp high

Post by popeye62 »

I don't think you can use the stylus and drum as the engine is running too fast and I don't think there is anywhere to connect it to. On the face of it, it seems to be an issue with the measuring equipment. How old is the vessel? How many total hours on the engine? Have you taken a set of readings on the other genny at the same load? The engine doesn't seem to have any performance issues. Is all the maintenance up-to-date? Bursts of smoke may just be load changes. You had to put load on to take the readings? What is the load on each genny when paralleled during normal sea load? Does load drift from one genny to the other or is it steady? Do you have a shaft alternator?
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Re: Diesel generator - Pcomp high

Post by ThasleemH »

yes there is a indicator cock for each unit and the connection is same , i have used it to measure pmax . you will be only getting the parallel lines, and you will have to measure with the scale provided with equipment .i did that to verify my other equipment was giving proper values,last time it gave me almost same values for pmax. that was on another geny.
vessel is 21 yrs old and this particular geny has done 85000 plus running hours total.
this geny is due for top overhaul, awaiting spares for the same . currently overhauling fuel pumps which are due.
Havent got the opportunity to take another perfromance yet .will be taking a performance after all fuel pumps are overhauled .
all other values are normal .my only issue is pmax being almost same as the pcomp. i havent got a clue why that is happening , given the history of replacing injectors which were pressure tested to satisfactory.
loads vary from around 480 to 500kw plus on this genei, and other genie is a smaller capacity genie which will have around 380 to 450kw plus .
we actually have 4 geny's , two 1250 kw and two 1050kw . so it varies depending on which geny's are on load .
but when two same cap. genies are run parallel they share the load almost the same , load keeps shifting though .power drawn by this geny is lesser compared to other same cap geny.
yes this geny's are used for electrical power generation , all are connected to respective alternators.
will revert with performance and updates
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