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strange combustion in 510rpm 4stroke marine diesel engine
2

strange combustion in 510rpm 4stroke marine diesel engine

strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Very strange,

We have experimental v12 engines, 9000hp each, but they smoke like hell.  People think we're burning cokes or something.

If we look at the P-a diagram of the combustion (pressure vs crank angle)We see that the ignition delay is rather long. The initial ignition is very "agressive".  It rises very fast, more an explosion than a combustion.  And most strange of all, the rest of the cycle, the controlled combustion, has always a tripple peak curve.  Somehow the pressure in the cylinder goes up and down in peaks, instead of just going up or down.  If I look at it, I think there are 3 explosions, a big one followed by 2 small ones instead of one smooth combustion.  Does anybody has ever seen anything like this before?? Does anybody knows a web adress where combustion problems are explained by P-V or P-a diagrams.

I will try to upload a graph later.

I must admit that the engines are running at 70% max, because of crankpinbearing problems.  Maybe caused by the same strange combustion????

And also I will admit, because the turbochargers are surging a lot, we reduced the scavenge air temperature to a very low  30°C only.  We use 180 cSt HFO, but even on MDO, she smokes like hell.

The TDC pressure is 60 bars, pressure peaks during combustion go up to 95 bars.

I hope anyone has any idee???

RE: strange combustion in 510rpm 4stroke marine diesel engine


It would be most helpful to all if you could explain more about when it smokes and what is meant by "experimental".

RE: strange combustion in 510rpm 4stroke marine diesel engine

Norcape I would guess that your engine is running to little boost or the injection pressure is to low.

From the fact that you are also seeing mega pressure rises I would also say that you may be to advanced on your injection timing - however increasing the boost will compensate for this.

In effect you are injecting the fuel into the cylinder before combustion can occur, then when conditions are right for combustion the whole charge is burning in one go - I bet the engine is vey noisy as well.

My recommendation would be to increase the boost as much as possible, this will reduce the smoke. Then adjust the rail pressure & timing to bring back SFC & Emissions.

Thanks

MS

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
They always smoke.  Manouevring in port or at full load at sea, there's always a big black cloud comming out of the funnel.  It has always been there! from newbuilding!

The engines are experimental.  They are built by a big japanese shipyard/steel company.  They thought it was a must to have there own engine design.  They built six of these engines, and afterwards cancelled the whole project.

2 prototypes ashore, 2 in our vessel and 2 in the sistership.  They al have the same smoke problem.

So there has never been any follow up on the engines. It stayed an experiment. The shipyard company nowadays makes engines under license smile  MAN's they told me.

RE: strange combustion in 510rpm 4stroke marine diesel engine

I've seen these triple peaks on gasoline engines where cylinder ionisation has been datalogged in attempst to use ionization currents as an analogue of cylinder pressure.
The triple pressure-pulse plots I saw were associated with knocking due to over-advance. Does that tie up with over-advanced fuel injection in a big diesel?

Bill

RE: strange combustion in 510rpm 4stroke marine diesel engine


Norcape, how is the engine being throttled? Is it by means other than control of fuel delivery?


RE: strange combustion in 510rpm 4stroke marine diesel engine

Hello everybody:

According to the post, I can understand that the cylinder pressure graph shows "after firing" phenomena, with pressure increases during the expansion stroke.

If this is it, let me tell you that we have to stand up to a similar situation in our medium speed Diesel engines, 514 RPM, above 88% of maximum load. The manufacturer when asked about this subject said that, the reason for the "after firing" indication is a pressure oscillation in the measuring channel between the combustion space and the measuring point.

The amplitude of the oscillations may vary depending on engine load, speed, volume in the bore (between combustion space and measuring device, etc.).

They handed over a graph with lab tests at full load , showing the measurement of the firing pressure, simultaneously in the combustion chamber and from the "indicator valve" on top of the cylinder head (where normally is connected the measuring device).

The two curves are really quite different. The curve of the "in cylinder" measure is certainly smooth all along the combustion arc; but the second one, shows those peaks.

In our engines, with loads around aprox. 88%, those peaks do not appear.

Hoping this can help you

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
I have been thinking about bad measurements.  But the measurements with the same equipement on the auxiliary engines (2x 8 cylinder diesels (750 rpm) shows a clean nice graph.  Both measuring points are at the indicator valvese.  Both have a valve, and a length of pipe.

But the main engines have 2 bends and the lenght of the pipe is almost the double.  

It is a possible.  Big question?? How can we be sure??

RE: strange combustion in 510rpm 4stroke marine diesel engine

When measuring the cylinder pressure at the indicator valve you will get a totally incorrect pressure curve. The compression may be fairly good but the combustion will (seem to) be delayed and the start of combustion too steep. There will also be oscillations in the pipe from the combustion chamber to the indicator valve. Three pressure peaks sounds like oscillations. There may of course be something fundamentally wrong with the design of the engine but that is impossible to analyse without thorough investigations. If you need to analyse the combustion you need to put the pressure transducer into the combustion chamber. The quality of the pressure curve can be analysed by plotting a pV diagram with logarithmic scales on the x- and y-axis. You should get a straight compression line and almost straight expansion line. I think Heywood, Internal Combustion Engine Fundamentals has something about that. If you want to see the influence of the pipe you can put a piece of pipe and two bends on the indicator valve of one cylinder on you auxiliary engines. You will get a different pressure curve.

The smoke problem sounds like bad injection. At high loads you should have some kind of boost pressure and if the engines are still smoking the problem should be elsewhere. I assume the engines are quite old and then new more efficient turbochargers and higher boost would help but if the injection is bad no turbocharger can cure the problem.

The injection nozzles are dimensioned for 100% (or 110%) load and if you only run 70% load you could decrease the injection nozzle hole area by 30%. Do not decrease the area too much since this will increase the injection pressure and increase the load on the pump cam and roller. Smaller holes should improve combustion and decrease smoke. You can also have a look at the injection nozzle hole angles. Look at the piston where the fuel sprays are hitting and make a drawing of the combustion chamber and see if it seems logical. Your guess will be as good as the original guess the Japanese made. As always, only change one parameter at the time.

For this you would need new nozzles and there may be companies interested in making nozzles for 48 cylinder burning HFO if the OEM is not interested. You can also write “Powered by XXX” with 5 m high letters on the side of the ship if the engine maker is not interested in helping you smile

RE: strange combustion in 510rpm 4stroke marine diesel engine

I think the conglomerate that owns the shipyard and built the engines also builds some decent motorcycles, but this may have been their first and last foray into big Diesels.

I wouldn't paint their name on the boat, or threaten to do so, yet.  Instead, find their engine guy, ask what he would do differently if he had the chance, and solicit his help in figuring out how these engines are different from the MAN engines that superseded them.  That might give you a finite chance of success at improving their performance wrt smoke.

Mike Halloran
Pembroke Pines, FL, USA

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello, I'm back from the ship again.  Thanx for all your responses.

I have been checking some things out, on your advices.

1. Is there a way so I can add a picture or a graphic to this board???

2. Pressure ossicillations in the measuring tube:

I've been checking this out.  There are 3 curves of 90 degrees in the pipe and 2 curves of 45 degrees.  I have been studying the pulses and there are much more peaks than the three I mentioned before.  It seem like we're having some kind off a harmonic.  Different sinusus with different wavelength causing a mix off positive and negative resonances.

I contacted the manufacturer of the measuring device, he said it's impossible.  But I did the same test, with full trottle and with this only one cilinder at minimum fuel injection (while the other 11's are at full load.)  And guess what, the pulses and peaks are almost the same.  Even if there is no combustion any more.

So maybe the measuring fault is indeed the cause of the "tripple peaks"

3. Smoke:  The 2 turbo's of one engine has been fitted with smaller nozzle rings, we have more boost air pressure, the exhaust temperature is lower, but... still smokes like hell, no improvement visual.

When we changed a cilinder head last weak, I noticed there' s a burn pattern on the piston.  It's a print of the 8 injector conusses.  I checked it on the injector test bench, and downward angle is nearly 25 degrees.  I have no idee what influences the swirll of the compression have on this conus, but it looks like the injector is just spraying its fuel on the piston instead of in the air??????

I have asked the chief engineer if he could look the details of the injector up for me.  Maybe the downward angle is not correct.  I will try to convince the chief to ask the question to the Bossch representative.  (it are there injector tips!)

4.  A big question remains.  What causes the problem, bad injection, to low a compression, not enough air??
The bosses are convinced it is the last option, but I start to have second thoughts. So I begged the chief engineer for an exhaust gas analysis.  That will tell us if there is yes or no enough air inside the cilinder.

One thing for sure, this story will be continued!!!!!!!

And if I find a way to put pictures on the forum, I will show you the details.

RE: strange combustion in 510rpm 4stroke marine diesel engine

My _limited_ understanding says:

- Diesels always run with excess air.

- Low-smoke Diesels use higher injection pressure or other means to get a more finely atomized injection spray.


Maybe your chief can get the Bosch rep to take on your boat as a personal project; he could get some good PR out of it.

Mike Halloran
Pembroke Pines, FL, USA

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
I finally discovered it, it was here al the time, right before my Eyes,

Picture of the ship with the obvious big black cloud, both at sea at full load and in port at part load.



RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
OK Pictures of the piston with the combustion marks.  The marks shows the spot where the injector puts the fuel.

Is it correct to state that there may not be a visual spot like this on the piston??  

Is it correct to state that the marks are to close to the center of the piston??

Does anybody recognise such pattern??



RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
I scanned a drawning of the engine.  In the close up of the cilinder top, I've drawn in red what I GUESS is the injection at this moment.  In Green I have drawn what I THINK it should be.

The red patern is drawn, based upon measuring the mark on the piston, and the estimated angle of injection (visual on the test bench).  I haven't found anny official information about the nozzle.





Is there any nozzle specialist who can confirm this??  Or are there any other options, remarks, warnings???

I have to convince the bosses that we need to try another nozzle tip!!

RE: strange combustion in 510rpm 4stroke marine diesel engine

I am not a diesel expert, but info I have seen on diesel combustion (including a couple dozen research papers) would indicate that you want the green angle.

I also notice that there is no swirl to the pattern. Most modern diesels induce swirl to get more complete combustion. You only get the proper air/fuel mixture on the outside of the fuel stream from each nozzle hole. As the fuel enters the cylinder the outside particles start shearing off and atomizing into small enough droplets to combust cleanly. By inducing swirl you spread the stream out, help atomiz the fuel faster, and creat more area with the proper ratio. You can get too much swirl (which obviously isn't your problem :) ), which causes the tail of one stream to run into the one next to it which no longer helps.

Along with changing the angle you may want ask Bosch about changing the number of holes to 9 or 10. This will affect your atomization characteristics as well. More holes should improve the situation, but you also have to consider how much of the injector tip is left.

Have you measured the injection pressure? Low pressure would limit the fuel atomization. What is you timing set to? Do you know what the injector duration is?

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello jbthiel, thanx for your reply

There is a swirl in the cilinder.  After some years, Mitsui changed the cilinder heads and installed swirl plates at the inlet valves.
This was done to force the inlet air in the cilinder under a certain angle, and so introduce a swirl trough the cilinder.  But maybe the fuel doesn't get to the swirl pattern area"??
These swirlplates have been taken out for several years because they didn't improve combustion, and they get dirty very soon.  We got new ones now, but we have to clean them every month!! (2x2x12 swirl plates = a hell of a job).
The design of the piston doesn't improve swirl.  There are 4 area's sunk in the piston for the valves.  So you got some "onstructions" standing just in the flow of the swirl.

The Fuel injectors are set to open at 400 bar.  After some running time, that pressure drops.  The spring in the injector get worn out or something.  It happens that we take out an injector and the opening pressure has dropped as low as 260 bars???? (after 2500 running hours)

What actual pressure the fuel pump reaches during injection, I don't know.  I haven't measured it, I don't have the tools to do so.

The pump starts the compression at 14,5 degrees before TDC.  I do not know the duration of the injection.
  

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
History

The ship in her early days, under the name Tipperary as she was built...  Smoking!!!

RE: strange combustion in 510rpm 4stroke marine diesel engine


The 4 valve notches are almost universal on Diesel engines.

Compared to a truck engine, the spray pattern shown looks similar but more intense. The aim looks about right but I have not seen the pattern extend up onto the flat part of the piston. Each area is also rather wide. It's almost as if the injector is designed to work with a larger piston.

  

RE: strange combustion in 510rpm 4stroke marine diesel engine

Here is a picture of a CAT medium size engine (8-11L) spray pattern. A Cummins picture a saw seemed to indicate the future injectors might get even flatter in the coming years. There is a lot of work going on right now to analyse the actual atimization in a running engine - this allows much more accurate computer models which should improve the engines quicker and cheaper.



I also found some info that the small-med sized engines are going to increase the number of injector holes to 8+ for emissions, power, and efficiency. They want to reduce the holes from the current minimum of 125um to ~50um. (or 0.005" to 0.002") Some research by GE on locomotive engines was looking at 10 holes nozzles.

That injection pressures sounds kind of low to me, but I have no experience with engines this big. Sounds like you are "pouring" the fuel in. :)

RE: strange combustion in 510rpm 4stroke marine diesel engine

Hello everybody:

Hi Norcape.  Running medium speed engines on residual fuel oils, under high operating temperatures conditions,  piston crown and exhaust valves deposits build-up and corrosion are a significant problem. There are also problems with deposits and corrosion on turbochargers (nozzles and blades) and in the exhaust gas boiler (when a waste heat boiler is installed).

But, in addition to the stated above,you must have to take into account that deposits (like that on the piston crown of the pictures) can be a result of one or a combination of the following facts:

- Problems with the combustion: rich or lean mixture.
- Injectors tips damaged or leaking.
- Injection pumps working out of order.
- Earlier or late injection timing.
- Delayed (more than normal) ignition: gives as result unburnt fuel.
- Inadequate fuel viscosity.
- Turbochargers malfunctioning.
- High water concentration in the scavenge air (if the water separator and cooler drainage system are not
  operating correctly).

Regarding with your piston, the exterior area of the flower shape shadow on the piston crown is an indication of unburnt fuel. The piston deposits can be, as well, residue from the thermal degradation of cylinder lubricant.

It would be advisable to check out the lube oil quality, this is TBN (Total Base Number), Calcium content, etc., and of course, the sulphur content of your fuel oil. Sometimes, depending on the values of these components and the conditions of operation,  they become together in really "bad boys".

As a general information on this subject, you can visit this site: http://energy.bmstu.ru/eo2/diesel/d11eng.htm#examples

I hope this can help you.

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello 21121956,

This is truly a educating site.  I've seen and learned a lot.  I will need some time to process everything smile

Tomorrow I go back to the ship for another 14 days. I will search and find as much details about the current injection nozzles as possible.  There must be some details somewhere.  Injection angle, velocity, ... even if it was just a production number...

I will also search for details from the newbuilding.  What tips did they use with what kind of injection pattern.  There must be something somewhere.

And finally I will try to convince the boss to ask the nozzle facturer if these are the correct nozzles for the engine.  

I hope it is succesfull

Greatings

Norcape

RE: strange combustion in 510rpm 4stroke marine diesel engine

I like what jbthiel said.  There is no turbulence in this chamber to mix the air with the fuel.  Look at the squish band in the cat chamber in his second post.( Black, flat area on the right side)   When the piston gets to TDC, the air trapped between the head and the squish band is expressed into the combustion bowl at high velocity, creating a highly turbulent 3-dimensional swirl shaped like a doughnut.  

Also, the pattern on top of your piston indicates direct droplet impingement on the relatively cool piston top.  This probably delays combustion significantly and results in low efficiency.  Instead of tiny droplets bursting into flame, you have a puddle of fuel on top of the piston sizzling like a drop of water in a hot skillet.  So a lot of your diesel fuel just gets scorched, and goes out the stack as soot instead of going into your prop shaft as mechanical work.  

Flatter injector pattern, smaller droplet size, are things you can do easily.  New pistons with Different piston crown and a Ricardo chamber would probably be the best thing, but then you really WOULD have a prototype engine.  Fooling around with injector timing migh pay off: either inject it at the instant of greatest turbulence, or advanced enough so that it does not squirt directly onto the piston crown.  

RE: strange combustion in 510rpm 4stroke marine diesel engine

ISTR that the fuel used is often heated just to make it flow, so this idea might be problematic:

I'm wondering if refrigerating the fuel going into the injectors would raise the injection pressure and improve atomization?

Mike Halloran
Pembroke Pines, FL, USA

RE: strange combustion in 510rpm 4stroke marine diesel engine

"There is no turbulence in this chamber to mix the air with the fuel."

The toroidal motion you mention was certainly something that was aimed for in European truck diesel engines a few years back.

The re-entrant bowl with centre peak in the crown of the piston was there to get the squish motion to provide this fast-moving air 'toroid' into which the fuel was injected.

Norcape mentions the swirl plates fitted to the ports of these big marine engines - the 6 litre truck diesels I had a minor involvement with had a fairly complex twist cast into their inlet ports to get the inlet air to rotate in the cylinder during the inlet stroke and the majority of the compression.
In doing this, the 'toroid' was not only rotating in on itself but rotating about the vertical axis of the cylinder as well, with the object of maximising mixing.

JimCasey, when you mention the 'Ricardo' chamber, aren't you referring to the Ricardo Comet chamber used in indirect-injection engines?
This ship's engine piston, etc., looks just like it's smaller direct-injection truck brothers to me.
http://mmc-assess.tuwien.ac.at/data/sfrm/alsaffil/kolben1.jpg

For what it's worth, IMHO (hate that, but it seems right here):
White/grey smoke:
Engine too cold
Injection too late
Light levels of (dark) smoke:
Under rated load, performing nicely
Lots of smoke (per the pictures)
Injector holes too big
Injection pressure too low
Injection too late / continues too long
Injector not suited to the type of fuel in use
(e.g. fuel too viscous/cold?)

Bill

RE: strange combustion in 510rpm 4stroke marine diesel engine

I fully agree about the intake port shape, but I didn't want to get into that because of Norcape's experience with excessive contamination and the unlikelyhood that this radical of a modification being done. I have seen the "dog leg" intake ports on everything from a 1.9L VW TDI to a med-large (~15L?) CAT engine.
On many of the new 4-valve diesels the valves are twisted compared to the traditional gasoline design. The short runner goes straight in, but the long one has a "dog leg" to induce the swirl.

As for the piston, it doesn't have the vertical lip like the latest pistons. (mexican hat vs. toriodal) I think that will limit the amount of mixing that is going to happen. If you had the swirl plates installed right before the pictures were taken it doesn't look like they were doing anything. (except increasing your workload :P )

I think the best thing to concentrate on is the injection system (pressure, angle, # of holes, etc.) You might also ponder if there could be improvements made to the swirl plates to induce more swirl without adding a ton of restriction.

WGJ - agree with everything, but I would add that adding fuel too quickly can also result in incomplete combustion. (though that doesn't appear to be an issue here) The inner part of the stream doesn't get a chance to properly atomize.
See my thread 71-26352 from July02.

RE: strange combustion in 510rpm 4stroke marine diesel engine

Changing the injector nozzle angle would definetly help the impingment problem.  I would also be sure that you are using the correct gasket for the injector.  You may want to experiment with thicker gaskets to reduce impingment.  Are there any inpingement marks on the head?
Measuring the peak injection pressure would be useful.  If it is indeed low, then reduceing the nozzle area would raise the pressure and lengthen the injection period.  On high speed diesels the injection period  usually occurs before combustion is initated.  Medium and slow speed diesels can control burn rates based on injection rates.

More holes of smaller diameter, keeping the same wall thickness in the injector, will also increase the length of the injection spray.  Hard to tell from picture if there is any impingement on the cylinder walls?  
Looking at the photos, infact perhaps more penetration is required.  Making the L/R ration bigger would help in this situation.  Leaving the nozzle wall thickness (L) the same, and reducing the hole size results in more penetration.  The resulting spray pattern would be longer and narrower
(reducing impingement on the piston). More holes of smaller size, so that the total nozzle area is the same, would not change injection pressure.

I would assume that changing the injection cams is not feasible.

Try changing the injection timing from pump port closing of 14.5 degrees BTDC, to about 12 degrees.  Later injection should result in less fuel being injected before combustion initiation.  Less ignition delay, smother pressure rise rates.  Shiming pumps to achieve late injection may be possible.

RE: strange combustion in 510rpm 4stroke marine diesel engine

Norcape,

Good day. There is nothing could be changed on your engine now unless your management or your owner are willing and it would be costly. Please check first and try to analyse shop test of this engine. If you can find this shop test result, you can see different parameters at different loads. And you will see power curves. All ships engines are tested before and during sea trial, this will not pass classification society where vessel belongs if during those tests, engine emitted too much smoke.

Brgds,
cengrtecs

RE: strange combustion in 510rpm 4stroke marine diesel engine

Hi all!

cengrtecs is absolutely right, the original testbed report is the best starting point in order to analyse properly the problem. Best thing to do is to compare, at similar rev's and loads, the actual engine parameters to those at the factory's testbed.

Some other feelings:
injection timing:
14° seems rather late for me! for example, we operate 600rpm stationary units on IF380 HFO, those units start injection at 25° (initial timing to be checked in testbed report)

turbocharger surging:
this occures mainly in two situations: actual air volume delivered by the TC is too high for the engine > generates surging!
The TC can deliver too much air to the engine when the exhaust nozzle ring is seriously clogged, what often results in exessive TC speed and charge air pressure...

injector opening pressure:
400 Bars is not so bad, our above mentionned engines have the injectors adjusted at 350 Bars, after 2000hrs, we find some injectors that dropped to 260 - 280 Bars and service them

smoke:
understood your engines run relatively low loads upto 60-70%. In that load area, smoke is quite normal (but not as much as shown on your pictures) Our 600rpm engines (8500 HP) are allmost smoke free from 80-85% upto full and overload.
Boost pressure is around 2,2 Bars at full load.

Could you put the initial tesbed reports in this thread together with your actual measurements & readings?



RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello everybody,

Thanx for your repies:

I'm back from the ship and i've got the following items:

We did tests on the injector test bench and found the average injection angle to be 124 degrees.  This matches the  center part of the mark on the piston.  Together we searched all the books we have but cannot find an official injection angle.
There exist a modified injector. They made the bore of the hole longer.  Is this to reduce the velocity of the fuel??  The term low velocity nozzle has been used.  This modified type exist since 1989, and it was especially for smoke reduction.
Right now we used the old type nozzles, but the chief engineer said this was only because the previous time there where no modified nozzles ready to use??

We did a unit last week, it was already 3 months overdue!  I took some pictures, and this is what we found:



Obviously one of the injector holes was plugged by the carbon.

If we have a look at the side of the piston, we can see plenty carbon build up.  It has been "grinding" the liner with a damaged liner (worn surface) as a result.  The top piston ring was broken on one spot.  Probably it was stuck by the carbon.  (increased blow by?)



Once the piston was out, I took some detailed pictures of the marks.  The wite ruler is placed directly on top of the mark.  It shows the 3D form of the piston on the place of the mark.



Overhere a cut out detail.  The ruler above shows it dimensions in inches.



So what do you guys think of these pictures??


We mentioned the swirl plates at the inlet valves before.  There seems to be a little misunderstanding, so I took a picture as well.  The pipe in the center is the support of the valve seat grinding tool.  But it shows the position of the inlet valve stem.  The white dots everywhere is dust from this grinding process.
Originally there where 3 vanes, but the one in the back is grinded away already, because it was obstructing the air flow to much.



And now the "good news".  The ship has been spotted in the port of Rotterdam for smoking.  Now there is a bit of official pressure on the company to do something.
A specialist has been invited to do some measuring of the engine.  It will take a couple off months before everything will be organised.

Some of you mentioned the original test results.  I can make a copy, but...

Original test were made on diesel oil, not on heavy fuel.
Since the original test, there has been some modifications (nozzle rings on the turbo, increased cooling water temperature, modified fuel pumps (the original ones could not handle the HFO as there were supposed to de) ...

But, what we see today is:  The max combustion pressure is less high then original.  The exhaust temperatures are higher then originally.  The boost air pressure is also higher then originally.

I will try to take a copy with me next time.

Greatings and happy xmas to all of you     
 

RE: strange combustion in 510rpm 4stroke marine diesel engine

Here's a link to a company (DUAP) which is specialized in Diesel injection systems on large Diesel engines. They might also be able to help you: http://www.duap.ch/ (The company is better than what their website might indicate.)

(I haven't read the entire thread, but regardless of the size of the engine, fuel should always be kept away from the 'cold' cylinder walls. The piston crown looks rather flat to prevent this from happening).

RE: strange combustion in 510rpm 4stroke marine diesel engine

Nice investigation work! IMHO the green spray should be much better than the red one. Fuel that is laying on the piston will not burn. You want air and fuel mixing in the combustion chamber. One problem you may run into is spraying fuel onto the cylinder walls but looking at your recent pictures I cannot imagine that cylinder wear will get worse than it is now.

If the injector opening pressure really drops from 400 to 260 bars the injection event must be totally different. But I assume that the engines are still smoking with 400 bars opening pressure and new nozzles so this is not the root cause.

The swirl plates look very interesting but I do not think they are more than plasters and they cannot fix the original problem. If they really need cleaning every month there must be quite a lot of backflow through the intake valves. Either the valve timing is really wrong or then the turbines or exhaust pipes are clogged. Do you measure the exhaust back pressure?

It is almost like you are breaking some law of physics in your engine now. Higher charge air pressure should give higher cylinder pressures and lower exhaust temperatures. If the root cause is a delayed combustion then there will be more energy to the turbine and the boost will go up. The exhaust temperature may go up too but cylinder pressure will go down. Clogging of the turbine may also give a similar effect. The fuel pumps could be worn or wrongly made or then the TDC mark on the flywheel can be wrong.

I think there may several design issues that are wrong with these engines and then adding some wear and clogging then you end up where you are now.

RE: strange combustion in 510rpm 4stroke marine diesel engine

The swirl plates seem to have been optimized for ease of manufacture.  It appears that the halves of each plate will fight each other, e.g. one half is bent to induce cw swirl and the other half is bent to induce ccw swirl.

Mike Halloran
Pembroke Pines, FL, USA

RE: strange combustion in 510rpm 4stroke marine diesel engine

Mike is right. The swirl plates won't work. I would try it without them, or fabricate ones that will work.

Regards

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RE: strange combustion in 510rpm 4stroke marine diesel engine

In even a well designed compression ignition engine you can make it smoke by over fueling it.  All that black stuff going up the stack is unburnt fuel which is not contributing anything to crankshaft horsepower.

I am not a boat person, but I have owned trucks and I had drivers that thought that power was everything and they would have injectors from higher HP engines put into my engines by their buddies and they would smoke like all get out.  Whether they actually got more power by doing that or just the placebo effect because they thought they had souped the thing up is debatable.  (They did manage to burn up some expensive engines.)

When I would put the right injectors back in, it would run as designed without excess smoking in all but the most abusive driver error situations (mashing the gas when there weren't enough rpm's to suppport the fuel being added.)

I would suggest having the injectors modified to put in slightly less fuel so that the fuel that is put in can combust and produce the power you want.  Has anyone done any combustion calculations regarding fuel air ratios?

rmw

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello, everybody

There seems to be a little misunderstanding about the swirl plates.

Originally, they were not installed.  It was a original Mitsui modification, because they thought the fuel was not mixing with the air.  Or the scavenging cycle left some parts of the combustion space with exhaust gasses.
So they made this swirl plates to let the air "swirl in the cylinder".  Not around the valve.

So I put this extra picture of the cylinder head, You can see both air inlets with the swirl plates.  Everybody can imagine the purpose.  Question is will it work if the valves are in front of it???



The swirl plates are getting very dirty.  I know when the engine is idling, we have some back flow through the inlet ports.  And this is a ferry.  We are in port every day and every day, we have to pass a lock.  During the time in the lock, the engines are idling for half an hour, sometimes even longer.

RMW: For the question about overfueling it.  I don't think were overfueling cause the engine runs only at 70%.  This is because we had serious problems with the crankpin bearings.

But even when arriving in port, with a hot engine and reduced power, she still smokes like hell!

One extra question rose about the fuel spray on the piston.  The engine is stopped after idling.  And maintenance is always done after we passed the lock.  Is it possible that what we see on the piston burns away when the engine is working full power??  What we see is only the result of the manouvring through the lock??

Greetings

Norcape  

RE: strange combustion in 510rpm 4stroke marine diesel engine

Diesel needs to be injected onto the piston cavity in order to get it to disperse properly. Before they were capable to manufacture injection nozzles with several orifices, they used to spray one single jet straight down directly onto the piston cavity, where it was dispersed and redirected to the center of the combustion chamber. Injection angle always depends on the shape of the cavity on the piston crown. (Fuel speed is too high such that it would stop and sit on the piston crown.)

Also, if the diesel is injected such that it hits the cylinder walls (too flat) there's a high probably that fuel will not be thrown back to the center of the combustion chamber, rather it  will be dispersed onto the cylinder walls (cooler and larger area) without getting the hot air in the center needed to burn properly.
Diesel engines always run lean. Ideally all the fuel is in the center of the combustion chamber and there is a fuel-free insulating air cushion sitting on the cylinder walls in order to increase combustion temperature and ensure complete combustion.

In the picture from jbtiel the cavity in the piston crown prevents fuel from reaching the cylinder walls eventhough the injection angle is relatively flat. Also, dispersing and evaporating fuel on piston crown will assist cooling it.

RE: strange combustion in 510rpm 4stroke marine diesel engine

Now I see.

The right hand port will swirl the charge into mostly free space, but the left hand port will swirl the charge into the head of the right hand valve.

The right hand valve is swirling against a cylinder wall which may carry fuel to the wall. I wonder if aiming it in slightly might help. Probably not as to get effective swirl, the air must run around and so will be contained by the cylinder wall.

Does swirl really help or does it just act as a centrifuge to throw more fuel against the cylinder wall.

My thoughts for what there worth bearing in mind I am not a diesel guy and especially not a big diesel guy.

A fuel shot, through high pressure multiple fine aperture injectors at a steeper angle more to the centre of the piston.

Inject fuel at higher pressure for shorter duration.

Ensure injection timing is optimal.

Ensure valves are sealing.

Ensure cam timing is correct and suitable.

A deeper smaller diameter dish in the piston.

Maybe higher coolant temperature.

Maybe preheat the fuel.

Maybe higher engine oil temperature (to let pistons get hotter.

Remove one or even both swirl plates.

Increase compression ratio or turbo boost.

Regards

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RE: strange combustion in 510rpm 4stroke marine diesel engine

Ah.  Now I see what the engine guys were trying to do.

The swirl plates as shown would induce some swirl in the chamber, with the valves full open.  With the valves less than completely open, they just get in the way, and in the presence of swirl, might induce the backflow you detected.

I wonder if removing one set of swirl plates from each cylinder would help?  Have you tried that?



Mike Halloran
Pembroke Pines, FL, USA

RE: strange combustion in 510rpm 4stroke marine diesel engine

I read this post with great interest and my opinion on the possible cause is based on the following assumptions; the stroke is in the 375 to 400 MM range and the fuel injection on time is in the 8 to 12 millisecond time frame.  The great photos show the injection pattern on the top of the piston and the injectors are identified as on a 124-degree angle.

However, my rough calculations show that at even at the low 510 RPM the piston would move far enough down the bore (over 20 MM) for the fuel injectors to continually spray ATDC on the bare cylinder walls.  I also assume the engine has relatively cooler cylinder walls (due to unlimited cooling source) and would condense the injected fuel thus always causing smoking even at low power.

Since this smoking has happened when it was new, I assume that the inherent design is basically wrong.  The main area of the problem is the lack of a true deep bowl in the top of the piston and the angle of attack of the injectors that correspond with this deep piston bowl design that would prevent this from happening.

Again, just some food for thought.
al1

RE: strange combustion in 510rpm 4stroke marine diesel engine


Smoking all the time is certainly supportive of poor engine design. However, fuel delivery is about equally capable of creating the same problem.

Some engines, such as the Detroit 71 Series 2-strokes, are very sensitive to injector parameters. Even with the ability to fully adjust injector timing on the engine, there are still nearly a dozen different injectors available. Most all in the name of smoke.

RE: strange combustion in 510rpm 4stroke marine diesel engine

You indicated that you had some nozzles with a larger center hole.  If the outside diameter is the same, then this would reduce the l/d ratio resulting in less penetration.  This would reduce the possibility of impingement on the cylinder wall.  By the looks of the pistons, the carbon buildup, impingement is probably happening.  Try the other nozzles.

Also, it is unlikely that the spray is impinging at low load or idle.  The marks on the psiton would indeed be from full(70%) load.

Even though the angle is 124 degrees, you may still have the wrong injector gasket, so that the spray pattern is not positioned in the cylinder correctly.  If you have excess inpingment on the piston, add another injector gasket or use a thicker one, to raise the nozzle.  This may reduce the smoke.  
Are there any impingement marks on the head?

RE: strange combustion in 510rpm 4stroke marine diesel engine

Hello,

Hot exhaust & low combustion pressure, I would again suggest to check properly the injection timing.
As I already wrote last time, the announced 14° timing seems very late for me! A timing of 24 - 25° looks more usual for this size & speed of engine as I checked on deutz and Pielstick.
Has somebody other values to compare with? What's captured on the original test report?

Regards!

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
Hello guys, I'm back from the ship.

We had some more problems, a crankpin bearing has gone bad and damaged the shaft.  So there was little time to do some experiments.

But as an answer about injection timing:

We take P/V diagrams and very clear P/crankangle diagrams.  These shows us that the combustion starts at about TDC.  For the current conditions, the timing is correct.  If we can shorten the ignition delay period, we will have to retard the timing.  I will try to bring forward such a graph so you will see it.

We have tried to advance the timing to 16.5° , but this gave us such a hard sound that we put it back to 14.5° immediatly

Greetings

RE: strange combustion in 510rpm 4stroke marine diesel engine

Hello everybody:

Hi Norcape. Please take a look to this document, I know it is not the source of solution for your problem, but certainly it can help in understanding possible causes of the problem.
http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/technical_papers/sulzer/paper_lowsfuels_welsh.pdf

Go ahead and do not give up, all in the forum, I am sure, are supporting you the best we can.

RE: strange combustion in 510rpm 4stroke marine diesel engine

What is the latest on this project?

RE: strange combustion in 510rpm 4stroke marine diesel engine

(OP)
An update on the project...

Because of a bad bearing shell, they had to refinish one of the crankpins, so everything has been a little bit to busy.

BUT:  The office has agreed.  Next month a specialist will come to measure the complete engine.  They say he will need 5 days to do all the test he needs.

I hope he will come up with something.µ

RE: strange combustion in 510rpm 4stroke marine diesel engine

Norcape,

Here are some thoughts:

1) Check your lubrication oil system for adequate volume and pressure.....bearings need oil.....better too much than not enough, especially on an engine with crankshaft problems.

2) I doubt the swirl devices are doing much.  The extreme inward air movement from the swish area of the piston at TDC most likely cancels out the little rotation air movement generated by the swirl devices.  Of greater concern is the possibility of one of those little fins breaking off and wiping out the entire cylinder and causing other major engine damage.

3) The fact that swirl devices are getting dirty indicates some reverse flow of burnt exhaust gases.  I wonder about the timing of the intake valves on these experimental engines.  Or maybe the intake charge pressure isn't high enough or maybe the exhaust back pressure is too high.  I wonder if the turbo is properly sized.

4) The injector pressure dropping so much over time concerns me.  Yes, it should drop a little, but I am not sure if it should drop that much.  I wonder if the spring is of adequate strength for the task because it seems to get excessively weaker during use.

5) The fuel impingment pattern on the piston seems a little aggressive.  All that fuel hitting that relatively cool piston does not make for a clean burn.  As a jet of fuel travels through the highly pressurized combustion chamber, the fuel molecules on the outside edge of the jet atomize first.  So as the jet continues it travel it actually becomes smaller in diameter until there is no more jet remaining.  Hence a jet of fuel will only travel so far.  Knowing this and the obvious large diameter of your cylinder bore, I doubt that raw fuel is reaching the cylinder walls.  Instead the fuel most likely is not atomising well because it comes into contact with the relatively cool piston.  So to improve the fuel atomizing, you could try a new injector nozzle design.  I would suggest more injector holes but much smaller in diameter.  Currently you have 8 holes of a certain diameter which have a total sum area.  And you are only running your engines at 70% of max power.  And due to the smoke problem, you are probably over-fueling your engines.  And the diameter of you holes are probably 110% of what is needed (assuming they were even designed).  Therefore maybe Bosch or some aftermarket custom supplier could make custom nozzle tips for you.  Maybe 12 or more lazer cut or EDM machined holes with a total area of about 60% of your current situation.  Also, reducing the angle of the holes will help by not allowing the fuel to hit the piston.

In summary, more injector holes will help spread the fuel more evenly in the combustion volume.  An improved angle of the holes (like your green spray pattern) will help.  And smaller holes will make small jets of fuel which will travel shorter distances before becoming totally atomized.

I hope some of these ideas will help.  Be sure to tell us what the engine specialist reports.

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