Power loss on MAN 6L40/45 2

[alanmort]

I lose power/performance from a 6L 40/45 600rpm MAN engine. After T/C overhaul the engine runs at full performance for about 1500 - 2000 hrs and then drops off so the CPP pitch limit drops from 16.5 to 11-12 by about 4000 hrs. The limit is caused by exhaust temp limits of 480 deg C. The T/C is originally ABB VTR 354 but is now mostly pattern parts. Fuel is IFO 380. All scavenge air leaks have been cured as have exhaust leaks. Engine room temp is about 50C.

 

[rovineye]

Are these individual cylinder sensors or one of the turbo exhaust flows?

If individual cylinder sensors, is it always a high value (as opposed to mean deviation) and is it always the same cylinder?

 

[alanmort]

Exhaust temps are individual units plus inlet to T/C. Sensors are checked against calibration unit periodically but are not changed at unit overhaul

 

[rovineye]

But what is giving you the power reduction?

Is it a single cylinder high temp? If so, always the same cylinder, or is there more than one high or can it be different cylinders at different times?

Single cylinder hi deviation from other cylinders?

High turbo inlet?

 

[alanmort]

The power loss is even on all cylinders. It is a vicious circle type of thing, T/C rpm drops which gives less scavenge air pressure which, in turn, gives higher exhaust temps. This normally corrected by T/C overhaul but the improvement is relatively short lived. We now overhaul T/C at 200 hr intervals instead of 8000 hr.

 

[alanmort]

Correction, interval should read 2000 hr

 

[rovineye]

I am not familiar with this model MAN, so I guess I am missing something.

In my case, if turbo slows down and exhaust temps increased, I get a load reduce signal from the safety system. This can be from either (for instance)

1. cylinder #8 high temperature

2. cylinder #8 has a higher mean average temperature compared to the other cylinders.

For me, my power management system then derates that generator in either case. For you it adjusts CPP I assume. But either way, the limitation is caused by one scenario or the other (or something similar), and for me identifiable to a single cylinder, unless it is turbo inlet temp. So if your safety system works similarly, you should know exactly what is causing the load reduction. But of course that is only a start in defining your problem.

Maybe the only real help I can give you is to suggest a users group. There are users groups for almost all MAN models. I got hooked up with the users group for our model by calling MAN Germany, and after only a surprisingly few transfers, I was given the contact of a person in a users group for our model. That is where I believe you will get really specific help.

Being electrical, I start my focus on the sensors, which is why I have been trying to drill down on what specific sensor is initiating the action.

 

[chief]

You have a problem with the air supply to your engine. Try waterwashing your T/c with a mix 50%water, 25% detergent (TEEPOL) 25%light diesel or kerosene. A couple of pints is sufficient. ENSURE you give the mix a good stirring before feeding in the air intake filter. This will also clean the air side of your intercooler.
Read off your charge air supply before and after, you will see a big change. Also check the stack exhaust, smoky before and clear afterward.

Offshore Engineering&Design

 

[alanmort]

Many thanks for help so far, will try and find a user group.
The temp rises are common to all cylinders, not just one and sensors are checked regularly as errors normally show up as extreme, and impossible, fluctuations.
The air supply is very possible. The T/C's are washed every 6 days with an impulse system which puts water in for 6 seconds every 6 mins and the whole process takes 36 mins.
Will talk to my Superintendent about washing with the mixture suggested.

 

[alanmort]

Further to washing, what exhaust inlet temp to turbochargers?

 

[chief]

This mix was recommended to me many years ago by the Brown Boveri mechanics. It is a lot cheaper than the proprietary chemicals and more effective. The reason I emphasised giving the mix a good stir just before use, is because the light diesel will separate out to the top if left standing and will 'pop'your safeties. Lesson learned because of a bone idle Motorman.

Waterwashing sometimes can not shift the oily dirt build-up on your T/C air side blades and after cooler.


Offshore Engineering&Design

 

[alanmort]

Have, sometimes, got no improvement when overhauling T/C. Rotors cleaned and re-balanced by shore company. Not seen to be very dirty when dismantled. Have tried 3 different types of nozzle ring.