Low charge air pressure

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Bilge Dweller
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Low charge air pressure

Postby griff » Sat Oct 05, 2013 11:02 am

Just completed a major overhaul on one of our genys, a daihatsu 6DK-28. Turbocharger was sent ashore for overhaul.

Since running it up the charge air pressure is about 0.4 bar lower than before the overhaul ( the normal pressure with max available load was around 1.4 bar). The exhaust temps are higher higher than normal as well and the peak pressures lower than previous readings. The manual points to a dirty turbocharger, dirty cooler or lack of engine room ventilation.

The t/c is clean as its just been overhauled and we've checked the compressor blades. The air cooler wasn't touched during the overhaul and there's nothing blocking it (also the charge air temp is normal). There's plenty of ventilation, one fan vent blasts right on to the t/c!!

All engine parameters are normal apart from the ones stated above.

Anybody any ideas?

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Re: Low charge air pressure

Postby Madzng » Sat Oct 05, 2013 11:47 am

Have heard of instances where similar to your description below has happened and it is also described by ABB in the attached file, page 29.

In short the deposits that build up on the worn parts and keeps clearances tight and the turbocharger efficient. When the turbocharger is cleaned, and returned to service, the parts that are worn will have a greater clearance resulting in less efficiency.

ABB states that normal performance will return once the deposits build up again, but I guess that depends on how much needs to build up.

What was done to the turbocharger, were are parts replaced?
Tips for the Operator (New Edition) 2011.pdf
Tips for the operator - ABB
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Big Pete
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Re: Low charge air pressure

Postby Big Pete » Fri Oct 11, 2013 12:35 am

It is fairly well known that as the Turbine becomes fouled, the gas flow is constricted, this increases the back pressure in the exhaust manifold and the exhaust is forced through th narrowed passages in the Turbine at higher velocity. This means more momentume and Kinetic energy in the gas for the Turbine to recover, hence higher turbocharger revs and higher scavenge pressure.
It appears that this has masked the effects of wear on the Turbine and cleaning the Turbocharger has revealed the problems.
I would have thought that if the T/C had been thoroughly overhauled all the dimensions would have been checked against the makers specification and any worn parts replaced.
Maybe it was a cheap overhaul??

The ship I am on is only 3 years old and has just drydocked, mainly because the anodes for the cathodic protection system had failed. It turned out they had initially been installed by the contractor that gave the cheapest quote. According to the amkers there should have been 2 x 50kg Copper anodes in each of the box coolers, the installing company only fitted one, hence the ship had to drydock 2 years early. (But it was cheaper when they built the ship!)

You only get what you pay for.

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Bilge Dweller
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Re: Low charge air pressure

Postby trophychris » Thu Oct 24, 2013 11:58 am

Check your intercooler with a water manometer connected across it. Measurement should be in mmWG in the engine test sheets.
If any higher than the test sheet figure, remove the intercooler core and clean in a ultrasonic cleaning bath if available.
As a guide most medium speed engine intercoolers should have only about 300-600 mm WG across them.
Have seen dirty intercoolers as the problem sooo many times, especially when they "look" clean but inside the core it is a different story and the turbo is blamed.
The only measurement that is important when determining the condition of the intercooler is the pressure drop in mmWG.
Hope this helps :)

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D Winsor
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Re: Low charge air pressure

Postby D Winsor » Mon Oct 28, 2013 3:58 am

You should also check during the overhaul that the correct nozzle ring was installed.
I've seen it in the past where a "reconditioned" ring was installed causing problems where the profile of the nozzles were changed enough to cause boost problems
Are there protective screens in the turbo inlet exhaust pipes? I've seen it when these screens are choked or plugged cause issues with turbo performance.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Re: Low charge air pressure

Postby thenorwegian » Sun Nov 24, 2013 6:36 am

Have you measured P-comp?
Was fuel injectionpumps and injectors overhauled at same time?
Anything done with camshaft or geartrain?
As mentioned above, measure pressuredrop across scav.air cooler (anything above 2-250mm-clean it..)

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Re: Low charge air pressure

Postby astat101 » Thu Jul 16, 2015 2:50 am


I know a company called vestas aircoil who manufacture and design charge air coolers. They have a charge air cooler cleaning facility, maybe that is an option for you.

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