EXHAUST GAS HIGH TEMPERATURE AND T/C SURGING!!!!

[luigiguida]

Hello,
I'm new at this forum.

I'm the tech Manager for a General Cargo Ship equipped with two Yanmar 8Z 280 ET built on 1990.

After six months inoperative, we started both main engines without any problems but, once increasing the RPM the exhaust gases rised the temperature up to more than 500°C in less than one minute, all cylinders, both engines... The maker indicates normal temperature on a range between 360 and 400°C.

We checked propellers, reductors, cleaned air coolers, checked fire timing, cleaned T/C including changing bearings, gaskets, oil and seals. Still no results.
Checked fuel pumps, nozzles, compression test, economizer.
No results.
The engine burns gasoil, and the same gasoil which remained on board for long time.... could it be the gasoil quality?

Shall we hire a magiciant?

Thanks for the attention
Luigi Guida
+39 39 39 158 293
operations@gmshipping.it

 

[luigiguida]

Forgot to say that T/C is also surging, like "breathing on waves".

 

[LostHippie]

2 stroke or 4 stroke?

Sounds to me like an overloading condition, what kind of speed control (governor) do you have on this thing?

 

[L4189]

My first guess is you are not getting enough airflow if you are getting this result with no load. Did you check to see if anyone uncapped the exhaust pipe.

 

[luigiguida]

Thamks for the answers.

The engine is 4 strokes.
Governors have been checked and work perfectly.
We comletely dismantled the air coolers, presently circulating Acid and hot water and will remain for aT LEAST 24 HRS MORE. It is our Superintendant opinion that there is not enough air (Air cooler chocked).

Mr L4189 makes me wonder about uncapping exhaust pipes, what you mean?

 

[L4189]

What I mean is that if you run the engine rpm up with no load you get a high exhaust temperature most probably because of low air volume. You should be having black exhaust. A turbo surges because its blocked downstream. Its seems you checked everything but the exhaust back pressure. Maybe some birds built nests in the exhaust pipe. I don't know.

 

[itsmoked]

Also you might consider checking the T/C system. I'd pull one T/C out of its well and drop it into boiling water. See if it correctly reads 100C. You don't want to mess with the wires just pull it and move it as little as necessary to reach the water bath. You could have an electrical problem causing a general offset to all the T/Cs and be chasing a phantom.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[luigiguida]

Thanks for the answers, thank you very much indeed!
Keith made a good point, infact i also checked gases temperature by a laser thermometer.... same result.
We ordered to check is the complete air cooler system (inlet and outlet), it has been totally dismantled and boiled 24 hrs with water and acid, lot of fouling inside. Presently reassembling everything... keeping fingers tightly crossed and waiting for results.
Meanwhile, for Mr L4189, we fully checked the exhausts system, even with endoscope, clean and free, the smoke is colourless even if engine is loaded at 25%, thus no carbon or fat combustion, nor nests or clogged.

Looks like we're actually chasing a ghost! (and loosing 2500 Usd per day....)

 

[luigiguida]

something stupid....
All tests we're doing are with the Ship berthed and fastened on the quay with her mooring ropes.
How this could affect the engine loading condition?
I mean if we run the engine at 25%, is it a real 25% or a bigger loading condition?
If so, will the exhaust temperature be higher than expected????????

Thanks for the attention
Luigi

 

[L4189]

Sounds like what you did is what they call in tug boats a "dead push" as in pushing against a bridge abutment to load up the engines to full power, and since the propeller is in a stalled condition the engine will load up faster at a lower rpm than running free. However, since tugs are way overpowered in relation to the power needed to reach hull speed I'm not sure exactly how it effects your situation.

 

[DuncanM]

You should be running the gasoil through a purifier from bunker tanks to daytanks; this will remove any water/debris which could have accumulated. I wouldn't worry too much about fuel quality.

Any results after you cleaned the aircoolers? High exhaust temp is generally either insufficient air or too much fuel; and you state the injectors were checked.

Is the engine making expected boost pressure?
Can you de-clutch or run at zero propellor pitch?
Is there an 'exhaust boiler'?
Has anyone looked down the funnel from the top or from an access door near the top?

 

[chief]

Would appear you have a blockage on the air side of your turbo-charger intercooler. This would account for the surging T/C and high exhaust. Verify the blockage by taking air pressure and temperature readings on the inlet and outlet of the t/c intercoolers.
A simple and non intrusive method of cleaning both intercoolers and air side of the T/C is to make a mixture of 50% water 25% diesel and 25% detergent (Tee-pol). Add using an injection pot on the T/C pour in the air intake filters.
This will rid you of the ghost, but will require regular treatment.
Check the air inlet source for the engine, you may have an oil laden air atmosphere.
Also check the engine crankcase breathers are venting adequately to a clear area.

Offshore Engineering&Design

 

[luigiguida]

Looks like it was the air coolers, on one of the two engines we solved the problems, T/C is no more surging and temperature is under control.
Now remaining engine no. 2, still surging after cleaning the air cooler, trying to bypass the cooler to check temperature after less than one minute test. If T/C will not surge, it clearly means that we need a spare cooler. if not, we're going to call ghostbusters.