Two-stroke marine diesel engines operating on distilate fuels

[CHSARANT]

Dear all,

Recently we received a notice re future environmental legislation on fuel sulphur contents. Major engine maker suggests use of distillate fuels (MDO and or MGO).

Naturally this raises the question regarding viscosity control and lubricity of distillate fuels, since most engine makers place a lower viscosity limit of 2 cSt at engine inlet.

An MGO (DMA grade) with min. viscosity of 1.5 cSt at 40 C as per ISO8217:2005 will need cooling to abt. 22 C in order to get the min 2 cSt that maker is requiring and if for safety margin you choose to have 3 cSt at engine inlet, then fuel should be cooled at abt 2 C.

These temps can only be archived with a cooler and or refer plant, according to my understanding, which will complicate the engine fuel supply system.

Has anyone relevant experience and can offer some guidelines on above? Any ways to bypass the problem without modification of fuel supply system?

Also same fuel will have to be used of Aux. engines and Boilers. Any special considerations for these systems?

Thanks and best regards,


Never disagree with an idiot. He will bring you to his level and will beat you by experiance

 

[CH5OH]

I have some XP with using lighter fuel on a diesel engine
build to run on HFO, though auxialary equipment designed to run on blend (IFO30).The engines has been running on GO for extensive period.(720, constant rpm)
observations:
-eriosion around inlet ports fuel pumps, with a delayed injection point as a result
-erosion on injector needles, with exhaust temperature deviations as a result
(we lowered the opening pressure from 650bar to 300bar, which resulted in regaining lifetime of injectors)
-increase of fuel content in oil bath.
as fuel pump barrels/plunjers are machined to operate on a elevated temperature, the fuel pump leakage increases, running on a low temp,low viscosity fuel (GO,1.5cst)

considerations:
cooling the GO or MDO to an extend the viscosity becomes acceptable, is not very cost effective.
what about operation cost going from HFO to MDO?
Although it would complicate the fuel system considerate, desulferising HFO o/b mai be an option.
Aux engines:would run fine on MDO/GO but have to follow up on above mentioned items
Boiler:caloric value of GO/MDO is lower than HFO, boiler needs to increase air and fuel supply.
ME:if converting to GO/MDO,keep allowance for decoking of fuel system.

 

[xjar]

The statement that caloric value of GO/MDO is lower than HFO is technically incorrect. At the same temperature GO/MDO has a higher caloric value.

 

[CHSARANT]

Dear CH5OH,

Firstly thanks for your reply.

Quote

Although it would complicate the fuel system considerate, desulferising HFO o/b mai be an option.

Unquote

Sounds interesting (pls send some details), but if you somehow lower the sulphur content of HFO then, you lower the lubricity of the fuel (pls correct if wrong), which again will create the prob. we are trying to overcome.

Also ancillary fuel systems like circulating pumps and or fuel oil booster pumps have a specific lower limit of viscosity they can cope with.

Still collecting data and options, on how to proceed with the specific requirement.

Brgds.


Never disagree with an idiot. He will bring you to his level and will beat you by experiance

 

[CH5OH]

xjar,
the remark as made, keeping in mind the boiler fuel pump is likely to be a volumetric pump.To obtain same caloric value
of the boiler, the fuel pump needs to deliver more fuel.
caloric value/kg is in favour of MDO,caloric value/liter is in favour of HFO.
Most likely, the boiler is equiped with an auxiliary burner for GO/MDO and a main burner for HFO with atomising steam)
if the auxiliary burner lacks capacity,the HFO burner needs to be converted (nozzles burners)

 

[jmw]

Going to low sulphur... suggest a visit to CIMAC homepage and newsletter archives plus working groups.
e.g. this comment:

http://www.cimac.com/workinggroups/Index1-working-groups-fuels-and-lubricants.htm

This group includes representatives from Man B&W.

JMW

http://www.ViscoAnalyser.com

 

[CH5OH]

chsarant,
i dont know about lubricity of sulphur, i do know of its superieur cleaning capability, when combined with H2O (turbo and exhaust boiler wash,lol)
the degradation mechanisms as described earlier, to my opininion have to do with coping with a lower vapour pressure and viscosity)
lower vapour pressure:cavitation on high flow fluctuation area's:fuel pump inlet ports,plunjer helix and injector needles.
viscosity:higher internal leakage on fuel injection,booster and circulating pumps

To coope with 2015 or 2020 legislation I guess you have following options:

-just shift installation to GO/MDO and expect:
initial decoking of installation (abrasives)
increased maintenance cost (increased cost as a result of decoking > result of running on lower sulphur content)

-converting installation for GO/MDO only operation:
the clearances between plunjer and barrels could be made smaller, when running only on cold MDO/GO.
debottlenecking with regards to minimum and maximum flow requirements (smaller volumetric caloric value and increased leakage)

-desuphurising fuel:
temperature+pressure+catalisator=desulphurising
effort engineering package > effort replying threat

 

[WillShi]

MAN B&W have a standard cooler which is indirect. Beware of direct cooled type as engine manufacturers says 'use them at your peril'...your guarantee will go out of the window if you still have one, and you have a problem with engine after fitting a non authorised cooler. Speak to you engine maker. If your main engine fails you are sitting duck, so I think it needs careful consideration.

I assume you are aware of the EU Directive on burning low sulphur fuels in port also... for this there are special safety issues regarding the boilers..