Operation on Low-Sulphur Fuels Two-Stroke Engines on Low Sulp.pdfMAN B&W Diesel A/S, Copenhagen, Denmark Contents: Operation on Low-Sulphur Fuels Two-Stroke Engines Introduction

MAN B&W Diesel A/S, Copenhagen, Denmark

Contents:


Contents:


Contents:


Contents:


Contents:


Contents:


Contents:


Contents:


Contents:


Contents:

Operation on Low-Sulphur FuelsTwo-Stroke Engines

Introduction ........................................................................... 3

Latest Emission Control Regulations .................................. 3

- IMO.................................................................................... 3

- EU ..................................................................................... 3

Incompatibility of Fuels ........................................................ 4

Ignition and Combustion Characteristics ofLow-Sulphur Fuels ................................................................ 5

- Case story ......................................................................... 6

Changeover between High and Low Viscosity Fuels ......... 7

- Case story ......................................................................... 7

Fuel Viscosity at Engine Inlet ............................................... 8

Correlation between Low-Sulphur Fuel,

Cylinder Lube Oil BN and Cylinder Lube Oil Feed Rate ...... 9

Fuel and Cylinder Lube Oil Auxiliary Systems ..................... 11

Summary................................................................................ 14

References ............................................................................ 14

3

Operation on Low-Sulphur FuelsTwo-Stroke Engines

Introduction

The average sulphur content of fuel oilused for marine diesel engines is 2.7%.This will undoubtedly change with thecoming emission legislation, which willlower the emission limits of SOx, NOx,particulate, HC and CO.

So far, the authorities have reduced theSOx content in the exhaust gas by intro-ducing limits on the content of sulphurin the fuel oil used. This is a much moreefficient and straightforward solution,obtained from the refining process, thanthe installation of separate complicatedSOx cleaning facilities on board eachvessel. However, this solution still re-quires that it is feasible for the refineriesto lower the sulphur level at a reason-able cost and effort. So far, the questionis whether there will be sufficient low-sulphur fuel oil available in the future,and whether marine diesel and gas oilswill be used to any wider extent. This isa somewhat political question, whichwill not be discussed in this paper.

However, we will highlight for the MarineIndustry, the technical areas whichMAN B&W Diesel expects will be af-fected when changing from higher sul-phur fuel oils to lower sulphur fuel oils.

Most MAN B&W two-stroke engines oftoday are operating on fuels with sul-phur levels higher than 1.5%. This givesus much experience with high-sulphurfuels. However, on the basis of opera-tion on power stations and special ma-rine vessels designated for operation onlow-sulphur fuel, we have created theguidelines described in this paper.

It should also be mentioned that ontestbed all two-stroke engines are op-erated on standard environmentallyfriendly fuel oil, which is typically a land-based diesel oil with a very low sulphurcontent and viscosity but, also in thiscondition, the two-stroke engine oper-ates successfully as long as the neces-sary precautions are being taken.

Latest Emission ControlRegulations

The IMO

The IMO Annex VI of MARPOL 73/78,Regulations for the Prevention of AirPollution from Ships, has just been ratifiedand will take effect as from May 2005.

IMO has indicated that, in future, furtherlimitations will be imposed on SO

x as

well as on other components in theexhaust gas.

The EU

The EU has introduced separate regu-lations to cut sulphur dioxide (SO

2)

emissions from ships.

In reaching a political agreement on theCommission’s marine fuel sulphur pro-posal, the Environment Council hasagreed to reduce ships’ yearly SO

2emissions in the EU by over 500,000tonnes from 2007, to the benefit ofhuman health and the environment.

Currently, marine fuel has a maximumsulphur content of 5% or 50,000 partsper million (ppm), compared with petrolfor cars, which will have 10 ppm from2007. As part of its 2002 ship emissionsstrategy, the Commission presented aproposal for a directive to reduce thesulphur content in marine fuels used inthe EU. The main provisions were:

• a 1.5% sulphur limit on fuels used byall ships in the Baltic Sea, the NorthSea and the Channel. Today’s politicalagreement incorporates this provision,and sets implementation dates start-ing on 19 May 2006

• the same 1.5% sulphur limit on fuelsas used by passenger vessels onregular services between EU portsfrom 1 July 2007. EU Ministers haverubber-stamped this and brought thedeadline forward to 19 May 2006

• a 0.2% sulphur limit on fuels used byinland vessels and seagoing ships atberth in EU ports. The Council hasagreed to delay a tighter 0.1% limituntil 1 January 2010, to allow single-fuel ships time to adapt their fueltanks. A further two year delay wasoffered to 16 unifuel ferries serving theGreek islands.

Fig. 1: Technical code

Thus, the SOx limit applies to all vessels

in the category of ships with an enginepower output of more than 130 kW.The NO

x limit is only for vessels where

the keel was laid after 1 January 2000.

The general international limit on sulphurwill be reduced from 5% to 4.5%through the ISO 8217 fuel standard.

However, in restricted areas like theBaltic Sea, the English Channel and theNorth Sea, the limit is 1.5% sulphur, whichwill be enforced as from 19 May 2006.

4

The alternative to reducing the amountof SO

x in the exhaust gas is to clean

the exhaust gas using the scrubbertechnique. So far, only a few plants areoperating with such a solution, and it isstill considered primarily a test for largerengines.

At the same time, some companies aretalking about emission trading which, inprinciple, means that the possibility ofpolluting more than the specified limitscan be bought from ships that are pol-luting less than they are allowed to, seeFig. 2. Whether emission trading can beapplied in the marine sector in the sameway as emissions trading between powerstations is still rather unclear, as theadministrative load would be extensive,and the possibility of checking for com-pliance with such trading rules wouldbe limited.

Fig. 2: Trading of emission between X and Y

Incompatibility of Fuels

In near future, ocean-going ships entering coastal waters will have to switch froma heavy fuel oil (HFO) to a lower viscosity distillate fuel, in order to comply with thelow-sulphur requirement if a low-sulphur HFO is not available.

Due to the current considerable price difference, we do not expect change-oversfrom HFO to DO or GO, see Table I. However, an operator could be forced tochange over for reasons of fuel availability.

Table I: Average bunker prices in US$/ton, October 2005

Grade IFO380 IFO180 MDO MGO

Fujairah 298 313 552 555

Houston 291 313 689

Rotterdam 265 285 523 580

Singapore 323 335 538 543

Source: www.bunkerworld.com/prices

Ship X

Ship Y

Emission limit

High level

Low level

Trading

Ship X

Ship Y

Emission limit

High level

Low level

Trading

Low-sulphur HFO will, expectedly, havea somewhat higher price than the HFOon the market today, due to increasingdemand and the cost of the desulphuri-sation process.

When switching from HFO to a distillatefuel with a low aromatic hydrocarboncontent, there is a risk of incompatibilitybetween the two products. The change-over procedure takes quite some time,during which there will be a mix of thetwo very different fuels for an extendedperiod of time. The asphaltenes of theHFO are likely to precipitate as heavysludge, with filter clogging as a possibleresult, which in turn will cause fuelstarvation in the engine.

Even though incompatibility seldomoccurs, the most obvious way to avoidthis is to check the compatibility between

the fuels before bunkering. This can bedone manually with a kit on board, orvia an independent laboratory. The latteroften being too slow a process, as theship will already have left the harbourbefore the laboratory returns with thetest result. Therefore, in practice, and inthe event that the fuel supplier is notsupplying both low and high sulphurfuels, the incompatibilities will not bediscovered until both fuels are on board.

BP Marine has found that even thoughthe TSP (Total Sediment Potential) andTSE (Total Sediment Existing) values ofthe fuel are completely satisfactory, stillor small number of fuel deliveries giverise to complaints of filter blocking,excessive sludge, etc. It is suspectedthat most at these incidents are due tofuel incompatibility. When blending forlow-sul-phur fuel more cases ofincompatibility might be seen.

5

Ignition and CombustionCharacteristics of Low-Sulphur Fuels

The interest in fuel oils’ ignition quality onthe basis of the calculated CCAI or CCIvalues, or by measuring the fuel in anignition instrument such as the FIA (FuelIgnition Analyser), has never, in our ex-perience, been greater than now. In theCIMAC Heavy Fuel Oil Work Group, weare comparing fuel samples and serviceexperience and, today, there are defi-

nitely more reports of cases where a poorliner and piston ring condition is thoughtto be due to a low ignition quality. Theinvestigations indicate that a low-sul-phur fuel has often been used whenthis happens, and the question iswhether new oils from the spot markethave characteristics which have so farbeen overlooked and, therefore, oughtto be investigated further.

When focus is narrowly on the fuel oils,the drawback can be that some opera-tors, when experiencing unacceptable

conditions in the combustion chamber,may be prompted to blame the fuelwithout taking other possible causesinto consideration, such as insufficientcleaning of the fuel oil, type of cylinderlube oil, and feed rate.

The below test results (Figs. 3 and 4),of the ignition and combustion propertiesmeasured on a FIA-100 Fuel CombustionAnalyzer, show the effects of a mixtureof fuels, Ref. [3]. Whether or not this fuelwould have a negative effect on theperformance of a two-stroke engine isopen to doubt, but the test unquestion-ably illustrates that the fuel consists of amixture of very different fuels with verydifferent flashpoints, resulting in an irreg-ular heat release in the test set-up.

The high temperature analysis illustratedin Fig. 3 apparently shows the threedistinct fractions used in blending thefuel, i.e.:

• heavy naphta (bp ≈ 190-270°C),

• heavy gasoil (bp ≈ 350-450°C), and

• residue (bp > 580°C).

A series of tests with fuels with expectedlow ignition qualities have been performedon MAN B&W two-stroke engines and,so far, we do not have any evidence toshow that the ignition quality has anyinfluence on the engine performance.

Lately, however, we have received reportsfrom ships with dual fuel systems, whereeither the auxiliary engines were difficultto operate, or damage to the combustionchamber was found. In addition to thetraditional CCAI or CCI values, which arenot considered being reliable, it is beingconsidered to introduce the ignition char-acteristics in the CIMAC fuel recommen-dation and the ISO 8217 fuel standard.

One step was taken earlier this yearwhen interested companies formed agroup that could provide for the defini-tion and measurements of ignition and

Fig. 3: SIMDIST (simulated distillation) recovery rate

Fig. 4: ROHR (rate of heat release) curve

6

combustion characteristics of residualfuels in a standardised approach, withthe aim of producing IP test methods.

The group’s name is EI Task Force ign/comb characteristics.

The group is looking particularly at theFIA test methods which, to our knowl-edge, are so far the best methods forsuch analyses. But the question iswhether it is possible to translate thetest results into engine performance.

The real task when using the FIA equip-ment is to generate a good test report,estimating the expected operation per-formance on any engine.

It is obvious that the slower the speedand the larger the dimensions of theengine, the less sensitive it will be to ig-

nition delays, but as an increasing num-ber of ships are designed with dual fuelsystems, where the same fuel is to beused in the auxiliary and main engines,both engine types should be able to op-erate on the fuel available on the market.

The industry therefore needs to followand consider low-sulphur fuel’s intro-duction on the market.

Case story

A well-known oil company had to payabout USD 5 mill. in compensation tofishing boat owners, after an incidentwith an environmentally friendly low-sul-phur diesel oil from one of their refineriesin Europe. The oil company’s investiga-tion showed that the problem wasprobably related to heavy blending

components causing incomplete com-bustion, deposits and, eventually, en-gine failure on the fishing vessels’ four-stroke medium speed engines. It shouldbe mentioned that some of the fishingboats had older-type diesel engines in-stalled.

One possible reason for the bad fuelperformance was thought to be a qual-ity slip during operation of thedesulphurisation unit, and the oil com-pany had to adjust the process in con-sequence of this incident.

The important message to the fuelcompanies is, consequently, that low-sulphur fuels must not jeopardise theoperational reliability of the engine.

Fig. 5: FIA test method Source: Fueltech AS

Analysis af Good or Bad quality HFO according to FIA!

7

Changeover between Highand Low-Viscosity Fuels

To protect the injection equipmentagainst rapid temperature changes,which may cause sticking/scuffing ofthe fuel valves and of the fuel pumpplungers and suction valves, thechangeover is to be carried out accord-ing to a specific MAN B&W changeoverprocedure.

Today, a changeover between fuels withmajor differences in viscosity is very rare,and is normally only carried out before amajor overhaul of an engine, or during along stop of the engine. Thus, in futurethis would call for a more frequent num-ber of changeovers according to thechangeover procedure on board, whichcauses a reduction of load and a slowchange in the temperature, becominghigher or lower, depending on the vis-cosity of the fuel changed to.

Case story – changeover fromDO to HFO

It is the rising of the diesel oil tempera-ture that represents the time limitingfactor deciding when the diesel oil canbe replaced with HFO.

According to the instruction manual,the temperature should not be changedby more than max. 2°C/min.For example, diesel oil is to be changedto HFO:

1.The system contains 40°C diesel oil

2.The diesel oil is heated to 80°C beforeadding the HFO.This takes (80 – 40)/2 = 20 min.20 min.20 min.20 min.20 min.

3.HFO is added at a temperature ofmax. 25°C higher than the diesel oil,i.e. at 105°C

4.However, the temperature rise shouldstill be max. 2°C/min.Therefore, it takes an additional(105 – 80)/2 = 12.5 min.12.5 min.12.5 min.12.5 min.12.5 min.

5.From now on, there should be onlyHFO in the system

6.The temperature is now raised from105 to 150°C = 22.5 min.22.5 min.22.5 min.22.5 min.22.5 min.

We therefore conclude that it takes 20+ 12.5 min. = 32.5 min. from the startof the changeover until HFO is in thesystem. Moreover, it takes another22.5 min., i.e. 55 min. from the start ofthe changeover, before the system isrunning on HFO at 150°C.

Fig. 6: Automatic system for changeover between fuels of different viscosity

In order to make thechangeover processmore secure and easy,MAN B&W Dieselsuggests the use ofan automatic controlsystem.

However, if so desired,this process can still becarried out manually inaccordance with MANB&W Diesel procedure.

For your guidance, wehave calculated thechangeover time for a380 cSt HFO and amarine diesel oil.

8

Fuel Viscosity at EngineInlet

In various chemical combinations, the sul-phur in the fuel oil has a lubricating effect.

The use of DO and GO with a sulphurcontent close to zero and, at the sametime, a low viscosity might cause fuelpump and fuel valve wear and, conse-quently, the risk of sticking (Fig. 7). Butthis situation needs to be consideredalso from a hydrodynamic point of view,so if the viscosity and, thereby, the oilfilm is thick enough, also low-sulphurfuels can be used.

This risk limits the viscosity at the engineinlet to min. two cSt. In special cases,with a very low viscosity gas oil and highambient temperatures, this might callfor cooling of the diesel oil before theproper viscosity can be obtained at theengine inlet. The viscosity of typical fuelsis shown in Fig. 8.

Fig. 7: Fuel pump plunger sticking

Fig. 8: Marine fuel viscosities

1

10

100

1000

10000

100000

-15 35 85 135

Temperature Degrees Celsius

Kinematic Viscosity

Marine Gas Oil

Marine Diesel Oil

IF-30

IF-60

IF-100

IF-180

IF-380

MBD limitmin. 2cSt

9

Correlation betweenLow-Sulphur Fuel,Cylinder Lube Oil BNand Cylinder Lube OilFeed Rate

Our experience with low-sulphur fueloperation and cylinder lubrication withlow-BN cylinder lube oil is primarily ob-tained from stationary engines, operat-ing at 100% load and 100% rpm in highambient conditions. Whether the samenecessity for low-BN cylinder lube oilapplies for marine engines as well will,as such, depend on the operationalprofile, engine size and overall enginecondition and, therefore, should beconsidered on a case-to-case basis.

It is therefore important to acknowl-edge the corrosion mechanisms prevail-ing on the cylinder liner, and knowabout the low-BN cylinder oil.

Acid corrosion, which is by far the mostinfluencing cause of wear seen in cylin-der liners, is basically the result of acondensation of the HFO sulphur com-pound. The corrosion is caused by thecombination of water being presentduring the combustion process, and athermodynamic condition where thetemperature and pressure are below thedew point curve of the sulphur trioxide.Even though the water mist catcher ofthe scavenge air cooler removes waterdroplets, the scavenge air is saturatedwith water vapour when entering thecylinder.

It has not been clearly mapped, assuch, how much sulphur trioxide isformed, and what is the necessary timeframe before the acid corrodes the sur-face of the liner wall, and when newcylinder oil must be fed to the liner sur-face in order to neutralise the sulphur.

In order to neutralise the acid, the cylin-der lube oil contains alkaline compo-nents – usually calcium salts. The BaseNumber (BN or TBN) is a measure of

the cylinder lube oil’s ability to neutraliseacid. The higher the BN, the more acidcan be neutralised.

The BN is therefore an important pa-rameter in controlling the corrosion onthe cylinder liner surface. Controlledcorrosion – not avoiding corrosion – isimportant to ensure the proper tribologyneeded for creation of the lubricating oilfilm. If the neutralisation of the acid istoo efficient, the cylinder liner surfacehas a risk of being polished, i.e. thelube oil film is damaged and the risk ofscuffing increases.

In other words, operating the enginewith an unmatched BN/fuel sulphurcontent could increase the risk of eitherscuffing or excessive corrosive wear.Fig. 10 shows the same cylinder liner,first where BN70 has been used, andthen where BN40 has been used forthe same type of low-sulphur fuel.

Based on experience, MAN B&W Dieselfinds it essential for a good cylinder con-dition and overall engine performancethat an “open” graphite structure is kepton the cylinder surface, so that a hydro-dynamic oil film is kept between the pis-ton rings and cylinder walls at all times.

Therefore, running on low-sulphur fuel isconsidered more complex due to therelationship between liner corrosion andscuffing resistance, dry lubrication prop-erties from the sulphur content (or lackof same), the interaction between theBN in the cylinder oil and the detergencylevel, possible surplus of alkaline addi-tives, the piston ring pack, etc.

The total alkaline content of the cylinderoil has to match the sulphur content inthe fuel oil in accordance with theequation: Dosage F x S%, where F =0.21-0.25 g/bhph, based on a BN70cylinder oil. The minimum feed rate forproper oil distribution and oil film thick-ness has so far been set to 0.5 g/bhph,

Fig. 9: Chemical conversion of S to H2SO4

Fig. 10: Cylinder liner surface

‘Open’ graphite structure withgood tribological abilities

‘Closed’ graphite structure withreduced tribological abilities

[0 [0 [0 [0 [022222]]]]] [0] [0] [0] [0] [0] [H [H [H [H [H

2 2 2 2 2 0]0]0]0]0]

SO2

S SO3

Fast100% Conversion

Slower0.3 - 7 %

Conversion

EquilibriumPressure & Temp.

Dependent

H2SO4

10

which at the above-mentioned equationwill be reached at 2% sulphur. Thismeans that the theoretical limit, usingan ordinary BN70 oil, is 2%.

As an example, an engine using 1%sulphur fuel at a dosage of 0.5 g/bhphwould be overadditivated.

Therefore, a fuel with a sulphur contentas low as 0.5% could call for a combi-nation of a low cylinder oil dosage anda low-BN oil (BN40-50).

When this is said, it is essential that theactual cylinder and piston ring conditionis inspected. With its unique distributionof oil film, the Alpha Lubricator, seeFig.11, which is used for cylinder lubrica-tion on MAN B&W engines, has shownthat a lube oil feed rate down to 0.5 g/bhph can be reached.

It has also been shown that thanks tothe low cylinder lube oil feed rate, manyengines can use low-sulphur fuel andstill use BN70 cylinder oil.

It is therefore important to acknowledgethat before changing from BN70 toBN40-50, it is important to evaluate theengine’s actual condition after the firstoperating period on low-sulphur fuel.

The complexity of designing a low-BNcylinder oil consists in achieving the properdetergency level, which is seldom atthe same high level as BN70 oils.

Therefore, we recommend that the low-BN cylinder oil type is selected very care-fully. All the major oil companies havelow-BN cylinder oils available today.

For how long the engine can run onlow-sulphur fuel and BN70 cylinder oil isindividual, but it is not expected to resultin any unsatisfactory conditions in thecourse of the first weeks, where the en-gine can be inspected for optimisation ofthe feed rate and lube oil BN level.

However, MAN B&W Diesel recommendthe following practical approach.

Fig. 11: Alpha Lubricator

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

1,10

1,20

1,30

1,40

1,50

1,60

1,70

0 1 2 3 4 5

Sulphur %

Ab

so

lute

do

sag

es

(g/k

Wh

)

BN70, F x S%, whereF = [0.26-0.34]g/kWh

BN40,

Fx

S%, where

F=

70/40

x[0

.26-0

.34] g/

kWh

Fig. 12: Use of BN40 vs. BN70 cylinder oils

Practical Approach

The correlation between fuel sulphur level and cylinder oil can be shown as follows:

Fuel sulphur level <1%: BN40/50 recommendedChangeover from BN70 to BN40/50only when operating for more thanone week on <1% sulphur

Fuel sulphur level 1-1.5%: BN40/50 and BN70 can be used, see Fig. 12

Fuel sulphur level >1.5%: BN70 is recommended.

11

Fig. 13: One MDO settling tank and one HFO settling tank – fo system No. 1

Fuel and Cylinder LubeOil Auxiliary Systems

As low-sulphur fuel oil is more expensive,the higher sulphur fuel oil is preferredwhere accepted to be used. To enablethe vessel to operate on low-sulphur fuelin restricted areas and switch to heavyfuel outside restricted areas, a dual fuelsystem is necessary.

For newbuildings, and as retrofit on ex-isting engines if necessary, MAN B&WDiesel proposes three different fuel sys-tem configurations for engines operatingon both high and low-sulphur fuel oils.

The ship’s fuel oil system, from bunker-ing tanks through the settling tanks,treatment system and service tanks, maybe affected by a frequent change in fueloil type. Therefore, depending on thechangeover frequency, various configu-rations may be relevant, the principalones being listed below (unbiased):

Fuel oil system, No. 1

One MDO + one HFO system:One bunkering, settling, centrifugingand service tank system for MDO, andone for HFO. Often several separatebunker tanks (heated) are available inthe ship, enabling use of different bunkeroils. Systems are merged before thepressurising (supply) stage leading tothe engine circulating system. Auxiliaryengines are usually fed from the joinedsystems, i.e. they burn the same fuelsas the main engine. Also referred to asthe “Unifuel” concept. It is possible torun the auxiliary engines on a separatefuel, i.e. by closing off the line from theHFO system to the auxiliary engines.


One MDO + two HFO settling tanks:One bunkering and settling system foreach type of HFO. Possibly with addi-tional bunker tanks. The HFO system iscommon from centrifuge(s) onwards,

MDO Storage Tank (25°C)

Se

ttlin

gTank

(25

°C)

ServiceTank(day)35°C

Se

ttlin

ga

nk

(60°C

)

Bunker Storage Tank 1 (45°C)



Centrifuge(s)(40°C)

Centrifuge(s)(95 � 100°C)


MGO(Boiler Support)( Inert Gas) etc

HFO Supplypump

HFO Circulatingpump

If unifuel system

To Gensets

T

MDO Storage Tank (25°C)

Se

ttlin

gTank

(25

°C)


Se

ttlin

ga

nk

(60°C

)




Centrifuge(s)(40°C)

Centrifuge(s)(95 � 100°C)


MGO(Boiler Support

Inert Gas )etc.

HFO Supplypump

HFO Circulatingpump

If unifuel system

To Gensets

T

Fig. 14: One MDO settling tank and two HFO settling tanks – fo system No. 2

Fig. 15: One MDO settling tank and two sets of HFO settlingand service tanks – system No. 3

12

common from centrifuge(s) onwards,i.e. it is identical to fuel oil system No. 1,but with an additional settling tank foralternate HFO types. Unifuel or sepa-rate fuel.


One MDO + two separate HFO systems:Two separate bunkering, centrifugingand settling and service tank systemsfor each type of HFO. The two HFOsystems are completely separate up tothe joining point before the supplypumps pressurising the engine circulat-ing system. Unifuel or separate fuel.

From the onset, the ship’s fuel oil systemis perhaps one of the most complicatedsystems on board. Naturally, introducingmultiple fuel oil systems implies consid-erable additional complexity to the shipdesign in general and to the engineroom design in particular. For the threealternatives, the additional equipmentlisted in table II is conceptually envisaged.

Fuel oil system: Additional equipment

No. 1 • Base case – no additionals

No. 2 • Possibly additional bunker tank(s)• Possibly an additional bunkering system for the

additional bunker tank(s)• Possibly enhanced bunker-heating system to accommodate different fuel characteristics (pumping temperature, flash point, viscosity, etc.)• One additional settling tank • One additional transfer pump to the settling tank

No. 3 • All of those associated with system No. 2• Possibly an additional set of fuel oil centrifuges• Possibly an additional centrifuge room, including sludge tank, etc.• Additional service (day) tank• Additional piping and instrumentation

Regarding the auxiliary system for thecylinder lube oil handling, there are sev-eral cylinder lube oil system constella-tions that could be implemented to allowvarious degrees of adaptation to anyspecific bunker oil sulphur content. Be-low, we have listed the technical solu-tions used today.

Cylinder oil system, No. 1

One cylinder oil system:A conventional system, see Fig. 16.Ability to handle one cylinder lube oil ata time, i.e. running with a fixed basenumber. The feed rate can be manuallycontrolled and is seldom adjusted.


One cylinder oil system where the engineis equipped with electronicAlpha lubricators:Also ability to handle one cylinder lubeoil at a time, i.e. running with a fixed base

Fig. 16: One cylinder oil system

Fig. 17: One cylinder oil system, engine is equipped with

Cylinder Oil

Storage Tank

Cylinder Oil

Service Tank

3m

Cylinder Oil

Storage Tank

Cylinder Oil

Service Tank

3mCylinder Oil System No. 1

20

40

60

80

0 2 4 6

Fuel sulphur (%)

BN

(mg

KO

H/g

)

Cylinder Oil System No. 2

0 2 4 6

Fuel sulphur (%)

Feed

rate

Cylinder Oil

Service Tank

Cylinder Oil

Storage Tank

Cylinder Oil

Booster UnitPower/Heating

Cylinder Oil

Service Tank

Cylinder Oil

Storage Tank

Cylinder Oil


Cylinder Oil

Service Tank

Cylinder Oil

Storage Tank

Cylinder Oil


Table II: Additional FO system equipment

13

Fig. 18: Two independent cylinder oil systems

number. The electronic lubricator (verymuch) eases the adjustment of feed rateand, thereby, the alkalinity influx, seeFig. 17.


Two cylinder oil systems:Consists of two cylinder lube oil storageand service tank systems, see Fig. 18.Systems are joined before the engineflange via a changeover valve. Ability tohandle two different cylinder lube oils, aconventional BN oil (usually BN70) andmaybe a low-BN oil (e.g. BN50 or BN40).

In general, the complexity of the cylin-der lube oil system increases 1 through3, but not as much as the similar in-crease for the fuel oil systems, simplybecause the fuel oil system is moreextensive (more components and morespace consuming).

One way of preparing the ships couldbe to install a partition in the cylinder oilstorage tank (Fig. 19), instead of arran-ging two cylinder oil tanks. Thereby, thetank can be filled in the following way:

• BN70 cylinder oil on both sides of the partition

• BN40 cylinder oil on one side and BN70 on the other.

In the more complex system, separatepiping from each side of the partitionedstorage tank can lead to the servicetank, which may also be partitioned.

The systems shown can be combinedin numerous ways, and variations of thedescribed systems can be chosen. Youare welcome to contact MAN B&WDiesel in Copenhagen, Denmark, forspecial requirements, or if further infor-mation is needed.

Cylinder OilStorage Tank 1

Cylinder Oil

Service Tank 1


Cylinder Oil

Service Tank 2

3m

Cylinder Oil



Cylinder Oil

Service Tank 1


Cylinder Oil

Service Tank 2

3m

Cylinder Oil


Cylinder Oil


Cylinder Oil System No. 3 A

0 2 4 6

Fuel sulphur (%)

BN40/50 BN70

0 2 4 6

Fuel sulphur (%)

Fe

ed

rate

BN40/50 BN70

20

40

60

80

0 2 4 6

Fuel sulphur (%)

Cylinder Oil System No. 3 B

20

40

60

80

0 2 4 6

Fuel sulphur (%)

BN

(m

gK

OH

/g)

Cylinder OilStorage tank

Cylinder oilService Tank

3m

Ma

in

eng

ine

Cylinder OilStorage tank

Cylinder oilService Tank

3m

Ma

in

eng

ine

Fig. 19: Partitioning of cylinder oil storage and service tanks

14

Summary

It is inevitable that the exhaust gasemission from marine engines will befurther regulated, and we expect thatmany new engines, and especially exist-ing engines, will eventually have to beoperated on low-sulphur fuel. This willbe the case even though exhaust gasscrubbers and/or emission trading havebecome possible by the time new regu-lations are introduced.

On MAN B&W two-stroke engines, nodifference in the engine performance isconsidered between DO/GO and HFOoperation, where the HFO used todayhas a sulphur content of 2.7% on average.

However, operators have to take thenecessary precautions, and the marineindustry has to consider what generalapplication the new low-sulphur fuelsare being designed for, especially withregard to the fuel compatibility betweenfuels, and ignition qualities.

References

[1] EU, Environment – Air Pollution– Fuel Quality Monitoring

[2] “The Interaction between Low- sulphur Fuel and Lubricants”, by Kjeld Aabo, MAN B&W Diesel A/S

[3] “FIA-100 – Fuel CombustionAnalyzer for HFO”, by Jan KjetilPaulsen, Fueltech AS, Norway,November 2004

Documents

Operation on Low-Sulphur Fuels Two-Stroke Engines on Low Sulp.pdfMAN B&W Diesel A/S, Copenhagen, Denmark Contents: Operation on Low-Sulphur Fuels Two-Stroke Engines Introduction