guidelines for fuels and lubes purchasing operation on heavy

Guidelines for Fuels and Lubes PurchasingOperation on Heavy Residual Fuels

3Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

Contents

Fuel Oil Quality ................................................................................................ 5

Analysis Data ................................................................................................... 6

Fuel Oil Stability ............................................................................................... 8

Fuel Oil Treatment ............................................................................................ 8

Centrifuging Recommendations ........................................................................ 9

Fuel Sampling ................................................................................................ 11

Supplementary Fuel Oil Treatment .................................................................. 11

Fuel Oil System .............................................................................................. 13

Operational Aspects ....................................................................................... 14

Low-sulphur Fuel Operation ........................................................................... 15

Off-spec. Fuels............................................................................................... 15

Lube Oil Blending on Board ............................................................................ 17

Cylinder Oil, Low Speed Diesels ..................................................................... 18

Performance Verification of Cylinder Oils ......................................................... 19

Fuels and Lubes for Stationary Two-stroke MAN B&W Engines ...................... 19

List of References .......................................................................................... 20


Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels MAN B&W Two-stroke Engines

Fuel Oil Quality

MAN Diesel’s engines are designed to

operate in accordance with the unifuel

principle. For specific guidelines for fuel

and lube oils for gensets, contact MAN

Diesel in Augsburg, Germany.

For guidance on purchase, reference

is made to ISO 8217, BS6843 and to

CIMAC recommendations regarding

requirements for heavy fuel for diesel

engines, edition 2003. According to

these, the maximum accepted grades

are RMH 55 and K55. The mentioned

ISO and BS standards supersede BS

MA 100, in which the limit is M9.

For reference purposes, an extract from

the relevant standards and specifica-

tions is shown in Table I.

Based on our general service experi-

ence, and as a supplement to the above-

mentioned standards, MAN Diesel issues

a guiding fuel oil specification, shown

in Table I.

Residual marine fuel standards

Category ISO-8217 (Class F)

Characteristic

Unit

Limit

RMA 30

RMB 30

RMD 80

RME 180

RMF 180

RMG 380

RMH 380

RMK 380

RMH 700

RMK 700

Test method reference

Density at 15 ºC

kg/m3

max.

960,0

975,0

980

991.0

991.0

1010.0

991.0

1010.0

ISO 3675 or ISO 12185 (see also 7.1)

Kinematic vis-cosity at 50 ºC

mm2/s a

max.

30,0

80.0

180.0

380.0

700.0

ISO 3104

Flash point

ºC

min.

60

60

60

60

60

ISO 2719 (see also 7.2)

Pour point (up-per) b - winter quality - summer quality

ºC

max. max.

0 6

24 24

30 30

30 30

30 30

30 30

ISO 3016 ISO 3016

Carbon residue %(m/m) max. 10 14 15 20 18 22 22 ISO 10370

Ash %(m/m) max. 0.10 0.10 0.10 0.15 0.15 0.15 ISO 6245

Water %(v/v) max. 0.5 0.5 0.5 0.5 0.5 ISO 3733

Sulphur c

%(m/m)

max.

3.50

4.00

4.50

4.50

4.50

ISO 8754 or ISO 14596 (see also 7.3)

Vanadium

mg/kg

max.

150

350

200

500

300

600

600

ISO 14597 or IP 501 or IP 470 (see also 7.8

Total sediment potential

%(m/m)

max.

0.10

0.10

0.10

0.10

0.10

ISO 10307-2 (see also 7.6)

Aluminium + Silicon

mg/kg

max.

80

80

80

80

80

ISO 10478 or IP 501 or IP 470 (see also 7.9)

Used lubricating oil (ULO) - Zinc - Phosphorus - Calcium

mg/kg

max. max. max.

The fuel shall be free of ULO d 15 15 30

IP 501 or IP 470 (see 7.7) IP 501 or IP 500 (see 7.7) IP 501 or IP 470 (see 7.7)

a Annex C gives a brief viscosity/temperature table for information purposes only. (1 mm2/s = 1 cSt)b Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the vessel operates in both the northern and southern hemispheres.c A sulphur limit of 1.5 % (m/m) will apply in SOx emission control areas designated by the International Maritime Organization, when its relevant protocol comes into force. There may be local variations. d A fuel must be considered to be free of ULO if one or more of the elements zinc, phosphorus and calcium are below or at the specified limits. All three elements must exceed the same limits before a fuel shall be deemed to contain ULO.

Table I

6 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

In both tables the data refers to fuel

oils as delivered to the ship, i.e. before

onboard cleaning. Fuel oils within the

limits of this specification have, to the

extent of their commercial availability,

been used with satisfactory results in

MAN B&W two-stroke low speed diesel

engines.

It should be noted that current analysis

results do not fully suffice for estimating

the combustion properties of fuel oils.

This means that service results could

depend on oil properties which are not

known beforehand. This applies espe-

cially to the tendency of the fuel oil to

form deposits in combustion cham-

bers, gas passages and turbochargers.

As mentioned, the data refers to the fuel as

supplied, i.e. before the treatment.

If a fuel oil exceeding the data in Table I is

to be used, the engine builder or MAN

Diesel should be contacted for advice.

Analysis DataViscosity

Viscosity cannot be considered a qual-

ity criterion in its own right for fuel oils,

and is stated only for handling reasons

(pumps, preheaters and centrifuges).

Density

Density is related to the fuel quality be-

cause fuels derived from extensive re-

finery processing are left with a higher

carbon content, are more aromatic

and thus heavier. Therefore, fuels with

a high density are also high in carbon

residue and asphaltenes.

The water separation ability of the fuel

oil is ensured by limiting the density for

reasons of centrifuging, as stated in the

specification.

Density is normally measured at higher

temperatures, and the density at 15°C

is calculated on the basis of tables

which, depending on their origin, date

of issue, and the data on which they are

based, could give slightly differing den-

sities at 15°C.

Whereas the limit of 991 kg/m3 must

be observed when traditional centrifuges

(before 1985, purifier – clarifier) are used,

1010 kg/m3 is accepted provided that

modern centrifuges capable of hand-

ling fuels of such density are installed.

Flash point

The flash point limit is set as a safeguard

against fire only.

Pour point

The pour point indicates the minimum

temperature at which the fuel should

be stored and pumped. Temperatures

below the pour point results in wax for-

mation.

Sulphur

The corrosive effect of sulphuric acid

during combustion is counteracted by

adequate lube oils and temperature

control of the combustion chamber

walls.

The cylinder lube oil feed rate must be

according to the MAN Diesel recom-

mendation. The sulphur content has a

negligible effect on the combustion pro-

cess.

Carbon residue

The carbon residue is measured as

Conradson Carbon or Microcarbon.

Fuels with a high carbon residue con-

tent could cause increased fouling of

the gasways, necessitating more fre-

quent cleaning, especially of the turbo-

charger and exhaust gas boiler.

Some changes in combustion, requir-

ing adjustment of maximum pressures

for reasons of economy, could also be

attributed to a high carbon residue con-

tent. Part of the carbon residues repre-

sents asphaltenes.

The effect of asphaltenes on the com-

bustion process is similar to that of the

carbon residue. Asphaltenes also af-

fects the fuel oil lubrication properties.

Fuels with a high content of asphaltenes

may tend to emulsify with water.

Water

Water in the fuel should be removed by

centrifuging the fuel before use. This

applies especially to salt water, the

sodium content of which can result in

deposits on valves and turbochargers.

If the water cannot be removed online,

homogenising after centrifuging is recom-

mended.

Ash

Ash represents solid contaminants as

well as metals bound in the fuel (e.g.

vanadium and nickel). Part of the ash

could be catalyst particles from the refin-

ing process.

Catalyst particles are highly abrasive.

Solid ash should be removed to the

widest possible extent by centrifug-

ing, and cleaning can be improved by

installing a fine filter after the centrifuge

(e.g. 50 μm).


Vanadium, magnesium and sodium

Vanadium is bound in chemical com-

plexes in the fuel and, consequently,

cannot be removed.

Vanadium deposits can be very hard,

and may cause extensive damage to

the turbocharger nozzle ring and tur-

bine wheel. The only way to remove

vanadium deposits is to disassemble the

components and erase the deposits me-

chanically.

Sodium is normally present in the fuel

as a salt water contamination and may,

as such, be removed by centrifuging.

Sodium can also reach the engine in

the form of airborne sea water mist.

Vanadium, in combination with sodium,

may lead to exhaust valve corrosion

and turbocharger deposits. This can

occur especially if the weight ratio of

sodium to vanadium exceeds 1:3, and

especially in the case of a high vana-

dium content.

MAN Diesel has limited data to show

that the level of sodium and vanadium

in combination, and in this ratio, has led

to the above-mentioned complications

on MAN B&W engines.

For lower contents of sodium and va-

nadium, the weight ratio is considered

of less importance (for a vanadium con-

tent less than 150 mg/kg).

Magnesium, either present in the fuel,

in salt water contamination or intro-

duced via additives can, to some ex-

tent, increase the melting point of the

vanadium, thus preventing the forma-

tion of deposits.

Aluminium and silicon

The limit to aluminium and silicon has

been introduced in order to restrict the

content of catalytic fines, mainly Al2O3

and SiO2, in the oil. 80 mg Al and Si

corresponds to up to 170 mg Al2O2 and

SiO2.

Catalytic fines give rise to abrasive

wear, and their content should, there-

fore, be reduced as much as possible

by centrifuging the fuel oil before it

reaches the engine.

MAN Diesel recommends that 80 ppm

of catalytic fines before the centrifuge

is reduced as much as possible by the

fuel centrifuge and, as a guideline, the

level should in any case not exceed 15

ppm after the centrifuge, see Ref. [1]

and Ref [2].

Ignition quality

Normally applied analytical data for fuel

oil contain no direct indication of igni-

tion quality, neither do current specifi-

cations and standards. However, this is

not an important parameter for engines

with high compression ratios.

In a few cases (less than five), we have

observed that the fuel had such poor

ignition quality that the engines could

not operate properly. Analysis of the

fuel in question revealed that these

fuels had all been contaminated by

chemical waste.

Tests performed together with fuel ana-

lysing institutes give indications of the

ignition and combustion qualities of the

different fuels. Test instruments utilising

a constant volume combustion technol-

ogy have been developed and are cur-

rently being used for marine fuel testing

at a number of fuel laboratories and build-

ers of marine diesel engines worldwide.

The test presents the Rate of Heat Re-

lease, reflecting the actual heat release

process and, thus, the combustion

quality of the fuel tested. By the use of

calibration fuels, a recorded ignition de-

lay in combination with the combustion

quality can be converted into an instru-

ment-related Cetane number.

The test results reflect the differences

in ignition and combustion properties of

diesel engine fuels resulting from varia-

tions in the chemical composition of the

fuels being tested.

However, these test results do not re-

flect the functions of the actual com-

bustion in the diesel engine, because

the tests are conducted at different

conditions/mechanisms than exist in

the engine.

With the modern high compression ra-

tio engines, the denoted differences in

the fuel, both good and bad, are not at

the level indicated by the test results.

The cetane number in an ignition qual-

ity test might, as such, only provide an

indication of the difference in the fuels,

but not whether this will have an influ-

ence on the engine performance.


Fuel Oil Stability

Fuel oils are produced on the basis of

widely varying crude oils and refinery

processes. Due to incompatibility, such

fuels can occasionally tend to be unsta-

ble when mixed, for which reason mix-

ing on board should be avoided to the

widest possible extent.

A mixture of incompatible fuels in the

tanks can result in rather large amounts

of sludge being taken out by the centri-

fuges or even lead to centrifuge blocking.

Inhomogeneity in the service tank can

be counteracted by recirculating the

contents of the tank through the cen-

trifuge. This will have to be carried out

at the expense of the benefits derived

from a low centrifuge flow rate as de-

scribed below.

With the introduction of new IMO emis-

sion regulations and the fuel sulphur

limit in SECAs (sulphur emission control

areas), more blending of fuels to com-

ply with the regulations is taking place.

For this reason, the risk of incompat-

ibility of fuels is also higher.

Fuel Oil Treatment

Fuels supplied to a ship must be treat-

ed on board before use. Detailed infor-

mation on fuel oil system layout can be

found in the CIMAC Recommendations

issued in 2005, Volume 9, concerning the

design of heavy fuel treatment plants for

diesel engines. Practically all fuel speci-

fications refer to fuel as supplied and,

as such, serve primarily as purchasing

specifications. Furthermore, the data in

a standard fuel analysis serves to adjust

the onboard treatment and is actually of

little use to the operator when referring

to the engine operational data.

Hence the basic design criterion is that

engines must be capable of accepting

all commercially available fuel oils, pro-

vided that they are adequately treated

on board.

For this purpose, a well-designed fuel

oil treatment system is a must. General

minimum recommendations for the lay-

out of such a system have been speci-

Fig. 1: Pressurised uni-fuel oil system for both main engine and gensets

Diesel oil

Heavy fuel oil

Heated pipe with insulation

- - - - - - - - - -

Automatic de-aerating valve

From centrifuges

Diesel oilservice

tank

Heavy fuel oilservice tank

Heater

Boosterpump

Supply pumps Circulatingpumps

Fuel oildrain tank

Main engine

Deck

Common fuel oil supply unit

To fresh water cooling pump suction

Full flow filterOverflow valve adjusted to 4 bar

Venting box

Auxiliary engines

Auxiliary engines

Auxiliary engines


fied and should be complied with in

order to ensure proper treatment of the

fuel permitted by the guiding specifica-

tion. The operation of the fuel prepara-

tion system is the responsibility of the

operator. Good results require both the

correct system and the correct opera-

tion of the system.

The fuel oil system consists of a clean-

ing plant (comprising centrifuging) and

a pressurised fuel oil system.

Fig. 1 shows the pressurised fuel oil

system common for MAN B&W main

and GenSet engines.

Centrifuging Recommendations

Fuel oils, whether HFO or DO, should

always be considered as contaminated

upon delivery and should therefore be

thoroughly cleaned to remove solid as

well as liquid contaminants before use.

The solid contaminants in the fuel are

mainly rust, sand, dust and refinery cat-

alysts. Liquid contaminants are mainly

water, i.e. either fresh water or salt wa-

ter.

Impurities in the fuel can cause damage

to fuel pumps and fuel valves, and can

result in increased cylinder liner wear

and deterioration of the exhaust valve

seats. Also increased fouling of gas-

ways and turbocharger blades could

result from the use of inadequately

cleaned fuel oil.

Effective cleaning can only be ensured

by using a centrifuge. We recommend

that the capacity of the installed centri-

fuges should, at least, be according to

the centrifuge maker’s specifications.

To obtain optimum cleaning, it is of the

utmost importance that the centrifuge

is operated with as low a fuel oil viscos-

ity as possible, and that the fuel oil is al-

lowed to remain in the centrifuge bowl

for as long as possible.

Temperature of HFO before centrifuges

It is often seen that the HFO preheat-

ers are too small, or the steam supply

of the preheater is limited, or that they

have too low a set point in tempera-

ture. Often the heater surface is partly

clogged by deposits. These factors all

lead to reducing the separation tem-

perature and hence the efficiency of the

centrifuge.

In some cases, the temperature of the

HFO from the preheater is unstable and

fluctuates, which again results in im-

proper cleaning of the fuel.

In order to ensure that the centrifugal

forces separate the heavy contaminants in

the relatively limited time that they are

present in the centrifuge, the centrifuge

should always be operated with an inlet

temperature of 98°C.

A temperature decrease has to be fol-

lowed by a reduced throughput to en-

sure the same cleaning efficiency, see

Fig. 2.

The fuel is kept in the centrifuge as long

as possible by adjusting the flow rate

through the centrifuge so that it corre-

sponds to the amount of fuel required

by the engine without excessive recir-

culation. Consequently, the centrifuge

should operate for 24 hours a day ex-

cept during necessary cleaning.

Centrifuges with separate feed pumps

with a capacity matched to the engine

output are to be preferred.

Taking today’s fuel qualities into con-

sideration, the need for maintenance of

the centrifuges should not be underes-

timated.

100

90

80

70

77 90 92 94 96 98 100

Capacity for same separation (%)

cSt at 50 C

180 cSt300 cSt700 cSt

o

Fig. 2: Relationship of throughput and temperature


On centrifuges equipped with adjusting

screws and/or gravity disks, their cor-

rect choice and adjustment is of special

importance for the efficient removal of

water.

The centrifuge manual states which

disk or screw adjustment should be

chosen on the basis of the density of

the fuel.

The normal practice is to have at least

two centrifuges available for fuel clean-

ing purposes, operating in serial or par-

allel mode.

For old type centrifuges, results from

experimental work on the centrifuge

treatment of today’s residual fuel quali-

ties have shown that the best cleaning

effect, particularly in regard to removal

of catalytic fines, is achieved when the

centrifuges are operated in series, i.e.

in purifier/clarifier mode.

For the automatically operating centri-

fuges delivered from the mid-1980s,

suitable for treating fuels with densi-

ties higher than 991 kg/m3 at 15°C, it

is recommended to operate the centri-

fuges in parallel, as this results in reduced

throughput, i.e. longer retention time in the

centrifuge. However, the maker’s specific

instructions should be followed.

In this context, see section on high

density fuels. If the centrifuge capacity

installed is on the low side, in relation

to the specific viscosity of the fuel oil

used, and if more than one centrifuge is

available, parallel operation should be

considered as a means of obtaining an

even lower flow rate. However, in view

of the above results and recommenda-

tions, serious consideration should be

given to installing new equipment in

compliance with today’s fuel qualities

and flow recommendations.

For determination of the centrifuging

capacity, we generally advise that the

recommendations of the centrifuge

maker be followed, but the curves in

Fig. 3 can be used as a guide.

It is recommended that new centrifuges

have gone through a separation perfor-

mance standard test according to the in-

dustry standard CWA 15375.

In order to check the performance of

the centrifuge, fuel samples taken reg-

ularly before and after the centrifuge

should be analysed.

High Density Fuels

In view of the fact that some fuel oil

standards incorporate fuel grades with-

out a density limit, and also the fact

that the traditional limit of 991 kg/m3

at 15°C is occasionally exceeded on

actual deliveries, some improvements

in the centrifuging treatment have been

introduced to enable treatment of fuels

with higher density.

Since the density limit used so far is, as

informed by centrifuge makers, given

mainly to ensure interface control of the

purifier, new improved clarifiers, with

automatic desludging, have been in-

troduced, which means that the purifier

can be dispensed with.

With such equipment, adequate sepa-

ration of water and fuel can be carried

out in the centrifuge, for fuels up to a

density of 1010 kg/m3 at 15°C.

Therefore, this has been selected as

the density limit for new high density

fuel grades.

Thus we have no objections to the use of

such high density fuels in our engines,

provided that these types of centrifuges

are installed. They should be operated

in parallel or according to the centri-

fuge maker’s instructions.

Rate of flow, related to rated capacity of centrifuge80

60

40

20

200 400 600 1500 3500 7000 sec RI/100 Fo

%

Fig. 3: Centrifuge makers´ capacity specification


Fuel SamplingSampling

To be able to check whether the speci-

fication indicated and/or the stipulated

delivery conditions have been complied

with, we recommend that a minimum

of one sample of each bunker fuel lot

be retained. In order to ensure that

the sample is representative for the oil

bunkered, the sample should be con-

tinuously taken at the ship manifold

throughout the bunkering period. This

is done by a continuous collection of

drip sample during the bunker delivery,

see Ref. [3].

This is without including the BDN (bun-

ker delivery note) for compliance with

IMO Annex VI.

Analysis of samples

The samples received from the bunker-

ing company are frequently not identi-

cal with the heavy fuel oil actually bun-

kered. It is also appropriate to verify the

heavy fuel oil properties stated in the

bunker documents, such as density,

viscosity and pour point. If these values

deviate from those of the heavy fuel oil

bunkered, there is a risk that the heavy

fuel oil separator and the preheating

temperature are not set correctly for the

given injection viscosity.

Sampling equipment

Several suppliers of sampling and fuel

test equipment are available on the

market, but for more detailed and ac-

curate analyses, a fuel analysing insti-

tute should be contacted.

Supplementary Fuel Oil Treatment

In a traditional system, the presence of

large amounts of water and sludge will

hamper the functioning of a clarifier, for

which reason a purifier has been used

as the first step in the cleaning process.

With the new automatic desludging

clarifiers, the purifier can, as mentioned,

be dispensed with. We consider the re-

moval of solids to be the main purpose

of fuel treatment.

Although not necessarily harmful in its

own right, the presence of an uncon-

trolled amount of water and sludge in

the fuel makes it difficult to remove the

solid particles by centrifuging.

Therefore, the following additional equip-

ment has been developed:

Homogenisers

Homogenisers are used to disperse

any sludge and water remaining in the

fuel after centrifuging. A homogeniser

placed after the centrifuge will render

fresh water (not removed by centrifug-

ing) harmless to the engine.

Homogenising may also be a means

to cope with the more and more fre-

quently occurring incompatibility prob-

lems, which are not really safeguarded

against in any fuel specification. Both

ultrasonic and mechanical homogenis-

ers are available.

Homogenisers can also be used for

moderate emission control in conjunc-

tion with emulsification of freshwater

into the fuel.

Homogenisers installed before the fuel

centrifuge can, when considering the

full range of the ISO 8217 fuel specifi-

cation, reduce the efficiency of the cen-

trifuge and, thus, the cleanliness of the

fuel delivered to the engine. The sodi-

um will not be removed from the fuel in

the form of salt water. The cat fines and

other abrasive material might be split

up into very small particles, which are

difficult for the centrifuge to separate

and which will still have a harmful wear

effect on the engine components.

Installation of homogenisers before the

centrifuge, see Fig. 4, is therefore not

advisable.


In order to reduce the NOx level in the

engine exhaust gas, water can be add-

ed to the fuel oil to create an emulsion.

Clean freshwater should be used, and

this is homogenised into the fuel oil at

a maximum ratio of approx. one part of

water to two parts of fuel oil. The water

emulsion can be stable with HFO but

with lighter fuels, such as gas oil and

diesel oil, it may be necessary to add

an emulsifier to the fuel oil before ho-

mogenising the fuel and water. The ho-

mogeniser is located between the HFO

service tank and the engine, i.e. after

the fuel oil purifiers.

Fine filters

Fine filters are placed directly after the

centrifuge, or in the supply line to the

engine, in order to remove any solid

particles not taken by centrifuging. The

mesh is very fine, i.e. down to 5 μm.

Homogenising before a fine filter can

reduce the risk of fine filter blocking by

the agglomeration of asphaltenes.

To F.W. coolingpump suction Full flow filter

Mainengine

Circulating pumps

Acceptable locationof homogeniser

Supply pumps

Heavy fuel oilservice tank

Dieseloil

servicetank From diesel centrifuges

Fuelstorage

tank

Suggested location of homogeniserby some suppliers.

Not acceptablefor engine performance

Deck

Automatic deaerating valve

Venting tank

Diesel oilHeavy fuel oilHeated pipe with insulation

To drain tank

F.O. draintank

TSA

304

PI PI

PSA307

TI TI

VSA303

Centrifuges

Preheater

TE 8005

PT 8002

VT 8004

Fig. 4: Pressurised fuel oil system, with homogeniser


Fuel Oil System

A pressurised fuel oil system, as shown

in Fig. 1, is necessary when operating

on high viscosity fuels. When using high

viscosity fuels requiring high preheating

temperatures, the oil from the engine

fuel oil system to the return line will also

have a relatively high temperature.

The fuel oil pressure measured on the

engine (at fuel pump level) should be

about 8 bar, which is equivalent to a cir-

culating pump delivery pressure of up

to 10 bar. This maintains a pressure mar-

gin against gasification and cavitation in

the fuel system, even at 150°C preheat.

In order to ensure correct atomisation,

the fuel oil temperature must be ad-

justed according to the specific fuel oil

viscosity used.

An inadequate temperature can influ-

ence the combustion and could cause

increased wear on cylinder liners and

piston rings, as well as deterioration

of the exhaust valve seats. Too low a

heating temperature, i.e. too high vis-

cosity, could also result in a too high

injection pressure, leading to excessive

mechanical stresses in the fuel oil sys-

tem.

In most installations, heating is carried

out by means of steam, and the viscosity

is kept at the specified level by a viscosity

regulator controlling the steam supply.

Depending on the viscosity/tempera-

ture relationship of the fuel oil (the vis-

cosity index), an outlet temperature of

up to 150°C might be necessary, as in-

dicated on the guidance curves shown

in Fig. 5, which illustrate the expected

heating temperature as a function of the

specific fuel oil viscosity in cSt/50°C.

The recommended viscosity meter set-

ting is 10-15 cSt. However, service ex-

perience has shown that the viscosity

of the fuel before the fuel pump is not

a too critical parameter, for which rea-

son we allow a viscosity of up to 20 cSt

after the heater. In order to avoid too

rapid fouling of the heater, the temper-

ature should not exceed 150°C.

7 43

10 52

12 5915 69

20 87

30 125

cSt SecRW

Normal heating limit

Approximate pumping limit

10 15 25 35 45 55 cSt/100 Co

30 60 100 180 380 600 cSt/50 Co

200 400 800 1500 3500 6000 sec. RW/100 Fo

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

Temperature after heater

Co

Approximate viscosityafter heater

Viscosity of fuel

Fig. 5: Heating chart for heavy fuel oil


Operational Aspects

All low speed engines from and in-

cluding the K-GF types (from around

1973) are equipped with uncooled, all-

symmetrical lightweight fuel injection

valves.

These allow constant operation on

heavy fuel, due to the built-in possibility

of circulating heated heavy fuel through

the high-pressure fuel pipes, and fuel

valves during engine standstill.

In view of the emission regulations and

the increased use of low-sulphur fuels,

a special procedure is made to protect

the engine when changing between fu-

els (see the chapter: ‘‘Low-sulphur Fuel

Operation’’).

If a change to diesel oil is necessary as

a result of, for instance, the need for

a major repair of the fuel oil system, a

prolonged stop, or the use of very low-

sulphur fuels, as required by environ-

mental legislation, the heavy fuel in the

system can be changed with diesel oil

at any time, provided the change-over

procedure is followed, even when the

engine is not running. See also the en-

gine instruction book.

During engine standstill, the heated fuel

oil circulating through the fuel system

does not require the same low viscosity

as recommended for injection.

Thus, in order to save steam, the heat-

ing temperature may be lowered by

some 20°C, giving the circulating oil a

viscosity of up to 30 cSt.

The temperature should be raised to

the recommended service value, as il-

lustrated in Fig. 5, about 30 minutes

before starting-up is expected.

As previously mentioned, the heating

temperature must not exceed 150°C,

and during operation it is not necessary

to apply pipe heating by means of heat

tracing. When running on diesel oil, the

heat tracing system must not be used

at all.

However, it should be noted that the

pipe heating system on drain pipes

should remain in operation when run-

ning on heavy fuel.

Engine

Compatibilityof mixed fuels!

Tank systemconsiderations!

Fuel change-over unit

Viscosity!

OilBN10-40-70!

High S% Low S%

Fig. 6: Considerations to be made to before changing between high/low sulphur fuels

Fig. 7: Recommended cylinder oil feed rates depending on the fuel sulphur level


Low-sulphur Fuel Operation

Today, there are ECAs (emission control

area, based on EU and IMO regulations)

in the Baltic Sea, the North Sea and the

English Channel. And more such areas

are expected to come. In the USA, the

EPA (Environmental Protection Agency)

is considering to designate Long Beach

an ECA very soon.

The sulphur content has an impact on

the sulphur acid emission to the air, sea

and land, as well as a major impact on

the particle level in the exhaust gas.

Even though MAN B&W two-stroke en-

gines are largely insensitive to the fuel

quality, changing between fuels with

different levels of viscosity is an impor-

tant consideration to make.

The cylinder lube oil base number must

be considered. Operating on normal

BN70 cylinder oil for too long when

burning low-sulphur fuel will prevent

controlled corrosion on the cylinder lin-

ers.

The mechanism is a creation of an ex-

cess of deposits originating from the

cylinder oil’s additives. Low-BN oil is

available from the major oil companies,

and recommendations on the use of

low and high-BN oils are also available.

The fuel change-over process must fol-

low the thermal expansion of both the

fuel pump plunger and the barrel, and

a procedure has been created to avoid

causing damage to the fuel pumps.

An automatic change-over unit will be

available in 2009.

In order to ensure the creation of a hy-

drodynamic oil film between the fuel

pump plunger and barrel, a viscosity of

2 cSt is required at the engine inlet. This

may be difficult to achieve for some DO

and GOs, and some operators may

have to introduce a cooler in the fuel oil

system to ensure a satisfactory viscos-

ity level.

The ignition quality of a fuel oil is not

an issue for MAN B&W two-stroke en-

gines. MAN Diesel has conducted a

number of research tests showing that

the MAN B&W two-stroke engine is in-

sensitive to the poor ignition combus-

tion quality fuels on the market today.

A separate booklet called ‘‘Low-sulphur

fuel operation’’ is available from MAN

Diesel, Ref. [4].

Off-spec. Fuels

Several selected off-spec. fuels (i.e.

beyond ISO 8217) have been tested

on MAN B&W’s two-stroke research

engine:

� Natural gas

� Bitumen

� Orimulsion

� Tallow

Our research facility in Copenhagen is

available for such testing. In the event

that off-spec. fuels are considered for

use on MAN B&W engines, it is recom-

mended that MAN Diesel is contacted

for further information regarding opera-

tional experience and any necessary

precautions.

Table II shows the guiding biofuel spec-

ification for MAN B&W two-stroke low

speed diesel engines.

MAN Diesel can be contacted for fur-

ther recommendations on the use of

biofuels.

Guiding Biofuel Specification for MAN B&W

Two-stroke Low Speed Diesel Engines 1)

Designation

Density at 15 oC kg/m3 1010

Kinematic viscosity at 10 oC 2) cSt 55

Flash point oC >60

Carbon residue % (m/m) 22

Ash % (m/m) 0.15

Water % (m/m) 1.0

Sulphur 3) % (m/m) 5.0

Vanadium ppm (m/m) 600

Aluminium + Silicon mg/kg 80

Sodium plus potassium ppm (m/m) 200

Calcium ppm (m/m) 200

Lead ppm (m/m) 10

TAN (Total Acid Number) mg KOH/g 4) <25

SAN (Strong Acid Number) mg KOH/g 0

1) Valid at inlet to centrifuge plant 2) Pre-heating down to 15 cSt at engine inlet flange is to be ensured 3) Lodene, phosphorus and sulphur content according to agreement with emission controls maker 4) Experience shows that a high Total Acid Number has influence on the time between overhaul of the engine fuel system and, therefore, need to be adjusted accordingly

Table II


Lubricating Oil Qualities

Low speed diesel rust and oxidation in-

hibited alkaline engine oils of the SAE

30 viscosity grade should be chosen

for circulating oil. The oils should have

adequate dispersancy/detergency to

keep the crankcase and the piston

cooling spaces free from deposits.

For engines with an integrated gear

driven Power Take Off (PTO), a mini-

mum FZG load level (Foursquare gear

oil test) of 8 should be observed. For

electronically controlled engines, a min-

imum FZG load level of 10 is required.

Contamination of system lube oil

Increase of BN (Base Number) and vis-

cosity of the system lube oil during op-

eration is unavoidable.

The piston rod stuffing box separates

the combustion and scavenge air

spaces from the crankcase. Therefore,

lube oil will not be severely contami-

nated with combustion products and

used cylinder lube oil. However, some

cylinder lube oil leaks through the stuff-

ing box, down into the system lube oil

sump. This is revealed by increasing

BN and viscosity levels of the system

lube oil.

Normally, the increase will stop after

some time and remain at a stable level

where topping up with new system lube

oil, to make up for normal consump-

tion, will balance the degree of contam-

ination of the system oil with cylinder

lube oil.

Water may also contaminate system oil.

Excess water levels may harm tin-alu-

minum bearings, for which reason MAN

Diesel recommends that the water level

does not exceed 0.2% (0.5% water al-

lowed for shorter periods of time), Ref.

[5].

In some cases, fuel has been seen

leaking through the fuel pump umbrel-

la sealings into the system oil. Fuel is

known to form deposits on hot spots,

i.e. in the piston undercrown space. It

is therefore important to keep the rec-

ommended overhaul intervals on fuel

pumps to secure that the pump pack-

ings/sealings are replaced.

BN level consideration

The increase in BN can influence the

ability of the oil to reject water by the

usual centrifuging. Water together with

calcium compounds from oil additives

may form calcium hydroxide recom-

mended to ensure calcium carbonate

and build up a deposit of lacquer on

the bearings. Another risk is the in-

creased sludge formation when water

is present.

Experience shows, however, that many

engines are operating with up to 30 BN

(starting from approx. 6 BN) without

any operational problems, and without

any changes in the lube oil performance

that give reason for renewing the oil.

Table III

International brands of lubricating oils which have been applied with satisfactory results on MAN B&W engines, on a

large number of vessels

Lubricating oils - Low speed main engines

Type Circulating oil Cylinder oil

Requirement SAE 30, BN 5-10 SAE 50, BN 60-80 SAE 50, BN 40-50

Oil company

BP Energol OE-HT 30 Energol CLO-50M/CL 605 Energol CL 505/CL-DX 405

Castrol CDX 30 Cyltech 70/80 AW Cyltech 40 SX/50 S

Chevron (Chevron, Texaco, Caltex)

Veritas 800 Marine 30

Taro Special HT 70

Taro Special HT LS 40

Total Atlanta Marine D 3005 Talusia HR 70/Talusia Universal Talusia LS 40

Exxon Mobil Mobilgard 300 Mobilgard 570 Mobilgard L540

Shell Melina 30/30S Alexia 50 Alexia LS

* depending on load profile and sulphur content, see MD recommendation for cylinder feed rate


An increase in BN to an equilibrium

value of up to 25 in BN and in viscosity

from SAE 30 to SAE 40 is considered

normal, and no action is called for. An

increase beyond that is not really harm-

ful and can, in most cases, be counter-

acted by new low-BN topping oil.

The circulation oil consumption on the

MC/ME/ME-B/C/S engines is very low

because the engines are designed to

have fewer leaks and because of the

much reduced stuffing box oil drain,

compared to previous engine types,

causing a higher increase in BN and

viscosity. Therefore, it may be neces-

sary to add some new oil to the lube oil

sump at times to ensure a proper qual-

ity and BN level of the lube oil. This is

done by exchanging part of the circula-

tion oil in the sump based on an analysis

of the oil.

Lube Oil Blending on Board

A new blending-on-board (BoB) con-

cept makes it possible to add addi-

tives to the engine system oil and then

utilise it as cylinder lube oil. By top-

ping up the thereby used system oil,

a steady renewal of the oil is ensured

as well as improved viscosity control

and cleanliness. The oil suppliers get

the advantage of supplying only one oil

and a limited amount of additives. The

traditionally consumed cylinder oil is re-

placed with the blended lube oil.

Furthermore, the idea with the BoB

concept is that the operator will ulti-

mately be able to adjust the cylinder oil

BN to the current fuel sulphur level by

changing the blending ratio. In 2007,

MAN Diesel issued a No Objection Let-

ter (NOL) on a BN70 blend. The NOL

applies to a specific additive in a spe-

cific system oil.

Testing of a BN60 blend on is ongoing,

on an engine in service, and the condi-

tion is so far found to be satisfactory.

Technically, it is currently being investi-

gated how the blending-on-board con-

cept could cover all BN levels on just

the same additive package.

Some considerations must be made in

this respect:

� System oil condition prior to blending

must be acceptable

� Quality control of the additives must

be ensured

� Technical performance of additive

package in different concentrations

(BN40, BN50, BN60…) must be

clarified

MAN Diesel shares a common inter-

est with the oil companies – to keep

the lube oil expenses predictable and

optimal. Therefore, also in this field it

is of the utmost importance to ensure

the reliable performance of the blended

products. This requires continuous veri-

fication tests.

No-objection letters will be issued as

the tests with BoB and lower BN oils

are successfully concluded.

MAN Diesel can be contacted for infor-

mation on the test status.


Cylinder Oil, Low Speed Diesels

For engines operating on heavy residual

fuel oil, a cylinder oil with a viscosity of

SAE 50 and BN of 70 is recommended.

In most cases the high BN cylinder lubri-

cant will also be satisfactory during tempo-

rary operation on diesel oil/gas oil.

In general, changing the cylinder oil

type to correspond to the fuel type

used (i.e. bunker fuel or diesel oil/gas

oil) is considered relevant only in cases

where operation on the respective fuel

type is to exceed two weeks. However,

cylinder oil feed rate adjustments might

be required.

There is a high risk when using BN70

cylinder oils in connection with frequent

bunkering of low-sulphur fuels, with a

sulphur content of below to 1.5%, see

Ref. [6]

The main problem has been the ac-

cumulation of unused cylinder oil ad-

ditives, resulting in excessive deposits

on the piston topland. This has led to

high wear, and to a situation where in-

creased lubrication does not improve

the condition. On the contrary, in-

creased lubrication increases the for-

mation of deposits, leading to accelera-

tion of the problem.

It has been established that a certain

degree of controlled corrosion en-

hances lubrication, in that the corro-

sion generates small “pockets” in the

cylinder liner running face from which

hydrodynamic lubrication from the oil in

the pocket is created. The alternative,

no corrosion, could lead to bore polish

and, subsequently, hamper the crea-

tion of the necessary oil film on the liner

surface, resulting, eventually, in accel-

erated wear. Controlled corrosion – not

avoiding corrosion – is therefore crucial,

and adjusting the BN to the fuel oil sul-

phur content is essential.

Low alkaline cylinder lubricants are

therefore available on request from the

major lubricating oil suppliers.

Table III shows typical lube oils used

on marine applications together with

the fuel oils specified in Table I. In or-

der to control and prevent uncontrolled

sulphur corrosion, it has become the

industry standard for marine engines to

use cylinder lubricants with a BN of 70

in combination with the average marine

fuels, i.e. 380 cSt and 2.7% sulphur

content.

Special running conditions because of

frequent bunkering of low-sulphur fuels

and environmental fuel regulations (by

the authorities or self imposed), requir-

ing the use of low-sulphur fuel and spe-

cial running conditions, might call for

a lowering of the total alkaline additive

content. This can be done by lowering

the dosage towards our minimum feed

rate or, alternatively, by using one of the

specially designed cylinder oils with a

lower BN and with full detergency.

Service tests with such specially de-

signed low-BN oils have shown good

results. However, it may be difficult to

determine whether changing to a BN40

or BN50 cylinder oil will be adequate for

operation of ultra-low sulphur fuels. A

lower BN than 40-50 might be the fu-

ture oil for low-sulphur operation.

For this reason, we recommend that

you contact MAN Diesel, or the engine

builder, before operation on ultra-low

sulphur fuel.

General

It should be considered that, irrespective

of the sulphur content being high or low,

the fuels used in low speed engines are

usually low quality heavy fuels.

Table IV

Stationary applications

Ambient conditions Stationary engines Marine engines

Tropical Design

Maximum Average Minimum

Cooling water temp. yearly site yearly site yearly site 32°C 25°C

Air inlet temp. climatic cond. climatic cond. climatic cond. 45°C 25°C

Blower inlet pressure Depends on height above sea level 1000 mbar 1000 mbar


Therefore, the cylinder oils must have

full capacity in respect of detergency

and dispersancy, irrespective of the BN

specified. This is a technology which

has to be mastered by the lube oil sup-

pliers, who can individually tailor a cylin-

der lube oil to the relevant fuel.

Breaking-in cylinder lube oils for testbed

running

In addition to determining the optimum

oil design for normal operation of the

two-stroke MAN B&W engines, we

also investigate and test various lube

oil designs in cooperation with the oil

companies to find the optimum cylinder

lube oils for testbed running.

Most builders of MAN B&W two-stroke

engines are using low-sulphur DO fuels,

primarily for environmental reasons.

This, in combination with a relatively

high running-in lube oil dosage, re-

quires a high detergency level in the

oil. Therefore, we generally recommend

the use of a BN70 cylinder oil, irrespec-

tive of the sulphur content of the fuel oil.

When introducing alucoating on piston

rings and semi-honed cylinder liners,

we also introduced a shorter running-

in period which, furthermore, limits the

period in which excess cylinder lube oil

is supplied, and improves the running-

in conditions. This means that the en-

tire running-in period, up to 100 hours,

is fully acceptable for using BN70 cylin-

der lube oils.

Performance Verification of Cylinder Oils

All oils listed have gone through a per-

formance test for about 4,000 running

hours on a relevant engine type in ser-

vice and have, during the test, been in-

spected by engineers from MAN Diesel,

in cooperation with the oil supplier.

When satisfactory results have been

achieved, MAN Diesel issues a ‘Let-

ter of No Objection’ for the use of the

oil on MAN B&W two-stroke engines.

However, MAN Diesel does not assume

responsibility for any damage caused

due to the quality of an oil mentioned in

a ‘Letter of No Objection’. The perfor-

mance of the oil is the responsibility of

the oil supplier. It is up to the operator

to obtain guarantees from the oil sup-

plier that the oil is suitable for operation

on the plant in question in conjunction

with the currently used fuel.

If an oil on the list fails to provide ac-

ceptable performance, then MAN

Diesel will work together with the oil

company to clarify the reasons and, if

needed, have a better oil introduced.

If an oil fails, the ‘Letter of No Objec-

tion’ will be withdrawn.

The list should not be considered com-

plete, and oils from other companies

may be equally suitable. Upon request,

MAN Diesel will inform whether a given

oil has been tested and whether the

test results were acceptable.

Further information about the oil test

and ‘Letter of No Objection’ can be

obtained by contacting MAN Diesel in

Copenhagen.

Fuels and Lubes for Stationary Two-stroke MAN B&W Engines

Stationary engines operate at load pat-

terns and ambient conditions which

differ widely from those of their marine

counterparts. This is illustrated in Fig. 8

and Table IV showing the typical oper-

ating conditions for both applications.

Thus, Fig. 8 shows that for stationary

engines, the average load is 95-100%

during 8,000 hours, or more, per year in

operation, whereas for marine engines

the average load is around 80% and,

furthermore, often only for 6,000 hours

per year in operation. This means that

stationary engines typically have a more

than 60% higher load factor than ma-

rine engines.

Stationary engines are exposed to

widely varying ambient conditions, i.e.

higher and lower air and cooling water

temperatures, see Table IV. Further-

more, stationary engines are frequently

exposed to fuel oils of non-marine qual-

ities. The fuel is often delivered from

one permanent supplier, meaning that

the quality from this supplier, good or

bad, will prevail.

Fig. 8: Typical load profile during a year in opera-tion

60

70

80

90

100

110

0 2,000 8,000hours

Time in service over one year

% load

Marine

Stationary

4,000 6,000


Therefore, lube oils, especially cylinder

oil, have to be individually selected and,

at times, even individually specified and

optimised in order to match the fuel oil

available.

Table III shows typical lube oils to be

used for marine applications together

with the fuel oils specified according to

ISO 8217. In order to control/prevent

sulphur corrosion, it has become the

industry standard for marine engines to

use cylinder lubricants with a BN of 70

for use with the average marine fuels.

This simple rule does not apply to sta-

tionary engines, where the sulphur level

in the fuel usually remains constant, i.e.

at the level set by the supplies avail-

able, or, when regulated by local leg-

islation, often shows a decreasing ten-

dency over the lifetime of the plant.

Hence, the constant use of a higher

than average sulphur content, possibly

even higher than that found in the ma-

rine specification, will call for the use of

a higher BN, and for this situation lube

oils with a BN of up to 100 are avail-

able.

Correspondingly, long-term use of

lower-than-average sulphur fuels will

call for the use of lower BN lube oils, as

described for low-sulphur marine fuels.

In addition, the engine load for station-

ary engines is usually very high, and the

ambient temperature is often higher as

well, ref. Fig. 8 and Table IV.

Hence, temperatures are high in the

combustion chamber, and the need to

counteract cold corrosion with alkaline

additives is lower, thus reducing the BN

requirement.

List of References

[1] “Heavy Fuel Oil Treatment”, Service

Letter SL05-452, Kjeld Aabo, MAN

Diesel, Copenhagen, Denmark

[2] “Marine diesel engines, catalytic

fines and a new standard to ensure

safe operation”, by Alfa Laval, BP

Marine and MAN B&W Diesel

[3] “Guidelines for the sampling of fuel

oil for determination of compliance

with Annex VI of MARPOL 73/78”,

Resolution by the IMO Marine En-

vironment Protection Committee,

MEPC 96

[4] “Operation on Low-sulphur Fuel”,

by Kjeld Aabo, MAN Diesel,

Copenhagen, Denmark, publica-

tion no.: 5510-0001-01ppr, Janu-

ary 2006

[5] “Cylinder Lubrication Guidelines

Operation on Fuels with Varying

Sulphur Contents All MC/MC-C

and ME/ME-C type engines Mk 6

and higher, with Alpha ACC Sys-

tem”, and “Cylinder Lubrication

New ACC Guidelines All MC/MC-C

and ME/ME-C type engines Mk

6 and higher, with Alpha ACC

System”, Service Letters SL05-

455 and SL07-479, Henrik Rol-

sted, MAN Diesel, Copenhagen,

Denmark

MAN Diesel & TurboTeglholmsgade 412450 Copenhagen SV, DenmarkPhone +45 33 85 11 00Fax +45 33 85 10 [email protected]

MAN Diesel & Turbo – a member of the MAN Group

All data provided in this document is non-binding. This data serves informational purposes only and is especially not guaranteed in any way. Depending on the subsequent specific individual projects, the relevant data may be subject to changes and will be assessed and determined individually for each project. This will depend on the particular characteristics of each individual project, especially specific site and operational conditions. Copyright © MAN Diesel & Turbo. 5510-0041-02ppr Aug 2014 Printed in Denmark

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