Challenges in operation with low sulphur fuel

1. 1
Challenges Associated with the Use of Low Sulphur Fuels
John E. Kokarakis 1)
, Emmanuel J. Kokarakis2)
, Agamemnon Apostolidis 3)
1)
Bureau Veritas, john.kokarakis@gr.bureauveritas.com
2)
University of Crete, kokomanoschem@gmail.com
3)
Enterprises Shipping & Trading SA, agamemnon.apostolidis@gmail.com
Abstract
In compliance to MARPOL VI, regulation 14, ships
need to burn 0.1% sulphur fuel after January 1st
2015 in
the ECA areas. The present study deals with the
challenges associated with the utilization of low sulphur
diesel, MGO or DMA grade. The issues dealt are the
lack of lubricity, the need for different lube oil, the low
viscosity of fuel and inability to sustain full film
lubrication, potential stability and incompatibility
issues. Shipping companies need to guide the crews with
transparent and thorough fuel change-over procedures.
At the same time they need to implement necessary
design modifications to accommodate 0.1% sulphur fuel
and cope with the increased cost of fuel. The financial
burdens in operational costs for various cases are also
discussed.
Keywords
Low sulphur, ECA, MARPOL VI, fuel cost, MGO
1. Introduction
Since January 1st, 2010 marine vessels berthing at EU
ports for more than two hours are required to operate on
0.1% sulphur Middle Gas Oil, MGO. Also on January
1, 2010, the California Air Resources Board, CARB,
has mandated commercial vessels to operate on 0.1%
sulphur MGO, when entering California waters 24 miles
from port. The revised MARPOL Annex VI, Regulation
14 has adopted progressive reduction in SOx emissions
from the engines at the designated Emission Control
Areas (ECAs). After January 1st 2015 the sulphur limit
in marine fuels will be 0.1% in all ECAs.
The introduction of 0.1% sulphur distillate fuels within
ECAs results in a number of key issues that ship
operators, charterers and equipment manufacturers have
to deal with. The proposed work identifies and presents
the risks and challenges associated with the extended
time of fuelling Main Engine, Auxiliary Engines and
Boilers by distillates satisfying the MARPOL limit.
Furthermore operational measures and procedures as
well as design modifications will be presented in order
to mitigate the risks associated with implementation of
the regulation.
Fuel temperature and viscosity, lubricity or lack thereof,
lubricating oil selection, need for distillate cooling, risk
of MGO evaporation/gassing due to lower flash point or
heat transfer, blending of fuels during change-over, fuel
injection adjustment in conventional and electronic
main engines, need for additional/segregated MGO
storage tanks on board – not adjacent to heated tanks,
are critical areas when using ultra-low sulphur fuel.
The introduction of the ultra-low sulphur fuel has also
increased the ship operation costs in addition to impact
on ship operation and design. The consequences in
terms of operational and voyage costs are presented for
a number of worldwide trading ships for different
segments (Bulk Carriers and Tankers) based on up to
date collected figures
2. Lack of Lubricity
Lubricity is the ability to generate a hydrodynamic
lubrication film (oil wedge). To ensure that a given low
sulfur marine gas oil has sufficient lubricating value, the
fuel must be tested under the ISO 12156-1 (EN 590)
High Frequency Reciprocating Rig (HFRR) protocol.
This standard calls for a maximum wear scar rate of 460
microns. Refineries add a lubricity additive in case the
EN590 requirement is not fulfilled. A higher HFRR
(Fig. 1) means less lubricity.
Reduced lubricity in low sulfur fuels poses the risk of
improper lubrication of marine fuel pumps, resulting in
excessive wear and premature failure. Special lube oils
must be used to add lubricity and prevent carbon
deposition, called lacquering. The largest contribution
to diesel fuel lubricity comes from trace amounts of

2. 2
Figure 1: HFRR Test (SVITOL, 2012)
surface-active polar compounds forming a protective
layer on the metal surface, thus improving boundary
lubrication. The most active polar materials naturally
occurring in diesel fuel are hetero-compounds
containing nitrogen and oxygen. The Hydro-
desulphurization (HDS) process which removes sulfur
content also removes these polar compounds, resulting
in very poor lubricity characteristics and exposing
pumping systems to damage and potential catastrophic
failure. As a result of the lowered lubricity, the fuel is
less tolerant of water and dirt. The lower fuel lubricity
can be seen as abrasive wear of fuel system
components. Fuels that have a lowered lubricity may
not provide adequate lubrication also to plungers, to
barrels, and to injectors.
The fuel’s lubricity may be enhanced with additives.
Vessel owners should request the results of emissions
bench tests conducted by independent laboratories
confirming that the additive has no adverse effect on
emissions.
Proper lubrication in a marine plunger/barrel fuel pump
depends on a balance between both hydrodynamic
lubrication and boundary lubrication. Hydrodynamic
lubrication occurs when two surfaces are in motion to
each other and are separated by a liquid film that carries
the applied load. The result is low friction and minimal
wear between the two surfaces. Boundary lubrication
occurs when this liquid film becomes thin to the point
that that it attains the same thickness as the surface
roughness of the high points of the two interfacing solid
surfaces. For proper protection against this surface to
surface contact, the fuel must have sufficient lubricity to
prevent increased friction and wear. Boundary
lubrication is critical in three different situations,
namely on initial start-up with insufficient liquid film, at
low speed operations when not enough fuel is pumped
to provide a satisfactory film and at very high speed
operation when high pressure within the pump
diminishes the film thickness. A viscosity range 12-16
centistokes is sufficient to provide adequate
hydrodynamic lubrication. Viscosity of low sulfur MGO
varies from 1.5-3.0 cSt. In that case the protective fuel
film between the surfaces of the barrel and plunger
becomes dangerously thinner resulting in increased
metal to metal contact even if fuel viscosity is increased
through chilling or cooling. The difference between
boundary and hydrodynamic lubrication is depicted in
Fig. 2.
a) Hydrodynamic Lubrication
b) Boundary Lubrication
Fig. 2: Hydrodynamic and Boundary Lubrication
(STLE, 2008)
Lighter fuel oils traditionally have lower lubricating
properties. Their hydrodynamic lubrication ability can
be assessed by the Sommerfeld number which is as a
function of the viscosity:
(1)
where  is the absolute viscosity, N are the revolutions
per minute, P is the load per unit projected bearing area,
r is the shaft radius and c is the radial clearance. The
effect of the Sommerfeld number is reflected by
Petroff’s equation correlating Sommerfeld number and
friction for various lubrication modes. This is the so
called Stribeck curve (Ludema, 1996) shown in Fig. 3.

3. 3
Fig. 3: Petroff’s law-Stribeck curve (Ludema, 1996)
Gear and screw type pumps used for fuel transfer rely
almost exclusively on boundary lubrication. Lack of it
results in wear and loss of pumping pressure and
volumetric capability.
A higher number means a stronger oil film. When a
screw pump operates with low sulphur fuel, the
Sommerfeld number might not be high enough to
sustain full oil film condition, and the pump operates in
boundary zone. Thus the moving parts are not separated
by a film, with metallic contact taking place. Working
condition of the pump is determined by lubricity (HFRR
value), rotation speed, viscosity and differential
pressure. Differential pressure is the total pressure
against which a pump must work. Under the blue line in
Figure 3, the pump is running under full-film condition.
Within the red zone, the pump might be operating in
boundary zone. The HFRR value becomes important,
since the pump is working with a completely or partly
broken oil film. Previous experience shows that this
state of operation occurs when operating below 1.6 cSt.
Figure 4 shows the critical area is below 1.6 cSt
(Bergström et al, 2010).
Fig. 4: Differential pressure limits (Bergström, 2010)
Unfortunately the IMO regulation only regulates the
sulphur content and no other fuel specifications are
addressed. Low sulphur fuel with good lubricity
characteristics is expected to be more expensive.
Owners should not opt for less expensive fuel qualities,
which will result in wear of fuel pump and injection
components, bad combustion and engine wear and
damages.
3. Fuel Stability
HDS removes a large measure of aromatic content,
resulting in reduced ignition quality. It also removes
naturally occurring anti-oxidants that provide both
physical and thermal stability of the fuel. Absence of
natural anti-oxidants leads to the formation of hyper-
peroxides, which can result in acid corrosion attack of
fuel pump systems and pump seal failure. Hyper-
peroxide accumulation in fuel results in excessive
deposits and emissions and formation of high carbon
polymers affecting combustion. At high concentrations
peroxides can damage or degrade certain plastics and
elastomers, particularly at high temperatures. Oxidation
process also produces gums, polymers and other
insolubles. Standards to detect hyper-peroxide
contamination are available.
The inherent instability of low sulfur fuel poses four
critical threats to safe marine engine operation, namely
degraded ignition quality, excessive engine deposits, an
increase in visible particulate emissions and excessive
sludge production and fuel system fouling. Reduced
stability of the fuel can also result in increased
emissions. Low sulfur marine fuels often produce
excessive unburned hydrocarbon and visible particulate
emissions (smoke opacity). Poor stability may result in
the formation of gum and sludge during storage as well
as deposit formation on injection nozzles and gumming
of valves.
An oxidative stability (ISO, 1995) requirement was also
introduced for the distillate grades. This requirement
was included in order to address the reduced oxidative
stability of distillates.
Poor physical stability can result in problems with fuel
compatibility, particularly when transitioning from
operation on heavy fuel to low sulfur marine gas oil.
Since some marine gas oils will be stored aboard the
vessel for prolonged time periods, fuels of poor stability
characteristics will suffer accelerated degradation,
resulting in reduced ignition quality and degraded
engine operation.

4. 4
4. Low Fuel Viscosity
Low sulphur distillates have relatively low viscosity,
ranging from 1.5 to 3.0 cSt. Fuel pumps depend upon an
appropriate viscosity to meet required volumetric
capacity, an especially important consideration in
maintaining proper feed rates. ISO 8217 states
minimum viscosities for DMX, Distillate Marine Oil of
Class X, of 1.4 cSt at 40 o
C and DMA, Distillate Marine
Oil of Class A, of 1.5 cSt at 40 o
C (ISO 2010). A rule of
thumb value advised by the makers is 2Cst at engine
inlet (MAN, 2014). Ambient temperature in an engine
room easily reaches 40 o
C and sometimes even higher –
in some cases as much as 55 o
C. Adding excessive heat
from pipes and engines will raise the temperature even
further; and as a consequence viscosity will fall, causing
a significant change of operating conditions in the
system. Mercifully, the lower the viscosity at 40o
C the
more gradual the fall of viscosity with temperature rise
as depicted in Figure 5.
Figure 5: Viscosity versus temperature (MAN, 2010)
The lower viscosity will reduce the film thickness
between the fuel pump plunger and casing and in the
fuel valves leading to excessive wear and possible
sticking, causing failure of the fuel pump. Special fuel
injection pumps may be available that are more suitable
for this type of fuel, such as tungsten carbide coated
pumps, or a fuel pump lubrication system could be
installed. Any new types of fuel injection equipment
installed to address lubrication issues shall be certified
by the engine maker to maintain engine compliance
with emission standards and may require re-certification
of engines.
Heavy fuel oil at the fuel pumps is about 150°C because
the fuel must be heated due to its high viscosity. Marine
distillate fuel, introduced at ambient engine room
temperature, could cause the fuel pumps to seize if
introduced too fast, due to a combination of thermal
contraction and low lubricity. This could cause sudden
loss of propulsion or auxiliary power.
A decrease in fuel viscosity may cause an increase in
fuel leakage between the pump plunger and barrel. The
leakage can lead to hot start and low fuel setting start
difficulties, especially in worn fuel pumps. It is
advisable to make distillate hot start checks at regular
intervals so that the limits of operating conditions for a
particular engine are determined. Loss of capacity in
fuel supply pumps is due to low viscosity with fuel
leaking around pump rotors. Leakage of fuel through
the high pressure fuel pump barrel, plunger, suction and
spill valve push rods occurs on slow speed engines. This
leakage may result in a higher load indication position
of the fuel rack and may require adjustment of the
governor for sustained operation on low viscosity fuel
or may results in worn pump’s elements (enlarged
clearances). As an internal leak is part of design and is
used in part to lubricate the pumping elements, it can
cause too high leak rate and in consequences lead to
smaller than optimal injection pressures resulting in
difficulties during start and low load operation.
Some of the pump leakages are attributable to the use of
nitrile seals which shrink as a result of the reduced
aromatic content of the fuel. The lack of lubrication also
results in fuel pump sticking and seizures with barrel
plunger type pumps, and severe failures in rotary type
pumps. As most fuel pumps are either screw pumps or
gear pumps, it is important to check if the pumps are
able to operate with the lower viscosity of the new fuel,
as there is a risk of increased wear and tear as well as
breakdown if the pump is unsuited for the viscosity.
Fuel pumps running continuously during periods of
inactivity may heat up, causing the temperature of the
fuel to increase and thereby the viscosity to decrease.
Pumps must be shut off when not required.
In testing conducted under the American Standard Test
Method, ASTM D5001-89 BOCLE Test, (ASTM,
1989), it was discovered that viscosity played
essentially no role in fuel pump failure – but rather, the
inherent lubricating value of the fuel determined the
extent to which fuel pump wear occurred. Viscosity
plays essentially no role in providing sufficient fuel
lubricity for either rotary of plunger/barrel type fuel
pumps. On the other hand we should remember that a
major difference between the pump types is the effect
viscosity has on the capacity of the pump. In the
positive displacement pumps which constitute the fuel
supply and injection pumps the flow increases with
viscosity (Viking, 2014). The higher viscosity liquids

5. 5
fill the clearances of the pump resulting in a higher
volumetric efficiency. This effect is depicted in Figure
6.
Fig. 6: Flow rate vs viscosity (Viking 2014)
5. Cylinder Oil for MGO
Engines operating on heavy fuels require a higher total
base number (TBN) lubricant to address high sulphur
content. Unless the lubricant is changed to a lower
TBN, engines operating for extended periods on 0.1%
MGO still using a high TBN lubricant run the risk of
accumulating excessive calcium salt deposits in the
combustion chamber, among other damages. For fuel
with sulphur content of over 1 percent and up to the
sulphur cap of 3.5 percent a BN 70 or above lubricant
should be used. If a ship is to use Low-Sulphur Fuel Oil
(LSFO) for a period longer than two weeks, the
lubricant should be a lower BN lubricant, namely a
BN17 or a BN25 (MAN-BW, 2014). A typical cylinder
oil segregation is depicted in Figure 7.
Figure 7: Cylinder oil segregation
High Total Base Number (TBN) lube oil in combination
with low-sulphur fuel increases the risk of scuffing on
the cylinder liner. The deposits are more solid when less
oil TBN additives are neutralized by sulphuric acid.
Therefore careful monitoring of the cylinder liner
condition when operating on low sulphur fuel oil, and if
necessary change to low TBN cylinder oil or reduce the
feed rate in accordance with the engine makers
recommendations will be required.
Total base number (TBN) is a measure of a lubricant's
reserve alkalinity. The higher the TBN, the more acid
can be neutralized. It is measured in milligrams of
potassium hydroxide per gram (mg KOH/g). TBN
determines how effective the control of acids formed
will be during the combustion process. The higher the
TBN, the more effective it is in suspending
wear‐causing contaminants and reducing the corrosive
effects of acids over an extended period of time. Marine
grade lubricants generally will run from
15‐50mgKOH/g, but can be as high as 70 or 80mg
KOH/g this high level is designed to allow a longer
operating period between changes, under harsh
operating conditions. When the TBN is measured at
2mg KOH/g or less the lubricant is considered
inadequate for engine protection, and is at risk for
allowing corrosion to take place. In the past unbalance
between the fuel sulphur level and lube oil TBN has
resulted in lacquering of liners, with consequential high
lube oil consumption and carbon build up on pistons
with increased damage risks.
Figure 8: Abrasive effect of fines on liner
The alkaline components form deposits on the piston
crown land that can disrupt the oil film between the
piston rings and the cylinder liner, and hence the risk of
metal-to-metal contact, seizures and scuffing increases.
The period for which the engine can be run on low
sulphur fuel and high BN cylinder oil is very dependent
on engine type and mode of operation. It is not expected
to result in any unsatisfactory conditions in the course

6. 6
of a few days. Cylinder oil feed rates should also be
considered and engine manufacturer recommendations
must be followed. The operation of two stroke engines
on high BN cylinder oil at high feed rates while using
low sulphur distillate fuel can lead to rapid piston crown
deposit accumulation resulting in severe scuffing.
It has been established that a certain level of controlled
corrosion enhances lubrication, in that the corrosion
generates small “pockets” in the cylinder liner running
surface from which hydrodynamic lubrication from oil
in the pocket is created. In other words, controlled
corrosion is important to ensure the proper tribology
needed for creation of lubricating oil film.
6. Catalytic Fines and Asphaltenes
Mechanically damaged catalyst particles (aluminum
silicate) utilized in the refining process, cannot be
removed completely, and are found in blended heavy
fuel. Correct fuel purifying and filtration onboard ships
have a removal efficiency of approximately 80 to 90%
for catalytic fines. In order to avoid abrasive wear of
fuel pumps, injectors and cylinder liners, the maximum
limit for aluminum and silicon defined in ISO 8217 is
40–60 mg/kg depending on the viscosity (ISO, 2010).
There are still reported problems with catalytic fines
especially in low sulphur fuels. More efficient methods
during the refinery process have led to the size of the
catalytic fines being dramatically reduced. This creates
a problem for the shipboard purifier to remove them
effectively, as the purifier relies on gravity for
separation of the fines. Consequently some of the small
fines are passing through to engines causing damage.
Cat fines content (Al/Si) in low sulphur fuel is high,
causing high wear in rubbing surfaces of cylinders,
liners, (Figure 8) from (Parker, 2009) and piston rings
(Figure 9) from (Motor-ship 2013). If content is less
than 15 ppm wear and tear is minimized. Fuel needs to
be purified continuously to reduce cat fine content.
Figure 9: Cat fines embedded on piston ring
When switching from heavy fuel to a low-aromatic
distillate fuel, some of the heavier asphaltic material the
asphaltenes could be precipitated from the heavy fuel. If
this happens, fuel filters could clog and fuel pumps
could stick, causing sudden loss of power. Asphaltenes
are n-heptane insoluble and aromatic soluble. Fuel oil
with high level of asphaltenes will result in injector
malfunction and heavy carbon deposits.
The fuel change-over procedure takes quite some time,
during which inevitably there will be mixing of two
very different fuels. Mixing distillate with residual fuel
may cause the asphaltenes in the residual fuel to
precipitate as heavy sludge, with filter clogging as a
possible result which, in extreme cases, will cause fuel
starvation in the engine leading to engine shutdown.
Another associated issue can be injection pump sticking
due to deposits between the plunger and barrel.
Incompatibility can be minimized through on board
compatibility test kits used when bunkering both HFO
and low sulfur fuel called Spot Test Method for
Assessing Fuel Cleanliness and Compatibility (ASTM,
1995). It is expected though, that a given bunker of low
sulfur MGO could remain aboard anywhere from 3-12
months, more than sufficient time for the fuel to degrade
and cause fuel system fouling and combustion
problems.
No refinery in Europe or the United States produces a
low sulfur distillate with a sulfur content of 0.1%. 0.1%
sulfur marine gas oils are a product of blending a low
sulfur automotive diesel with a small amount of
conventional distillate with higher sulfur content. Such
blending poses a higher risk of fuel incompatibility.
7. Blending and Impact on Tank Arrangement
The experience in terms of low sulphur fuel blending is
varying. Blending of low sulphur fuel oils may lead to
additional quality problems such as instability,
incompatibility, ignition and combustion difficulties and
an increase of catalytic fines. A ship which does not
have a tank arrangement that permits segregation of fuel
beyond the storage tanks will have to develop special
procedures for fuel mixing. One way to do this is to
reduce the level in the settling tank to about 20% of
capacity before filling with the alternate fuel several
days before entering an ECA. This can lead to high
consumption of expensive low sulphur fuel.
Consideration should be made to install a segregated
fuel system on any ship that regularly trades in ECAs.
Low sulphur fuel tanks should not be located adjacent to
hot walls of HFO tanks.

7. 7
Consider the fuel storage, settling and service tank
arrangement. This will determine if fuel switching can
be done by segregating or by blending fuels.
Segregating fuels is the preferred method as it allows
much quicker switching and there is less potential for
compatibility issues. Segregation can be carried out on
ships that have separate fuel storage, settling and service
tanks. Most ships built after 1 July 1998, because of
SOLAS requirements, have double service tanks and
more than two storage tanks, so the possibility for
segregation exists. Some owners are installing an
additional set of service and settling tanks for low
sulphur fuel oils. Additional storage tanks are installed
for the same reasons. Segregated tanks will simplify
changeover procedures and bunker management. The
differences in cost between low and high sulphur heavy
fuel oils as well as between heavy fuel oils and low
sulphur diesel oils, has led some owners to consider
separating fuel treatment and service piping systems.
Blending high density fuel oil with low density fuel
gives the highest risk of incompatibility, while blending
two low density fuel oils represents the lowest risk. The
blending ratio should in any case be as small as
possible.
The blending of Fatty Acid Methyl Ester, FAME shall
not be allowed. Ship owners and operators must be
aware that there is the possibility that this kind of fuel
may be provided in areas where low sulphur marine fuel
supplies are limited. In such cases it should be
established with the supplier as to the allowed FAME
content before ordering.
Fuel tanks should comply with the following
regulations:
-Regulation II-1/26.11 of SOLAS (Capacity &
Arrangement).
-IACS Unified Interpretation SC 123: Machinery
installation – Service Tank Arrangements.
Due to the lower density of gas oil, the actual quantity
of fuel, in tons, contained within a tank will be reduced
compared to HFO. This would be reflected in the
amount of fuel injected per fuel pump stroke resulting in
a higher fuel rack setting for a given load irrespective of
the higher calorific value of the gas oil.
8. Fuel Change-over
Switch from HFO to LSF is not a simple procedure. For
example, temperature fluctuations during the switching
process in the engine can lead to short-term variations in
viscosities, energy contents as well as fuel flows in the
engine system. Potential consequences are alterations in
the combustion process that may even cause the main
engines to stop.
Heat provided to HFO might cause vapor lock of MGO
during change-over due to vaporization of the more
volatile low sulphur fuel. In order to prevent this kind of
troubles, it is important to establish an appropriate
changeover procedure between HFO and low sulphur
fuels. Gas oil has a cleaning effect on systems normally
run on HFO. This may clear accumulated sludge
materials within the system, with the possibility of fuel
filter fouling or fuel injection equipment faults.
Additionally seals and joints may leak. This is
compounded by the reduced temperature of operation.
Ships using separate fuel oils are required when entering
or leaving an ECA to carry a written procedure showing
how the fuel oil change-over is to be done, allowing
sufficient time for the fuel oil service system to be fully
flushed. Before fuel switching, it is generally
recommended to reduce ship power to 30%-70% of
Maximum Continuous Rating.
Avoiding thermal shock to the fuel system is one of the
critical elements in a fuel switching procedure. Engine
manufacturers normally offer guidance on the maximum
allowed rate of temperature change in fuel systems,
such as the commonly used rate of 2°C/minute. If a ship
is using HFO heated to about 150°C prior to switching
to MGO at 40°C, the temperature difference is 110°C.
Under these conditions and considering a 2°C/minute
permitted rate of change, the fuel switching process
should take a minimum of 55 minutes to complete
safely. Incidents of loss of propulsion off the coast of
California can be attributed to the switch over from hot
residual heavy fuel oil to comparatively cool gas oil
with occurrence of «thermal shock" to the engines. Loss
of power in coastal areas can have dire consequences.
Marine Information Safety Bulletin 14-01 addresses the
issue of fuel switch-over..
Purifiers should be adjusted to suit the new fuel. Make
sure the suction and return pipes go to the correct tanks.
If operating on MGO, a separate purifier may be in
operation. If there is fuel valve injector cooling on the
engine, this may need to be turned off or on during fuel
switching. After switching to MGO, fuel valve cooling
may not be needed and if this is the case it should be
turned off to prevent over-cooling of the fuel. Oil fuel
heaters should be bypassed for the low sulphur fuel
otherwise air-locks in the fuel supply system may occur.
The lower sulphur content would make it possible to use
catalysts to reduce NOx levels. This in turn makes it
possible to operate at higher combustion temperatures
and higher efficiency. Empirical data though indicates

8. 8
that the catalyst raises the CO2 emissions because of the
rise in fuel consumption. Low-sulphur fuels in the
future will make Selective Catalytic Reactor, SCR
technology more attractive.
Close monitoring of fuel systems, fuel treatment plants
as well as frequent fuel and lube oil quality checks by
analyses and creating awareness about the importance
of good change-over procedures will be necessary to
avoid unnecessary wear and damages to installations.
For the lowest viscosity distillates, a cooler may not be
enough to cool the fuel sufficiently. In such a case, it is
recommended to install a chiller. The chiller uses a
refrigerant to dump the heat from the fuel.
Many ships carry out fuel switching by manually
changing over a single three-way valve to control the
fuel source. If the fuel switching is done at high power
levels the change is carried out in a relatively short
period since the fuel circulates at a high rate through the
mixing tank. Rapid change from HFO to MGO can lead
to overheating the MGO, causing a rapid loss of
viscosity and possible ‘gassing’ in the fuel system.
Rapid change from unheated MGO to HFO can lead to
excessive cooling of the HFO and excessive viscosity at
the fuel injectors, again causing loss of power and
possible shutdown. If a single changeover valve is
provided, it is recommended to carry out fuel switching
with the engine at low power levels so the fuel change
will occur gradually. If fuel switching is sought at
higher power levels, the fuel switching system may
have to be modified, including the possible installation
of an automated fuel changeover system that changes
the fuel in a timed and regulated manner. Such
automated systems are now being offered by some
engine makers and by fuel system equipment suppliers.
(Figure 10)
Figure 10: DIESEL switch for auto change-over
(MAN-BW, 2014)
It is noted that switching from colder MGO to HFO is
more critical with respect to potential seizures due to
thermal expansion.
9. Boilers and Main Engines
Considerable modification to these units must be made,
including changes in burners, atomization, and
installation of additional fuel pumping and storage
equipment. All three common burner types normally
supplied for marine boiler installations are affected.
Pressure jet burners are typically used on smaller boiler
types and can run on MGO. Lower viscosity may cause
an increase in the fuel flow rate through the nozzle at
the risk of increasing smoke emission. Steam atomizing
burners are typically used on medium and larger boiler
types and run on MGO. The lower viscosity of MGO
may cause over-firing. Compressed air can be used as
the atomizing medium, or change of the lance to a type
that does not heat the fuel in the same way as the
traditional lance.
Flame monitoring sensors may not be suitable for gas
oil use because of the differing spectral emission ranges
and this may result in false alarms, boiler shutdowns
and in the worst case undetected flame failures.
Combustion air settings may need to have been adjusted
for the use of gas oil.
For 4-stroke engines low fuel viscosity is generally
speaking not a severe problem, but in severe cases with
too low viscosity damage to the fuel injection
equipment may occur, and the running parameters of the
engine are affected. ISO 8217 increased minimum
viscosity from 1.50 cSt at 40°C to 2.00 mm²/s (cSt) at
40°C for DMA and DMB grade. Low viscosity fuels
can also lead to the engine not delivering the full
designed power output as the design amount of fuel is
not delivered by the pump. This has led most 2- and 4-
stroke engine builders to request a minimum viscosity
of the fuel before the fuel injection pump of about 2.0
mm²/s (cSt).
Low sulfur, low viscosity fuels have low density
compared to HFO. This results to lower volumetric
energy content. More fuel volume must be supplied to
the engine to maintain equivalent power. Engine
governors and automation need to be able to adjust to
the changes in fuel rack position and governor settings.
Some components of the engine will require different
maintenance intervals and changes of the alarm settings

9. 9
(temperature, viscosity, fuel pressure) depending on the
currently used type of oil fuel.
10. General Considerations
The calorific value of low sulphur fuels is typically a
little higher than that of HFO. In some cases, it may be
necessary to re-adjust the air/fuel ratio, especially for
steam atomizing burners.
Only DMA grade satisfies the Sulphur limits and has
flash point over 60 o
C. The majority of marine fuel oils
meeting the 0.10% limit would be expected to be
categorized as DMA grade. In order to prevent
bunkering of fuels with a flashpoint lower than 60 ºC, it
is necessary to confirm in the Bunker Delivery Note that
the flashpoint of the fuel oil is 60 º
C or above. The
possibility of automotive type fuels with extremely low
sulphur contents being supplied exists. These road fuels
may not meet the minimum marine fuel oil flash point
limit of 60o
C thus raising statutory compliance issues.
Temperatures which would likely be experienced in
service need to be established. On that basis it would
then be possible to determine what action to take like
installation of coolers/chillers or replacement of
sensitive machinery components such as the gear type
fuel supply pumps and fuel injection system
components. Low sulphur fuels may have a substantial
wax content. Installation of coolers or chillers will
depend on the available cooling water refrigerating
capacity. Attention must be given to the temperature of
these fuels. Fuel temperature must not be reduced so
that solidification or wax deposit problems occur. This
can lead to filter blockages and fuel starvation of the
machine. Identifying the cloud point from the bunker
delivery receipt for the fuel may be a good indication as
to when this waxing may start.
11. Financial Considerations
Fuel containing a maximum of 0.1% sulphur will be
more expensive. Implementation of the regulation
imposes a challenge in combination with increased fuel
costs as well as implementation difficulties. Availability
and affordability of low-sulphur fuels should have been
analyzed beforehand as well as the risk of a modal shift
on the basis of the densities of transport modes. In
response to the 0.1% limit new types of fuels other than
distillates are introduced. These fuels also known as
“hybrid” fuels are created by blending with higher
viscosity value and slightly lower price. Some
disadvantages of this generation of fuels are the
incompatibility with other fuels, the high pour point,
presence of cat fines and the need to lower their
viscosity by heating as with HFO. Furthermore hybrid
fuels have much higher Cetane Numbers than MGO
increasing the risk of diesel knock. They are much
lighter than HFO and they tend to wash away residues
from HFO causing equipment/filter clogging. Their
lower specific gravity needs to be accounted for since it
is necessary to be purified due to the presence of
catalytic fines. Global availability of these fuels is also
another problem. It is advisable that Operators obtain
Engine Maker’s No Objection Certificate prior to using
hybrid fuels. Extension of insurance coverage for these
fuels as well as strict quality control will open the door
for wider utilization. Charterers favor hybrid fuels
because they reduce their fuel bills by about 50 USD per
metric ton. A critical issue is their acceptability in the
California ECA which requires the utilization of
distillate fuels (CARB, 2011). It must be remembered
that in the US there can be local state legislation which
is more stringent than equivalent federal legislation.
New ships are easy to design to burn distillates alone.
Dispensing with two types of oil quality means no dual
system of oil tanks and pipes is necessary. Moreover, no
more oil pre-heating is required and the number of
separators can be reduced. This also means that the
volumes of sludge which need to be collected and
disposed of are also considerably reduced. The use of
distillates is also associated with permanent higher costs
for lubricants.
The costs for the low-sulphur oil strongly raise the
voyage costs. Frequently changing from HFO to
distillates and the associated matching of fuel and
lubricating oils is a highly complex process which
requires extreme care. It demands very close
cooperation between the ship managers and the bunker
suppliers who know their products best, as well as
highly trained engine room staff. The failure to satisfy
these requirements raises the risk of mechanical shut-
downs, mechanical damage, blocked filters, damaged
pumps, etc.
Manufacturing a greater proportion of lower sulphur
fuels will tend to increase CO2 emissions due to
increased refinery energy use.
It may be necessary to fit some or all of the following:
a. new fuel pumps
b. fuel injector nozzles
c. fuel line coolers

10. 10
d. new return lines
Owners are very likely to cope with low availability of
low sulphur compliant fuels. This fact makes the
solution of scrubbers an attractive alternative. It is
necessary to perform a Return Of Investment, ROI,
study prior to choosing such solutions. ROI depends on
fuel price differentials, engine power as well as time
spent in the ECAs. It is critical that chartering contracts
have clear allocation of liability between owners,
charterers and bunker suppliers. Charterers for example
should bear the risk bunkering fuel which is non-
compliant. Owner losses including the ones from fines
should also be included. A clause keeping the vessel on-
hire in case of detention/delay due to off-spec fuel is
also to be added in the cratering contract. BIMCO Fuel
Sulphur Content Clause (BIMCO 2005), can be used for
guidance. Incorporation of the BIMCO Clause to the
contract implies that the vessel can burn fuel of the right
sulphur content for her intended trade areas. Owner is
thus responsible to make capital investments through
approved retrofit plans to make the vessel compliant.
Equipment modifications and tank cleaning impose
increased time delays and costs which must be
contractually accounted for. Responsibility for
complying with system of sampling , fuel segregation
and record keeping rests exclusively with the Owner.
12. Conclusions
The utilization of low sulphur fuel in shipping is not
new. Although there are many challenges associated
with the use of distillates all of them can be tackled.
Every ship is different and she has “her own soul”.
Consequently what might be OK for one vessel may not
befit the other. It appears that the solution to the
challenges involves a lot of trial and error adapting the
fuel system gradually. The introduction of the 0.1%
limit will entail significant financial burden to shipping.
The fuel bills will be significantly higher to absorb the
high cost of desulphurization at the present. Segregated
storage and transfer and distribution systems for fuel
and lube oil impose a financial toll as well as the need
for space optimization. The potential addition of sensors
and meters, coolers and/or chillers will up the bill even
higher.
It is necessary to develop and implement production
techniques for low sulphur fuels which will be low cost
and of reduced complexity. These techniques must also
be capable of yielding the millions of tons of fuel every
year to avoid having availability problems. The one
million dollar question is if there is enough for every
ship trading in the ECAs. The oil industry responding to
this challenge will blend fuels, produce distillates, and
explore biodiesels like FAME aiming to cover the
demand for low sulphur fuel. As a result there is going
to be a non-uniformity in the bunker market and large
differences in the quality of fuel. Harmonized fuel
quality standards and sampling and analysis must be
implemented to avoid problems.
13. References
ASTM D5001, 1989, “Standard Test Method for
Measurement of Lubricity of Aviation Turbine Fuels by
the Ball-on-Cylinder Lubricity Evaluator (BOCLE)”
ASTM D4740, 1995, “Standard Test Method for
Cleanliness and Compatibility of Residual Fuels by
Spot Test”
Bergström A, Berggren J., 2010, “Switching to Low-
Sulfur Fuels in the Commercial Marine Industry”,
http://www.colfaxfluidhandling.com/admin/modules/article_m
anager/uploads/7923-LowSulfur%20Wht%20Ppr-6.pdf
BIMCO, 2005, https://www.bimco.org
California Air Resources Board (CARB), 2011, 17 CCR,
Section 93118.2, Title 17.
ISO 12205, 1995, “Petroleum products -- Determination
of the oxidation stability of middle-distillate fuels”
ISO 12156-1, 2006, “Diesel fuel -- Assessment of
lubricity using the high-frequency reciprocating rig
(HFRR) -- Part 1: Test method”
ISO 8217, 2010, “Fuel Standard for marine distillate
fuels”
Ludema K., 1996, “Friction, wear and lubrication: a
textbook in tribology”, USA
MAN-BW, 2010, “Operation on Low-Sulphur Fuels”,
MAN-BW, 2014, “Guidelines for Operation on Fuels
with less than 0.1% Sulphur”, Service Letter SL214-
593/DOJA
Motorship, 2013, “On-line measurement of catalytic
fines in HFO systems”
http://www.motorship.com/news101/fuels-and-oils/on-
line-measurement-of-catalytic-fines-in-hfo-systems
Parker Kittiwake, 2009, “Optimizing uptime in a global
downturn”,
http://www.kittiwake.com/news/2009/04/optimising-
uptime-in-a-global-downturn/

11. 11
STLE, Society of Tribologist & Lubrication Engineers,
2008, http://www.stle.org
SVITOL 2012, Divisione di Petronas Lubricants,
http://www.svitol.it/en/extras/laboratory-tests/hfrr-test-en
U.S. Coast Guard District Eleven, 2014, “Preventing
Losses of Propulsion and Improving Fuel Switching
Safety”, MARINE SAFETY INFORMATION
BULLETIN 14-01
Viking Pumps, 2014, “When to use a Positive Displacement
Pump”,
http://www.pumpschool.com/intro/pd%20vs%20centrif.pdf
14. List of Abbreviations
ASTM - American Standard Test Method
CARB - California Air Resources Board
CO2 - Carbon Dioxide
DMA – Distillate Marine Oil of Class A
DMB – Distillate Marine Oil of Class B
DMX - Distillate Marine Oil of Class X
ECA - Emission Control Areas
EN - European Norm
EU - European Union
FAME - Fatty Acid Methyl Esters
HDS - Hydro-desulphurization (
HFRR - High Frequency Reciprocating Rig
HFO - Heavy Fuel Oil
IMO - International Maritime Organization
ISO - International Organization for Standardization
LSFO – Low Sulphur Fuel Oil
MARPOL - International Convention for the Prevention
of Pollution From Ships
MGO - Middle Gas Oil
SCR - Selective Catalytic Reactor
SOLAS – Safety Of Life At Sea
TBN – Total Base Number