Fuel oil is obtained from petroleum distillation and is classified into different grades based on properties like boiling point, viscosity, and carbon chain length. Higher numbered fuels have higher boiling points, viscosities, and carbon chain lengths. Fuel oil is used for heating and power generation. It requires heating and treatment to remove contaminants before use in ship engines. Combustion in engines involves ignition delay, rapid uncontrolled combustion, and controlled combustion phases.

1. GRADES OF FUEL
 Fuel oil, (also known as marine fuel or furnace oil) is a
fraction obtained from petroleum distillation, either as a
distillate or a residue.
 Broadly speaking, fuel oil is any liquid fuel that is burned
in a furnace or boiler for the generation of heat or used
in an engine for the generation of power.

2. GRADES OF FUEL
 The boiling point and carbon chain length of the fuel
increases with fuel oil number.
 Viscosity also increases with number, and the heaviest
oil has to be heated to get it to flow.
 Price usually decreases as the fuel number increases.
 Number 1 fuel oil is a volatile distillate oil intended for
pot-type burners (kerosene).
 Number 2 fuel oil is a distillate home heating oil. This
fuel is sometimes known as Bunker A.
 Number 3 fuel oil was a distillate oil for burners
requiring low-viscosity fuel. ASTM (American Society for
Testing and Materials) merged this grade into the
number 2 specification.

3. GRADES OF FUEL
 Number 4 fuel oil is a commercial heating oil for burner
installations not equipped with pre-heaters.
 Number 5 fuel oil is a residual-type industrial heating oil
requiring preheating to 77–104 °C for proper atomization
at the burners. This fuel is sometimes known as Bunker
B.
 Number 6 fuel oil is a high-viscosity residual oil
requiring preheating to 104–127 °C. The residue may
contain various undesirable impurities including 2
percent water. This fuel may be known as residual fuel
oil (RFO), by the Navy specification of Bunker C.

4. GRADES OF FUEL
 Bunker oil is generally any type of fuel oil used aboard
ships.
 We can distinguish between two main types: distillate
fuels and residual fuels.
Marine fuels are classified using the “Bunker ABC”:
 Bunker A corresponds to the distillate fuel oil No. 2
 Bunker B is a No. 4 or No. 5 fuel oil
 Bunker C corresponds to the residual fuel oil No. 6
 No. 6 is the most common oil, that's why "bunker fuel" is
often used as a synonym for the No. 6 residual fuel oil
which requires heating before the oil can be pumped.
No.5 or No.6 also furnace fuel oil (FFO).

5. GRADES OF FUEL
 In the maritime field fuel oils are distinguished as
distillate fuels, intermediate fuels and residual fuels:
 Distillate fuel is composed of petroleum fractions of
crude oil that are separated in a refinery by a boiling or
"distillation" process.
 Residual fuel or "residuum" is the fraction that did not
boil, sometimes referred to as "tar" or "petroleum pitch".

6. GRADES OF FUEL
 MGO (Marine Gas Oil): a distillate fuel oil (No. 2,
Bunker A)
 MDO (Marine Diesel Oil): a blend of MGO and HFO
 IFO (Intermediate Fuel Oil): a blend of MGO and
HFO, with less gasoil than MDO
 MFO (Medium Fuel Oil): a blend of MGO and HFO,
with less gasoil than IFO
 HFO (Heavy Fuel Oil): a residual fuel oil (No. 6,
Bunker C)

7. GRADES OF FUEL
 Marine fuels are traditionally classified according to their
kinematic viscosity.
 This is a valid criterion for oil quality as long as the oil is
produced by atmospheric distillation only.
 Today, almost all marine fuels are based on fractions from
more advanced refinery processes and the viscosity itself
says little about the oil's quality as fuel.
 Despite this, marine fuels are still quoted on the international
bunker markets with their maximum viscosity set by ISO 8217
as marine engines are designed to use different viscosities of
fuel.
 The density is also an important parameter for fuel oils since
marine fuels are purified before use to remove water and dirt.
Therefore, the oil must have a density which is sufficiently
different from water.

8. GRADES OF FUEL
Distillate Fuel Kin. Viscosity
[mm²/s]
at 50°C
Density
[g/cm³]
at 15°C
DMX 1.4 ... 5.5 −
DMA 1.5 ... 6.0 < 0.890
DMB < 11 < 0.900
DMC < 14 < 0.920
Distillate Bunker Oils (ISO 8217)

9. GRADES OF FUEL
Residual Fuel Kin. Viscosity
[mm²/s]
at 50°C
Density
[g/cm³]
at 15°C
RMA 30 < 30 < 0.960
RMB 30 < 30 < 0.975
RMD 80 < 80 < 0.980
RME 180 < 180 < 0.991
RMF 180 < 180 < 0.991
RMG 380 < 380 < 0.991
RMH 380 < 380 < 0.991
RMK 380 < 380 < 1.010
RMH 700 < 700 < 0.991
RMK 700 < 700 < 1.010
Residual Bunker Oils (ISO 8217)

10. FUEL OIL TREATMENT

11. FUEL OIL TREATMENT
 In order to ensure effective and sufficient cleaning
of the HFO (removing water and solid
contaminants) the fuel oil specific gravity at 15
degC should be below 0.991.
 Higher densities—up to 1.010—can be accepted if
modern centrifugal separators are installed, such as
the systems available from Alfa-Laval (Alcap).

12. FUEL OIL TREATMENT
 Alfa-Laval’s Alcap system comprises a water transducer and
ancillary equipment including an EPC-400 control unit.
 Changes in water content are constantly monitored by the
transducer which is connected to the clean oil outlet of the
separator and linked to the control unit.
 Water, separated sludge and solid particles accumulate in the
sludge space at the separator bowl periphery.
 When separated sludge or water force the water towards the
disc stack minute traces of water start to escape with the
cleaned oil and are instantly detected by the transducer in the
clean oil outlet.
 The control unit reacts by triggering a sludge discharge or by
allowing water to drain off through a separate drain valve,
thereby re-establishing optimum separation efficiency.

13. FUEL OIL TREATMENT
 The separators should be in continuous operation
from port to port.
 To maintain a constant flow through the separators
individual positive displacement-type pumps
operating at constant capacity should be installed.
 The separation temperature is to be controlled
within +/–2 degC by a preheater.

14. FUEL OIL TREATMENT
 The fuel oil heater may be of the shell and tube or plate
heat exchanger type, with electricity, steam or thermal
oil as the heating medium.
 The required heating temperature for different oil
viscosities is derived from a fuel oil heating chart or
advised by the fuel testing lab.
 The viscosity meter setting, reflecting the desired fuel
injection viscosity recommended for an engine by the
engine builder, is typically 10–15 cSt.
 To maintain a correct and constant viscosity of the fuel
oil at the inlet to the main engine the heater steam
supply should be automatically controlled, usually
based on a pneumatic or electronic control system.

15. FUEL OIL SYSTEM

16. PROCESS OF COMBUSTION
 This is an exothermic reaction (one in which heat is
liberated by the action) between a fuel and oxygen.
 Liquid fuels consist of carbon, & hydrogen, in the
form of hydrocarbons, with small quantities of
sulphur & traces of other metallic impurities such as
vanadium.
 A typical fuel analysis, by mass would be:
C = 85%, H2 = 12%, S = 3%,
with a C.V. of 44000 KJ/Kg. (19000 BTU/lb.)

17. PROCESS OF COMBUSTION
 The oxygen is obtained from the air, which can be considered
to contain 77% nitrogen & 23% oxygen by mass.
 The nitrogen plays no active part in the combustion process
but it is necessary as it acts as a moderator.
 With pure oxygen, the combustion would be violent & difficult
to control & it would produce very high temperatures, creating
cooling, metallurgical & lubrication problems.
 The reactions, which occur, are:
2H2 + O2 ----------- 2H2O – liberating 142 MJ/kg. H2.
C + O2 -------------- CO2 – liberating 33 MJ/kg. C.
S + O2 --------------- SO2 – liberating 9.25 MJ/kg. S.
2C + O2 --------------2CO – liberating 10 MJ/kg. C.

18. PROCESS OF COMBUSTION
 Fuel is injected into the clearance volume towards
the end of the compression stroke, as a fine mist of
very small droplets, which have a surface area
many times that of the accumulated fuel charge.
 These droplets are rapidly heated by the hot
compressed air, which has a temperature of
between 550* to 650*C, causing vaporisation.
 The vapour mixes with air and when the mixture
exceeds the spontaneous ignition temperature,
(S.I.T.) combustion begins.

19. PROCESS OF COMBUSTION
 Combustion will only occur within limits in the air/fuel
mixture.
 If too much air is supplied all the fuel will be burnt but
the excess of oxygen & nitrogen will carry away
heat.
 If too little air is supplied incomplete combustion will
occur, when all the hydrogen will be burnt but only
part of the carbon, with the remainder only burning to
carbon monoxide or not burning at all.
 In diesel engine practice it is usual to supply
between 100 & 200% excess air by mass, though
15% is sufficient for a steady flow combustion
process (boiler).

20. PROCESS OF COMBUSTION
Combustion in Diesel Engines
1. Start of Injection
2. Beginning of Ignition
3. Maximum Pressure
4. End of Injection
5. End of Ignition
6. End of After Burning
1 – 2 : Ignition delay period,
2 – 3 : Rapid / Uncontrolled Combustion,
2 – 5 : Ignition Period,
3 – 5 : Controlled Combustion,
5 – 6 : After Burning

21. PROCESS OF COMBUSTION
 First Phase of Combustion
Ignition delay period is the time span between commencement
of fuel injection and the start of fuel ignition.
The fuel emerges into the cylinder as small liquid particles,
which are surrounded by hot compressed air.
They receive heat from the air and more volatile constituents of
the fuel vaporize.
During the ignition delay period a large part of the fuel charge is
prepared for combustion.
During the ignition delay, the injector continues to inject the fuel
and, if this has built up a sufficient quantity, the rapid
combustion and pressure rise will be quite violent, causing
detonation and shock loading creating a noise termed diesel
knock.

22. PROCESS OF COMBUSTION
 Second Phase of Combustion
Rapid or uncontrolled combustion usually occur just after
the ignition of the fuel vapours.
After ignition commences flame propagation proceeds very
quickly in the fuel vapour or air mixture, accompanied by
rapid temperature and pressure rise.
Towards the end of the rapid pressure rise a point is
reached where the rate of pressure rise falls away quickly,
and the curve flattens out towards the maximum pressure
point.
The point where the rate of pressure rise changes and
approaches the maximum pressure point is the end of the
second phase of combustion.

23. PROCESS OF COMBUSTION
 Third Phase of Combustion
Controlled combustion is regulated by the rate at which
fuel continues to be delivered.
The end of injection occurs approximately at or slightly
beyond the maximum pressure point.
Combustion in diesel engines can be termed as a
‘controlled explosion’.

24. PROCESS OF COMBUSTION
 After Burning
After burning is said to occur when the third phase of
combustion extends over a long period.
It may be caused by incorrect fuel grade, bad atomization, poor
or excess penetration, incorrect fuel temperature, incorrect
injection timing, insufficient air supply, or any combination of
these.
Slow burning, high viscosity, high density, high carbon content
fuels may also cause after burning of a serious nature leading to
engine damage.
After burning creates high exhaust temperatures and may cause
overheating of the engine in severe cases.
There is a loss of thermal efficiency when after burning occurs,
due to greater loss of heat to exhaust gases and the transfer of
large amount of heat to the cooling water.
There is a risk of damage to exhaust valves and scavenge fires.

25. PROCESS OF COMBUSTION
The actual start of fuel delivery depends on injection pump timing, which is
usually given in crankshaft angle before TDC and indicates the moment
when the pump plunger begins compressing the fuel.
The time from delivery start to the injection start is the injection delay.
The moment of injection start, given in crankshaft angle before TDC, is
called the injection timing.
Injection timing depends to a great extent on fuel properties and on
geometrical parameters of the pump, high pressure tube, and injector.

26. COMBUSTION CHAMBER DESIGN
The essence of a diesel engine is the introduction
of finely atomized fuel into the air compressed in
the cylinder during the piston’s inward stroke.
It is the heat generated by this compression that is
crucial in achieving ignition.

27. COMBUSTION CHAMBER DESIGN
Direct injection (Open chamber)
 The fuel is delivered directly into a single combustion
chamber formed in the cylinder space, atomization being
achieved as the fuel issues from small drillings in the nozzle
tip.
 For complete combustion of the fuel to take place, every
droplet of fuel must be exposed to the correct proportion of air
to achieve complete oxidation, or to an excess of air.
 In the direct injection engine the fuel/air mixing is achieved by
the energy in the fuel spray propelling the droplets into the
hot, dense air.
 Additional mixing may be achieved by the orderly movement
of the air in the combustion chamber, which is called ‘air
swirl’.

28. COMBUSTION CHAMBER DESIGN

29. COMBUSTION CHAMBER DESIGN
Indirect injection (Pre-chamber)
 Where indirect injection is exploited, some high speed
engines retain a pre-chamber in the cylinder head into
which fuel is injected as a relatively coarse spray at low
pressure, sometimes using a single hole.
 Combustion is initiated in the pre-chamber, the burning
gases issuing through the throat of the chamber to act
on the piston.
 Fuel/air mixing is achieved by a very high air velocity in
the chamber, the air movement scouring the walls of the
chamber and promoting good heat transfer.

30. COMBUSTION CHAMBER DESIGN
 Thus the wall can be very hot-requiring heat resistant
materials—but it can also absorb too much heat from the
air in the initial compression strokes during starting and
prevent ignition.
 It is these heat losses that lead to poor starting and
inferior economy.
 Further forms of assistance, such as glow plugs, have
therefore sometimes been necessary to achieve starting
when ambient pressures are low.
 The throttling loss entailed by the restricting throat also
imposes an additional fuel consumption penalty.

31. COMBUSTION CHAMBER DESIGN
 SEMT-Pielstick, achieved an ingenious combination of
the two systems by dividing the pre-chamber between
cylinder head and piston crown.
 At TDC a stud on the piston enters the pre-chamber to
provide a restricted outlet.
 On the expansion stroke the restriction is automatically
removed and fuel economy comparable with normal
direct injection engines is attainable.

32. COMBUSTION CHAMBER DESIGN
In the early days many ingenious varieties of combustion
chamber were used, inorder to reduce, or to use modest,
injection and combustion pressures.
A growing emphasis on economy and specific output,
coupled with materials development and advances in
calculation methods allowing greater loads to be carried
safely, has left the direct injection principle dominant in
modern medium speed and high speed engine practice.

33. FUEL INJECTION

34. FUEL INJECTION
A fuel injection system must achieve the following:
- Supply an accurately measured amount of fuel to each
cylinder
- Supply the fuel at the correct time at all loads with rapid
opening and closing of the fuel valve
- Inject the fuel at a controlled rate
- Atomize and distribute the fuel in the cylinder

35. FUEL INJECTION
Atomization:
- The break-up of fuel into minute particles so as to ensure an
intimate mixing of air and fuel oil.
- It is the break-up of the fuel charge into a very small particles
when it is injected into the cylinder.
- Proper atomization facilitates the starting of the burning and
ensures that each minute particle of fuel is surrounded by
oxygen with which it can combine.

36.  Atomized fuel has high surface area exposed to the
high air temperature that causes rapid evaporation
and mixing.
 This is governed by the size of the injector nozzle
holes and the difference between the fuel injection
pressure and compression pressure of air in the
cylinder.

37. FUEL INJECTION
Penetration:
- Ability of the fuel spray droplets to spread across the
combustion space so as to allow maximum utilization of
volume for combustion.
- It is the distance that
the fuel particles travel
or penetrate into
combustion chamber.

38. FUEL INJECTION
 To use all the air in the combustion space it is
necessary to give the fuel particles sufficient energy
to enable them to penetrate to the extremes of the
space.
 This is controlled by the fuel pressure, the size of
the particle & the length to diameter ratio of the
nozzle hole.

39. FUEL INJECTION
Turbulence:
- The swirl effect of the air charge in the cylinder which in
combination with atomized fuel spray gives intimate
mixing and good overhaul combustion.
- It refers to the air movement pattern within the
combustion chamber at the end of compression.
- The spray pattern of the fuel is cone-shaped.

40. FUEL INJECTION
 To aid mixing of fuel with air and atomization, friction between
the fuel & air is needed.
 Friction is a function of the relative velocity between the fuel
particle and the air, and may be obtained by either of two
methods.
 a) Fuel seeks air.
 a) The air is static or slow moving and the mixing energy is
obtained from the fuel particles.
 Injection pressures of 200 to around 1000 bars are needed
from multi-holed nozzle injectors.
 Advantages are, simplicity, economy and easier for cold
starting the engine. The latter because little air movement
means reduced heat loss to the cold liner and piston crown
(also assists in the burning of heavy fuel).
 Disadvantages are in producing and sealing high fuel
pressures.

41. FUEL INJECTION
b) Air seeks fuel
 The air is made to swirl rapidly at the end of the
compression stroke by using a pre-designed combustion
chamber. Single holed nozzles and lower fuel pressures are
used, 70-100 bars.
 Advantages are simplicity of injection, equipment and rapid
combustion (useful in high speed engines).
 Disadvantages are complicated combustion chambers and
high rate of heat loss to surroundings. Causes difficulties in
cold starting, sometimes needing cylinder combustion space
heating system.
 In practice, a combination is often used minimum fuel
pressures being used with a small degree of swill produced
by vaned inlet valves or tangentially cut scavenge ports.
 Quantity of swirl causes half the liner circumference to be
traversed during combustion.

42. FUEL INJECTION
Impingement:
- Excess velocity of fuel spray causing contact with metallic
engine parts and resulting in flame burning.

43. FUEL INJECTION
- The fuel is delivered by the fuel pumps to the fuel injectors or
fuel valves.
- For the fuel to burn completely at the correct time it must be
broken up into tiny droplets in a process known as
atomization.
- These tiny droplets should penetrate far enough into the
combustion space so that they mix with the oxygen.
- The temperature of the droplets rise rapidly as they absorb the
heat energy from the hot air in the cylinder, and they ignite
and burn before they can hit the relatively cold surface of the
liner and piston

44. FUEL INJECTION

45. FUEL INJECTION
 Fuel injectors achieve this by making use of a spring loaded needle
valve.
 The fuel under pressure from the fuel pump is fed down the injector
body to a chamber in the nozzle just above where the needle valve
is held hard against its seat by a strong spring.
 As the fuel pump plunger rises in the barrel, pressure builds up in
the chamber, acting on the underside of the needle.
 When this force overcomes the downward force exerted by the
spring, the needle valve starts to open.
 The fuel now acts on the seating area of the valve, and increases
the lift.
 As this happens fuel flows into the space under the needle and is
forced through the small holes in the nozzle where it emerges as an
"atomised spray".
 At the end of delivery, the pressure drops sharply and the spring
closes the needle valve smartly.

46. FUEL INJECTION
 Some injectors have internal cooling passages in them
extending into the nozzle through which cooling water is
circulated. This is to prevent overheating and burning of
the nozzle tip.
 Injectors on modern 2 stroke crosshead engines do not
have internal water cooling passages. They are cooled
by a combination of the intensive bore cooling in the
cylinder head being close to the valve pockets and by
the fuel which is recirculated through the injector when
the follower is on the base of the cam or when the
engine is stopped.

47. FUEL INJECTION

48. FUEL INJECTION
Troubles with fuel injectors:
1. Over heating OR under cooling:
If cooling of the injector is reduced, either by fuel valve
cooling system or poor heat transfer to the cylinder head,
then the working temperature of the injector will rise. This
can cause:-
– Softening of the needle and seat which increases the
possibility of nozzle leakage and/or,
– Fuel to expand/boil out of the fuel sac, leading to carbon
trumpet formation, and increased levels of HC and smoke
in the exhaust gases.

49. FUEL INJECTION
2. Over cooling:
More common on older vessels with separate fuel valve
water cooling systems.
When the injector is over cooled, the tip of the injector falls
below the condensation temperature and acid corrosion
due to the sulphur in the fuel oil occurs.
This can severely corrode the injector tip, causing the
spray pattern to be affected.

50. FUEL INJECTION
3. Leakage from Nozzle:
This fault will produce carbon trumpets as the dribble of
fuel burns close to the tip and the carbon deposits remain.
The formation of the trumpets will have a progressive
affect by influencing the spray pattern of the fuel, and this
can be detected in the increased exhaust gas temps and
smoke levels.

51. FUEL INJECTION
4. Weak spring:
This will cause the injector to open and close at a lower
pressure.
Thus the size of the fuel droplets will increase during these
injection periods.
Increased droplet size at the start of combustion will
decrease the maximum cylinder pressure (late
combustion), whilst increased droplet size at the end of
combustion will increase the exhaust temperature and
smoke (afterburning).
Causes of a weak spring are usually metal fatigue, due to
an excessive number of operations.

52. FUEL INJECTION
5. Slack needle:
Slight leakage between the needle valve and its body is
required to provide lubrication of the moving parts.
However excess leakage due to a slack needle will allow a
greater quantity, and larger size of fuel particle to pass
between the valve and body.
The quantity of leakage should not influence injector
performance unless excessive, but dirt particles between
the needle and body can increase friction and make the
needle action sluggish.
The cause of a slack needle is usually poor filtration of the
fuel causing wear between needle and body.

53. FUEL INJECTION
6. Poor atomization:
This will increase the size of the fuel droplets, which will
increase the time required for combustion.
Thus engine noise, exhaust smoke, exhaust temperatures,
etc., will increase.
Poor atomization can be caused by low injection pressure
(fuel pump wear), high fuel viscosity and nozzle hole
obstruction such as carbon trumpets.

54. FUEL INJECTION
7. Poor penetration
This will reduce the mixing which occurs between the fuel
and air, and will increase the over-rich areas in the centre
area of the cylinder.
This will increase the time required for combustion as the
fuel/air mixture is not correct in many areas, and hence
afterburning, exhaust temps, and smoke will increase.
Causes of poor penetration is reduced injection pressure,
and nozzle hole blockage such as trumpets or sac
deposits.

55. FUEL INJECTION
8. Over penetration
 This will occur when the air density within the cylinder is
reduced, or with over-size holes.
 The liquid stream travels too far into the cylinder, so that
a high level of liquid impingement on the liner wall takes
place.
 This will remove the liner lubrication, and once burning
will greatly increase the liner wall temperature, and its
thermal stress.
 If this over penetration is caused by prolonged low
power operations, then “slow speed” nozzles should be
fitted.

56. FUEL INJECTION
 Slow steaming nozzles can be used when regular and
prolonged engine operation is required between 20-50%
power.
 The nozzle hole diameter is reduced to
i. Reduce the penetration that will occur into the less
dense cylinder air
ii. Keep the atomisation level and injection pressure
sufficient, as mass flow rate is reduced.
 If the engine is operated for long period on low levels of
power/speed with `normal’ size injector nozzles, then the
atomisation will reduce, thus engine noise, mechanical
loading, exhaust smoke, exhaust temps, and fuel
consumption will increase

57. FUEL INJECTION
Maintenance of fuel injector:
o Injectors should be pressure tested, overhauled or
changed in line with manufacturers recommendations.
 Springs can weaken with repeated operation leading
to the injector opening at a lower pressure than
designed.
 The needle valve and seat can wear which together
with worn nozzle holes will lead to incorrect
atomization and dribbling.
 Proper cooling should be made during operation.
Cooling passages to be cleaned during overhaul.

58. FUEL INJECTION
 The valve body and valve needle should always
be considered as a unit, not as two separate
pieces and they should be renewed together.
 The holes should be cleaned and cleared properly
without damaging by blown with compressed air.
 The valve needle must be perfectly fluid tight
when in the closed position and must open and
close smartly.