This document provides information on diesel propulsion systems and two-stroke diesel engines. It begins with learning objectives about familiarizing students with marine diesel engines. It then describes the operating cycles of internal combustion engines, including the Otto, Diesel, and dual cycles. It explains the four-stroke cycle and two-stroke cycle of compression ignition engines. Details are provided on the intake, compression, power, and exhaust strokes. The timing diagrams of the four-stroke and two-stroke cycles are illustrated. Valve timing and overlapping are also discussed.

1. MTM 3202
Diesel propulsion systems

2. Diesel propulsion systems

3. INTERNAL COMBUSTION ENGINES

4. • Course Learning Objective: Familiarize
students to the basic cycle and design features
of modern marine diesel engines
Specific Objectives:
- Define the theory and principle of Internal Combustion Engine
- Describe basic operations of working cycle
- Identify the engine timing diagram
- Describe differences and advantages of 2S & 4S

5. Principle of I.C.E
• An internal combustion engine is one in
which the fuel is burnt within the engine ->
usually of the reciprocating type.
• It involve system where combustion of the
fuel and the conversion of the heat energy
from combustion to mechanical energy
takes place within the cylinders (ICE)

6. I.C.E. CATEGORIES
– Spark ignition engines use gaseous or volatile
distillate fuels -> work on a modified Otto
cycle -> operate on the 2 or 4 – stroke cycle.
– Compression ignition engine use distillate
liquid fuels -> work on either 2 or 4 – stroke
cycle and normally designed to operate on the
dual-combustion cycle (Otto and Diesel cycle)

7. Otto cycle
• In the Otto cycle the theoretical pressure –
volume diagram is formed from : two constant –
volume and two adiabatic processes.
• The air in the cylinder is compressed
adiabatically.
• Heat is added to the air at constant volume ->
Work is done during the adiabatic expansion
and -> then heat is rejected at constant volume

8. Otto Cycle
Pressure (Pa)
C
P2
D
P1
B
A
V1 V2
Volume (m3)
A–B : Adiabatic compression
B–C : Heat received at constant volume (combustion)
C–D : Adiabatic expansion
D–A : Heat rejected at constant volume (exhaust)

9. Otto Cycle
• 1. The induction stroke takes place at A. Although in theory the
pressure should be the same as atmospheric, in practice it's rather
lower. The amount of petrol air mixture taken in can be increased
by use of a supercharger.
• 2. A to B is the compression stroke. Both valves are closed. The
compression is adiabatic, and no heat enters or leaves the
cylinder.
• 3. Ignition occurs at C. The gases resulting from the ignition
expand adiabatically, leading to the power stroke.
• 4. D to A the gas is cooled instantaneously.
• 5. At A the exhaust stroke occurs and the the gases are removed
at constant pressure to the atmosphere.
• 6. Strange as it may seem, the piston does half a revolution at A.
Actually it's slightly in practice, as the the valve timing is more
complex.

10. Diesel cycle
• In the diesel cycle the theoretical pressure-
volume diagram is formed from two adiabatic
operations, one constant-pressure and one
constant-volume operation.
• Air is compressed adiabatically, then heat is
added at constant pressure. Adiabatic expansion
takes place and then heat is rejected at constant
volume

11. Diesel Cycle
Pressure (Pa)
B C
P
D
A
V1 V2
Volume (m3)
A–B : Adiabatic compression
B–C : Heat received at constant pressure
(combustion)
C–D : Adiabatic expansion
D–A : Heat rejected at constant volume

12. Diesel cycle
• 1. The induction stroke takes air in ideally at constant
volume, pressure at temperature.
• 2. The compression stroke takes place from A to B.
The air is compressed adiabatically to about 1/20 of its
original volume. It gets hot.
• 3. From B to C fuel is injected in atomised form. It
burns steadily so that the pressure on the piston is
constant.
• 4. From C to D the power stroke moves the piston
down as adiabatic expansion takes place.
• 5. D to A cooling and exhaust occurs.

13. Dual cycle
• In the dual cycle, air is compressed
adiabatically, then heat is added, partly in
a constant volume process and the
remainder in a constant pressure process.
• Expansion takes place adiabatically and
then heat is rejected at constant volume

14. Pressure (Pa)
C D
P
E
B
A
V1 V2
Volume (m3)
A–B : Adiabatic compression
B–C : Heat received at constant volume
C–D : Heat received at constant pressure
D–E : Adiabatic expansion
E–A : Heat rejected at constant volume

15. COMPRESSION IGNITION
ENGINE
• Compression ignition engine works on dual cycle
• The fresh air enters each of the engine cylinders
and is compressed by the upward movement of the
piston.
• The compression causes the temperature and
pressure of the fresh air to increase
• Fuel injectors or fuel valve will supply the fuel oil in
fine spray when the piston is nearly at top dead
centre

16. • The fuel will then be mixed with air
(compressed) and burn inside the cylinder
when the piston is at TDC.
• The expanding gases on top of the piston
(completed combustion) will push the piston
moving it downward and rotating the
crankshaft .
• The cycle will be repeated until the engine
stops

17. Cycle of Operations
• Four strokes of CI engine are as
follows:-
– Suction Stroke / Induction Stroke
– Compression Stroke
– Explosion Stroke / Power Stroke
– Exhaust Stroke

18. SUCTION STROKE
• In which the air is admitted to the
engine cylinder

19. COMPRESSION STROKE
• In which the charge of fresh air is
compressed by the piston, and
fuel is injected just before the
point of maximum compression

20. POWER STROKE
• In which the air- fuel mixture is
ignited by the heat produced by
compression of air
• The pressure rises due to fuel
combustion and pushes piston
downwards to drive the engine

21. EXHAUST STROKE
• Exhaust valve opens at the end of
power stroke
• The expanded burnt gases are
exhausted / expelled from the
cylinder

22. • The four strokes in duel cycle of CI engine
are completed in two revolutions of the
crankshaft.
• There are thus two piston strokes in each
revolution of the crankshaft

23. FOUR STROKE ENGINE
INLET VALVE CYLINDER HEAD FUEL INJECTOR EXHAUST VALVE
PISTON
CYLINDER
LINER
CRANKSHAFT
DIRECTION
CRANK PIN
INDUCTION STROKE / COMPRESSION STROKE POWER / EXPANSION STROKE EXHAUST STROKE STROKE
EXHAUST
SCAVENGE STROKE

24. How strokes are executed
• Strokes are executed by combination of
valves and gears

26. SUCTION / INDUCTION STROKE
• Piston draws air into cylinder
during downward movement or
stroke through opened inlet valve.
(suction effect)
• Exhaust valve and fuel injector are
closed
• At the end of the stroke (BDC) the
inlet valve close, which inside the
cylinder now full with fresh air.

27. COMPRESSION STROKE
• Stroke begins when the
piston starts to move
upward (from BDC to TDC).
• Inlet valve, exhaust valve
and fuel injector remain
closed.
• The air which is trapped in
the cylinder is now
compressed rising in
temperature

28. POWER STROKE
• Before the piston reaches
TDC(approx.15 – 20o), the
fuel injectors supply fuel oil in
a fine spray(end approx.
15-20o after TDC)
• The mixture (fuel oil and air)
ignites and explodes while
the piston crosses TDC
• High pressure (expansion of
the gases) on top of the
piston push the piston
downward towards BDC

29. EXHAUST STROKE
• Stroke begins when the piston again
starts to move upward (from BDC to
TDC) as in compression stroke,
however only exhaust valves are
opened.
• The exhaust gases are expelled from
the cylinder through the exhaust valve
ports.
• At the end of the stroke (TDC), the
exhaust valve closes but inlet valve is
opened starting the cycle once again

30. Power produced
• Power produced by a 4-stroke cycle engine in
kW is given as
PLAN
Power =
2
P= Mean effective pressure, kN/m2
L= Stroke length, m
A= Area of cylinder bore, m2
N= Revolution/second

31. 4 - STROKE CYCLE
9
PISTON POSITION
8 3 4
10 9 5
3 4 5 8 10
2 6
1
2
6
DIRECTION 7
PRESSURE
1 1/7

32. 4 - STROKE CYCLE
• 1-2 Suction stroke ends
• 2-3 Compression stroke. Inlet valve closed and
piston moved upwards to compress the
trapped air (Temperature rises).
• 3-4-5 Fuel injector in operation. Combustion
occurs (mixture of compressed air and fuel)
• 5-6 Due to expansion of gases piston
moves downward. (Power stroke)
• 6-7-8 Exhaust stroke. Exhaust valve opens and
piston moves upward removing gases.
• 8-9-10 Overlapping period: both exhaust and inlet
valves are open.
• 10-1 Suction stroke – piston moves downward.
Exhaust valve closed and inlet valve open.
• 1- the rest – The cycle continues until the
engine stops

33. Exh. v/v
closes
Fuel Fuel
injection injection
begins ends
PO
COMPRESSION STROKE
W
E
ER
T STROK
Inlet v/v
ST
opens
RO
SUC
KE
Rotation
EXHAUS
TIO
N STR
Inlet v/v OKE
closes Exh. v/v
opens
FOUR STROKE TIMING DIAGRAM

34. VALVE OVERLAPPING
It can be defined as the period when inlet and exhaust
valve were open at the same time.
E.g.,
• Inlet valve opened before the piston reached TDC at
the end of exhaust stroke, say 20o before TDC.
• Exhaust valve remained open and will be closed at
certain degree of the piston movement after TDC,
say 20o after TDC.
• By providing overlapping period on 4 – stroke engine,
the residual exhaust gases will be expelled effectively
with the rushing in of fresh air.

35. VALVE OVERLAP
TDC
OVERLAPPING PERIOD
Inlet v/v Exh. v/v
opens closes

36. 2-Stroke cycle diesel engines

37. • Learning Objective: Know the basic cycle
and design features of modern marine diesel
engines
Specific Objectives:
• Describe the operation cycle process of a
2-stroke diesel engine.
• Identify the 2-stroke engine timing diagram

38. TWO STROKE CYCLE
• The two stroke cycle is so called because
it takes two strokes of the piston or one
revolution of crank shaft to complete the
processes needed to convert the energy
in the fuel into work.

39. Why 2-Stroke Cycle Engines
• We know 4-stroke cycle engine gives only
one power stroke out of 4 strokes of the
piston or one power stroke in two
revolutions of the crank shaft.
• This makes engine’s power to weight
ratio low mainly because three strokes
consume power against one which
produces

40. 2S
• In the two stroke engine, cycle is completed in two
strokes of the piston or one revolution of the
crankshaft.
• Thus out of 3 power consuming strokes of the 4-
stroke cycle two strokes are saved
• Engine thus produces one power stroke in every
revolution of the engine which is two times in
comparison to 4-stroke cycle
• This improves power to weight ratio of the engine
and reduces its size for same power.

41. 2S
• 2-Stroke cycle is achieved by eliminating suction
and exhaust strokes of the 4-stroke cycle
• In order to eliminate suction and exhaust
strokes, some special arrangements are
required to be provided for:-
-.charging air into cylinder without suction from
piston
- Exhaust gases must be expelled out of the
cylinder without assistance from piston

42. Power
Piston Comp
stroke
stroke
Exst port Exst port
Inlet air Piston
Inlet air port
port

44. The crankshaft is revolving
clockwise and the piston is
moving up the cylinder,
compressing the charge of
air.
Because energy is being
transferred into the air,
pressure and temperature
increase.
By the time the piston is near
the top of the cylinder
(known as Top Dead Center
or TDC) the pressure is >100
bar and the temperature >
500°C

45. Just before TDC fuel is injected
into the cylinder by the fuel
injector.
The fuel is "atomised" into tiny
droplets. Being very small, these
droplets heat up very quickly and
start to burn as the piston passes
over TDC.
The expanding gas from the fuel
burning in the oxygen forces the
piston down the cylinder, turning
the crankshaft.
It is during this stroke that work
energy is being put into the
engine; during the upward stroke
of the piston, the engine is having

46. As the piston moves down the
cylinder, the useful energy
from the burning fuel is
expended.
At about 110° after TDC the
exhaust valve opens and the
hot exhaust gas (consisting
mostly of nitrogen, carbon
dioxide, water vapour and
unused oxygen) begin to
leave the cylinder.

47. At about 140º after TDC the
piston uncovers a set of ports
known as scavenge ports.
Pressurized air enters the
cylinder via these ports and
pushes the remaining
exhaust gas from the
cylinder, "scavenging".
The piston now goes past
BDC and starts moving up
the cylinder, closing the
scavenge ports. The exhaust
valve then closes and
compression begins.

48. The two stroke cycle can also be illustrated on
a timing diagram.
1 -2 Compression
2 - 3 Fuel Injection
3 - 4 Power
4 - 5 Exhaust Blowdown
5 - 6 Scavenging
6 - 1 Post Scavenging
1. approx 110º BTDC
2. approx 10º BTDC
3. approx 12º ATDC
4. approx 110º ATDC
5. approx 140º ATDC
6. approx 140º BTDC

49. 4 5 5
6 4
PISTON POSITION
6
7 3 7
3
2 8
8
2
1 1 PRESSURE

50. • 1-2 Scavenging period, both exhaust and inlet
ports are open.
• 2-3 Scavenge stroke ends. Exhaust ports remain
open to ensure only fresh air remains in the
cylinder.
• 3-4 Compression takes place. Both ports closed.
The air is then compressed by the upward
movement of the piston.
• 4-5-6 Fuel injector is operational supplying fuel oil.
• 6-7 Due to expansion of gases, piston moves
downward. (Power stroke)
• 7-8 When piston crown/top ring passes the exhaust
ports, exhaust begins
• 8-1 When the piston passes the inlet ports, Scavenging
begins and fresh air fills the cylinder, thus pushing the
remaining exhaust gases out

51. Fuel Fuel
injection injection
begins ends
ON
POW
SI
ES
ER
R
MP
STR
CO
OK
Rotation
E
Scavenge Scavenge
ports ports
close open
Exhaust Exhaust
SCAVENGE
ports ports
close open
EXHAUST
TWO STROKE TIMING DIAGRAM

52. The 2 stroke
crosshead engine
works on exactly
the same principle
and cycle as the 2
stroke trunk piston
engine.

53. The disadvantages of the two stroke
trunk piston engine are that:
It has a low overall height, lubricating
oil splashed up from the crankcase to
lubricate the liner can find its way into
the scavenge space, causing fouling
and a risk of fire.
There is also the likelihood of liner and
piston skirt wear, allowing air into the
crankcase. This can supply the
required oxygen for an explosion
should a hot spot develop.
The crankcase oil must have additives
which can cope with contamination
from products of combustion, and the
acids formed during combustion due to
the sulphur in the fuel.

54. The majority of 2 stroke engines encountered at sea are of the "crosshead" type.
In this type of engine the combustion space (formed by the cylinder liner, piston
and cylinder head), and the scavenge space are separated from the crankcase by
the diaphragm plate.
The piston rod is bolted to the piston and passes through a stuffing box mounted
in the diaphragm plate. The stuffing box provides a seal between the two spaces,
stopping oil from being carried up to the scavenge space, and scavenge air leaking
into the crankcase.
The foot of the piston rod is bolted to the crosshead pin. The top end of the
connecting rod swings about the crosshead pin, as the downward load from the
expanding gas applies a turning force to the crankshaft.
To ensure that the crosshead reciprocates in alignment with the piston in the
cylinder, guide shoes are attached either side of the crosshead pin. These shoes
are lined with white metal, a bearing material and they reciprocate against the
crosshead guides, which are bolted to the frame of the engine. The crosshead
guides are located in-between each cylinder.
Using the crosshead design of engine allows engines to be built with very long
strokes - which means the engine can burn a greater quantity of fuel/stroke and
develop more power. The fuel used can be of a lower grade than that used in a
trunk piston engine, with a higher sulphur content, whilst high alkalinity cylinder
oils with a different specification to that of the crankcase oil are used to lubricate
the cylinder liner and piston rings and combat the effects of acid attack.

55. SCAVENGING
• To ensure a sufficient supply of fresh air for
combustion by removing all remaining exhaust gases
by blowing with these fresh air.
• Supercharging is a large mass of air that is supplied to
the cylinder by blowing it in under pressure either by
electrically driven auxiliary blower or exhaust gas
driven turbocharger.
• The flow path of the scavenge air is decided by the
engine port shape and design and the exhaust
arrangements.

56. SCAVENGING PERIOD
It can be defined as a period when inlet and exhaust
are open at the same time:
• Remaining exhaust gas will be expelled from the
cylinder through exhaust ports or exhaust valve (if
fitted).
• Fresh air which has collected in the scavenge
manifold rush into the cylinder
• Scavenging period: Normally when piston is at
BDC, (or as per maker or engine design or the location of the ports
itself)

57. SCAVENGING METHODS
• CROSS/DIRECT – FLOW SCAVENGING
• LOOP SCAVENGING
• UNIFLOW SCAVENGING

58. Cross/direct flow
scavenging
Exhaust
manifold
Scavenge
manifold

59. Loop scavenging
Exhaust
manifold
Scavenge
manifold

60. 2 stroke engines do not have exhaust
valves; With scavenge ports in the cylinder
liner, they are fitted with exhaust ports
located just above the scavenge ports.
As the piston uncovers the exhaust ports on
the power stroke, the exhaust gas starts to
leave the cylinder.
When the scavenge ports are uncovered,
scavenge air loops around the cylinder and
pushes the remaining exhaust gas out of
the cylinder.
This type of engine is known as a loop
scavenged engine. Note that the piston
skirt is much longer than that for a uniflow
scavenged engine. This is because the skirt
has to seal the scavenge and exhaust ports
when the piston is at TDC.

61. TWO STROKE ADVANTAGES
• Compactness in relation to the power output. Not required
to increase brake mean effective pressure or the engine
speed to increase rating.
(High bmep increases the stresses on engine components,
greater rate of cylinder wear, whilst the alternative of higher
speed, valve flutter may become a serious problem)
• Each out-stroke being a working stroke gives more even
turning for the same number of cranks, consequently a
lighter flywheel may be employed.
• The reversing operation of rotation is simplified since there
is less valve gear to contend with.

62. OTHER ADVANTAGES
• Fewer moving parts and lower maintenance
• Lower specific fuel consumption
• No gear loss
• Simplicity in construction
• Longer life time
• Higher reliability (product)
• Low lubricating oil consumption
• Better ability to burn low quality fuel oil

63. FOUR STROKE ADVANTAGES
• Good volumetric efficiency, good combustion
characteristic and positive exhaust scavenging.
• The thermal and mechanical efficiencies are
slightly better than 2S engine.
• Only half the quantity of the heat generated in
the cylinders has to be dealt within a given time,
so that efficient lubrication of the piston and
cooling of the cylinder is more easily
accomplished.

64. OTHER ADVANTAGES
• Lower initial cost for equivalent power
• Ease of installation
• Lower weight per unit power
• Saving in weight and engine room length
• Increased cargo capacity
• Free choice of propeller speed through
gearing
• Suitable for electrical power take off

65. Supercharging/Turbocharging
• Process of pushing a higher pressure air
charge into the cylinder greater than
atmospheric pressure, so that extra mass
of air can be delivered into cylinder to burn
more fuel and produce extra power.
• Turbocharging can increase power output
of engine by 60%

66. Turbocharging
• Very effective pressure charging.
• Utilizes 20% of waste heat in exhaust gas
which contains 35% of fuel heat.
• How?

67. •By increasing mass of air in cylinder, more fuel can be
burned and correspondingly power output will be
increased
•Various methods can be adopted:
–Electrically powered auxiliary blower
–Utilization of heat energy from exhaust gas to
drive a single stage impulse turbine directly coupled to
a simple blower (free running unit) called exhaust gas
turbocharger
Turbocharger utilizes free energy of exhaust
gases and hence improves efficiency of the engine

68. Typical heat balance of an
engine
Useful Output (Brake Power) 34%
Cooling Loss 30%
Exhaust Loss 26%
Friction, Radiation, etc. 10%
-------
Total Heat Input
100%

69. Turbocharger
System

70. Advantages
• Increased power for an engine of the same
size OR reduction in size for an engine with
the same power output.
• Reduced specific fuel oil consumption ->
mechanical, thermal and scavenge efficiencies
are improved due to less cylinders, greater air
supply and use of exhaust gasses.
• Thermal loading is reduced due to shorter
more efficient burning period for the fuel
leading to less exacting cylinder conditions.

72. Risk
• Crankcase explosion
• Scavenge fire

73. Design consideration
• Types of fuel and fuel oil system design
• Types of lubricating oil and lubricating oil systems
• Cooling systems
• Waste heat utilization systems
• Intake and exhaust valve systems
• Starting air systems
• Instrumentation system
• Control and automation system
• Installation items
• Safety features

74. Summary
• Principle of ICE
• Theoretical Cycles
• Basic principle of operations of working cycle
• Cycle & Timing Diagram
• Principles of Scavenging & Arrangements
• Advantages of 2S & 4S
• Structural differences
• Overlap of Inlet & Exhaust

75. References
• Introduction to Marine Engineering,
• Marine Engineering , Roy L. Harrington, SNAME, 198
• El-Hawary, F. (2001). Ocean Engineering Handbook. CRC
Press, UK.
• Calder, Nigel (2007): Marine diesel engine: maintenance,
troubleshooting and repair.