Two Stroke Engines

Two Stroke Engines
Εργαςία Αγγλικών
Γενοβζηοσ Λάμπροσ
Αναλαμπιδάκθσ Μάνοσ
Γεωργακάκοσ Μάνοσ
Γεωργόπουλοσ Γιώργοσ

Advantages and Disadvantages of Two
Advantages:
Stroke Engines
• Two Stroke Engines have high power output due to the fact that they have
a power stroke for every two strokes and can work reliably with low
graded fuel.
• Lower weight and high power output means high power to weight ratio, in
other words more cargo.
• Low maintainance costs.
Disadvantages:
• Two Stroke Engines have high fuel consumption rates.
• Two Stroke Engines are not particularly eco-friendly due to the pollution
they produce.

Two-Stroke Engine Process
• The Induction Step, also called the intake or
suction step, pulls in the fuel and air mixture
into the crankcase as shown below

• The Crankcase compression occurs during the
downward stroke of the piston. The valve is
forced closed due to the high pressure within
the crankcase and as a result, the mixture is
compressed within the crankcase during this
step.

• At the Transfer Step, the compressed air-fuel
mixture moves from the crankcase towards
the main cylinder. This movement also helps
in the expulsion of the previous contents of
the main cylinder, aiding in the previous
cycle’s Exhaust Step. A downside to this step is
that fresh fuel can also be expelled along with
the exhaust gas.

• The Compression Step compresses the air-fuel
mixture within the main cylinder of the engine
as the piston rises. This movement is caused
by the flywheel momentum. During this point,
the Induction Step for the next cycle is also
happening underneath the piston.

• During the Power Step the spark plug ignites
the fuel mixture. As the burning mixture
expands, the piston is driven downward,
completing the two-stroke cycle.
The Crankcase Compression Step for the next
cycle occurs at the crankcase during the Power
Step of the current cycle.

• The exhaust gases produced are released
during the Exhaust Step. Simultaneously, the
Transfer Step of the next cycle happens at this
point.

Main Reasons Why Two-Stroke
Engines are used in Ship Vessels
The reason as to why any ship manufacturer should end up using a two
stroke engine comes when you compare it to a Four-Stroke engine and
the main advantages it has compared to it.
The advantages are:
• Efficiency
• Power Generation
• Maintainance Costs/ Reliability
Two-Stroke Engines are superior to Four-Strokes when it comes to use
in ship vessels due to the fact that in the long run they prove to be
more reliable and more cost efficient than their counterparts. The
initial cost of installation of a two stroke engine may be higher than
that of the Four-Stroke Engine but the fact that two stroke engines run
on much lower graded fuel compensates for all disadvantages and also
reduces the operating cost of the ship.

While the two-stroke engine consumes fuel per two strokes, as
opposed to the per four strokes of the four-stroke engine, it also has
the advantage of being able to burn low-grade fuel oil. A high cost
reduction can be applied in such cases, and would therefore be
more profitable, which is a huge advantage for merchant ships.
Comparing the two-stroke and four-stroke engines under a standard
operating setting, the design of the two-stroke engine is more
efficient as it reduces thermal and mechanical losses. In addition,
energy is conserved more since the two-stroke engine has less heat
transfer from the engine to the cooling system than that of the fourstroke.

Common Problems Found In
Two-Stroke Engines
• Stuck Fuel Rack: This is one of the most common problem
with oil fired 2 stroke marine engines. The governor
controls the fuel pump delivery through a fuel rack, which
is a combination of mechanical links. Sometimes the fuel
rack gets stuck leading to lack of fuel supply in
the concerned unit which results in either fluctuation in the
engine RPM if running or engine will not start from
standstill.
• Solution: All the mechanical links of the fuel rack must be
well lubricated and greased before starting the main
engine. If after starting the main engine, the engine rpm is
constantly fluctuating even at lower speed in calm weather,
check all the fuel rack as one or more of them must
be stuck.

• Starting Air Valve Leakage: Any leakage from the
starting air valve will lead to hot gasses going back to
the engine air line, which may contain thin oil film.
Such mixture of oil and film can lead to starting air line
explosion. This kind of explosion is not very common
now-a-days due to safety features incorporated in the
air line (bursting disk in MAN and relief valves in
SULZER/ Wartsila engines). However, one cannot
overlook the possibility of malfunctioning of such
devices which can lead to explosion.
• Solution: Normally, there is no remote monitoring of
temperature for the air line supplying air to starting air
valve. The best way to determine such fault is to check
the temperature of the air line manually during
maneuvering. This problem is more likely to occur
when the engine is started frequently and not when
engine is running continuously.

• Fuel Leakage/ Fuel Valve Malfunction: Problems
in the fuel system are also commonly observed in
the main engine. When there is a deviation in
temperature of one unit, the fuel system,
especially the fuel valve needs to be checked.
Overhauling and pressure testing of fuel valve
must be done as per PMS. If the engine is
maneuvered in diesel oil, there are chances of
leakage from the pump seals. Also if the fuel
treatment is improper and the fuel temperature
is not maintained, it can lead to cracks and
leakages in high pressure fuel pipe.
• Solution: Any leakage in the main engine fuel oil
system can be determined from the “high
pressure leak off tank” level and alarm.

• Sparks in the Main Engine Exhaust At
Funnel: Marine engineers normally
experience getting a call from bridge officer
informing about sparks coming out from the
funnel, which is the main engine exhaust.
Sparks from funnel occur due to slow
steaming and frequent maneuverings, which
build unburnt soot deposits on the EGB boiler
path.
• Solution: Frequent cleaning (monthly) of the
exhaust gas boiler to be preferred by the ship
staff to avoid this problem.

• Sparks in the Main Engine Exhaust At
Funnel: Marine engineers normally
experience getting a call from bridge officer
informing about sparks coming out from the
funnel, which is the main engine exhaust.
Sparks from funnel occur due to slow
steaming and frequent maneuverings, which
build unburnt soot deposits on the EGB boiler
path.
• Solution: Frequent cleaning (monthly) of the
exhaust gas boiler to be preferred by the ship
staff to avoid this problem.

• Starting Air Leakage: This is also one of the most
underrated yet common problems related to marine
engines. The control air supplies air to different parts
and systems of the main engine. It is always in open
condition when the engine is in use. Small leakages are
normal and can be rectified only by tightening or
replacing the pipes or joints.
• Solution: When the Engine room machinery is in
working condition it is difficult to hear any air leakage
sound. The best way is to trace all the air lines and
feeling all the connections/ joints by hand for air
leakage. The easiest way to find air leakages is when
there is an intentional black out done for any job. At
this moment all the machinery will be in “stop”
position and leakage sound (a hissing noise) will be
loud and clear. Note the leakage area to perform the
repairs later.

• Stuck Air Distributor: Air distributor is
responsible for maintaining the air supply which
opens the starting air valve in the engine
cylinders. Since it’s a mechanical part, it is prone
to malfunctioning, especially getting stuck. The
main engine will not start if air distributor does
not supply air to open the starting air valves as no
air will be present in the cylinder to commence
fuel combustion
• Solution: Many engines such as MAN B&W have
their air distributor located at the end, with
inspection cover, which can be opened when the
engine is not running for inspection and
lubrication to avoid this problem.

• Malfunctioning of Installed Gauges: It is very
important to have local parameter gauges on
various systems of the main engine. To note
down the readings in the log book, it is always
recommended to take the the local readings
rather than remote readings. Often
engineers find that one or two gauges
(pyrometer, pressure gauges, manometers
etc.) installed in the main engine are not
working or in dilapidated condition. The
reason for such condition can be due to loose
parts and connections, and even vibrations.

• Faulty Alarms and Sensors: The main engine is
fitted with various sensors, which measure and
transmit actual data to alarm console. Due to
factors such as vibration, high temperature,
humidity, dust etc. these sensors can malfunction
leading to false alarms.
• Solution: A routine checks needs to be performed
on all engine room sensors and alarms. Different
main engine safety alarms and trips also to be
tried out at regular basis and faults to be
attended immediately.
• Do you know any other common 2-stroke marine
engine problems which should be added to this
list? Let’s us know in the comments below.