Engine General

Question 1

Overheating start air branch to single unit

Answer 1

• Request bridge slow down and stop
• Inform chief
• Close off fuel to this unit either electrically or using plunger to take p/p off cam or use an isolation v/v on the branch if there is one

Reason: Start air valve could be passing, allowing hot combustion gases through which could cause a start air explosion

Question 2

How do crankcase doors work?

Answer 2

• They work like relief valves
• The pressure inside overcomes the spring and releases the pressure inside the crankcase from the primary explosion
• It then closes after pressure equalises to prevent a secondary explosion.
• There is a flame arrestor in the form of an oil wetted gauze which cools any flames trying to escape the crankcase while they are being released.
• There are also deflection plates to deflect the escaping pressure away from any personnel passing by.

They open @ 0.1-0.2 bar over pressure
They are required on engines with a bore of >200mm and power rating of >2250kw so they are not present on lifeboat engines.

Question 3

What are indicator cocks for?

Answer 3

They are used for venting pressure and monitoring for water in the cylinder while using the turning gear and
Also used for testing cylinder firing pressure

Question 4

What are the tie rods for?

Answer 4

The tie rods hold the entablature, A-frame and bed plate under compression
While tie rods are under tensile stress

Question 5

Constructional differences between 2 stroke and 4 stroke

Answer 5

2 stroke has a piston rod, crosshead, crosshead bearing and guides, telescopic pipe, stuffing box, 1 exhaust valve per unit, 2 stroke crankshaft is semi-built and therefore not drilled.

4 stroke has rocker arms, gudgeon pin, 2 inlet v/v and 2 exhaust v/v per unit. Also has a longer piston skirt to spread the load from side thrust which acts on the cylinder wall due to the connecting rod pushing sideways on the piston (reduces wear and scuffing on the liner). It also keeps the piston and rings aligned to maintain the seal.

Question 6

ME HT temp is high? Causes?

Answer 6

• Inform bridge & request slow down & stop if navigationally safe to do so
• Go down and verify local temp reading is same as the ECRs
• Change 3 way bypass on HT cooler for full cooling flow
• Check LT cooler and perform back flush by closing SW inlet and opening backwash valve to remove marine growth
• Change over active sea chest if problem persists

• Apart from the above cooler problems, it could also be that the pre-heat valve is left open or passing.

Question 7

What do you do if the ME LO level has dropped more than expected?

Answer 7

-Sound the LO sump tank to confirm level
-check LO piping
-check LO cooler
-check purifier for leaks and sound sludge tank

Question 8

ME fuel injection pressure?

Answer 8

450-550 bar For Wartsila 12V46C
~300bar for 2 stroke

Question 9

Ways of reversing an engine

Answer 9

Start air is reversed by the distributor timing.

Exh v/v is done only on an electrically controlled engine. (No camshaft)

Fuel is done in 3 ways:
• Axial Displacement - Piston shifts the camshaft so that the roller is sitting on the other cam
• Lost motion - oil is inside the fuel pump between the cam follower and fuel pump plunger. When this oil buffer is full it is ahead fuel timing, it basically acts as a solid buffer with no effect. Then we take oil out to create a soft buffer which prevents the plunger from being moved until the follower gets further up (Lost motion).
• Flip the roller using a pneumatic ram

Question 10

What is ‘knocking’ on an engine?

Answer 10

When the combustion happens before TDC

Question 11

Why do we do the crankshaft deflections?

Answer 11

To check that the alignment of the crankshaft is within manufacturer’s tolerances and we plot a continuous graph of these measurements to identify any problematic trends.

Question 12

Why use the turning gear before starting the engine?

Answer 12

To clear any moisture on top of the piston crown
To ensure the engine is effectively lubricated and the crankshaft is turning freely

Question 13

What are the big bearings made of?

Answer 13

White metal which is mostly tin & antimony
Usually has a copper backing
Has a low coefficient of friction and can support high loads

Question 14

Overhaul of a diesel-generator injector

Answer 14

Inform chief + duty
Stop gen + cool down
Isolate DG -> FO, TG, SA, LOTO
Check tools + spare available
RA + PTW
Open cylinder head cover + drain FO from injector
Remove FO p/p connections
Open injector locking nut + extract injector from the pocket
Take injector to workshop, disassemble + clean it with enviromate, reassemble with new nozzle and O-rings and check set pressure, spray pattern & atomisation
Clean + lap injector pocket
Put everything back and test

Question 15

Effects of early & late injection

Answer 15

• Early injection - Severe stress loading at piston rod, connecting rod, crosshead bearing & bottom end bearing.
Very high unit temperature, cooling water & exhaust gases

• Late injection - Uneven thermal distribution throughout the piston & liner, potentially causing liner cracking. Heavy Carbon deposits on piston & liner due to improper combustion.
FO washdown can occur due to improper combustion.

Question 16

Principle of Turbocharger

Answer 16

Converts heat energy from exhaust gases pushing the turbine to kinetic energy to driving the compressor, introducing additional air to the cylinders to boost combustion and efficiency

Question 17

What is blow-by and blow-back

Answer 17

Blow-by is when exhaust gases pass the piston rings due to wear

Blow-back is when the combustion pressure is higher than the Scav air pressure and the exhaust gases pass through the Scav ports. Can be caused by back pressure on TC due to blockage of economiser flow, creating higher resistances at the exhaust valve.

Question 18

Name the 3 piston rings

Answer 18

Top - compression ring
Middle - scraper ring
Bottom - oil control ring

Question 19

When do we turbo wash the engine and how?

Answer 19

Turbowash weekly @ 50% load FW

Walnut shell clean nightly (turbine side)

Symptoms?
TC rpm dropping
Scav air pressure dropping
Exh gas temp rising + difference between cylinders increasing
Engine struggling to reach high load
Economiser back pressure increasing

Why wash?
Affects TC speed, compressor efficiency + air mass flow, scav air pressure
TC fouling causes higher SFOC, exh temps, smoking, uneven firing.

Question 20

ME misfires, fuel rail pressure low, booster pump pressure high

Answer 20

Inform bridge, request slow down
Inform Chief
Change to 2nd fuel filter
Check for water in FO service tank
Ensure all v/v are in line with ME fuel rack

Question 21

Actions if turbocharger is repeatedly surging

Answer 21

Inform CE
Request slow down

Causes:
- Propeller going in and out of the water
- Pressurised air in the exhaust manifold
- Improper power distribution
- Dirty TC filter

Question 22

How does an oil mist detector work?

Answer 22

There is an infrared light, barrier & sensor. When oil mist is present, this light will refract off the oil mist and the sensor will pick it up and convert it to an electrical signal, raising the alarm and shutting down the engine (slowdown for 2 stroke)

Question 23

2 types of turbocharger and their differences

Answer 23

• Constant flow turbochargers are designed for consistent engine loads.
They feature a larger exhaust manifold to dampen the pulsating nature of the exhaust gases from individual cylinders, creating a smoother flow of gases to the TC. They can be less responsive to sudden changes in engine speed.

• Pulse turbochargers embrace the pulsating nature of the gases and feature a smaller exhaust manifold. Makes them more responsive to fluctuating power demands.

Question 24

High exhaust gases in one unit, what could the cause be?

Answer 24

Sticky fuel rack
Tappet clearance
Injector spring / incorrect fuel atomization
Combustion air low or high temp

Question 25

What is Benzene?

Answer 25

• Benzene is an aromatic hydrocarbon found in fuel • Aromatic hydrocarbons in fuel such as benzene are unusually stable and have the following properties: - High ignition temp - Slow flame progression - Soot forming tendency. Basically you don’t want too much of this benzene as it can make combustion poor & uneven and can cause after-burning and high thermal loading on the crown as a result + increased soot buildup.