Main Engine

Question 1

Explain the procedure for starting the 2 stroke main engine from cold.

Answer 1

• Inform Bridge and/or chief engineer
• Check LO sump level, cylinder LO, governor LO
• Pre heat to 60 degrees with CW system, check coolers and exp tank
• Start LO pump, check pressure, temps, leaks, cooler
• Start LO purifier
• Check stern tube LO + pumps + intermediate bearing LO
• Check FO service tank level, (maybe start FO purifier at this point?)
• Check engines FO system in operation and lined up but not open to engine yet.
• Open indicator cocks, engage the turning gear, and with the bridges permission to turn it over atleast 2 full revolutions. Observe TG amps and someone observes indicator cocks. (if water comes out, could be JW through liner)
• Disengage TG and switch off control panel
• Compressor checks - LO, drains, CW, check lines
• Drain air receiver of ‘milky’ oily water
• Open start air valve
• Call bridge for permission to blow on air ahead and astern while someone observes indicator cocks again
• Close indicator cocks, close the turbo charger drains
• Make sure aux blower is in auto
• Check remote lever is mirrored with local before changing engine to remote control
• Monitor engine while bridge test it

Question 2

Explain the procedure for stopping the main engine.

Answer 2

• Call bridge to seek permission
• Press ‘finished with engine button’ (ECR and Bridge)
• switch bridge and ecr button
• proceed to shutdown plant
• Call bridge
• Engine in stop condition

Precautions after shutdown

• Change to local
• Engage turning gear to block start
• Shut main start air valve and drain
• Keep LO pump running for about 30 mins for main bearings to cool down
• Close fuel
• Lock out tag out all

Question 3

What to do if the HT in ME is too hot?

Answer 3

-Inform bridge and ask to reduce load of engine
-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 for blockage and if any present then perform back flush by closing LT inlet and opening backwash valve to remove marine growth
- Change over sea chest if blocked

Question 4

What pressure does the ME fuel injector supply oil at and what are some of the problems that may occur in the pipeline

Answer 4

-Fuel injector opens at 350 bar and injects fuel at 800 bar.
-problems may occur when the pipeline has any leak due to the high energy of the fuel. Any leaks are highly flammable

Question 5

Explain the operation of exhaust valve on a 2 stroke engine

Answer 5

-the engines cam will open the valve through a roller and a high pressure fuel pump which sends oil to a piston which applies force greater than the air spring pressure (7 bar)
-timing of this injection depends on the size of the cam
-the spring air will then close the valve after the pistons pressure is released and the valve will be seated on the cylinder head.
-the valve will also spin due to exhaust gasses acting on the fin on the spindle in order to create even wear on the seat.

Question 6

What are the 2 main mountings found on the Main engines crankcase (for LO)

Not OMD or explosion doors

Answer 6

LO flow sight glass - used to visually inspect for LO flow to ensure the LO pump is delivering enough pressure so the pistons crown is being cooled

Temp Gauge- is used for monitoring against a set spot and compares the temp to other units. High temp could indicate friction is happening and a hot spot may occur

Question 7

Why and how do we test tappet clearance on 4 stroke engines?

Answer 7

-we test tappet clearance to account for thermal expansion of the valves due to hot gasses or for the engines preheating, the high temps can change the shape of the valve.
-we test for tappet clearance during the fuel injection stroke as the valves will be closed. The clearance should be measure below the rocker arm.

Question 8

How many cams on a 2 stroke engine and what is their purpose?

Answer 8

For 2 stroke engines we need 2 cams per unit.

1 for fuel injection
1 for exhaust valve

And an extra cam for the entire engine for timings

Question 9

What will happen if the tappet clearance on a 4 stroke engine is incorrect.

Answer 9

-if the clearance is set too high the valve will be open for a shorter period time
-if it’s too low then the valve will open for too long
- this can lead to early or late suction or discharge, this leads to incomplete combustion which would mean less efficiency

Question 10

What is the diaphragm on a 2 stroke engine (location and purpose)

Answer 10

A diaphragm is a sealing device or component on a ships ME

Its purpose is to seal the scavenge space and the LO drain pipe.

It stops water from entering the engines lubricating system

Question 11

What to do if ME LO level drops?

Answer 11

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

Question 12

Explain 2 stroke LO systems

Answer 12

-LO is taken from the ME sump tank via suction from the main LO pump (positive displacement) pump oil out of the sump at 3 bar.
-It then will pass through a filter to remove any debris.
-The hot oil is then sent through a cooler where it is cooled by LT water (3 way valve used for flow)
-It then passes through the main LO filter
-The LO is then sent to the ME at 45°C (controlled by 3 way valve)
-The LO travels down the reciprocating telescopic pipe into crosshead, lubricating the crosshead bearings.
-It then travels 2 ways. 1 is up the piston rod to piston crown and back to crankcase. The 2nd way is down drilled holes in the conrod to the bottom end bearing where it spills out into the crankcase.
-A fixed pipe is used to lubricate the main bearings on the crankshaft as it is too weak to drill holes into due to it being semi-built in parts.
-Cylinder oil is gravity fed from a gravity tank and injected into the cylinder through quills. It has a higher TBN.

Question 13

What to do before setting tapper clearance on a 4 stroke engine

Answer 13

Before working on an Aux Eng make sure to:
- seek permission from bridge and C/E
- turn A/E on MANUAL and LOCAL
-close starting air valve

-Before setting tappet clearance, set the selected unit to firing TDC using the turning gear and the markings on the flywheel. If the markings are not visible, use the turning gear until you feel both push rods are loose (indicating both valves are closed)

Question 14

Purpose of the tie rods

Answer 14

The tie rods hold the entablature, A-frame and bed plate under compression

Question 15

constructional differences between 2 stroke and 4 stroke

Answer 15

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 had a bigger piston skirt to withstand lateral forces.

Question 16

What is TBN?

Answer 16

It is a measure of the reserve alkalinity in the oil which combats the sulfur in the fuel as it is acidic and will cause corrosion.

Question 17

TBN of oil in the following:
4 stroke
2 stroke cylinder
2 stroke crankcase

Answer 17

Max 40
Max 70?
Max 10?

Should measure about 5 lower when doing TBN test

Question 18

4 stroke engine parameters

Answer 18

LO = 4.5 bar 65 degrees
FO = 6.5-7 bar 115 degrees (HFO visc = 20cSt)
HT = 4-4.5 bar 80 degrees into engine 87 out, through CAC1 then 94 degrees out
LT = 3 bar 40 degrees through CAC2 then 45 out CAC2
T/C LO = 3 bar 95 degrees
Charge Air = 2.5 bar 50 degrees
Main Bearings temp = 80-87 degrees
Exhaust gases = 350-400 degrees
TC in = 510 degrees
TC out = 340-350 degrees
Economiser in = 340-350 degrees
Economiser out = 270 degrees

Question 19

Draw timing diagrams for 2 stroke and 4 stroke

Answer 19

(Drawings)

Question 20

Describe the ME departure preparation procedure

Answer 20

-Inform C/E and bridge
-Start Pre Lube
-Start pre heating of ME
-Make sure the fuel oil, expansion tanks and engines sump levels are ok.
-Run LO pump and JCW pump
-Open the indicator cocks, engage the turning gear and rotate the engine.
-Disengage the turning gear and close the indicator cocks.
-Test the engine with air and fuel
-Change control over to bridge
-Record in the log book

Question 21

Explain the methods for cleaning the Turbo charger

Answer 21

-Air side cleaning in the compressor side

-On turbine side:
-We can do dry cleaning at full speed with some broken wall nut shells
-We can do water washing at low RPM and exhaust temp

Question 22

How can we reverse a 2 stroke engine?

Answer 22

Air- We can use a distributer which reverses the starting air timing for ahead and stern

Exhaust Valve- We can only use this to reverse electrically controlled engines via a solenoid

Fuel- LO can be supplied to a rotary vein cam (SERVO) or by using a roller shift.

Question 23

Blow back vs blow by

Answer 23

Blow back - The air pressure is higher in cylinder so exhaust gasses are pushed back into the scavenge space and now hot grasses are in the scavenge space.

Blow by- Air in the cylinder leaks past the piston ring seal

Question 24

How can high back pressure occur in turbo charger

Answer 24

This could be due to a blockage in the economiser causing the turbocharger to lower its rpm and the scavenge pressure will drop (charged air will drop for 4 stroke)