Engines

Question 1

What is scavenging?

Answer 1

When air supply is at a pressure greater than the exhaust gas, the remaining exhaust gas is removed and new charge air administered.

Question 2

What is uniflow scavening?

Answer 2

Fresh air enters through inlet ports on the lower end of the liner and exhaust gases leave from the upper exhaust valve.

Scavenging air enters through angled ports to generate rotational movement of the air, ensuring greater scavenging and fuel efficiency.

Question 3

How does a turbocharger work?

Answer 3

A turbine wheel, driven by exhaust gases from the engine, is rigidly coupled to a centrifugal type air compressor. The air is sucked in through a filter/silencer and compressed, raising the temperature and pressure. The air must then be cooled to increase its density and avoid engine overheating when admitted to combustion space.

Question 4

Two-stroke terminology?

Answer 4

Bedplate - The foundation of the engine and supports the crankshaft.
A Frame - Forms the crankcase, supports the cylinder block, provides mounting points for the guide bars and take side thrust of crosshead bearing.
Cylinder Block - Supports the cylinder liner and its retaining stud bolts and normally forms the scavenge space.
Tie Rods - Extends from the lower face of the bedplate to the upper face of the cylinder block and keeps the engine structure in compression.
Crosshead - Translates the reciprocating motion of the piston into semi-rotary motion at the connecting rod.

Question 5

How do you react if there is a crankcase explosion?

Answer 5

1) Inform the bridge.
2) Slow down the engine, preferably stop.
3) Engage turning gear.
4) Stay in control room.
5) Review alarm trends.
6) Wait at least 20 minutes, allow cooling.
7) Inspect for fault.

Question 6

How do you prepare an engine for sea?

Answer 6

1) LO, FO and JCW must be opened up and circulated to bring the engine up to the correct operating temperature.
2) Obtain permission from the bridge and turn the engine to ensure lubricating oil over all moving parts. Check the indicator cocks are open and leave running for twenty minutes.
3) Check the indicator cocks are blowing out air and not water. Water would indicate a fault in the cylinder head or liner and fuel with the fuel injectors.
4) Disengage the turning gear and drain air bottles of water and open air start valves to engine.
5) Start auxiliary blower fans to supply combustion.
6) Seek permission from the bridge to turn over on air, first in ahead then in astern. Check indicator cocks again.
7) Close indicator cocks and test again on fuel.
8) Pass control to bridge if all is good.

Question 7

24 hours prior to departure checklist.

Answer 7

• Ensure fuel tanks are at correct levels.
• Open heating to service tanks to at least 40C.
• Ensure jacket water header tank is at correct level and all system valves are open.
• Start the jacket water circulating pump and check the pressure. Check returns to header are running freely.
• Preheat jacket water to at least 60C.

Question 8

6 hours prior to departure checklist.

Answer 8

• Start lubricating oil purifiers to warm through the oil.
• Start the lubricating oil pumps for the M/E, camshaft and cross head system. Check sight glasses for oil flow and pressures.
• Check oil levels in the sump, turbochargers and shaft bearings.

Question 9

1 hour prior to departure checklist.

Answer 9

• Test the bridge and local control of the steering gear by operating from port to starboard on each pump, then with both running.
• Start the CPP pump and test pitch control, checking pressures and levels.
• Start the main gear lubricating pump, checking pressures and levels.
• Start the standby generator and connect to the switchboard.
• Operate the cylinder lubricators and turn over the M/E, inspecting indicator cocks.
• Drain the air receivers of water.
• Switch on the OMD.
• Start the stern tube lubricating oil pump and check header tank levels.
• Take readings of fuel settling and service tanks and cylinder lubricating oil daily service tank.

Question 10

15 minutes prior to departure checklist.

Answer 10

• Open the main air receiver valves and the main start air valve.
• Ensure all main air compressors are ready for use.
• Blow the M/E over on air ahead and astern with indicator cocks open.
• Close the indicator cocks, turbocharger drains etc.
• Set the auxiliary blower to automatic.
• Turn over the M/E on fuel, ahead and astern.
• Inform the bridge the M/E is ready for use and switch to bridge control.

Question 11

What is a crankcase explosion?

Answer 11

An explosion that occurs due to an oil mist and a hotspot.

Question 12

Causes of a crankcase explosion.

Answer 12

• The normal contents of a crankcase is air.
• If oil is atomised it becomes an oil mist, mixed with said air.
• If a hotspot occurs and the vapour reaches said hotspot and is within the range of flammability, then the explosion will occur.

Question 13

Why do hot spots occur?

Answer 13

• Failure of lube oil to bearings, sprockets etc.
• Temperature is around 280-400 degrees above the LO flash point.

Question 14

How can one tell if there is a hot spot?

Answer 14

• Hand feel to crankcase door.
• Abnormal noise in the crankcase.
• Irregular running of the engine.
• Bearing LO temperature increase.
• Bearing temperature sensors.
• OMD
• Smelling & appearance of dense oil mist.

Question 15

How to prevent a crankcase explosion?

Answer 15

• There should be adequate cooling of the engine.
• Proper purification and analysis of lube oil.
• Lube oil filter to be changed over & cleaned as per schedule.
  -Ensure proper cylinder lubrication by checking the condition of piston, piston rings and liner through scavenge ports.
  -Clean scavenge space as per schedule & drain scavenges space regularly.
• Maintain the stuffing box gland sealing in good condition.
• All running gears maintenance & checks to be carried out as per PMS.
• Be alert & rectify for any abnormal noise in crankcase.
• All safety trips & alarms fitted on M/E to be tried out for satisfactory.
• Proper watch on all running gears temperature & pressure to be maintained.
• Blow through all sampling tubes of Oil Mist Detector (OMD) regularly.
• Zero adjustment & sensitivity of OMD to be checked regularly.
• Check for oil leakage at crankcase explosion relief doors & check for the operation by hand.
• Check flame trap for cleanliness and intact condition.

Question 16

Actions in the case of a crankcase explosion?

Answer 16

1) Inform CE and bridge.
2) Reduce engine speed.
3) Increase lubrication.
4) Keep clear of crankcase relief door, keep fire extinguisher ready and open skylight.
5) Stop engine, open indicator cocks, engage turning gear and turn engine with lube oil.
6) After 30 minutes, stop lube oil pumps and open crankcase door.
7) Try to locate the hotspot by hand and looking for change in colour.
8) Make permanent repair.
9) Make thorough inspection of the crankcase.
10) Pay attention to hot bearings, piston, bottom end bolts, guides and piston rod around stuffing box.
11) Start lube oil pumps and check for proper flow of oil from every lubricating point.
12) Gradually increase engine speed and outside feel over until satisfied.

Question 17

What are crankcase safety devices?

Answer 17

1) Breather pipe with flame trap
2) Crankcase exhaust fan.
3) OMD
4) Crankcase relief doors.
5) Bearing temperature sensor.
6) LO return temperature sensor.
7) Routine LO tests for viscosity, flash point and contamination.

Question 18

Why is breather pipe fitted to crankcase?

Answer 18

• To reduce pressure build up.

Question 19

Why is the crankcase relief valve fitted?

Answer 19

• To release any sudden rise of internal pressure with large free escape area to prevent a secondary explosion.

Question 20

Causes of high bearing temperature?

Answer 20

1) Improper oil viscosity.
2) Insufficient lubrication.
3) Misalignment of shaft or bearings.
4) Foreign matters in oil.
5) Score in journal.
6) Poorly fitted bearing.
7) Improper oil clearance.

Question 21

What is a blow past?

Answer 21

Hot gas or flame passed through the piston rings and cylinder liner from the combustion space.

Question 22

Sources of oil coming into the air bottle?

Answer 22

• Excessive oil level of compressor.
• Excessive cylinder lubrication.
• Defective oil scraper rings.
• Oil vapours inhaled from engine room atmosphere.

Question 23

What is the purpose of the charge air cooler?

Answer 23

1) To reduce air temperature & increase density of charged air.
2) More fuel can be burnt and more power obtained.
3) Reduce exhaust gas temperature and engine thermal load.
4) Increase scavenging efficiency, safe working temperature.

Question 24

What is the normal Pmax on a 2-stroke?

Answer 24

180-195 bar

Question 25

Normal exhaust gas temperature after combustion in a 2-stroke?

Answer 25

600 degrees

Question 26

Normal charge air pressure?

Answer 26

0.3-0.7 bar

Question 27

Power ratio between 2-stroke and 4-stroke?

Answer 27

1.8:1

Question 28

What is cross-flow scavenging?

Answer 28

Inlet and exhaust ports are opposite one another at the bottom end of the cylinder liner. Simplifies the engine construction and minimises maintenance costs. Used in old sulzer engines.

Question 29

What is loop-flow scavenging?

Answer 29

Exhaust port is above the inlet port at the bottom end of the cylinder liner. Air passes transversely over the piston and is forced out of the exhaust ports.

Question 30

Indications of a scavenge space fire?

Answer 30

1) Increased scavenge temperature. 2) Turbocharger surging. 3) High exhaust gas temperature. 4) Loss of engine power and reduction in rpm due to the back pressure created under the piston space. 5) Smoke leaving the scavenge drains. 6) Paint blisters on scavenge doors.

Question 31

Causes of a scavenge fire?

Answer 31

1) Excessive liner wear. 2) Worn piston rings or loose grooves. 3) Broken piston rings or seized. 4) Dirty scavenge space. 5) Poor combustion due to leaky valves or timings. 6) Insufficient or excess lubrication.

Question 32

Actions in the case of a scavenge space fire?

Answer 32

1) Inform CE and master. 2) Reduce engine rpm and stop. Shut off fuel. Stop blowers. Engage turning gear. 3) Use fixed fire fighting systems or boundary cooling, keeping clear of the doors. 4) Increase lubrication, if this is the source of fuel then don't. 5) Fire could be due to leaky fuel pump so lift up. 6) Keep scavenge drain closed. 7) Monitor temperatures and wait for it to burn itself out. 8) After confirming the fire is extinguished allow to cool and then open for inspection and cleaning.

Question 33

What are reasons for a high exhaust gas temperature?

Answer 33

1) Fuel pump and delivery valve supplying excess fuel. 2) Engine timings wrong. 3) Valve seat damage leading to blow-by during compression and combustion. 4) Air supply to T/C insufficient. 5) Clogged turbocharger. 6) Scavenge and exhaust manifold clogged. 7) Scavenge air leak.

Question 34

What are consequences of high exhaust gas temperatures?

Answer 34

1) Valve lifetime reduced by up to 50%. 2) Cylinder liners wear faster. 3) Piston rings and piston worn down or damaged.

Question 35

How long should you wait before opening crankcase doors after an explosion?

Answer 35

30 minutes.

Question 36

Regulations on crankcase relief doors? What regulation?

Answer 36

SOLAS II-1-27: - 200mm cylinder diameter or crankcase volume of 0.6m3 must have a crankcase relief valve. - Over 300mm, relief valve required on each door. - NO less than 45cm2 and minimum 115cm2/m3 of gross crankcase volume. - Opening pressure is 0.07 bar internal

Question 37

Regulations on crankcase relief doors? What regulation?

Answer 37

SOLAS II-1-27: - 200mm cylinder diameter or crankcase volume of 0.6m3 must have a crankcase relief valve. - Over 300mm, relief valve required on each door. - NO les than 45cm2 and minimum 115cm2/m3 of gross crankcase volume. - Opening pressure is 0.07 bar internal

Question 38

How does a crankcase relief door work?

Answer 38

- The spring is set to open at a set pressure and as such the valve opens allowing the pressure out. - A deflector is fitted on the outside of the engine to safeguard crew from the outflowing gases. - Inside the engine there is an oil wetted gauze / flame arrestor to stop flames leaving the crankcase. - After operation the valve will close automatically under the action of the spring.

Question 39

How do you check the opening pressure of a crankcase relief valve?

Answer 39

Using the formula Pressure = Force / Area - Rod fitted onto the crankcase door and pulled until we have a reading on the spring scale as to the force until it opened. - You know the area of the door from the manual. - Use the formula to calculate.

Question 40

How would you change from HFO to a low sulphur fuel?

Answer 40

Before changeover: 1) Top-up service tank level. 2) Discuss with the crew about the changeover procedure and when it will be done. 3) Start a generator on the new fuel. 4) Keep clean filters spare. 5) Stop the purifier and change over to the new fuel. 6) Keep the drawing for the fuel lines ready and study them. Changeover: 1) Reduce the load on the engine to about 30%. 2) Close heating to fuel oil heaters and let the temperature come to 100C. 3) Keep the DO valve open but the crossover valve still in HFO position. 5) Changeover gradually, monitoring fuel oil pressure. 6) Note the time and location of the vessel and make logbook entries. 7) Monitor new temperatures and viscosity. 8) Open the cooler to maintain viscosity. 9) Shut off fuel line trace heating. 10) Keep an eye out on for dirty filters. 11) Shut return valves to settling tanks. 12) Check engine room for leaks and abnormal noise. 13) Check temperature of each unit. After changeover: 1) Check HFO settling tank is not increasing. 2) Backflush filter changed to 12 hours or even more. 3) Check noise from pumps. 4) Drain tank level. 5) Note time and location of ship and note in logbook.

Question 41

What is a power card and what is its purpose?

Answer 41

A graph of pressure against time. - Calculates indicated power of the engine. - Determines peak and compression pressures. - Evaluate combustion process inside the engine. - Evaluate scavenging and exhaust conditions.

Question 42

How does the stuffing box work?

Answer 42

- As the piston rod passes through, the lube oil from the crankcase is scraped off by the lower set of rings and drained back to the crankcase through drillings. - Any lube oil that passes this primary set is drained to a piston rod drain tank. - As the piston passes down through the stuffing box, the top rings will scrape off contaminated cylinder oil to the bottom of the scavenge space, where it is drained from the scavenge space drains

Question 43

What are the main reasons for cylinder wear?

Answer 43

1) Frictional 2) Corrosion due to heavy fuel and water. 3) Abrasion due to hard particles. 4) Adhesion or scuffing which is the local welding between the piston rings and liner.

Question 44

What is the difference between a wet sump and a dry sump?

Answer 44

A wet sump stores the engine in the sump whereas a dry sump stores the oil in an external tank.

Question 45

Main engine trips?

Answer 45

1) Low lube oil pressure. 2) Overspeed. 3) Cooling water temp high high. 4) OMD. 5) E-stop.

Question 46

Main engine alarms?

Answer 46

1) Water temp high. 2) Water low pressure. 3) Air cooler high temperature. 4) Fuel oil high temp. 5) Fuel oil low pressure. 6) Control air low pressure. 7) Thrust bearing high temp. 8) Exhaust temp high. 9) Bearing temp high. 10) Scavenge air temp high slow down.

Question 47

What are the safety devices fitted to the main engine?

Answer 47

1) Crankcase relief door. 2) Scavenge space relief door. 3) Cylinder head relief valve. 4) Starting air relief valve. 5) Starting air flame trap. 6) OMD 7) Rotation direction interlock. 8) Turning gear interlock

Question 48

What is the purpose of the gudgeon pin?

Answer 48

Connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot upon as the piston moves.

Question 49

What contaminants are you looking for in LO and what could they indicate?

Answer 49

1) White metal - bearing failure 2) Water - water leakage 3) Discolouration - Contamination/needing replaced 4) Strong smell of fuel - Unburnt fuel contamination

Question 50

What are the problems with having oxygen and CO2 in the cooling water?

Answer 50

Oxygen = corrosion CO2 = Acidic, lower pH

Question 51

What is the purpose of a turbocharger?

Answer 51

Increase the efficiency of the engine by using the energy from the exhaust gas and increase the mass of the air induced allowing more fuel to be burned leading to a greater power output.

Question 52

What are the advantages an disadvantages of a rotary vane steering gear?

Answer 52

Advantages: 1) Pure torque with no sideways thrust. 2) Very compact. 3) Produces constant torque regardless of rudder angle. Disadvantages: 1) Can be unreliable as seals between chambers will wear. 2) If a vane jams the entire system will become inoperative. 3) Limited to 90 bar due to sealing arrangements.

Question 53

What are the two different types of turbocharger?

Answer 53

Axial: - Exhaust gas enters along the axis of the shaft. Radial: - Exhaust gas enters in at a 90 degree angle on the turbine and exits along the trailing edge of the blade.

Question 54

What is the difference between pulse and constant pressure turbocharging?

Answer 54

Constant pressure: - Exhaust gas into a common manifold then into turbine. Pulse: - Pipes from each cylinder arranged in small diameter to boost up pressure pulse to prevent energy losses where it reaches the turbine nozzles and further expansion takes place.

Question 55

What are the advantages and disadvantages of a constant pressure turbocharging system?

Answer 55

Advantages: 1) Good performance at high load. 2) More suitable for high output engine. 3) No need for cylinder grouping. 4) High turbine efficiency. 5) Smooth work transfer at turbine. 6) Reduction in SFOC. Disadvantages: 1) When running at low speeds can supply inadequate air quantity for scavenging. 2) Requires auxiliary blowers. 3) Poor response in changing load.

Question 56

What are the advantages and disadvantages of a pulse turbocharging system?

Answer 56

Advantages: 1) Efficient at low load and low speed. 2) No need for blower. 3) Highly responsive to change in engine condition. 4) High available energy at turbine. 5) Good turbocharger acceleration. Disadvantages: 1) Complicated exhaust grouping. 2) Different sizes of exhaust pipe are needed for spare. 3) High pressure exhaust from one cylinder would pass into another cylinder adversely effecting combustion efficiency.

Question 57

How does a turbocharger work?

Answer 57

1) Exhaust gas from the cylinders exits and is pushed onto the turbine nozzles which due to the heat and pressure release causes it to spin. 2) Once spinning the turbine is connected via bearings to a centrifugal compressor. 3) The exhaust gas exits via the funnel. 4) The compressor spinning causes suction from the engine room which draws air through a filter and compresses it before being discharged to the charge air cooler.

Question 58

What is turbocharger surging?

Answer 58

High pitch vibration of audible level coming from the compressor end of the turbocharger.

Question 59

What are reasons for turbocharger surging?

Answer 59

1) Improper power distribution - Air consumption necessary will differ. 2) Dirty or damaged filter. 3) Dirty turbine. 4) Worn out bearings. 5) Fouled air cooler. 6) No water circulation in CAC. 7) Carbon deposits in scavenge ports. 8) High receiver temperature 9) Faulty exhaust valve. 10) Fire in the EGB. 11) Issues with fuel supply (low pressure, water in fuel, low temperature, sticking plunger.) 12) Sudden change in load. 13) Change in ambient conditions.

Question 60

How is the turbocharger lubricated?

Answer 60

1) Ball bearings are used on the compressor and turbine side. 2) There are oil sumps on both sides of the turbocharger where oil is sprayed onto the bearing by means of an attached rotor driven gear pump.

Question 61

What could cause the OMD to be set off by accident?

Answer 61

Pre-heating of engine not put on leading to an increase in humidity in the crankcase.

Question 62

What regular maintenance must be carried out on the main engines to ensure good condition and operation?

Answer 62

1) Regular monitoring of parameters. 2) FO & LO filters - 250hrs 3) Air filters on TC - 250hrs 4) Crankcase inspection & tappets - 1000hrs 5) Fuel injectors - 1000hrs 6) Deflections, stuffing box and scavenge space - 2000hrs 7) Valves, camshaft - 4000hrs 8) Cylinder head, exhaust valve, piston - 8000hrs

Question 63

What is the equation regarding frequency and pole pairs?

Answer 63

f = (P*N) / 120 Where: f = Frequency P = Number of poles N = Synchronous speed (rpm)

Question 64

What are the usual temperatures of fuel going from storage to pumps?

Answer 64

Storage - 40 (10 above pour point) Settling - 80 Service - >80

Question 65

Why do we slow turn the engine?

Answer 65

To prevent damage from water or fuel: Water could cause hydraulic lock. Fuel could cause auto-ignition.

Question 66

What is the purpose of piston rings?

Answer 66

1) Seal the combustion chamber of gases. 2) Help with transferring heat to the cylinder liner. 3) Lubricate and scrape down oil.

Question 67

What are the 3 types of piston rings?

Answer 67

1) Top compression ring 2) Intermediate compression ring 3) Oil control ring

Question 68

What is the purpose of the top piston ring?

Answer 68

Seal off the majority of the combustion gases to ensure maximum power output of the engine.

Question 69

What is the purpose of the middle piston ring?

Answer 69

Helps with finishing the combustion sealing and oil scraping.

Question 70

What is the purpose of the bottom piston ring?

Answer 70

Used for oil control to lubricate the cylinder liner.