SOME BASICS Q & A PART- 3

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Codes of safety working practices:

Candidates must be familiar with a book “code of safe working practices” available on board vessels. It is very important to identify safeties to encounter hazards.

To be complied with the company check lists but in the general it will cover followings:

  • Assessment of atmosphere
  • Ventilation
  • Illumination (safety)
  • Permit to work
  • Self contained B/A set stand by
  • Ladder required as appropriate
  • Man standby at entry position
  • Communication should be established

Q: What precautions should be taken before decarbonizing a M/E unit?

Ans:  Company policies are relevant. In general they are

  • Immobilization granted
  • Turning gear engaged
  • Starting air valve shut off
  • System, staring air line vented
  • Starting air distributor inlet valve shut
  • Appropriate notices given
  • Fuel, cooling etc valves in appropriate position
  • Over head crane tested.

Methods of maneuvering, including bridge control Systems and Variable pitch propellers.

 Bridge Control Procedures

Engine should be tested from ECR(Engine Control Room) first to ensure safe operation. If satisfactory, control is change over to bridge and engine should be tested ahead and astern, telegraphic printer checked working Properly.
Bridge alarm panel checked, in order. During maneuvering speed program may be cancelled, while at full away condition load up program should remain on to speed up gradually. Maximum rpm can be limited from ECR

Variable pitch Propellers:

While testing engine or vessel ahead and astern movements, only propeller pitches are adjusted to get desired movements. Engine need not to stop for ahead/astern moves. Engine clutch/declutch mechanism can be utilized as appropriate. Hydraulic oil level, pressure, and pumps should be checked.

Pitch control  – tried out from bridge or control room as well from local control.

Emergency Control:

Q:  With respect to main engine, what is emergency control?

Ans: Should main engine remote operation is not working, it may be operated from emergency / local control stand which will cover following:

  • Manual Fuel Control
  • Manual Air control
  • Manual Reversing

Q:    What action you are going to take in the event of a black out or M/E failure?

a) Inform bridge/chief engineer

b) Engineers call alarm may be raised for additional help

c) Emergency lighting/emergency generator will be active

d) identify the problem, preferably start other generator which are not in service and restore power.

e) Run appropriate cooling pumps reset all needful breakers, start all other plants

f) Prepare main engine and restore same after informing bridge

g) Check all the Standby machineries and emergency equipments at ready mode

Working principle and constructional details of a air compressor, air receivers, and associated equipment:

Candidates should have understand the efficiency of inter coolers, P-V diagrams gain in efficiency.

Q: What is the working principle of the main air compressor?

Ans: Reciprocating motions are used to in conjunction with the spring loaded non -return suction and delivery valves to achieve compressed air. Intercoolers are used to acquire gain in efficiency.

Q: Describe the construction of the main air compressor you used in our last ship.

It was a in line reciprocating 2 stage compressor. First stage piston relatively larger and second stage piston smaller in comparison, materials respectively aluminum and cast iron. Both stages were having the spring loaded suction and discharge non-return valves. Inter stage cooler and after coolers were there.

Q: Other than in line, what are the different type of compressor are used?

Tandem type of compressor are the other type commonly used. First stage piston relatively larger, second stage piston exists on top of above relatively of smaller size

Q: Why the bumping clearance is important?

Bumping clearance should be optimum. The more clearance volume increases, volumetric efficiency and hence capacity decreases.

Q: How do you take bumping clearance?

Remove suction & discharge valve assembly from the unit, place a small ball of lead wire on the piston edge. Then rotate the flywheel by the hand and to take the piston at TDC. Remove & measure the thickness of the lead wire ball.

Q: What is function of intercooler & after cooler?

Ans: Intercooler:       

 i) Decreases air temp

ii) Reduces work done

iii) Maintains safe lubrications

iv) Increase compressor efficiency

After-cooler:      

 i) Separate oil and water from compressed air

ii) Reduces air temperature before filling the receiver

Q: What mounted safeties are incorporated with the main air compressor?

i) Relief valves are fitted at the discharge of the each stage

ii) incorporated discharge non return valve

iii) Bursting discharges are fitted with the intercoolers to protect from over pressure due to tube leakage

iv) Un-loader/drain valves

Q: What safeties are incorporated for compressor protection?

  1. Low pressure alarm, stop for lube oil
  2. ii) Jacket high temperature/air discharge high temperature, alarm, stop.

Q: Describe the special features for the main air receivers?

i) Manhole door is elliptical in shape, for the ease of opening and consider strength of the pressure vessel

ii) Circumferential and longitudinal welding seams are existing.

iii) Relief valve fitted (if isolated from relief valve, fitted with fusible plug, melting point 150°C.

iv) Drain valve, pressure gauge

v )  Pressure switch for the cut in /cut off air compressor auto running

Operations, Testing Power, and the running adjustment to maintain performance:

 Candidates should know how to use the indicator machine, taking power cards, draw cards etc and know how to measure engine power.

Q: If an individual unit of M/E shows high exhaust temp, what should you do ?

i) If the parameter goes beyond limit, that case engine power/rpm may have to be reduced informing bridge and chief engineer. Need to find out fault.

ii) check the funnel smoke and check the pyrometer is correct, fuel rack in order.

iii) Fuel injection equipment, fuel valve, fuel pump may be faulty. Take power card to understand the fuel injection, all units peak pressure may be compared

iv) Compression pressure can be checked from above, to have an idea about liner wear/piston rings.

v) Exhaust valve operation can be checked visually or light spring card can be taken to ensure the problem with exhaust valve or not

vi) check particular unit scavenge drain line

vii) Should all above are in order, consider mistiming of  late injection or mistiming of early opening.

Q: Main engine all units exhaust temps are high what could be the reason?

Consider it is the common problem for all, hence it can be of followings:

  • Faulty governor or fuel linkage
  • Fuel quality to be assessed
  • Problem with T/C, scavenging not enough
  • T/C Air filter dirty
  • Scavenge Air temperature high
  • Residual temperature low, responsible for incorrect injection
  • check fuel load, if the vessel is at shallow water
  • Ships hull fouled
  • in worst case due bad quality of fuel injection equipment may be worn.

Q: How do you calculate POWER from the conventional method?

take power card (in-phase diagram)
Where: PmLAN in KW = POWER ……………… (1)
Pm = MEAN EFFECTIVE PR. , L= STROKE LENGTH,
A= AREA OF PISTON , N= REVOLUTION

Q. Calculate area of the diagram by using planimeter, check length of diagram

Calculate the mean height of diagram, which is n = area (mm²)/ length(mm)

                     Now MEP= h (mean height, mm) x spring scale (bar/mm)

                         i.e MEP found in bar or, MEP is (barx10²) kN/m²

from (1) we get power= PmLAN kW for one cylinder. For total engine, the result of the other cylinders to be accounted for.

Safe and efficient operation and maintenance of the marine diesel Engine

candidates should aware of the working principles of various main and auxiliary machineries. Should know how to decarb. a particular 2 stroke or 4 stroke engine unit and relevant inspections. To be familiar with the operation recommended by the manufacturer, specially while during operation with defective components.

Q: What is the indication of black/blue smoke?

Black smoke indicate incorrect /incomplete combustion. Blue smoke indicates the burning of LO with the combustion. Smoke should be clear.

Q: What are the causes of scavenge fire?

i) Blow past through liner and piston rings
ii) Due to incorrect fuel injection
iii) Due to lack of cooling, breaking of Cylinder lube oil film
iv) Excessive cylinder lubrication by lube oil give the undue fuel & cylinder film breakage will cause hot gas to blow by, consequence scavenge fire

Q: What action are you going to take with above ?

i) Inform bridge/chief engineer officer

ii) Slow down engine to extinguish fire

iii) Scavenge drain can be checked carefully

iv) shut off fuel to the particular unit

v) Increase cylinder lubrication to give adequate sealing

vi) check funnel, scavenge drain, scavenge temp. if satisfactorily return to normal with appropriate rpm.

vii) if  the above are not successful, not extinguished, stop engine, engage turning gear, mask T/C air filter, use fixed CO2 / steam to extinguish.

viii) On completion, inspect and rectify the fault then start engine