MOTOR & MEP ORAL QUESTIONS & ANSWERS PART-5

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Q What is crash maneuvering?

Ans– The crash maneuvering is usually done to avoid any type of collision or crashing of ship to any other ship or structure (Jetty, land, Iceberg etc). In this type of maneuvering the main engine is subjected to severe stress and loading, but the safety of ship and life is assured.

Q How to Perform Crash Maneuvering

Ans– Crash maneuvering is turning the engine in opposite direction to reduce the heading speed of the ship. After certain time, the ship stops & starts streaming in the astern direction. This is done by supplying starting air at about 30 bars from the air receiver to the main engine. The stopping air is known as brake air.

The brake air when suddenly injected in to the engine cylinder, will try to resist the motion of the piston & the rotation of the crankshaft & propeller.

Procedure

Following Procedure is to be followed when a navigational officer calls engine room & says that we have to stop immediately to avoid the collision

  • When there is an emergency like collision, grounding etc. the controls are transferred immediately in to the Engine room controls
  • The bridge will give astern direction in the telegraph, acknowledge the same
  • When the telegraph is acknowledged only the starting air cam will reverse its direction but the fuel cam will remain in its running position due to running direction interlock since engine is still running in the ahead direction.
  • The fuel lever in the engine control room is brought to ‘0’.
  • As soon as the rpm of the main engine drops below 40 % of the Maximum Continuous Rating (MCR) rpm of the engine, give break air few times in short time frame.
  • The break air will inject with the astern timing setting inside the ahead moving piston which will resist the piston motion.
  • Since fuel will not inject till running direction interlock opens, as soon as the rpm drops near to the 0, give fuel & air kick by bringing fuel lever to minimum start setting.
  • When carrying out Crash Maneuvering, some safeties need to be bypassed to avoid tripping of the engine in mid of  the emergency.
  • When the ship stops & situation is under control, a detailed Main engine inspection is to be carried out when there is a chance.

Q Differentiate between Sulzer- RD, RND & RTA and RT-Flex

Ans– RT Flex series- It is the latest and the toughest engine from Wartsila Sulzer with maximum automation installed. It consists of a common rail fuel injection method and uses fully integrated electronic system based on a high performance computer eliminating parts like fuel pump, fuel cam, chain drive etc. resulting in reduced maintenance.

Q Differentiate between MAN B&W engines.

Ans- MAN B&W

KEF series-

  • It was introduced about 20 years ago
  • Exhaust valves which are push rod operated
  • Pulse type turbo charging system
  • No servomotor was fitted in this engine and reversing is done with mechanical means.

KGF Series

  • The KGF series was similar to KEF series
  • Exhaust valve rotator with roller bearing
  • Reversing cam is held in a hub which is keyed in to the shaft
  • Cam shaft is turned in the same direction for reversing and the pressure required for reversing is about 40 bars.
  • No direct link between chain drive and engine cam shaft.

Q Difference between RTA and SMC

     SMC

  • S/B ratio – 3.8
  • Wasted stud
  • Helix jerk type fuel pump
  • Super VIT
  • Puncture valve in fuel pump
  • Cross head pressure-4.8 bar
  • Telescopic pipe for lubrication
  • Quills at single level
  • Cylinder lubrication injection between first and second ring 1200 before TDC
  • Tie rod are not near
  • Two keeps for the upper half of main bearing cover
  • Chain drive

RTA

  • S/B ratio – 3.4
  • Jack bolt- 150 tilted to vertical
  • Spill controlled suction valve fuel pump
  • VIT
  • Cut out device is given to raise the roller of fuel pump 0.5 mm above the cam – 1800
  • Cross head pressure-16 bar
  • Articulated pipe for lubrication
  • Quills at both level
  • Cylinder lubrication injection based on differential pressure
  • Tie rods are near because of jack bolts
  • One keeps for the upper half of main bearing cover
  • Chain drive

Q Difference between MEB and MC-C

     MEB

  • Electro-hydraulic controlled like exhaust valve, fuel pump etc
  • Chain drive smaller than MC-C
  • Alpha lubricator
  • Less SFOC
  • Less Cylinder oil consumption
  • No camshaft
  • Electronic governor
  • Less smoke emissions

MC-C

  • Conventional roller and guides for controlling like exhaust valve, fuel pump etc
  • Chain drive bigger
  • Mechanical lubrication
  • High SFOC
  • High Cylinder oil consumption
  • Camshaft controlled
  • Electro-mechanical governor
  • Appreciable smoke emissions

Q Conversion from RTA to RT-Flex

  • Remove following things from RTA
  • Camshaft
  • Fuel oil pump actuator
  • Exhaust valve actuator
  • Starting air distributor
  • Camshaft drive
  • VIT
  • Reversing servomotor
  • Fuel linkages

Add following things to RT-Flex

  • WECS-9500 electronically controlled program
  • Common rail system for fuel injection and exhaust valve opening servo oil
  • Supply unit
  • Crank angle sensor

Q Conversion from MC to ME.

Ans– 1. Remove Camshaft and reversing attachments (fuel pump roller and starting air cams) from MC

2. Remove Chain Drive of the engine.

3. Remove Fuel pumps actuating gear, Exhaust valve actuating gear (Pumps) and starting air distributor.

4. Attach Cylinder control system in each unit (CCU) comprising of the starting air control, electronic fuel injection control, & exhaust valve electronic actuation. The latter two systems are operated by the Hydraulic Control Unit (HCU).

5. Provide system oil at 200 bars for operating HCU of each cylinder unit via the cylinder control system.

6. Attach a common hydraulic oil supply unit.

7. Attach a Tacho system unit in the crankshaft which gives engine speed signal to the CCU.

8. All these added systems are controlled by the electronic main operating panel via solenoid valves & electronic signals.

9. Add double walled hydraulic pipes                                                                                                              

10. Remove conventional cylinder lubrication system & replace it with Alpha Adaptive Cylinder Lubrication Control Unit (ACC).

11. Remove conventional Piston & replace it with OROS type modern piston.

MC/ME- THICK SHELL

a. Thick shell

b. 2 Keep/cover

c. White metal 30-60 mm

White metal bearings- they are antifriction, tin based & white metal alloy called BABBIT consists of:

Tin (Sn) – 88% – Soft matrix to allow small changes in alignment between bearing & journal       

Antimony (Sb)- 8% – Hard wear resistant cubes to absorb and transmit load                                       

Copper (Cu)- 4% – To segregate and hold the antimony cubes in tin matrix.

d. Vertical distance adjusted by shims

e. Steel back strong enough to take the load.

f. It does not have Nip

g. They can be wipe out at temperature of  750C

h. Held in position with the help of guided screws which passes through the upper and lower shells

i. Having Lip all over the circumference for easy seating

j. Can be repaired

k. No compactness to engine

MC-C/ME-C – THIN SHELL

a. Thin shell

b. 1 Keep/cover

c. Tri-metal of 0.5-2 mm

Tri metal bearings- They are of 3 main layers and then a steel backing shell.                                                    

1st layer- FLASH- 1 micron Tin/Lead to protect against corrosion before installing the bearing                                              

2nd layer- OVERLAY- 20 micron thick white metal                                                                                                  

3rd layer- INTERLAY– 5 micron thick nickel dam helps to reduce corrosion of white metal in 2nd layer       

4th layer- LINING– 1mm thick Lead/Bronze                                                                                                       

Shell (bottom)- it is backing shell for shape & support

d. Vertical distance are predetermined and can not be adjusted afterwards

e. Wall thickness of 2-2.5% of the journal diameter

f. Having guide screws in lower shell only

g. Should be fully supported for the full length as no strong steel back

h. It has Nip circumferentially

i. Embeddability

j. They can be wipe out at temperature of 1200C

k. Can be only replaced not repaired

l. No Lip

m. Long life

n. Better dissipation of heat

o. Good load carrying capacity

p. Gap between two transverse girders reduce hence provides compactness to engine

Q Bearing difference between RTA and SMC     

RTA- bearing

  • Jack bolts for holding  the keeps(150)
  • Upper half in one piece
  • Both bearing shells lined with white metal- Sn 88%, Sb 8% and Cu 4%
  • Dowell pin is there for locating the bearing upper keep to the lower keep
  • Lubricating oil goes from the bottom shell and then from behind the bottom shell it goes up to the grooves and then enters to the journal pin and upper bearing

SMC- bearing

  • Wasted stud for holding the bearings and keeps
  • Upper half of keep is in two pieces
  • Tri-metal thin shell bearing- FOIL
  • Lubrication is from the top
  • Counter sunk screws are there for holding the bearing

Q Thrust bearing

Ans– The thrust bearing serves the purpose of transmitting the axial thrust of the propeller through propeller shaft & intermediate shafts to the ship’s hull. The thrust bearing is incorporated in the aftermost part of engine bedplate. The crankshaft is provided with the thrust collar which transmits the thrust to a number of segments mounted in a thrust shoe on either side of the thrust collar. The thrust shoes rest on the surfaces in the thrust bearing housing & are held in place by means of 4 stoppers. The segments have white metal cast on the wearing faces against the thrust collar.

The thrust bearing is lubricated from the pressure lubrication system of the engine. The oil is supplied between the segments through spray pipes & spray nozzles.

The thrust bearing is provided with alarm, slow-down, & shut-down devices for low lube oil pressure & high segment temperature.

Q How Can Air Line Explode

Ans– For a fire to happen, it has to complete the 3 sides of the fire triangle namely-Heat, Fuel & Air. In an air starting system of the main engine, fuel may be present in the form of lube oil carried over from the air compressor. Moreover, oxygen is present in the system in abundance. The heat source may come from a leaking starting air valve installed on the cylinder head & the combination of these three in proper ratio will lead to an air line explosion.

Precaution and Prevention

Relief Valve- sulzer: It is installed on the common air manifold which supplies air to the cylinder head. Generally installed at the end of the manifold & it lifts the valve in the event of excess pressure inside the manifold. The advantage of the relief valve is it will sit back after removing the excess pressure & thus continuous air is available to engine in case of manoeuvring or traffic.

Bursting Disc-man b&w: It is installed in the starting air pipe & consist of a perforated disc protected by a sheet of material which will burst in case of the excessive pressure caused due to air line explosion. It also consist of a protective cap such constructed that if the engine is required to run even after the disc has been ruptured, the cap will cover the holes when it is turned. This will assure that in manoeuvring or traffic air is available for engine at all time.

Non Return Valve: Positioned in between the Air Manifold & Air Receiver, it will not allow the explosion & its mixture to reach the air bottle because of the unidirectional property of the N.R. valve.

Flame Arrestor- sulzer: It is a small unit consisting of several tubes which will arrest any flame coming out of the cylinder through leaking start air valve. It is installed on every cylinder before the start air valve.

Q For prevention of the starting air line explosion following measures to be performed:

  • Assure that all safety devices fitted are working correctly
  • Draining of the air bottle is carried out every watch
  • Auto drain to be checked for the proper functioning
  • Air compressor is well maintained to avoid oil carry over
  • The oil separator at discharge of the compressor is working efficiently
  • The starting air manifold pipe to be cleaned and check for paint deformation which will indicate overheating of the pipe
  • Starting air valve to be overhauled regularly to avoid leakage
  • Starting air valve seat to be inspected and lapped