As a recently appointed Chief Engineer you are requested to survey the crosshead of a main engine folloing unscheduled repair due to bearing failure.
1. Outline the information you would request prior to the survey
2. Describe the survey procedure you would adopt stating, with reasons, the areas which should receive particularly close attention.
3.State, with reasons,what information you would you would request and the operations require to observe after reassembly of the crosshead.
Answer:1. Information requested prior to survey
* Previous survey report,engine running hours when survey was carried out,Details of recoded clearances,details of any possible marking on pin,bearing condition.
*Recent L.O analysis,any deteriration in the lubrication quality due to contamination by cylinder oil or fuel may give a guide to why the bearing failed.
*Sample of any detritus found in LO filters, plus any records of anything found in the days leading up to the failure.If white metal found it may indicate that the bearing material was failing over a period of time.
2.
Assuming that the crosshead pin and piston rod assembly is resting on the support brackets bolted to the guides and that the conrod is swung down to crankcase door level.
Inspect bearing half in the con rod(the loaded half)for evidence of scoring,squeezing,wiping,cracking of bearing metal.Scoring will indicate hard particles in LO OR DAMAGE to crosshead pin.Squeezing and cracking points toward overloading,whilst wiping will indicate poor lurication and overloading.Some manufacturers have an overlay of a lead/tin alloy on the tin aluminium bearing metal,and state that bearing should be replaced if the overlay has worn away.Other manufacturers have wedges machined in the bearing material and recommend replacement when wedges are reduced to half original width.
If it is cosidered necessary to inspect the top half of the bearing, then the con rod must be reconnected,the engine turned to BDC and the top bearing cover lifted.
3.On reassemly the crosshead pin and the guide shoe clearances should be taken and recorded.Excessive clearances will not allow a LO film to be built up when the rubbing speed is at a maximum.The engine should be turned through several revolutions and the turning motor ammeter observed for any change in load.This ensure that there is no binding between moving parts.The oil pumps should be switched on and the flow through the bearing and guide shoes observed. this will ensured that there is no binding between moving parts
Monday, May 31, 2010
Tuesday, May 25, 2010
Marine Engine Q & A- Rudder
Learning Objectives :
At the end of the lesson the student should be able to do the following:
1. Understand the forces acting on a rudder and size the rudder stock and steering gear power requirements.
2. Describe how the formula for the force on a rudder is derived.
3. Calculate the torque acting on the rudder.
4. Calculate the shear stress on the rudder stock by applying the Torsion
Equation
5. Calculate the required minimum diameter of a rudder stock for a given
material.
6. Calculate the work done on the rudder for a given rotation.
7. Understand the effect of rudder action on ship stability.
8. Describe the various form acting on a ship with respect to transverse
stability when the ship is turning.
9. Calculate the ships angle of heel due to form acting on the rudder.
10. Calculate the ship’s angle of heel due to centrifugal and centripetal force
11 Calculate the ship’s final angle of heel due to all heeling forces.
Subject: RUDDERS
At the end of the lesson the student should be able to do the following:
1. Understand the forces acting on a rudder and size the rudder stock and steering gear power requirements.
2. Describe how the formula for the force on a rudder is derived.
3. Calculate the torque acting on the rudder.
4. Calculate the shear stress on the rudder stock by applying the Torsion
Equation
5. Calculate the required minimum diameter of a rudder stock for a given
material.
6. Calculate the work done on the rudder for a given rotation.
7. Understand the effect of rudder action on ship stability.
8. Describe the various form acting on a ship with respect to transverse
stability when the ship is turning.
9. Calculate the ships angle of heel due to form acting on the rudder.
10. Calculate the ship’s angle of heel due to centrifugal and centripetal force
11 Calculate the ship’s final angle of heel due to all heeling forces.
Subject: RUDDERS
Thursday, May 20, 2010
Marine Engine Question & Answer
With reference to main propulsion engine turbochargers:
state how in - service performance checks are undertaken for EACH of the following:
i) the gas side;
ii) the compressor;
iii) the suction filter;
iv) the after cooler.
describe the action to be taken to allow the main engine to operate in the event of a turbocharger failing such that it may not be used.
a.
i) The efficiency of the gas side of the turbocharger can be assessed for a given power setting by the speed of the turbocharger and the gas temperature differential across the turbocharger. This gives an indication of the amount of energy in the exhaust gas which is being utilised. Fouling on the nozzle ring and blades will alter their profile and lead to a decrease in the energy conversion.
ii) A decrease in the performance of the compressor can be deduced from a decrease in scavenge pressure for a given turbocharger speed at a particular power setting. Usually caused by fouling of the compressor wheel/ diffuser.
iii) A dirty suction filter will result in similar symptoms to those given in (ii) above. However a manometer fitted across the suction filter will show an increase in differential pressure.
iv) A drop in the efficiency of the aftercooler can be detected by an increase in scavenge air temperature after the cooler or by the scavenge air temperature control valve for the cooling water opening fully to keep the air temperature at the required setting. If this is because of fouling on the air side then an increase in the pressure differential across the air cooler will show on the manometer. If fouling is on the water side, then the pressure differential across the air cooler will not have increased, but there will be a reduction in the temperature difference between the cooling water inlet and outlet.
It should be noted that all the above faults could result in surging of the turbocharger as all will affect the mass delivery rate for a particular engine power.
b.
This will depend on the type of engine, turbocharging system, and number of blowers.
For a 4 stroke pulse turbocharged engine fitted with a blower at either end.
Remove damaged rotor, air casing, and filter/silencer.
blank gas casing, so that the exhaust gas can pass through the casing
blank off air outlet to engine inlet manifold.
operate engine with single blower. Engine load will be reduced for efficient combustion.
For a 2 stroke crosshead engine with a single constant pressure turbocharger, then either the rotor can be removed in a similar manner to that above, and the exhaust gas routed through the blanked off casing or alternatively the rotor can be locked in position, the gas inlet and outlet blanked off, whilst the exhaust gas is routed through an emergency bypass pipe. On MAN-B&W engines to improve the air flow to the auxiliary blower, the expansion compensating piece (bellows) between compressor outlet and air cooler inlet may have to be removed. On Sulzer RTA engines, the doors on the scavenge space are opened to improve air flow to the auxiliary blower. Engine power will be limited by the amount of scavenging air the auxiliary blower can supply, but will probably be limited to 'slow ahead'. To improve air supply to the engine the machinery space exhaust fans can be changed over to supply, and canvas trunking rigged up to direct air into the auxiliary blower.
state how in - service performance checks are undertaken for EACH of the following:
i) the gas side;
ii) the compressor;
iii) the suction filter;
iv) the after cooler.
describe the action to be taken to allow the main engine to operate in the event of a turbocharger failing such that it may not be used.
a.
i) The efficiency of the gas side of the turbocharger can be assessed for a given power setting by the speed of the turbocharger and the gas temperature differential across the turbocharger. This gives an indication of the amount of energy in the exhaust gas which is being utilised. Fouling on the nozzle ring and blades will alter their profile and lead to a decrease in the energy conversion.
ii) A decrease in the performance of the compressor can be deduced from a decrease in scavenge pressure for a given turbocharger speed at a particular power setting. Usually caused by fouling of the compressor wheel/ diffuser.
iii) A dirty suction filter will result in similar symptoms to those given in (ii) above. However a manometer fitted across the suction filter will show an increase in differential pressure.
iv) A drop in the efficiency of the aftercooler can be detected by an increase in scavenge air temperature after the cooler or by the scavenge air temperature control valve for the cooling water opening fully to keep the air temperature at the required setting. If this is because of fouling on the air side then an increase in the pressure differential across the air cooler will show on the manometer. If fouling is on the water side, then the pressure differential across the air cooler will not have increased, but there will be a reduction in the temperature difference between the cooling water inlet and outlet.
It should be noted that all the above faults could result in surging of the turbocharger as all will affect the mass delivery rate for a particular engine power.
b.
This will depend on the type of engine, turbocharging system, and number of blowers.
For a 4 stroke pulse turbocharged engine fitted with a blower at either end.
Remove damaged rotor, air casing, and filter/silencer.
blank gas casing, so that the exhaust gas can pass through the casing
blank off air outlet to engine inlet manifold.
operate engine with single blower. Engine load will be reduced for efficient combustion.
For a 2 stroke crosshead engine with a single constant pressure turbocharger, then either the rotor can be removed in a similar manner to that above, and the exhaust gas routed through the blanked off casing or alternatively the rotor can be locked in position, the gas inlet and outlet blanked off, whilst the exhaust gas is routed through an emergency bypass pipe. On MAN-B&W engines to improve the air flow to the auxiliary blower, the expansion compensating piece (bellows) between compressor outlet and air cooler inlet may have to be removed. On Sulzer RTA engines, the doors on the scavenge space are opened to improve air flow to the auxiliary blower. Engine power will be limited by the amount of scavenging air the auxiliary blower can supply, but will probably be limited to 'slow ahead'. To improve air supply to the engine the machinery space exhaust fans can be changed over to supply, and canvas trunking rigged up to direct air into the auxiliary blower.
Sunday, May 9, 2010
Marine Engine Q & A - Indicator card
With reference to engine performance monitoring:
explain how it is determined that a faulty indicator is the reason for diagram deformation rather than an engine fault.
describe the ways in which an indicator can give a false diagram.
describe how engine performance may be assessed when the use of an indicator is not suitable.
a.
Power Card From 2 Stroke Engine
A typical indicator diagram from an engine in good operating condition is shown opposite. Note that the curves are smooth, and that maximum pressure occurs just after TDC.
The length of the atmospheric line is the same as the length of the diagram which is in direct proportion to the length of the piston stroke.
Indicator diagrams are taken to compare power outputs of the engine cylinders and to help in cylinder and combustion diagnostics. They are not viewed in isolation, but as part of an overall picture which includes exhaust temperatures, fuel rack settings and scavenge pressures. Should a diagram indicate a low power for a particular cylinder, whilst the other readings are as they should be, and the draw card does not show any faults with combustion, then it would be sensible to check the indicator equipment before proceeding further.
Draw card (out of phase diagram)
If the diagram is jagged throughout the whole diagram then this would be an indication of a fault with the equipment. However, if the diagram is jagged around TDC then this is indicative of a fuel injection fault which can be confirmed and analysed by taking an out of phase card. If the diagram has a flat top, this is again is showing a fault with the equipment.
b.
Indicator cam out of phase with engine. This can be checked by taking a compression card where the compression and expansion lines should coincide.
Choked indicator cock. These should be blown through before taking cards.
Leaking indicator cock. Detected by hearing.
Sticky indicator piston. Should not happen with well maintained piece of equipment. Will give jagged diagram.
Wrong spring fitted. Diagram will have a flat top (weak spring) or be to short (strong spring: note this will only affect outcome if wrong spring constant is used)
Indicator cord wrong length. Drum will not rotate fully during engine cycle.
c.
Power cards using mechanical equipment previously discussed is only accurate on engines operating at low revs (ie slow speed engines). They are not normally attempted with medium or high speed engines because of the higher speeds causing vibrations in springs and drive mechanisms.
In these cases, because power in the engine is related to the peak or maximum cylinder pressure, this is measured using a peak pressure indicator. This can be a mechanical device, using compression of a spring to indicate pressure or a pressure transducer linked to a digital read out.
It is more accurate to use the difference between the peak and the compression pressure when assessing cylinder powers and attempting to balance the engine. The compression pressure is taken at about 80% MCR with fuel shut off the cylinder.
In addition the other cylinder parameters must be taken into account: Exhaust temperatures, fuel pump rack setting, scavenge pressure and temperature are the most usual. It should be noted that if this method is used as a basis for engine balancing, then it must be known that the fuel injection equipment is in good condition and correctly timed.
Modern computer equipment now allows power and out of phase diagrams to be taken for engines operating at any speed.
explain how it is determined that a faulty indicator is the reason for diagram deformation rather than an engine fault.
describe the ways in which an indicator can give a false diagram.
describe how engine performance may be assessed when the use of an indicator is not suitable.
a.
Power Card From 2 Stroke Engine
A typical indicator diagram from an engine in good operating condition is shown opposite. Note that the curves are smooth, and that maximum pressure occurs just after TDC.
The length of the atmospheric line is the same as the length of the diagram which is in direct proportion to the length of the piston stroke.
Indicator diagrams are taken to compare power outputs of the engine cylinders and to help in cylinder and combustion diagnostics. They are not viewed in isolation, but as part of an overall picture which includes exhaust temperatures, fuel rack settings and scavenge pressures. Should a diagram indicate a low power for a particular cylinder, whilst the other readings are as they should be, and the draw card does not show any faults with combustion, then it would be sensible to check the indicator equipment before proceeding further.
Draw card (out of phase diagram)
If the diagram is jagged throughout the whole diagram then this would be an indication of a fault with the equipment. However, if the diagram is jagged around TDC then this is indicative of a fuel injection fault which can be confirmed and analysed by taking an out of phase card. If the diagram has a flat top, this is again is showing a fault with the equipment.
b.
Indicator cam out of phase with engine. This can be checked by taking a compression card where the compression and expansion lines should coincide.
Choked indicator cock. These should be blown through before taking cards.
Leaking indicator cock. Detected by hearing.
Sticky indicator piston. Should not happen with well maintained piece of equipment. Will give jagged diagram.
Wrong spring fitted. Diagram will have a flat top (weak spring) or be to short (strong spring: note this will only affect outcome if wrong spring constant is used)
Indicator cord wrong length. Drum will not rotate fully during engine cycle.
c.
Power cards using mechanical equipment previously discussed is only accurate on engines operating at low revs (ie slow speed engines). They are not normally attempted with medium or high speed engines because of the higher speeds causing vibrations in springs and drive mechanisms.
In these cases, because power in the engine is related to the peak or maximum cylinder pressure, this is measured using a peak pressure indicator. This can be a mechanical device, using compression of a spring to indicate pressure or a pressure transducer linked to a digital read out.
It is more accurate to use the difference between the peak and the compression pressure when assessing cylinder powers and attempting to balance the engine. The compression pressure is taken at about 80% MCR with fuel shut off the cylinder.
In addition the other cylinder parameters must be taken into account: Exhaust temperatures, fuel pump rack setting, scavenge pressure and temperature are the most usual. It should be noted that if this method is used as a basis for engine balancing, then it must be known that the fuel injection equipment is in good condition and correctly timed.
Modern computer equipment now allows power and out of phase diagrams to be taken for engines operating at any speed.
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