Y4 Oral / Main Engine
Describe how to prepare the main engine from cold to ready-to-start-maneuvering, and any tests that are necessary.
1. Before a large diesel is started it must be warmed through by circulating hot water through the jackets, etc. This will enable the various engine parts to expand in relation to one another. 2. The various supply tanks, filters, valves and drains are all to be checked. 3. The lubricating oil pumps and circulating water pumps are started and all the visible returns should be observed. 4. All control equipment and alarms should be examined for correct operation. 5. The indicator cocks are opened, the turning gear engaged and the engine turned through several complete revolutions. In this way any water which may have collected in the cylinders will be forced out. 6. The fuel oil system is checked and circulated with hot oil. 7. Auxiliary scavenge blowers, if manually operated, should be started. 8. The turning gear is removed and if possible the engine should be turned over on air before closing the indicator cocks. 9. The engine is now available for standby. The length of time involved in these preparations will depend upon the size of the engine.
What percentage of Engine Speed does the Overspeed Operate at?
10-15% maximum Speed.
What is the Pressure between an Engine Fuel Pump and Injector?
250-350 bar.
What would cause a Crankcase Explosion?
A Crankcase Explosion could be caused by the formation of a Hot Spot i.e. the overheating of a bearing, which in turn could cause an oil mist to be generated. If this Oil Mist is allowed to build up, an explosive condition could occur where the Oil Mist can be ignited by Piston Blow By or the Hot Spot itself.
What Interlocks are there on the Start Air System?
An Interlock to prevent Fuel being Injected An Interlock on Turning Gear and An Interlock CCP System, pitch has to be on Zero before Starting Engine.
What is the Critical and Barred Range on an Engine?
At certain engine speed, the frequency of rotation maches the natural frequency of the engine components creating a resonant condition. This is referred to as Critical Speed. The high stresses associated with resonant condition start to build up as Critical Speed is approached and do not come back to a safe value until speed is beyond Critical Speed. The unsafe stresses either side of Critical Speed are known as Flank Stresses, this is known as the Barred Speed Range.
What are the reasons for not enough Scavenge/Charge Air?
Blocked Air Filter on Turbo Charger, A Faulty Turbo Charger
What causes Blue Smoke in Combustion i.e. in the Exhaust?
Blue Smoke would indicate that Excessive Lub Oil was being burnt in Combustion.
Give the various operating pressures and temperatures of an engine you are familiar with.
CATERPILLAR 3196 6 cyl, 4 stroke MDE Power-492 kW Rated speed=2500 rpm Cruising Speed=1800 rpm Displ.=12 l Bore=130 mm Stroke=150 mm Lube oil=28 l
What can you do to prevent Scavenge Fires?
Conscientious maintenance of the Engine and regular inspection and cleaning of Scavenge Air Spaces will help prevent Scavenge Fires.
What Measuring Devices are there on the Cylinder Head of a 4 Stroke Engine?
Exhaust Temperature Pyrometer and a Jacket Water Outlet Thermometer.
How can Exhaust Valve Leakage be confirmed?
Exhaust Valve Leakage can be confirmed by taking an Indicator Card, the Card should be taken with Fuel "On" and "Off" the Unit. If the Valve is leaking, the compression pressure and maximum pressure will be low.
What Safety Devices are fitted to the Main Engine Crankcase?
Explosion Door/Relief Valves and Oil Mist Detectors.
What Interlocks are there on the Start Air System?
First ensure all the Engine Indicator Cocks are Open for all Cylinders, then Isolate the Air Supply to the Timing Valves, this will ensure no Pilot Air is supplied to the Air Start Valves when the Auto Valve is Opened. Then Operate the Auto Valve, any air discharge from the Indicator Cocks will indicate a leaking or Passing Air Start Valve.
Explain Heavy Oil Fuel System from Bunker Tanks to Engine
Fuel is pumped from the Fuel Oil Double Bottoms via a Transfer Pump to a Fuel Oil Settling Tank where it is heated. The Fuel Oil Purifiers/Centrifuges take suction from the Settling Tank via Purifier Heaters, pass through the Purifiers, where any water and impurities are removed and passed on to the Service Tank which also has a set of Heating Coils. From the Service Tank the Fuel then passes via a Flowmeter to the Mixing Tank, from where the Booster Pumps take suction, discharging to the Fuel Oil Heaters, where the correct Fuel Oil Temperature/Viscosity is achieved for correct Fuel Combustion in the Engine. The Fuel then passes through the Viscosity Regulator which controls the Heater Temperature, then on to the Fuel Oil Filters (which are heated), to the Fuel Pumps, then to the Fuel Injectors via Double Skin/Wall High Pressure Pipe. Any surplus Fuel returns via a Regulating Valve from the Fuel Pumps back to the Mixing Tank. Diesel Oil can also be used in the System and is fed to the System via a three-way valve. Note: When Diesel is used, no heating is required.
What is an indication in the Exhaust Gas of Good Combustion?
Grey Smoke indicates Good Combustion.
How do you purify HFO?
Heavy Fuel Oil is purified using a Centrifugal Separator, which operates by the principle of Centrifugal Force separating two liquids, in this case Fuel Oil and Water by means of a Cylindrical Interface between the two. The positioning of this Interface being very important for the correct operation.
Give an example of the density of Heavy Oil, Lub Oil and Diesel Oil.
Heavy Fuel Oil: 950kg/m3 Lub Oil: 870kg/m3 Diesel Oil: 880kg/m3
What are the Alarms and Trips on a Lub Oil System for the Main Engine?
High Lub Oil Temperature Alarm Low Lub Oil Pressure Alarm High Lub Oil Filter Differential Alarm Low Lub Oil Sump Level Alarm Low Lub Oil Pressure Shut Down Alarm Stand By Lub Oil Pump Cut In Alarm.
How is a Medium Speed Engine Reversed (without CPP)?
In Medium Speed Diesel Engines, reversing is achieved by the use of Duplicate Cams for the Air Inlet Valves, Exhaust Valves and Fuel Pumps. Air Start Distributor Timing is also changed by means of Camshaft Movement or by a Directional Air Supply being admitted to the Start Air Distribution, to reposition Cams. To engage correct Cams for Ahead and Astern Movements, the Camshaft slides axially in its Bearings. This movement is controlled by the Camshaft Reversing Gear, which is normally a Servo Piston. Motion of the Piston being directly transmitted to the Camshaft. Note: In a Slow Speed, only Duplicate Fuel Cams required.
What would you do if the Jacket water Temperature started to Rise?
Inform Bridge and reduce load on Engine, Investigate Problem, which could be a Fouled Cooler.
What is Loop Scavenging in a 2-Stroke Engine?
Loop Scavenging is where the Incoming Air passes over the Piston Crown, then rises towards the Cylinder Head forcing Exhaust Gases down and out the Exhaust Ports, just above the Inlet Port. The advantage of Loop is that no Exhaust Valve is required.
Name Main Engine Shutdowns.
Low Lub Oil Pressure High Jacket Water Temperature High Main Bearing Temperature Overspeed Oil Mist Detection
Explain a Main Engine Lub Oil System
Lub Oil for an Engine is stored at the bottom of a Crankcase known as the Sump, or in a Drain Tank located beneath the Engine. The Oil is drawn from this Tank through a Strainer by one of two Pumps in parallel, one Pump being on Stand-by. The Pump discharges the Oil into one of a pair of Fine Filters, it is then passed through a Cooler before entering the Engine and being distributed to the various Branch Pipes. The Branch Pipe for a particular unit may feed the Main Bearing, for instance. Some of this Oil will pass along a Drilled Passage in the Crankshaft to the Bottom End Bearing and then up a Drilled Passage in the Con-rod to the Gudgeon Pin in a Trunk Piston Engine or Crosshead Bearing in a Crosshead Engine. An Alarm at the end of the Distribution Pipe ensures that adequate Pressure is maintained, by the Pump. Pumps and Fine Filters are arranged in duplicate with one as standby. After use in the Engine, the Lub Oil drains back to the Sump or Drain Tank for re-use.
What are Normal Jacket Water Temperatures and Pressures?
Normal Jacket Water Pressures are between 2-3 bar, temperatures 70-80∞C, Alarm Point at 85∞C and Shut Down at 90∞C
How many Starts do you require to get from an Air Receiver without Recharging?
On a Reversible Engine: 12 Starts On Engines with CPP Propellers: 6 Starts.
Explain how you would go about removing a piston from a main engine for maintenance
PREPARATION 1. Risk assessment + permit to work 2. Isolate, tag out 3. Correct PPE, tools, lifting equipment tested and parts available 4. Engine preparation - Engine shut down. - Start air shut off and turning gear engaged. - Air to exhaust valve spring isolated - Fuel oil to unit isolated. - Cooling water to unit isolated and drained down. - Lubricating Oil off. REMOVAL 1. REMOVE CRANKCASE DOOR 2. MOVE CROSS HEAD DOWN FAR ENOUGH TO GET ACCESS TO STUFFING BOX AND SCREWS TO PISTON ROD 3. RELEASE STUFFING BOX BY REMOVING INNERMOST SCREWS FOR STUFFING BOX FLANGE 4. REMOVE SCREWS FROM PISTON ROD 5. MOUNT THE TWO DISTANCE PIECES TO PISTON ROD FOOT TO PROTECT LOWER SCRAPER RING AND TO GUIDE THE STUFFING BOX 6. DISMOUNT CYLINDER COVER 7. MAKE A SCRATCH MARK IN LINER AND PISTON CLEANING RING TO ENSURE CORRECT MOUNTING 8. REMOVE PISTON CLEANING RING 9. CAREFULLY GRIND DOWN ANY WEAR RIDGES ON TOP OF CYLINDER LINER 10. TURN CROSSHEAD TOWARDS TDC WHILE CHECKING STUFFING BOX LINES CORRECTLY WITH DISTANCE PIECES 11. TURN TO TDC 12. TOP OF PISTON IS NOW FREE OF CYLINDER LINER 13. CLEAN LIFTING GROOVE OF PISTON CROWN BY GRINDING 14. MOUNT LIFTING TOOL SO THAT THE TWO CLAWS OF THE TOOL FIT INTO LIFTING GROOVES. FIT THE THIRD ADJUSTABLE CLAW. 15. LIFT PISTON OUT OF CYLINDER LINER 16. LOWER PISTON ROD FOOT AND STUFFING BOX THOUGH OPENING OF PLATFORM 17. PLACE THE TWO HALVES OF THE SUPPORT AROUND THE PISTON ROD AND SECURE WITH SCREWS 18. LAND THE PISTON ON THE SUPPORT 19. REMOVE LIFTING TOOL FROM PISTON CROWN 20. PLACE A COVER OVER THE OPENING FOR THE STUFFING BOX IN THE BOTTOM OF THE CYLINDER LINER
What are the rough Lub Oil Pressures on the following, on a 2 stroke Engine: Piston Cooling; Crosshead Bearings and Main Bearings?
Piston Cooling: 6-7 bar Crosshead Bearing: 4-5 bar Main Bearing: 2.5-3 bar 1 Bar=1.02 kg/sq. cm
What would cause Excessive Exhaust Temperatures?
SINGLE CYLINDER 1. Incorrect Fuel Pump Timing i.e. late Injection causing after-burn. 2. Too much Fuel, 3. Leaking Fuel Injector 4. Burnt out Exhaust Valve. ALL CYLINDERS 1. High Scavenge Temperature, 2. Charge Air Cooler Fouled, 3. Turbo Charger Air Filters Dirty or Fouled, 4. High Engine Load.
Why is Simultaneous Injection of Fuel Oil and Starting Air into a Main Engine Cylinder Undesirable and How is it Prevented?
Simultaneous Injection of Fuel and Starting Air into a Cylinder is Undesirable as it could lead to an Explosion in the Start Air System. It is prevented by means of Interlock, which prevents Fuel being Injected when the Air Start Auto Valve is Open. The Interlock Operates a Stop Solenoid, which keeps the Fuel Rack at Zero Position.
Give a rough indication of Engine Speed ranges i.e. Slow, Medium and High Speed.
Slow Speed: 100-150 rpm Medium Speed: 300-850 rpm High Speed: 850-3000 rpm
What is the Diffuser Plate in a Turbocharger?
The Diffuser Plate in a Turbocharger is found on the Compressor side, it converts the Velocity/Kinetic Energy from the Compressor into Pressure.
What should you do to ensure that there is no Water Leakage into the Engine Cylinder before preparing Main Engine for Sea?
The Engine should be Turned using Turning Gear with Indicator Cocks open, keeping a close eye on the Cocks for any signs of Water Discharge. Immediately prior to Starting, the Engine should be Kicked on Air. Note: 2 Stroke Engines should be Turned at least one Revolution, where a 4 Stroke should be Turned two Revolutions.
What is the First Indication of a Leaking Exhaust Valve?
The First Indication of a Leaking Exhaust Valve is a rise of Exhaust Gas Temperature at the outlet of the Valve.
Crankcase Inspections: Frequency, Procedure and Reasons they are carried out
The Frequency may vary from different Engine Manufacturers but is roughly around 5000 hrs. Inspections are also carried out after any work has taken place in the Crankcase. Procedure is as follows: 1. Remove Crankcase Doors from both sides of the Engine. Relief Valves can be checked at the same time as the Doors are off. 2. Inspect condition of all bolt locking devices, replace any damaged components. 3. Turn Engine over using Turning Gear, ENSURE NO-ONE is in Crankcase while doing this and that the Indicator Cocks are Open. 4. Check condition of Camshaft Drive Gears. 5. Start Main Lub Oil Pump and check Oil Flow from Bearings and Piston Cooling Parts. 6. Check for any Leakage from Internal Oil Pipes and Galleries. 7. Check for any damage of Camshaft Lobes 8. Check for any evidence of Water Leakage from Lower Cylinder Liner "O" Rings. 9. Replace any damaged Crankcase Door Joints. 10. Record any Defects.
How does an Oil Mist Detector Work?
The Oil Mist Detector uses a Photoelectric Cell to measure small increases in Oil Density. A Motor driven Fan continuously draws samples of Crankcase Oil Mist through a measuring tube. An increased meter reading and an Alarm will result if any Crankcase sample contains excessive Mist when compared to either Clean Air or to the other Crankcase Compartments. The Rotary Valve, which draws the sample, then stops to indicate the Suspect Crankcase Compartment. The Alarm will cause an Engine Slow Down or Shut Down.
How does the Overspeed Trip Work?
The Overspeed Trip works by shutting the Fuel Off to the Engine. There are various types of Trips, Mechanical Types, which work on the principle of Flyweights, or Electrical Types, which work on the principle of a Speed "pick-up" operating a Stop Solenoid.
How does a Turbo-charger work?
The Turbo-charger mainly consists of a Turbine and a Compressor assembled as a single unit on a Shaft. The exhaust gas from the Engine flows through a water-cooled gas inlet (cooling from Engine Jacket Water System) to a nozzle ring, which directs gases at the Turbine Rotor Blading. This force causes the Rotor to rotate at High Velocity. The gases leaving via a water-cooled gas outlet casing, to an exhaust pipe and to atmosphere. The air required for the Diesel Engine is drawn in by the Compressor via a combined Silencer/Filter. The entry passage after the filter is then divided into splitters which prevent draught losses and guide the air to the compressor, the air being drawn in axially by the compressor and discharged radially at high velocity to the diffuser, which changes much of the velocity to pressure. From the diffuser the air passes into the Volute Casing, changing the rest of the airs Kinetic Energy to pressure before being discharged to the Charge Air Cooler and to the Engine for Combustion.
What Action would you take in the event of the Main Engine Oil Sump Level Rising? What could be the Problem and how would you fix it?
The action to be taken would depend on how fast the level was rising and what was causing it to rise. It could be due to the Lub Oil Filling Valve being left open. But, if it were due to Water or Fuel entering the Sump, the Engine would have to be Stopped as soon as it was Safe to do so. Tests would be carried out to tell if it were Water or Fuel. If it were Fuel, you can normally smell this in the Oil, but a Flow Stick Test can be done. Water has a tendency to form the colour of the Oil, depending on extent of contamination. If it were Fuel, the most likely cause would be a faulty Injector; therefore it would be changed. If it were Water, it could be coming from a Cracked Liner or Liner 'O Rings, therefore possible Liner change to solve the Problem. The Oil may have to be changed, depending on extent of Contamination, but the Lub Oil Purifier may be able to cope with it.
What Action would you take in the event of the Main Engine Oil Sump Level Rising? What could be the Problem and how would you fix it?
The action to be taken would depend on how fast the level was rising and what was causing it to rise. It could be due to the Lub Oil Filling Valve being left open. But, if it were due to Water or Fuel entering the Sump, the Engine would have to be Stopped as soon as it was Safe to do so. Tests would be carried out to tell if it were Water or Fuel. If it were Fuel, you can normally smell this in the Oil, but a Flow Stick Test can be done. Water has a tendency to form the colour of the Oil, depending on extent of contamination. If it were Fuel, the most likely cause would be a faulty Injector; therefore it would be changed. If it were Water, it could be coming from a Cracked Liner or Liner 'O' Rings, therefore possible Liner change to solve the Problem. The Oil may have to be changed, depending on extent of Contamination, but the Lub Oil Purifier may be able to cope with it
What is the Purpose of a Volute Casing in a Turbo Charger?
The purpose of a Volute Casing in a Turbo Charger is to change the Air Velocity in to Pressure. It also ensures a Constant Velocity of Air leaving the Turbo Charger by accommodating for the gradual increase in quantity of Air that builds up at the circumference of the Compressor.
What is the purpose of the Crankcase Oil Mist Detector?
The purpose of the Oil Mist Detector is to detect the build up of Oil Mist in the Crankcase, generated from a Hot Spot. The Detector will then give an Alarm, either Shut Down or Slow the Engine Down and give and indication of which Unit the Oil Mist is generated.
What Preventative Maintenance should be Frequently done to Diesel Engine Start Air Receivers?
They should be drained of Accumulated Moisture.
What are the Symptoms of a Scavenge Fire?
When a Scavenge Fire has broken out, the Scavenge Air Temperature and the Exhaust Temperature of the Unit in question will increase considerably and in some cases the Turbocharger may start Surging. Even Hot Spots on the Scavenge Trunking can be found.
What would you do in the Case of a Crankcase Explosion?
When the Alarm sounds, the Engine Speed must be reduced to slow and permission obtained to stop the Engine. Inform Chief Engineer. When an Engine has stopped under Alarm Conditions under no circumstances must any doors or inspection windows be opened. Oil should continue to be circulated and time allowed for the Hot Spot to cool. The early opening of doors could cause an explosion due to ingress of air. During Cooling down Period, the Engine Room Staff must keep clear of the side of the Engine fitted with Explosion Doors. After a period of at least 20 minutes, stop the Lubricating Oil Pump, cut off all Air and engage Turning Gear. The Access Doors should then be opened and Personnel must keep clear of possible flames. Under no circumstances should naked lights be used nor should anyone be permitted to smoke. Examination should then take place for any squeezed out bearing metal or loose bearing metal in the Crankcase. Heat discoloured Metal Parts or blistering of Paintwork must be investigated. The Ceiling of the Crankcase and Guide Bars should also be observed. If the Crankcase is clear, the Camshaft Drive and Main Thrust Bearing should be inspected for signs of overheating. Should any damage be found, then a permanent repair must be put in hand immediately. After repair, Lub Oil should be checked for Free Flow. The Engine should then be run in i.e. 15 mins, then check components for signs of overheating, then half an hour at half speed, again check, then one hour full speed, then check again. Note: Varying times have been quoted for the Cooling Down Period and no set rules are available
What is Uniflow Scavenging?
With Uniflow Scavenging, the Incoming Air enters at the Lower End of the Cylinder and Leaves at the Top. The Outlet at the Top of the Cylinder being a Large Exhaust Valve. The advantage of Uniflow is the simple design of the Liner, plus it is the most efficient.
What would be your first indication that there was water in the Sump?
Your first indication would be from your Lub Oil Purifier. Or even possibly from water in Lub Oil Tests, if done Regularly.
