End Test Questions Flashcards
Describe 5 functions of Lub Oil
To be used as a sealant between dissimilar metals
To provide lubrication between metals using methods such as boundary and hydrodynamic
To provide cooling by acting as a cold medium and carrying the heat energy away
To clean and flush equipment as the oil moves through its channels
Noise reduction by dampening the sound waves produced
Describe 4 essential properties of a Lub Oil
Viscosity is the measurement of a substances resistance to flow due to internal shear stress
Viscosity Index is the measure of change of viscosity with variations in temperature
Pour point is the temperature where the substance no longer flows and changes state to a semi-solid
Flash point is the temperature at which an oil will ignite if exposed to a flame
Explain the difference between boundary and hydrodynamic lubrication
The main difference between the two forms of lubrication is that hydrodynamic lubrication requires movement for the lubricating to occur such as a shaft and bearing with the centrifugal force creating an oil wedge underneath the shaft, whereas boundary lubrication will still provide lubrication regardless of movement and just acts as a lubricating interface between two materials to stop friction buildup.
State the advantages and disadvantages of using grease as a lubricant
Advantages;
Prevents debris entering an bearing
Holds solid additives in place such as graphite
Doesn’t require a complex retention system to keep it in place
The fluid level doesn’t need to controlled accurately
Disadvantages;
Doesn’t dissipate heat very well compared to circulating oil
Have a poor viscosity index
High viscosity causes resistance to motion which makes in an suitable for high speed applications
Difficult to handle in regards to change output, metering and draining
Explain the 3 key areas we test for when testing lub oil and what can affect them
Viscosity; We test for the viscosity of the oil as this is important to maintain optimum lubricating function. It provides optimum film thickness to reduce friction and maximise efficiency. Viscosity could be reduced due to contamination or adding or the incorrect oil
Water; we want to avoid having water in the oil as it will effect its key mechanical properties especially its flashpoint which could lead to the activation of the OMD
Insolubles; this could be an indication of wear and further investigations can identify what component is failing
State why the heating of the cooling system is an essential part of diesel engine design
Due a substances viscosity index the viscosity of a liquid is dependent on on the temperature it is at. As we need the fuel to be a certain viscosity for efficient injection we need to control the viscosity by controlling the heat using heaters in the system such as steam or electric. This becomes more relevant with HFO rather that MGO but heaters are still used regardless to keep the fuel at optimal temperature/ viscosity.
We also don’t want the liquid to fall below the pour point so heaters also keep the fuels hot enough to avoid that.
Explain what you understand by the phrase TBN
The total base number is a measurement of the oil capacity to neutralise the acidity of the oil caused by combustion by combatting it with alkalinity
Explain the importance of controlling TBN
If the total base number drops excessively then it will lose its ability to combat the acidity caused by combustion and the increased acidity level of the oil will cause excessive corrosion inside the engine on key components such as the piston head which in turn will lead to poor combustion.
Explain what conditions need to exist for MBG to develop
As microbial growth are living organisms so if there is excessive water in the fuel system then that will provide a base of them to feed on and this will allow them to develop. There will be nutrients in the water which combined with a warm temperature we keep the fuel at and an increased acidity of the fuel will also help the MBG develop more rapidly
How would you identify MBG developing in the fuel/oil system
A smell of rotting eggs
Sludge build up in the sump
An increased level of acidity
Pitting in the journals as well as black stains throughout the engine
An increased sliminess of the substance
With the aid of a sketch, explain how an Engine Mounted Centrifugal Lubricating Oil Filter functions
Draw it
Actions to be taken if MBG is discovered in the fuel /oil system
Inform the chief engineer and check the bunker sample of the fuel to see if that’s where the contamination has come from.
Biocides and fungicides will kill the MBG but if it’s had time to develop then there will be excessive sludge i’m the system so a total system overhaul should take place so a complete drain/ clean and refresh with fresh oil/fuel
When managing Lub / fuel oil what does a purifier do
A purifier removes water and some debris from a substance using centrifugal force and a control water interface to control the discharge of the fuel/water. It works using the concept of centrifugal forces and different masses.
When managing Lub / fuel oil what does a clarifier do.
A clarifier uses centrifugal force to and the different masses of debris and oil to separate the debris out of the oil. It also separates some water out of the oil but that is not its primary purpose
Describe the 3 major causes of Cylinder Liner wear
Corrosion caused by the acidic products of combustion
Abrasion caused by solid particles breaking through the lubricating film
Micro-seizure is a breakdown of the lubricating film leading to metal to metal contact
Describe the requirements for the manufacturing, location and construction of fuel/lubrication components
The filter must be placed in a position to where if that was a leak or a spray the oil would not hit any hot components of the engine
The bowl must be of metal construction
The changeover handle must be designed in such a way that the handle blocks the cover of the live filter preventing the filter from being accidentally opened
There must be a save all of sufficient depth underneath
There must be a drain fitted on the bowl
There must be a vent fitted
There must be a differential pressure alarm or high vacuum alarm fitted to alert to a blocked filter
State what regulations control the construction of fuel/lubrication components
SOLAS Chpter II-2
Class and flag requirements
Explain 6 areas of Bunker management that need to be considered to ensure fuel will be useable for its time onboard the vessel
Use oldest fuel first
Do not mix different fuels in tanks as could lead to contamination and S.G could be different affecting purifier efficiency
Draining off system and checking sample for water and MBG
ensure fuel is of correct grade and density in comparison to your samples
Make sure you have the correct gravity disc fitted to your purifier to minimise waste into the sludge
The tank gets pressed up to 95% to minimise condensation and free surface effect, consider IG Plant
Sulphur content needs to be recorded and calculated where to use ie using the higher sulfur content is non restrictive zones as they can’t be used it SCEAs
State and explain the reasons for choosing a Central Cooling System
Cheaper materials for pipes and valves due to the reduced corrosion occurring from S.W in system
Constant temperature of coolant in the system regardless of what climate the ship is in
Reduces maintenance on the system due to using fresh treated water less chance of blockages compared to using S.W
Less side ship valves required as no need to take multiple suctions of S.W
State the reason for the cooling water header tank
It has a multitude of uses including;
An expansion tank to account for increases and decreases in the level dependant on system temperature
A dosing tank that chemicals can be added to the system which will then be circulated around the system
Accounts for small leaks on the system and provides the system with a head of pressure
Gives air in the system a point to vent off to if a deairator isn’t fitted
A point to visually inspect the cooling water checking for issues such as MBG
With reference to diesel engine turbochargers, describe the functions served by the following;
Inducer
Diffuser
Volute casing
Nozzle ring
Firtree blade root
Damping wire
Inducer; the inlet to the fresh air compressor side that first comes into contact with the air, it begins to speed up the air before it hits the compressor wheel increasing the efficiency of the charger
Diffuser; captures and slows down the outgoing air from the compressor wheel which converts its kinetic energy into further pressure which makes the charger more efficient
Volute casing; a snail like spiral shell that encases the compressor wheel and directs the compressed air in the right direction while also decreasing the area which in turn increases the pressure of the air entering the scavenge space
Nozzle ring; directs the exhaust gas onto the driving turbine at the correct angle and location to Make the exhaust gas work in the most efficient way
Firtree blade root; the method of connecting the compressor fins onto the compressor wheel main fins, it adds stability and increases strength which allows it to operate at such high RPMs
Damping wire; it is added between blades on the turbine wheels and is used to dissipate vibration which reduces overall wear of the blades increasing the blades lifespan.
Explain why there is a need to test engine coolant and frequency of the tests
Engine coolant needs to be tested to establish it has sufficient levels of chromate, lack of chlorides and its alkalinity levels. These help keep the system at maximum efficiency and minimise risks of defects or corrosion which would eventually lead to unexpected maintenance. These tests should be conducted weekly.
State the Advantages of a plate type heat exchanger over a tubular one
Total stripping allows for inspection and complete mechanical inspection
Ease of maintenance, easy to open up and clean or remove plates
Damaged plates can be replaced individually rather than the whole stack
High efficiency due to the corrugated plates and flow distribution
Good corrosion resistance
Size can be altered by adding or removing plates
Single frame can be used for cooling several different liquids
Smaller than tubular
For Galvanic corrosion to take place, explain the 4 conditions that must be met in the system
An anode
An cathode
An electrolyte
A path way for the electrons to flow
Describe the advantages of air coolers as opposed to water coolers
No chance of water contamination into another system
No freezing point
Less wear from corrosion caused from water related issues
More compact and can be worked on without having to drain a system
