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39 Cards in this Set
- Front
- Back
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4 Stroke Engine -Why inlet valves do not open at TDC and do not close at BDC? |
Inlet Valves open 15* before TDC to allow fresh charge air to fill the combusting chamber and remove fine deposits on top of piston ; they are removed through exhaust valve together with exhaust gas.
Inlet Valve close after BDC as air continue to enter due to air momentum. Allowing increased air intake into combusting chamber and reducing resistant to motion when piston change direction after BDC.
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4 Stroke Engine -Why exhaust valves do not close at TDC and do not open at BDC. |
Exhaust valves close later than TDC to increase overlapping period (removing fine traces of exhaust gas) and allow removal of fine deposits on top of piston.
Exhaust valves open before BDC since hot air gases does not do any more significant work on piston ; allowing hot air gases to come out on its own thus increasing exhaust period. (Exhaust Blow Down) |
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Advantages of Cross Head Piston TELL Me (ALLD) |
1. Able to use cheaper fuel (lower quality) |
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Advantage of Trunk Type Piston WUT? (LFC) |
1. Less head room required compared to X-head 2. Fewer working parts compared to X-head 3. Cheaper than X-head since the design allow for mass production |
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Why is Viscosity important to u? |
-Measure of resistance to flow -When Heated up less viscous -Measured in centistoke -Determine the lubricating valve needed to lubricate the fuel pump and injector. -Less viscous gives finer and equally divided droplets -More viscous gives big chunky droplets and longer spray time
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Whut is Ignition Quality? |
-The ability for fuel to ignite by itself or under certain circumstances in combustion chamber -Indication of time necessary for fuel to ignite after it has been injected to combustion chamber -Lower Ignition Quality > Delayed combustion |
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Simi Flash Point? |
-At certain temp fuel gives off vapour -Vapour ignite (flash) when heated by external flame -Index of fire hazard and lowest permitted Flash Point is 60*c |
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Semo Pour Point? |
-Temp which fuel will flow on its own under certain circumstances -Indication to temp to be heated to before pumping fuel
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Tell me 3 important factors affecting fuel combustion! |
1. Atomization 2. Penetration 3. Turbulence |
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OMG. Stages of Combustions? |
1. Ignition Delay 2. Rapid Combustion 3. Steady Burning Period 4. After Burning Period |
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How does
Ignition Quality Of Fuel
Affect combustion |
Should have ability to ignite by itself and as high as possible to. |
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How does
Timing of injection
Affect Combustion |
Correct timing > Correct Injection > Correct Combustion > More Power > Less Fuel Consumption
Too Early > Won't ignite > Why? > Pressure and Temp too low > A Pool of fuel on combustion chamber before combustion |
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How does
Compression Pressure
Affect Combustion |
Too low > temp also low > delayed vaporization of fuel > delayed ignition
Factors Affecting Compression Pressure are: 1. Condition of Piston Rings 2. Liner Surface 3. Clearance Volume |
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Okkar Min. Tell me 4 function of lubricant
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1. Reduce Friciton 2. Remove Heat 3. Act As Sealant 4. Dampen Noise 5. Protect from corrosion
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Crankcase LUB OIL Desirable Properties (AAC DLO TV) |
Anti Foam - prevent intermittent flow
Alkalinity - Moderate to neutralize acidic contaminants from combustion
CorrosionProtection - from moisture condensation & combustion products of fuel containing sulphur
Detergency - clean contaminats of combustion & corrosive producuts (ie. carbon & sulphur)
LoadBearing - able to support the static weight of the running gear as well as the fluctuating combustion load.
OxygenStability - prevent oxidation & formation of organic acids
ThermalStability - moderate
Viscocity - viscous enough to form and maintain full fluid film
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Cylinder LUB OIL Desirable Properties (AAC DLO TV) |
AntiFoam - Usually not a problem
Alkalinity - High, neutralize acidic by products from combustion
Detergency - Normal, to clean the combustion products such as carbon & sulphur compunds
LoadBearing - High, withstand the extreme pressure exerted by the piston ring face onto the linerwall
Oxygen stability - High, prevent oxidation especially in oxygen rich ENV in combustion chamber
ThermalStability - High, maintain lubrication property at prevailing high temp in combustion chamber. Else, oil film can breakdown and cause friction associated problems.
Viscosity - High, provide sealing effect between the ring and liner wall
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How lub oil deteriorates, whilst it is in service? |
1.Contamination by solid and metal particles
2.Property Change > High Temp > Oil Crack > tarry material form> stick on ring and cause problems
3.Oxidation from organic acids from oil combining with oxygen in the air
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Maintaining LUB OIL
LET FOO |
1.Lub oil must be analyzed regularly and treated accordingly.
2.Engine and accessories should be maintained in good order. thus reducing the contaminations from pistion blow by & foreign matter.
3.Temperate & Pressure should be kept normal
4.Filters must be cleaned regularly. Before and After filter pressure gauges should be used to monitor the condition of the filter
5. Oil must be purified regularly
6. Oil must be changed when deteriorated |
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LUB Oil Maintenance on boardShip |
*Settling > simplest > no remove dissolved material > explain how it is settled
*Centrifuging > explain centrifuging > Purifier to separate water > Clarifier to separate solids.
*Filtering > widely used > oil is passed through material such as cotton, glass fibre or between closely stacked discs. Foreign particles are caught and held in absorbent filter. |
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Define the term SCAVENGING |
It is the process of getting rid of exhaust gases with the aid of fresh air so that a fresh charge of air is ready for the next compression stroke. |
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Loop Flow?
Cross Flow?
Uni Flow?
Keyword: Expel exhaust gases |
You Know This |
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Pulse System vs Constant Pressure |
In pulse system exhaust gases from main engine goes into the turbocharger in pulse manner where as in constant pressure system, exhaust gas from main engine goes into common manifold at higher pressure than atmospheric to expand in constant pressure & goes into turbocharger in constant pressure |
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Supercharging?
Surging? |
SuperCharging - process of pushing higher pressure air charge into cylinder. Pressure at beginning of compression in cylinder higher than ATM pressure. Essential in 2 stroke as there is very little time given for scavenging and exhausting.
Turbo-charging - Very effective method of pressure charging. Uses 20% of waste heat in exhaust gas which contain 35% of heat in fuel.
Surging - Air pressure in blower lower than delivery pressure will cause air delivery to breakdown. Followed by an immediate backward wave of air through the blower which continue until the delivery resistance decreased sufficiently for air delivery to resume.
Mentioned period of breakdown of air delivery is called surging and is manifested as irregular howling noise from the turbocharger. |
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Advantages of SuperCharging
HII LLL |
Higher Output Improved Combustion Improved Thermal Efficiency
Lower specific fuel consumption Less weight, space, cost to produce same power Lower exhaust temperature |
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Why da charge air is cooled before admitted into cylinder? |
To remove heat from charge air as to compensate temperate increased in turbocharger.
Temp level reduced lead to lower thermal load on the engine.
To increase the air density in engine cylinder which improve performance.
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Staring Air Line Automatic?
Starting Air Distributor?
Starting Air Valve? |
SALA -Mounted between the MAV & SAD, SAV -This valve open automatically when engine conditions are set to starting position -controlled by pneumatic means with air passed vented through pilot valve
SAD -Consist of series of valves (one 4 each cylinder) -Mounted adjacent to CAMs -CAMs determine whether to open the SAD valve to a certain cylinder. -When opened air is passed on to the SAV mounted on the cylinder head -Result? Compressed air enter the cylinder and causes engine to rotate
SAV -Mounted on cylinder head -Controlled by CAMs -Suppy of starting air comes from common starting air pipe fitted the length of the engine which branch into separate connection to each cylinder |
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List types of INTERLOCK |
1. Turning Gear
2. Running Direction
3. Telegraph
4. Fuel Stops fuel injection into cylinder when any of important support system's pressure or temp is abnormal (e.g : lub oil, jacket cooling water, piston cooling, cam lub) |
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STATE the function of diesel engine governor. |
* Governor is a device which automatically controls or limits the speed of engine by adjusting the amount of fuel put into the engine.
* Adjust the rate of fuel in such a way that engine speed remain steady despite a change in load. |
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2 Types of Governor? |
1. Mechanical
2. Hydraulic |
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Definition OF TERMS
Speed Regulation
Hunting
Speed Droop
Sensitivty |
Speed regulation is change in engine's sustained or final speed when the load is changed from zero to full or vice-versa , without adjusting the governor
Hunting is the repeated and rhythmic speed fluctuation due to over control of the governor
Speed Droop is change in governor rotatiing speed, which causes gov's output shaft to change to full open to full close throttle position or vice-versa
Sensitivity refers to the time it takes for gov to react to minute changes. |
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CrankCase explosion what causes it? |
>Poor maintenance & negligent operation >Explosions have one thing in common, "hotspot" >hotspot could occur any moving elements in the crankcase (bearings >Hotspot provide heat to vapourize oil >Oil vapour mixed with air and heat from hotspot BOOM!
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TellMe WilliamWin OMD workings. |
>OMD uses PEC to detect optical density of oil mist in crankcase. >Motor driven fans continuously draw sample of oil through measuring tube and reference tube >Oil mist from a particular chamber is drawn to measuring tube through rotary valve and oil mist from the whole crank case is drawn into REF Tube >Alarm will sound if there is any abnormality in oil mist detected. >SHUTDOWN or SLOWDOWN depends on the intensity of Alarm. |
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Describe the precautionary measures to be taken, in order to prevent |
=Keep air bottles free of oil & water by regular draining & inspect periodically.
= Main starting air line & all other high pressure lines must be drained &
=Air starting valves in the cylinder head should be properly maintained.
=Open high pressure air from the bottle to the lines slowly. Equalize the pressure |
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FIRE! FIRE! SCAVENGE FIRE! WHAT TO DO! |
Keep Calm. +Reduce Speed of Engine +Change fuel to diesel (if required) +Shut fuel injection to affected cylinder +Increase lubrication +Shut scavenge space +Switch engine off +Engage turning gear +Flood scavenge space with steam, CO2 or other extinguishable materials |
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FireTube & WaterTube |
Fire tubes boiler has fire tube bank attached Conduct flue gas from furnace Submerged in water inside the boiler Heat xfer take place across the fire tube from flue gas to water, producing steam
WaterTube boilers are fitted with water tube bank. Conducts boiler water Xposed to furnace HeatXfer take place from flue gas from furnace to water inside the tubes, producing steam.
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WaterTube Adantages?
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85% efficient Safer since there is less water content in boiler compared to water tube High Pres & Temp steam production Able to produce steam quickly from cold condition Small and Lightweight |
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SafetyValve? BottomBlowDownValve? AirVentValve? To purge. Corrosion in the conden MainSteamStopValve?
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You know this. I know you know.
MSSV - to isolate boiler steam pressure from process or/and steam plants. Not used as a throttling valve and must be open fully or close fully. Open slowly to prevent sudden rise in pressure |
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TurnDOWN FOR WHAT? |
Max Fuel Through Put / Min Fuel Through Put
Indicate the ability of burner to cope with variation of boiler load without losing efficiency of atomization. |
