Motor Flashcards
(9 cards)
Describe the procedure for preparing amain engine, from cold, for sea service. (16)
Open the steam heating valve to heat jacket water and run the jacket cooling water pump to increase the temperature of the liners.
Start the main engine system oil and crosshead oil pump
Start fuel oil purifiers and continue to circulate the fuel from the service tank to the settling tank
Open steam to heat the settling and service tank according to the fuel viscosity
Check the level of HT and LT expansion tank, Main engine sump tank and top-up if required.
Start the fuel oil supply and booster pump and let fuel circulate through the engine to warm up the fuel injectors
Start the Main air compressor and top up the air bottles.
Drain the air bottles, settling and service tank for any water/ sludge at the bottom
Check the temperatures and pressures of the Jacket cooling system, Fuel oil system, Lube oil system and LT pump. They should be within range.
After the cylinder liner temperature is above 60°C, ask permission from the bridge to turn the engine and inform CE.
Start the additional generator for sufficient reserve power as auxiliary blowers will be started.
Open the indicator cocks and engage the turning gear and turn the engine atleast two revolutions and manually operate cylinder lubrication.
Check for any water coming out from the indicator cock while the engine is being turned.
Disengage the turning gear and blow through the engine with air and observe all indicator cocks
Close the indicator cocks and ask permission from the bridge to try out the engine Kick the engine in Ahead and Astern direction to try out the engine After everything is satisfactory, give the control to bridge.
Describe how modern diesel engines are pressure charged. (8)
(b) State TWO reasons for cooling the charge air before it enters the engine. (8)
Describe how modern diesel engines are pressure charged. (8)
Modern diesel engines use a turbocharger to pressure charge the air.
• The turbocharger has two sides:
• Turbine side – driven by exhaust gases.
• Compressor side – compresses fresh air.
• Exhaust gases spin the turbine, which turns the compressor.
• The compressor draws in and compresses air before it enters the engine.
• The compressed air is hot, so it passes through a charge air cooler (intercooler).
• Cooling the air makes it denser, meaning more oxygen enters the cylinder.
• More oxygen allows more fuel to burn efficiently.
• This results in more power and better fuel efficiency.
(b) State TWO reasons for cooling the charge air before it enters the engine. (8)
- Cooler air is denser (C)
• More air molecules fit into the same space.
• This means more oxygen enters the cylinder, allowing more fuel to burn.
• Result: More power and efficient combustion. - Improves combustion quality (I)
• With denser air, the air-fuel mix burns more completely.
• This leads to lower smoke and fewer unburnt particles in the exhaust.
• Helps the engine run cleaner and smoother. - Reduces thermal stress and knocking (D)
• Cooler air helps keep cylinder temperatures lower.
• Prevents pre-ignition (knocking), which can damage pistons and valves.
• Extends the life of engine components. - Protects performance and engine parts (P)
• Lower intake temperatures keep lubrication effective (less oil breakdown).
• Helps turbocharger and intercooler work efficiently.
• Maintains consistent engine performance under heavy load.
Describe the procedure for preparing amain engine, from cold, for sea service. (16)
• Start all pre-heating systems, Lube oil, Fuel oil and Water
• Start lubrication system pumps, and circulate ensure correct sump level
• Start cooling water circulation pumps; ensure correct head level leaving room for expansion
• Drain Air bottles and charge them to the correct starting pressure
• Drain the fuel oil settling and service tanks of water and sludge, ensure heating is on
• Open all indicator cocks of the main engine
• Check all system temperatures are adequate; begin circulation of fuel oil in injectors and pumps
• Inform the bridge the engine is to be turned, begin turning the engine on turning gear
• Operate cylinder lubrication by hand
• Ensure adequate oil and water flow through all check glasses, including turbochargers
• Check Intermediate shaft bearing oil levels
• Check gear box oil level, CPP Hydraulic oil reserve and stern seal
• Inform the bridge you are going to kick the engine on air, Disengage turning gear, ensure main fuel top valves are closed
except drains and kick for 3 revolutions
With reference to Jacket Cooling Water treatment of a diesel engine:
(a) State the chemical tests caried out (6)
(b) State the frequency of testing (2)
(c) Explain why it is necessary to keep the test results within certain limits (4)
(d) State the action to be taken to rectify an abnormal test result (4)
(a) Chemical Tests Carried Out (6 marks)
- Nitrite Test
• Purpose: Measures nitrite levels, which act as oxygen scavengers.
• Why: Nitrite reacts with oxygen to form nitrate, preventing corrosion inside cooling passages.
• Memory Tip: “Nitrite fights rust by grabbing oxygen.” - Chloride Test
• Purpose: Detects chloride ions (salt contamination) in the water.
• Why: Chlorides are corrosive and can cause pitting corrosion.
• Memory Tip: “Chloride = Salt = Corrosion Risk.” - pH (Alkalinity) Test
• Purpose: Ensures the water remains slightly alkaline (typically pH 8.5–11).
• Why: Acidic water causes corrosion; alkaline water protects surfaces.
• Memory Tip: “Keep it basic to protect the base (metal surfaces).”
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(b) Frequency of Testing (2 marks)
• Weekly testing is standard.
• OR as per the ship’s Planned Maintenance System (PMS).
Memory Tip: “Weekly water check keeps the engine in check.”
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(c) Why Keep Test Results Within Limits (4 marks)
• Ensures safe and efficient engine operation.
• Prevents corrosion, cavitation, and scale formation.
• Protects engine parts like cylinder liners, water jackets, and pump seals.
• Maintains conditions within manufacturer’s recommended limits.
Memory Tip: “Limits = Longevity. Stray too far = decay.”
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(d) Action to Rectify Abnormal Results (4 marks)
1. Retest the sample to confirm the result.
2. If still abnormal, inform the Chief Engineer.
3. Follow manufacturer’s instructions for corrective action.
4. Adjust chemical dosing (e.g., add inhibitor or fresh water).
Memory Tip: “Retest – Report – Refer – Remedy.”
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Quick Recap Mnemonic: “NCP-FIRM”
N – Nitrite (oxygen scavenger)
C – Chloride (salt test)
P – pH (alkalinity)
F – Frequency = Weekly or PMS
I – Importance = Prevent corrosion, follow specs
R – Rectify = Retest, Report, Remedy
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With reference to Jacket Cooling Water treatment of a diesel engine:
(a) State the chemical tests caried out (6)
(b) State the frequency of testing (2)
(c) Explain why it is necessary to keep the test results within certain limits (4)
(d) State the action to be taken to rectify an abnormal test result (4)
a) The chemical test carried out on the cooling water of a diesel engine are:
Nitrite test: Nitrite is added to closed cooling systems as an oxygen scavenger. Nitrite will react with any free oxygen to produce nitrate. Removing oxygen helps to prevent corrosion from occurring.
CHLORIDE test - This is to test for chlorides in the water.
PH test (Alkalinity) - To ensure Cooling Water stays alkaline and does not cause a corrosive attack
(b) Testing is done weekly or as per the Planned Maintenance Schedule.
(c) For the safe and efficient operation of the engine, whilst ensuring operation within manufacturers’ specifications.
(d) Retest, if still abnormal inform the Chief Engineer and following manufactures guidelines administer the correct course of treatment.
Q4
With reference to inlet and exhaust valve on a four stroke diesel engine:
(a) Explain why the correct tappet clearance are essential (8)
(b) State the results of the tappet clearances being
(i) Too big (4)
(ii) Too small (4)
(a) It ensures that the valves close properly when they expand as they get to operating temperature and it also helps ensure proper timing is maintained. If there was no clearance the valve would expand against the fixed piston of the rocker arm, while cam on base circle and would therefore expand into the cylinder causing loss of compression and burning of the valve and seat.
(b) (i) Too large a clearance will cause the valve to open late and close early. This causes noise and may eventually break the impacting surface and, also cause a consequent disturbance in engine performance.
(ii) With too small a clearance, not only there is a chance that the valve will not close properly when it comes up to temperature, but it will also open early and close late. In extreme cases, it may prevent the valve from closing completely and, also cause a consequent disturbance in engine performance.
Q4
With reference to inlet and exhaust valve on a four stroke diesel engine:
(a) Explain why the correct tappet clearance are essential (8)
(b) State the results of the tappet clearances being
(i) Too big (4)
(ii) Too small (4)
Q4
With reference to inlet and exhaust valve on a four stroke diesel engine:
(a) Explain why the correct tappet clearance are essential (8)
Both inlet and exhaust valves actuated together, this is done by means of a tappet. A tappet clearance is ensured and must be
correct to allow for thermal expansion of the valve, tappet and rocker gear during running service. A clearance is provided
between the valve stem, tappet and rocker arm for this purpose.
• To ensure that the valves close fully and at the correct time.
• To ensure open at correct time especially when the engine is upto temperature and the valve stem has expanded
from its cooled length.
• Differential expansion of the intervening cylinder blocks compared to the oil bathed pushrods needs to be
accommodated with a positive tappet clearance to ensure that the valves are never held of their seats for any
operating scenario/temperature regime.
(b) State the results of the tappet clearances being
(i) Too big (4)
• If the clearances are too large, valves will open late and close early and have reduced lift. There will also be more
noise and wear from the impact of the working surfaces. Poor scavenging of exhaust gas and reduced power will
be noted
(ii) Too small (4)
If the clearances are too small, the valve will open early and close late and in extreme cases the valve may not
fully close at all. This will cause poor compression, blow past of hot gasses and eventual wear out the valve and
seat face. This will also lead to a lower power output.
Describe, with the aid of sketches, the procedure for testing a boiler gauge glass (16)
The procedure for testing a boiler gauge glass
Check for leaks on cocks. First, close the steam and water cocks and open the drain. Nothing should blow out if steam and water cocks are not leaking;
In order to check that the water cock connection to the boiler is clear, open and close the water cock to see if water blows out;
In order to check that the steam cock connection to the boiler is clear, open and close the steam cock to see if steam blows out;
Close the drain cock.
Open the water cock. Water should gradually rise up to the top of the gauge glass. Then open the steam cock and the water in the glass should fall to the level of the water in the boiler.
Describe, with the aid of sketches, the procedure for testing a boiler gauge glass (16)
- Close S, close W and open D to drain the gauge glass
- Open S to prove flow of steam, W shut and D open
- Shut S, Open W to prove flow of water, D remains open
- Shut D, W & S, crack open W to allow to fill gauge glass
- When filled with water crack open S to balance out gauge
glass to working pressure of boiler - Open both W & S fully
