Motor Flashcards
Q1 With reference to scavenge fires:
(a) State FOUR possible contributing factors;
(4)
(b) Explain how EACH factor mentioned in
(a) contributes; (8)
(c) State FOUR indications. (4)
(a) FOUR possible contributing factors for scavenge fire are:
Damaged or worn piston rings
Leaking fuel injector
Over-lubrication of cylinder
Lack of regular maintenance and scavenge space cleaning
(b) Answer will be here soon :)
- a) State FOUR important factors which contribute to the initiation of a scavenge space fire.
-Damaged or worn piston rings allowing blowby of hot gases.
-Excessive cylinder lubrication which is drained down to scavenge spaces.
-Blowback of exhaust gases caused by exhaust back pressure or deposits on exhaust ports, fouling of grid before turbine inlet, fouling of turbine blades, choking of EGB or economiser gas outlet.
-Lack of regular maintenance and scavenge space cleaning allowing build-up of carbon deposits.
(c)FOUR indications of scavenge fire are:
High scavenge temperature in one or more units
Turbocharger surging
Increased scavenge pressure
Paint discoloration
- With reference to large slow speed diesel engine:
a) State four possible factors leading to a scavenge space fire.
- Engine running low speed causing scavenge air to be low pressure.
-Too much LO being admitted into the cylinder.
-Broken/worn piston rings allowing blowby of hot gases.
-Scavenge drain blocked causing fuel build up.
b) State four indications of a scavenge fire.
-Smokey exhaust from the funnel.
-High exhaust gas temperatures.
-High scavenge air temperature.
-Burning/bubbling paint on the engine side.
Q2 Describe, with the aid of sketches, the operation of a 4 stroke cycle diesel engine.
(16)
16 marks
- At the bottom of the down stroke (BDC), the inlet valve opens, and a fresh charge of air enters the cylinder.
- Both inlet and exhaust valves are in the closed position, the piston moves up the cylinder compressing the charge air, heating it as it is compressed.
- Atomised fuel is injected, and auto-ignition occurs due to the superheated compressed charge air, the expansion of hot gasses drives the piston down.
- As the piston travels down, the exhaust valve opens. This stays open until after the air inlet valve (ports) closes to ensure complete scavenging.
Q3 (a) Answer the following:
(i) State why the simultaneous injection of fuel oil and starting air into a main engine cylinder is undesirable. (2)
(i) Explain how simultaneous injection of fuel oil and starting air is prevented. (4)
(b) Answer the following:
(i) Explain how a leaking air start valve is detected while the engine is running. (4) (ii) Describe the actions to be taken upon discovery of a leaking air start valve. (6)
(a) (i) This is undesirable because the fuel would ignite and the product of combustion (hot gases) would be allowed in the starting air line and that could, in turn, cause an explosion in the starting air line.
(ii) This is prevented by an interlock in the engine starting system. Control air acts to open the puncture valve (of the fuel pump), thus returning fuel oil from the discharge side to the suction side, preventing injection to take place.
(b) (i) Leakage on the air start valve is shown by overheating of the branch pipe connecting the starting air valve to the starting air rail. The temperature of each supply pipe is normally checked (by touch or by IR temperature gun)
(ii) Actions to be taken upon discovery of a leaking start valve
Inform the Bridge and CE, and request permission to reduce engine load to a minimum
Isolate the affected unit (operate puncture valve, etc.);
When navigationally safe, stop the engine and fix the problem.
Q4 With reference to main starting air
compressors:
(a) State THREE maintenance procedures that maintain their efficiency: (6)
(b) Describe the procedure for the manual starting of a compressor. (10)
- With reference to main starting air compressors:
a) State three maintenance procedures that maintain their efficiency.
-Regular replacement of the air suction filter.
-Regular lubrication of motor bearings.
-Inspecting inlet and discharge valves for condition and seating.
b) Describe the procedure for manual starting of a compressor.
Check the sump oil is at the correct level. Ensure cooling water lines are open and flowing. Ensure stage drains and discharge valves to receiver are open. Deisolate, switch the compressor to local oi the starting panel and press start. Observe drain valves for any oil or water discharges, and then close the drain valves. Monitor the stage temperatures and pressures.
THREE maintenance procedures that maintain their efficiency are:
Monitoring the condition of the suction air filter and replacing it at regular intervals will ensure unrestricted airflow.
Overhauling the valves at regular intervals so that the accumulated carbon deposits can be cleaned. Cleaner valves will not cause compressed air to leak.
Check the level of lube oil and top up as required. Use the correct grade of Lube oil. While filling, the funnel and hoses should be clean. The presence of dirt or metal particles will damage to bearings and crankshaft
(b) Procedure for manual starting of compressor:
Check the level of the sump and top up if required.
Ensure the cooling water inlet and outlet valves are open
Ensure the compressed air outlet valve is open
Ensure the air bottle filling valve is open
Open each stage drain valve of the compressor.
Start the compressor
Once the compressor speeds up, close all the stage drains
Observe the pressure of each stage for proper running and observe for any leaks.
Check the cooling water inlet/ outlet temperature.
Q5 List FOUR safety or alarm devices fitted to an automatically controlled auxiliary boiler indicating how EACH of these devices may be tested. (16)
WHRS & Boiler
- List four safety or alarm devices fitted to an automatically controlled auxiliary boiler indicating how each of these devices may be tested.
Gauge glass: tested by carrying out gauge glass blow-down procedure.
Flame failure: remove the photo-electric cell and cover it to simulate flame failure.
Ignition failure: isolate the ignition transformer and begin the start sequence, the burner will lock out after purge.
Low fuel oil temp: turn off the fuel oil heaters and allow the fuel to cool, tripping the burners.
Four safety or alarm devices fitted to an automatically controlled auxiliary boiler:
Safety Valve:
This valve automatically releases excess steam to prevent overpressure and potential explosions. Testing involves actuating the valve manually (often by a lever or lifting mechanism) to verify it opens at the correct pressure setting.
Low Water Level Alarm/Cut-off:
This device sounds an alarm and/or shuts down the boiler if the water level falls to a Low level or low-low, preventing overheating and damage. Testing involves simulating a low water condition (safely, following manufacturer’s instructions) to ensure the alarm activates and the cut-off functions correctly. This might involve lowering the water level slightly or using a test switch, depending on the system’s design.
High-Pressure Cut-off:
This device shuts down the boiler if the steam pressure exceeds a safe limit. Testing involves safely increasing the boiler pressure (within controlled parameters) to the high-pressure cut-off point to verify the boiler shuts down.
Flame Failure Sensor/System:
This device detects the absence of a flame in the burner and automatically shuts down the fuel supply to prevent the buildup of flammable gas. Testing involves safely simulating flame failure (e.g., by temporarily interrupting the fuel supply or removing the flame eye from the burner). This should verify that the fuel supply is shut off and the system triggers an alarm.
Q1
With reference to scavenge fires:
(a) State FOUR possible contributing factors; (4)
(b) Explain how EACH factor mentioned in (a) contributes; (8)
(c) State FOUR indications. (4)
- With reference to large slow speed diesel engine:
a) State four possible factors leading to a scavenge space fire.
- Engine running low speed causing scavenge air to be low pressure.
-Too much LO being admitted into the cylinder.
-Broken/worn piston rings allowing blowby of hot gases.
-Scavenge drain blocked causing fuel build up.
b) State four indications of a scavenge fire.
-Smokey exhaust from the funnel.
-High exhaust gas temperatures.
-High scavenge air temperature.
-Burning/bubbling paint on the engine side. - a) State FOUR important factors which contribute to the initiation of a scavenge space fire.
-Damaged or worn piston rings allowing blowby of hot gases.
-Excessive cylinder lubrication which is drained down to scavenge spaces.
-Blowback of exhaust gases caused by exhaust back pressure or deposits on exhaust ports, fouling of grid before turbine inlet, fouling of turbine blades, choking of EGB or economiser gas outlet.
-Lack of regular maintenance and scavenge space cleaning allowing build-up of carbon deposits.
Q2 Describe, with the aid of sketches, the operation of a 4 stroke cycle diesel engine. (16)
Induction/Inlet - The intake stroke begins at top dead centre, and as the piston moves down, the intake valve opens. The downward movement of the piston creates a vacuum in the cylinder, causing a fuel and air mixture to be drawn through the
intake port into the combustion chamber. As the piston reaches bottom dead centre, the intake valve closes.
Compression - The compression stroke begins with the piston at bottom dead centre and rising up to compress the fuel and air
mixture. Since both the intake and exhaust valves are closed, there is no escape for the fuel and air mixture, and it is compressed to a fraction of its original volume. At this point, the fuel and air mixture is ignited
Ignition/Power - The power stroke begins when the fuel and air mixture is ignited, burns and expands and forces the piston
down. The valves remain power stroke ends as the piston reaches bottom dead centre.
Exhaust - The exhaust stroke begins when the piston nears the end of the power stroke and the exhaust valve is opened. As
the piston moves upward towards top dead centre, it pushes the burnt gases, resulting from the ignition of the fuel and air
mixture, out of the combustion chamber and through the exhaust port. As the piston reaches top dead centre, ending
the exhaust stroke, the exhaust valve closes, and the intake valve opens to begin the intake stroke for the next cycle
Q3
(a) Answer the following:
(i) State why the simultaneous injection of fuel oil and starting air into a main engine
cylinder is undesirable. (2)
(ii) Explain how simultaneous injection of fuel oil and starting air is prevented. (4)
(b) Answer the following:
(i) Explain how a leaking air start valve is detected while the engine is running. (4)
(ii) Describe the actions to be taken upon discovery of a leaking air start valve. (6)
(a) (i) This is undesirable because the fuel would ignite and the product of combustion (hot gases) would be allowed in the starting air line and that could, in turn, cause an explosion in the starting air line.
(ii) This is prevented by an interlock in the engine starting system. Control air acts to open the puncture valve (of the fuel pump), thus returning fuel oil from the discharge side to the suction side, preventing injection to take place.
(b) (i) Leakage on the air start valve is shown by overheating of the branch pipe connecting the starting air valve to the starting air rail. The temperature of each supply pipe is normally checked (by touch or by IR temperature gun)
(ii) Actions to be taken upon discovery of a leaking start valve
Inform the Bridge and CE, and request permission to reduce engine load to a minimum
Isolate the affected unit (operate puncture valve, etc.);
When navigationally safe, stop the engine and fix the problem.
Q4
With reference to main starting air compressors:
(a) State THREE maintenance procedures that maintain their efficiency: (6)
(b) Describe the procedure for the manual starting of a compressor. (10)
- With reference to main starting air compressors:
a) State three maintenance procedures that maintain their efficiency.
-Regular replacement of the air suction filter.
-Regular lubrication of motor bearings.
-Inspecting inlet and discharge valves for condition and seating.
b) Describe the procedure for manual starting of a compressor.
Check the sump oil is at the correct level. Ensure cooling water lines are open and flowing. Ensure stage drains and discharge valves to receiver are open. Deisolate, switch the compressor to local oi the starting panel and press start. Observe drain valves for any oil or water discharges, and then close the drain valves. Monitor the stage temperatures and pressures.
