Motor Flashcards
Q1
With respect to Main Propulsion Engines, state the immediate action to be taken as Engineer Officer of the watch in the event of EACH of the following, stating ONE reason why EACH action is necessary:
(a) Turbocharger repeatedly surging; (4)
(b) Air start manifold/branch pipe overheating local to one unit; (4)
(c) Low scavenge air temperature alarm; (4)
(d) Engine misfires, fuel rail pressure low alarm activates, booster pump pressure high. (4)
(a) In the event of Main propulsion engine Turbocharger surging, the immediate action is to reduce the load/ slow down the engine after informing to bridge and CE. Repeated surging causes damage to the turbocharger due to the vibration when spinning back. This could be caused by the propeller being crashed into water in rough weather, causing rapid load fluctuations on the engine. Reducing the speed will reduce load, thus reducing load fluctuations and stops surging.
(b) An overheated air start manifold/ branch pipe has the danger of starting air line explosion. The immediate action would be to inform CE and bridge, request to slow down the engine and if possible, the engine to be stopped. The air start valve has to be repaired or replaced. The engine should not be started until the air pipe is cooled down as it can cause an explosion. If repairs could not be taken place, the engine would have to be run with the fuel pump lifted.
(c) Low scavenge air temperature alarm may be due to low coolant inlet temperature. The immediate action would be to reduce the seawater flow rate to the cooler. Reduce the cooling water flow rate/increase the temperature of the cooling water to prevent water moisture from condensing on the liner and washing off the lubricating oil. This prevents scuffing and corrosion caused by the removal of lubrication oil.
(d)Engine misfires “fuel rail pressure low” alarm activates, and booster pump pressure high may be due to clogged filters or leaks. The immediate action would be to change over to the other filter. If the pressure is low even after changing the filter, then request permission from the bridge to slow the engine down and/or reduce its load and inform CE.
Turbocharger surging during heavy weather (4)
Inform bridge & Chief engineer, reduce the load of the Main engine or reduce pitch to meet the load requirement of the propeller when it’s outside the water to prevent surging and damage to T/C
b.
Air Excessive vibration from turbocharger at full sea speed (4)
Inform bridge & chief engineer, request to slow down main engine to minimise vibrations to analyse and investigate the reason for vibrations
C.
Air start manifold/branch pipe overheating local to one unit (4)
Inform the bridge of the situation and Chief Engineer, request that the engine be slowed or stopped.
Remove the fuel supply to that unit and open the indicator cock. This would minimise damage/ explosion within the air start line.
d. Low scavenge air temperature alarm (4)
Reduce the flow through air cooler as air too cold will cause thermal shock to engine. Reduce the cooling SW flow rate and cooling water control to manual mode if on automatic. This is because condensation could form on the liner if temperatures are too low and it could be washed away and corrosion could occur
e. Engine misfire, “fuel rail low pressure alarm”, booster pump pressure high(4)
Inform the bridge and chief engineer and request the engine be slowed down. Change over fuel oil pressure filters to maintain supply as the filter may be blocked. Check and inspect fuel pump as this could be failing causing misfire due to lack of fuel
f. Excessive vibration of air start branch pipe to one cylinder during manoeuvring (4)
Inform bridge & Chief engineer, request the engine to be slowed down or stopped, cut off fuel to affected unit, this is to reduce the risk of an explosion in the air start system by reducing load
High Main Bearing Temperatures (4)
Inform bridge & chief engineer, request the engine be slowed down and check lubrication flow and monitor the temperatures, this will allow you to reduce the high temperature bearing and prevent damage to bearing
Q2
(a) State TWO differences between a trunk type and a crosshead type diesel engine. (4)
(b) Describe, with the aid of sketches, the combustion process of the two-stroke compression ignition engine. (12)
(a) Crosshead type diesel engine
The piston fastens to a vertical piston rod, whose lower end is attached to a “crosshead” that then connects to a connecting rod.
Uses inlet (scavenge) ports for air admission.
Trunk type diesel engine
The piston is connected directly to the upper end of the connecting rod (using a swivelling gudgeon pin).
Uses inlet valves
Explain the constructional differences between 2-stroke slow speed and 4-stroke medium speed engines > No intake valves found on two stroke engines (Scavenge ports instead of inlet valves)
> Crosshead bearing found on two stroke engines, this helps piston run straight in the liner
> 2 Stroke has one large exhaust valve on the cylinder head, whereas 4-stroke has multiple inlet and outlet valves
> 4-Stroke connects piston to connecting rod by gudgeon pin, this allows connecting rod to rotate
> 2-stroke has stuffing boxes which seal the cylinder space from crankcase, whereas 4-strokes doesn’t
> 2 stroke is much larger in size with an A frame compared to the 4 stroke as piston stroke is much larger.
> some 2 stroke ME electronically controlled engines are camshaft less which control the lubrication and fuel pumps
whereas 4 stroke needs camshaft to control these.
> 2 stroke has Auxiliary blowers to aid in scavenging whereas 4 strokes have multiple inlet valves.
Q3
Describe the procedure to change the fuel supply system of the main propulsion engine from high viscosity fuel to low viscosity fuel such as diesel oil whilst on passage. (16)
When it is required to change over the main engine fuel system from HFO to MGO, obtain the approximate time from the bridge to enter the SECA area so that we can start purification of the MGO tank for about 48 hours and keep the MGO service tank full.
Changeover from HFO to MGO means changeover from high temperature to low temperature. The changeover should be carried out in a controlled manner at a low load (25 - 40% MCR), and the fuel temperate gradient must not exceed 2°C/ min.
Before the changeover is to be done, check the FOBAS calculator for the change-over time required, and steam heating to the fuel oil heater shall be shut accordingly.
Proceed as follows for the changeover.
Shut the steam to the FO heater tracing lines and wait for the temperature to reach below 90 degrees or wait till the viscosity reaches 18cSt.
Reduce the main engine load to 25 - 40% MCR.
Make sure the temperature reduction does not exceed 2°C/ min.
Open the MGO service tank outlet valve and open the MGO inlet valve to the FO module.
The temperature will now gradually decrease until it reaches the temperature in the MGO service tank.
When the viscosity is reached below 8cst, open the valves to the cooler so that viscosity does not drop too much, as this will cause the problem of lubrication to the fuel pumps.
Wait until all the fuel in the system is flushed with MGO.
The load can now be slowly increased up to a max of 75% as long as the temperature change gradient is kept below 2°C/min.
Change the 3-way valve to the MGO cooler slowly to avoid thermal shock and temperature gradient and confirm cooling water valves are open.
After the changeover is complete, inform the bridge and note down the following.
Date and time of completion of fuel changeover
Ships position - latitude and longitude
The volume of MGO in each tank on completion of fuel changeover
Tank identity
Tank quantity
Signature of a responsible officer.
Q4
With reference to main diesel engine starting air lines:
(a) Describe the main cause of a starting air line explosion. (8)
(b) Explain how a leaking start air valve can be identified while the engine is running. (4)
(c) State four different safety devices which can be incorporated in to the starting air line to limit the damage caused by an explosion. (4)
1C)
State four different safety devices which can be incorporated in to the starting air line to limit the damage caused by an explosion. (4)
Bursting Disc - Safety Valves on manifold
Non return valves
Flame trap gauze
Relief valves
Q5
State FOUR tests which are required for boiler water, giving a reason for EACH test. (16)
(b) Describe, with the aid of sketches, the combustion process of the two-stroke compression ignition engine. (12)
During the exhaust and intake stroke, scavenging begins with the piston at BDC. At this point intake ports are uncovered and exhaust valve is open. Super charger forces air into cylinder expelling the gases from previous cycle and clean air admitted for new cycle.
On the compression stroke As the piston moves towards TDC, it covers the intake ports, the exhaust valve close and seal upper cylinder as
piston continues upwards the air is compressed at
high pressure and temperature where heat is generated by compression.
On the power stroke Just after TDC compression stroke ends atomised fuel is injected at this point
and the intense heat causes fuel mto ignite causing combustion and forces the piston down
-Start Position: Exhaust valve open, scavenge ports uncovered, cylinder is full of air and piston is at
BDC.
-Compression: Exhaust valve shuts, as the piston drives up the cylinder liner, the scavenge ports are
covered. The air trapped inside the cylinder is compressed causing a substantial temperature
increase.
-Injection: Just before TDC, fuel is injected into the hot air mass and begins to combust.
-Expansion: Combustion products expand, causing an increase in pressure in the combustion
chamber which drives the piston downwards.
-Exhaust: Exhaust valve opens, just before BDC, the scavenge ports are uncovered resulting in
pressurised scavenge air entering the cylinder. The high-pressure air purges the gases past the
exhaust valve.
