Motor Flashcards
State, with reasons, EIGHT areas or items which should be checked by the duty engineer before taking over the watch. (16)
EIGHT areas or items which should be checked by the duty engineer before taking over the watch are:
Check the funnel - this is to check for the colour of smoke, which may indicate a problem with the main engine.
Check which Generators are online - this is to ensure that there is sufficient power available and temperatures and pressures are correct.
Check the load on the generators - this is to make sure that the generators are not being over or under loaded. Also if only one generator is required, to conserve fuel.
Check engine room bilges - this is done to check the level because a bilge alarm may indicate a leak.
General Engine room condition - this is done so that the OOW has a good idea of what to expect on their watch. For instance, if there was a leak on a previous watch that was repaired but not yet cleaned up, it prevents the OOW from reinvestigating a solved problem.
Check the alarm monitoring system and warning lights - this is to ensure that the system is working and that in the event of a problem, the OOW will be notified.
Check the pressures and temperatures of online machinery (M/E, Generators, OWS etc) - this is to check that all values are within expected ranges and if not to question the previous watchkeeper as to why. Check any ongoing work - this is done to familiarise themselves with all work going on so they are aware of what machinery is available for use and what is not. Also in the event of an alarm on the system being worked on, it can be dealt with appropriately.
Q2
With reference to diesel engine turbochargers, describe the functions served by the following parts:
(a) Inducer (2)
(b) Diffuser (4)
(c) Volute casing (2)
(d) Nozzle ring (2)
(e) Fir-tree blade root (4)
(f) Damping Wire (2)
(a) The inducer is the smaller part of the compressor wheel that draws in ambient air and directs it towards the impeller. Its main functions are:
Feeding air smoothly into the impeller
Boosting atmospheric air to a higher pressure
Guiding air into the eye of the impeller
(b) The diffuser is located at the discharge end of the compressor. Its functions include:
Slowing down the airflow before boosting its pressure
Delivering uniform airflow to the compressor
Converting kinetic energy (velocity) into pressure energy
(c) The volute casing is placed just after the impeller. Its main function is to:
Convert kinetic energy of the air into pressure energy
Increase the pressure of the air before it enters the engine
(d) The nozzle ring is part of the turbine inlet. Its functions are:
Guiding exhaust gases onto the turbine wheel
Increasing the velocity of the exhaust gases to drive the turbine
(e) The fir-tree blade root is a design feature of the turbine blades. Its functions are:
Evenly distributing stress across the blade
Providing easier blade replacement due to its secure fit
(f) The damping wire is used in the turbine blades. Its function is to:
Dampen vibrations caused by centrifugal forces
Q3
With reference to the diesel engine cooling system:
(a) Explain why cooling is necessary (4)
(b) State the purpose of EACH of the following:
(i) Jacket water heater (4)
(ii) Jacket water drain tank (4)
(iii) Header tank (4)
a) Cooling is necessary in a diesel engine to prevent overheating which can lead to engine failure, cooling will reduce thermal stresses in engine components and maintain optimal operating temperature.
Q4
With reference to a small diesel engine that requires the use of a starting handle:
(a) State the procedure for starting (8)
(b) State EIGHT reasons that would cause difficulty in starting (8)
(a) Procedure for starting:
Check oil and cooling water level.
Dip fuel tank to ensure sufficient fuel for operation.
Check air filters to ensure no blockage.
Check that engine is not in gear and free to rotate
In order to use the starting handle, check that the decompression mechanism has been operated and rotate the engine to check it is free to operate.
Crank handle slowly and build up pressure.
Once speed has picked up, close compression lever.
(b)
No fuel due to empty tank
Blocked filters, faulty injector.
Low compression due to worn rings
Burnt exhaust gases
Incorrect adjustment of decompression lever.
Q5
With reference to auxiliary boilers:
(a) Explain how scale forms on the heating surfaces (8)
(b) State TWO reasons why scale is undesirable (4)
(c) State how scale build up is prevented from forming in steam boilers (4)
a) Boiler scale is caused by impurities being precipitated out of the water directly onto heat transfer surfaces or by suspended matter in water settling out on the metal and becoming hard and adherent. Scale formation increases due to high concentrations of calcium and magnesium salts within hard water. Only pure distilled water should be used to make up the system. Due to the operating temperatures of the water, when it boils of to steam the hardness salts are forced out of solution. These salts then form as scale on all surfaces clogging and restricting flow. It also acts as a heat insulator.
(b) It causes overheating and failure of boiler tubes. It acts as an insulator on the internal surfaces reducing heat transfer, which reduces boiler efficiency;
(c) Hardness salts (which cause scale), can either be prevented/removed before they enter the boiler, through effective water treatment, or, once in the boiler, by blowing down to dilute the boiler water and also adding chemicals like sodium carbonate and di-sodium phosphate to stop scale forming. They turn the permanent hardness salts into sludge instead. The sludge is then drained off the boiler.
Q3
With reference to the diesel engine cooling system:
(a) Explain why cooling is necessary (4)
(b) State the purpose of EACH of the following:
(i) Jacket water heater (4)
(ii) Jacket water drain tank (4)
(iii) Header tank (4)
(ii) Jacket water drain tank (4)
(iii) Header tank (4)
Main Coolers - To Remove Heat from the system
Circulation Pumps - To circulate the water within the
system
3 Way Thermal Regulating Valve - To maintain a
constant operational temperature & regulate amount of
water around system
De-Aerating Tank - To remove Oxygen bubbles from
the system & vapour & gases
Circulating Pump – Circulate water around system at a
certain pressure
Pre-Heater – To maintain correct temp of cooling
water before main engine (Can be bypassed)
FWG – Create water using waste heat from main engine
