Turbocharger Page 27-28 Flashcards
What is the function of main engine turbochargers?
To make use of and reduce the amount of waste energy from exhaust gas and to provide a high pressure air charge for efficient scavenging.
What are two advantages of fitting turbochargers?
Increase the efficiency of the engine and reduce wastages found within older mechanical driven superchargers.
How are turbochargers cooled and lubricated?
The bearing journals are lubricated from the main engine lubrication oil system via a header, to maintain lubrication after the engine is stopped. Some older turbines have built in pumps driven from the turbine ends with a small oil reserve. The casings of older turbochargers are cooled with a water jacket off of the HT system of the main engine. Newer turbines use air from the compressor side as a cooling medium.
Describe the operational principles of a main engine exhaust gas turbocharger.
Exhaust gas coming from the exhaust manifold passes the exhaust grid to rotate the turbine wheel of the TC at a higher RPM. On the same rotating shaft, the centrifugal compressor is fixed, which induces ambient air through the air filter. The compressed air pressure is achieved via a diffuser ring and through the air cooler.
What is the function of suction filters in a turbocharger system?
The function of suction filters on the air side of TC is to filter the air supply to the centrifugal compressor and scavenge ports.
What is the function of exhaust grids in a turbocharger system?
The function of exhaust grids on the exhaust side of TC is to prevent damage to the turbine wheel from any large matter particulates such as broken piston rings.
What is the function of a charge air cooler?
The function of the charge air cooler is to reduce the scavenge air temperature and consequently change the volume/mass ratio, allowing a greater mass of air to the fixed volume of the cylinders.
What are two reasons for fitting an exhaust gas turbocharger to an engine?
To increase the mass of air in a cylinder for a given speed, allowing more fuel to be burned, resulting in more power. To reduce specific fuel consumption, as a greater mass of air makes combustion more efficient.
What is the effect of dirty or restricted air filters?
Would result in poor combustion due to a reduced amount of air, indicated by darker exhaust gas and higher exhaust gas temperature.
What is the effect of a restricted exhaust gas turbine?
Result in turbine speed being reduced for given power, indicated by a rise in exhaust gas temperature and lower charge air pressure.
d. Describe with the aid of a sketch, the operational principles of a main engine exhaust gas turbocharger (5)
How is the exhaust gas turbocharger cleaned?
The exhaust gas turbine can be cleaned by means of nutshell medium while the ship is running full ahead over 90 RPM. The outlet valve of the receiver should be closed, and the lid screwed off. The nutshell should then be emptied into the receiver. After closing the lid, open the compressed air valve to build pressure, then open the outlet of the receiver to divert the nutshell into the turbine, cleaning away carbon deposits. The air should be left on until the cleaning medium has all left the receiver, usually around 2-3 minutes, then close the compressed air valve at the inlet and close the outlet valve on the receiver.
What immediate action should be taken for turbocharger surging during heavy weather?
Inform the bridge and 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 the turbocharger.
What should be done in case of excessive vibration from the turbocharger at full sea speed?
Inform the bridge and Chief Engineer, request to slow down the main engine to minimize vibrations and analyze the reason for the vibrations.
What action is required for air start manifold/branch pipe overheating local to one unit?
Inform the bridge and Chief Engineer, request that the engine be slowed or stopped. Remove the fuel supply to that unit and open the indicator cock to minimize damage or explosion within the air start line.
What should be done when a low scavenge air temperature alarm sounds?
Reduce the flow through the air cooler as air that is too cold will cause thermal shock to the engine. Reduce the cooling seawater flow rate and set cooling water control to manual mode if on automatic.
What immediate action should be taken for an engine misfire with a ‘fuel rail low pressure alarm’?
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 the fuel pump as it could be failing, causing misfire due to lack of fuel.
What action is required for excessive vibration of the air start branch pipe to one cylinder during manoeuvring?
Inform the bridge and Chief Engineer, request the engine to be slowed down or stopped, and cut off fuel to the affected unit to reduce the risk of an explosion in the air start system.
What should be done for high main bearing temperatures?
Inform the bridge and Chief Engineer, request the engine be slowed down, and check lubrication flow while monitoring the temperatures to reduce high temperature bearing and prevent damage.
