Marine Engine Question & Answer

With reference to main propulsion engine turbochargers:

state how in - service performance checks are undertaken for EACH of the following:
i) the gas side;

ii) the compressor;

iii) the suction filter;

iv) the after cooler.


describe the action to be taken to allow the main engine to operate in the event of a turbocharger failing such that it may not be used.



a.

i) The efficiency of the gas side of the turbocharger can be assessed for a given power setting by the speed of the turbocharger and the gas temperature differential across the turbocharger. This gives an indication of the amount of energy in the exhaust gas which is being utilised. Fouling on the nozzle ring and blades will alter their profile and lead to a decrease in the energy conversion.

ii) A decrease in the performance of the compressor can be deduced from a decrease in scavenge pressure for a given turbocharger speed at a particular power setting. Usually caused by fouling of the compressor wheel/ diffuser.

iii) A dirty suction filter will result in similar symptoms to those given in (ii) above. However a manometer fitted across the suction filter will show an increase in differential pressure.

iv) A drop in the efficiency of the aftercooler can be detected by an increase in scavenge air temperature after the cooler or by the scavenge air temperature control valve for the cooling water opening fully to keep the air temperature at the required setting. If this is because of fouling on the air side then an increase in the pressure differential across the air cooler will show on the manometer. If fouling is on the water side, then the pressure differential across the air cooler will not have increased, but there will be a reduction in the temperature difference between the cooling water inlet and outlet.

It should be noted that all the above faults could result in surging of the turbocharger as all will affect the mass delivery rate for a particular engine power.

b.

This will depend on the type of engine, turbocharging system, and number of blowers.

For a 4 stroke pulse turbocharged engine fitted with a blower at either end.



Remove damaged rotor, air casing, and filter/silencer.

blank gas casing, so that the exhaust gas can pass through the casing

blank off air outlet to engine inlet manifold.




operate engine with single blower. Engine load will be reduced for efficient combustion.

For a 2 stroke crosshead engine with a single constant pressure turbocharger, then either the rotor can be removed in a similar manner to that above, and the exhaust gas routed through the blanked off casing or alternatively the rotor can be locked in position, the gas inlet and outlet blanked off, whilst the exhaust gas is routed through an emergency bypass pipe. On MAN-B&W engines to improve the air flow to the auxiliary blower, the expansion compensating piece (bellows) between compressor outlet and air cooler inlet may have to be removed. On Sulzer RTA engines, the doors on the scavenge space are opened to improve air flow to the auxiliary blower. Engine power will be limited by the amount of scavenging air the auxiliary blower can supply, but will probably be limited to 'slow ahead'. To improve air supply to the engine the machinery space exhaust fans can be changed over to supply, and canvas trunking rigged up to direct air into the auxiliary blower.