18 April 2016
Power generation is a continuous requirement on board ships. A blackout situation even for few minutes can lead to devastating results such as grounding, collision etc., resulting in heavy losses and danger to the ship and its crew.
A ship is equipped with multiple generators/ auxiliary engines to supply continuous power at all times. These power generating units are watched over and maintained by ship engineers.
A sensible ship engineer will try to run minimum number of generators at any given period of time and look for maximum load, which not only ensures goodwill for the auxiliary engines but also reduces overall fuel consumption and harmful emissions. This can happen when the auxiliary engine rated output is achieved without any deviation in the engine parameters (temperature, pressure etc.).
If the engine performance is deteriorating, it will result in reduced output with high exhaust temperature and low peak pressure. The reduced output of one generator will require another generator to run in parallel and compensate the power demand.
Ship engineers must know the probable reasons which can lead to reduced power output of auxiliary engines.
Following are 20 possible causes, which will lead to reduced power output and performance of an auxiliary engine on board ship:
The fuel oil pressure is lower than requirement, which can be due to faulty fuel oil attached pump or the fuel oil viscosity is very low
The fuel oil pressure will also drop when the fuel grade is changed from HFO to MDO/ MGO/LSFO. This will lead to decrease in engine performance
If the fuel pump parts i.e plunger and barrels are worn out, the fuel will leak out and the fuel pressure will drop at the discharge point
If the fuel temperature is inadmissibly high (>60 deg C), the fuel viscosity will reduce and it will affect the fuel pressure
If there is high difference firing pressure in between individual cylinders, it will lead to reduction in overall output of the engine
Blocked or dirty line filters in the fuel oil system will reduce the oil pressure and hence the performance
The clearance between intake/ exhaust valve and its guides is of extreme importance. If the clearance is more than required, the combustion mixture will leak out from this gap and reduce the engine performance
A damaged exhaust valve or seat will not seal properly causing blow-by of exhaust gasses on combustion. This will increase the exhaust temperature and reduce engine output
If there is a flaw in the exhaust piping installation or the silencer is fouled, it will lead to high exhaust gas pressure and increase in exhaust temperature of all units
A contaminated exhaust manifold will lead to hindrance in the exhaust gas flow and increase the exhaust temperature
Correct amount of fresh air supply is a must for efficient combustion, if there is reduction in the scavenge air supply, the combustion will be incomplete, which will reduce the engine output
When a ship plies in hotter temperature regions (For e.g near equator or Gulf regions in summers) the atmospheric air sucked by T/C compressor is already at higher temperature. If this air is not cooled properly, it will decrease the performance of the engine
If the scavenge air pressure is low, the amount of air required for combustion to each the cylinder will not be sufficient, which will lead to incomplete combustion
If the cooler controller is set at higher temperature, the temperature of the output air supplied to the engine will be higher, which is not good for engine performance. Similarly, if the setting is on the lower side, the resulting combustion will not be efficient
A contaminated and dirty charge air cooler will not allow seawater to cool the air properly, leading to increase in exhaust temperature
If the sea water temperature is on the higher side, the air cooled by it in the air cooler will be warmer than normal which will lead to high exhaust temperature
The air coolers provided with S.W bypass valve controls the cooling medium i.e seawater. If the bypass is open more than required, then the air supplied to the engine will have higher temperature
Fouled or damaged part of turbocharger will lead to either problem in the passage of exhaust gas or less amount of fresh air supply. These will lead to sudden reduction in the output of the engine
Leaking scavenge air from the inlet pipe to the cylinder will result in less supply of air and incomplete combustion
Wrong tappet clearance will allow inlet/ exhaust valves to open more or less than required. This will result in either inappropriate combustion or the combustion mixture drawing out of the chamber at an earlier stage.