Marine diesel engine is the main equipment installed on a ship thus monitoring of engines should be a very important job on routine maintenance.Exhaust gas temperature,it is also referred to as EGT,is the critical operating parameter that should be took a close eyes into while the main engine is on normal operation,it is a common problem that the exhaust gas has had an excessive high temperature,which will finally lead to shorter engine life.The causes that result in an EGT failure are many but can fall into these categories listed below.
1.Leakage in Exhaust valves
A leaking exhaust valve can lead to a decrease in oil & oxygen mixture inside the cylinder,which will eventually result in a reduction in the mass of air and after combustion occurs in the exhaust pipes.
2.injection timing is not properly set
Too less fuel injection advanced angle will delay the injections of fuel oil inside of the cylinders,which will cause the rest of the oil burns inside of the exhaust pipe.
3.Exhaust Valve Timing is not set properly
Unburned oil will step to the exhaust pipe if the exhaust valve opens way too early.
4.Bad oil atomization
A bad atomizer will result in inefficient burning of fuel oil gas,which will lead to after-burning once it goes into the exhaust pipe.
5.Installation of fuel oil atomizer is bad
Gaskets of atomizer is not installed correctly,a thick gasket would most likely results in an inappropriate position of fuel spray nozzle.
6.Compression pressure inappropriate
1.Gaskets between cylinders and cylinder liners are too thick,resulting in an reduction in compression pressure due to increased cylinder volume,the delay of ignition will result in the post burning.
2.Excessive wear of cylinder ring would most likely cause a reduction in compression prussure because the gas will enter into the crank case.After burning happens when unburned oil goes into the exhaust pipe.
7.Turbocharger faults
Bearing of turbocharger damaged leading to a reduction in rotation speed,the amount of air enters into the combustion chamber will be less than normal thus resulting in the unburned fuel oil goes into the exhaust pipe.There are many causes of a high prussure drop inside of the turbocharger such as a dirty air filter,carbon deposits on the surfaces of nozzle ring and waste gas impeller.
8.Fuel injector failure
Secondary injection may result from a failure fuel injector,and will result in the after burning of an diesel engine.It results in the reduction of power one cylinder generated whereas the rest cylinders have a high load.
9.Charge air cooler failure
I’ve already discussed something about the marine diesel engine charge air cooler ,if the pipes for fresh water fouling inside of the charge air cooler,it may result in the insufficient heat exchange which will cause charged air to warm up.As a result of that,the exhaust gas will also has a higher temp.Clogged air channel inside of the charge air cooler will cause the amount of air charged into the cylinders to decrease,insufficient burning is the main reason for high exhaust gas temperature.Turbocharger and charge air cooler are two parts of the diesel engines that are most likely result in a high EGT,high exhaust gas temperature would happen if the charge air cooler is clogged,sometimes it would even make the whole ship stop running.
10.Controllable pitch propeller ship with shaft generator or offshore drilling unit circumstances
It is normal for this kind of ship when diesel engine is either in idle load or low load conditions,the total amount of exhaust gas is too less to drive the turbocharger efficiently,charged air is not sufficient for the oil mist waiting for burn,that will also cause the exhaust gas has an excessive high temperature.When the engine load reach to its normal level it will draw in much more fresh air thus the black smoke and high EGT will be eliminated.
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