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Marine Auxiliary Diesel Engines
You come on your watch and find that the Chief Engineer has written a note instructing you to change over the generators because the 250 hour routine of the running generator is due. You have a cup of coffee to start your “day" (or night as your watch timing may be). Still sleepy eyed, you take a round, check the various parameters of the running machineries and then go to the generator platform. After checking the level of the oil and opening all the valves you blow through the engine and then close the indicator cocks. Now you give it an air kick and open the fuel… but the engine does not pick up and stops. You try again and the same result. Wide alert, with a thousand dreaded causes floating in your subconscious, you are now awake. So you wear your thinking hat and start troubleshooting.
Sounds familiar! I bet it does. Every marine engineer has faced such a day. In addition to having all tricks up his sleeve, the marine engineer must be good in troubleshooting. It is not worthwhile to open the pump just because there was air in the system and you could not diagnose it correctly.
Marine auxiliary diesel engines are used for the production of electricity on board merchant ships. They are called auxiliary because the main diesel engines are used for the propulsion of the ship. The auxiliary engines are generally four stroke diesel engines.
This article briefly tries to explain the various causes of engine problems. It is hoped it would prove beneficial for junior engineers as well as practicing marine engineers.
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The engine does not start
You have lined up the valves and opened the indicator cocks as you want to do an air blow through. It is to check if any incompressible fluid has leaked into the combustion spaces. You press the starting air button and hear the sound of air escaping but the tachometer does not move. Suspecting that the tachometer wire as broken, you check the flywheel only to find it is not rotating either. What could go wrong? The following are a list of suspected reasons for the fault:
1. The air receiver pressure is low. Please check the pressure of the air receiver and start the compressors.
2. In case the air receiver pressure is satisfactory, check the starting air valve on the air bottle and the valves in the line.
3. Check for any leakage in the starting air piping.
4. The individual air starting valves on the cylinder heads might be stuck or sticky.
5. The air distributor might be faulty and not allowing air into the cylinders. Try rotating the engine with the turning gear and restart.
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The engine turns on air but does not run on fuel
In this case the engine is turning on air, but does not pick up on fuel. You try giving a longer kick and put the fuel lever at a higher notch, but still the generator stops. The starting air pressure is now low and the air low pressure alarm is sounding. All the compressors have started automatically and are running continuously. You are waiting for the pressure to build up and try yet again. Well if such is the case you need to stop and investigate the reasons for the failure to start. They could be one of the following:
1. Fuel does not reach the fuel injection pump because there is air in the system.
2. The fuel oil filters are choked.
3. The fuel line valve is not open.
4. The trips have been not reset after the last stopping.
5. Fuel oil service tank is at low level. Beware the other generator is also going to stop.
6. There is water in the line.
7. The fuel valves are faulty and not giving proper atomization or are choked.
8. The fuel pump timing is wrong.
9. Leaking fuel injection pipes.
10. Seized plungers of the fuel pumps.
11. Fuel rack linkage stuck in position.
12. Seized delivery valves or broken plunger springs in injection pump.
13. The engine is cold.
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During starting the safety valve blows
You are humming a song and go about the generator starting business. You have blown through the generator by air and when you start it again and give the fuel there is a loud sound “TAT TAT TAT." You jump behind the water cooler, thinking it is a crankcase explosion and God have mercy on your soul. Suddenly realization dawns: the safety valve that has lifted. The safety valve lifted because there is an uncontrolled combustion inside the cylinder which can be due to the following:
1. Defective fuel oil valves.
2. Wrong fuel pumps timings.
3. The opening pressure of the safety valve is low caused by a broken spring or a loosened nut.
4. Engine is over cooled.
5. Fuel linkage problems or fuel rack stuck in maximum position.
6. Dripping fuel injectors.
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The reasons of the hunting of the engine or the engine having an unstable speed or rpm. Trouble shooting and the conclusion of the article.
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Hunting of the engine
The engine has started but there is a fluctuation in the RPM. You think that the tachometer cable might have broken but you hear the sounds of acceleration and de-acceleration. The governor linkages are moving like crazy sometimes increasing the RPM and sometimes decreasing it. The auxiliary engines have an Isochronous governor, which means that the engine has to operate at a constant speed after starting. "Iso" means same and "chronus" means speed and thus it is supposed to be a constant speed governor, unlike the main engine governor, which you can run at various speeds. The hunting of the engine can be due to the following reasons:
1. The tachometer or its wire may be out of order. They may be rubbing, or the pin might have turned round and is about to give in. Try lubricating the wire, or changing the tachometer. But if you can hear the hunting by sound do not touch it as it might be working after all.
2. The fuel line may be having air. Yes!, now you remember you had changed the filter but had forgotten to purge the air and prime the system. This is a good time to do it.
3. The engine is cold and leads to uneven combustion. This can be caused by forgetting to put the engine on pre-heating after stopping last time.
4. Faulty governor. The governor oil is supposed to be removed and spaces flushed with clean kerosene, before filling up with oil again. Sometimes the pilot valves have some sludge stuck and hence the hunting.
5. Some fuel injectors getting stuck and firing intermittently. This might happen in engines which are run on Heavy fuel oil. These engines are supposed to be changed over to diesel oil for approximately half an hour before stopping. The half an hour figure is only a rough guide line, practically the purpose is to flush the pipe lines.
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This article tried to discuss in brief the various starting problems that can be encountered in the operation of auxiliary engines. There are a wide variety of problems which can happen and would be discussed in the subsequent articles. It is advised that the remaining articles may also be read to give the reader a clear understanding on the troubleshooting of marine auxiliary diesel engines.
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Diesel Engine Transient Operation: by Constantine .D. Rakopoulos & Evangelos G. Giakoumis
Introduction to Marine Engineering: by D.A. Taylor
Marine Auxiliary Machinery: by H.D. Mc.George
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All Photographs by Mohit Sanguri, Chief Engineer