Air Coolers and Cleaning
Engines are turbocharged to increase the amount of air entering the engine and allow more fuel to be injected. As the turbocharger is compressing the air, an increase in charge air temperature will occur. This will reduce the density of the air entering the engine. To reduce this effect the air is cooled which is the function of charge air cooler. There is also the added benefit that cooling the air reduces the engine thermal road.
Air coolers should be regularly drained as large quantities of water can be removed from the air during the cooling process. In tropical conditions, where the air is very humid, as much as 1000kg of water per hour can be produced.
Maintenance consists of cleaning the air and water sides of the tubes and inspecting the anodes in the water headers. The air side will gradually become fouled with oily deposits, which can be monitored by measuring the air differential pressure. Engine manufacturers usually have the limit for the differential pressure indicating when the cooler should be cleaned.
The air side can be cleaned on a regular basis. While the engine is in service, small dosing pots can be filled with diluted air cooler cleaner. Only special cleaners that are designed for this must be used.
Eventually the air cooler will require more thorough cleaning. On large engines there may be a circulating system for cleaning the air coolers. For smaller coolers these may have to be removed and soaked in a special solvent or cleaned ultrasonically. A typical air cooler cleaning system is shown in figure below.
Air Cooler Cleaning System
The air cooler cleaner can be circulated in undiluted form and should be circulated for at least 12 hours, depending upon the degree of fouling. The air cooler should be hosed with clean freshwater after cleaning.
On the water side the tubes should be cleaned by brushing through with special tube brushes. This is ideal for removing soft deposits and slime, but if the tubes have scale or hard marine growth inside, it may require cleaning with a high pressure hose or de-scalant.
Leaking tubes can be a problem with air coolers and usually appears in the form of excessive water at the drains. It is possible to find the tube leak and plug it while the engine is running. The procedure is as follows:
- Reduce engine speed. The air temperature after the turbocharger must be less than 70 degree Celsius
- Isolate the cooling water and remove the cooler headers
- Completely cover the tubes at one end of the cooler with a thick joint sheet. This can be held in place by end cover.
- Brush soapy water over the other ends of the tubes. Leaking tubes will produce bubbles, which should be marked.
- Plug leaking tubes with tapered copper or wooden plugs.
IF A TUBE IS SUSPECT FIRST MAKE SURE THAT THE DRAIN WATER IS SEAWATER, AS IT MAY BE NOTHING MORE THAN THE CONDENSATE FROM THE CHARGE AIR. LEAKING LINER SEALS CAN ALSO BE A SOURCE OF WATER, SO CHECK EXPANSION TANK LEVEL IS NOT FALLING.
Troubleshooting
(click column header to sort results)
PROBLEM
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CAUSE
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|---|---|---|
Charge air temperature too high
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High engine room temperature
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High sea water temperature
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Cooling system out of balance (low low)
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Fouled air side of tubes
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Fouled water side of the tubes
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Charge air temperature too low
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Defective cooler controller
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Sea water temperature too low
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High pressure drop on air side
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Air cooler fins fouled
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Defective pressure gauge
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High pressure drop on water side
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Fouled tubes on water side
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High coolant flow
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Defective pressure gauge
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External water leakage
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Leaking joint on tube plate or pipe line connection
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Internal water leakage
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Leakage between tube and tube plate
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Holed tube
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