kool keel diesel engine

Discussion in 'Diesel Engines' started by carlos bairo, Sep 28, 2010.

  1. TeddyDiver
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    TeddyDiver Gollywobbler

    You overcome the "precise calc" (and it's quite simple with tube) with a thermostate better, don't need another pump for the other circ. Then you need anyway means to warm the hotel water. So why complicate things?
     
  2. singleprop
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    singleprop Junior Member

    Thanks for your reply...Let me try to explain it:

    The keel cooling system is using an internal circulation pump on the engine -and the keel cooling water is normally running straight through the engine and back in the keel cooling circuit. A correctly sized keel cooler will lower the temperature about 20 degrees. Normally it takes about 5 mins to get the water up to this temperature.

    If the (too large) keel cooler is too effective the return water going to the engine will have approximately the same temperature as the sea water (so reduced by much more than 20 degrees. This means that the engine will always be running too cold.

    If the cold keel cooling water instead is run straight through the heat exchanger (using the raw water pump to circulate the keel cooler water) the thermostat on the heat exchanger will control the amount of cooling flow (circulated by the internal circulation pump) through the heat exchanger. Since the temperature of the keel cooling water is cold and stable, the themostat will now be operating in a very small range and therefore reduce cycling and thermal schoks to the engine...

    With this set-up it doesn't matter if your keel cooler is too big since the heat exchanger will.

    I know there are some draw backs like having to use 2 pumps, but if the engine is running at a better temperature then I think it is worth the effort.

    Is there another way of keeping up the engine temperature with too large a keel cooler?
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    No becouse you can install a thermostate into this circuit directly.. The keel cooler is the heat exhanger (comparable to radiator in car engines).
     
  4. singleprop
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    singleprop Junior Member

    I might not understand you correctly (or maybe not understanding keel cooling at all):confused:
    Since there is only one circuit: through the engine - to the keel cooler - and back to the engine - a thermostat cannot be used. Where would it divert the fluid to?

    see this link for better visualization (the last two drawings): http://www.depcopump.com/catalog107/81.pdf

    Since there is no thermostat, the keel coolers would normally have to be designed very carefully to avoid the over cooling of the engine.

    Maybe you can explain better where such a thermostat should be or if your are using more than one circuit?
     
  5. michael pierzga
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    michael pierzga Senior Member

    Ahoy Carlos !! would be better if you described the vessel. A Keel cooler is a radiator, like on a car. Closed system, header tank... very simple... Thousands of simple motorized skiffs in the world, with power plants taken directly from agricultural machinery. Ive seen them use the radiator , mufflers, transmission.... all the bits. A challenge for a keel cooled, or radiator cooled or air cooled, engine in a boat is the exhaust and its noise and heat.

    many solutions to the problem on simple boats. Is your boat a simple open boat ? Seek out designer Robb White, vessel Rescue Minor....don't remember if it was keel cooled but it was a marinized tractor engine with innovative strategies employed in its adaptation to marine use.. Boatdesign net readers will know who Robb White was and may be able to direct you to his writings..
     
  6. apex1

    apex1 Guest

    Not large enough the surface of the average keel.*

    And Teddy was right (of course), on the thermostat issue.

    Regards
    Richard
    edit: have forgotten the numbers

    * to get rid of the heat, a 100kW motor requires 2m² of metal surface in Aluminium and 6m² in steel. Paint that, and you can double the numbers. Valid at 20°C water temp and 8kn boatspeed. Operate in the Carribbean double the numbers, operate at average sailing speed of 4-5 kn, double the numbers.
    So, figure out what you would need to make the keel your cooler! A tanker.
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

    Roll down the page a bit.
    http://www.wallothnesch.com/e/cool/coole21.htm
    Thermostate is inside. One inlett and two outlets. One outlet back to engine and other to keel cooler. Like in any other properly done setup wheather the cooling is done with a radiator or whatever..
     
  8. singleprop
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    singleprop Junior Member

    http://www.johnson-pump.com/JPMarine/PDF_docs/MarineCatalogue-US.pdf see page 39

    Thanks Teddy.

    So we assume that the keel cooler is capable of cooling the return water down to seawater temperature before entering the engine (no heat build-up in the cooling fluid):

    Would the cold keel cooling water create cycling between open and closed and thereby create a permanent warm-up/cool down cycle of the engine (where the valve is closed during warm-up and open when at correct operating temperature), thereby creating expansion stress on the engine and thermostat?

    Or does the thermostat open partially and stay there if there are no load changes on the engine?

    see the 2 drawings in the link (page 39). By following the direct cooling schematic (but replaced with direct keel cooling-not raw water) the thermostat is closed when the engine is cold and the pressure valve is open. When the engine is warm the thermostat is partially or fully open and the pressure valve would be partially or fully closed.
     
  9. apex1

    apex1 Guest

    Of course does the thermostat open partially when required. Same in your home.

    Richard
     
  10. Landlubber
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    Landlubber Senior Member

    Pic of the system

    This may help explain the deal
     

    Attached Files:

  11. singleprop
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    singleprop Junior Member

    Richard, the assumption in the previous posts is that the keel cooler is so efficient (way too big) that the cooling water has reached the sea water temperature when it returns to the engine.
    I am sure there are many different types of thermostats in different applications but I assume that your reply is related to marine engines and that most normal marine engines have this type of thermostats. Thanks.
     
  12. apex1

    apex1 Guest

    The opposite Mate!

    Assuming you are still thinking your keel would be the cooler, you don´t have to worry about a thermostat. It does not work. See my post above.

    Richard
     
  13. singleprop
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    singleprop Junior Member

    Apex, Do you know where this thumb rule comes from, its close to Dave Gerr 's rule, he uses steel, 29.4 degree water, 8 kts, and comes up with 0.050m2 /kW., but that include allowance for surface paint. So 100 kW would be 5 m2, all incuded according to Gerr.

    Back to my last post: If a cooler is too efficient would it result in the thermostat cycling and creating thermal stresses?
     
  14. apex1

    apex1 Guest

    When you install the right thermostat, your cooler could have square miles of surface.
    But surface is where the shoe pinches.

    Your 5m² "all included" are not really in accordance with my comment, are they?

    No, I cannot recall where the rule comes from, but I can tell you for sure that reducing the surface to the theoretical minimum will cost you much, much money.
    A single coat of paint one could nearly neglect in the calculations. The average coating one has to apply on a steel keel not.
    So, in Maine Gerrs figures work (on bare tubing), in tropical waters and on a painted keel they do not.

    Richard
     

  15. singleprop
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    singleprop Junior Member

    I think I know what you are talking about - area. I have made the assumption that area is WAY WAY WAY bigger than required (as mentioned several times) - resulting in sea water temperature in the return to the engine...

    And you are saying that the thermostat will open and close slowly and therefore will NOT result in thermal stresses of either the engine or the thermostat.

    Have I understood you correct this time?
     
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