Minimum area and speed of air intake

Discussion in 'Boat Design' started by ldigas, Jan 3, 2012.

  1. ldigas
    Joined: Feb 2011
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    Location: Zagreb, Croatia

    ldigas Senior Member

    For an engine of 324kW and diesel generator of 20kW air requirement according to specs comes up to about 30m3/min. (0.5m3/sec).

    Are there some recommended values of areas of air vents and maximum speeds of air inflow?

    I have two air vents, each 0.05m2 ... which comes up to air speed of 5m/s which seems a bit too much, but I have no "feeling" for those values. Is it too much?

    All empirical formulas and maybe someone's personal experience would be appreciated.
     
  2. Boatbuilder RPR

    Boatbuilder RPR Previous Member

    Your intake area is insufficient and that will remain so, no matter the airspeed.

    500 hp / 370kW require some 30m³ of combustible air per minute and a minimum of 0,2 m² diam. air intake.

    Thats a proven rule of thumb, not a formula.

    In a cramped engine compartement, under the blue sky of the Red Sea, with several other utilities running, you will notice what "minimum" means! It means: not much power left, due to overheated engine room. And after a year or two you can see it on the bills.

    All major engine manufacturers provide substantial data sheets where you can interpolate the truth of that "laymans calculation".

    Regards
    RPR
     
  3. ldigas
    Joined: Feb 2011
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    Location: Zagreb, Croatia

    ldigas Senior Member

    The dealers (who sold the engine and all components) had no stand on the minimum air vent area nor speed, when I asked them (not an unknown "engine manufacturer", either).

    You say, "minimum" ... does that "minimum" mean it is enough, or should it be increased to let's say, 0.4m2. I don't really have much "manouvering space" regarding that, but it's better to think of something while it is on paper, then later while in build.
     
  4. Boatbuilder RPR

    Boatbuilder RPR Previous Member

    To double the space is not sensible. Even 0,2 m² are a big hole in a boat! But I recommend at least a safety margin of 30% over the recommendations or requirements.

    If the dealer is unable to provide such data, kick his ***, get your money back and find a pro!
    What do you expect is his first service (warranty) worth???

    RPR

    maybe I have the data, which engine?
     
  5. ldigas
    Joined: Feb 2011
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    Location: Zagreb, Croatia

    ldigas Senior Member

    It is not my engine, I'm doing the project for the owner (who already bought the engine, it's been delivered and so on ...).
    Apart from that, I have all the data on the engine air requirement, just not these other things.

    Appreciate the offer, though! :)
     
  6. Boatbuilder RPR

    Boatbuilder RPR Previous Member

    Hmm,

    Name, Make, Model, year would do, I don´t need the name of the owners daughter.
     
  7. ldigas
    Joined: Feb 2011
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    Location: Zagreb, Croatia

    ldigas Senior Member


    Okey, okey ... fair enough :))) LOL :)))

    Yanmar 6LY3-STP, the year is either 2010 or 2011. It was delivered, oh I don't know, two months ago or so.
     
  8. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    The less resistance to intake airflow, the more max output and the better the efficiency at all throttle settings. The larger the better. There is no real minimum except that it limits max output, i.e. you will not get full rated power with a restricted air supply. it is just like not having the throttle open all the way.

    You must also make sure there is adequate ventilation in the engine compartment apart from air supply. Again the bigger the better.

    Always provide the maximum that is practical.
     

  9. Boatbuilder RPR

    Boatbuilder RPR Previous Member

    In all respect, may I contradict?

    It is not all power, it is sufficient cooling as the prior task. We can skimp on 100 hp in most cases, but we cannot skimp on engine room cooling if we want to keep our equipment functional.

    so, please don´t talk the people into risky "recalculations". The "minimum" requirements provided by engine manufacturers are really nothing but that.

    >"Yanmar 6LY3-STP, the year is either 2010 or 2011. It was delivered, oh I don't know, two months ago or so"<

    Shitty choice.

    And they do not deliver proper data even for builders. Hence I would not install them if given for free.

    RPR
     
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