Dave,
If you burn 10 g/hr, and are returning 15 g/hr to the tanks, that is 15*6 = 90 #/hr of gasoline, with a specific heat of ~.7Btu/#, that means you can transfer 90* 0.7 = 63 Btu/hr/degF rise in gasoline temperature. Your coolant flow is probably about 25 gallons/minute, = 25*60 = 1500 gallons/hour = ~1500*8 = 12000 #/hour. For a 10 degree rise in gasoline temperature you would get a 630/12000 = 0.0525 deg F drop in coolant temperature.  Doesn't seem worth it.
 
* note: I used rounded figures for densities and flow rates and heat capacities. The fact remains that the flow mismatch makes this not do much.
Bill Schertz
KIS Cruiser # 4045

    ----- Original Message -----
    *From:* DaveLeonard <mailto:daveleonard@cox.net>
    *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
    *Sent:* Sunday, February 06, 2005 11:46 PM
    *Subject:* [FlyRotary] Heating the Fuel

    In anticipation of the new turbo, I am considering ways to improve
    coolant cooling.  Besides the obvious more air, more ducting, more
    radiator; I have been again toying with the idea of a heat
    exchanger.  This time coolant to fuel.  The plan would be to use a
    typical oil/water exchanger but use fuel instead of oil.  I would
    use the fuel on the way back to the tank, and the coolant after it
    has already been cooled by the radiator.  The fuel would then go
    back to the nice metal tank of the RV.
         I am looking for input on the implications of heating the fuel.  I
    expect it would reach max temps of about 190 (usually a
    little cooler) but quickly cool once in the tank.  Can the fuel
    tolerate that temp without vaporizing?  It will probably expand in
    the tank but I don't expect that will occur faster than it is used
    up.  I have no guess as to what temp will become steady state for
    the fuel pumped out of the tank.  My guess is that it will not be
    much warmer than normal, but a slight increase in temp may help
    with vaporization.
         The last question is how much will it cool the coolant.  My hope
    is about 10 deg but I doubt it will be quite that much.  I know
    others have considered using the fuel to cool (Tracy) and I would
    appreciate your thoughts.
         Dave Leonard