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Why don't we monitor crankcase temperature?

in 912 / 914 Technical Questions 7 years ago

  • Re: Why don't we monitor crankcase temperature?

    by » 7 years ago

    I'm presently trying to figure out the cooling capacity of a radiator, not that I actually NEED that to live my life, but rather as personal education on the subject. ;-)
    From the installation manual, there is a total of 1,5 l (0.4 gal (US) of coolant in our airplanes.
    If I assume that the pump circulates that quantity 3 times during one minute, that's 1.2 gal. per minute. I also assume that the water is at around 212 deg., and that the IN-OUT temp. differential in the radiator is 1 degree.
    According to a calculator on the internet, that would give a cooling capacity of 1000 BTU/hour.
    That doesn't seem very high... At home, my air conditioning unit is a 15000BTU, and the amount of cold air it can produce is not, hmm, impressive. (Of course, the in-out temp-diff is much higher than in our airplane calculations here.)
    So maybe that 1000 BTU/Hr is not bad at all, but I have difficulty visualizing how good (or bad) it is.
    Any takers?
      
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  • Re: Why don't we monitor crankcase temperature?

    by » 7 years ago

    Unfortunately...
    it is a lot more complicated than that and much is counter intuitive. But have fun and education is all good. However I was told that a good rule of thumb is that minimum coolant flowrate needs to be about 1l/hp (I know mixing units horrible) so that is about 100L/min for a 100 hp engine, or 26 gal/min for those of you from behind the hamburger curtain.

    Also ICE engines are at best 30% efficient and generally they throw away 1/3 in the exhaust 1/3 in the radiator and 1/3 in the shaft. So you need to dump 100hp out the radiator (75kw) or god only knows what a BTU is...
      
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  • Re: Why don't we monitor crankcase temperature?

    by » 7 years ago

    Wow! 100L per minute is enormous, almost 2 L per second!
    No way the little pump on the 912 can do that.

    That 100HP worth of heat in the radiator is 75KW, and 75 KW/Hr is also equivalent to (gulp) 256,000 BTU!

    I'll have to think this further. I think I'll get my old books out.
    Meanwhile, I'll consider installing a spraybar system in front of my radiator, LOL

    Cheers
      
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  • Re: Why don't we monitor crankcase temperature?

    by » 7 years ago

    LOL indeed,
    the amazing thing is that it all works so well. Wonderful what 100 year+ of development will get you...
      
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  • Re: Why don't we monitor crankcase temperature?

    by » 7 years ago

    It is always useful to refer to the Installation Manual for the 912ULS engine. Chapter 75-00-00

    Flow Rate = ~60l/min = ~16gal/min @5800rpm
    Heat Flow = 28kW/sec = 27BTU/sec = 95,000 BTU/hour. (~8 Tons)
    Recommended Radiator area = ~500cm^2 = ~80in^2

    The installation Manual assumes 0.4 gallons for the engine and small hoses.
    The radiator and the 25mm hoses are not included.
    Over-assuming 1 gallon of total coolant gives under 4 seconds to circulate the entire volume.
    1 gal = 8lbs ... 27btu/8lbs = ~3.5°F/sec times 4 seconds = ~14°F Temp differential in the circuit.

    ~ ~ ~ A Side Bar.

    BTU = 1055 Joules = ~0.95kW
    Historically, it is the amount of heat required to raise one pound of water one degree Fahrenheit.

    One TON of Water Ice will absorb ~12,000BTUs as it melts.

    Back in the 1800's, a 1 Ton mechanical Refrigeration unit would be installed in place of a 1 Ton "Ice Box".
    People were familiar with Tons of Ice and the Power of a Horse in those days. BTUs and Ft-Lbs /sec fell on deaf ears.

    A whole house air conditioner might be a 15 Ton unit, not 15,000 BTU.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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