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  • Cooling requirements and fuel efficiency

    Discussion in 'Calculations' started by davies, May 29, 2012.

    1. davies

      davies New Member

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      Hi,
      Does anyone here know how to calculate cooling requirements for 4cylinder IC engines and how the fuel efficiency is calculated?

      Regards
      Davies
       
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    3. Erich

      Erich Well-Known Member

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      Fuel efficiency is Energy out/Energy content of the fuel burned.

      The load on the cooling system is

      Energy content in fuel burned - Power output- energy going out in the exhaust stream.
       
    4. mhjones12

      mhjones12 Well-Known Member

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      The thermal energy lost is your cooling requirement. If you have a 100hp engine, with a thermal efficiency of, say, 20% (a reasonable estimate), then your thermal power lost (i.e. cooling requirement) would be 80hp = 60kW = 3400Btu/min. This is of course operating at maximum power. I don't know if typical engines are designed to sustain operation at max power, but it at least gives you an upper limit.

      The theoretical maximum thermal efficiency is based on the compression ratio (see http://en.wikipedia.org/wiki/Otto_cycle). If you want to measure the efficiency of your engine, you would need a dynamometer (dyno). Load the engine at a specific RPM, measure the fuel intake, and efficiency is power in (energy in fuel/time) over power out (measured by the dyno). The efficiency in general will change as a function of power output and RPM.

      If the fuel efficiency you are looking for is a miles per gallon (MPG), then you would have to look up the standardized tests. I don't know what organizations produce these, but for the US I would check ASME, SAE, or perhaps fueleconomy.gov.
       

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