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Combustion energy

  1. Jan 28, 2015 #1
    hello!

    I tried to find online but no luck

    can you tell me please what is exactly the energy from a combustion? let's say of 1 mole of gasoline

    is it mechanical waves? it is light? is it temperature?

    I need to know the details, how much of it in the various types of energy, and what exactly type of energy

    any hint?

    thanks!
     
  2. jcsd
  3. Jan 28, 2015 #2

    russ_watters

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    Staff: Mentor

    It is thermal energy (heat). Depending on the method of combustion it may be released without light(radiation), but typically a significant fraction is radiation. The rest is released through conduction/convection from the exhaust gases (in a heater) or pressure drop (in a piston).
     
  4. Jan 28, 2015 #3
    Like russ said, what you get from combustion is heat. The fuel is said to posses chemical energy. On combustion, it releases heat or thermal energy. This heat can be converted to various forms based on our requirements.
     
  5. Jan 28, 2015 #4
    but it's not heat that drives a piston, but mechanical waves because of the rapid expansion of air due to the rapid production of many gases
    what is this percentage?

    also, what is the amount/percentage of light energy?
     
  6. Jan 28, 2015 #5
    In the combustion chamber, the temperature of the working fluid goes as high as 2000 °C. This causes the pressure of the gases in the combustion chamber to increase to a great extent. This high pressure pushes down the piston. So basically, heat is converted to mechanical energy.
     
  7. Jan 28, 2015 #6
    The heat of combustion is a precisely defined quantity. It assumes that you start out with 1 mole of the material being combusted (say gasoline) and a stoichiometric quantity of oxygen, both at 25 C and 1 atm, and you end up, after complete reaction, with the reaction products at 25 C and 1 atm in your calorimeter. The heat of combustion is the amount of heat you need to remove from the calorimeter to achieve this final state.

    Chet
     
  8. Jan 28, 2015 #7

    russ_watters

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    Not "waves", just pressure. But yes, that's what I said. Recognize though that pressure energy and thermal energy are related and the release of pressure energy also releases thermal energy. So it is both that are driving the piston (and the thermal energy created most of the pressure energy anyway).

    As I said, the ratio varies, but in a car about 30% is converted in that way.
    Again it varies, but in a car it is pretty small: a fraction of the heat loss in the engine block. Maybe 5-10% of the total.
     
  9. Jan 28, 2015 #8

    russ_watters

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    Staff: Mentor

    Thats a good way to put it: chemical energy is converted to heat a
     
    Last edited by a moderator: Jan 28, 2015
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