Understanding Combustion Energy: Types, Distribution, and Details

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    Combustion Energy
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Discussion Overview

The discussion revolves around the nature of energy produced from the combustion of gasoline, specifically focusing on the types of energy involved, their distribution, and the mechanisms by which they drive processes such as piston movement in engines. Participants explore various forms of energy, including thermal, mechanical, and light energy, as well as the relationships between them.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that combustion primarily produces thermal energy (heat), which can be converted into other forms based on requirements.
  • Others argue that mechanical waves, resulting from the rapid expansion of gases, are responsible for driving a piston, questioning the role of heat in this process.
  • One participant describes the heat of combustion as a precisely defined quantity, contingent on specific conditions of temperature and pressure.
  • There is a discussion about the relationship between pressure energy and thermal energy, with some suggesting that both contribute to piston movement.
  • Participants inquire about the percentage of energy converted into mechanical work and light energy during combustion, with estimates varying based on context.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of energy conversion in combustion, particularly regarding the roles of heat and mechanical waves. There is no consensus on the exact percentages of energy types produced or their contributions to engine function.

Contextual Notes

Participants reference specific conditions for measuring the heat of combustion, but there are unresolved questions regarding the exact percentages of energy types and their definitions. The discussion reflects a range of assumptions and interpretations about energy conversion processes.

physior
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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!
 
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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).
 
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.
 
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?
 
physior said:
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?
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.
 
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
 
physior said:
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?
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.
also, what is the amount/percentage of light energy?
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.
 
siddharth23 said:
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.
Thats a good way to put it: chemical energy is converted to heat a
 
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