First, and for the subject in hand, let's define combustion as the air-burning (oxidation) of a gas, liquid, or solid, evolving heat and often light.
Secondly, let's define what is a flame. In technical parlance, a flame is defined as the totality of the gaseous mass in a combustion reaction, disregarding its degree of luminosity.
Adiabatic flame temperature (AFT), as its name implies, is the
theoretical highest (perfect and complete) combustion temperature that can be achieved in a space surrounded by heat-impermeable walls, ie
adiabatic combustion, carried out with the minimum (stoichiometrical) amount of air. It is a "characteristic" of each and every fuel.
If air were supplied in excess, the adiabatic temperature would be reduced by the heat being absorbed by the xs air.
Some published values, in
oC:
CO, 2,452
H
2, 2,210
Methane, 2,065
Ethane, 2,105
Propane, 2,115
Butane, 2,132
Ethylene, 2,343
Propylene, 2,255
Butylene, 2,221
Acetylene, 2,632
In actual practice, at temperatures [≥]1500
oC there are already appreciable reactions of endothermic dissociation of H
2O and CO
2 that bridle any further temperature rise. The decomposition products actually burn later on in lower-temperature zones.
Beside those effects, in industrial fired heaters, the combustion is never adiabatic, since a part of the liberated heat is transmitted in
status nascendi by radiation to the cooler heat-absorbing sections of the heating chamber, and a small part is even lost by conduction through the chamber walls.
Besides, air is not always available to complete the combustion process at one go, and is frequently supplied in primary and secondary doses, a fact that adds to the reduction of the maximum attainable temperature.
Therefore
flame temperatures, or
combustion temperatures, would be the actual thermometric expression of the complex thermal balance in a particular combustion chamber.
Because of the varying spacial effects taking place in a real combustion chamber there is no exactly-defined
flame temperature.
A more commonly-accepted definition would be the
final key-temperature at which the combustion products actually
leave the combustion space.
This extended post is incomplete, but is meant to give an idea on the subject in hand.
![[smile] [smile] [smile]](/data/assets/smilies/smile.gif)