This is a chart of adiabatic flame temperatures for common fuels. The adiabatic flame temperature is the theoretical temperature of a flame, assuming complete combustion and no work done or heat transfer to or from the environment.
Adiabatic Flame Temperature at Constant Pressure
Note most fuels burn in air around 1950 °C or 3500 °F. This is because common fuels are all organic compounds that burn breaking C-H, C-C, and O2 bonds to form CO2 and H2O molecules. Fuels with carbon-nitrogen triple bonds burn much hotter. Metals burn in oxygen with flame temperatures hotter than those of most fuels. Naturally, flame temperatures are higher when fuels burn in pure oxygen as opposed to air. Also, note the table lists theoretical flame temperatures, produced by complete combustion with no heat loss. Real-world flames burn a bit lower. Temperature also depends on the part of the flame measured.
Constant Volume vs Constant Pressure
Adiabatic combustion occurs at either constant volume or at constant pressure. Most combustion in everyday life occurs at constant pressure because air or oxygen freely flows into the flame, while combustion products flow away from it. A campfire is an example of constant pressure combustion. Constant volume combustion, on the other hand, occurs in a confined space. Combustion inside the cylinder of an engine is an example of a constant volume situation. Adiabatic flame temperatures at constant volume are higher than those at constant pressure. This is because some energy goes into changing the volume at constant pressure. For example, the adiabatic flame temperature for methane is around 2326 K at constant volume and 2236 K at constant pressure.
- Babrauskas, Vytenis (2006-02-25). “Temperatures in flames and fires“. Fire Science and Technology Inc.
- Haynes, W. M. (2015) CRC Handbook of Chemistry and Physics (96th ed.). CRC Press. ISBN 978-1482260960.
- Kuo, K. K. (1986). Principles of Combustion. John Wiley & Sons, New York.