Adiabatic Flame Temperature: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Heat capacities for gases increase with temperature.
  • Heat capacity equations are only applicable over a specified temperature range, and thus more than one heat capacity equation may be needed to cover the large temperature range needed for adiabatic flame temperature calculations. Heat capacities equations used outside their temperature range can be very inaccurate; they may even give negative heat capacities. 
  • The adiabatic flame temperature is significantly lower with air instead of O2 as the oxidizer. Increasing the percent of excess air further decreases the flame temperature.
  • For the high adiabatic flame temperatures obtained with O2 as the oxidizer, dissociation reactions that form CO, O2, and H2 must be taken into account. These endothermic reactions have a large effect, and flame temperatures calculated without considering them can be in error by more than 1500 K. 
From studying this module, you should now be able to:
  • Calculate the adiabatic flame temperature when a fuel burns completely.
  • Understand how using oxygen, air, or excess air affects the adiabatic temperature.
  • Explain what additional reactions need to be considered when using pure O2 to burn a fuel. 

Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder