Thermal Energy Released by Combustion
The full value of heat combustion is not realized in real practice for two reasons:
• The latent heat of vaporization of the water produced by combustion is not obtainable.
• Dissociation becomes significant at temperatures above 1650oC.
As much as the heating value of hydrogen is 121,000 kJ/kg, whereas that of carbon is 32,800 kJ/kg, the higher the proportion of hydrogen in the fuel, the high its heating value.
Though, from practical considerations, the FAR ratio is more significant than the above factors, under favorable lean-mixture circumstances, practically all the thermal energy ideally obtainable from combustion can be acquired. When the FAR is richer than stoichiometric, the fuel cannot be burned entirely.