How to use this calculator
Pick a fuel (or enter CxHyOz), then the air as percent theoretical air or percent excess air. With less than 100% theoretical air some carbon leaves as CO. Enter the product pressure for the dew point.
Formulas
Worked example
Propane, C₃H₈, with theoretical air
- ath = 3 + 8/4 = 5 kmol O₂, so the air is 5 × 4.76 = 23.8 kmol per kmol fuel.
- AF = 23.8 × 28.97/44.10 = 15.6 kg air/kg fuel.
- Products: 3 CO₂ + 4 H₂O + 18.8 N₂.
- HHV = [3(393 520) + 4(285 830) − 103 850]/44.10 = 50 340 kJ/kg; the LHV (water as vapor) is 46 350 kJ/kg.
Frequently asked questions
What is the difference between HHV and LHV?
The higher heating value counts the heat released when the water in the products condenses; the lower heating value leaves the water as vapor. The difference is the water’s latent heat.
Why does the dew point of the products matter?
If exhaust surfaces fall below it, water condenses and, with sulfur in the fuel, forms corrosive acid. It is the saturation temperature at the water vapor partial pressure.
What happens with less than 100% theoretical air?
There is not enough oxygen to burn all the carbon to CO₂. The calculator assumes all hydrogen burns to water and the carbon that can’t reach CO₂ leaves as CO.