Combustion Calculations
Fundamentals of Combustion and its Modeling
- Refer to the following useful articles on the basics of combustion and its CFD modeling
- Basic combustion is discussed in premixed and non-premixed flames
- CFD Modeling of Turbulent combustion
Calculation of Mass flow rate of air and fuel
- In the following table, the mass flow rate of actual air can be calculated based on given fuel composition and excess air conditions
- Key input and out for combustion calculate
- Enter Inlet temperature (F), excess air (%), fuel composition of natural gas ( % mole fraction) and the fuel firing rate (10∧6 Btu/hr) of the burner
- The output is given for the mass flow rate of air and air in pounds per hour (lb/hour), and the enthalpy of flue gases
Combustion Calculation for Gas Firing
Inputs
- 12-component fuel gas table (CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, H₂, CO, CO₂, N₂, H₂S, C₂H₄) with mol % entry
- Excess air %, air preheat temperature, fuel temperature, ambient temperature
- Humidity of combustion air
- Furnace absorbed duty (MW), thermal efficiency, stack temperature, radiation loss %
Calculations
| Parameter | Method |
|---|---|
| HHV / LHV | Mole-fraction weighted sum from component database |
| Stoichiometric Air | O₂ balance per combustion reaction |
| Adiabatic Flame Temperature | Enthalpy balance (LHV + sensible air heat) solved against flue gas sensible enthalpy via bisection; Cp from Smith–Van Ness polynomial coefficients |
| Furnace Exit Temperature (FET) | Heat balance — flue gas enthalpy after subtracting absorbed duty + radiation losses |
| Flue Gas Composition | CO₂, H₂O, excess O₂, N₂, SO₂ per mole balance |
| Heat Balance | Fired duty, absorbed duty, stack loss, radiation loss breakdown in MW and % |