Adiabatic Flame Temperature
Estimate the adiabatic flame temperature, T_ad = T_initial + LHV ÷ (m × cp), from the lower heating value LHV (kJ/kg fuel), the mass of combustion products per kg fuel m, the average specific heat of the gases cp (kJ/kg·K) and the initial temperature. The result, in °C, is the maximum theoretical temperature the gases would reach if all the combustion energy heated the products, with no heat loss. It is an upper bound: real flames are cooler (radiation losses, dissociation, excess air). It sets the thermal severity on materials and NOx formation. Enter the LHV, the gas mass, the cp and the initial temperature.
Result
—
Adiabatic flame temperature
The adiabatic flame temperature is the maximum theoretical temperature that the gases from a combustion would reach if all the released energy went into heating them, with no heat loss to the surroundings (hence 'adiabatic'). An energy-balance estimate is T_ad = T_initial + LHV ÷ (m × cp), where LHV is the lower heating value (the energy released per kg of fuel), m is the mass of combustion products generated per kg of fuel (fuel + air), and cp is the mean specific heat of those hot gases. In essence: all the chemical energy (LHV) turns into sensible heat that raises the temperature of the gas mass. It works as an important upper bound: real flames always run cooler than the adiabatic temperature, for several reasons — radiation and conduction losses to the walls; excess air (the extra air soaks up heat without releasing energy, lowering the temperature, which is why lean burners run cooler); and, at very high temperatures (>1800 °C), the dissociation of the molecules (CO₂ and H₂O break apart, absorbing energy, a thermodynamic limit). Typical values: methane in air reaches ~1950 °C of adiabatic temperature (stoichiometric); in pure oxygen, far more (~2800 °C, used in cutting torches). The adiabatic flame temperature is crucial, since it sets the thermal severity that materials and refractory linings must withstand, the heat transfer achievable in furnaces, and — critically — the formation of NOx (nitrogen oxides), which climbs exponentially above roughly 1500 °C; lowering the flame temperature (with excess air, flue gas recirculation or staged combustion) is the main NOx control strategy. Enter the LHV, the gas mass, the cp and the initial temperature.
Related Tools
Boiler Efficiency
Calculate the thermal efficiency of a boiler by the direct method, η = (m_steam × Δh) ÷ (m_fuel × LHV) × 100%, comparing the useful heat absorbed by the water/steam (steam flow × enthalpy gain) with the energy released by burning the fuel (fuel flow × lower heating value). The result, in %, shows how much fuel energy actually reached the steam; the rest is lost in flue gases, blowdown, radiation and unburnt fuel. Well-run industrial boilers reach 80–90%. Enter the steam flow, enthalpy gain, fuel flow and LHV.
CO₂ Volume Produced
Calculate the CO₂ volume produced in complete combustion of a hydrocarbon C_xH_y, V_CO₂ = x × 22.4 ÷ M, from the number of carbon atoms x and the fuel molar mass M (g/mol). The result, in Nm³ of CO₂ per kg of fuel, is the carbon dioxide generated by complete burning — information for emission inventories, exhaust system sizing and gas analysis. Each carbon atom in the fuel becomes one CO₂ molecule. Methane produces ~1.4 Nm³/kg. Fuels with more carbon per unit mass (coal, heavy oils) produce more CO₂. Enter x and the fuel molar mass.
Karlovitz Number
Computes the Karlovitz number of a turbulent premixed flame, Ka = (u'/S_L)^1.5 · (ℓ_t/δ_L)^−0.5, comparing the chemical time of the flame front with the turnover time of the smallest eddies (Kolmogorov scale). Ka below 1 means the laminar flame structure survives the turbulence (wrinkled and corrugated regimes); between 1 and 100 eddies penetrate the preheat zone and thicken the flame; above 100 the reaction zone itself is broken. Together with the Damköhler number it forms the axes of the Borghi diagram, used to pick combustion models in CFD. Peters' form is adopted; integral scale and flame thickness must share the same unit. Enter the velocity fluctuation, the laminar flame speed, the integral length scale and the laminar flame thickness.
Theoretical Maximum CO₂
Calculate the theoretical maximum CO₂ percentage in dry flue gas from complete combustion of a hydrocarbon C_xH_y, CO₂max = x ÷ (x + (x + y/4) × 3.762) × 100%, from the carbon x and hydrogen y atoms. The result, in %, is the CO₂ obtained with perfect stoichiometric combustion (no excess air) — the reference value of gas analyzers. Methane has CO₂max ≈ 11.7%; coal, ~18-20%. Comparing the measured CO₂ with the theoretical maximum indicates the excess air: the lower the measured CO₂ relative to the maximum, the more excess air diluting the gases. Enter x and y.
Excess Air (from Flue Gas)
Calculate the excess air of a combustion from the oxygen in dry flue gas, EA = O₂ ÷ (20.9 − O₂) × 100%, from the measured O₂ percentage in the stack. The result, in %, shows how much air was supplied beyond stoichiometric — measured by the leftover oxygen in the exhaust gases. Some excess air (10-30%) is needed to ensure complete combustion (avoid CO and soot), but too much wastes energy heating useless air that leaves hot through the stack. Gas analyzers measure O₂ and compute the excess air to optimize combustion efficiency. Enter the O₂ percentage in the gases.
Acid Dew Point of Flue Gas
Computes the temperature at which sulphuric acid starts to condense on the cold surfaces of a boiler, using the Verhoff and Banchero correlation: the reciprocal of the absolute dew point temperature is a combination of the logarithms of the partial pressures of water vapour and sulphur trioxide in the flue gas, plus the product of those two logarithms. The result is the thermal floor of the design — keeping the stack, the economiser and the air preheater above it is what prevents the acid corrosion that eats steel in a few weeks, and it is why heavy fuel oil boilers throw away up the stack heat they could otherwise recover. SO₃ is what rules here, not humidity, and the reason is the range each one spans: water vapour barely leaves the 5% to 15% band in a flue gas, which accounts for 11 °C end to end, while SO₃ varies by orders of magnitude with the sulphur in the fuel — going from 1 to 10 ppm alone raises the dew point by almost 22 °C. The Verhoff and Banchero correlation was adopted, with partial pressures in millimetres of mercury at atmospheric pressure, as it is the one most used in boiler design, in its original form with the interaction term between the two logarithms; the later Okkes correlation returns 1 to 8 °C lower for the same composition, so treat the value as a reference and not as an exact limit. Enter the water vapour content and the SO₃ content of the flue gas.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.