Calculator
Formula Used
For an adiabatic, steady combustion process (no heat loss), the energy balance can be written on an enthalpy basis:
Using a reference temperature Tref, we compute sensible enthalpies from heat capacity:
The calculator solves for Tad so the product sensible enthalpy matches the reactant sensible enthalpy plus released chemical energy.
How to Use This Calculator
- Enter the reactant initial temperature and your reference temperature.
- Select how you will provide heat release, then enter the values.
- Choose a heat-capacity model and enter effective Cp inputs.
- Keep Cp and Q on the same basis, such as per mol fuel.
- Press Calculate. Results appear above the form immediately.
- Use the export buttons to save a CSV or PDF report.
Example Data Table
These values are illustrative. They are not a full chemical-equilibrium solution.
| Case | T0 (K) | Tref (K) | Q (kJ) | Reactants Cp (kJ/K) | Products Cp (kJ/K) | Estimated Tad (K) |
|---|---|---|---|---|---|---|
| Methane-air, demo basis | 298.15 | 298.15 | 802.3 | 1.20 | 1.35 | ~892 |
| Preheated reactants | 600 | 298.15 | 802.3 | 1.20 | 1.35 | ~1158 |
| Higher effective Cp products | 298.15 | 298.15 | 802.3 | 1.20 | 1.70 | ~770 |
Article
1) Adiabatic flame temperature in one sentence
Adiabatic flame temperature (Tad) is the peak temperature a reacting mixture can reach when reaction heat is converted into product sensible enthalpy with no heat loss. This calculator applies an enthalpy balance with user-supplied heat release and effective heat-capacity data to estimate Tad quickly.
2) Typical values you can use for sanity checks
For stoichiometric mixtures near 1 atm and 298 K reactants, Tad is often around 2200 K for methane–air and can be near 2400 K for hydrogen–air. Lean or diluted mixtures trend lower, sometimes below 2000 K. These numbers are approximate but help catch unit mistakes.
3) Why mixture strength and dilution change Tad
Tad rises when a larger fraction of released energy heats fewer “inert” moles. Excess air adds nitrogen that absorbs energy without adding heat release, increasing the total product heat capacity. Exhaust-gas recirculation, steam injection, or CO2 dilution similarly raise Cp and reduce Tad, supporting thermal NOx control.
4) Preheat temperature shifts the whole balance
Preheated reactants carry extra sensible enthalpy before ignition. In the balance, that sensible term adds to Q, so Tad increases even if fuel energy is unchanged. As a quick estimate with constant Cp, increasing T0 by 300 K can add roughly (Cp,reactants/Cp,products)×300 K to Tad on the same basis.
5) Constant Cp versus temperature-dependent Cp
Constant Cp gives a closed-form Tad and is excellent for fast comparisons. However, Cp usually increases with temperature as molecular vibrational modes activate, so constant Cp can overpredict Tad at high temperatures. The polynomial Cp(T) option integrates Cp(T) and uses an iterative solver, typically yielding a more conservative estimate.
6) Pressure, dissociation, and why real Tad is lower
Above roughly 2000 K, dissociation of CO2 and H2O into CO, H, O, and OH can absorb energy and reduce temperature compared with a frozen-composition model. Higher pressure suppresses dissociation and can increase equilibrium Tad. This calculator does not compute equilibrium, so treat the result as an upper-bound style estimate.
7) Engineering uses: materials, emissions, and sizing
Tad is a practical design signal for refractory selection, combustor liner cooling, and turbine inlet temperature budgeting. It also correlates with thermal NOx potential: lower Tad generally reduces NOx formation rates. Use Tad trends to compare fuels, dilution strategies, and preheat levels before running detailed equilibrium and CFD studies.
8) Data checklist for reliable inputs
Keep a consistent basis for Q and Cp (per mol fuel, per kg mixture, or per batch). Use a standard reference temperature such as 298.15 K. If you use polynomial Cp, choose coefficients that keep Cp positive up to your Tmax bound. Finally, validate against a known case to confirm your scaling and units.
FAQs
1) Is this an equilibrium adiabatic flame temperature?
No. It is an energy-balance estimator using effective heat capacities. Equilibrium requires species composition, pressure effects, and dissociation modeling, which usually lowers Tad compared with frozen-composition estimates.
2) What basis should I use for Cp and Q?
Any basis works if it is consistent. If Q is per mol of fuel, then Cp must represent total mixture heat capacity per mol of fuel for reactants and products.
3) Why does Tad decrease when I add excess air?
Excess air adds mainly nitrogen that increases product heat capacity but does not add chemical energy. The same Q is distributed across more thermal mass, reducing the temperature rise.
4) When should I choose polynomial Cp(T)?
Use polynomial Cp when temperatures are high or when you want a more conservative estimate. Cp often increases with temperature, so Cp(T) typically predicts lower Tad than a constant Cp.
5) What if my polynomial Cp makes Cp negative?
Cp must remain positive for physical realism and solver stability. Adjust coefficients or reduce the temperature range. The calculator warns if Cp becomes non-positive during the iteration.
6) Can I include heat losses or burner efficiency?
Not directly. You can approximate losses by reducing Q to an “effective” heat release, such as Qeff = ηQ, where η is a fractional efficiency between 0 and 1.
7) Why can my Tad look too low or too high?
Common causes are inconsistent basis, wrong units, or unrealistic Cp values. Check that Q and Cp match the same reference and scaling, then compare with an approximate known Tad to validate.