What is adiabatic flame temperature?

Adiabatic flame temperature is the maximum temperature a combustion reaction can reach when all of the heat released stays in the products, with no energy lost to surroundings, radiation, or dissociation. Real flames are always cooler due to these losses.

What is equivalence ratio (phi)?

Equivalence ratio (phi) is the ratio of actual fuel-to-oxidizer to the stoichiometric fuel-to-oxidizer ratio. Phi = 1.0 means exactly the right proportions for complete combustion. Phi 1.0 (rich) has excess fuel. AFT peaks near phi = 1.0.

Why is hydrogen's AFT so high?

Hydrogen has a very high heating value per unit mass and produces only water vapor on combustion. With no nitrogen dilution (in pure O2), the heat concentrates entirely in the product water, yielding the highest AFT of common fuels.

How accurate are these results?

The stoichiometric values are based on well-established tabulated data accurate to within a few percent. The equivalence-ratio correction is a simplified parabolic model; for precise off-stoichiometric analysis, use full equilibrium solvers like NASA CEA or CHEMKIN.

Why is AFT higher in pure oxygen than air?

In air, nitrogen absorbs a large fraction of the combustion heat without contributing to energy release. Replacing air with pure oxygen removes this dilution, so the same heat is absorbed by fewer moles of product gas, producing a much higher temperature.

Adiabatic Flame Temperature Calculator

Estimate the theoretical adiabatic flame temperature for common fuels burning in air or pure oxygen at any equivalence ratio.

Combustion Parameters

Fuel

Oxidizer

Equivalence Ratio (φ) (0.3 – 2.0)

Stoichiometric — ideal fuel/air ratio

Select parameters and click Calculate

Reference: Stoichiometric Adiabatic Flame Temperatures

Tabulated values at phi = 1.0, initial reactants at 25 °C. Simplified educational estimates.

Fuel	Formula	In Air (°C)	In O2 (°C)

Summary

This tool calculates the adiabatic flame temperature (AFT) — the maximum theoretical temperature reached when a fuel combusts with no heat loss to the surroundings. Select a fuel and oxidizer, enter an equivalence ratio (phi = 1.0 for stoichiometric), and the calculator returns estimated AFT in both Celsius and Fahrenheit. Results use tabulated stoichiometric reference values with a simplified correction for fuel-rich and fuel-lean mixtures. It is intended for educational use and quick engineering estimates, not precision combustion modeling.

How it works

Select a fuel from the dropdown (methane, propane, hydrogen, ethanol, or butane).
Choose the oxidizer: air (21% O2, 79% N2) or pure oxygen.
Enter the equivalence ratio phi (1.0 = stoichiometric, <1 = lean, >1 = rich).
The tool looks up the tabulated stoichiometric AFT for that fuel/oxidizer pair.
A simplified correction factor scales the temperature for off-stoichiometric conditions.
Results are displayed in Celsius and Fahrenheit alongside a reference table for all fuels.

Use cases

Estimate furnace or burner operating temperatures for engineering design.
Compare fuel efficiency in combustion chemistry courses.
Check whether a mixture is above the auto-ignition threshold.
Evaluate oxygen-enriched combustion vs. air combustion trade-offs.
Understand how equivalence ratio affects flame temperature in gas turbines.
Quick reference for combustion safety assessments.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu