What is adiabatic flame temperature?

It is the temperature combustion products reach when the entire heat of combustion is absorbed by the products with zero heat loss to the surroundings. It represents the upper bound of real flame temperatures.

Why is hydrogen's adiabatic temperature lower than some hydrocarbons?

Although hydrogen has a very high LHV per kg, its combustion produces only water vapor. Water has a higher heat capacity than CO2, so it absorbs more energy per degree, resulting in a slightly lower temperature than expected from LHV alone.

How does excess air affect flame temperature?

Excess air (lean mixtures, φ < 1) dilutes the products. The same heat release must now raise the temperature of a larger mass of gas, so flame temperature drops. This is the primary mechanism used by low-NOx burners to control peak temperature.

What is the equivalence ratio (phi)?

Phi (φ) is the actual fuel-to-air ratio divided by the stoichiometric fuel-to-air ratio. φ = 1 is stoichiometric, φ 1 is rich (less air than needed). It is the reciprocal of lambda (λ).

How accurate are these estimates?

Within ~2–5% of rigorous equilibrium calculations (e.g. NASA CEA) for near-stoichiometric conditions. Accuracy decreases for very rich mixtures (φ > 1.3) where dissociation and partial combustion matter most.

Adiabatic Combustion Temperature Calculator

Name: Adiabatic Combustion Temperature Calculator
Availability: InStock
Author: Nham Vu

Select a fuel, enter the air-fuel equivalence ratio and initial reactant temperature to estimate the adiabatic flame temperature.

Combustion Inputs

Fuel Type

LHV

44,500 kJ/kg

Stoich AFR

14.7 : 1

Equivalence Ratio (φ) — φ = 1 is stoichiometric

Lean (φ 0.5) Stoich (φ 1.0) Rich (φ 1.5)

Initial Reactant Temperature

Temperature of fuel + air before ignition

Select a fuel and press Calculate

Fuel Reference — Adiabatic Flame Temperature at Stoichiometric, 25 °C Reactants

Fuel	LHV (kJ/kg)	Stoich AFR	T_ad (°C)	Notes
Methane (CH₄)	50,050	17.2 : 1	~1,950	Natural gas / CNG primary component
Propane (C₃H₈)	46,350	15.7 : 1	~1,995	LPG; slightly higher T_ad than methane
Hydrogen (H₂)	119,960	34.3 : 1	~2,210	Highest LHV/kg; products are H₂O only
Gasoline (~C₈H₁₈)	44,500	14.7 : 1	~2,030	Typical pump gasoline blend
Diesel (~C₁₂H₂₆)	42,500	14.5 : 1	~2,020	Compression ignition; similar to gasoline
Ethanol (C₂H₅OH)	26,800	9.0 : 1	~1,920	Lower LHV offset by lower product mass

Summary

Select a fuel, enter the air-fuel equivalence ratio and initial reactant temperature to estimate the adiabatic flame temperature.

How it works

Select a fuel from the preset list — its lower heating value (LHV) and stoichiometric air-fuel ratio load automatically.
Set the equivalence ratio (phi, φ): 1.0 = stoichiometric; < 1.0 = lean (excess air); > 1.0 = rich (excess fuel).
Enter the initial reactant temperature (fuel + air before ignition).
The calculator finds the mass of products per unit mass of fuel, then applies T_ad = T_in + LHV / (m_products × Cp_products).
Results show adiabatic flame temperature, temperature rise, and an equivalence-ratio sweep chart.

Use cases

Estimate burner exit temperature for gas turbine combustor preliminary design.
Compare adiabatic temperatures across fuels when evaluating alternative energy sources.
Assess lean-premixed combustion margins to avoid autoignition or blowout.
Validate equilibrium combustion software outputs against a quick analytical estimate.
Classroom demonstration of how excess air (lean mixtures) lowers flame temperature.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu