Combustion Reaction Calculator
Use the responsive form below. It shows three columns on large screens, two on smaller screens, and one on mobile.
Example Data Table
These sample rows help users understand typical stoichiometric combustion behavior before entering custom values.
| Fuel | Formula | Balanced combustion | Stoichiometric O2 (mol/mol fuel) | Notes |
|---|---|---|---|---|
| Methane | CH4 | CH4 + 2O2 → CO2 + 2H2O | 2.0000 | Common natural gas reference fuel. |
| Ethanol | C2H6O | C2H6O + 3O2 → 2CO2 + 3H2O | 3.0000 | Fuel oxygen lowers outside oxygen demand. |
| Octane | C8H18 | 2C8H18 + 25O2 → 16CO2 + 18H2O | 12.5000 | Useful gasoline-style benchmark example. |
Formula Used
For a generic fuel CxHyOzNnSs, the calculator applies complete combustion stoichiometry with configurable oxidizer composition.
| Item | Formula |
|---|---|
| Fuel molar mass | MW = 12.011x + 1.008y + 15.999z + 14.007n + 32.06s |
| Stoichiometric oxygen demand | O2,stoich = x + y/4 + s - z/2 |
| Actual oxygen supplied | O2,actual = O2,stoich × (1 + excess air / 100) |
| Air requirement | Air = O2,actual / oxygen fraction |
| Main products per mole fuel | CO2 = x, H2O = y/2, SO2 = s, N2 = n/2 + (N2/O2 ratio × O2,actual) |
| Excess oxygen in products | O2,excess = max(0, O2,actual - O2,stoich) |
| Volume at STP | Volume = total moles × molar volume / 1000 |
How to Use This Calculator
- Enter a simple CHONS fuel formula such as
CH4,C2H6O, orC8H18. - Choose whether your fuel quantity is in moles or kilograms.
- Enter excess air percentage for real operating conditions.
- Keep oxygen fraction at 21% and nitrogen-to-oxygen ratio at 3.7619 for normal dry air, or change them for enriched oxidizers.
- Click the calculate button to show results above the form.
- Review the balanced equation, oxygen demand, flue gas volumes, species table, and Plotly graph.
- Use the CSV and PDF buttons to export your results.
Frequently Asked Questions
1. What formulas does this calculator accept?
It accepts simple molecular formulas containing carbon, hydrogen, oxygen, nitrogen, and sulfur. Examples include CH4, C3H8, C2H5OH, and C8H18. Parentheses, radicals, ions, and hydrate notation are not supported in this version.
2. What does excess air mean?
Excess air is the percentage of oxygen-bearing oxidizer supplied above the exact stoichiometric requirement. Positive excess air leaves unused oxygen in the exhaust and usually lowers flame temperature while helping complete combustion.
3. Why does oxygen inside the fuel reduce O2 demand?
Fuel-bound oxygen already contributes to product formation. Because some oxygen atoms are carried inside the molecule, the external oxidizer needs fewer O2 molecules to fully convert carbon to CO2 and hydrogen to H2O.
4. Why is nitrogen included in the product stream?
Air contains a large amount of nitrogen, and that nitrogen largely passes through combustion unchanged. The calculator adds nitrogen from the oxidizer stream and any nitrogen already present in the fuel to the final product mixture.
5. What is the difference between wet and dry flue gas?
Wet flue gas includes water vapor. Dry flue gas removes water and reports the remaining gases only. Dry-basis reporting is common in stack analysis because it simplifies comparison between fuels and operating conditions.
6. Can I use this for oxygen-enriched combustion?
Yes. Adjust the oxygen fraction and the nitrogen-to-oxygen ratio to represent your oxidizer. For pure oxygen, set oxygen fraction to 100 and nitrogen-to-oxygen ratio to 0. That setup removes inert air nitrogen and shows the idealized oxygen-fed combustion products.
7. Why are exported volumes based on STP?
Standard reference conditions make gas-volume comparisons easier. This calculator uses a configurable molar volume at STP, so you can keep the default or change it to match the reference basis used in your lab, class, or project.
8. Does this model include incomplete combustion products?
No. This page assumes complete combustion and calculates CO2, H2O, SO2, N2, and possible excess O2. It does not estimate CO, soot, NOx, dissociation, flame temperature, or equilibrium chemistry.