Air–Fuel Ratio Calculator
Stoichiometric A/F is the air needed to burn the fuel completely: octane needs 15.0896 kg air/kg fuel.
Negative for a rich mixture.
15.0895983612298 kg air/kg fuel
Full answer, then cut to fewer decimals (not rounded):
- 15.0895983612298 kg air/kg fuel
- 15.089598361229 kg air/kg fuel
- 15.08959836122 kg air/kg fuel
- 15.0895983612 kg air/kg fuel
- 15.089598361 kg air/kg fuel
- 15.08959836 kg air/kg fuel
- 15.0895983 kg air/kg fuel
- 15.089598 kg air/kg fuel
- 15.08959 kg air/kg fuel
- 15.0895 kg air/kg fuel
- 15.089 kg air/kg fuel
- 15.08 kg air/kg fuel
- 15.0 kg air/kg fuel
- O₂ needed per mol of fuel x + y/4 − z/2
- 12.5 mol
- Air needed per mol of fuel (× 4.76)
- 59.5 mol
- Fuel molar mass
- 114.232 g/mol
- Actual air–fuel ratio
- 15.0896 kg/kg
- Equivalence ratio φ = AFst/AF
- 1
- Excess air factor λ
- 1
Step-by-step solution
- CₓHᵧOz + (x + y/4 − z/2)(O₂ + 3.76 N₂) → x CO₂ + (y/2) H₂O + 3.76(x + y/4 − z/2) N₂
- Air = 12.5 × 4.76 × 28.97 = 1723.72 g per 114.232 g of fuel
- A/F = 15.0896
Air–Fuel Ratio Formula
A/F = (x + y/4 − z/2) × 4.76 × 28.97 ÷ M_fuel
CₓHᵧOz fuel; 4.76 mol air per mol O₂
Worked Example
Octane C₈H₁₈ burned with the theoretical amount of air:
- CₓHᵧOz + (x + y/4 − z/2)(O₂ + 3.76 N₂) → x CO₂ + (y/2) H₂O + 3.76(x + y/4 − z/2) N₂
- Air = 12.5 × 4.76 × 28.97 = 1723.72 g per 114.232 g of fuel
- A/F = 15.0896
Air needed per mol of fuel (× 4.76): 59.5 mol · Fuel molar mass: 114.232 g/mol · Actual air–fuel ratio: 15.0896 kg/kg · Equivalence ratio φ = AFst/AF: 1 · Excess air factor λ: 1
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Example: rp = 10, T₁ = 300 K, T₃ = 1200 K, ideal compressor and turbine: Thermal efficiency η = 48.2053 %.
Frequently asked questions
What is the equivalence ratio?
φ = (A/F)stoich ÷ (A/F)actual: φ < 1 is lean (excess air), φ > 1 rich.
Why 4.76 moles of air per mole of O₂?
Air is about 21 % O₂ and 79 % N₂ by volume, so each mole of O₂ comes with 3.76 moles of N₂.
Sources
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Air–Fuel Ratio Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/air-fuel-ratio-calculator/
IEEE
Scientific Converters, "Air–Fuel Ratio Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/air-fuel-ratio-calculator/