Air-Fuel Ratio (AFR)
Calculate air-fuel ratios, lambda (λ), equivalence ratio (φ), and analyze combustion stoichiometry for various fuels. Essential for engine tuning, burner optimization, and combustion analysis.
Sample Examples
🚗 Gasoline Engine
Typical automotive gasoline engine at stoichiometric conditions
Internal Combustion Engine
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🚛 Diesel Engine
Diesel engine with lean burn for efficiency
Compression Ignition Engine
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🌾 E85 Ethanol Blend
E85 fuel (85% ethanol, 15% gasoline) in flex-fuel vehicle
Alternative Fuel Vehicle
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🔥 Natural Gas Burner
Industrial natural gas burner with 10% excess air
Industrial Burner
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🍖 Propane Grill
Propane grill with rich mixture for better flavor
Cooking Appliance
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⚡ Gas Turbine
Gas turbine with ultra-lean burn for low NOx emissions
Power Generation
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⚖️ Mass-Based Calculation
Calculate AFR from known air and fuel masses
Laboratory Analysis
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Calculation Mode
Mass-Based Calculation
Volume-Based Calculation (Alternative)
Environmental Conditions
Related Calculators
Combustion Reaction Calculator
Balance combustion reactions and calculate stoichiometric coefficients
Open CalculatorCombustion Analysis Calculator
Analyze combustion products and determine fuel composition
Open Calculator⚠️For educational and informational purposes only. Verify with a qualified professional.
What is Air-Fuel Ratio (AFR)?
The Air-Fuel Ratio (AFR) is the mass ratio of air to fuel present in a combustion process. It is a critical parameter in combustion engineering, engine design, and emissions control.
Formula: AFR = Mass of Air / Mass of Fuel
The AFR determines whether a mixture is:
- Rich: Too much fuel (AFR < stoichiometric) - incomplete combustion, higher emissions
- Stoichiometric: Perfect balance (AFR = stoichiometric) - complete combustion
- Lean: Too much air (AFR > stoichiometric) - may cause misfires, higher NOx
How to Calculate Air-Fuel Ratio
There are several methods to calculate AFR:
1. Mass-Based Calculation:
Measure the mass of air and fuel directly:
AFR = m_air / m_fuel
2. Volume-Based Calculation:
Convert volumes to masses using densities:
AFR = (V_air × ρ_air) / (V_fuel × ρ_fuel)
3. From Lambda:
If lambda is known:
AFR = λ × AFR_stoichiometric
When to Use AFR Calculations
AFR calculations are essential in:
- Engine Tuning: Optimize performance and fuel economy
- Emissions Control: Meet environmental regulations
- Burner Design: Industrial and residential heating systems
- Alternative Fuels: Analyze ethanol, biodiesel, natural gas blends
- Research: Combustion studies and fuel development
- Diagnostics: Troubleshoot engine performance issues
Key Formulas
Air-Fuel Ratio:
AFR = m_air / m_fuel
Lambda (λ):
λ = AFR_actual / AFR_stoichiometric
λ < 1: Rich mixture | λ = 1: Stoichiometric | λ > 1: Lean mixture
Equivalence Ratio (φ):
φ = 1 / λ = AFR_stoichiometric / AFR_actual
φ > 1: Rich mixture | φ = 1: Stoichiometric | φ < 1: Lean mixture
Excess Air:
Excess Air (%) = (λ - 1) × 100 (for lean mixtures)
Air Density (Ideal Gas Law):
ρ_air = P / (R × T)
Where R = 287 J/(kg·K) for dry air
Common Fuel Stoichiometric AFR Values
| Fuel | Formula | Stoichiometric AFR |
|---|---|---|
| Gasoline | C8H18 | 14.7 |
| Diesel | C12H23 | 14.5 |
| Ethanol | C2H5OH | 9.0 |
| Methane | CH4 | 17.2 |
| Propane | C3H8 | 15.7 |
| Methanol | CH3OH | 6.5 |
| Natural Gas | CH4 | 17.2 |
📚 Official Data Sources
⚠️ Disclaimer: AFR values are for reference. Actual combustion depends on conditions and equipment. Not a substitute for professional engine tuning.