Fuel to Air Mixture Ratio Calculator

Calculate the air-fuel ratio (AFR) for common fuels or determine the mass of air or fuel needed for complete combustion. Select a fuel, input mass values, and view results in standard, step-by-step, or chart views.

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Result

Calculation Steps

AFR Visualization

Formulas

Air-Fuel Ratio Calculations

The air-fuel ratio (AFR) is calculated as follows:

1. Mass Basis

AFR = m_air ÷ m_fuel

Where:

  • AFR: Air-fuel ratio (mass basis)
  • m_air: Mass of air (kg)
  • m_fuel: Mass of fuel (kg)

2. Molar Basis

AFR = (moles_air × M_air) ÷ (moles_fuel × M_fuel)

Where:

  • moles_air: Moles of air
  • M_air: Molar mass of air (≈28.97 g/mol)
  • moles_fuel: Moles of fuel
  • M_fuel: Molar mass of fuel (g/mol)

3. Stoichiometric Combustion

CαHβ + a(O₂ + 3.76N₂) → bCO₂ + cH₂O + dN₂

Where:

  • a = α + β/4 (moles of air)
  • b = α (moles of CO₂)
  • c = β/2 (moles of H₂O)
  • d = 3.76 × (α + β/4) (moles of N₂)

Usage Notes:

  • Inputs must be positive numbers.
  • Results are rounded to 3 decimal places.
  • Molar mass of air is assumed as 28.97 g/mol.

How to Use the Fuel to Air Mixture Ratio Calculator

  1. Select Fuel: Choose a fuel type from the dropdown (e.g., Methane, Gasoline).
  2. Choose Mass Input: Select whether to input mass of fuel or air.
  3. Enter Mass: Input the mass in kilograms.
  4. Choose Display: Select standard, step-by-step, or chart view.
  5. Calculate: Click “Calculate” to process inputs.
  6. View Results: Review the AFR and calculated mass.
  7. Reset: Click “Reset” to clear fields.

Frequently Asked Questions (FAQs)

What is the air-fuel ratio (AFR)?

The air-fuel ratio (AFR) is the mass of air required to completely combust a given mass of fuel. It’s critical for optimizing combustion in engines, turbines, and other devices.

How is AFR calculated?

AFR is calculated as the mass of air divided by the mass of fuel (AFR = m_air / m_fuel) or using molar ratios: AFR = (moles_air × M_air) / (moles_fuel × M_fuel).

What is the stoichiometric AFR?

The stoichiometric AFR is the minimum air needed for complete combustion, calculated using the balanced combustion equation: CαHβ + a(O₂ + 3.76N₂) → bCO₂ + cH₂O + dN₂.

How does Lambda relate to AFR?

Lambda (λ) is the ratio of actual AFR to stoichiometric AFR. Actual AFR = λ × Stoichiometric AFR (e.g., 14.71 for gasoline).

Why is AFR important in combustion?

AFR determines combustion efficiency, affecting power output, fuel economy, and emissions in engines, turbines, and rockets.