Lambda Afr Calculator

Lambda (λ) and Air-Fuel Ratio (AFR) Calculator

Use this calculator to convert between Lambda (λ), Actual Air-Fuel Ratio (AFR), and Stoichiometric Air-Fuel Ratio. Enter any two values to calculate the third.

— Select Fuel Type — Gasoline (14.7) E85 (9.76) Methanol (6.4) Diesel (14.5) Propane (15.7) Natural Gas (17.2) Custom

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stoichAFRInput.disabled = true; break; case "methanol": stoichAFRInput.value = "6.4"; stoichAFRInput.disabled = true; break; case "diesel": stoichAFRInput.value = "14.5"; stoichAFRInput.disabled = true; break; case "propane": stoichAFRInput.value = "15.7"; stoichAFRInput.disabled = true; break; case "natural_gas": stoichAFRInput.value = "17.2"; stoichAFRInput.disabled = true; break; case "custom": stoichAFRInput.value = ""; stoichAFRInput.disabled = false; stoichAFRInput.focus(); break; default: stoichAFRInput.value = ""; stoichAFRInput.disabled = false; break; } } function calculateAFR() { var stoichAFR_str = document.getElementById("stoichAFR").value; var lambdaValue_str = document.getElementById("lambdaValue").value; var actualAFR_str = document.getElementById("actualAFR").value; var resultDiv = document.getElementById("result"); resultDiv.className = "calculator-result"; // Reset class resultDiv.innerHTML = ""; var stoichAFR = parseFloat(stoichAFR_str); var lambdaValue = parseFloat(lambdaValue_str); var actualAFR = parseFloat(actualAFR_str); var validInputs = 0; if (!isNaN(stoichAFR) && stoichAFR > 0) validInputs++; if (!isNaN(lambdaValue) && lambdaValue > 0) validInputs++; if (!isNaN(actualAFR) && actualAFR > 0) validInputs++; if (validInputs !== 2) { resultDiv.innerHTML = "Please enter exactly two positive values to calculate the third."; resultDiv.classList.add("error"); return; } if (isNaN(stoichAFR) || stoichAFR <= 0) { // Calculate Stoichiometric AFR if (isNaN(lambdaValue) || lambdaValue <= 0) { resultDiv.innerHTML = "Error: Lambda cannot be zero or negative."; resultDiv.classList.add("error"); return; } if (isNaN(actualAFR) || actualAFR <= 0) { resultDiv.innerHTML = "Error: Actual AFR cannot be zero or negative."; resultDiv.classList.add("error"); return; } var calculatedStoichAFR = actualAFR / lambdaValue; resultDiv.innerHTML = "Calculated Stoichiometric AFR (AFR_stoich): " + calculatedStoichAFR.toFixed(3) + ""; } else if (isNaN(lambdaValue) || lambdaValue <= 0) { // Calculate Lambda if (isNaN(stoichAFR) || stoichAFR <= 0) { resultDiv.innerHTML = "Error: Stoichiometric AFR cannot be zero or negative."; resultDiv.classList.add("error"); return; } if (isNaN(actualAFR) || actualAFR <= 0) { resultDiv.innerHTML = "Error: Actual AFR cannot be zero or negative."; resultDiv.classList.add("error"); return; } var calculatedLambda = actualAFR / stoichAFR; resultDiv.innerHTML = "Calculated Lambda (λ): " + calculatedLambda.toFixed(3) + ""; } else if (isNaN(actualAFR) || actualAFR <= 0) { // Calculate Actual AFR if (isNaN(stoichAFR) || stoichAFR <= 0) { resultDiv.innerHTML = "Error: Stoichiometric AFR cannot be zero or negative."; resultDiv.classList.add("error"); return; } if (isNaN(lambdaValue) || lambdaValue <= 0) { resultDiv.innerHTML = "Error: Lambda cannot be zero or negative."; resultDiv.classList.add("error"); return; } var calculatedActualAFR = lambdaValue * stoichAFR; resultDiv.innerHTML = "Calculated Actual Air-Fuel Ratio (AFR_actual): " + calculatedActualAFR.toFixed(3) + ""; } else { resultDiv.innerHTML = "Please enter exactly two positive values to calculate the third."; resultDiv.classList.add("error"); } }

Understanding Lambda (λ) and Air-Fuel Ratio (AFR) in Engine Tuning

In the world of internal combustion engines, the precise mixture of air and fuel is critical for optimal performance, fuel economy, and emissions control. Two key metrics used to describe this mixture are the Air-Fuel Ratio (AFR) and Lambda (λ).

What is Air-Fuel Ratio (AFR)?

The Air-Fuel Ratio (AFR) is simply the mass ratio of air to fuel present in an engine's combustion chamber. For example, an AFR of 14.7:1 means there are 14.7 parts of air for every 1 part of fuel by mass.

• Stoichiometric AFR (AFR_stoich): This is the chemically ideal air-fuel ratio where all the fuel and all the oxygen in the air are consumed during combustion, with no excess of either. For gasoline, the stoichiometric AFR is approximately 14.7:1. However, this value varies significantly depending on the fuel type:
  • Gasoline: ~14.7:1
  • E85 (85% Ethanol): ~9.76:1
  • Methanol: ~6.4:1
  • Diesel: ~14.5:1
  • Propane: ~15.7:1
  • Natural Gas: ~17.2:1
• Actual AFR (AFR_actual): This is the real-time air-fuel ratio measured or targeted by the engine's control system. It can be different from the stoichiometric ratio depending on the engine's operating conditions and tuning goals.

What is Lambda (λ)?

Lambda (λ), also known as the excess air factor, is a dimensionless value that expresses the actual air-fuel ratio relative to the stoichiometric air-fuel ratio. It provides a universal way to describe the richness or leanness of an air-fuel mixture, regardless of the fuel type.

The formula for Lambda is:

λ = AFR_actual / AFR_stoich

• λ = 1.0 (Stoichiometric): This indicates a perfect, chemically balanced mixture where all fuel and oxygen are consumed. This is the target for catalytic converters to operate efficiently, minimizing harmful emissions.
• λ < 1.0 (Rich Mixture): A rich mixture means there is more fuel than theoretically needed for complete combustion.
  • Typically used for maximum power output (e.g., λ = 0.85 – 0.95 for gasoline engines under heavy load) as it helps cool combustion and prevent detonation.
  • Results in higher fuel consumption and increased CO (carbon monoxide) and HC (hydrocarbon) emissions.
• λ > 1.0 (Lean Mixture): A lean mixture means there is more air than theoretically needed for complete combustion.
  • Often used for improved fuel economy (e.g., λ = 1.05 – 1.15 for gasoline engines under light load).
  • Can lead to higher NOx (nitrogen oxide) emissions and potentially higher combustion temperatures, which can be detrimental if too lean.

Why are Lambda and AFR Important?

Understanding and controlling Lambda and AFR are fundamental for:

• Engine Performance: Tuning for a slightly rich mixture (λ < 1.0) often yields maximum power, while a stoichiometric mixture (λ = 1.0) is ideal for emissions.
• Fuel Economy: Running slightly lean (λ > 1.0) can improve fuel efficiency, especially during cruising conditions.
• Emissions Control: Modern engines rely on precise AFR control (targeting λ = 1.0) to allow the catalytic converter to effectively reduce pollutants.
• Engine Longevity: Extremely lean mixtures can cause excessive combustion temperatures, leading to engine damage (e.g., burnt valves, melted pistons). Extremely rich mixtures can wash oil from cylinder walls and foul spark plugs.

How to Use the Calculator:

This calculator allows you to easily convert between these values. Simply input any two of the following, and the calculator will determine the third:

1. Stoichiometric Air-Fuel Ratio (AFR_stoich): You can select a common fuel type from the dropdown to pre-fill this, or enter a custom value.
2. Lambda (λ): The dimensionless ratio of actual to stoichiometric AFR.
3. Actual Air-Fuel Ratio (AFR_actual): The real-world air-fuel ratio.

Examples:

• Example 1: Calculating Actual AFR for a rich gasoline mixture.
  • Fuel Type: Gasoline (AFR_stoich = 14.7)
  • Lambda (λ): 0.88 (a common target for maximum power)
  • Calculation: AFR_actual = 0.88 * 14.7 = 12.936
  • Result: Actual Air-Fuel Ratio (AFR_actual): 12.936
• Example 2: Calculating Lambda for a lean E85 mixture.
  • Fuel Type: E85 (AFR_stoich = 9.76)
  • Actual Air-Fuel Ratio (AFR_actual): 10.5
  • Calculation: λ = 10.5 / 9.76 = 1.076
  • Result: Lambda (λ): 1.076
• Example 3: Determining Stoichiometric AFR for an unknown fuel.
  • Lambda (λ): 1.0 (known to be stoichiometric)
  • Actual Air-Fuel Ratio (AFR_actual): 15.7
  • Calculation: AFR_stoich = 15.7 / 1.0 = 15.7
  • Result: Stoichiometric Air-Fuel Ratio (AFR_stoich): 15.700 (This suggests the fuel might be Propane)

By using this calculator, tuners, mechanics, and enthusiasts can quickly and accurately determine these crucial engine parameters, aiding in precise engine calibration and diagnostics.