Air to Fuel Ratio (AFR) Calculator
What is the Air to Fuel Ratio (AFR)?
The Air to Fuel Ratio (AFR) is a critical measure in internal combustion engines and industrial burners. it represents the ratio of the mass of air to the mass of fuel present in a combustion process. For a gasoline engine, the "perfect" ratio where all fuel and all oxygen are consumed is 14.7:1. This is known as the stoichiometric ratio.
Understanding Lambda (λ)
Lambda is a dimensionless value that describes the ratio of the actual AFR to the stoichiometric AFR for a specific fuel.
- λ = 1.0: Stoichiometric (Ideal balance)
- λ < 1.0: Rich mixture (Excess fuel, lack of air)
- λ > 1.0: Lean mixture (Excess air, lack of fuel)
Common Stoichiometric Ratios
Different fuels require different amounts of oxygen to burn completely. Here are common reference values used in this calculator:
- Gasoline: 14.7:1
- Diesel: 14.5:1
- Ethanol: 9.0:1
- Methanol: 6.4:1
- Propane (LPG): 15.5:1
Example Calculation
If an engine draws in 29.4 grams of air and 2 grams of gasoline fuel:
AFR = 29.4 / 2 = 14.7
Lambda = 14.7 (Actual) / 14.7 (Stoic) = 1.0
In this case, the engine is running at a perfect stoichiometric ratio.
Why it Matters
Maintaining the correct AFR is vital for several reasons. A rich mixture often produces more power but results in poor fuel economy and high carbon monoxide emissions. A lean mixture is more fuel-efficient but can lead to high nitrogen oxide (NOx) emissions and, if too lean, can cause engine damage due to excessive heat (detonation/knocking).