What is Air-Fuel Ratio (AFR)?

The Air-Fuel Ratio (AFR) is a critical measurement in internal combustion engines that defines the mass ratio of air to a solid, liquid, or gaseous fuel present in a combustion process. For internal combustion engines, the AFR determines whether the engine is running efficiently, producing maximum power, or emitting excessive pollutants.

Understanding Stoichiometric Ratio

The stoichiometric ratio is the theoretical point where all the fuel is burned completely with all the available oxygen. For gasoline, this ratio is approximately 14.7:1, meaning 14.7 pounds of air are required to burn 1 pound of fuel. When an engine runs at this ratio, the catalytic converter works at peak efficiency to reduce emissions.

Rich vs. Lean Mixtures

A Rich Mixture occurs when there is more fuel than necessary for complete combustion (e.g., 12.5:1 for gasoline). Rich mixtures are often used under high load to keep cylinder temperatures down and prevent engine knock, though they decrease fuel economy. A Lean Mixture occurs when there is more air than fuel (e.g., 16.0:1). While lean mixtures can improve fuel economy, they increase combustion temperatures and can lead to engine damage if not carefully managed.

How to Use the AFR Calculator

To use this tool, follow these simple steps:

1. Select your Fuel Type from the dropdown menu (Gasoline, Diesel, Ethanol, etc.). Each fuel has a different stoichiometric point.
2. Enter the Air Mass and Fuel Mass. You can use any unit (grams, pounds, kilograms) as long as you use the same unit for both inputs.
3. Click Calculate Ratio to see your result.

What is Lambda (λ)?

Lambda is a dimensionless value that represents the ratio of the actual AFR to the stoichiometric AFR. A Lambda value of 1.0 means the engine is at the perfect stoichiometric balance. A value below 1.0 indicates a rich mixture, while a value above 1.0 indicates a lean mixture. Performance tuners often use Lambda because it is consistent across different fuel types.