ABTF (Air-to-Fuel) Ratio Calculator
Optimize Combustion Efficiency & Engine Performance
Calculation Results
Understanding the ABTF (Air-to-Fuel) Ratio
The ABTF (Air-to-Fuel) Calculator is a critical tool for automotive engineers, performance tuners, and hobbyists. It measures the mass ratio of air to fuel present in a combustion process. Determining the correct ABTF is the difference between peak engine efficiency and catastrophic mechanical failure.
What is Stoichiometric Ratio?
The stoichiometric ratio is the theoretical point where all fuel is burned completely with no excess air. For standard unleaded gasoline, this ratio is 14.7:1. This means 14.7 pounds of air are required to burn 1 pound of fuel. The ABTF calculator helps you identify how far your current mixture deviates from this ideal point.
The Importance of Lambda (λ)
While AFR (Air-Fuel Ratio) is specific to the type of fuel used, Lambda is a universal measurement.
- Lambda = 1.0: Perfect stoichiometric mixture.
- Lambda < 1.0: "Rich" mixture (excess fuel). Better for cooling and power under load.
- Lambda > 1.0: "Lean" mixture (excess air). Better for fuel economy but runs hotter.
Practical ABTF Example
Imagine you are tuning a turbocharged engine using E85 fuel. You measure 11.64 kg of air entering the cylinder and inject 1.2 kg of fuel.
- Actual AFR: 11.64 / 1.2 = 9.7:1
- Stoic for E85: 9.7
- Lambda: 9.7 / 9.7 = 1.0
In this case, the engine is running at a perfect stoichiometric ratio for the specific fuel type, despite the number being lower than the 14.7 used for gasoline.
Tuning for Performance vs. Economy
Most performance applications aim for a slightly Rich mixture (Lambda 0.82 – 0.88) to prevent "knock" or detonation caused by high combustion temperatures. Conversely, cruising at steady highway speeds often utilizes a Lean mixture (Lambda 1.02 – 1.05) to maximize every drop of fuel.