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Easily calculate the air-fuel ratio (AFR) of diesel or petrol engines and boilers with our simple Air Fuel Ratio Calculator. Learn formulas, ideal ratios, and more.
Understanding the air-fuel ratio (AFR) is essential for optimizing engine performance, improving fuel efficiency, and reducing emissions. Whether you're working with a diesel engine, a petrol engine, or a boiler system, the air-fuel ratio tells you how much air is mixed with fuel during combustion.
To make it easy for anyone to calculate this, we’ve developed an Air Fuel Ratio Calculator that simplifies the process. With just a few inputs, you’ll instantly know whether your mixture is lean, rich, or stoichiometric.
Let’s explore what the air-fuel ratio means, how to calculate it, and how to use our calculator.
The Air Fuel Ratio (AFR) is the ratio of air to fuel present during combustion in an engine or boiler. It is typically measured by weight. A perfect or stoichiometric ratio ensures that all the fuel burns completely using all the available oxygen in the air.
To calculate the AFR using our calculator, you’ll need:
Once you enter these values into the calculator, it will give you the AFR result.
Here’s the basic formula used in our calculator:
Air Fuel Ratio (AFR) = Mass of Air / Mass of Fuel
For example:
That means you have a stoichiometric mixture for a petrol engine.
| Engine/Boiler Type | Ideal AFR Range |
|---|---|
| Petrol (Gasoline) Engine | 14.7:1 |
| Diesel Engine (Idle/Light Load) | 18:1 to 40:1 |
| Diesel Engine (Full Load) | 14.5:1 to 18:1 |
| Natural Gas Boiler | 10:1 to 12:1 |
| Heavy Oil Boiler | 14:1 to 16:1 |
| Biomass Boiler | 6:1 to 12:1 |
Use the following guide:
| AFR Value | Mixture Type |
|---|---|
| < 14.7 | Rich |
| = 14.7 | Stoichiometric (Petrol) |
| > 14.7 | Lean |
Note: Diesel engines often run lean by design, especially at idle.
Diesel engines operate differently from petrol engines. They often run with excess air, especially when not under heavy load. Here's an example:
If a diesel engine uses 200 kg of air and 10 kg of diesel fuel:
AFR = 200 / 10 = 20:1
This is a lean mixture, common for efficient combustion in diesel engines.
For a natural gas boiler, if you're using 100 kg of air and 10 kg of fuel:
AFR = 100 / 10 = 10:1
This is within the ideal range for complete combustion.
Knowing your air-fuel ratio is essential for engine tuning, combustion control, and fuel efficiency. A rich mixture may give more power but wastes fuel and causes pollution. A lean mixture may save fuel but lead to engine knocking or incomplete combustion.
With our Air Fuel Ratio Calculator, you don’t need to worry about complex math or guesswork. Just input your air and fuel values, and the tool does the rest.
Whether you're a mechanic, engineer, student, or enthusiast, this calculator is the simplest way to monitor your AFR.
For petrol engines, 14.7:1 is ideal. For diesel, it ranges from 18:1 to 70:1 depending on the load.
Use the formula: AFR = Mass of Air / Mass of Fuel.
It's stoichiometric for petrol engines, but lean for diesel engines.
12.5 AFR is rich for petrol engines and extremely rich for diesel.
Yes, the same formula applies for boilers, just input the air and fuel mass correctly.