what is the stoichiometric air/fuel ratio?

The product of mixture strength and actual A/F ratio is called stoichiometric air/fuel ratio.

Stoichiometric A/F ratio = mixture strength actual A/F ratio

How to calculate stoichiometric air-fuel ratio?

Stoichiometric A/F ratio = mixture strength actual A/F ratio

Where,

A = denotes air

F = denotes fuel

stoichiometric air-fuel ratio definition:

A mixture that contains sufficient oxygen for the complete combustion of the fuel is called a stoichiometric air-fuel mixture.

Example:
Stoichiometric mixture for a gasoline engine:

The Stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel which means that it burns all fuel with no excess air. The stoichiometric air-fuel mixture for the gasoline fuel is about 14.7:1 which means that for every one gram of fuel, 14.7 grams of air are required.

The oxidation reaction is:

25 O₂ + 2 C₈ H₁₈ ----------------- 16CO₂ + 18 H₂0 + energy

What is an Air-fuel mixture?

The Air fuel ratio is the ratio between the mass of air and the mass of fuel in the fuel-air mixture at any point. While the mass is the mass of all constituents that compose the fuel and air.

How to calculate stoichiometrically air-fuel ratio?
How to determine the percentage of excess air?

The percentage of air in a mixture can be determined by the following formula:

percentage excess air = actual A/F ratio - stoichiometric A/F ratio/ stoichiometric A/F ratio

What is a weak or lean mixture?

A mixture that has an excess of air is called a lean or weak mixture. When the percentage of excess air gives positive results, the mixture would be weak or lean.

An ideal ratio of air to fuel that burns all fuel with no excess air is 14.7: 1 if the mixture greater than 14.7: 1, then it is considered a lean or weak mixture.

What is a rich mixture?

A mixture that has a deficiency of air is called a rich mixture. When the percentage excess air gives negative results, the mixture would be rich.

An ideal ratio of air to fuel that burns all fuel with no excess air is 14.7: 1 if the mixture lesser than 14.7: 1, then it is considered a rich mixture.

Air – fuel equivalence ratio:

For any mixture, the Air- fuel equivalence ratio is the ratio of actual air-fuel ratio to stoichiometry. It is represented by (lambda). A stoichiometric value of lambda is 1.0.

Lambda = actual air-fuel ratio / stoichiometric air- fuel ratio

For the rich mixture:

For a rich mixture the value of Lambda < 1.0

For the weak or lean mixture:

For a weak or lean mixture the value of Lambda > 1.0