A stoichiometric air-fuel ratio is the exact air-fuel ratio needed to burn the fuel in the mixture completely, leading to the complete combustion of the fuel. The stoichiometric ratio differs depending on fuel type.
The stoichiometric ratio for gasoline fuel is 14.7:1. This means that for every unit volume of fuel, 14.7 volume units of air are needed to burn the fuel in the mixture completely. This leads to clearer combustion in the engine, which reduces the emission of polluting particles and increases the efficiency of the engine. The stochiometric ratio for methanol is 6.4:1, and the stochiometric ratio for ethanol is 9:1.