Importance of air/fuel ratio in engine

Lambda
The lambda (A) value indicates how much the fuel-air mixture deviates from the ideal (stoichiometric) mixture ratio. Lambda equals 1 (^=1) with this mix ratio.
The lambda value can be calculated by dividing the actual air mass by the air mass required to burn all the fuel.
λ = actual air mass/required air mass
This required mass of air will depend on the mass of fuel injected and the type of fuel.
The required air mass is not the same for all fuels:
• 14.7 g of air to burn 1 g of gasoline.
• 14.6 g of air to burn 1 g of diesel.
• 15.5 g of air to burn 1 g of LPG.