Laminar flame speed is the speed at which an oxidation reaction takes place between the combustible constituents of a gas and oxygen at the surface of the inner core of the flame. It is dependent on the air fuel ratio, Lambda, and attains its maximum shortly before Lambda = 1.
Lambda = 1 is the condition where there is an ‘ideal’ air/fuel mix, known as stoichiometric. Lambda below 1 is a ‘rich’ mixture and Lambda greater than 1 is a ‘lean’ mixture.
For low concentrated gases, the laminar flame speed is the decisive criterion as to whether it is possible for the air gas mixture to be completely burned in the engine. The laminar flame speed of the gas must attain a minimal value of about 8cm/s at Lambda = 1 to ensure engine operation without a supporting gas to aid the combustion process.