The laminar flame speed correlation proposed by Guelder is given in Eqn. 14. It involves the use of fuel-dependent constants, so you must specify the fuel type.
The use of this method for general applications is recommended.
Gulder Laminar Flame Speed Properties
Fuel Name
Specifies the fuel name control mechanism option for CFM combustion.
You should select an existing fuel that has the closest chemical structure to the real fuel. Any differences will have effects on the solution, but should still be a good approximation.