Effect of inert and reactive admixtures on the initiation and propagation of laminar spherical flames

The initial stage of the propagation of discharge-initiated laminar spherical flame in stoichiometric natural gas- and isobutylene-oxygen mixtures containing krypton or carbon dioxide and in the hydrogen-air mixture at atmospheric pressure in a constant-volume bomb has been investigated by high-speed color cinematography. Dilution of the combustible mixtures with the admixtures increases the steady-state flame front formation time by a factor larger than 10. The phlegmatizing effect of carbon dioxide on hydrocarbon combustion is stronger than that of krypton. For given combustible mixtures, the ratio of steady-state flame front formation times is inversely proportional to the ratio of the temperature rise values for the flames. The introduction of a minor amount of a reactive admixture (1.2% isobutylene) into the stoichiometric hydrogen-air mixture greatly increases the steady-state flame front formation time.