Effects of Ultra Lean Premixed Gas on Extinction of Lean Premixed Flame.

Abstract

Effects of ultra lean premixed gas (ULG) on extinction of adjoined lean premixed flame have been studied numerically, using a detailed chemical model of 177 reaction steps with 32 species. The extinction phenomena of the methane / air flame formed in the counterflow of lean mixtures can be divided two distinct regimes depending on fuel concentrations of leaner side mixture. With the equivalence ratio of the leaner side mixture above approximately 0.4, twin flames are in existence and strongly interact each other. With the leaner side below 0.4 ; the ULG condition, the interaction is weak and the thicker side mixture mainly influences the extinction. However, the ULG side condition affects the extinction boundary slightly even in the weak interaction region. Though the visible flame and the CH peak in the ULG side cannot be observed, the calculated heat release profiles reveal that the reaction in the ULG side exists even in this region. This heat release which is supported with molecular level heat and mass transfer from the flame prevents the heat loss of the flame and extends extinction limits. These diffusion-controlled phenomena play a key role on the effects of the ULG on the flame extinction in the weak interaction condition.