Experimental investigation in extinction of turbulent non-premixed disk stabilized flames

Abstract

In order to describe flame stability of turbulent, non premixed flames, the flow-, mixing- and reaction properties and the corresponding turbulence characteristics have been investigated in a concentric burner with partially blocked air exit and variable geometry. As fuel, natural gas with about 95% CH4 and several mixtures of natural gas with N2 or H2 were used, to get certain variations in the reaction kinetics and the laminar burning velocity Sl. The first part of the paper tests a previously suggested model, which describes flame stability in accordance with premixed flames based on Peclet numbers formed with the flow velocity on the one hand and with the laminar burning velocity on the other hand. Therefore the influence of systematic variations of geometry and Sl on the stability limits has been investigated and the assumption of premixed flame areas in the stabilization area has been confirmed: that means stoichiometric conditions, at least timely averaged, can be found in this area. The herein presented modification of this model overcomes the disadvantage, that the applicability of the used original model was restricted to a single fuel/air—ratio for each geometry, by taking the influence of the different flow conditions into consideration. In particular the depending turbulence properties in the stabilization zone, which control heat and mass transfer and therefore increase the effective flame speed, are used to replace the laminar flame speed Sl by a correlation between the turbulent flame velocity St and Sl. As a result of this modification the shape of the blow off limit for different geometries and fuel compositions can be described by a single correlation.