IMPACT OF CO_2/N_2/Ar ADDITION ON THE INTERNAL STRUCTURE AND STABILITY OF NONPREMIXED CH4/AIR FLAMES AT LIFTING

摘要

The authors focused on how adding CO_2 to the air influences the transition from an attached flame to a lifted flame issued from a coaxial nonpremixed methane-air jet. To discriminate between effects due to a diluent (dilution, thermal, or chemical impacts), chemically and thermally inert N_2 and chemically inert Ar were also investigated. Flame lifting always occurs, essentially controlled by the critical flow-rate ratio, (Q_(diluent~I)Q_(air))_(lifting) CO_2 has the strongest ability to break flame stability, followed by N_2, then by Ar. A unique attachment height and OH thickness characterize lifting for all the diluents; lifting is attained once the same critical flame edge propagation speed is reached. (Q_(diluent~I)Q_(air)I(Q_(diluent)~I Q_(air) _(lifting) is the affine parameter of similarity laws describing H_a and EpoH evolutions with dilution. Aerodynamics competes with dilution to impose lifting and boundary effects cannot be ignored in a fine analysis. The flame behaves differently according to whether lifting results from aerodynamics or dilution.