Combustion regimes stability based on liftoff and blow-off measurements of oxy-fuel flames in an internal recirculation combustion chamber

Abstract

The effect of dilution on the static stability of turbulent oxy-methane flames was evaluated in an equivalence ratio range of 0.6 to 1.0 with CO2 mole fraction ranging from 0% to 71.8%. A set of experiments was carried out in a lab scale combustor with internal recirculation. The anchored flame, lifted flame, and MILD regimes were established keeping the bulk velocity of the O2/CO2 mixture stable at 30 m/s. Measurements of the reaction zone were carried out by OH∗ chemiluminescence. The anchored flame presented a jet flame macrostructure stabilized at the burner’s nozzle with CO2 mole fraction varying from 0% to 42.9% at stoichiometric conditions. The lifted flame exhibited oscillations in terms of the topology and of the liftoff height in the range of 42.9% to 60% CO2 mole fraction. The MILD regime occurred from 60% to blow-off occurred at 71.9% CO2 mole fraction. In the MILD regime, the chemical reactions were uniformly distributed inside the combustion chamber, in addition to a considerable reduction in OH∗ intensity. The maximum OH∗ intensity in the MILD regime decreased by 89% when compared to the anchored flame case. Liftoff and blow-off were assessed in the equivalence ratio range of 0.6 to 1.0. Regardless of the equivalence ratio, both phenomena exhibited a correlation with the laminar flame speed rather than the adiabatic flame temperature. Such a correlation suggests that laminar flame speed is a representative parameter of changes in species transport and chemical kinetics caused by dilution.