Stability and Combustion/Emission Characteristics of Stratified Dual-Swirl Oxy-Methane Flames: Effects of Oxygen Fraction

Abstract

The stability, combustion, and emission features of stratified oxy-methane (CH4/O2/CO2) flames stabilized over a dual annular counter-rotating swirl (DACRS) burner, developed for gas turbine combustion applications, were investigated experimentally. The experiments were performed at fixed velocity ratio (Vr = Vp/Vs = 3.0) in both the primary and secondary streams at a constant primary stream velocity, Vp of 5 m/s and at fixed primary stream equivalence ratio, φp = 0.9, and over ranges of oxygen fractions (OFp for the primary stream, OFs for the secondary stream) and secondary stream equivalence ratios. Measurements of flame macrostructure, temperature profiles, and exhaust emissions were recorded to characterize the flames and validate future numerical models. The testing findings revealed no flame flashback within the operational ranges of OFp and OFs and up to φs = 1.0. However, the near stoichiometric operation of the primary stream (φp = 0.9) at OFp = 0.38 permitted the main secondary flame to tolerate exceptionally lean conditions (φs = 0.397 at OFs = 0.34 and φs = 0.223 at OFs = 0.39), raising the thresholds for the flame blowout. Increasing OFp from 0.21 to 0.38 significantly reduced φS at blowout from 0.537 to 0.223, corresponding to a decrease in the combustor's global equivalence ratio (φg) at blowout from 0.554 to 0.254 at global oxygen fraction (OFg) from 0.38 to 0.39. Lower OFp values caused earlier flame lift-off, indicating the greater influence of OFp on flame macrostructures.