On the effects of oxygen fraction on stability and combustion characteristics of dual-swirl oxy-methane flames: An experimental and numerical study

Abstract

The effects of oxygen fractions of primary and secondary streams on flow/flame interactions, flame stability and macrostructure, and combustion and emissions characteristics of premixed oxy-methane (CH4/CO2/O2) flames were studied experimentally and numerically in a dual annular counter-rotating swirl (DACRS) burner for applications of clean power production in gas turbines. The primary stream oxygen fractions (OFp) of 34 % and 25 % were paired with secondary stream oxygen fractions (OFs) ranging from 25 % to 39 % at fixed primary stream equivalence ratio (φp = 0.9), fixed velocity ratio of 3.0 by the primary (of 5 m/s) and secondary (of 1.667 m/s) streams, and over ranges of secondary stream equivalence ratios (φs). The results showed that at OFp = 34 % and OFS = 39 %, the pilot flame supports a lean secondary flame down to φs = 0.434 at combustor global equivalence ratio (φg) of 0.467. Flame flashback concerns were not seen in the operative OFs zone until the secondary stream reached stoichiometric operation (φs = 1.0). The widths and forms of the inner and outer recirculation zones (IRZ and ORZ) are not significantly affected by changes in OF. Reducing φg and OFg resulted in decreases in Damköhler number (Da), laminar flame speed, and CO emissions.

Keywords

• Gas turbine
• Premixed combustion
• Swirl burner
• Rotating flow -
• Stratified flames
• Lean combustion