Experimental Study on the Effects of Reynolds Number Ratio on Flame Stability, Macrostructure, and Emissions in Dual Annular Burner for CH4 and CH4/H2 Combustion

Abstract Flame stability is crucial for many industrial and aviation applications. Flow parameters, notably Reynolds number and velocity, significantly affect combustor power and flame characteristics. Thus, the influence of the Reynolds number ratio (RR = Reout/Rein) from 1 to 2.5 was investigated for CH4 and CH4/H2 fuel in a dual annular jet burner. Twenty percent of the fuel volume for CH4/H2 combustion was hydrogen. For each RR, the global equivalence ratio varied from stoichiometric to lean blowoff (φg = 0.48), while power ranged from 2.9 to 17.8 kW. The static stability analysis indicates that increasing the RR decreases the lean blowoff limit by approximately 2%. Reynolds number ratios also change the flame macrostructure transitioning from M-shaped flame to V-shaped flame for methane combustion at stoichiometric conditions. At RR = 1, three shear layers are anchored at the central bluff body and inner annulus in the M-shaped flame. However, at higher RR, only the center shear layer is anchored on the bluff body forming V-shaped flame. For CH4/H2 combustion at stoichiometric conditions, the flame shape forms the M shape consistently with the increased flame front for RR of 1–2.5. Additionally, emission analysis showed that higher RR produced more thermal NOx at higher combustor power, while CO emission was found to be highest at RR = 1.5 for methane combustion. For hydrogen-blended methane combustion, the emission of CO and NOx were found to be decreased compared to methane combustion.