Experimental study on combustion characteristics and lean blow-out limits of non-premixed oxy-methane flames in a porous-plate reactor

The combustion characteristics and lean blow-out (LBO) limits of non-premixed oxy-methane flames in a face-to-face two-porous-plates reactor are experimentally investigated in this study. The reactor mimics the process of oxygen permeation and oxy-fuel combustion inside high-temperature membrane reactors (HTMRs). The fuel (CH₄) was supplied together with CO₂ in the main longitudinal stream while the oxygen was supplied via the upper and lower rectangular porous plates. The experiments were conducted over ranges of equivalence ratio (0.5, 0.7 and 1.0), CO₂ percentage in the oxidizer mixture (0, 27, 35, 55 and 70%), and fuel firing rate (0.5, 0.75, 1.0, 1.5, 2, 2.5 and 3 kW). At fixed CO₂%, there was insignificant increase in flame length while increasing the equivalence ratio. The flame luminous intensity was found to be decreasing while increasing CO₂%. Increase in the LBO limit was obtained with the increase in the equivalence ratio at fixed fuel firing rate. The minimum limit of O₂% to allow for a visible flame was found to be about 21% (79% CO₂) at stoichiometric condition. The increase in fuel firing rate decreased CO₂% at blow-out condition due to attainment of the required flow speed that overwhelmed the increase in flame speed.