Inhibition of atmospheric lean and rich CH 4/O 2/Ar flames by phosphorus-containing compound

Abstract

The mechanism of flame inhibition by phosphorus-containing species (PCSs) is known to involve their effect on the recombination of atoms and free radicals in flames. Chemical inhibition of laminar atmospheric methane/oxygen flames by trimethylphosphate over a range of equivalence ratio has been studied experimentally, using the heat flux method for measurement of burning velocity and molecular beam mass spectrometry for measurement of concentration profiles of both stable and labile species, and with numerical modeling using detailed chemical kinetic reaction mechanisms. Concentrations of H and OH in flames with and without the inhibitor were obtained by measurements and modeling. The addition of the inhibitor reduces the maximum concentrations of H and OH (in the reaction zone) in the lean and rich flame. This reduction is much larger in the rich flame than in the lean one. The concentration profiles of PCSs—PO, PO 2, HOPO, HOPO 2, and H 3PO 4 were measured and simulated for rich and lean flames stabilized on a flat burner. According to flame speed measurements for inhibited CH 4/air flames over a range of ϕ, the inhibition effectiveness E i increases in the range of ϕ = 0.8–1.2 and then decreases with a further increase of ϕ. The increase in E i in the range ϕ = 0.7–1.2 is attributed to a change of PCSs composition. The reduction in E i for ϕ > 1.2 can be explained by a decrease in the concentration of active PCSs due to an increase in the concentration of inactive species, such as CH 3PO 2 and other products of incomplete combustion of TMP. The inhibition effectiveness E i versus ϕ correlates with change of H and OH concentration at addition of TMP in flame. Validation of the previously developed model for inhibition by PCSs has shown that in spite of some discrepancies it adequately describes many experimental results.