Experimental and modeling study on the effects of dimethyl methylphosphonate addition on CH4/air and C3H8/air laminar premixed flames

Abstract

The present study aimed to address the limitations of existing kinetic mechanisms for dimethyl methylphosphonate (DMMP) by experimental measurements and kinetic optimization. Some new experimental data on laminar flame speeds of CH₄/air and C₃H₈/air mixtures doped with DMMP are obtained through the heat flux method, particularly in the rich combustion region where data are previously scarce. The results verify that, as the equivalence ratio increases, the inhibitory efficiency of DMMP decreases for methane and propane flames, but gradually increases for hydrogen flames. Subsequently, a new optimized DMMP mechanism is proposed utilizing the particle swarm algorithm to adjust the pre-exponential factors of 26 P-containing reactions within their uncertainty domains. The results demonstrate that the optimized mechanism not only improves the laminar flame speed of the DMMP-doped hydrocarbon flames (H₂, CH₄, and C₃H₈) in the stoichiometric and rich regions, but also improves the description of ignition delay time for the lean H₂/DMMP and the rich CH₄/DMMP mixtures. In addition, the updated model shows moderate to significant improvements in species concentration predictions, particularly in reproducing the CO yield during DMMP oxidation in Shock Tube, the HOPO of DMMP pyrolysis in Jet-Stirred Reactor, and the H-radicals of doped premixed flame in Flat Burner. In summary, the updated model offers a more comprehensive and accurate portrayal of the existing measurements including the laminar flame speed, ignition delay time, and species concentration.