Experimental and numerical investigation of the gas-phase effectiveness of phosphorus compounds

The effectiveness of phosphorus-containing compounds as gas-phase combustion inhibitors varies widely with flame type. To understand this behavior, experiments are performed with dimethyl methylphosphonate (DMMP) added to the oxidizer stream of methane-air co-flow diffusion flames (cup-burner configuration). At low volume fraction, phosphorus (via DMMP addition) is shown to be about four times as effective as bromine (via Br-2 addition) at reducing the amount of CO2 required for extinguishment; however, above about 3000 mu L/L to 6000 mu L/L, the marginal effectiveness of DMMP is approximately zero. In contrast, the diminished effectiveness does not occur for Br2 addition. To explore the role of condensation of active phosphorus-containing compounds to the particles, laser-scattering measurements are performed. Finally, to examine the behavior of the flame stabilization region (which is responsible for extinguishment), premixed burning velocity simulations with detailed kinetics are performed for DMMP addition to methane-air flames. Analyses of the numerical results are performed to understand the variation in the inhibition mechanism with temperature, agent loading, and stoichiometry, to interpret the loss of effectiveness for DMMP in the present experiments. Copyright (C) 2015 John Wiley & Sons, Ltd.