EXPERIMENTAL STUDY AND MODELING OF THE EFFECT OF PHOSHORUS- CONTAINING COMPOUNDS ON PREMIXED ATMOSPHERIC METHANE-OXYGEN FLAME STRUCTURE AND PROPAGATION VELOCITY

摘要

Organophosphorus compounds (OPC) are known to be effective fire retardants and fire suppressants and are perspective candidates for replacement of halons forbidden for production by Montreal Protocol. Appreciable progress in the comprehensive study of the flames doped with OPC achieved in recent years resulted in the creation of number of kinetic models of OPC destruction in flames and the mechanisms of their action on a combustion process. The study of Twarowski who discovered that the products of phosphine oxidation catalyze the recombination of H and OH radicals, proposed and refined the kinetic mechanism of this process that preceded the appearance of these models. PO, PO_2, HOPO, HOPO_2 and OP(OH)_3 were identified in the flame doped with OPC and their concentrations were measured. One of the first published models for OPC destruction in a flame was the model of the destruction of dimethyl methylphosphonate (DMMP) in a H_2/O_2 flame proposed by Werner and Cool and based on the theoretical calculation of Melius. Unfortunately, this model was insufficiently validated by experimental data. Authors of the present papers proposed the models for the destruction of TMP and DMMP in a H_2/O_2 flame slightly different from the model. The simulated structure of subatmos-pheric H_2/O_2 flames doped with TMP and DMMP was in satisfactory agreement with experimental results. The model was refined later and applied for simulation of structure of CH_4/O_2 flame doped with TMP at a pressure of 0.1 bar and calculation of its burning velocity at P=1 bar. The results were compared with experimental data obtained by the authors of the model. Babushok and Tsang, proposed a kinetic model, composed of the stages with participation of OPC from the model of Werner and Cool, 79 reactions from the Twarowski mechanism (including reactions of phosphine oxidation with participation of PH_3, PH_2, PH), and several stages of interaction of CH_3 and CH_3O with phosphorus oxides. The rate constants of main Twarowski reactions have been modified including their dependencies from the temperature. Unfortunately, there are no published data on simulated structure of a flame doped with OPC using this model that could facilitate validation of the model by comparing the calculated data with experimental results. This model was applied only for calculation of burning velocities of stoichiometric CH_4/air flame at a pressure of 1 bar. The investigations of Westbrook and co-workers devoted to the development of mechanisms of destruction and pyrolysis of OPC in flames are of great interest. This study is significant because the results of the calculation of thermo-chemical properties of OPC obtained using BAC-MP4 and PM3 codes are presented and compared with published data. The kinetic model of DMMP and TMP destruction in a flame includes 202 reactions involving 41 phosphorus-containing species. At the same time the model takes into consideration practically all intermediates. Rate constants of many reactions are proposed by the authors. Rate constants of the reactions of the Twarowski mechanism have been modified. Comparison of calculated data obtained with a help of this model with experimental results on structure of subatmopheric H_2/O_2 flame doped with DMMP and TMP demonstrated satisfactory agreement not only for stable flame species but also for labile phosphorus-containing species PO, PO_2, HOPO and HOPO_2. The mechanism predicts the promoting effect of TMP and DMMP additives on H_2/O_2 flame stabilized on a flat burner at a pressure of 0.062 bar. In the work neither scheme of reactions in a flame nor rate constants are presented. Nevertheless, there is a reference to the kinetic data on the web site.