Study on the inhibition mechanism of ammonium dihydrogen phosphate on the pyrolysis gas flame of red pine wood

Abstract

Ammonium phosphate-based fire extinguishers are widely used in forest fires due to their low cost and effectiveness against solid combustibles. However, the mechanism by which ammonium phosphate interacts with pyrolysis gas flames is not well understood, and there is a lack of precise experimental validation and correction of the chemical kinetics models regarding the suppression mechanism. Therefore, this study utilized NH4H2PO4 powder as a fire extinguishing agent and constructed a PLIF experimental system suitable for NH4H2PO4/red pine pyrolysis gas/air interactions. Through experiments, the changes in the concentration of OH radicals with different amounts of extinguishing agent at various equivalence ratios were measured. By employing Chemkin software, the study comprehensively analyzed the kinetic regulation mechanism of NH4H2PO4 on red pine pyrolysis gas flames from aspects such as chemical inhibition, sensitivity of elementary reactions, chemical reaction pathways, and chemical thermodynamics. The study revealed the characteristics and mechanisms of NH4H2PO4 powder inhibition, identifying R1092, R1098, R1116, and R1120 as the primary elementary reactions suppressing flame combustion. The mutual inhibition cycles formed among these reactions were found to be the main reasons for the suppression of H and OH radicals in the flame. Moreover, PO2 was identified as the primary phosphorus-containing fire extinguishing agent responsible for extinguishing the flame.