The role of chemistry in the retardant effect of dimethyl methylphosphonate in flame-wall interaction

Organophosphorous compounds can act as chemical inhibitors for fire suppression and have recently received significant attention in the combustion community due to their potential to induce flame extinction through a radical recombination process. To optimize their use, a comprehensive understanding of the extinction dynamics is essential. In this study, mixtures of methane with dimethyl methylphosphonate (DMMP) are investigated in laminar conditions, with a specific focus on flame-wall interaction. The ultimate objective is obtaining a deeper insight into the flame quenching process, which is synergistically enhanced by heat transfer to the wall and the chemical retardant effect of DMMP. Detailed chemistry information is implemented by setting up an ad-hoc skeletal kinetic mechanism. This is developed and validated for flame configurations with increasing complexity, including freely propagating premixed flames, head-on-quenching flames, and side-wall quenching flames. The results indicate that the skeletal mechanism is able to reproduce available experimental data for flame speed and ignition delay time, as well as the main flame features and quenching characteristics in flame-wall interactions for an increasing level of DMMP. Simulations of a side-wall quenching burner, incorporating a secondary fuel injection through a porous insert at the wall, are carried out. Chemical analyses provide detailed insight into the role of flame retardant during the flame quenching process. The results show that the HOPO/PO2 2 catalytic cycle is of major importance for the suppressant effect, further supported by the formation of CH3PO2 3 PO 2 as an intermediate, increasing the formation of HOPO itself. Moreover, the CO mass fraction is observed to increase also because of the radical scavenging effect, inhibiting the conversion to CO2 2 via CO + OH -> CO2 2 + H. Overall, this study advances the understanding of the chemical features of flame quenching in the presence of flame retardants containing implications for fire safety applications.