Thermochemical state analysis of DMMP on non-premixed boundary layer flames

Abstract

Boundary layer flames (BLFs), established near flammable “active” walls in fire scenarios, are fueled by gaseous volatiles released during the thermal degradation of wall materials. Their suppression is essential for fire safety and often relies on the use of flame retardants. This study investigates the inhibition effectiveness of dimethyl methylphosphonate (DMMP), a phosphorous-based flame retardant, by analyzing its impact on non-premixed flames in a counterflow configuration. The counterflow flame is a suitable reference configuration since it offers a controlled environment for resolving the relevant transport and chemical effects, while also allowing a direct comparison with experimental data from the literature. Using methane as a reference fuel, the numerical framework is validated for undoped and DMMP-doped flames, and then used to examine how strain rate, oxidizer temperature, and injection location (fuel or oxidizer side) influence flame inhibition. To connect with near-wall conditions, boundary conditions from a non-premixed BLF generated in a side wall quenching (SWQ) setup, are also applied in the counterflow simulations. The results show that DMMP promotes combustion at low strain rates and high flame temperatures, but acts as an inhibitor at higher strain rates and lower flame temperatures. The injection location strongly influences inhibition efficiency: due to transport limitations, in a methane non-premixed flame at atmospheric conditions nearly 100 times more DMMP must be issued from the fuel-side compared to oxidizer-side injection to reach a comparable flame inhibition. Furthermore, lower oxidizer temperatures enhance inhibition by increasing DMMP penetration into the reaction zone. Since flame retardants are typically released with the fuel in real fires, these findings hint towards challenges and opportunities for achieving effective suppression.