Numerical investigation of the chemical and physical effects of halogenated fire suppressants addition on methane–air mixtures

Abstract

Previous experimental and numerical studies have demonstrated the unwanted promotion effect caused by potential halon replacements added to hydrocarbon–air mixtures. To explore this abnormal phenomenon, the chemical and physical contributions of the addition of C6F12O (Novec 1230) and C2HF5 (HFC-125) on the laminar flame speeds of the CH4–air mixtures are numerically investigated. Numerical simulations are conducted using the CHEMKIN-PRO software with newly developed fluorinated compounds’ mechanisms. Based on the interaction between the chemical effect and the physical effect, the equivalence ratio zone is divided into synergistic zone and antagonistic zone. Furthermore, the fuel-like characteristics of C6F12O and C2HF5 are also studied. In the lean CH4–air condition, the agents contribute to increasing the equivalence ratio, thus increasing the flame speeds chemically but cooling the mixture physically. When the actual equivalence ratio of the agent–CH4–air mixture is larger than 1.10 (for the C2HF5 addition) or 1.20 (for the C6F12O addition), the agents create an over-rich fuel mixture, thus decreasing the flame speed chemically. The contribution of the chemical effect is studied under different initial temperature and pressure conditions. The results indicate that increasing the temperature slightly lowers the chemical contribution, whereas increasing the pressure largely increases the chemical contribution. Additionally, a sensitivity analysis is conducted to interpret the large chemical component increase under high pressure conditions.