4. Conclusion
For finding an alternative halon fire extinguishing agent for use in aircraft cargo compartments, R123 may have advantages over R125 as fire suppressants. To understand the different between R123 and R125, Fire extinguishing experiments with the addition of R123 and R125 to methane/air combustion systems were carried out, and detailed studies were also carried out in the thermal decomposition mechanism and fire extinguishing mechanism.
To explore the fire-extinguishing effectiveness of R123 and R125, the MEC, flame shape, flame height and temperature changes were studied through the cup-burner experiments. The MEC of R123 and R125 on suppressing the methane-air flame were 7.31 % and 8.91 % respectively, the comparison of flame shape and flame height variations showed that R123 had excellent fire extinguishing performance. The temperature change is not obvious when the concentration of R123 is less than 6 %, and the temperature changes sharply when approaching the fire extinguishing concentration indicate that the addition of R123 prompts the flame reaction kernel to move until extinguished.
The theoretical results directed that R123 by pyrolysis or reaction with free radicals would produce F·, Cl· and CF3· groups, these groups were very easy to react with H· and OH· to interrupt the combustion chain reaction. By analyzing the calculation of the reaction of R123 and R125 with free radicals, respectively, the Cl· produced by R123 had a greater impact on flame extinguishing than F·. Noteworthy, the theoretical calculation results are in good agreement with the experimental results.