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.