Experimental Study on Inhibition Effect of CF₃I over Methane/Air Combustion in an Explosion Vessel

Abstract

CF₃I is a potential replacement of HALON fire extinguishing agents. However, it emits very toxic gases when applied against fire. So all possible schemes to reduce its amount should be evaluated for it to come into practical use. CF₃Br, which has close chemical characteristics with CF₃I, is known to have an enhanced combustion inhibition effect when it is mixed with some inert gas. It is easily anticipated that CF₃I also has such effect, but it has not been studied yet. This paper reports an experimental study on reduction of explosion limit concentration of methane/air mixture when CF₃I is added solely or together with some inert gas. When CF₃I was added solely to a stoichiometric mixture of methane and air, explosion pressure observed in an explosion vessel decreased as concentration of CF₃I increased. However, the profile of explosion pressure curve with concentration was quite different with the case of CF₃Br. In the case of CF₃Br, the explosion pressure decreased monotonically as the concentration increased, and no explosion occurred after the concentration exceeded the limit value. On the other hand, in the case of CF₃I, the explosion pressure decreased as the concentration increased just as in the case of CF₃Br, while the concentration was smaller than about 8%. Then the explosion pressure increased as the concentration increased. It reached a peak pressure, and decreased again until the concentration reached the limit value (51.5%). The enhanced inhibition effect was also observed when CF₃I was combined with nitrogen or carbon dioxide.