Investigation Of The Chemical And Physical Effects Of Halogenated Fire Suppressants On Methane-Air Mixtures

Halogenated hydrocarbons are a kind of promising halon replacements,however,recent studies have shown that some halogenated compounds caused combustion promotion effect in fuel lean condition,which lead to the increasing of temperature and pressure.The flame inhibition effect of halogenated compounds can be attribute to the chemical and physical effects,the combined action of those two effects caused combustion promotion or inhibition.In experiments,it is difficult to separate the chemical and physical effects,while using numerical simulation,we can separate the chemical and physical effects,thus leading to clear results that are unobtainable from experiments.In present study,we artificially modified the reaction constant of elementary reactions which relate to C6F12O and C2HF5 to turn the chemical effect on or off.The results showed that the equivalence zone can be divided into two sections:synergistic effect zone and antagonistic effect zone.The assumption that the function of low-concentration fluorinated halon replacements in lean fuel-air mixtures is to primarily cool the flame and change the stoichiometric was validated computationally.When the equivalence ratio of agent-CH4-air mixture reaches ??1.10 or ??1.20,a further agent adding will cause a fuel-rich condition,which decreases the flame speed chemically and physically.The results indicated that temperature rise leads to the decrease of chemical effect while the pressure rise increases the chemical effect.The flame inhibition efficiency of CF3I is comparable with CF3Br and CF3I is environmental friendly since it does not destroy the ozone layer.In present study,we measured the laminar flame speed of methane-air-CF3I mixtures using the counter-flow configuration.The experimental date agree well with the calculated value.In contrast to C6F12O and C2HF5,CF3I inhibited the methane-air flame in fuel lean condition.For? = 0.6,0.3%CF3I addition reduced the flame speed to 52.4%of the uninhibited flame speed.Then we separated the chemical and physical effects of CF3I and found that the chemical effect of CF3I always decreased the flame speed.As the equivalence ratio changed from ? = 0.6 to ? = 1.3,the chemical effect decreased at first then increased.