The mechanisms of suppressing a laminar methane-air co-flow diffusion flame formed on a cup burner with water vapor have been studied experimentally and numerically. The methane burned in a steel cup surrounded by a g...The mechanisms of suppressing a laminar methane-air co-flow diffusion flame formed on a cup burner with water vapor have been studied experimentally and numerically. The methane burned in a steel cup surrounded by a glass chimney. A mist generator produced fine droplets delivered though the glass chimney with air. These droplets were heated into water vapor when they went though the diffuser. The extinguishing limit was obtained by gradually increasing the amount of water vapor to replace the air in the coflowing oxidizer stream. Results showed that the agent concentration required for extinguishment was constant over a wide range of the oxidizer velocity, i.e., a so-called "plateau region". The measured extinguishing mass fractions of the agents were: (16.7 ± 0.6)% for H2O, (15.9 ± 0.6)% for CO2, and (31.9 ± 0.6)% for N2. The computation used the Fire Dynamics Simulator (FDS) de- veloped by the NIST. The numerical simulations showed that the predicted water vapor extinguishing limits and the flickering frequency were in good agreements with the experimental observations and, more importantly, revealed that the sup- pression of cup-burner flames occurred via a partial extinction mechanism (in which the flame base drifts downstream and then blows off) rather than the global extinction mechanism of typical counter-flow diffusion flames. And the flame-base oscillation just before the blow-off was the key step for the non-premixed flame extinction in the cup burner.展开更多
This paper presents measurements of combus- tion species of low pressure laminar premixed flat meth- ane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spec- trometr...This paper presents measurements of combus- tion species of low pressure laminar premixed flat meth- ane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spec- trometry (SR-MBMS). Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates. Results show that SR-MBMS offers a powerful tool for studying fire suppression chemistry of ha- lon replacements, which may extensively detect combustion species in the inhibited flames, especially radicals and inter- mediates. The suppressant CF3H is completely consumed in the preheat zone of premixed flames and produces fluori- nated radicals such as CF3 and CF2. CF3 is the main radical participating in flame inhibition cycles in the reactive zone. Unlike HBr, HF produced by CF3H is very stable and will not act as a radical scavenger because the bond energy of H-F is much higher than that of H-Br, which is responsible for less effectiveness than conventional bromine-based sup- pressants.展开更多
基金Supported by the China NKBRSF project (Grant No. 2001CB409600)
文摘The mechanisms of suppressing a laminar methane-air co-flow diffusion flame formed on a cup burner with water vapor have been studied experimentally and numerically. The methane burned in a steel cup surrounded by a glass chimney. A mist generator produced fine droplets delivered though the glass chimney with air. These droplets were heated into water vapor when they went though the diffuser. The extinguishing limit was obtained by gradually increasing the amount of water vapor to replace the air in the coflowing oxidizer stream. Results showed that the agent concentration required for extinguishment was constant over a wide range of the oxidizer velocity, i.e., a so-called "plateau region". The measured extinguishing mass fractions of the agents were: (16.7 ± 0.6)% for H2O, (15.9 ± 0.6)% for CO2, and (31.9 ± 0.6)% for N2. The computation used the Fire Dynamics Simulator (FDS) de- veloped by the NIST. The numerical simulations showed that the predicted water vapor extinguishing limits and the flickering frequency were in good agreements with the experimental observations and, more importantly, revealed that the sup- pression of cup-burner flames occurred via a partial extinction mechanism (in which the flame base drifts downstream and then blows off) rather than the global extinction mechanism of typical counter-flow diffusion flames. And the flame-base oscillation just before the blow-off was the key step for the non-premixed flame extinction in the cup burner.
基金supported by the China NKBRSF(Project No.2001CB409600)
文摘This paper presents measurements of combus- tion species of low pressure laminar premixed flat meth- ane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spec- trometry (SR-MBMS). Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates. Results show that SR-MBMS offers a powerful tool for studying fire suppression chemistry of ha- lon replacements, which may extensively detect combustion species in the inhibited flames, especially radicals and inter- mediates. The suppressant CF3H is completely consumed in the preheat zone of premixed flames and produces fluori- nated radicals such as CF3 and CF2. CF3 is the main radical participating in flame inhibition cycles in the reactive zone. Unlike HBr, HF produced by CF3H is very stable and will not act as a radical scavenger because the bond energy of H-F is much higher than that of H-Br, which is responsible for less effectiveness than conventional bromine-based sup- pressants.
