| In recent years, the people who are engaged in the work of explosion or explosionsuppression are puzzled with the reality of gas explosion which happen frequently. And asducts are gradually used in big amount in industry, the phenomenon of flame propagating induct is paid more attention than before; therefore, the studies about it are increasing day byday. Undoubtedly, to study the mechanism of flame propagating in duct, as well as to seekafter the new ways or new methods of explosion suppression will benefit for both ofexplosion prevention and the security of production and people.Based on the reaslization above, the numerical simulation techniques are adopted to studythe premixed flame propagating in duct and activity of fire extinguishing in inert gases in thisarticle. The main works and conclusions are in the following:(1) The model of a two-dimensional closed-open pipe, as well as a group of governingequations of fluid and combustion are setup to study the premixed acetylene/air flamepropagating in duct. The equations are discretizated by Finite Volum Method, and specificheat of gases is set to be the function of temperature. The simulation shows that flamepropagates aroundly as a semi-sphere once the premixed gases are ingited. After some time,when the flame approaches the wall, the flame is rebounded. Then the flame reboundedinteracts with the gases which are produced from combustion. So in this way, the flame isstretched, and finally a "tulip" flame is formed. The flame stretch produces turbulent andmakes the reaction rate increase. Then a feed-back mechanism is formed, which makese theflame accelerate in duct. The comparison between simulation and experiment is made, and themaximum error is found to be less than 28%, so in this way the simulation is proved to beveracious and rational.(2) Open-open channels of tube and parallel plates are established, and flame extinguishingin channels in the effects of inert gases are studied. It is found that flame will extinguisheasier as the concentration of inert gases increasing. Once the concentrations increase to someextent, the quenching lengths of flame in tube and plates will not change. The reason forflame extinguishing easier in inert gases can be explained that premixed mixtures are dilutedwith the complement of inert gases, which eventually leads to the reduction of reaction rate.(3) The rules of flame extinguishing in tube and parallel plates are summerized. Some factors which affect fire extinguishment such as premixed gas reactivity, sizes of tube andplates, flame velocity et al are taken into account. It is found that the flame quenchinglengthes for propane and ethylene are in conic relation with diameters of the tube or widths ofthe parallel plates. However, as to acetylene flame, the rules in tube are different with that inparallel plates. In tube, the quenching lengthes are in exponatial relation with flame velocity,but in parallel plates, the relation is linearity. The comparison of flame extinguishing in tubeand plates are made, and it si proved that tube has better quenching effect than plates.(4) The mathematical model of flame extinguishing in tube is set up, and a formulation isgotten. From the formulation, it is can be seen that the quenching distance of tube is positiveproportional to one-third power of heat conductivity and molecular weight, but negativeproportional to one-third power of reaction rate of flame. |
