Experimental Study On Water Mist Suppressing Gas Jet Flame

As urbanization process accelerating, the population density and fuel consumption of city were continuously increasing, also fuel proportion has changed. Gas fuel, such as natural gas has become to the main fuel of urban life. While natural gas has been widely used, the risk of natural gas leak fire and explosion had increasd. Water mist has been received considerable attention for fire suppression in recent years due to many advantages, such as high fire extingushing effectiveness, less water consumption, no pollution to environment, safety to protect objects etc. Previous studies have focused on extinguishing effect of water mist to solid and liquid fuel. However there was not much research on mechanism of water mist extinguishing, and applying water mist directly to extinguish gas jet flame had been studied rarely. Thus, through simulation experiment, the effectiveness of water mist suppressing gas jet flame has been researched in this paper, and the mechanism and influence factors of water mist extingushing gas jet flame has been discussed in depth.A non-premixed methane jet flame experimental platform was built to simulate gas jet flame at different diameter circular nozzle and different gas flow. Through this experimental platform, flame structure and thermal radiation of gas jet flame has been studied. Then water mist system had been put on the jet flame experimental platform to study water mist suppressing gas jet flame in open space, and to study the interaction between water mist and gas jet flame in confined space.The gas jet flame was divided by nozzle exit's Reynolds number into three phases which were laminar diffusion phase, fully turbulent diffusion phase and the phase between them. Nozzle diameter and gas flow. have been changed to obtain flame structure at different Reynolds number. It was been found that the gas flow and Reynolds numbers at blowing out were increased with nozzle diameter. There was a phenomenon of low frequency pulsation flame in bigger diameter nozzles at low gas flow, also the flame hight and thermal radiation of the low frequency pulsation flame were different from the others. The flame hight's change with gas flow, nozzle diameter and Reynolds numbers was studied.The simulation experiment of water mist suppressing non-premixed methane jet flame in open space was carried out. It was been found that there were two kinds of extinguishing process.The nozzle exit's Reynolds number was been used to divide and judge the difficulty of water mist suppressing gas jet flame, and it was shown that the gas jet flame at near and fully turbulent diffusion was very difficult to extinguish. The main mechanism of water mist extinguishing gas jet flame in open space has been discussed, and it was appeared that the suppressing effect was directly depended on the endothermic power of effective water mist flux. Through analyzing the influence of water mist pressure on extingushing gas jet flame, it was been found that high pressure water mist had higher extinguishing efficiency than low pressure water mist. Different injecting methods has been attempted, and the results showed that side injecting and bottom injecting had great extinguishing efficiency.A simulation experiment has been carried out to study the interaction of water mist and gas jet flame in confined space. The results showed that water mist required much time to extinguishing obstacle fire and a little time to extinguish the fire of condition of delaying injecting water mist. It was appeared that in confined space, the bigger fire source power was, the easier water mist suppress fire. Because confined space could accumulate a lot of vapor, water mist has shown better extinguishing efficiency in confined space than in open space.