常重力细水雾添加剂效能评估方法

On the evaluation method for the screening efficient water mist additives under normal gravity

高效细水雾添加剂的研制需要准确、快捷、低成本的灭火效能评估方法。利用二维对冲火焰构型研究了筛选细水雾化学添加剂的方法。在燃料流量4.5 L/min下,利用包裹火向尾流火的转变点作为灭火剂效能评估的参考依据可以减少火焰对壁面的热损,突出添加剂的化学抑制作用。试验装置燃烧腔入口速度均一,湍流度小于2%,不同添加剂及灭火溶液浓度对燃烧腔入口水雾粒径分布的影响较小。在高应变率下,化学添加剂的化学作用是影响火焰熄灭的主要因素。利用本方法对4种无机添加剂进行了筛选,结果表明,火焰临界熄灭点数据波动小、精度高,4种化学添加剂对甲烷二维对冲扩散火焰的抑制作用从高到低依次为KCl、K3PO4、NH4H2PO4、FeSO4,其中FeSO4对火焰有助燃作用。

This article is inclined to discuss the possibility to use the configuration of the two-dimensional counter-flow flame to screen out the highly efficient water mist additives with the purpose to develop highly efficient water mist additives for the spacecraft. However,since the traditional cup-type combustor had to use the configuration of co-flow diffusion flame,it would become inappropriate to the development of the new fire suppressants in the case of the spacecraft for it is too expensive and inaccurate in addition to its results limited to the applications under the condition of normal gravity. The strain rates where the enveloped flame can be turned into the wake flame can be used to indicate the efficiency of the additives. The fuel-supplying current rate can be made to keep on at a rate of 4. 5 standard litre per minute so as to be able to reduce the heat loss from the flame to the combustion chamber wall. For the aforementioned purpose,we have managed to make the infilling speed at the inlet of the combustion chamber quite uniform with its turbulence less than 2% via a contracted section,whereas the diameter distribution of the fuel droplets can be tested and controlled through the particle shadow-graph system. The results of our experiments show that the changes of the additive types and concentrations have minor effect on the droplet diameter distribution. For example,for the 0. 1 g/m L of solutions including KCl,NH4H2PO4,K3PO4 and FeSO4,the measured mean sauter in diameter tends to be 30. 97 μm,31. 51 μm,32. 83 μm and 28. 80 μm,respectively. What is more,the critical strain rates that can be measured and worked out turn to be of quite high accuracy. At higher strain rates,we have also managed to reduce the impact of the buoyancy on the flame extinction while taking into careful consideration the chemical effects of the additives used. At the same time,we have also tested the efficiency of the four inorganic additives that are used with this method. The results of our investigation and experiments show that the suppression efficiency from high to low can be illustrated as KCl 〉K3PO4 〉NH4H2PO4 〉FeSO4,the last of which can even support the combustion under way. Moreover,with the increase of the concentration,KCl,K3PO4 and NH4H2PO4 tend to gradually lose their effectiveness in terms of the fire suppression. Thus,it can be seen that the method under study can be used to screen out the chemical additives of water mist quickly and accurately,which has made it valuable to develop the new additives to be used for the astronautic space mission.