N2和CO2抑制煤燃烧火焰特性对比试验研究

为了研究N_2和CO_2气体灭火剂在抑制煤明火燃烧特性方面的不同,通过搭建受限空间煤明火燃烧试验,分别开展了11.97%、16.81%、20.76%的N_2和10.79%、14.89%、20.32%的CO_2作用下煤明火燃烧抑制试验。鉴于火焰表面积变化与热释放速率变化呈正相关,基于火焰图像分析法开展试验研究。试验过程中,首先,通过数码摄像仪记录不同体积分数惰性气体作用下煤燃烧火焰面积的变化,然后利用Matlab软件进行火焰图像特征提取和"对比度增强"预处理,消除图像记录过程中存在的噪声,以便于有效进行火焰目标识别;其次,基于"阈值法"原理,利用Image-Pro Plus软件对预处理过的火焰目标进行识别和计算,进而实时获得试验过程中火焰表面积;最后,使用小波变换理论对火焰表面积变化曲线进行消噪处理,以获得火焰表面积变化趋势及主要波动信息。结果表明,CO_2比N_2具有更好的熄灭煤明火燃烧的能力,CO_2作用下煤火火焰表面积呈现指数下降,而N_2作用下呈现直线下降,且CO_2的灭火时间比N_2缩短了25%以上。该试验结果明确了N_2和CO_2在熄灭煤明火特性上的不同,弥补了CO_2仅比N_2具有更好的抑爆特性的认识。

Comparative experiment on the characteristics of inhibiting the flame spreading with N2 and CO2 in the process of coal spontaneous combustion

In order to pursue and explore the different characteristic features of N2 and CO2 for inhibiting the coal flame spontaneous combustion,this paper has done a series of contrast and comparative experiments and established an experimental platform for the coal flaming combustion in a confined space to observe and determine their inhibition effects on the coal flame combustion.The said contrast and comparative experiments have been done under the N2 concentration rates of 11.97％,16.81％ and 20.76％,respectively,under the CO2 concentration rates of 10.79％,14.89％ and 20.32％,respectively.Since the changes that may take place in the flame surface area are positively correlated with those in the heat release rate,the paper has adopted the flame image analysis method to record the changes of the flame surface area in the process of the coal flaming combustion under the different ratios of inert gases in the experiment process by using a digital video.And,next,in order to eliminate the noise in the recording process and identify and determine the target fire image effectively,we have also observed and analyzed the fire image features and described the fire images by using a contrast enhancement Matlab software.Furthermore,we have also identified and calculated the target fire forms and strengths based on the threshold methods,in hoping to trace the real-time changes of the flame surface area during experiment process by using the Image-Pro Plus software.And,last of all,we have also adopted wavelet transform theory so as to eliminate the noise of the flame surface area and make clear the changing trends of the flame surface area and the main fluctuation signals in the experiment process.The experimental results we have gained prove that the fire extinguishing power of CO2 turns out to be much better than that of N2 during the coal flame combustion,for the flame surface area tends to reveal an exponentially decreasing trend with CO2 extinguishing effects in coal combustion,whilst the flame surface area indicates a linear decrease trend with the use of N2.In addition,the extinguishing efficiency of CO2 has been found 25％ greater than that of N2.Thus,the results of our contrast and comparative experiments help to clarify the differences of characteristics and efficiencies in extinguishing the coal flame combustion between N2 and CO2,which makes up for our understanding in that CO2 enjoys more powerful explosion suppression capability than that of N2.