不同强度冲击波诱导沉积煤尘爆炸火焰传播特性

Flame propagation characteristics of deposited coal dust explosion induced by shock waves of different intensities

在全透明有机玻璃管道中,利用同步控制系统、高速摄像系统和高速粒子成像测速系统(PIV),从爆炸超压、火焰传播速度、火焰温度和复合火焰演化规律等方面研究了不同瓦斯爆炸强度条件下诱导沉积煤尘爆炸特性和复合火焰传播特性,并分析了煤尘卷扬湍流特征。实验结果表明:3种工况下,随着甲烷体积分数的增加,爆炸超压和压力上升速率明显增高,压力峰值来临时刻减小,且当体积分数超过8.5%后,压力曲线和压力上升速率曲线出现明显的振荡特征;复合火焰传播速度远大于纯瓦斯爆炸工况,且复合火焰传播速度-位置曲线均呈波动上升特征;甲烷的体积分数越接近当量比,爆炸超压、波前流速、火焰锋面温度及其温度上升速率越高;甲烷体积分数为9.5%和8.5%时,复合火焰呈“倒钩形”,之后很快出现火焰加速;而甲烷体积分数降至8.5%后,复合火焰亮度降低,结构呈现破碎和不连续的形态特点。PIV测试表明:甲烷体积分数为9.5%时,初始爆炸强度高,波前流速快,煤粉可随冲击波整体快速运动,卷扬区整体湍流强度较高,大大加快了煤粉与空气的混合速度,促进了卷扬煤粉的燃烧。较高的冲击波波前流速和火焰锋面温度2种参数相结合是造成甲烷/煤尘复合火焰不断加速的原因。

In a fully transparent organic glass pipeline,the explosion characteristics and flame propagation characteristics of deposited coal dust explosion induced by gas explosion were studied from explosion over-pressure,flame propagation speed,flame temperature and the evolution law of compound flame structure,using synchronous control system,high-speed camera system and high-speed particle image velocimetry system(PIV).The results showed that under three working conditions,the explosion overpressure and pressure rise rate increased obviously with the increase of methane volume fraction,and the arrival time of pressure peak decreased gradually.When the methane volume fraction exceeded 8.5%,the pressure-time curve and pressure rise rate-time curve showed some obvious oscillation characteristics.The propagation speed of the compound flame was much greater than that under pure methane explosion condition,and the velocity-position curve of compound flame showed the characteristics of fluctuation and rising.The closer the volume fraction of methane to the equivalence ratio,the higher the explosion overpressure,wave front velocity,flame front temperature and its temperature rising rate.When the volume fraction of methane was 9.5%and 8.5%,the compound flame was“barb shaped”,after that,the flame accelerated rapidly.However,when the volume fraction of methane decreased to 8.5%,the brightness of the compound flame was slightly lower,and the structure was broken and discontinuous.The results of PIV test showed that when the volume fraction of methane was 9.5%,due to the high initial explosion intensity and wave front velocity,the coal powder moved rapidly with the shock wave,and the turbulence intensity in the winch area was high,which greatly accelerated the mixing speed of pulverized coal and air,and promoted the combustion of pulverized coal.Therefore,the combination of higher shock wave front velocity and flame surface temperature is the reason for the continuous acceleration of methane/coal dust composite flame.