波纹管道阻火器内火焰传播的实验与数值模拟研究

对乙烯-空气预混火焰在波纹管道阻火器中的传播与淬熄过程进行了实验和数值模拟研究,实验结果显示:当乙烯接近当量浓度时,预混气体爆炸压力变化过程可分为4个阶段,等压燃烧阶段、缓慢上升阶段、快速上升阶段和压力振荡阶段;在爆炸过程中,由于反射压力波和火焰相互作用的影响,超压值出现多次振荡,压力振荡阶段一般可以持续数十毫秒;乙烯-空气火焰传播速度随管径增加、阻火单元波纹高度减小呈递增趋势,而且随着阻火单元厚度的增加,阻火器的阻火能力明显提高,可以更有效地使火焰淬熄。数值模拟结果显示:在管道封闭端点火后,火焰面呈半球形并以层流扩散的方式向四周传播;当火焰传播到管道壁面时,在管道壁面的约束作用下,火焰面发生变形,壁面附近的火焰逐渐超过了管道轴线附近的火焰,最后形成了“郁金香”状的火焰结构;当爆燃火焰经过阻火单元时,高温已燃气体被其吸收大量热量,同时在反应区产生的稀疏波作用下,气体温度逐渐降低、化学反应速率迅速减小,最终导致火焰被熄灭。通过模拟计算结果可以看出,在整个爆炸过程中,火焰传播速度与爆炸压力波动均较为明显。并提出了孔隙率和阻火单元厚度对火焰传播的影响机制。基于传热学理论模型,并结合实验数据,得出了爆燃火焰速度与爆炸压力之间的关系,为工业装置阻火器的设计和选型提供更为准确的参考依据。

Experimental investigation and numerical simulation of flame propagation and quenching process in the in-line crimped-ribbon flame arrester

An experimental system and numerical model were set up to investigate ethylene-air premix deflagration flame propagation and quenching by crimped-ribbon flame arresters in a horizontal pipe,closed at both ends.The deflagration suppression experiment showed that,when the concentration of the flammable gas was close to the stoichiometric ratio (6.6％ ethylene by volume),the evolution processes of explosion pressure for the premixed gas of ethylene-air in the pipe (D=32,80,400 mm) could be divided into four stages:isobaric combustion,slow rise,quick rise and pressure oscillation.During the explosion,due to the interaction between the reflected pressure wave and the flame,the overpressure value fluctuated several times,and the pressure oscillation lasted normally tens of milliseconds.The ethylene-air deflagration flame velocity gradually increased with the increase of the pipe diameter and the decrease of the crimp height.Furthermore,the performance of the flame arrester gradually increased with the increase of the element length.The simulation result showed that the flame front was formed in a semi-sphere shape and spread around in the form of laminar diffusion after ignition at the closed end on the left side.When the flame reached the wall,its shape enlarged under the restriction of the pipe.Then the flame velocity at the near wall gradually exceeded that at the pipe axis,and finally a "tulip" flame was formed.A big amount of heat was lost as the flame front contacted the arrester element,under the influence from the rarefaction waves formed in the reaction area,the chemical reaction rate decreased rapidly,and the flame temperature decreased gradually,which resulted in quenching.During the whole explosion process,the pressure wave and the flame velocity were accompanied by drastic fluctuations through the simulation calculation.The influence mechanism of the porosity and the element length on the flame propagation was analyzed numerically.Finally,the relationship between the deflagration flame velocity and the explosion pressure was derived based on the classic theory of the heat transfer and the experimental data.This study will serve as accurate reference for the design and selection of the crimped-ribbon flame arrester.