甲烷/空气混合物的火花着火敏感性分析

Theoretical study on electric spark ignition sensitivity of methane/air mixture

最小点火能、着火延迟时间和火焰传播速度是表征可燃气体着火危险性的重要参数。根据可燃气体的着火机理,通过建立数学模型并数值计算揭示了环境温度、火花能量对甲烷/空气混合物在电火花作用下着火过程的影响机制。结果表明:随环境温度上升,甲烷/空气混合物的最小点火能降低,着火延迟时间缩短,火焰传播速度增大;火花能量对火焰传播速度无影响,当火花能量逐渐接近最小点火能时,火花能量对着火延迟时间影响显著。

Minimum ignition energy,ignition delay time,and flame velocity are important parameters for investigating the flammability of combustible gases and designing relevant safety standards.Theoretical studies rarely involve the influence mechanism of actual working conditions,especially the high-temperature environment and the intensity of the ignition source,on the ignition of flammable gases by electric sparks.In this paper,a complete mathematical model for simulating the ignition of combustible gas mixtures by spark is established based on the ignition mechanism of flammable gas.To solve this model,the Taylor series was used to expand the first-order and second-order differential terms,and substitute the different expressions into the above-mentioned governing equations to obtain algebraic equations.The equations are discretized with equal-time and equal-space steps.Dev-C++software is used to program and calculate the discretization equations to solve the temperature distribution during ignition.The time step used is 1μs and the space step is 0.01 mm.The temperature distribution curve with respect to time and space during the ignition process is obtained.According to this distribution curve,the criterion of successful ignition in this study is determined.The influence of ambient temperature,spark energy and equivalent ratio on the minimum ignition energy,ignition delay time,and flame velocity are discussed.The results show that with the increase of ambient temperature,minimum ignition energy and ignition delay time of methane/air mixture decreases,flame velocity increases.The spark energy does not affect flame velocity since the spark energy can affect the flame propagation only in the initial stage of ignition.When the spark energy gradually approaches minimum ignition energy,there is a significant influence on the ignition delay time.The calculation results are compared with the previous experimental research,which provides a theoretical basis for the prevention of combustible gas explosion.