Study On Detonation Mechanism And Explosion Propagation Characteristics Of Methane Ignited By Hot Particles

Gas explosion is one of the main accidents that threaten the safety of coal mine production.Due to the complexity of coal mine working face,coal dust is often involved in gas explosion accidents,and it shows the characteristics of"starting from small deflagration and destroying in multiphase continuous explosion".At present,the research on the continuous explosion mechanism of coal dust/gas two-phase mainly focuses on the discussion of macroscopic phenomena such as explosion characteristic parameters and propagation laws,while the core mechanism of the interaction between gas and coal dust is still a difficult research point,and it is also a limitation of the two-phase explosion.The main obstacle to in-depth study of the propagation mechanism of successive explosions.The traditional explosion propagation mechanism believes that the explosion shock wave and the flame surface are the main ignition sources for igniting suspended dust and inducing continuous explosions.The thermal radiation propagation mechanism believes that the thermal radiation generated by the explosion is also a potential ignition source to promote continuous explosions.The thermal radiation propagation mechanism has been successfully applied to the explanation of many multiphase continuous explosion accidents in the world,such as the Bangsfield explosion accident in the United Kingdom in 2005.Inspired by the thermal radiation propagation mechanism,this paper believes that in a gas/coal dust explosion accident,the suspended coal dust in front of the explosion main flame can detonate the gas gas under the heating effect of the thermal radiation of the explosion products,forming a continuous explosion ahead of the main flame,and then Promote the continuous propagation of two-phase continuous explosions.It can be seen that the key to the propagation mechanism of thermal radiation lies in the continuous explosion caused by high temperature particles.Therefore,in order to grasp the core mechanism of the two-phase interaction in gas/coal dust explosion,this paper focuses on the key issue of high-temperature particle detonation of gas under thermal radiation.The main contents are as follows:Independently designed and built a non-contact high-temperature particle ignition synchronous imaging test system.a low-power continuous wave laser is used as a thermal radiation source to heat the target particles;a two-color infrared temperature measurement system is used to record the temperature history;a high-speed Schlieren imaging system is used to capture the heat exchange process between the particle and gas;a high-frequency pressure collection system is used to collect the pressure evolution process inside the explosion chamber.Each experimental equipment can realize one-button synchronous triggering through the combination of various triggering methods,which provides a complete hardware condition for multi-parameter synchronous and accurate measurement.Based on the above experimental platform,comparative experiments on gas detonation by inert silicon carbide particles and combustible bituminous coal particles were carried out.Through the high-speed camera and infrared temperature measurement system,the influence of the physical and chemical properties of particles and gas on the detonation parameters such as the minimum ignition energy,ignition delay time and ignition temperature were obtained,and the detonation mechanism of the detonation parameters under different working conditions were found.Through the Schlieren and pressure acquisition system,the formation and instability process of the explosion flame under different fuel-air equivalence ratios were studied,and it was found that the unique secondary ignition in the coal detonation experiment would lead to a higher explosion pressure.The experimental results show that,compared with inert silicon carbide particles,the unique pyrolysis reaction and devolatilization of coal particles after heating can significantly improve the difficulty of detonating gas,and also increase the explosion propagation power after detonating gas.A numerical calculation model for simulating gas detonation by inert high-temperature particles is established based on the experimental conditions and the above experimental data:the whole model is controlled by the unsteady Navier-Stokes equations with chemical reaction;the convection term in the model is controlled by the fifth-order WENO.The viscous term and the diffusion term are discretized by the sixth-order central difference scheme;the time term is discretized by the third-order explicit Runge-Kutta scheme;the gas combustion reaction path adopts the 84-step detailed chemical reaction model DRM-19 and A two-step simple chemical reaction model 2S-CH₄-BFER was used for control.The parameters calculated by the model are in good agreement with the experimental results,which verifies the rationality of the numerical model and the accuracy of the calculation results.On the basis of the established numerical model,the numerical calculation of gas detonation by high-temperature inert particles under different working conditions is carried out,and the ignition criterion suitable for the near-limit combustible gas mixture is found.Based on the ignition criterion,the chemical reactions of different gases are compared and analyzed.The model and the distribution law and influence mechanism of ignition parameters under different particle heating rates;at the same time,the concentration evolution law of important components in the gas phase region before and after ignition under different fuel-air equivalence ratios is discussed.In addition,the sensitivity analysis of the gas combustion DRM-19 model under different fuel-air equivalence ratios is also carried out.The elementary reactions are mainly the dehydrogenation cracking reaction of methane and the partial chain termination reaction;the change of the fuel-air equivalence ratio changes the consumption rate of methane and the generation rate of highly reactive radicals,resulting in different chemical reactivity of the gas mixture under different equivalence ratios.Therefore,in the actual production process,the explosion risk of the system can be reduced by reducing the temperature of the system,consuming free radicals and hindering the generation of free radicals,so as to achieve the effect of explosion suppression.