Comparative Study On Suppression Of CH₄,LPG,H₂ Explosion And Initial Flame Self-Acceleration By N₂-Ultrafine Water Mist

Gas explosion is one of the major disasters in China,once the explosion will bring a large number of casualties and property damage.If the explosion is not stopped in time will produce flames to accelerate the occurrence of deflagration or even explosive boom.Based on the 20L spherical explosion vessel and the constructed pipeline experimental platform,the authors conducted a comparative study on the inhibition of CH₄,LPG and H₂explosions by N₂-ultrafine water mist from the explosion pressure,flame propagation velocity,flame surface structure,flame instability parameters and turbulence characteristics of the explosion flow field,analyzed the effect of N₂-ultrafine water mist on the initial flame self-acceleration of common combustible gas explosions,and discussed the mechanism of its inhibition of methane explosions by combining Chemkin-Pro software.This study can provide theoretical support for the promotion of active two-fluid fine water mist explosion suppression technology,and also provide a reference for accident prevention during the production,transportation,storage and use of gas.The main findings are as follows:Research shows that:when adding N₂and ultra-fine water mist alone,CH₄,H₂explosion overpressure peak and maximum pressure rise rate significantly reduced,the peak explosion overpressure arrival time and maximum pressure rise rate arrival time extended,and the inhibition effect with the increase in the concentration of inhibitors and enhanced.For LPG when the ultra-fine water mist alone can significantly reduce the explosion overpressure,but can not effectively extend the explosion overpressure coming time,only 140 g/m³-280 g/m³ultra-fine water mist mass concentration can effectively reduce the rate of explosion pressure rise.However,when both N₂and ultrafine water mist act together can significantly improve the suppression effect of the three types of gas,280 g/m³ultrafine water mist and 24%N₂act together on CH₄,LPG and H₂,the peak explosion pressure is reduced by 48.2%,44.5%,36.1%,the maximum pressure rise rate is reduced by 95.4%,92.8%,72.0%,and the flame propagation rate decreased by 90.2%,68.9%,and 39.3%,respectively.From the analysis of the pressure,velocity and Markstein length of the three aspects of the synergistic effect of explosion suppression,N₂and ultra-fine water mist both acting on the LPG explosion pressure drop is greater than the sum of the single inhibitor effect drop,both acting on CH₄and H₂and the sum of the single inhibitor effect explosion pressure drop in the synergistic deviation rate are less than 5%.N₂and ultra-fine water mist under the action of flame propagation speed further reduced,the joint action of the flame propagation speed decline,although less than the sum of N₂and ultra-fine water mist alone,but the deviation value is less than 15%.N₂and ultra-fine water mist under the action of the explosion flame significantly upward,the number of flame cells decreased,Markstein length significantly increased,which indicates that N₂/ultrafine water mist acting together can better inhibit the initial flame instability of the explosion,the inhibition of flame propagation is better than a single inhibitor,effective prevention of flame acceleration or even burst,and 280 g/m³ultra-fine water mist and 24%N₂acting together on CH₄,LPG and H₂,the Markstein length increased by 1972.7%,927.3%and 446.7%,respectively,and the Markstein length enhancement was CH4>LPG>H2.In addition,it was found that for the same mass concentration of fine water mist action,the peak explosion overpressure with the reduction of water mist particle size and the explosion overpressure arrival time is significantly delayed,such as 280 g/m³of 12 um fine water mist and 24%N₂together,the maximum explosion pressure arrival time is extended by 54.3%,indicating that N₂/ultra-fine water mist together can be better synergistic explosion suppression.It can be found through the PIV flow field that N₂and ultra-fine water mist can well reduce the vortex volume distribution on the flame surface when they act,which indicates that N₂and ultra-fine water mist can reduce the energy exchange on the flame surface,reduce the flame propagation speed during explosion,and then weaken the explosion intensity.Through the simulation software,it can be found that N₂/ultrafine water mist can effectively reduce the generation rate and molar fraction of active radicals such as H,O and OH,indicating that the two together can effectively reduce the flame temperature and inhibit the ignition and explosion chain reaction of methane/air premixed gas.