Effect Of Jet Ignition Conditions On Propagation Characteristics Of Natural Gas Explosion

As a clean energy,natural gas(NG)can solve lots of environmental problems caused by coal and petroleum.In the process of production,storage,transportation and use,the easily diffused natural gas undergoes deflagration or even detonation ignited by jet ignition,causing personal injury and property damage.In view of the explosion risk of NG,the hot-jet ignition experiment is helpful to study the evolution law of natural gas explosion disasters which can provide reference for explosion protection.A multi-parameter(temperature,pressure and flame images)synchronous measurement system was established on the basis of the square flame propagation test pipeline platform.Experiments about the effects of hot jet ignition conditions on NG explosion overpressure,temperature,flame front shape and propagation velocity were carried out.The influence mechanism of open porosity of perforated plate,ignition section length,relief pressure and ignition position were investigated:(1)The flame is extinguished when it propagates to the perforated plate fixed at 1.5 m from the closed flange of the ignition end.The premixed gas in the experimental section is re-ignited by the hot jet gas after a while.The maximum explosion pressure,explosion temperature,the axial length of the re-ignition flame and the initial flame propagation velocity in the pipeline increase with the fall of the perforated plate open porosity.And the peak values are 208 kPa,1293°C and 73.1 m/s where the open porosity is 20%.The hot jet causes a series of explosions in the experimental section under the obstruction of the perforated plate.Therefore,the pressure curve fluctuates at the peak and maintains for a while.(2)The ignition section length affects the jet ignition capability and changes the flame acceleration distance in the experimental section,both of which have a nonnegligible influence on the flame propagation in the experimental section.The maximum explosion pressure,explosion temperature and flame propagation velocity in the pipeline rise all the time until the ignition section length increases to 0.9 m.With the further increase of ignition section length,the maximum explosion pressure,explosion temperature and flame propagation velocity fall monotonously.And the peak values of the maximum explosion pressure,explosion temperature and flame propagation velocity are 345 kPa,1378°C and 177.4 m/s,respectively.(3)In order to further increase the explosion pressure,the perforated plate is replaced by a membrane where the influence of buoyancy on the flame front structure is weakened.And the ellipsoidal flame front takes the place of the stepped and inclined asymmetrical ones with the increase of the flame speed.Influenced by the acceleration of the flame,the color of the flame front becomes darker and the turbulent fold becomes small and broken.The maximum explosion pressure,explosion temperature and the flame propagation velocity in the pipeline increase with the increase of the membrane relief pressure.And the peak values(405 kPa,1578 °C and 268.7 m/s)can be obtained when the relief pressure is 90 kPa.The ignition position has an effect on the flame propagation pattern,but shows no significant effect on the kinetic parameters of the NG explosion at the selected film strength(30 kPa).(4)The fact that explosion in the experimental section becomes more violent after membrane is applied can be explained for 3 reasons.Firstly,the shock wave released from the ignition section increases the initial pressure and initial temperature of the unburnt premixed gas in the experimental section.The distance between the methane molecules and the oxygen molecules is reduced,causing more frequent collisions,which is beneficial to the rapid combustion reaction.Secondly,the turbulence of the unburnt premixed gas in the experimental section gets intensified under the disturbance of the venting airflow,which is beneficial to accelerating the combustion reaction.At the same time,the premixed gas in the experimental section explodes under the induction of the venting flame,whose ignition energy is greater.