Study On Hydrogen Explosion Dynamics Near Explosion Suppression Limit

An increasingly prominent problem about environmental pollution has been caused by excessive use of fossil fuel.The exploitation and utilization of new clean energy is a prerequisite to carry out green development concept.As a clean and carbon-free energy carrier,there is a great prospect for hydrogen energy.However,due to lower ignition energy,wider flammability range and higher diffusivity,the hydrogen explosion accidents happen now and then.As an effective safety prevention technology,the hydrogen explosion suppression technology is attracting more and more attentions of scholars at home and abroad.The published works are lack of hydrogen explosion dynamics near explosion suppression limit,which is unable to provide guidance on studying the technology of hydrogen explosion suppression.In view of this,by changing inert gas type,inert gas content,equivalence ratio and initial pressure,this work is aimed at studying flame propagation characteristics and explosion pressure behavior near explosion suppression limit.Then the mechanism of hydrogen explosion suppressed by inert gas is revealed.The main contents and conclusions of this work are presented as follows:?1?When the content of carbon dioxide and nitrogen is relatively lower,the main controlling factor affecting unstable flame propagation are the diffusional-thermal instability and hydrodynamic instability.When the content of carbon dioxide and nitrogen is close to explosion suppression limit,the upward floating flame could be observed and the main controlling factor affecting unstable flame propagation is the buoyant instability.And the diffusional-thermal instability and hydrodynamic instability could be suppressed by the buoyant instability enhancement.When the suppression medium is carbon dioxide,the weakest flame floating phenomenon is observed at?=1.5.The buoyant instability is enhanced when the equivalent ratio deviates to rich and lean sides.When the suppression medium is nitrogen,the buoyant instability decreases with increasing equivalent ratio.For various suppression medium,the buoyant instability is enhanced by increasing initial pressure.?2?For a certain content of carbon dioxide and nitrogen,maximum explosion pressure and maximum pressure rise rate increase firstly and then decrease with increasing equivalence ratio.For a certain equivalence ratio,maximum explosion pressure and maximum pressure rise rate continue to decrease with increasing content of carbon dioxide and nitrogen.When the suppression medium is carbon dioxide,for?=0.6,0.8,1.0,1.5 and 2.0 conditions,the critical suppression ratio of carbon dioxide are 7.50,7.18,5.74,3.83,and 2.87 respectively.When the suppression medium is nitrogen,for?=0.6,0.8,1.0,1.5 and 2.0 conditions,the critical suppression ratio of nitrogen are 15.83,11.87,9.50,6.33,4.75 respectively.When inert gas content reaches the critical suppression ratio,the explosion pressure rise could be not detected.The critical suppression ratio of carbon dioxide and nitrogen continue to decrease with increasing equivalence ratio.The critical suppression ratio of carbon dioxide is lower than that of nitrogen,which means that the suppression effect of carbon dioxide on hydrogen explosion is stronger than nitrogen.?3?The adiabatic flame temperature,thermal diffusivity and mole fraction of active radicals continue to decrease with increasing content of carbon dioxide and nitrogen,which contributes to the decrease of laminar burning velocity.Compared with nitrogen,carbon dioxide not only directly participates in the elementary reaction OH+CO=H+CO₂ but also participates in the third body reactions like H+OH+M=H₂O+M,which will consume free radicals to produce steady intermediate products.And this is the reason why carbon dioxide is more effective on suppressing hydrogen explosion pressure.