Study On Chemical Kinetics And Duct-venting Of H₂/air/dilutions Explosions

Hydrogen energy has superior potential in improving environmental problems and development sustainability,but there is also a risk of explosion during transportation,storage and conversion.Moreover,the combination of explosion venting and explosion suppression measures has superior potential to reduce the hazards of explosion sites and surrounding buildings and personnel.According to the ideology of decoupling analysis,this study reveals the influence of the third-body effect and chemical effect of N₂/CO₂on the chemical reaction kinetics of hydrogen premixed flame,and the influence of venting conditions（Ordinary-venting vs.Duct-venting）and venting duct length（L=750mm,1000mm and 1250mm）on the suppression of hydrogen premixed flame by N₂/CO₂ under the same laminar combustion velocity（LBV）were discussed in detail.There is a close coupling relationship between adiabatic flame temperature T_ad,expansion ratio E,D-L instability and LBV of H₂/air/N₂ and H₂/air/CO₂ premixed flame.The sensitivity analysis shows that the H-producing reaction R4:OH+H₂<=>H+H₂O and H-consuming reaction R16:HO₂+H<=>H₂+O₂ have the greatest contribution to the promotion and inhibition of LBV of the two premixed gases,respectively.Compared with O/OH radicals,H radical plays a more important role in promoting LBV of hydrogen premixed flame.Moreover,the N₂/CO₂ third-body effect does not affect the laminar combustion parameters,the mole fraction of H/O/OH radicals and ROP.Hence,the inhibitory effect of N₂ on hydrogen premixed flame is dominated by thermal effect,while CO₂ suppresses hydrogen premixed flame through the synergistic effect of chemical effect and thermal effect.Under different venting conditions,N₂/CO₂ inhibited the reversal process of tulip flame,and produced a special"flame tongue"structure before the flame front formed the primary cusp,which formed"two tulip flames"on the upper and lower lips of the flame,and then disappeared and re-evolved into tulip flame.Duct-venting has an additional contribution to the increase of flame velocity,while the venting-duct has a stronger promoting effect on H₂/air/CO₂ flame velocity than H₂/air/N₂ flame velocity.The increase of the venting-duct length weakens the N₂/CO₂ inhibition effect on hydrogen flame velocity,and the inhibition effect of CO₂ is more sensitive than N₂ to the change of the venting-duct length.Under the same LBV condition,the stronger thermal effect of N₂ makes it better to restrain the explosion pressure of hydrogen premixed mixture than CO₂.Moreover,there is a linear relationship between the maximum explosion pressure P_max and LBV,and the accuracy of the linear prediction can be improved by considering the expansion ratio E.The maximum explosion pressure P_max of H₂/air/N₂ and H₂/air/CO₂ premixed gas is always dominated by the second peak pressure P_d caused by secondary explosion arose in the venting duct.The overpressure surge caused by the second explosion does not start from zero due to the influence of Helmholtz oscillation,but depends on oscillatory pressure.Thereby,the starting value of overpressure surge is called"Basic pressure".Moreover,the P_d strongly depends on the"Basic pressure",which causes24cm/s<LBV<144cm/s to become the disturbance zone of N₂/CO₂ diluted hydrogen premixed flame.Therefore,in order to ensure that the maximum explosion overpressure P_max in the duct-venting site can be predicted more accurately,the dilution concentration of N₂/CO₂ corresponding to the disturbance zone should be avoided.