Investigations On The Coupled Influential Mechanism Of The Flame Propagation And The Overpressure Of Natural Gas Explosion

Under the historical background of energy transformation,natural gas,as a clean highefficiency energy,has been widely used in the worldwide.However,natural gas is flammable and explosive,which brings nonnegligible safety hazard.Relative explosion accidents could happen frequently,which causes serious casualties and property loss.During a gas explosion,blast wave travelling fast with a wide influential range,is the main cause of serious explosion consequences.As a result,accurate overpressure prediction is the key method of performing effective safety management and developing relative safeguard procedures.The explosion overpressure is highly related with the flame propagation behaviors,and classical prediction models didn't take a full consideration on the obstacle acceleration effects,which results in large deviation from experimental data.In this research,an unconfined gas explosion experimental platform was designed and established.The premixed gas concentration and the obstacle structure were changed,and the flame propagation behavior and the overpressure variation were recorded.With the help of the parameters,such as Lewis number,the laminar burning velocity,the thermal expansion ratio and the blockage ratio,the flame acceleration processes of different concentrations and obstacle structure were analyzed.Meanwhile,the variation law of the maximum overpressure,the maximum pressure rising rate and the overpressure impulse was obtained.An overpressure prediction model considering the hydrodynamic instability and the obstacle induced turbulence was proposed.The obtained results provided experimental and theoretical support for the following technique developments of gas explosion prevention and mitigation.The main conclusions are as follows:Under the influence of the hydrodynamic instability and the obstacle induced turbulence,the flame combustion surface area was increased,the flame got accelerated,and the explosion overpressure went up.The effects of hydrodynamic instability became significant with large flame radius.Due to the rupture and regeneration of small cells,the flame propagation velocity tended to be oscillating.The “extinguishing effects” of the obstacle walls impeded the heat accumulation and the proceeding of the chain reaction,which could cause small speed oscillation.In the near field,the maximum overpressure almost remained the same.The blast wave travelled slower in the near field and faster in the far field.For the stoichiometric condition,the flame travelled faster,which led to higher maximum overpressure,maximum pressure rising rate and explosion overpressure impulse.With the increase of the obstacle height and the obstacle number per layer,the flame got more unstable,and the maximum overpressure,the maximum pressure rising rate and the explosion overpressure impulse increased.With the increase of obstacle cross section area,the number of obstacles decreased,causing higher maximum flame propagation velocity but lower average flame propagation velocity,and the maximum overpressure,the maximum pressure rising rate and the explosion overpressure impulse decreased.The blockage ratio couldn't completely measure the effects of obstacles on the flame propagation velocity and the overpressure.For uniformly constructed obstacles,the self-similar theory was adopted to describe the destabilized effect of the hydrodynamic instability,and the growth factor ? was used to measure the acceleration effect of the obstacle induced turbulence.On the basis of the acoustic theory,an overpressure prediction model for the unconfined natural gas explosion was proposed,which presented more precise prediction results than classical models,such as TNT equivalency model and TNO multi-energy model.