Study On The Deflagration Mechanism Of Acetylene/Air Premixed Gas Under Different Constraints

As a common industrial gas fuel,acetylene（C₂H₂）is widely used in energy and chemical fields and exhibits some hazardous aspects,with its wide flammability range and low ignition energy.However,there are few studies on the accidental explosion of C₂H₂and its influential factors,and the understanding of its explosion mechanism is insufficient.Therefore,this paper studies on the explosion characteristics and reaction mechanism of C₂H₂/air mixture under different constrains.The results provide scientific bases for the prevention and control of explosion disasters in the production and use of C₂H₂gas and the safe design of chemical reaction vessels.Using visual isobaric gas explosion device,27 L square explosion device and 20 L spherical explosion device,the influence of C₂H₂concentration,static placing time,ignition position,open or not of vent,container shape and size on the explosion characteristics of C₂H₂/air mixture were systematically studied.Combined with Chemkin numerical simulation,analyzed the gas phase combustion species,flame temperature,reaction process and the explosion mechanism of C₂H₂/air mixture in depth.The main conclusions are as follows:（1）The latex balloon was used to be constraint of C₂H₂/air gas cloud to carry out the gas deflagration in open space.When the balloon was not ruptured,the hydrodynamic instability caused the flame acceleration.With the increase of gas concentration,the flame changed from blue to cyan,through the analysis of gas phase combustion products,the solid particles produced were the main cause of the change in flame morphological characteristics.When the flame radius r was small,a bright area was formed between the C₂H₂flame front and the unburned gas,which gradually overlapped with the flame surface as the propagation velocity increased.Within the experimental concentration range,the maximum values of S_{b average}and S_uwere 13.07and 1.36 m/s,respectively,and both appeared at 10 Vol.%.Sensitivity analysis was carried out on the primitive reaction of affecting S_u,and the reactions produced active radicals H,O and OH would enhance S_u,whereas the active radicals consuming reactions restrained the S_u,and the H radical concentration could reflect the changing trend of S_uof C₂H₂/air mixture.When C₂H₂concentration was less than 10 Vol.%,the attenuation rate ofΔP₊measured at 20-30 m were lower than that measured between30 and 40 m,while the reduction trend ofΔP₊reversed as C₂H₂concentration was 14Vol.%.It was because that for the C₂H₂/air mixture with a higher fuel fraction,the stoichiometric volume fraction might be formed due to the transient flow of the unburned gas after the rupture,which would make the impact range of explosion overpressure wider.The S_b⁰and theΔP₊presented the same change trends along with the increasing static placing time,decreased at first for the influence of gas turbulence and then increased due to the effect of gas mixing uniformity.The stable combustion phenomenon was obtained when the static placing time was between 5 and 8 minutes.（2）Flame propagation in confined space was affected by ignition electrodes,hydrodynamic instability,pressure wave reflection and other factors,resulting S_brising increased first and then decreased.When r was less than r_c,flame acceleration due to hydrodynamic instability predominated,caused S_bto rise;when r>r_c,the inhibition of flame propagation by wall constraint and reflected wave enhanced and resulted in S_bfalling.r_cand S_breached maximum values,9.95 cm and 12.24 m/s,at the 12 Vol.%.As the concentration increased,P_exand（d P/dt）_exincreased at first and then decreased,reached their maximums at 14 Vol.%（1.70 MPa）and 12 Vol.%(93.51 MPa·s^-1),respectively.Since the C₂H₂decomposition reaction released heat,the explosion pressure remained high value within the experimental concentration range.Relative to the P₁and P₃measurement points,the combined reflection wave superposition strengthened the pressure value of P₂,and the P_{2 ex}was almost twice as much as P_{1 ex}and P_{3 ex}(P_{1 ex}≈P_{3 ex}).As the ignition position changed,the farther pressure measurement point was from the ignition center,the more fully mixture was burned,the larger P_exobtained.However,（d P/dt）_exwas not sensitive to change in the ignition position.For C₂H₂/air explosion in a vessel with a vent,P_exand（d P/dt）_exwere 66%lower and 49%lower on average than no vent condition.In the case of different shape size vessel constraints,C₂H₂/air mixture has a higher P_exvalue in the square vessel,conversely the（d P/dt）_exand K_stwere larger when explosion in spherical vessel.Figure[47]Table[11]Reference[121]...