The Research Of Premixed Flame's Propagation And Quenching In Narrow Channels

The investigations into premixed flame propagation in tubes or channels are significant to the deflagration suppression of flammable gas clouds in vessels or unconfined space. To provide theoretical and laboratorial references for deflagration suppression and the design of flame arresters, propagation mechanism and quenching condition of premixed unsteady flames in narrow channels were researched experimentally and then simulated numerically in this paper. The main work and conclusions are as follows(1) The experimental apparatus for flammable gases explosion and deflagration suppression in pipe were set up, realizing computer controlled ignition and synchronized measuring of the pressure and flame speed of the test points. The flame detector was designed to only measure the flame signal at right point, hence made the research on the process of flame and pressure propagation and development possible. Experiments were done on the explosion of premixed flame in a long pipe, from which the rules of flame propagation were obtained, and a semi-empirical equation was therefore concluded.(2) The propagation and quenching of premixed flame in multilayer wire mesh were studied experimentally, and the relation was got between quenching pressure or quenching speed and wire mesh parameters such as layers or meshes. A concept, suppression parameter, was introduced to indicate the effects of suppressing explosion pressure and flame speed for a multilayer mesh. The suppression parameter can be explained as the energy of the premixed flame before entering the multilayer wire mesh, and which will be quenched. Experiment showed that the suppression parameter could reflect the effects of suppressing explosion pressure and flame speed.The higher the suppressing parameter, the higher the suppressing explosion capacity of the multilayer wire mesh, and it means that for same premixed flames, the higher pressure and flame speed can be suppressed, for different premixed flame, the higher active premixed gas can be suppressed. This research method can provide a better way to determine the suppressing explosion capacity of other narrow channels.(3) Propagation and quenching of deflagration were modeled in narrow parallel plate channels. The maximum error between numerical simulation and experiment was 16.1%. Flame propagations under different conditions were considered, four modes of flame propagation in narrow parallel plate channels were discussed, and relationship among flame speed V, plate gap G, the valueâ–³T_w of rised wall temperature and quenching length Lq was got as followsFor a detemined plate gap G, the quenching time Lq/V was constant for a premixed flame.The larger the plate gap G, the lower parameter C, the more difficult to quench.For CH₄/Air premixed flameFor C₃H₈/Air premixed flameFor C₂H₂/Air premixed flameThe wall temperature rise T_w could make the coefficient f₂(â–³T_w) of parameter C lower, and decrease the quenching capacity.For CH₄/Air and C₃H₈/Air premixed flameThe higher the chemical activity of premixed flame, the lower the parameter C, the larger queching length was required, and it's more difficult to quench.Known parameter C above relationship, the quenching parameters of narrow channel can be determined. This method can be used to design the narrow channel to quench other premixed C-H flames.(4) Quenching of premixed falme deflagration in precision tubes were investigated. The relationship among flame speed V, valueâ–³T of initial gas temperature rised, diameter D of tube and quenching length Lq was got as followsFor a premixed flame with higher chemical activity, its parameter C was lower, quching this flame was more difficult.For a detemined tube diameter D, a higher flame speed V made the quenching time Lq/V smaller, and parameter C higher.For premixed flame CH₄/Air, C₃H₈/Air and The initial gas temperature rise could decrease the quenching capacity in precision tubes. The higher initial gas temperature T, the much lower temperature coefficient f₃(â–³T) for C₂H₂/Air premixed flame, which showed that higher initial gas temperature T makde it more difficult to quench this premixed flame.For CH₄/Air and C₃H₈/AirFor C₂H₂/Air(5) Mixing different inert gases in premixed flammable gases, quenching of deflagration were numerically simulated both in narrow parallel plate channels and tubes respectively, getting the optimal quenching concentrations of inert gases, and the quenching rules of the flammable gases in their optimal quenching concentrations as well.The quenching properties in narrow channels among differrent gases of C₃H₈/O₂/Inert gase and C₃H₈/Air were similar.The relaltionship between channel gap G and parameter C was shown as followsAmong the C₃H₈/O₂/Inert gas He, C₃H₈/O₂/Inert gas Ar and C₃H₈/O₂/Inert gas N₂, the parameter C of C₃H₈/O₂/Inert gas He was maximum, that of C₃H₈/O₂/Inert gas N₂ was minimum, which showed that quenching capacity of He was the highest, that of N₂ was the lowest.The quenching properties in tubes between gases of C₃H₈/O₂/Inert gas He and C₃H₈/Air were similar. But the Inert gas He made the parameter C higher, which improved the quenching effects.The conclusions above are of great significance to the design of micro deflagration suppressing constructions in complex narrow channels, providing references to the research on their long term-performance as well as suppression effect change due to temperature raise, especially.