Study On Propagating Mechanism And Quenching Of Premixed Flames In Narrow Channels

The investigations into premixed flame propagation in tubes or channels are great important for design and application of flame arresters, and deflagration suppression of flammable gas clouds in vessels or unconfined space. Aiming to provide theoretical references for deflagration suppression and the design of flame arresters, propagating mechanism and quenching condition of premixed unsteady flames in narrow plate channels are simulated numerically in this paper. The main work and conclusions in this paper are as follows.(1) Based on Arrhenius combustion model, governing equations of hydrodynamics and species equations, two-dimensional theoretical model for propagation of premixed unsteady flames in narrow channels is built. Based on improved SIMPLE algorithm, a two-dimensional program code applicable to simulating deflagration flame is compiled in VC++ language.(2) Some computational problems, such as mass diffusion, heat transfer, Stokes' first problem, combustion in constant volume, and transient flow of air in plate passage are simulated to validate the procedure. In the simulation to one-dimensional deflagration of premixed acetylene-air flame, combustion speed and flame thichness are computed, and grid independence of numerical solution is analyzed.(3) Flame propagation and quenching in closed-open narrow channels are simulated, main conclusions are as follows.1) Effects of mass diffusion coefficient and heat loss on walls on flame shape are investigated. The results show that the increase of mass diffusion coefficient contributes to tulip-shaped flame. As mass diffusion coefficient is smaller than heat diffusion coefficient, named as Lewis number is bigger than or equal to one, mushroomed-shaped flame tends to form, while tulip-shaped flame tends to form as Lewis number is less than one. Heat loss at the cold walls is adverse to the formation of tulip-shaped flame. For adiabatic wall, tulip-shaped flame forms as length heightratio of narrow channels is less than 40, while, for isothermal wall, tulip-shaped flame forms as length height ratio of narrow channels is less than 30.2) By introducing non-dimensional quasi-extinction space, heat supply rate into analysis, the relationship of heat release of chemical reaction, heat loss on wall and flame propagation and quenching in narrow channels are analyzed systematically, and the criterion of flame propagation and quenching in narrow channels is put forward.(4) Flame propagation and quenching in open-open narrow channels are studied experimentally and theoretically. Experimental results show that, as channel height is given, quenching length is proportional to critical flame propagation speed approximately. The computed results show the same conclusion. The computed results are consistent with the experimental results as a whole.