Numerical simulation of the upward propagation of a flame in a vertical tube filled with a very lean mixture

Abstract

Keywords: Laminar flames Lean flammability limit Flame aerodynamicsUpward propagation of a premixed flame in a vertical tube filled with a very lean mixture is simulated numerically using a single irreversible Arrhenius reaction model with infinitely high activation energy. In the absence of heat losses and preferential diffusion effects, a curved flame with stationary shape and velocity close to those of an open bubble ascending in the same tube is found for values of the fuel mass fraction above a certain minimum that increases with the radius of the tube, while the numerical computations cease to converge to a stationary solution below this minimum mass fraction. The vortical flow of the gas behind the flame and in its transport region is described for tubes of different radii. It is argued that this flow may become unstable when the fuel mass fraction is decreased, and that this instability, together with the flame stretch due to the strong curvature of the flame tip in narrow tubes, may be responsible for the minimum fuel mass fraction. Radiation losses and a Lewis number of the fuel slightly above unity decrease the final combustion temperature at the flame tip and increase the minimum fuel mass fraction, while a Lewis number slightly below unity has the opposite effect.

Experimental and numerical study of cap-like lean limit flames in H2-CH4-air mixtures

“…However, a different mechanism of the lean limit methane/air flame was suggested by Shoshin et al [8,9] , who pointed out that local radiative heat loss becomes significant due to the formation of stagnation zone of combustion products near the flame tip, which leads to a local low temperature. Higuera and Muntean [10,11] numerically investigated the effects of tube diameter and radiative heat loss on the lean limit methane/air flame in a vertical tube using a thermaldiffusive model, and confirmed the radiative extinction hypothesis. Shoshin et al [12] studied lean limit methane/air flames propagating in a 24mm diameter tube and found that the lean limit is lower than that for the standard flammability tube and that the local flame speed is negative around the leading point of the flame front.…”

A Review on Ruben’s Tube as Acoustic Propagator

“…Upward propagation of a premixed flame in a vertical tube has a very lean mixture of gas [20]. By using a single irreversible Arrhenius reaction model, this experiment underwent a numerical simulation with high activation energy.…”

Effect of radiation losses on very lean methane/air flames propagating upward in a vertical tube

“…( 5)-( 7) are the energy, fuel, and product (CO 2 ) conservation equations, with the reaction and radiation terms given by Eqs. (8) and (9). Eqs.…”

“…They found that the stretch is due mainly to the strain rate of the flow; that it is of the order of the inverse of the residence time of the gas across a planar flame propagating in the mixture; and that it is maximum at the tip of the flame front, where extinction begins at the flammability limit. The flow on both sides of an axisymmetric steadily rising flame front was further investigated by Higuera [9], with emphasis on the structure of the vortical flow downstream of the flame front and the generation of vorticity at the flame. The results accurately determine the shape and stretch of the flame and point out a possible instability of the vortical flow.…”