Flame Propagation in Closed Vessels and Flammability Limits

Abstract

Flame propagation in near-limit mixtures of ethylene and air has been investigated by using a spherical vessel. A model of the flame behavior in closed vessels has been formulated, which takes into account the complete motion equation and the heat losses by the flame to the surroundings. The model forecasts two possible mechanisms of flame failure: the "homogeneous" flame extinction due to the exchanges of the rising flame towards the unburned gases, and the "heterogeneous" extinction due to conductive heat losses to the walls after flame impingement on the vessel top. The theory and the experimental data fairly agree; in particular the dependence of the measured "heterogeneous" limit on the igniter position is explained.

Influence of the ignition source location on the determination of the explosion pressure at elevated initial pressures

“…This is evidenced by visual observation (Cashdollar et al, 2000;Crescitelli, Russo, Tufano, Napolitano & Tranchino, 1977;Furno et al, 1971), thermocouple measurements at different locations inside the explosion vessel (Pekalski et al, 2004) and analysis of combustion products (Crescitelli et al, 1977;Pekalski et al, 2004). The underlying reason for the failure to propagate downwards is the effect of natural convection: if the buoyant rise velocity of the flame kernel is larger than the flame velocity, the flame is seen to travel only upwards (Andrews & Bradley, 1973;Crescitelli et al, 1977;Lovachev, 1971). The upward movement, however, takes some time to develop and in small vessels the flame will have reached the walls before any substantial rise has occurred.…”

Comparison and evaluation of methods for the determination of flammability limits, applied to methane/hydrogen/air mixtures

“…Therefore, an other criterion was required to determine whether or not the flame was propagating away from the ignition source, allowing a better comparison with the experimental results of the tube method. Based upon the knowledge that lowering the ignition source leads to higher explosion pressures if the mixture supports flame propagation [23], a new method was devised. Two series of tests were done, one with central ignition and the other with the ignition source lowered by 40 mm.…”

Calculation of the upper flammability limit of methane/air mixtures at elevated pressures and temperatures

“…For near-limit flames, which only propagate upwards, the flame stretch rate is proportional to the upward velocity of the flame kernel. Crescitelli et al [22] found that the upward velocity v of a spherical flame kernel with neglect of the drag force is given by…”