Homogeneous and stratified vented gas explosions

Abstract

Explosion tests were carried out in four medium-scale test-vessels incorporating closed, vented, duct vented and interconnected vessels. A systematic investigation into the influence of homogeneous and stratified mixtures was undertaken by varying mixture reactivity, ignition position, injection position and mixture composition. A feature of this work has been the similarities in explosion phenomena between stratified and homogeneous explosions and between partially filled and fully filled geometries to the conclusion that the explosion severity recorded in stratified mixtures towards the lean flammability limit was in many cases much higher than the fuel concentration would normally suggest. Stratified mixtures with global equivalence ratio around stoichiometric produced significantly lower pressures than their homogeneous equivalents. However, stratified (globally) near-limit mixtures produced overpressures that were several hundred mbar higher than those of the equivalent homogeneous mixtures. Even beyond the flammable range (globally) the stratified mixtures produced significant overpressures. The phenomena discussed in this thesis illustrate the difficulty in designing adequate protection for such vented, duct vented and interconnected geometries, since even relatively small pocket of weak fuel-air mixtures produced relatively severe explosions. This can have implications for the safety design of inter-connected installations which are not intended to be subject to flammable mixtures. While it is an important conclusion from the work presented in this chapter that close to the flammability limits the stratified explosion severity was greater than its global concentration would normally indicate, it should be stressed that homogeneous stoichiometric tests still constitute the worst case tests. Therefore, it is not the suggestion of this work that the design of vented vessels should be modified to represent the maxima obtained in stratified work. However, the value of this research in the field of post-explosion investigation is clear.