Scale effects on the external combustion caused by venting of a confined explosion

This article describes a field-scale experimental study of the external jet explosion caused when a confined explosion vents gas into a cloud of the same mixture. By inducing turbulence in the chamber prior to ignition in mixtures of natural gas and oxygen enriched air, it has been possible to study systematically the effects of unburned gas exit velocity and fuel reactivity on the peak external overpressures. A direct comparison has been made between explosions with similar exit velocities but with very different fuel reactivities. It has been observed that the external overpressures increase with jet exit velocity up to a critical value of the velocity, above which the overpressures remain roughly constant. This trend has been associated with the onset of turbulence quenching in the external combustion zone. The peak overpressure-jet velocity relationships have been collapsed into a single correlation against an effective Karlovitz number, which is proposed as a way of extrapolating to much larger experimental scales.