Experimental Study Of Backdraft In A Compartment With Different Opening Geometries And Its Mitigation With Water Mist

Abstract

This paper presents the results of reduced-scale experimental tests to study backdraft in a reduced-scale compartment (1.2 m x 0.6 m x 0.6 m), fitted with six end opening geometries and two ceiling opening geometries. The experimental variables included the fuel flow rate, the time during which the fuel was burned, and the opening geometries. The quantities recorded before backdraft included temperature and the concentrations of oxygen, carbon dioxide, and carbon monoxide. To quantify the effect of backdraft, the gas velocities in the opening and also the pressures in the compartment were measured. The effects of different opening geometries on the occurrence of backdraft are discussed. This study shows that the mass fraction of unburned fuel (i.e., the unburned methane in this study), whose critical value varies with the opening geometry, is a key parameter determining the occurrence of backdraft. In addition, the experimental results using water mist, generated by a downward-directed pressure nozzle that was operated at pressure of 0.2 MPa, to mitigate backdraft are presented. The experimental results show that water mist is an effective mitigating tactic able to suppress backdraft in a compartment primarily by means of diluting the gas in the compartment and reducing the mass fraction of unburned fuel, rather than by a thermal mechanism of cooling.