Experimental study of the dispersion of a fire suppression agent through a real size nozzle of an aircraft cargo cabin extinguisher system

Most of active fire suppression systems consist on injecting an agent into the volume set on fire. In the case of
aircraft cargo cabin, the agent used up to date is Halon 1301. In fact, the current level of safety, according to
the FAA, is that provided by a volumetric concentration of 6% Halon 1301 throughout a protected fire zone for a
duration of 0.5 seconds. However, Halon 1301 is known to contribute to the depletion of Earth’s atmospheric ozone
layer, and it is going to be ban in the incoming years. The FAA has already defined an equivalent level of safety in
terms of the performance (concentration and spatial distribution) of the alternative agent. In this work, two different
alternative agents are tested. An injection system has been assembled in order to control the injection pressure
and the injection duration, in other words, the agent injected mass. The discharge volume is a rectangular constant
volume constant pressure vessel of approximately 0.85m 3 . This vessel is provided with two consecutive transparent
windows of 0.75 × 0.75m in order to ensure optical access to the whole injection and mixing process. Liquid phase
distribution of the agent inside the vessel is measured by means of Diffuse Back-light Illumination (DBI) technique.
Vapor phase distribution, when present, is measured through the single-pass Schlieren technique. Results show a
poor performance in terms of spatial distribution of the two alternative agents. The sprays result in narrow jet with
little atomization: small cone angle and fast penetration rate. This occurs mainly due to the different thermodynamic
properties of these two fluids compared to Halon 1301. Changes in the injection system nozzles need to be done
to improve the fire suppression agent distribution into the volume.