Experimental study of extinguishing shielded fires by a low-pressure multi-orifice water mist nozzle

The performance of a water mist system to suppress shielded fires is analyzed experimentally in this work. The diesel pool fire is used as the fire source in an enclosure with 2.4 m × 2.4 m × 3.1 m measurements, and a mechanism is designed to provide different shielding conditions by changing the obstacle size and height. The characteristics of a low-pressure multi-orifice nozzle including the drop diameter and the velocity are studied by a Phase Doppler Particle Analyzer (PDPA) system. In total, 10 cases with diverse shielding conditions are defined and different parameters including the temperature distribution, the gas concentrations, and the extinguishing time are measured. Based on the present data, mist droplets in some shielded fire scenarios were able to bypass the obstacle, overcome the fire plume thrust, and suppress the fire. In fire scenarios with the same obstruction size, the reduction of the distance between the obstacle and the nozzle led to an increased block ratio and consequently, the extinguishing time was decreased. It was found that the temperatures in the central axis above the fire and the lateral temperatures declined quickly in cases with short suppression time.