Numerical and Experimental Study on Discharge Offset of High-Boiling-Point Fire Extinguishing Agents in Local Application with Inclined Installation

In the design of local application fire extinguishing systems, nozzles sometimes cannot be installed vertically due to space constraints and must be inclined. During inclined discharging, the discharge cone coverage pattern changes, and the high-concentration area shifts toward the front of the discharge direction, resulting in insufficient concentration at the rear of the fire source and compromising extinguishing effectiveness. Therefore, the nozzle aiming point must be offset toward the nozzle installation side. This discharge offset can compensate for the concentration deficiency at the rear of the discharge direction and ensure extinguishing effectiveness. This paper takes perfluorohexanone as the research object and, for the K100 swirl-core atomizing nozzle, conducts CFD numerical simulations and 70B pan fire full-scale extinguishing validation tests on discharge offsets at different inclination angles (90°, 75°, 60°, 45°). The research shows that the nozzle installation angle should not be less than 45°, and the offset increases as the angle decreases. The offsets of the K100 nozzle at 90°, 75°, 60°, and 45° are 0 mm, 66.34 mm, 101.34 mm, and 175.86 mm, corresponding to 0, 0.08R, 0.12R, and 0.22R (R is the protection radius), respectively. Compared with carbon dioxide standards, the offset required for perfluorohexanone is much smaller than that for carbon dioxide (approximately 1/2 to 1/3 of that of carbon dioxide at the same installation angle). A calculation formula for the offset based on the protection radius R is proposed, providing a design basis for precise nozzle positioning in local application systems under confined spaces or complex installation conditions. The generalizability of the proposed offset model is further validated through additional experiments using perfluoroheptanone, a high-boiling-point agent with similar physicochemical properties to perfluorohexanone.