Abstract: This study comparatively investigates the droplet characteristics and fire extinguishing performance of perfluorohexanone and perfluoroheptanone under identical local application conditions. A droplet size measurement system and a 2A wood crib fire test were conducted using the same nozzle configuration and charging conditions. The droplet size results indicate that, under the same discharge pressure, perfluoroheptanone exhibits significantly larger characteristic diameters (D10, D50, D90 and D99) than perfluorohexanone, with a higher proportion of large droplets and a more stable jet structure. In contrast, perfluorohexanone produces smaller and more uniformly distributed droplets with better dispersion characteristics. The 2A wood crib fire tests demonstrate that both agents can successfully extinguish the fire under the same 20 kg charging condition; however, perfluoroheptanone achieves a shorter extinguishing time, higher peak nozzle pressure, and greater mass flow rate, resulting in a faster fire suppression response. Comprehensive analysis shows that droplet size distribution and jet momentum characteristics play a crucial role in local application fire suppression. Larger droplets with stronger momentum are more capable of penetrating flame plumes and wood crib structures, facilitating the formation of a locally high-concentration extinguishing zone in the combustion core region and thereby improving suppression efficiency. The results provide experimental support for the engineering application and design optimization of fluorinated ketone agents in local application fire extinguishing systems.

Key words: perfluorohexanone, perfluoroheptanone, local application, droplet size, fire extinguishing performance