Abstract: In order to study the effectiveness and mechanism of single and double nozzle water mist in suppressing n- heptane pool fire，the droplet size of water mist with single and double nozzles and the suppression of a 20 cm n-heptane pool fire were studied in a simulated cargo compartment of a half volume aircraft. The results show that the cooperation of the double nozzles will lead to the collision between the droplets and secondary breakup, which is helpful to improve the atomization effect. Based on the measurement and calculation of fuel surface temperature, the average temperature of flame zone state and oxygen concentration in cabin, the dominant mechanism of water mist suppression with single and double nozzles is analyzed. The results show that the average time of single nozzle water mist fire extinguishing is 283.14 s, and the water consumption is about 3.54 L. The fuel surface cooling is the main mechanism of fire suppression. The average time of double nozzles water mist fire extinguishing is 212.22 s, and the water consumption is about 5.31 L. Flame cooling is the main mechanism of fire suppression.

Key words: double nozzles, low-pressure twin-fluid water mist, n-heptane pool fire, droplet size, fire extinguishing mechanism