Tests are conducted in a low-pressure combustion chamber of 3 × 2 × 4.65m3 in volume to investigate the effect of low pressure on the drainage and expansion characteristics of AFFF (Aqueous Film-Forming Foam). A manipulator equipment with the frequency of 4 Hz and the amplitude of 32cm is designed for the foaming of AFFF in the chamber. The parameters of expansion and drainage ratio are obtained under two different ambient pressure of 101kPa and 30kPa. Two fluorocarbon surfactants contained commercial AFFF (AFFF1 is type of 3% and AFFF2 is the type of 6%) that were used in precious studies are both diluted into different quality percentage resolutions, and then achieve foaming in a 130ml measuring cylinder with a cone bottom. The foaming expansion ratio and drainage time are obtained based on the recorded videos. Experimental results show that the expansion ratio of both AFFF1 and AFFF2 resolutions (the expansion ratio <6) is lower under the pressure of 30kPa than that under 101kPa. The drainage time (25% and 50%) of AFFF1 is increasing in the lower pressure environment. On the contrary, 50% drainage time of AFFF2 is shorter under 30kPa than that under 101kPa, but 25% drainage time of AFFF2 is almost the same under two ambient pressures. The variations under low pressure environment are obvious and various from each other, but the further tests should be conducted to reveal and explore the mechanism.

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