Experimental study of n-Heptane pool fire behavior in an altitude chamber

Abstract

Constrained by the experimental conditions, field fire tests at high-altitude areas can only examine a limited number of low pressure environments. To explore more low pressure environments, an altitude chamber of size 3×2×2m has been built to simulate static low pressure environments in the range from 101kPa to 30kPa, as well as dynamic pressure environments depressurized from 101kPa to 30kPa at different descent rates. Then by aid of the altitude chamber, low-pressure fires under both static and dynamic pressures were tested. In the static fire tests, four static pressures, i.e. 101kPa, 75kPa, 64kPa and 40kPa were examined through automatically adjusting the pumping speed to maintain a fixed static pressure in the altitude chamber. In the dynamic fire tests, depressurization processes with three descent rates from 101kPa to 30kPa were examined in the altitude chamber through pumping gas and simultaneously replenishing air at the rates of 0, 15 and 20Nm3/h. The tested pool fire sizes were 6-cm-diameter and 10-cm-diameter round pans filled with a 2-cm-height layer of 99% pure liquid n-Heptane, and in the static tests cold water were laid beneath the fuel layer in order to cool the fuel. Multi-point axial flame temperature, radiative heat flux, mass burning rate, chamber pressure and hi-speed flame videos etc. were measured for each test. Some special phenomena were observed from the hi-speed flame videos for the liquid pool fires during the depressurization, e.g. the flame shifted from turbulent to laminar and its base turned blue as pressure drops, then at low enough pressure a polyhedral flame appeared and swirled in the pan. The flame temperature and radiative heat flux were analyzed in correlation with mass burning rate and pressure to reveal the pressure effect on fire behavior.