Investigation of the Burning Mechanism in an Enclosure Fire with a Horizontal Ceiling Vent

This article adopted the method of numerical simulation to study heat release rate change rule and oxygen concentration variation when different opening size was changed within a small space, where there was a constant source of power in the space and an opening at the top level in the corner. Meanwhile, the constitutive factor affecting the burning mechanism of fire was further explored. As simulation results showed, (1) with the increase of opening size and larger amplitude of heat release rate vibration, In the later periods of the experiment, the frequency of heat release rate vibration is basically consistent with the frequency oxygen concentration changing at the nearby fire source. (2) With the increase of opening size, the amplitude of oxygen concentration changing under the bottom of opening is smaller, replenishment of outside cold air at larger opening is more stable, and oxygen quality replenished in the experimental box is increased. Meantime, oxygen quality replenished in the experimental box and participating in oxygen quality is increased obviously with the opening increase, opening size impacts the fire source combustion in the later period of the experiment directly. The oxygen concentration would decrease after a certain period of time in the fire development, unstable combustion “Ghosting flame” and “Oscillating fire” would happen due to the lack of oxygen when oxygen concentration near the combustion source is lower than 0.14.