Experimental Study of the Effect of Opening Factor on Self-Extinguishing and Blue Ghosting Flame in Under-Ventilated Compartment Fire

Blue ghosting flame and self-extinguishing are two typical flame behaviors in ventilation-controlled compartment fires. However, the study of the evolution of these two behaviors with opening factor and heat release rate (HRR) is incomplete. In this study, the experiments were performed in a 1/2-scale compartment model with openings of six different sizes. The temperature, oxygen concentration and carbon monoxide concentration in the compartment under different propane supply rates were recorded and analyzed. The results showed that the flame transformed from the stable stage to blue ghosting flame or extinguishment with the increase of the total HRR. When there is a blue ghosting flame and self-extinguishing, the combustion spontaneously regulates the oxygen concentration in the compartment and changes the trend of the oxygen concentration decreasing with the total HRR. The blue flame not only reflects that the real HRR is in an unstable state, but also changes the evolutionary trend of the ceiling temperature. The critical HRR for the appearance of blue ghosting flame and self-extinguishing behavior increases linearly with the opening factor. The value of the Global Equivalence Ratio stabilized around 0.73 only after the opening factor was greater than 0.0145. The blue ghosting flame cannot return to stability and is extinguished when the difference between the entrainment rate and the air consumption rate exceeds the limit of spontaneous regulation of combustion.