Simulation study on flame characteristics and heat transfer mechanisms of a rectangular fire source attached to a pyrolysis wall

Abstract

To investigate the flame characteristics and heat transfer mechanisms of a rectangular fire source attached to a pyrolysis wall of PMMA, a numerical study was conducted on fire sources with varying burner aspect ratios and heat release rates. The results indicate that numerical simulation effectively captures the evolution of flame morphology and the changes in the solid pyrolysis region. The study found that under pyrolysis conditions, the flame temperature near the PMMA wall gradually increases during the initial stage, while in the later stages of combustion, the near-wall flame temperature begins to decrease. Meanwhile, changes in the burner configuration affect the pyrolysis process, leading to variations in the onset range of the temperature decrease near the wall at different heights. Additionally, changes in the aspect ratio and heat release rate influence flame characteristics, causing distinct impacts on heat transfer to the pyrolysis wall. Increasing the aspect ratio reduces the incident radiative heat flux received by the wall, altering the contribution of the highest temperature range to the mass loss rate. In contrast, increasing the heat release rate has a smaller effect on the heat flux distribution across the PMMA panel during the steady stage. Instead, it accelerates the PMMA pyrolysis process, thereby increasing the total volume percentage of temperature ranges above the pyrolysis temperature, which in turn increases the mass loss rate. However, it has minimal effect on the contribution of the highest temperature range to the mass loss rate.