Flame interaction effects on the flame structure of twin parallel rectangular fires

Abstract

The present study experimentally investigates the flame interaction mechanism of twin parallel rectangular fires, with a particular focus on the evolution of flame structure. A series of propane-fueled flame tests are conducted with varying burner aspect ratios (L/W), burner spacings (S), and heat release rates (${\dot{Q}}_L$). Temperature and velocity distributions, as well as the geometrical parameters of the flames, are measured and discussed. Results show that the flame length of the twin fires increases monotonically as S decreases within a specific range of L/W and ${\dot{Q}}_L$, where the occurrence of flame merging plays a significant role. As L/W or ${\dot{Q}}_L$ continues to increase, the flame length first rises and then declines as S decreases, reflecting the impacts of air entrainment restriction. A merged twin flame can be divided into three distinct regions based on the radial distribution of the flame temperature: the merging region, the transition region, and the fully merged region. The radial distribution demonstrates a bimodal distribution in the merging region, an unimodal yet non-self-similar distribution in the transition region, and a self-similar distribution in the fully-merged region. Furthermore, it was observed that both temperature and velocity half-width of the twin flames increase as S decreases within specific ranges for L/W and ${\dot{Q}}_L$. As L/W or ${\dot{Q}}_L$ continuously increases, the height at which twin flames merge approaches their base, resulting in an expansion of the flame and subsequently leading to an increase in temperature or velocity half-width as S increases. The axial temperature or velocity of the non-merged twin flames increases as S decreases. As flame merging occurs, the flow from each twin flame converges at a merging height; this convergence facilitates an increase in axial velocity. At this point, higher values of S create additional room for air entrainment before flame merging occurs, further enhancing the axial velocity of the merged flame. This trend becomes increasingly pronounced as ${\dot{Q}}_L$ increases.