NUMERICAL STUDY OF CHARACTERISTICS OF BURNING PHENOMENA IN EQUIDISTANT SQUARE ARRAYED N-HEPTANE FIRES

Merging of large-scale city fires and forest fires causes rapid acceleration of fire growth. Once a merging fire occurs, it becomes more difficult to suppress, with greater potential damages. In particular, merging fires may induce fire whirls in windy conditions. However, the details of interactions in multiple fires that cause fire merging have not been fully clarified. For the interactions in multiple fires, the inter-fire distance among fires greatly affects the merging phenomenon. The objective of this paper is to examine the detailed merging conditions, particularly the burning rate increase and total heat release rate, by numerical simulation of reduced scale fires. The burning behavior of n-heptane in n x a fire arrays is examined, using the fire simulation software, FDS by NIST. In addition, another simple model is employed. The number of array matrix, n, is varied, together with the inter-fire distance. The simulation results show that there are considerable differences between both simulations and experiments. However, the differences between the simpler simulation Method II and experiments are fewer than the simulation Method I. The following possibilities are considered: (1) The oil pan size affects the difference, but the results between simulations and experiments are so large. (2) The grid size for simulations may have some effects on the simulation results due to the resolution, (3) the experimental results may not always be precise, since the burning rates in the experiments are measured by the bum-out time and (4) the wind caused by merging fires may reduce the radiative heat flux to the adjacent fuel. The relationship between flame length and burning rate and the relationship between flame length and radiative heat flux are well-correlated.