Physical models of flame height and air entrainment of two adjacent buoyant turbulent jet non-premixed flames with different heat release rates

Abstract

This paper investigated the flame height and air entrainment of two adjacent buoyant turbulent jet non-premixed flames with the same base dimension whilst having different heat release rates (HRRs). Propane was used as fuel. The HRR of one of the burners was fixed at 8, 16, 24, 32 and 40 kW, respectively. By increasing the HRR of the other burner, the interaction behaviors of two jet flames were studied under various burner spacings. A total of 15 categories of HRRs combinations of two jet flames were conducted in this work. Two flames heights are different to lead the heat pressure on both sides of the flame to be non-axisymmetric. And the interaction law, air entrainment mechanism etc. become more complicated than two same HRRs flames. Results showed that with increasing burner spacing, the flame merging behaviors can be divided into three stages. The flame height firstly deceases to a minimum value, then slightly rises again and finally maintains stable due to the weak interaction of non-merging flames. Two effective weighting factors are supposed to quantize the maximum and minimum flame heights to derive a flame height model which then is validated using the experimental data in literatures. The merging point height increases with increasing HRR and burner spacing. Based on the air entrainment mechanism of two interaction flames, a general method for calculating the global volume air entrainment is presented to build a physical entrainment model. Above flame height and physical entrainment models are suitable for the calculation with two flames combinations with the same and different HRRs, which greatly extends the application scope of interaction fires. In addition, two creative methods of calculating flame height and global air entrainment volume have been provided a reference for the research on the combustion behaviors of multiple flames with different HRRs combination.