Abstract
This study explores the scale effects in scramjet combustors operating at Mach 2.52. A comparative analysis was carried out on two geometrically similar combustors with a flow rate ratio of roughly 2:1. Additionally, a smaller-scale combustor with shortened-isolator was also examined. The global equivalence ratios were set to 0.13, 0.19, and 0.27, corresponding to Scram, Dual, and Ram modes. The scale effect laws vary among three combustion modes. As the equivalence ratio increases, the transition from Scram to Ram mode exhibits hysteresis in the large-scale combustor. The inherent mechanism for the inconsistent scale effects under different combustion modes is the nonlinear growth of diffusion flame with scale variation. In Scram mode, premixed flame occupies most of the reaction zone. The small-scale combustor manifests more potent combustion due to the higher mixing efficiency. In Dual mode, diffusion flame in the small-scale combustor has been significantly enhanced, resulting in higher combustion intensity. In Ram mode, the combustion reaction is dominated by diffusion flames, and the impact of the mixing process on combustion is further weakened. Therefore, the flowfields with different scales are similar.
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