Characteristics of reaction zone in a dual-mode scramjet combustor during mode transitions

The mechanism of controllable combustion modes (scramjet and ramjet) is one of the most significant challenges for dual-mode ramjet/scramjet engines. The detailed characteristics of the reaction zone during the transitions of combustion modes within the Hyshot II combustor are numerically investigated with 7 species-7 steps hydrogen/air reaction mechanism and the thickened flame model (TFM). In the case of continuous increasing or decreasing equivalence ratios (ERs), the critical ERs for the mode transitions are 0.474 or 0.539, respectively. As the ER increases or decreases, the location of the leading shock of the combustor shock-train moves upstream or downstream, respectively. When the ER continuously increases, the pressure ratio at the leading shock to the outlet of the isolator is greater than when the ER continuously decreases. Inversely, the mass-weighted average Mach number inside the combustor for a continuously increasing ER is less than that for the continuously decreasing ER. In the scramjet mode, the primary combustion reaction zone is located at the rear of the combustor. In the ramjet mode, combustion occurs in the separation zone at the middle of the combustion chamber, while the reaction zone is closer to equilibrium at the critical ER of 0.474 as compared to the scramjet mode. (C) 2020 Elsevier Masson SAS. All rights reserved.