“…At the equivalence ratio of 0.8, all these flames grow thick above the cavity. The CH* distributions of cases 1–3 and 5 present a similar pattern of which belong to the cavity shear layer stabilized mode, 21 but a weaker flame could be seen in case 5. However, the CH* distribution of case 4 is quite different from other cases, which looks like in the combined cavity shear-layer/recirculation stabilized mode and presents the highest flame height near the cavity ramp at the same equivalence ratio.Figure 6.Time-averaged CH* chemiluminescence images for all cases.…”
This study experimentally investigated the combustion process in a cavity-based supersonic combustor at the inflow condition of Mach 2.92 with stagnation pressure 2.6 MPa and stagnation temperature 1530 K. Time-averaged flame distribution and oscillation characteristics were revealed by post-processing CH* chemiluminescence images. Wall pressures along the combustor bottom wall were also measured to provide quantitative information. Representative cascaded injection set-ups upstreaming the cavity were selected to compare ethylene flame characteristics. It is found that the combustion process is approaching thermal chocking when increasing the equivalence ratio to 0.8 according to the one-dimensional analysis of the Mach number distribution. At the same equivalence ratio, increasing the number of the cascaded injectors by lowering the injection pressure is not beneficial for the combustion enhancement, indicating that the injection pressure is also a key factor affecting the combustion heat release. However, increasing the injection pressure can cause obvious flame oscillations above the cavity as well as increasing the axis distance of the injectors. As a result, the injection scheme with two cascaded injectors which have the injection distance of 0.1 and 0.4 time the length of the cavity floor, respectively, upstreaming the cavity is suggested as a favorable scheme for scramjet applications.
“…At the equivalence ratio of 0.8, all these flames grow thick above the cavity. The CH* distributions of cases 1–3 and 5 present a similar pattern of which belong to the cavity shear layer stabilized mode, 21 but a weaker flame could be seen in case 5. However, the CH* distribution of case 4 is quite different from other cases, which looks like in the combined cavity shear-layer/recirculation stabilized mode and presents the highest flame height near the cavity ramp at the same equivalence ratio.Figure 6.Time-averaged CH* chemiluminescence images for all cases.…”
This study experimentally investigated the combustion process in a cavity-based supersonic combustor at the inflow condition of Mach 2.92 with stagnation pressure 2.6 MPa and stagnation temperature 1530 K. Time-averaged flame distribution and oscillation characteristics were revealed by post-processing CH* chemiluminescence images. Wall pressures along the combustor bottom wall were also measured to provide quantitative information. Representative cascaded injection set-ups upstreaming the cavity were selected to compare ethylene flame characteristics. It is found that the combustion process is approaching thermal chocking when increasing the equivalence ratio to 0.8 according to the one-dimensional analysis of the Mach number distribution. At the same equivalence ratio, increasing the number of the cascaded injectors by lowering the injection pressure is not beneficial for the combustion enhancement, indicating that the injection pressure is also a key factor affecting the combustion heat release. However, increasing the injection pressure can cause obvious flame oscillations above the cavity as well as increasing the axis distance of the injectors. As a result, the injection scheme with two cascaded injectors which have the injection distance of 0.1 and 0.4 time the length of the cavity floor, respectively, upstreaming the cavity is suggested as a favorable scheme for scramjet applications.
“…Many factors will influence the flame stabilization mode, such as air stagnation temperatures [8], equivalence ratio [9], injection distance [16], and fueling schemes [17]. In this paper, ER, jet scale (diameter), and distance between adjacent jet orifices are studied in detail.…”
Jet scale affects the mixing and combustion of fuel and inflow. With the increase in the scale of scramjet combustors, the study of large-scale jets is particularly significant. The effects of jet scale on flame stability in scramjet combustors were studied by direct-connect combustion experiments. In this paper, the flame distribution characteristics of different jet scales were compared by using similar jet/inflow momentum ratios. The inflow Mach numbers were 2.4 and 3.0, and the total temperature was 1265 K and 1600 K, respectively. The results show that, when the equivalence ratio increases, the combustion intensity increases. Under the condition of same momentum ratio, the increase of jet scale is conducive to fuel injection into the core mainstream, increasing heat release, and the flame stabilization mode will change from cavity stabilization mode to jet-wake stabilization mode. Increasing the distance between jet orifices is not beneficial to combustion, and may even lead to blowoff.
“…In this study, turbulent combustion in a cavity was chosen as an example for demonstrating the capability of the new proposed framework. The cavity commonly serves as a flame stabilizer in combustors, especially for transonic and supersonic combustion systems [40,41]. It is also a simplified prototype of gas turbine combustors.…”
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