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Influence of strut on cavity at subsonic speeds: Ignition characteristics

In high-speed airflow, the use of cavity and struts in combination can improve fuel distribution and flame-stabilization, but may weaken the ignition performance. Herein, the lean ignition characteristics of several cavity–strut flame holders in a tandem turbine-based combined cycles combustor are experimentally investigated with the flow fields by using particle image velocimetry and high-speed chemiluminescence imaging techniques. Additionally, the effects of the strut structure parameters on the lean ignition performance in the cavity are studied. Experimental results indicate that changes in structural parameters have the opposite effects on the ignition performance and the flame-propagation performance. Reducing the strut inclination angle has a contrary function with the decrease in the cavity–strut space, which also transforms the flame-stabilizing mechanism between strut-stabilizing and cavity-stabilizing, accompanied by the flame morphology behind strut changes from no-flame to intermittent-flame, and finally continuous-flame. The lean ignition limit changes with the structure parameters, mainly due to the inverse change in the mass exchange rate and cavity residence time. Compared with the single cavity, the proper cavity–strut combined structure has a wider lean ignition limit at high subsonic speeds due to the advantage of simultaneously increasing the mass exchange rate and cavity residence time.