Performance study of a central reentrant step pilot-flameholder in a dual-mode combustor

The augmented/ramjet combustion chambers are characterized by wide operating ranges, large flow state variations, and harsh operating conditions. The reliable ignition of these chambers urgently needs to be achieved. To improve the pilot ignition and blowout performance based on the centerbody in augmented/ramjet combustion chambers, a reentrant step flameholder is proposed on the basis of a conventional backward step. In this paper, the flow characteristics, ignition and blowout boundary under the non-premixed inflow, dynamic ignition process and flame stabilization mechanism of the reentrant step flame holder are investigated by using an experimental method with numerical simulation. The results show that the reentrant step flame holder exhibits better ignition and blowout performance than the conventional step flame holder without increasing the flow resistance. The ignition and blowout equivalence ratios of the reentrant step flame holder decrease by 22.86 % and 24.34 %, respectively, compared with those of the conventional step flame holder. The radial reentrant expansion is more effective than the axial reentrant expansion. Analyzing different reentrant structures shows that radial expansion can shorten the ignition delay time and improve the time-averaged integral flame intensity; axial expansion can improve the time-averaged integral flame intensity and reduce the flame pulsation rate; and the structure Da30Dr30 (the conventional step structure expands axially and radially by 30 mm simultaneously within the centerbody.) whose pilot flames are all stabilized in front of the reentrant step flame holder under different incoming flow conditions, exhibits the best ignition and blowout performances.