Effects of sleeve divergence angle of dual-stage swirl cup on the ignition performance

Due to the effective decrease on the exhaust smoking, pollutant emission and lean blowout limit, the swirl cup has a wide application in the combustor design. The flow field and two-phase atomizing field downstream of the swirl cup are greatly affected by the sleeve. To investigate the influence of the variation of the sleeve geometry on the ignition performance of the combustor used in jet engine with Chinese aviation kerosene RP-3, three dual-stage swirl cup with different sleeve divergence angles, namely 60°, 70°, and 80°, were examined under normal inlet temperature and normal inlet pressure. The first-stage of the swirl cup uses oblique holes as swirler which is in the anticlockwise direction, while that of the second-stage employs radial blades as swirler in the clockwise direction. High speed imaging was used to obtain the transient process of the combustor ignition. Numerical simulation was used to assist the analysis on the experimental results. It was found that the ignition process in the single dome combustor can be divided into four stages, namely 1) the formation of a flame kernel, 2) the upstream propagation of the flame kernel to the swirl cup exit, 3) the flame stabilization in the swirl cup, and 4) the flame spread from the swirl cup to the primary combustion zone. With the sleeve divergence angle increased from 60° to 80°, the size of the central recirculation zone, the divergence angle of the swirl flow, and the spray angle at the swirl cup exit increased, and the lean ignition fuel/air ratio was reduced by 38%.