Effects of the Recess Length of the Pilot Stage on the Lean Blowout Limits for the Multipoint Lean Direct Injection Combustors

Abstract

Abstract The lean blowout (LBO) limits are critical for the performance of multipoint lean direct injection (MPLDI) combustors. The recessed pilot stage is a promising method to improve the LBO limits for the MPLDI combustors. In the present study, experiments are conducted to investigate the effects of the recess length of the pilot stage on the LBO limits for the MPLDI combustors. Five types of configurations with different recess lengths (0 mm, 7.5 mm, 15 mm, 22.5 mm and 30 mm) of the pilot stage are utilized. It could be concluded from the experimental results that the recessed pilot stage is an efficient method to improve the LBO limits for the MPLDI combustors. Compared with the configuration whose pilot stage is flush mounted, the maximum improvement of the LBO FAR could reach about 42 % by recessing the pilot stage for 22.5 mm. When the recess length is short, the LBO FAR decreases quickly with the increasing of the recess length. When the recess length is long, the LBO FAR decreases slowly with the increasing of the recess length. The mechanism for the function of the recessed pilot stage is revealed by carefully designed numerical simulations to be the suppression of the effect of the disturbance air.