Experimental and numerical study of flow and ignition and lean blowout characteristics of jet-cooled wall flameholder in a dual-mode combustor

The wall flameholder is one of the credible alternatives to realize pilot ignition in augmented/ramjet combustors. To overcome the ablation for a long-term operation, two types of jet cooling, external-inhaled air and pressure-driven jet cooling, are proposed for the wall flameholder. In this work, the flow and combustion process in a laboratory scale rig is studied for different cooling schemes and cooling conditions using experimental and numerical methods. Flow analysis in pressure-driven jet cooling scheme shows that the flow field of flameholder is influenced significantly by the cooling hole angle on the oblique plate alpha and on the rear plate beta. In particular, the cooling jet angle combinations (alpha = 30 degrees, beta = 30 degrees) and (alpha = 90 degrees, beta = 150 degrees) are the two schemes with the most different characteristics. To investigate the effects of jet cooling type and cooling jet angle on the flow, ignition, and lean blowout (LBO) characteristics, the two distinctively different angle combinations are applied to form two kinds of jet cooling schemes mentioned above. Results suggest that the jet cooling type has less impact on the flow field but more influence on the flow loss than the cooling jet angle. The ignition performance of cooling schemes with alpha = 30 degrees and beta = 30 degrees is better than that of those with alpha = 90 degrees and beta = 150 degrees, but it has a more significant flow loss. The LBO limits of external-inhaled air cooling are lower than that of pressure-driven jet cooling. Moreover, the ignition and LBO limits decrease gradually with the increased mainstream temperature and they are only slightly affected by the mainstream velocity. Notably, the pressure-driven jet cooling scheme can slightly reduce the flow loss but it leads to a deteriorated ignition and LBO performance. The external-inhaled air cooling scheme with alpha = 30 degrees and beta = 30 degrees has an excellent ignition and LBO performance, and the ignition and LBO limits increase with the increasing cooling air flow rate and the decreasing cooling air temperature. (C) 2022 Elsevier Masson SAS. All rights reserved.

Automated summary

The study investigates the flow and combustion process in a laboratory scale rig with different cooling schemes and conditions for the wall flameholder. The results show that the cooling type has less impact on the flow field but more influence on the flow loss compared to the cooling jet angle. External-inhaled air cooling has lower lean blowout limits than pressure-driven jet cooling, and the ignition and LBO limits decrease with increased mainstream temperature. The pressure-driven jet cooling scheme reduces flow loss but deteriorates ignition and LBO performance.