| Supplemental firing in a vitiated oxidizer stream can result in degraded combustion stability. As an option, rich-burn, quick-mix, lean-burn (RQL) style combustors have been shown to provide low emissions and high stability in gas turbine applications. The present work addresses the development and characterization of an RQL combustor, optimized for combustion in a vitiated environment. In order to achieve this, three combustor mixing air-to-main air mass ratios, five levels of swirl, and four designs of circumferentially distributed radial mixing jets, were evaluated at levels of vitiation between 21% and 17% inlet oxygen concentration. It was determined that, with a combustor air mass ratio of 2.5, the lowest emissions levels were achieved, and the sensitivity of emissions levels to the inlet oxygen concentration was minimized while maintaining an acceptable level of stability. In addition, it was determined that the number of mixing jets in the mixing zone did not have a substantial effect on the NOx emissions level, but that decreasing the number of mixing jets improved the emissions levels of CO. Furthermore, it was observed that (1) NOx emissions are primarily a function of rich zone flame temperature and flame length, and (2) it is possible to reduce the emission of NOx relative to levels at the combustor inlet. The results of this study establish that RQL combustors are viable for providing stable, low NOx performance in supplementary firing systems. |
