Turbulent CH 4 /H 2 /air premixed and stratified flames were investigated using a dual-swirl injector that employed the same main swirler but incorporated different pilot nozzle configurations (peg and swirl). The novel peg-type induces localized vortical structures through geometric protrusions, whereas the swirl-type forms a globally swirling flow field characterized by sustained azimuthal motion. The peg-pilot flames demonstrated improved stability near the LBO limit compared with the swirl-pilot flames. Conversely, the swirl-pilot flames resulted in lower NO x emissions owing to the dilution of burned-gas within the IRZ. Irrespective of pilot configuration, stratified operation suppressed flame lift-off but increased NO x emissions compared with premixed operation, primarily due to less effective fuel–air mixing. OH-PLIF and PIV were employed to resolve the flame structure and flow field. These results reveal how pilot geometry and mixture stratification jointly govern flame anchoring, recirculation structures, and NO x formation, thereby informing the design of dual-swirl injectors for hydrogen-blended fuels. • Peg- and swirl-pilot configurations were comparatively examined in turbulent CH 4 /H 2 /air dual-swirl flames. • Peg-pilot flames exhibited improved stability near the lean blow-out limit. • The swirl-pilot flame enhanced the fuel–air mixing and recirculation, resulting in advantageous NO x emission characteristics. • Compared with premixed flames, the stratification reduced flame lift-off and increased flame surface density. • OH-PLIF and PIV resolved flame macrostructures and flow–flame interactions.
Kim et al. (Fri,) studied this question.