Experimental and numerical simulation study of the effect of mixing on the characteristics of swirl/non-swirl micromix flames

Micromix combustion technology is anticipated to address challenges related to the instability and high emissions associated with hydrogen-containing fuel combustion. The direct influence of fuel-air mixing on combustion characteristics underscores the importance of selecting an appropriate mixing scheme. Specifically, this paper explores the impact of mixing characteristics on the stability and emissions of swirl and non-swirl micromix combustors used for syngas combustion in an IGCC gas turbine. Numerical simulations were employed to analyze component distribution, vortex structures, and uniformity indices. Experimental investigations included determining lean blowoff boundaries, capturing flame OH* images, and measuring emissions. The study found that the mixing uniformity of non-swirl nozzles was inferior to that of swirl nozzles, resulting in a lower lean blowoff limit for non-swirl nozzles and reduced NO emissions for swirl nozzles. However, the mixing effect had minimal impact on CO generation. At dimensionless axial distances x < 0.8, mixing was predominantly influenced by the injection flow momentum ratio (J). Beyond this point (x = 0.8), the uniformity of swirl nozzle mixing significantly improved. The location of the reaction zone was closely tied to J, with stability and NO emissions within the reaction zone showing a negative correlation with the mixing uniformity index.