Experimental and numerical investigation of the stabilization mechanism of methane micromix flames with jet-impinging structure.

• The effect of jet-impinging structures on flame stability is investigated. • The jet-impinging structure contributes to the enhancement of the near-field turbulence intensity of the micro-mixing nozzle jet. • Reducing the flame stretch rate of the shear layer contributes to flame anchoring. Micromix combustion has the potential to achieve ultra-low NOx emissions. The jet-impinging structure is generally applied for micromix nozzles to obtain a well-mixing performance. However, its influence on flame stability is worth investigating, especially for natural gas flames, characterized by limited flame stability. In this study, the effect of the jet-impinging structure was investigated experimentally and numerically. Combustion characteristics, including flame shapes, OH* distributions, and lean blow-off limits, were obtained experimentally for two types of nozzles. Compared with the round nozzles without the jet-impinging structure, the flames generated by the micromix nozzles with the jet-impinging structure have lower lift-off height, shorter flame height, and lower lean blow-off equivalence ratio. Numerical simulations show that the jet-impinging structure contributes to increasing the turbulence intensity, as a result, the turbulent flame propagation is enhanced. Meanwhile, the structure produces thicker shear layers which decrease the local flame stretch rate, and local extinctions caused by flame stretching are partially avoided. In general, this work demonstrates the viability of applying the jet-impinging structure to extend the flame stability limit and generate compact flames. [ABSTRACT FROM AUTHOR]