Investigation of elevated pressure effects on combustion characteristics of combined micro-mixing flames

Micro-mixing (MM) combustion technology offers advantages such as enhanced flame stability and reduced pollutant emissions. Experimental investigations are conducted on a typical low heating value syngas under varying inlet air pressures (P₃) ranging from 0.1 to 0.6 MPa and equivalence ratios (φ) spanning 0.52 to 0.73. This study provides an in-depth analysis of combustion dynamics, flame structure,and pollutant emission characteristics. The findings reveal that the MM flame mode predominantly resides within the continuous stirred reaction zone, with a local curvature radius on the millimeter scale, indicating the presence of numerous small-scale wrinkles across the flame front. With the increase of P₃, the OH distribution area markedly contracts and concentrates toward the combustion chamber head. The flame width exhibits only a slight fluctuation of <5 % throughout the entire pressure variation range, indicating that axial compression is the dominant mechanism by which pressure affects flame morphology, and the coefficient of variation (CV) of OH spatial distribution uniformity (SDU) exhibits non-monotonic pressure dependence, undergoing critical behavioral transition at P₃ = 0.3 MPa. NO emission exhibits a rapid increase with rising P₃ and φ, however, under the tested conditions, NO level remains below 5 ppm (@15 %O₂).