Experimental evaluation and mechanism analysis of combustion performance enhancement in composite wall-assisted methane/air mixtures

This work presents numerical and experimental investigations of the impact of composite walls on the flame stabilization and output characteristics in methane/air-fueled combustors by imposing low/high thermal conductivity materials on the outer/inner layers. Effects of composite material, wall thickness, and inlet velocity are assessed. It is numerically shown that the implementation of composite walls enables the U-shaped flame in the traditional quartz combustor to become inverted V-shaped with one or two peaks. This is also accompanied by the flame location shift approaching the inlet, signaling enhanced flame stability, along with high output performance. To unravel the underlying mechanism, a detailed analysis is performed in terms of flame/wall coupling, flame surface heat release rate, and stretching. Meanwhile, further reducing the thermal conductivity of the outer layer material such as SiO2 aerogel, the V-shaped flame transforms into a planar flame, which has a stronger ability to resist destabilization. Further experimental analysis reveals that optimizing the composite wall properties enables the blowout limit to be increased from 1.17 m/s to 1.9 m/s, a percentage increment of 62.3 %, as compared to the quartz combustor. This work sheds light upon how the composite wall contributes to flame stabilization improvements by properly arranging the wall materials.