Experimental and numerical investigation on non-premixed CH4/air combustion in a micro Swiss-roll combustor

This paper reports the experimental investigation and numerical analysis of the non-premixed CH4/air com-bustion in a micro Swiss-roll combustor. Six flame patterns were observed in the experiment, namely, single flame, twin flames, pulsating flame, obviously asymmetric flame, extinction and blow-off. A global map is drawn for these combustion regimes based on systematic experimental observation. The lower combustible limits of the nominal equivalence ratio (phi) and inlet methane flow rate (FM) are 0.4 and 0.02 L/min, respectively. Moreover, the blow-off limit increases significantly as the equivalence ratio is increased from 0.7 to 0.8. Furthermore, it is found that both the maximum and average surface temperature of the combustor cover show a non-monotonic variation versus the nominal equivalence ratio, and their maximum and minimum values appear at phi = 0.9 and 0.8, respectively. Numerical simulation can reproduce the flame shapes successfully. In addition, the asymmetric flame structures in the vertical direction were also discovered through numerical simulation. The comparative analysis demonstrates that the buoyancy effect leads to asymmetric flow field in the vertical cross section of the combustor. As a result, the reaction heat and fuel conversion ratio in the combustion chambers change non-monotonically with the equivalence ratio, which leads to a similar variation manner of the surface tempera-ture. In summary, the present study provides a deep insight into the characteristics of non-premixed combustion in micro Swiss-roll combustors.