Experimental investigations on the combustion behavior of methane-air mixtures in a micro-scale radial combustor configuration

Experimental investigations on combustion stability limits for methane-air mixtures in a radial micro-scale combustor configuration are herein reported. To study the flame stability characteristics in this radial combustor configuration, two circular quartz plates were arranged parallel to each other and a fuel-air mixture was supplied at the center of the plates. The plates were externally heated to create a positive temperature gradient condition in the flow direction to simplify the heat recirculation process through the solid walls. The fuel-air mixture emanating from the center was subjected to a positive wall temperature gradient and a negative velocity gradient in the radial combustor configuration. Various stable and unstable flame propagation modes were observed during the experimental investigations. The appearance of these modes was a strong function of mixture flow rate, channel width, temperature distribution and mixture equivalence ratio. The effects of wall temperature and mixture equivalence ratios were investigated for a range of mixture flow rates. These investigations showed that the combustion zone moved linearly outward with the increase in the mixture flow rate. At intermediate channel widths (similar to 2.5 mm), an unstable combustion mode appeared. In this combustion mode, large-scale random fluctuations in flame radius were observed along with the leakage of large amounts of unburnt fuel. Exhaust gas analysis was carried out to compare the combustion performance in stable and unstable combustion modes. Based on the experimental investigations, recommendations are made to facilitate the efficient design of a combustor for micro gas turbine applications.