Hollow bluff body-stabilized natural gas-air premixed flames

The effects of hollow bluff body geometry, surface curvature, blockage ratio, mixture residence time, impinge-ment strength, heat recirculation eddy size, Reynolds and Froude numbers were all investigated via 10 bluff body shapes. It was found that duplicating the wake flow zone and increasing the mixture flow velocity inside the bluff body cavity via a disc configuration provide a maximum blow-off velocity of 49 m/s. Enlarging the bluff body exterior surface area and the flow wake width in addition to elongating the mixture residence time inside the bluff body cavity via a trapezoidal configuration yield a minimum lean limit of 0.42. Having grooves on the bluff body exterior surface or providing a concave surface part at the wake region favorably develops flow turbulence and intensive heat recirculation. The bluff body cavity height should be adjusted at an optimum value which keeps a high impingement velocity onto the combustor hot surface via a large vortex and simultaneously allows enough mixture preheating length. The stability limits were thus correlated to the geometrical and thermal effective parameters in addition to Reynolds and Froude numbers.