Studying Bluff Body-Assisted Combustion with Fuel-Air Mixture Internal Preheat

Abstract

Lean premixed flames could only stabilize over limited operating conditions, therefore a good understanding of flame stabilization and blowoff phenomena are of a great importance. This research work investigated bluff body assisted-combustion with internal preheating of the fuel-air mixture before entering the combustion zone. Ten hollow bluff body shapes with different geometries were tested experimentally. Examining the stabilization of lean premixed flames anchored to hollow bluff bodies with internal preheat requires the investigation of several interacting factors such as blockage ratios, geometrical attributes, residence time inside and outside the bluff body, preheating, momentum of downward reactive jet, and buoyancy of hot combustion gases. Both the lean operation limit (i.e., equivalence ratio) and stabilization limit (i.e., blowoff velocity) have proved to be significantly affected by the reactive jet downward impingement onto the burner bottom surface as well as the wake zone on the top of the bluff body. Enlarging the turbulent impingement zone while keeping the mixture exit as close as possible to the burner base hot surface pronounced more intensive heat recirculation that is effectively associated with wider stability limits of the flame. The resultant burning capacity becomes thus correlated to the non-dimensional temperature differences namely the preheated bluff body temperature ratio (BTR) and preheated mixture temperature ratio (MTR).