Combustion Characteristics of a Two-Dimensional Twin Cavity Trapped Vortex Combustor

Abstract

Trapped vortex combustor (TVC) is a relatively new concept, having potential application in gas turbine engines. In this work, an attempt has been made to characterize the 2D twin cavity TVC experimentally in terms of its visible flame length, pollutant emission level, and exit temperature profile. Besides this, numerical results are also discussed to explain certain intricacies in flow and flame characteristics. Experimental results reveal that visible flame length value is sensitive to mainstream Reynolds number (Rems), primary (cavity) air velocity (Vp), and cavity equivalence ratio (Φc). For a particular Rems and Φc, an increase in Vp results in longer flame length; whereas, flame length gets shortened at higher mainstream Reynolds number cases. Numerical studies indicate that shortening of flame length at higher Rems cases is caused due to quenching of flame at the shear layer by the incoming flow. An attempt has been made to correlate flame length data with the operating parameters and Damkohler number (Da); Da takes care of flame quenching effects. Moreover, it is also brought out that the emission profile at the combustor exit is dependent on primary air velocity, mainstream Reynolds number, and cavity equivalence ratio. Emission studies indicate that higher primary air velocity cases make the carbon monoxide (CO) and unburned hydrocarbon (UHC) emission levels to lower values. Reduction in emission level is caused mainly due to the flame merging effects. Besides this, the influence of cavity flame merging on the exit temperature profile uniformity is also brought out. This study reveals that merging of cavity flames is essential for the optimized operation of a 2D trapped vortex combustor.