Effect of inlet and outlet configurations on blow-off and flashback with premixed combustion for methane and a high hydrogen content fuel in a generic swirl burner

The paper analyses new data for three fuels, natural gas, methane and Coke Oven Gas (COG) in two swirl burners. Flashback and blowoff can be correlated with the inlet tangential velocity, not the inlet mass flow, over a range of swirl numbers from 0.8 to more than 4. Geometry and fuel type are important. The correlation gives best fit for a particular outlet geometry and with higher hydrogen content fuels. The correlation still holds with methane and natural gas, especially with confinement. Analysis of the correlation infers that both blowoff and flashback occurrences are governed by the shear layer surrounding the Central Recirculation Zone (CRZ). The CRZ acts to control the width and strength of the shear flow region. Blowoff was found to occur when the CRZ was extensive and well develop and could be modeled by a well stirred reactor system. Two modes of flashback were found, both of which could be characterized by the same correlation of inlet tangential velocity. The first flashback case occurred at lower swirl numbers when the flame attached to the burner rim and flashed back through the outer boundary layer. At higher swirl numbers the CRZ and associated flame located next to its boundary extended back over the fuel nozzle inside the swirl chamber. Flashback occurred when the flame suddenly moved radially outwards towards the inlets. A clear trend was established for COG; as the swirl number was increased from 0.8 to 1.5 blowoff slightly worsened, whilst flashback improved. Thus higher swirl numbers are tentatively favored for flashback protection for higher hydrogen content fuels.