Effect of high levels of confinement upon the aerodynamics of swirl burners

Abstract

Swirl burners are now widely used and there is much current interest in those which are confined in furnaces and enclosures of small area ratio. Improved understanding can minimize capital and running costs by restricting the overall size of the combustion system and reducing the system's total pressure drop. The objective of this investigation was to obtain, from the described combustor configurations, detailed isothermal aerodynamic information, which could be correlated with parallel studies carried out in the burning state, so as to produce furnace design parameters for the stabilized combustion of low calorific value fuels. An extensive series of aerodynamic tests carried out on a swirl burner/furnace combination of area ratio A/sub f//A/sub e/ = 4, so as to produce various aerodynamic flow patterns suitable for the stabilization of flames produced by low calorific value gas (CV approximately 360 to 500 kcal/m/sup 3/ approximately 40 to 55 Btu/ft/sup 3/) are described. The desired flow pattern was of a large central reverse flow zone surrounded by an annulus of forward moving flow, this region to extend for a length of about one furnace diameter from the burner exit. The results showed that indeed a central reverse flow zone was produced, but more » of annular form with a central forward flow region reducing the desired size and strength of the reverse flow region. It was found that certain types of bluff body stabilizers inserted into the exit of the swirl burner would decrease the strength of the central forward flow region and at the same time increase the size and strength of the center recirculation zone with beneficial effects to flame stabilization. Optimum swirl numbers were found to be in the range 0.95 to 1.2; higher swirl numbers have a deleterious effect upon the reverse flow zone by reducing it in length. Increasing the furnace exit diameter had only a small effect upon the aerodynamics of the system. « less