Concentric multi-annular swirl burner: Stability limits and emission characteristics

A new type of multi-annular swirl burner is described which has some distinct advantages e.g. wider stability limits, turn down ratio, volumetric heat release rate, etc., over the conventional single annular tangential entry (or vane type) swirl flame stabilizer. The multi-annular swirl burner described herein makes use of the principle that under turbulent conditions high volumetric heat release rates can be achieved by matching the concentrations and directions of flow of reactants in such a way that regions of high fuel concentration overlap regions of large shear stresses in the flow. Noise emission and species concentration characteristics were obtained from this burner and are discussed here in this paper, however NO x levels will be reported in a later paper. Measurements are presented of the three components of mean and r.m.s. turbulence velocity, probability density distribtuion of velocity, distribution of mean temperatures, stability limits, quality of combustion and the emission of noise. A low NO x emitting performance of this burner is also inferred. A laser anemometer used to obtain the velocity measurements comprised of an argon-ion laser, a bleached radial rotating diffraction grating as beam splitter and frequency shifter, transmission and collecting optical components, a photomultiplier, a pulse counter and signal processor. The anemometry results show the apparent differences between the noncombustive and combustive flows. No evidence of the presence of the precessing vortex core which is normally present in conventional swirl generators at high swirl number has been found in this multi-annular swirl burner. The dissipation of the pressing vortex core and the spread of turbulence levels over a larger are at the burner exit reveals this burner to be potentially attractive from the point of view of better mixing of reactants and also from the point of view of unacceptable oscillations which can be present in conventional swirl generators.