No abstract

No abstract

No abstract

A new regime of extreme turbulence dened as the ratio of turbulence intensity to laminar ame speed u'/S L from 25 to 243 was characterized for six premixed ames using a new piloted Bunsen burner (called Hi-Pilot). The ames studied had u'/S L values several times larger than those of previous related studies and integral scales and turbulent Reynolds numbers as large as 41 mm and 99,000, respectively. Layer thicknesses were determined from planar laser-induced uorescence (PLIF) images of OH and formaldehyde. Preheat layer thickness was found to increase to sixteen times the laminar value. Residence time of eddies in the ame appears to be important, since the ame tip had preheat regions that were thicker than at the ame base. Reaction layers were not broadened, remaining below twice the laminar value. Four of the cases were predicted to lie in the Broadened Preheat -Thin Reaction layer (BP-TR) regime and the measurements conrmed that they had a BP-TR structure. However, two cases went far beyond the predicted boundary for the Broken Reactions (BR) regime but measurements showed that they were not broken but retained their BP-TR structure. Thus the regime of BP-TR is measured to persist over a wider range than previously predicted. One explanation is that the turbulent eddies may become weakened by the thick, viscous preheat layer before they arrive at the reaction front. Distributed reactions were not observed in the six cases that were selected.

No abstract

No abstract

No abstract

This paper first reviews recent ideas that explain why swirl has a strong stabilizing effect on a flame. Then some measurements are discussed that were obtained using a complex gas turbine fuel injector/mixer operated at realistic levels of swirl and multiple recirculation zones. While swirl is known to have several beneficial effects that improve the mixing and flame stabilization within a gas turbine combustor, swirl also can lead to some undesirable effects. A precessing vortex core can be a source that drives a combustion instability. In addition, swirl affects the unsteady anchoring location of a flame, which also can lead to combustion instabilities, as are observed in our experiment. Interactions between the recirculation zones are observed. The observed large scale unsteady motions cause serious problems for CFD simulations, since the measured mean velocities and turbulence levels on the combustor centerline are much larger than the computed values. Reasons for this difference are associated with unsteady motions.