Swirl flow structure and flame characteristics in a model lean premixed combustor

The swirling flow in a lean premixed prevaporized (LPP) combustor model (LPP chamber) is studied, making use of high-speed photography, Laser Doppler Velocimetry (LDV), sound probes, fine-wire thermocouples, and suction probes for chemical gas analysis. The experimental study, which involved parametric changes of Re , S , and phi, extends from the combustor primary zone to the premixing chamber and was conducted with and without reaction, burning either gaseous propane or liquid fuel assisted with preheated air at 300 degreesC. Measurements show that the swirling flow mixture that enters the primary zone of the combustor chamber shows evidence of a PVC structure, for S > 0.5, that embraces the central recirculation zone (CRZ). Furthermore, reaction test results show that increasing the swirl number decreases CO and NOx concentrations at the combustor exit and reduces flame stability limits to levels close to the lean limit because of flashback. In addition, a detailed study of the reacting condition ( S =1.05, phi=0.5) was performed; the results indicate that the PVC is still present, embracing the base of the CRZ and staying in the inner shear layer, where the flame should also be stabilized, and contributing particularly to an abnormal radial distribution of W-rms . Large gradients of mean temperature andUnburnedHydrocarbons(UHC) concentration were found to be limited to the base of the CRZ.