Effect of Modulation of the Inlet Velocity and Equivalence Ratio Gradients on the Stabilization of Stratified Axisymmetric Bluff-Body Flames

Abstract

An investigation of ultralean stratified, disk stabilized, propane flames operated with acoustic modulation of the inlet velocity and fuel-air mixture profiles is presented. Transverse acoustic forcing was applied to the air, upstream of a double-cavity premixer section, formed along three concentric disks, which fueled the stabilization region with a radial mixture gradient. Measurements and supporting Large Eddy Simulations with a nine-step mechanism for propane combustion were performed to evaluate variations in the ultralean flame characteristics under forced and unforced conditions. The effects of forcing on the heat release profiles and on the interaction of the toroidal flame with the recirculation region are examined and discussed. The impact of the acoustic excitation of inlet conditions on the local extinction behavior is, also, assessed by monitoring a local stability criterion and by analyzing phase-resolved chemiluminescence images.

A Study of Recirculating Flow Fields Downstream of a Diverse Range of Axisymmetric Bluff Body Geometries Suitable for Flame Stabilization

“…A differential pressure manometer, Furness Controls (FCO520 AirPro), has been used to measure the pressure drop, with an accuracy of 0.25% of the reading value at 600 Pa. The overall accuracy of the measuring system has been estimated at about 2.5% [41]. Bulk, blocked velocities, at the annular afterbody exit plane (U bl ) varied from 6.60 to 10.2 m/s, resulting in Reynolds numbers from 1100 to 16,000.…”

“…These respective investigations concentrated on the study of the scalar mixing properties for different baffle shapes [38] and on the reacting properties with or without the impact of swirl [11,24,37,39], under stratified or fully premixed inlet mixture conditions. Additionally, investigations regarding the effect of both stratification and preheat on the reacting front have been presented in [12,30,40], while in [41] the authors have discussed the influence of acoustic modulation of the incoming velocity and equivalence ratio gradient on the combustion zone.…”

Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

“…The fluid flow was monitored by means of a pressure differential device (Furness Controls (FCO520 AirPro) and a thermocouple (Omega Datalogger 4 input thermometer HH1384, with K type thermocouple) instrumentation, with 0.25% of reading scale uncertainty. The overall accuracy of the measuring system was estimated at 2.5% [74]. In the stratified cases, the fuel was supplied directly in the hollow tube of 10mm up to the disk, B, where through its annular slot, was injected into the primary cavity.…”

“…However, few works have focused on the impact of continuous stratification produced by an equivalence ratio gradient profile entering the combustion zone [53,[72][73][74][75][76].…”