The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow

Abstract

The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow KAUST Repository a b s t r a c tThe stability limits, the stabilization mechanism, and the flow field structure of highly stabilized partially premixed methane flames in a concentric flow conical nozzle burner with air co-flow have been investigated and presented in this work. The stability map of partial premixed flames illustrates that the flames are stable between two extinction limits. A low extinction limit when partial premixed flames approach non-premixed flame conditions, and a high extinction limit, with the partial premixed flames approach fully premixed flame conditions. These two limits showed that the most stable flame conditions are achieved at a certain degree of partial premixed. The stability is improved by adding air co-flow. As the air co-flow velocity increases the most stable flames are those that approach fully premixed. The turbulent flow field of three flames at 0, 5, 10 m/s co-flow velocity are investigated using Stereo Particle Image Velocimetry (SPIV) in order to explore the improvement of the flame stability due to the use of air co-flow. The three flames are all at a jet equivalence ratio (U j ) of 2, fixed level of partial premixing and jet Reynolds number (Re j ) of 10,000. The use of co-flow results in the formation of two vortices at the cone exit. These vortices act like stabilization anchors for the flames to the nozzle tip. With these vortices in the flow field, the reaction zone shifts toward the reduced turbulence intensity at the nozzle rim of the cone. Interesting information about the structure of the flow field with and without co-flow are identified and reported in this work.

Highly stabilized partially premixed flames of propane in a concentric flow conical nozzle burner with coflow

“…They [15] found that the existence of the air coflow improves the flame stabilization. However the flame structure, the mixing field, and flame/flow field interaction were not investigated in their work.…”

“…The range of the mixture fraction fluctuations plays a crucial rule in the flame stabilization mechanism. Recently, the effect of the air coflow velocity on the stability of methane partially flames stabilized in CFCN burner was investigated by Elbaz et al [15].…”

“…The published data of turbulent partially premixed flames with inhomogeneous mixing field are not sufficient to fully describe the flame structure within the expected different regimes of partially premixed flames. Previous experimental investigations covered the stability of partially premixed flames as compared to non-premixed and fully premixed flames [6,[12][13][14][15][16]. The data showed that partially premixed flames are more stable than both non-premixed and fully premixed flames [12].…”

“…where different flame aspects were investigated, including the flow field structure [15,17], the flame structure [16,[18][19][20] and, recently, the mixing field structure [21]. Masri and his research group have also investigated turbulent partially premixed flames of methane and natural gas in a piloted concentric flow burner [1,6,13,22].…”

Evaluation of partially premixed turbulent flame stability from mixture fraction statistics in a slot burner

“…The characteristics and structures of partially premixed flames have been studied by means of advanced laser-based optical measurement techniques (Barlow et al, 2017;Elbaz et al, 2018Elbaz et al, , 2016El-Mahallawy et al, 2007;Li et al, 2009;Mansour et al, 1989;Mansour 70 et al, 2017a;Mansour et al, 2012;Meares et al, 2015;Meares and Masri, 2014;Yan et al, 2010) and experimental data were used to analyze the dependences of the degree of premixing (Meares et al, 2015;Meares and Masri, 2014) and the impact of different fuel compositions on flame stability (Yan et al, 2010). Lasers have been applied for example for Rayleigh/Raman measurements to determine local temperature and gas 75 composition in flames (Barlow et al, 2009;Brands et al, 2014;Cheng et al, 2012;Fuest et al, 2011Fuest et al, , 2015Fuest et al, , 2012Mansour et al, 1999;Mansour and Yung-Cheng, 1996;Raffius et al, 2017;Wehrmeyer et al, 1992).…”