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

Abstract

Partially premixed turbulent flames with non-homogeneous jet of propane were generated in a concentric flow conical nozzle burner in order to investigate the effect of the coflow on the stability and flame structure. The flame stability is first mapped and then high-speed stereoscopic particle image velocimetry, SPIV, plus OH planar laserinduced fluorescence, OH-PLIF, measurements were conducted on a subset of four flames. The jet equivalence ratio Φ = 2, Jet exit Reynolds number Re = 10,000, and degree of premixing are kept constant for the selected flames, while the coflow velocity, Uc, is progressively changed from 0 to 15 m/s. The results showed that the flame is stable between two extinction limits of mixture inhomogeneity, and the optimum stability is obtained at certain degree of mixture inhomogeneity. Increasing Φ, increases the span between these two extinction limits, while these limits converge to a single point (corresponding to optimum mixture inhomogeneity) with increasing Re. Regardless the value of Φ, increasing the coflow velocity improves the flame stability. The correlation between recessed distance of the burner tubes and the fluctuation of the mixture leads to optimum flame stability. The time averaged SPIV results show that the coflow induces a big annular recirculation zone surrounds the jet flames. The size and the location of this zone is seen to be sensitive to Uc. However, the instantaneous images show the existence of a small vortical structure close to the shear layer, where the flame resides there in the case of no-coflow. These small vertical structures are seen playing a vital role in the flame structure, and increasing the flame corrugation close to the nozzle exit. Increasing the coflow velocity expands the central jet at the expense of the jet velocity, and drags the flame in the early flame regions towards the recirculation zone, where the flame tracks and matches the spatial locations of low axial velocity fluctuations. At downstream, the flame is seen to conform to the passage of large scale structure. At Uc = 10 and 15 m/s, part of the primary reaction zone is rolled up towards upstream burner nozzle, anchoring the flame to the nozzle tip. This indicates that the

Stability Characteristics of a Turbulent Nonpremixed Conical Bluff Body Flame

“…The flame length is also known to be another parameter influenced by the co-flow velocity. Contrary to the widespread belief, in that increasing the co-flow decreases the flame length [36,37,42,43], it was experimentally shown [2,44,45] that, under certain circumstances (such as the co-flows velocities up to 3 m/s or the bluff body diameters smaller than 18mm) flames can elongate by the increasing the co-flow. In addition to these three parameters, the velocity and the momentum flux ratios of the fuel and air streams were found to have indirect effects on the recirculation strength [11,21] through the vortex formation mechanisms.…”

Flame flow field interaction in non-premixed CH4/H2 swirling flames

“…Attaching a diverging quarl to the swirl burner's exit leads to enhanced flame stability [25,[27][28][29]. In inhomogeneous mixture flames, the existence of the diverging quarl to the burner tip improves the flame stabilisation [30][31][32][33][34]. Thus, a diverging quartz quarl of 40 mm height and 15 o half cone angle was fixed to the air tube exit in this work.…”

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).…”