Scaling relations for the length of coaxial oxy-flames with and without swirl

Abstract

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Impact of co- and counter-swirl on flow recirculation and liftoff of non-premixed oxy-flames above coaxial injectors

“…Experiments are carried out on the Oxytec combustor, already used to investigate scaling relations for the length of non-premixed swirling oxy-flames [7] and the effects of inner co-swirl on flame stabilization [10].…”

“…The distribution of the axial Q 2,z and tangential Q 2,θ volume flow rates provides an adjustable swirl level S 2 . Assuming a solidbody rotation of the flow and a uniform axial velocity, the geometrical swirl number S 2 in the annular channel is given by S 2 = S m /(1+ Q 2,z /Q 2,θ ), where S m = 1.23 is deduced from geometrical considerations as in [7]. The inner stream is swirled with the help of seven removable sets of axial twisted vanes with trailing edge angles θ 1 = −60, -50, -30, 0, 30, 50 and 60 • , as illustrated in Fig.…”

“…Images are averaged over 100 snapshots. The Otsu thresholding method [23] is chosen to infer the flame front location from images [7,24]. The flame liftoff height z f is determined as the lowest point of the Otsu contour.…”

“…In non-premixed systems, swirl is also known to improve mixing between a fuel jet injected in the center of a swirled annular oxidizer stream [2][3][4][5][6][7]. Swirl can also be conferred to the central fuel stream [8][9][10].…”

Effects of Swirl on the Stabilization of Non-Premixed Oxygen-Enriched Flames Above Coaxial Injectors

“…remain in the jet like regime [26]. Second, when both the momen tum flux ratio J and the annular swirl number S 2 are high enough, the flow field is strongly modified with the appearance of a stable CRZ that pushes the reaction zone upstream and makes the flame more compact.…”