Flame stabilization in high pressure LOx/GH(2) and GCH(4) combustion

• Published in: Proceedings of the Combustion Institute 2007, Vol.31 (31)
• Main Authors: Singla, Ghislain, Scouflaire, Philippe, Rolon, Juan-Carlos, Candel, Sébastien
• Format: Article
• Language: English
• Subjects: Engineering Sciences; Reactive fluid environment
• ISSN: 1540-7489; 1540-7489
• DOI: 10.1016/j.proci.2006.07.094

Planar laser induced fluorescence (PLIF) of OH is used to examine flame stabilization in high pressure cryogenic flames formed by injecting a central jet of low speed liquid oxygen surrounded by a high speed gaseous stream of hydrogen or methane. In the LOx/GH(2) experiments injection conditions are transcritical as the chamber pressure is above critical but the temperature is below critical (p(LOx) = 6.3 MPa > p(c)(O-2) = 5.04 MPa, T-LOx = 80 K < T-c(O-2) = 150K). In the LOx/GCH(4) experiments the chamber pressure and LOx injection temperature are below critical p(LOx) = 2 MPa, T-LOx = 80 K. Hydrogen or methane are injected at room temperature T-GH2 = T-GCH4 = 288 K. LIF images delineate the flame edge in the injector nearfield. The two flames are stabilized in the vicinity of the liquid oxygen injector lip but the anchor point is found to lie closer to the lip in the LOx/GH(2) case and its displacement from shot to shot is of a smaller amplitude than that corresponding to the LOx/GCH(4) flame. Interpretation of these data is based on a previous analysis which indicates that stabilization is essentially controlled by a dimensionless group formed by comparing the lip thickness to the flame edge thickness Psi = h(s)/delta(f). It is found that Psi slightly exceeds unity in the LOx/GH(2) case essentially fulfilling the stability condition while Psi < 1 in the LOx/GCH(4) case. In this last situation the flame is thicker than the characteristic thickness h(s) and it is therefore sensitive to the high speed methane stream. Anchoring is imperfect and the flame edge moves with the turbulent eddies shed from the lip. Global stabilization is achieved dynamically but the reactive layer is not well established and the large amplitude motion of the edge is a symptom of a possible lift-off. Theoretical estimates indicate that LOx/GCH(4) flame stabilization requires a thicker lip size than the LOx/GH(2) propellant couple. (C) 2006 The Combustion Institute.