GB857384A - Flameholder for stabilising combustion in gas passages, such as the afterburners of aircraft jet engines - Google Patents

Abstract

857,384. Generating combustion products under pressure. UNITED AIRCRAFT CORPORATION. Oct. 20, 1958, No. 33412/58. Class 51 (1). A flameholder for use in combustion equipment such as reheat combustion equipment of a gas turbine jet propulsion engine, is adapted to have gas flow therethrough and comprises first means for changing the axial flow velocity profile of gas flowing therethrough so that the axialflow velocity of the gas is a minimum substantially along a cross-sectional axis of the flameholder and increases on each side thereof to a maximum at points furthest from the axis, also second means to cause diffusion of the gas passing through the flameholder so as to cause a reduction in the gas velocity and to form a stagnation point. The flameholder 20 shown in Fig. 1 is mounted within a jet pipe 12 and is of annular form comprising an inner wall 42 and an outer wall 40 radially spaced apart so as to form an open passage of divergent form in the downstream direction. A ring member 34 is disposed along the axis 44 of the cross-section of the flame holder and radially extending twisted vanes 36, 38 are disposed in the passages between the walls 34, 40 and 34, 42, the cross-sections of the vanes at sections AA, BB, CC and DD being shown in Figs. 3, 4, 5 and 6 in which case the gaseous streams in the passages 36, 38 are caused to swirl in the same direction. Alternatively the cross-sections of the vanes at sections AA, BB, CC and DD may be as shown in Figs. 7, 8, 9 and 10 in which case the gas streams in the passages 36, 38 are caused to swirl in opposite directions. In either case, the gas streams adjacent the axis 44 are given greater swirl than gas streams more remote from the axis so that the axial components of velocity of gas streams adjacent the axis are less than those of gas streams more remote therefrom. The radial distribution of the axial components of velocity is indicated in Fig. 11. The circumferential components of velocity on the other hand are greatest adjacent the axis 44 and least adjacent the walls 40, 42. Upon discharge from the vanes 36, 38, the gas streams enter a first diffuser section between planes 2-2 and 3-3 where the axial velocity components are reduced and the radial distribution thereof is as indicated in Fig. 14, the velocity component at the axis 44 being approximately zero so that a stagnation point is formed at 48. The gas streams pass into a second diffuser section between planes 3-3 and 4-4 wherein the axial velocity components are further reduced so that a region 54 of reverse flow is formed adjacent the flameholder axis 44 (see Figs. 2 and 15). In Fig. 16, four cascades of vanes 62, 36, 38, 64 are provided at the open upstream end of the flameholder; the vanes 62, 64 may be streamlined struts and the vanes 36, 38 may be inclined in opposite directions, as shown in Fig. 17 and 18, or in the same direction. The radial distribution of the axial components of velocity is of stepped form as shown in Fig. 19. In a further arrangement, five cascades of vanes are provided, and the vanes may be disposed so as to impart swirl in either the same or opposite directions. The vanes of these embodiments impart swirl components of velocity which may be undesirable, so in place of swirl vanes, flow resistance members as shown in Fig. 23 may be utilized. The flameholder is shown in section in Fig. 22 and a series of members 76 providing high resistance to flow is provided around the axis 44 thereof, and a series of members 78, 80 affording less resistance to flow is provided on each side of the members 76. The passages 74, 82 between the members 78, 80 and the flame holder walls 32, 30 respectively offer no resistance to flow. The radial distribution of axial velocity in this embodiment is as shown in Fig. 21 being least adjacent the axis 44 and greatest adjacent the walls 32, 30. Diffusion sections are provided downstream of the flow resistance members to form a stagnation point and a reverse flow region downstream thereof. In Fig. 24, the gas flowing near the axis 44 is passed through a passage 90 where it is subjected to sudden expansion, the inlet to the passage being through a series of small holes 96 in a plate 98. The velocity of gas flowing through the passages 92, 94 on either side of the central passage 90 is not reduced and the radial distribution of axial velocity at section 100-100 is similar to that as shown in Fig. 19. Flameholders in accordance with the invention may be combined with conventional V-section type flameholders as shown in Fig. 27. The outer wall 32 of the flameholder may be shorter in length than the inner wall 30 thereof, and similarly the vanes 36 in the outer cascade may be shorter in chordal length than the vanes 38 in the inner cascade.