WO1992021872A1

WO1992021872A1 - A flame holder device in afterburner tubes of turbojet engines having an air fan rotor of by-pass type

Info

Publication number: WO1992021872A1
Application number: PCT/SE1991/000378
Authority: WO
Inventors: Peter Ivarsson
Original assignee: Volvo Flygmotor AB
Current assignee: GKN Aerospace Sweden AB
Priority date: 1991-05-29
Filing date: 1991-05-29
Publication date: 1992-12-10
Anticipated expiration: 1993-11-29

Abstract

A flame holder device in afterburner tubes of turbojet engines, which have an air fan rotor of by-pass type, comprises at least one concentric annular flame holder element (34a) with V-like cross-sectional shape, the mouth of which is oriented in downstream direction, and supporting circumferentially spaced and radially extending arms (40), also having V-like cross-sectional shape. In order to avoid detrimental stresses and local overheating of the material of the device, which occur in conventional structures, the invention suggests that the radially outermost end portions (40a) of the arms (40) are located in the air duct (12) from the fan and have an inlet opening (40c) facing the air flow in said duct (12) for guiding of air therefrom into said arms (40), while the radially innermost portions (40b) of the arms are located adjacent to or within the core of the flow from the turbojet engine (10) for letting out said air thereinto.

Description

A FLAME HOLDER DEVICE IN AFTERBURNER TUBES OF TURBOJET ENGINES HAVING AN AIR FAN ROTOR OF BY-PASS TYPE

The present invention refers to a flame holder device in afterburner tubes of turbojet engines having an air fan rotor of by-pass type, comprising at least one concentric angular flame holder element with V-like cross-sectional shape, the mouth of which is oriented in downstream direc¬ tion, and supporting circumferentially spaced and radially extending arms, also having V-like cross-sectional shape. A flame holder device of this kind is substantially known from US A 4,259,839.

In conventional flame holder devices a surrounding flow of colder fuel-air mixture from the fuel spreaders of the afterburner tube is used as a local coolant for achieving a lower temperature of the material of the flame holder de¬ vice and hence increased operational reliability. A drawback of said cooling action is however that great local tempera¬ ture differences occur which cause extensive crack formation effects in connection with ignition and extinction of the afterburner when the temperature gradients in the flame holder device become particularly great. Furthermore, in ignited condition high heat stresses occur which in some cases might result in local burn-outs of the hottest area of the flame holder device. In fighter aeroplane engines operating with afterburners for increasing the thrust vari¬ ous operational disturbances of the afterburner occur in cooperation with gas loads from the core flow of the turbo¬ jet engine since the outlet temperature of the latter has a heavily detrimental effect on the durability of the flame holder device. In such cases conventional V-shaped elements suddenly brake down by burn-outs or cracking when metallic materials are used as structural materials in the flame holder device. The total restriction of the gas flow in the afterburner which can be obtained by means of such flame holder devices amounts to approximately 25-40 per cent and the fuel is injected upstream of the flame holder device.

From EP A2 0315485 is known a flame holder device in which for lowering of the material temperature of the flame holder parts portions of the surrounding flow from the air fan ro¬ tor are deflected. Certainly this reduces the heat stresses on the outer flame holder parts but still the most essential central flame holder portion is entirely subjected to the loads from the core flow of the turbojet engine.

The object of the present invention therefore is to provide a more reliable and permanent reduction of the temperature variations in the material of the flame holder device in connection with ignition and operation of the afterburner but also in the operation of the turbojet engine solely.

According to the invention, this is now achieved substan¬ tially in that the radially outermost end portions of the arms are located in the air duct from the fan and have an inlet opening facing the air flow in said duct for guiding of air therefrom into said arms, while the radial innermost portions of the arms are located adjacent to or within the core of the flow from the turbojet engine for letting out said air thereinto. Owing to said letting out of air from the fan into the core flow of the turbojet engine, which might be made at various distances from the centre axis, a reduction of the temperature of said core flow and hence reduced heat loads on the whole afterburner structure is provided.

By way of example the invention will be further described below with reference to the enclosed drawing on which Fig. 1 illustrates a central longitudinal section of a typical turbojet engine of double-flow type and equipped with an afterburner tube having a flame holder device according to the invention. Fig. 2 is an end view of the flame holder device taken along the line 3-3 in Fig. 1, Fig. 3 is a per-

spective view of a flame holder device used in the embodi¬ ment according to Fig. 1 and Fig. 4 is a vertical section of the flame holder device according to Fig. 2, taken along the line 4-4.

In Fig. 1 is shown a typical turbojet engine 10 having an air fan rotor 24 and an associated turbine 26 as well as a compressor wheel 28 and a compressor turbine 30. From the rear or right hand end of the turbojet engine 10 as seen in Fig. 1 a core gas flow 14 is discharged within a surrounding outer shell 16, which also defines an afterburner zone or area 18. Externally of the compressor wheel and the turbines 28 and 30 passes a surrounding air flow from the fan through a fan duct 12 and concentrically around the fan shaft 22 of the engine is arranged a diffusor or spreader cone 20. The fan shaft 22 extends centrally relative the shell 16. Fur¬ thermore, fuel injection rings 32 are mounted downstream of the compressor turbine 30. In this drawing figure it is also illustrated an angular flame holder 34 with V-like cross-section. At the rear end of the engine there are also primary and secondary annular orifice flaps 36, 38.

In Figs. 2-4 of the drawing are illustrated detail views of the typical flame holder device 34, which on an annular ele¬ ment 34a is provided with circumferentially spaced and radi¬ ally extending fan air deflecting arms 40, also having V- -like cross-sectional shape with the opening of the V di¬ rected downstream. According to the invention, with their radial outermost end portions 40a said arms thereby are located in the fan duct 12 and have an inlet opening 40c facing the flow of air from the fan for guiding such air into the arms. With their radial innermost portion 40b the arms 40 are located adjacent to or within the core flow 48 from the turbojet engine 10 in order to let out fan air thereinto. As is evident from the drawing, the arms 40 might be formed with various length of the inner portions 40b such that the various circumferentially spaced arms dis¬ charge their cooling fan air at different radial distance from the centre axis of the core flow.

Preferably, in the inlet openings 40c there might be mounted one or more guide blades 42 and on the inner portions of the arms there might be mounted at the rear side a guide plate element 44 which forms a channelling member with selected discharge level in the core flow 48.

It is suitable that the arms 40 of the flame holder device 34 be traversed by about 1-10 per cent of the fan air flow through the duct 12. The number of arms 40 might be between 12 and 24, eighteen having shown to be an optimum in tests. The transversal width of the arms 40 amount to between 25 and 60 mm and the annular element 34a has a radius of about 355 mm and a width of 60 mm in an afterburner tube having a radius of about 620 mm. The flame holder device 34 is suitably manufactured from a fibre-ceramic material or a nickel-chromium alloy.

Known V-flame holders of conventional type cause combustion disturbances in the form of humming noises at about 100 Hz in the afterburner tube. Pressure oscillations increase when the inlet temperature rises in the fan duct (i.e. the inlet temperature of the gas generator) . On the contrary, the inventive flame holder provides for an increased dampen¬ ing of the humming noise for increased engine inlet tempera¬ tures, i.e. an effect opposite to prior art.

Claims

1. A flame holder device in afterburner tubes of turbojet engines having an air fan rotor of by-pass type, comprising at least one concentric annular flame holder element (34a) with V-like cross-sectional shape, the mouth of which is oriented in downstream direction, and supporting circum¬ ferentially spaced and radially extending arms (40) , also having V-like cross-sectional shape, c h a r a c t e r ¬ i z e d i that the radially outermost end portions (40a) of the arms (40) are located in the air duct (12) from the fan and have an inlet opening (40c) facing the air flow in said duct (12) for guiding of air therefrom into said arms (40) , while the radially innermost portions (40b) of the arms are located adjacent to or within the core of the flow from the turbojet engine (10) for letting out said air thereinto.

2. A flame holder device according to claim 1, c h a r ¬ a c t e r i z e d i n that the circumferentially spaced arms (40) are made with varying length of their innermost portions (40b) in order to discharge the cooling fan air at different radial distances from the centre axis of the core flow of the turbojet engine (10) .