EP0059137B1 - Ignition device for fuel injected into a rapidly flowing gas stream - Google Patents

Description

The invention relates to a device for igniting fuel injected into a gaseous oxidizing medium in rapid flow, used in particular for igniting the heater of an aviation turbojet.

French patent No. 2,351,258 discloses an ignition device comprising an enclosure placed in a gas flow and provided with an ignition member such as a spark plug. This known device is characterized in that said enclosure receives through a grid or perforated inlet plate a fuel mixture which is ignited in said enclosure by said device, and is provided with a tubular conduit receiving at its upstream end a jet of fuel which it discharges, with gases taken up by said upstream end in said flow, in said enclosure downstream from said ignition member.

When the reheating (or post-combustion) is ignited, the ignition member such as a candle ceases to be supplied, so that the enclosure of the ignition device is not permanently lit.

The present invention relates to an improvement of the ignition device described above, the object of this improvement being essentially to improve the operation of the ignition device, in particular at high temperatures.

The fuel ignition device injected into a gaseous oxidizing medium in rapid flow is of the type which has just been indicated, and it is characterized in that the enclosure, provided with an ignition member such as a spark plug electric, further comprises a catalytic ignition element, which is disposed in said enclosure upstream from the downstream end of the tubular conduit intended to discharge a jet of fuel, and outside, for example, around said tubular conduit so that the initiation of combustion in said enclosure is ensured independently by the member or element once said element is brought to its operating temperature by the gases passing through said device.

The additional element of catalytic ignition, which is provided according to the present invention, offers a double advantage: on the one hand, as the element of catalytic ignition acts only on gases brought to an already high temperature, of the order of 350 ° C., this additional ignition device supplements the ignition member such as an electric candle, in the operating range of the turbojet engine which corresponds to the high gas temperatures, so as to increase reliability of the ignition device in this operating range. On the other hand, the catalytic ignition element being able to act permanently, without consuming energy, it makes it possible to use the ignition device according to the present invention to produce a pilot flame.

It was already known to use catalytic ignition elements in the technique of turbojets.

French Patent No. 1,454,312 describes a device for igniting fuel injected into a stream of oxidizing gas, comprising at least one catalytic element disposed in a circulation passage inside a mass of refractory material. It is also indicated therein that the catalytic element or elements can be used for post-combustion in the ejection nozzle of a turbojet. However, it follows from the above that such an ignition device, devoid of an ignition member such as an electric candle, malfunctions at low temperatures of the ejected gases.

On the other hand, the purely catalytic action ignition device which is described in this prior patent, needs to be supplied with a flow of pressurized air, derived from the outlet of the compressors of the turbojet; some of its achievements also require a special fuel supply. Compared to these previous embodiments, the ignition device according to the present invention therefore offers the additional advantage of not requiring any special supply of compressed air and possibly fuel, since, as already indicated in the patent 2 351 258, the ignition device according to the present invention is supplied directly by the hot gases which the turbine sends into the afterburner channel and by the jet of fuel coming from the injection rail mounted in said afterburner channel .

French Patent No. 2,382,584 describes a gas turbine in the combustion chamber of which are arranged, in series, a pilot burner, powered by a fuel injector and associated with a conventional electric ignition device, as well than a catalytic combustion zone, placed downstream of the combustion chamber. In fact, in the case of the arrangement described in this prior patent, the conventional ignition device and the catalytic element do not act on the same mass of gas, and they are clearly not arranged in the same device. ignition usable for the post-combustion of a turbojet engine.

US Pat. No. 4,040,252 describes a combustion chamber comprising an axial premix section, into which the fuel is injected, the stream of hot gases then being guided to a peripheral section, of annular shape, containing catalytic elements. In this case also, the means used to ignite the fuel in the premix chamber do not act on the same mass of gas as that which passes through the catalytic elements. Nor is it an ignition device for afterburning.

French patent 2,360,042 describes a combustion device comprising, in one form embodiment, an annular catalytic element surrounding a tube traversed by air. This element is associated with a thermal burner arranged downstream. However, the function of this burner is different from that of the invention because it is to depollute the incompletely burnt gases coming from the catalyst during the heating period of the latter; moreover, the gases produced by the appliance are intended to heat the air leaving the tube and not to ignite gases for post-combustion. This device, despite a resemblance of form is therefore very far from the device of the invention.

The ignition device according to the present invention is capable of two main embodiments; these differ from each other in that the catalytic ignition element is disposed in the enclosure, in a first embodiment, downstream of the part of the ignition member such as a candle, which penetrates in said enclosure, and, in the case of the other embodiment, at the level, and preferably facing the part of the ignition member such as a candle, which penetrates into said enclosure. Relative to the action of the ignition member such as a spark plug on the gas flow which passes through the enclosure, the action of the catalytic ignition element takes place in series in the case of the first form of realization, and in parallel in the case of the second.

By way of example, these two embodiments of the invention have been described below and illustrated diagrammatically in the accompanying drawing.

• Figure 1 is an axial sectional view of the first embodiment.
• Figure 2 is an axial sectional view of the second embodiment.
• Figure 3 is a sectional view along line III-III of Figure 2.

FIG. 1 represents in axial section an ignition device according to the present invention, which can be mounted in particular in the post-combustion channel of an aviation turbojet, like the ignition device 11 illustrated in FIGS. 1 and 2 of patent 2351 258.

In FIG. 1, the reference 1 designates an envelope of generally tubular shape, open at its two ends; this tubular casing 1 has a constant diameter over most of its length, and a slightly larger diameter in its upstream part 1a, which is arranged opposite the injection rail 2 and the anvil 3, as described in patent 2351 258. In the upstream end 1a of the tubular casing 1 is engaged a grid 4, which is fixed by its collar 4a to the wall of said upstream part 1a, by suitable means, for example rivets 5. The perforations of the grid 4 are determined so as to calibrate the flow rate of the gaseous mixture which penetrates inside the tubular casing 1 in the direction of the arrows f. As described in patent 2,351,258, a tubular conduit 6, for example metallic, is arranged inside the tubular casing 1, coaxially with the latter, the upstream end 6a of the tubular conduit 6 passes through a central hole of the grid 4 which thus serves as its support. An ignition member such as an electric candle 7 is engaged by its active end 7a inside the envelope 1, through an opening 1b arranged in the middle part of its side wall. The tightness of the envelope 1 at the level of the spark plug 7 is ensured by a sleeve 8.

According to the present invention, a catalytic ignition element, the assembly of which is designated by 9, is disposed in the tubular enclosure 1, upstream from the downstream end 6b of the tubular conduit 6, and around said tubular conduit 6. In this first embodiment, the catalytic ignition element 9 is also placed, in the enclosure 1, downstream from the part 7a of the spark plug 7 which enters the enclosure 1, said catalytic element 9 being placed between two transverse grids 10a and 10b. made of or coated with a refractory material, and inside an envelope also made of refractory material; in the embodiment considered, this refractory envelope is constituted by two half-shells, 11a and 11b, inserted between the two grids, 10a and 10b. The catalytic element, itself 9, is constituted for example by wire mesh or metallic foam, in particular platinum foam. Finally, the internal wall of the enclosure 1 and the external wall of the tubular conduit 6 are also coated with a refractory material, at least in their parts included between the two grids 10a and 10b. The assembly 9-10a-10b-11a-11b is preferably engaged with gentle friction in the annular space between the tubular casing 1 and the tubular conduit 6, so that it can be easily extracted from said annular space by the open downstream end of the tubular enclosure 1, so as to facilitate the exchange of the catalytic ignition element 9 when its operation ceases to be satisfactory. Stop means (not shown) will advantageously be provided, such as for example a circlip upstream of the grid 10a and a circlip downstream of the grid 10b, which can be accommodated in grooves provided for this purpose in the tubular casing 1.

The ignition device illustrated in FIG. 1 and previously described operates as follows: the injection rail 2 projects, by its upstream nozzles, 2a, fuel which is sprayed onto the anvil 3; the fuel thus sprayed is entrained by the flow of hot gases, coming from the turbine (not shown) in the direction indicated by the arrows f, the gas mixture entering the annular enclosure 1 through the perforations of the grid 4. In at the same time, the downstream nozzle 2b of the injection manifold 2 projects fuel into the tubular conduit 6, as described in the main patent. During the turbojet start-up period, the electric spark plug 7 is supplied and it effectively produces the ignition of the gaseous mixture which is in the annular space comprised between the tubular enclosure 1 and the tubular conduit 6; the combustion gas mixture then passes through the grid 10a, the catalyst element 9, and the grid 10b, then leaves the enclosure 1 through its open downstream end, at which the gas mixture causes the ignition of the fuel leaving the downstream end of the tubular conduit 6b, as described in patent 2351 258. During this start-up phase, the catalytic action of the catalyst element 9 is practically negligible due to its low temperature; its temperature however rises gradually by heat exchange with the gas mixture in combustion which crosses it.

When the catalytic element 9 reaches a temperature of the order of 350 ° C., said catalytic element functions as an ignition element, so that the electric spark plug 7 can cease to be supplied.

In FIGS. 2 and 3, which represent a second embodiment, the same references have been used to designate bodies which are homologous to those of the embodiment of FIG. 1. This second embodiment differs from that illustrated in the FIG. 1, only in that the catalytic ignition element 9 is disposed in the enclosure 1 at, and even opposite the part 7a of the electric spark plug 7 which enters the enclosure 1. Consequently, when the electric plug 7 is supplied and the catalytic element 9 has been brought to a sufficient temperature, the two ignition elements act in parallel on the gas mixture which passes through the annular space between the enclosure 1 and the conduit 6, whereas, under the same conditions, they acted in series on the gas mixture in the case of the embodiment of FIG. 1.

Claims (5)

1. Ignition device for the reheat of an aircraft turbojet engine comprising a chamber disposed in the post-combustion duct downstream of a fuel injection manifold in such a way as to receive on the one hand, through a grid or a perforate inlet plate a carburetted mixture which is ignited in the said chamber by the said device, and on the other hand, through the upstream end of a tubular duct by which the chamber is provided a jet of fuel, the device being characterised in that the said chambre (1) is provided with ignition means (7) such as an electric sparking plug includes additionally a catalytic ignition element (9) which is placed in the said chamber upstream of the downstream end of the tubular duct (6) intended to discharge a jet of fuel, and externally of, and for example around the said tubular duct (6) so that the priming of the combustion in the said chamber (1) is ensured in an independent way by the ignition means (7) or by the element (9) once the said element is brought up to working temperature by the gases passing through the said device.

2. Device in accordance with claim 1, characterised in that the catalytic ignition element (9) is placed in the chamber (1) downstream of the portion (7a) of the ignition means (7) such as a sparking plug, which extends into the said chamber.

3. Device in accordance with claim 1, characterised in that the catalytic ignition element (9) is placed in the chamber in the zone of, and preferably facing, the portion (7a) of the ignition means (7) such as a sparking plug, which extends into the said chamber.

4. Device in accordance with any one of claims 1 to 3, characterised in that the catalytic ignition element is placed in the chamber, in elongate form, between two transverse grids (10a, 10b) made of/or coated with a refractory material, and preferably inside a casing of refractory material (11a, 11b) inserted between the two grids.

5. Device in accordance with claim 4, characterised in that the internal wall of the chambers (1) and the external wall of the tubular duct (6) are also coated with a refractory material, at least in between the two grids.

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