EP0718559B1 - Fuel distribution system for the injection heads of a double annular combustor - Google Patents

Description

The present invention relates to the fuel supply of a two-head combustion chamber of a turbojet engine.

Aviation turbojets are subject to variable regimes. When they also equip military aircraft, they must emit the most low radiation possible, in the visible and infrared, in order to prevent the tracking of these planes, at all speeds.

It is therefore necessary to minimize the smoke emissions due carbon particles and red fumes produced by nitrogen oxides. These soot particles and red fumes are mainly produced at high diets.

Dual-head combustion chambers solve the pollution problem at high revs, because the so-called take-off head is optimized for full gas mode, and it supplies the combustion chamber with a sufficiently lean air-fuel mixture to reduce the production of smoke and the formation of large quantities of nitrogen oxide.

At low speeds, only the pilot head supplies the primary zone of the combustion chamber with a rich air fuel mixture to ensure the flame stability. This richness of the mixture can lead to a production significant smoke at low speeds.

On the other hand, the fact that the take-off head of the head are offset radially with respect to the axis of the turbojet engine, the temperature profile at the inlet of the high pressure turbine is not homogeneous at low speeds.

Finally, the fact that the take-off head is supplied with fuel only from 25% of the nominal thrust on the ground, the richness in the primary zone of the combustion chamber undergoes a noticeable fall in the vicinity of thrust.

It is already known to equip traditional combustion chambers with a single head with double injectors comprising two coaxial modules supplying separate areas of the combustion chamber by means of separate fuel systems and separate air systems. This state of the art is illustrated in particular by GB-A-2 214 630 which describes a double injector having two separate fuel supplies: a main supply associated with a first axial swirler to power a central module, and a secondary supply associated with a second axial swirler to supply an annular zone 106 by means of channels formed in the blades of the first swirler. The central module operates from low revs and the ring module works only at high speeds.

FR-A-2 421 342 also describes a two-module injector in which the central module is designed to operate only at high speeds.

GB-A-2 214 630 and FR-A-2 421 342 do not mention that these two module injectors can equip a take-off head with a chamber with two heads.

EP-A-527,629 describes a fuel supply system a two-headed annular combustion chamber, including a three-way valve controlling a circuit pilot head supply and first and second separate main supply circuits supplying all two the main head. The pilot head alone is powered at low idle speeds then a first and a second main circuit are successively opened during the revving.

The aim of the present invention is to propose a method supplying fuel to a two-headed combustion chamber which optimizes the operation of this room for all regimes.

on règle la richesse dans la zone primaire de la chambre de combustion aux bas régimes à une valeur au moins égale à 80 % du taux stoechiométrique et

on règle le débit de carburant fourni par le deuxième circuit de carburant à une valeur comprise entre 40 % et 50 % du débit total Wf de carburant fourni par ledit deuxième circuit de carburant et la tête pilote.

The invention therefore relates to a method for supplying fuel to a combustion chamber with two heads of a turbojet engine, said chamber comprising a pilot head equipped with a plurality of idle injectors and a take-off head radially distant from the pilot head. and equipped with a plurality of take-off injectors comprising a first fuel circuit, method according to which said combustion chamber is supplied with fuel by means of the idle injectors from low revs and said combustion chamber is further supplied in fuel at high revs via said first fuel circuits. In addition, said take-off head is equipped with take-off injectors comprising a second fuel circuit separate from the first fuel circuit. This process is characterized by the fact that said combustion chamber is supplied with fuel via said second fuel circuits from the lowest speeds,

the richness in the primary zone of the combustion chamber at low speeds is adjusted to a value at least equal to 80% of the stoichiometric rate and

the flow of fuel supplied by the second fuel circuit is adjusted to a value between 40% and 50% of the total flow Wf of fuel supplied by said second fuel circuit and the pilot head.

Advantageously, the first fuel circuit is supplied from 20% of the nominal thrust on the ground.

la figure 1 est une coupe axiale d'une chambre de combustion traditionnelle à deux têtes d'un turboréacteur ;

la figure 2 montre les courbes représentatives de la richesse dans les zones primaires d'une chambre de combustion traditionnelle à deux têtes en fonction de la poussée nominale au sol F00 ;

la figure 3 montre les courbes représentatives de la richesse dans les zone primaires d'une chambre de combustion à deux têtes en fonction de la poussée nominale au sol F00, cette chambre étant alimentée en carburant selon le procédé de l'invention ;

la figure 4 représente un injecteur de carburant à deux modules équipant la tête de décollage d'une chambre de combustion à deux têtes selon la présente invention ;

la figure 5 est une coupe selon la ligne VV de la figure 4 ;

la figure 6 est une coupe d'une chambre de combustion à deux têtes équipée de l'injecteur de carburant à deux modules de la figure 4.

Other advantages and characteristics of the invention will emerge on reading the following description given by way of example and with reference to the appended drawings in which:

Figure 1 is an axial section of a traditional combustion chamber with two heads of a turbojet;

FIG. 2 shows the curves representative of the richness in the primary zones of a traditional combustion chamber with two heads as a function of the nominal thrust on the ground F00;

FIG. 3 shows the curves representative of the richness in the primary zones of a combustion chamber with two heads as a function of the nominal thrust on the ground F00, this chamber being supplied with fuel according to the method of the invention;

FIG. 4 represents a two-module fuel injector fitted to the take-off head of a two-head combustion chamber according to the present invention;

Figure 5 is a section along the line VV of Figure 4;

FIG. 6 is a section through a two-head combustion chamber equipped with the two-module fuel injector of FIG. 4.

In Figure 1 there is shown by reference 10, a traditional two-head combustion, supplied with air by a diffuser 11 arranged downstream of a compressor not shown. This combustion chamber 10, of annular shape and axis 12, is delimited by an inner wall 13, a outer wall 14 and a chamber bottom 15 connecting the upstream ends of the inner wall 13 and outer wall 14. A passage 16 is provided between the downstream ends of walls 13 and 14 for the flow of hot gases to a turbine not shown. The chamber 10 is arranged between an inner casing 17 and an outer casing 18. These casings 17 and 18 are connected to the diffuser 11, and define with walls 13 and 14 annular passages 19 and 20 for the flow of primary air P which feeds the chamber 10 through orifices 21 formed in the walls 13 and 14, and for the flow of an air of cooling of walls 13 and 14.

The chamber bottom 15 is equipped with a plurality of injectors for takeoff 22 and a plurality of idle injectors 23 radially distant from the take-off injectors 22. A separating plate 24, directed towards the passage 16, is mounted on the chamber bottom 15 between the take-off injectors 22 and the idle injectors 23. This plate 24 separates the upstream zone from the chamber 10 in a first primary combustion zone supplied by take-off injectors 22, called "take-off head" 25, and in a second primary combustion zone supplied by the idle injectors 23 and called "pilot head" 26. The injectors 22 and 23 are supplied with fuel by separate circuits 27 and 28 and are associated respectively with groups of blades eddies 29 and 30 supplied with air by the diffuser 11, this air being intended for the vaporization of fuel. In the combustion chambers current with two heads, the idle injectors 23 operate from the bottom regimes and the take-off injectors 22 are only supplied above 25% nominal thrust on the ground F00.

The curve C1 represented in FIG. 2 represents the richness R in the primary zone in the vicinity of the pilot head 26, as a function of the thrust nominal F00 on the ground. Curve C2 represents the richness R in the area primary in the vicinity of the take-off head 25, and the curve C3 the richness minimum which corresponds to the lower operating limit.

It can be seen that the curve C1 presents a marked drop at 25 % of nominal thrust F00, value at which the take-off head is fueled. Below 25% of the nominal thrust F 00, the wealth in the primary zone is greater than 100% of the stoichiometric rate fuel / air, which ensures good flame stability, but results in however a production of smoke. Above 25% of the nominal thrust F00, the wealth in the primary zone is greater than 0.7 and less than 1.

According to the invention, the take-off head 25 of the combustion chamber 10 described above is equipped with take-off injectors 40 provided with two separate fuel systems. Each take-off injector 40 includes a injector body 41 in which a first fuel circuit 42 is provided intended to supply the take-off head 25 at high revs and a second fuel system 43 intended to supply the take-off head from below diets. An axial spin 44 is disposed around the downstream end of the body injector 41. The axial spin 44 is mounted inside a sleeve 45 which extends upstream by a radial flange 46 and downstream by a frustoconical wall 47 flared outwards. A radial spin 48 is mounted downstream of the flange radial 46 and upstream of a bowl 49 fixed on the chamber bottom 15. The second fuel circuit 43 passes through each of the fins 50 of the axial spin 44 and opens into the annular space 51 delimited by the sleeve 45 and the bowl 49 by orifices 52 formed in the sleeve 45.

The sleeve 45 and the frusto-conical wall 47 share the take-off head 25 in two modules. The axial module is supplied with fuel by the first fuel circuit 42 and in air by the axial spin 44. The second module is supplied with fuel by the second fuel circuit 43 and with air by the radial spin 48. The passages of tendrils 44 and 48 can be dimensioned to pass more or less air. The module receiving the most air can be either the axial module or the second module.

The idle injectors 23 and the second fuel circuit 43 are fueled together from the low regimes so that the richness of the primary zone is at least equal to 80% of the stoichiometric rate, so ensure flame stability and avoid fumes. The distribution of fuel, at low revs, between the second fuel circuit 43 and the idle injectors 23 of the pilot head is such that the second circuit of fuel 43 receives between 40% and 50% of the total flow. From 20% of the nominal thrust on the ground, the two fuel circuits 42 and 43 of the injectors takeoff 40 are fed simultaneously until full gas.

Figure 3 shows the representative curves C'1 and C'2 of the richness primary zones of a two-head combustion chamber supplied with fuel according to the process described above. As we can see, the riches of the pilot head and take-off head are less than 100% of the rate stoichiometric at low speed. This wealth is close to 1 in the diet corresponding to approximately 20% of the nominal thrust on the ground F00, then decreases around 0.7 to 0.8 around 30% of the nominal ground thrust for then increase regularly until full gas.

The fact of feeding the two heads from low revs allows a better homogenization of the fuel sheet. At low speeds, the temperature profile obtained is more favorable to the service life of the turbine high pressure.

Claims (2)

1. Method for supplying fuel to a two-head combustion chamber (10) of a turbojet engine, the said chamber comprising a pilot head (26) fitted with a number of idling injectors (23) and a take-off head (25) which is radially distant from the pilot head and fitted with a number of take-off injectors (22) comprising a first fuel circuit (42), according to which method the said combustion chamber (10) is supplied with fuel by means of the idling injectors (23) right from the low speeds, and the said combustion chamber (10) is also supplied with fuel at high speeds by means of the said first fuel circuits (42), and the said take-off head (25) is equipped with take-off injectors (40) comprising a second fuel circuit (43) separate from the first fuel circuit (42), characterized in that the said combustion chamber (10) is supplied with fuel by means of the said second fuel circuits (43) right from the lowest speeds, in that the richness in the primary zone of the combustion chamber (10) at low speeds is set to a value at least equal to 80% of the stoichiometric ratio, and in that the flow of fuel provided by the second fuel circuit (43) is set to a value of between 40% and 50% of the total flow Wf of fuel provided by the said second fuel circuit (43) and the pilot head (26).
2. Method according to Claim 1, characterized in that the first fuel circuit (42) is fed from 20% of the nominal thrust F00 on the ground.

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