EP1312863B1 - Improvements to turbomachine injectors - Google Patents

Description

The present invention relates to improvements made to fuel injectors for a turbomachine engine. It relates more particularly to adjusting the fuel flow injected into a turbomachine combustion chamber.

In known manner, a turbomachine engine comprises several injectors for supplying fuel and air to the combustion chamber during startup and normal operation of the engine of the turbomachine. Mainly, there are two types of injectors: the so-called "aeromechanical" injectors designed for two fuel flow rates (primary and secondary) depending on the operating phases of the engine (ignition, from low to full power), and the so-called "aerodynamic" injectors Which have only one fuel system for all phases of operation. The present invention is more particularly the injectors belonging to this first category.

The document US-A1-4491272 discloses an aeromechanical fuel injector for a turbomachine engine comprising two fuel supply circuits: a primary circuit corresponding to the low flow rates (for example for a phase of ignition and low power operation of the engine) and a secondary circuit intervening for medium and high flow rates (for example for subsequent operation phases up to full power).

This type of injector comprises in particular a stop valve intended to open for a first predetermined fuel supply pressure and remain open beyond this pressure in order to supply the primary fuel circuit. On the other hand, a metering valve arranged to open under a second predetermined supply pressure, greater than the first predetermined pressure, and remain open in response to an increase in this pressure, provides the supply flow rate. fuel secondary circuit. This secondary flow rate is regulated by means of metering slots provided at a valve head and whose passage sections vary as a function of the applied supply pressure: the higher the pressure, the higher the pressure. the sections of passage of the slots are important.

In practice, it is found that in a combustion chamber fed with fuel by several injectors such as that described above, there is heterogeneity in flow rate in the phase corresponding to average flow rates when these injectors are subjected to the same supply pressure. This heterogeneity is mainly due to manufacturing deviations between their respective metering valves and can reach up to 10%. The manufacturing or machining tolerances of the metering valves and their metering slots mean that the average fuel flow rates can not be identical for all the injectors of a given engine. FIG. 3 clearly shows the differences in flow rates ΔD ₁ and ΔD _{2 that} may exist at two different injectors 100, 102 of the same combustion chamber with respect to a calculated theoretical flow rate 104. This results in a heterogeneity in flow rates means between injectors detrimental to the proper functioning of the engine of the turbomachine.

Object and summary of the invention

The present invention therefore aims to overcome such drawbacks by proposing a fuel injector which makes it possible to reduce the heterogeneity in flow rate between injectors. An object of the invention is also to provide an injector for simplifying the implementation and improve the performance of the control of the average fuel flow rates.

For this purpose, there is provided a fuel injector for a turbomachine engine comprising an injector body having pressurized fuel admission means, a first valve mounted downstream of said pressurized fuel admission means and arranged to opening in response to a predetermined fuel pressure defining a first threshold pressure to admit fuel into the injector body, a second valve mounted downstream of said first valve and openable in response to a second fuel threshold pressure, greater than said first threshold pressure, for dosing at least a portion of the fuel admitted into said injector body to means for using this fuel, the fuel flow rate dosed to the fuel injection means; use being a function of passage sections made at said second valve, characterized in that it further comprises a diaphragm disposed between the pressurized fuel inlet means and the first valve in order to fix at a determined value the fuel flow admitted into the injector body.

The fuel flow admitted into the injector body is in particular a function of the diaphragm. It is fixed to a determined value by choosing an opening of the diaphragm according to the technical characteristics of each injector of the same combustion chamber. More precisely, a diaphragm is chosen for each injector as a function of its flow differences with respect to a calculated average flow rate. Thus, each injector of the same combustion chamber is provided with a diaphragm which can vary from one injector to another. In this way, it eliminates any risk of flow differences between the different injectors. In addition, the replacement of the diaphragm is easy since it does not require the disassembly of the two valves.

Advantageously, the injector further comprises adjustment means for defining a third fuel threshold pressure, greater than the second threshold pressure, from which the flow of fuel dosed to the means of use is solely a function of the fuel supply pressure.

The setting means for defining a third fuel threshold pressure advantageously comprise a stop to limit the stroke of the second fuel metering valve.

Brief description of the drawings

• la figure 1 est une vue en coupe longitudinale d'un injecteur de combustible de turbomachine selon l'invention ;
• la figure 2 est une courbe illustrant un exemple de réglage de débit d'injection dans une turbomachine avec la mise en oeuvre de l'injecteur de la figure 1 ; et
• la figure 3 est un graphique montrant un exemple d'écarts de réglage de débit d'injection dans une turbomachine de l'art antérieur.

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures:

• Figure 1 is a longitudinal sectional view of a turbomachine fuel injector according to the invention;
• FIG. 2 is a curve illustrating an example of adjustment of the injection flow rate in a turbomachine with the implementation of the injector of FIG. 1; and
• FIG. 3 is a graph showing an example of injection rate adjustment deviations in a turbomachine of the prior art.

Detailed description of an embodiment

Referring to Figure 1 which shows in longitudinal section a fuel injector for turbomachine engine according to the invention.

This injector is of the aeromechanical type, that is to say that it is designed to provide two fuel flow rates: a primary flow rate during a start-up phase of the turbomachine equipped with this injector and a low power operation phase, and a secondary flow for subsequent operating phases and up to full power.

According to the invention, the fuel injector 2 comprises, in an injector body 4, a fuel admission orifice 6 intended to receive the fuel under pressure coming from a suitable pump (not represented) and which opens into the a pre-admission chamber 8a after having passed through filtering means 9 of the strainer type. A sealing valve 10 for sealing the injector at a standstill is mounted in an intake chamber 8b disposed downstream of the pre-admission chamber 8a in the direction of flow of the fuel. It is conventionally formed of a valve head 12 and a valve stem 14 and is held in position by means of a tubular central portion 16 forming a valve support. The tubular central portion 16 further rests, by a cylindrical shoulder 17, on a first end of a cylindrical peripheral portion 18 which extends downstream from the central portion over a large part of the remaining internal volume of the injector body 4 and defining an annular primary fuel chamber 20 and an annular secondary fuel chamber 22.

The annular primary fuel chamber 20 communicates with the intake chamber 8b through a plurality of lateral holes 24 and through a strainer 25 defining fixed passage sections. The annular secondary fuel chamber 22 is connected to the intake chamber 8b through longitudinal bores 26 pierced regularly in the cylindrical shoulder 17 of the valve support 16. The seat of the sealing valve 10 is formed of a rim of a cylindrical liner 28 resting on the cylindrical shoulder 17 of the tubular central portion 16 and maintained in the injector body 4 sealingly via a sealing means 30 of the seal type. A coil spring 32 is disposed between the valve support 16 and the valve head 12 to allow adjustment of a predetermined fuel supply pressure defining a first threshold pressure S1 beyond which the seal valve 10 opens. The fuel present in the pre-admission chamber 8a then enters the intake chamber 8b and flows into the annular primary fuel chamber 20 through the lateral holes 24 before being discharged to a central ejection channel primary fuel 33 defining first means for using the fuel.

A fuel metering device 34 is also mounted directly in the annular secondary fuel chamber 22 so as to measure the fuel flowing from this chamber. It conventionally comprises a metering valve 36 of tubular shape provided at a first end of an opening 38 opening into a longitudinal bore 40 of the secondary fuel inlet, and at a second end forming a substantially circular shoulder forming a head valve 42 and supporting a second end of the cylindrical peripheral portion 18. The metering valve 36 also has side outlets 44 for the flow of secondary fuel. The valve head 42 comprises on its periphery fuel metering slots 46 opening into the longitudinal bore 40 and defining variable passage sections to second fuel utilization means. These slots 46 are shaped very precisely to measure the amount of fuel flowing from the annular secondary fuel chamber 22 to a receiving chamber 48 formed in the injector body 4 and opening towards a annular secondary fuel ejection channel 50 surrounding the central primary fuel ejection channel 33.

The metering valve 36 can slide in a cylindrical sleeve 52, one end of which has a circular recess 54 forming a valve seat. This sleeve is held on the cylindrical peripheral portion 18 sealingly via a sealing means 56 of the seal type. The bushing 52 also forms a bearing surface for one end of a helical spring 58, the opposite end of which is mounted in an annular retaining element 60 threaded onto the first end of the metering valve 36 and fixed thereto. by means of a ring 62 C. An annular shim 64 is disposed between the ring 62 at C and the annular retaining element 60 so as to adjust the load of the spring 58 and define a second threshold pressure S2, greater than the first threshold pressure S1, for which the metering valve 36 opens. This spring load is selected to allow the metering valve to open for the second threshold pressure S2 and remain open in response to an increase in supply pressure, the flow rate then being a function of the sections. passage of the dosing slots 46.

The injector 2 is further provided with a diaphragm 66 disposed between the inlet orifice 6 and the sealing valve 10. More specifically, the diaphragm 66 is mounted in the pre-admission chamber 8a upstream, in the flow direction of the fuel, the cylindrical liner 28 resting on the cylindrical peripheral portion 18. This diaphragm makes it possible to set the fuel flow rate admitted in the intake chamber 8b to a predetermined value. The opening of the diaphragm is chosen according to the characteristics of the injector (manufacture and machining of the metering valve and its slots, spring tension, effects of friction between the valve and the sleeve in which it slides ... ) and according to its flow differences with respect to a calculated average flow. This choice is therefore made so that the average flow rate curve as a function of the fuel supply pressure does not come out of a pre-established tolerance envelope. This tolerance envelope is pre-established according to a theoretical average calculated flow curve. For example, it can be defined by a maximum deviation of flow of the order of ± 5% from this theoretical average curve.

According to an advantageous characteristic of the invention, the fuel injector further comprises adjustment means for defining a third fuel threshold pressure S3, greater than the second threshold pressure S2, from which the fuel flow rate is measured. to the second means of use is solely a function of the fuel supply pressure. These adjustment means are in the form of a stop 68, for example mounted at the sleeve 52 so as to cooperate with the annular retaining element 60 to limit the stroke of the metering valve 36. This stop 68 is set for a predetermined fuel pressure corresponding to a flow rate close to full opening. It is also possible to consider mounting a ring (not shown) on the first end of the metering valve 36, this ring also to limit the stroke of the metering valve.

FIG. 2 clearly shows the effect of the diaphragm 66 on the differences in average flow rates that may exist at an injector 200 of a combustion chamber with respect to a calculated flow curve 202. In this figure, two curves 204 and 204 'were also represented. They form a tolerance envelope beyond which the differences in flow rates with respect to the theoretical average curve 202 are considered too important. For this tolerance envelope, a maximum flow difference of ± 5% was chosen. Thus, the presence of the diaphragm 66 makes it possible to considerably reduce the heterogeneity at the average flow rates between several injectors of the same combustion chamber. Furthermore, from the third threshold pressure S3, the fuel flow no longer depends on the machining characteristics of the spring and the slots, as well as on the friction of the injector valve, but on the pressure of the pressure. fuel supply and the passage section of the valve which is in abutment. From this third threshold pressure S3, the metering valve thus behaves like a fixed diaphragm.

Claims (5)

1. A fuel injector (2) for a turbomachine engine, the injector comprising an injector body (4) having pressurised fuel admission means (6), a first valve (10) mounted downstream from said pressurised fuel admission means and arranged to open in response to a predetermined fuel pressure defining a first threshold pressure (S1) so as to admit fuel into the injector body, a second valve (36) mounted downstream from said first valve and capable of opening in response to a second fuel threshold pressure (52) higher than said first threshold pressure so as to meter at least a fraction of the fuel admitted into said injector body for utilization means (48) for using said fuel, the metered fuel flow rate to the utilization means being a function of flow sections (46) formed through said second valve, the injector being characterised in that it further comprises a diaphragm (66) placed between the pressurised fuel admission means and the first valve so as to set the rate at which fuel is admitted into the injector body at a determined value.
2. An injector according to claim 1, characterised in that it further comprises adjustment means (68) for defining a third fuel threshold pressure (53) higher than said second threshold pressure, from which the metered flow of fuel to said utilization means takes place at a rate which is a function solely of the fuel feed pressure.
3. An injector according to claim 2, characterised in that said adjustment means comprise an abutment (68) for limiting the stroke of said second fuel metering valve.
4. A fuel injector (2) according to claim 1, characterised in that:

   - the first valve (10) delivers the fuel to first utilization means, the rate at which fuel is delivered being a function of flow sections (24) formed through said first valve;

   - the second valve (36) delivers the fuel to second utilization means (48) for said fuel; and

   - adjustment means (68) define a third fuel threshold pressure (S3) higher than said second threshold pressure, from which the metered flow of fuel to said second utilization means takes place at a rate which is a function solely of the feed pressure of the fuel.
5. An injector according to claim 4, characterised in that said adjustment means include an abutment (68) for limiting the stroke of said second fuel metering valve.

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