US20150369489A1

US20150369489A1 - Turbo machine combustion assembly comprising an improved fuel supply circuit

Info

Publication number: US20150369489A1
Application number: US14/764,152
Authority: US
Inventors: Jean-Pierre Badet; Hubert Pascal Verdier
Original assignee: Turbomeca SA
Current assignee: Safran Helicopter Engines SAS
Priority date: 2013-01-29
Filing date: 2014-01-23
Publication date: 2015-12-24
Also published as: ES2621948T3; JP6326429B2; KR20150121011A; JP2016505802A; CN105102789B; FR3001497B1; RU2646950C2; FR3001497A1; RU2015136584A; CN105102789A; CA2899508C; EP2951421B1; PL2951421T3; EP2951421A1; CA2899508A1; WO2014118457A1

Abstract

Turbo machine combustion assembly (1) comprising a combustion chamber (10), at least one starting injector (17), a plurality of main injectors (18) distributed at constant angular intervals around the circumference of the combustion chamber, each starting injector being positioned between two consecutive main injectors, equal distances therefrom, and a fuel supply circuit (40) supplying fuel to the injectors, in which assembly the combustion chamber is delimited by two axisymmetric walls—an external wall (14) and an internal wall (12)—which are connected by an annular chamber end wall (16), the fuel supply circuit being designed to supply at least one starting injector continuously, each continuously-supplied starting injector being oriented toward the chamber end wall and dimensioned to spread a spray (F) of fuel between 120° and 180° wide, and the flow rate of fuel injected by the main injectors (18′) between which the starting injectors are positioned being reduced by comparison with the flow rate injected by the other main injectors (18).

Description

FIELD OF THE INVENTION

The invention relates to the field of turbomachines, and more specifically the field of turbomachine combustion assemblies, comprising a combustion chamber and a plurality of injectors dedicated to starting and supplying fuel to the combustion chamber.

PRIOR ART

With reference to FIG. 1, turbomachines 1 conventionally include a combustion chamber 10 and a distributor 20 housed in a casing 30, the combustion chamber being delimited by axisymmetric outer 14 and inner 12 walls extending one inside the other and which are connected by an annular chamber end wall 16.
The casing also has an inner wall 32 and an outer wall 31 to which the inner 12 and outer 14 walls of the combustion chamber are respectively fastened.
A mixture of air and fuel is injected into the combustion chamber by a plurality of injectors, this mixture being combusted to generate the energy needed to propel the turbomachine.
Several types of injectors are positioned in a combustion chamber, including starting injectors 17, which form part of the ignition system comprising at least one spark plug. This ignition system makes it possible to set the airfuel mixture alight, initiate combustion and make it spread to the main injectors. The starting injectors generally enter the combustion chamber through an opening formed in the outer wall of the combustion chamber.
To characterize the injectors a quantity known as Flow Number (FN) is used, equal to the flow rate of the injector in L/h divided by the square root of the pressure difference in bars of the injected mixture between its pressure at the input and the output of the injector.
The Flow Number of the starting injectors is less than the Flow Number of the main injectors for a given turbomachine. The Flow Number of a main injector of a machine is typically of 3 to 10 times the Flow Number of a starting injector of the same machine.
The Flow Number of a starting injector is typically between 1 and 4, preferably between 1.5 and 2, while that of a main injector is typically greater than 4, for example between 5 and 15, and advantageously between 7 and 12.
This difference in Flow Number is the result of a difference in the functionality of the injectors: the initiation of the combustion in the chamber by the starting injectors requires a small quantity of fuel, while the continuation of combustion in the chamber by the main injectors in order to give the turbomachine its power requires a much higher flow rate. Of course the FN values of the main injectors or the starting injectors depend on the power and the thermodynamic cycle of the engine.
In socalled “rod” chambers, each main injector opens into a pre-evaporation rod 19, which includes a duct equipped with two exhaust openings opening into the combustion chamber.
During operation, the starting injectors initiate combustion by setting fire to the fuel using a spark plug, and thus heat the preevaporation rods.
The main injectors are then fueled to continue the combustion in the chamber by spraying fuel into the rod. During this step, the supply of fuel to the starting injectors stops and they are drained to avoid coking, which could cause them to clog up.
FIGS. 2 a and 2 b represent the fuel supply circuit enabling the implementation of this combustion cycle, respectively in the phase of ignition of the chamber, when the starting injectors are supplied with fuel, and in the phase of drainage of said injectors.
The fuel supply circuit 40 comprises a supply duct for the starting injectors 43, a fuel supply duct 44 for the main injectors 18, and a fuel distribution duct 42, in fluid communication with the fuel supply ducts and suitable for supplying them with fuel.
This circuit further has a circuit 46 for draining the starting injectors into the atmosphere, actuated by a starting electrovalve 47 which, when it is actuated as in FIG. 2 b, shuts off fluid communication between the distribution duct 42 and the supply duct 43 for the starting injectors.
The fuel supply circuit 40 also comprises a level valve 45, suitable for shutting off fluid communication between the fuel supply duct of the main injectors 44 and the rest of the circuit when the pressure in the fuel duct, downstream of its connection with the fuel supply duct of the starting injectors, is less than a predetermined threshold. This valve 45 thus opens upon an increase in the pressure of the distribution circuit following the increase in the flow rate of the fuel injected into the combustion chamber after the ignition has taken place to increase motor speed.
Finally, the combustion chamber includes an antiextinction function in the event of sudden reduction of the speed, to avoid having to reignite the combustion chamber when the turbomachine is at its poststarting speed.
This anti-extinction function is ensured by using a favored main injector 180, which is the injector predominantly powered if the fuel pressure in the supply circuit is too low. To achieve this, a distribution valve 48 is provided between the supply circuit 49 of the favored injector and the supply duct 44 of the other injectors to shut off fluid communication with this duct in the event of a decrease in the flow rate.
The supply circuit is therefore a complex assembly with a high production cost due to the large number of parts it includes.

OVERVIEW OF THE INVENTION

The aim of the invention is to solve the abovementioned problem, by proposing a turbomachine combustion assembly comprising a simplified fuel supply circuit.
Regarding this, the invention proposes a turbomachine combustion assembly, comprising:

- a combustion chamber,
- at least one starting injector, suitable for initiating combustion in the chamber,
- a plurality of main injectors distributed at a constant annular interval around the circumference of the combustion chamber, designed to supply fuel to the combustion chamber when combustion has been initiated, and
- a fuel supply circuit for the injectors,
  wherein the combustion chamber is delimited by two axisymmetric outer and inner walls extending one inside the other and which are connected by an annular chamber end wall, the combustion assembly being characterized in that the fuel supply circuit is designed to supply fuel to at least one starting injector continuously, so that said injector is supplied with fuel both throughout the initiation of the combustion and when fuel is supplied to the chamber when the combustion has been initiated,
  in that each continuously-supplied starting injector is oriented toward the chamber end wall and is dimensioned to spread a spray of fuel having an angular aperture in a first direction between 120° and 180°, and
  in that the flow of fuel injected by the main injectors between which the starting injectors are positioned is reduced by comparison with the flow injected by the other main injectors,
  and in that each starting injector is positioned between two consecutive main injectors, at equal distance therefrom.

Advantageously, but optionally, the combustion assembly according to the invention can further have at least one of the following features:

- the supply circuit is designed to supply all the starting injectors continuously.
- The ratio of the flow rate divided by the square root of the pressure difference of the fuel mixture between its pressure at the input and at the output of the injector, for the main injectors between which each starting injector is positioned, is less than said ratio for the other main injectors.
- Each continuously-supplied starting injector is dimensioned to spread a spray having an angular aperture between 15 and 35° in a second dimension orthogonal to the first direction.
- The combustion chamber is of the chamber with aerodynamic or aeromechanical injectors type.
- The chamber is of the pre-evaporation rod type, each pre-evaporation rod being shaped so that the fuel injected by the main injectors is directed toward the chamber end wall.
- The combustion chamber comprises:
  - on its inner wall, a plurality of air intake openings, and
  - on its outer wall, a plurality of socalled dilution openings,
    wherein the number and diameter of said openings are designed to distribute the air intake in the combustion chamber and to preserve the homogeneity of the temperature field in said chamber.
- The combustion chamber is a reverseflow chamber.
- The fuel supply circuit comprises:
  - a supply duct for the starting injectors,
  - a supply duct for the main injectors, and
  - a fuel distribution duct, in fluid communication with the supply ducts and designed to supply fuel to said ducts,
    the supply circuit further comprising a distribution system designed to shut off fluid communication between the fuel distribution duct and the supply duct of the main injector when the fuel pressure in the distribution duct is less than a predetermined threshold.
- The distribution system is further designed to distribute the fuel flow between main injectors having a reduced flow rate and the other main injectors.

Owing to the continuous supply of fuel to the starting injectors, the fuel supply circuit no longer needs to contain a drainage circuit.
In addition, the fact of continuously supplying fuel to the starting injectors makes it possible to keep the chamber ignited even in the event of a rapid decrease in the flow of fuel to the main injectors—for example in the event of a reduction of the turbomachine speed. The favored injector function, and the adaptation of the fuel supply circuit provided for this purpose are therefore removed.
Furthermore, the fact of adapting the spray of fuel spread by the starting injectors and reducing the flow rate of the main injectors adjacent to the starting injectors by comparison with that of the other main injectors makes it possible to preserve the homogeneity of the fuel in the combustion chamber, and therefore maintain the lifetime of the parts downstream of the chamber.

DESCRIPTION OF THE FIGURES

Other features, aims and advantages of the invention will become apparent from the following description, which is purely illustrative and nonlimiting, and must be read with reference to the appended drawings wherein:

FIG. 1, already described, represents an axial section view of a turbomachine of the prior art.

FIGS. 2 a and 2 b, also already described, represent a fuel supply circuit for the injectors of a turbomachine of the prior art, respectively in a phase of supplying the starting injectors, and during a phase of draining said injectors.

FIG. 3 a represents a partial section view of a turbomachine comprising a combustion chamber of the preevaporation rod type,

FIG. 3 b represents a partial section view of a turbomachine comprising a combustion chamber with aerodynamic or aeromechanical injectors.

FIG. 4 represents a fuel supply circuit for the injectors of a turbomachine.

FIG. 5 represents a crosssection view of a turbomachine,

FIG. 6 represents a partial perspective view of a combustion chamber of a turbomachine,

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

With reference to FIGS. 3 a and 3 b, a turbomachine combustion assembly 1 is represented, comprising a combustion chamber 10 and a casing 30 (represented in FIG. 3 b), the combustion chamber 10 being delimited by two axisymmetric outer 14 and inner 12 walls extending one inside the other and which are connected by an annular chamber end wall 16.
The casing also comprises an outer wall 31 (represented in FIG. 3 b) and an inner wall (not represented in FIG. 3 b) to which the inner 12 and outer 14 walls of the combustion chamber are respectively fastened.
The turbomachine 1 further comprises a plurality of fuel injectors, comprising at least one starting injector 17, preferably at least two starting injectors 17, and a plurality of main injectors 18, preferably at least three main injectors 18, for example eight main injectors.
The ignition system comprises at least one starting injector 17 and two spark plugs (not represented) suitable for setting the spray of fuel delivered by the injector 17 alight and thus initiating combustion in the chamber.
According to a first embodiment of the turbomachine, represented in FIG. 3 a, the combustion chamber is of the preevaporation rod type, wherein each main injector 18 opens into a preevaporation rod 19, itself opening inside the chamber. Each pre-evaporation rod comprises a duct opening via two openings into the combustion chamber.
The pre-evaporation rods 19 enter the combustion chamber through an opening formed in the outer wall 14 or in the chamber end wall 16 of the combustion chamber 10, and having a Tshaped section, the ends of which are curved toward the chamber end wall.
According to a second embodiment of the turbomachine, represented in FIG. 3 b, the main injectors 18 are of aerodynamic or aeromechanical type, and directly enter the chamber 10 through an opening formed in the chamber end wall 16.
Advantageously, the combustion chamber is of reverse flow type.
The turbomachine 1 also comprises a fuel supply circuit 40 for the injectors, said circuit being represented in FIG. 4.
The fuel supply circuit comprises a fuel injection inlet 41, by which the fuel enters the circuit along a fuel distribution duct 42.
The fuel distribution duct is connected to the starting injectors by a supply duct 43 for the starting injectors, and to the main injectors by a supply duct 44 for the main injectors.
The fuel supply circuit is designed to supply fuel to the starting injectors continuously, so that said injectors are supplied with fuel both during a step of initiating the combustion in which the fuel is set alight by the spark plug, and during the later step of supplying fuel to the chamber, when the combustion has already been initiated.
To proceed with the continuous supply of fuel to the starting injectors, the circuit comprises a distribution system 45 designed to shut off fluid communication between the fuel distribution duct and the supply duct for the main injectors, for example when the pressure of the fuel in the distribution duct is less than a predetermined threshold.
The fuel is thus directed in a way that favors the starting injectors, and it is only upon an increase in fuel pressure—for example following an increase in the speed of the turbomachine—that the main injectors are supplied.
Because the starting injectors are continuously supplied, it is not necessary to drain them. The drainage circuit is therefore removed and the fuel supply circuit is simplified.
Furthermore, the favored injector function is also removed due to the fact that the starting injectors perform this function by being permanently supplied with fuel: in the event of a drop in the speed of the turbomachine, the starting injectors remain supplied with fuel and take over the anti-extinction function by continuing combustion inside the chamber.
Due to this, the distribution valve of the injectors, which makes it possible to favor one main injector, is removed, and the fuel supply circuit is further simplified and made less expensive to manufacture.
The structure of the combustion chamber and the position of the injectors must be suitable for preserving a good homogeneity of the temperature fields inside the chamber and at the chamber output.
To do this, returning to FIG. 3 a, if the combustion chamber is of the pre-evaporation rod type, the starting injectors 17 and the outlet openings of the pre-evaporation rods 19 are oriented toward the chamber end wall 16.
Alternatively, in the case of a combustion chamber with aerodynamic or aeromechanical injectors, as illustrated in FIG. 3 b, the starting injectors 17 are oriented toward the chamber end wall.
In this way, the fuel is directly injected into the moving stream of combusting fuel, known as “recirculation”.
This increases the time that the fuel outputted by the starting injector 17 can spend in the primary area of the combustion chamber, i.e. the area wherein evaporation and combustion take place. The combustion of the fuel in the primary area is thus almost total, which allows the fuel injected by the starting injectors to behave in a similar way to the fuel injected by the preevaporation rods, so that the continuous use of said injectors has no negative effect on the overall combustion efficiency or the pollutant emissions.
In addition, starting injectors of “Flat Spray” type are used. i.e. of the type in which the crosssection of the spray F (see FIG. 5) has a large angular aperture in a first direction, between 120° and 180°, and a reduced angular aperture in a second direction, orthogonal to the first, between 15 and 35°.
The spray of the starting injectors is oriented against the chamber end wall so that the second direction, corresponding to the reduced angular aperture, is radial about the axis of the turbomachine, as illustrated in FIG. 5.
The use of Flat Spray starting injectors makes it possible to spread the regular contribution of fuel over a wider angular sector and thus to obtain a homogenous temperature field in the primary area of the combustion chamber.
In addition, with reference to FIG. 5, the main injectors 18 are regularly distributed around the circumference of the combustion chamber, i.e. with a constant angular interval between two consecutive main injectors.
The starting injectors are positioned between two consecutive main injectors and at equal distance therefrom, so that the openings of the pre-evaporation rods 19 into which the main injectors open are positioned facing the ends of the spray of the starting injectors.
In order to avoid a local over-richness of fuel in the combustion area in the vicinity of the starting injectors, i.e. a surplus of local flow generated by the constantly supplied starting injectors, the main injectors 18′ between which the starting injectors are positioned have a flow rate that is reduced by comparison with the flow rate of the other main injectors 18.
This reduction in flow rate can be obtained by reducing the Flow Number of the injectors 18′ by comparison with that of the injectors 18. Specifically, this has the advantage of supplying the main injectors 18 and 18′ with the same injection pressure, which makes it possible to simplify the fuel circuit upstream of the injectors.
By way of non-limiting example, the set of main injectors has a Flow Number greater than 4, for example between 5 and 15, advantageously between 7 and 12, but advantageously, the reduced Flow Number of the injectors 18′ is between 6 and 8, preferably equal to 7, and the Flow Number of the other main injectors is greater than or equal to 9. The Flow Number of the starting injectors, meanwhile, is between 1 and 4, preferably between 1.5 and 2.
Of course, the Flow Number of the injectors depends on variable parameters such as the size of the turbomachine, the number of injectors, or else the maximum fuel flow rate. Those skilled in the art will be able to adjust the value of the Flow Number of the various injectors used according to the turbomachine on which these injectors have been fitted.
Finally, for high-power speeds, the Flow Number values must be adjusted to minimize the difference in fuel flow rate between a chamber sector corresponding to a preevaporation rod and a sector corresponding to a preevaporation rod and a starting injector.
For example, if the turbomachine comprises eight main injectors, four of them can have a reduced Flow Number.
Returning to FIG. 5, if the flow rate of the injectors 18′ is reduced by comparison with that of the other main injectors 18, without the Flow Number being reduced, the distribution system 45 is also designed to distribute the fuel flow between the various types of injectors (i.e. distribute a lower flow to the injectors 18′). In this respect it can further comprise a supply duct 44′ for the injectors 18′, advantageously independent of the supply duct 44 for the injectors 18 to allow the fuel supplied to said injectors 18′ to be at a different pressure from that supplied to the injectors 18.
With reference to FIG. 6, a combustion chamber is represented in partial perspective view. The chamber includes a primary area, extending from the chamber end wall to an axial position corresponding to the axial position of the air intake openings 13 positioned on the inner wall 12 of the combustion chamber 10 known as “primary holes”, the axial position being measured parallel to the axis of the turbomachine. This axial position is for example positioned at about 40 mm from the chamber end wall.
The air intake openings 15 are distributed around the circumference of the combustion chamber so that, for each pre-evaporation rod 19, two air intake openings are facing one opening of the rod, and one air intake opening is facing the other opening of the rod.
A socalled dilution area extends from the primary area to an axial position corresponding to the axial position of dilution openings 15 positioned on the outer wall 14 of the chamber, this axial position being at approximately 70 mm from the chamber end 16.
The number and diameter of the dilution openings and/or that of the intake openings can be adapted in order to angularly adapt the rate of air intake into the chamber. This makes it possible to control the temperature field in the combustion chamber, for example to remove any hot spots generated by the instantaneous increase in fuel richness due to the continuous supply of fuel to the starting injectors. This adaptation makes it possible to preserve the lifetime of the parts of the turbomachine, particularly downstream of the combustion chamber.
For example, the dilution openings and intake openings can have a diameter between 4 and 7 mm, preferably between 5 and 6 mm. This makes it possible to remove any hot spots in the combustion chamber, which preserves the lifetime of the turbomachine parts. Of course, the number and size of the primary openings and the dilution openings depend on variable parameters such as the size of the turbomachine, the number of injectors or else the flow rate of air into the engine. Those skilled in the art will be able to adjust the number and size of the openings according to the turbomachine on which the combustion chamber has been fitted.
Thus, a turbomachine is proposed, the fuel supply circuit of which is simplified due to the continuous supply to the starting injectors, without impairing the lifetime of the parts of the turbomachine.

Claims

1. A turbomachine combustion assembly, comprising:

a combustion chamber,

at least one starting injector, suitable for initiating combustion in the chamber,

a plurality of main injectors distributed at a constant annular interval around the circumference of the combustion chamber, designed to supply fuel to the combustion chamber when combustion has been initiated, and

a fuel supply circuit for the injectors,

wherein the combustion chamber is delimited by two axisymmetric outer and inner walls extending one inside the other and which are connected by an annular chamber end wall, the combustion assembly being characterized in that the fuel supply circuit is designed to supply fuel to at least one starting injector continuously, so that said injector is supplied with fuel both throughout the initiation of the combustion and when fuel is supplied to the chamber when the combustion has been initiated,

in that each continuously-supplied starting injector is oriented toward the chamber end wall and is dimensioned to spread a spray (F) of fuel having an angular aperture in a first direction between 120° and 180°, and

in that the flow of fuel injected by the main injectors between which the starting injectors are positioned is reduced by comparison with the flow injected by the other main injectors,

and in that each starting injector is positioned between two consecutive main injectors at equal distance therefrom.

2. The turbomachine combustion assembly according to claim 1, wherein the supply circuit is designed to supply all the starting injectors continuously.

3. The turbomachine combustion assembly according claim 1, wherein the ratio of the flow rate divided by the square root of the pressure difference of the fuel mixture between its pressure at the input and at the output of the injector for the main injectors between which each starting injector is positioned is less than said ratio for the other main injectors.

4. The turbomachine combustion assembly according to claim 1, wherein each continuously-supplied starting injector is dimensioned to spread a spray (F) having an angular aperture between 15 and 35° in a second dimension orthogonal to the first direction.

5. The combustion assembly according to claim 1, wherein the combustion chamber is of the type having aerodynamic or aeromechanical injectors.

6. The combustion assembly according claim 1, wherein the chamber is of type comprising pre-evaporation rods, each pre-evaporation rod being shaped so that the fuel injected by the main injectors is directed toward the chamber end wall.

7. The turbomachine combustion assembly according to claim 6, wherein the combustion chamber comprises:

on its inner wall, a plurality of air intake openings, and

on its outer wall, a plurality of so-called dilution openings,

wherein the number and diameter of said openings are designed to distribute the air intake in the combustion chamber and to preserve the homogeneity of the temperature field in said chamber.

8. The turbomachine combustion assembly according to claim 7, wherein the combustion chamber is a reverse-flow chamber.

9. The turbomachine combustion assembly according to claim 8, wherein the fuel supply circuit comprises:

a supply duct for the starting injectors,

a supply duct for the main injectors, and

a fuel distribution duct, in fluid communication with the supply ducts and designed to supply fuel to said ducts,

the supply circuit further comprising a distribution system designed to shut off fluid communication between the fuel distribution duct and the supply duct for the main injectors when the fuel pressure in the distribution duct is less than a predetermined threshold.

10. The combustion assembly according to claim 9, wherein the distribution system is further designed to distribute the fuel flow between main injectors having a reduced flow rate and the other main injectors.

11. A turbomachine comprising a combustion assembly according to claim 10.