EP0401107B1 - Combustion chamber for ram jet - Google Patents

Description

The present invention relates to a supersonic combustion ramjet according to the preamble of claim 1.

Supersonic combustion ramjet engines are currently being studied for the propulsion of hypersonic vehicles, for example recoverable space planes with horizontal takeoff. The propulsion phase by supersonic combustion ramjet makes it possible to accelerate the vehicle by the speed - approximately Mach 6 - reached at the end of the propulsion phase by subsonic combustion ramjet, up to a speed of approximately Mach 15 to Mach 25.

In a supersonic combustion ramjet chamber, the air circulates at a speed which is always supersonic in the middle of the air stream, where the wall effects are hardly felt, and the fuel, generally hydrogen gas. is introduced through the wall of the chamber.

The injection of the hydrogen gas flow is generally carried out by holes or slots formed in the wall of the chamber. It is difficult to ensure a satisfactory mixture between hydrogen and air, and therefore to obtain good energy efficiency, without aerodynamic flow losses due to interactions or shocks between the air flow and the flow. injected hydrogen. In fact, an injection of hydrogen through holes directed towards the axis of the combustion chamber necessarily produces shocks between the gas flows. On the other hand, if the hydrogen is injected tangentially to the wall of the chamber, it tends to remain confined against the latter under the effect of air flowing at high speed into the chamber, and combustion occurs from incomplete because of the short air residence time in the room.

The present invention aims to provide a supersonic combustion ramjet chamber into which a flow of gaseous fuel can be introduced without creating damaging shocks with the air flowing in the chamber, at supersonic speed, while obtaining satisfactory energy efficiency. .

This object is achieved by means of a ramjet comprising a combustion chamber intended to be traversed longitudinally by an air flow at supersonic speed, and a first injection device for injecting into the chamber a flow of gaseous fuel with a speed entry into the chamber having a low amplitude transverse component, ramjet in which a second injection device is located downstream of the first, in the direction of the flow of air at supersonic speed, for injecting into the chamber a flow of gaseous oxidizer which contributes to detaching from the wall of the chamber the flow of gaseous fuel injected by the first injection device.

The first injection device preferably comprises a first wall part of the combustion chamber, for example a ring-shaped part, which is made of a material permeable to the flow of gaseous fuel to be injected into the chamber and which has a surface constituting a part of the interior surface of the chamber and an opposite surface in communication with a source of the gaseous fuel to be injected, so that the injection of the gaseous fuel flow is carried out by transpiration through the porosity of the porous material constituting of the first injection device.

The second injection device can be produced in the same way.

The use of a porous material through which the gas flow transpires is an injection means which is perfectly suitable for injecting the gas flow into the chamber with an input speed having a radial component of low amplitude.

The porous material is advantageously a porous composite material with a ceramic or carbon matrix. Such a material is particularly suitable for producing a device for injecting a gas flow into a ramjet combustion chamber. Indeed, such a material has thermostructural properties, that is to say a mechanical behavior at high temperature which makes it possible to produce an injection device constituting a structural element of the chamber. In addition, the porosity of this material can be controlled by acting on the volume ratio of fibers constituting its fibrous reinforcing texture and / or on the degree of densification by the material constituting the matrix.

A material of type C / SiC (reinforcement of carbon fibers and matrix of silicon carbide), or of type SiC / SiC (reinforcement of fibers essentially of silicon carbide and matrix of silicon carbide), or of type C / C protected (carbon fiber reinforcement, carbon matrix and anti-oxidation protection), may be suitable.

Preferably, the wall of the chamber, at least in its parts adjacent to the injection devices, is also made of non-porous composite material with ceramic or carbon matrix. The connection between the injection devices and the other parts of the wall of the combustion chamber can then advantageously be carried out by co-densification of the wall parts forming injection devices and of the other wall parts assembled in an incomplete state. densified. This co-densification is preferably carried out by chemical vapor deposition.

Injection methods other than by transpiration through a porous material may be used to inject the flow of gaseous fuel or the flow of gaseous oxidant. Fuel flow injection must be performed with a component low speed radial so as not to cause violent interactions or shocks with the supersonic speed air flow; it is preferably the same for the injection of the gas oxidant flow. Injectors or injection orifices opening into the chamber substantially tangentially to the wall thereof can be provided.

The invention will be better understood on reading the description given below, by way of indication, but not limitation, with reference to the appended drawing in which the single figure is a very schematic view, in axial section, of a ramjet with supersonic combustion constituting a particular embodiment of the invention.

In the example illustrated, the chamber 10 is of cylindrical shape with circular section and comprises, in the direction of air flow at supersonic speed (arrow A), an upstream sealed section 12, a first injection ring 20 for the injection of a flow of gaseous fuel, a central sealed section 14, a second injection ring 30 for the injection of a flow of gaseous oxidizer and a downstream sealed section 16. The interior surfaces of the sections 12, 14, 16 and injection rings 20, 30 define the continuous cylindrical internal wall of the ramjet chamber.

The outer surface of the ring 20 defines a chamber 22 for injecting gaseous fuel which communicates with a fuel source (not shown). The fuel is for example hydrogen which is injected in the gaseous state, the pressure prevailing in the injection chamber 22 being greater than that prevailing in the combustion chamber of the ramjet.

The ring 20 is made in a single piece of porous refractory composite material. The porosity of the material constituting the ring 20 gives the latter the permeability necessary to allow injection of the gaseous flow of hydrogen by transpiration through the injection ring. The hydrogen gas flow thus enters the chamber with a low radial velocity component. The flow of hydrogen injected into the combustion chamber is defined by the porosity of the injection ring, the length of the latter, and the pressure difference between the outer and inner surfaces of the ring.

The constituent material of the ring 20 is a composite material consisting of a refractory fibrous reinforcement partially densified by a ceramic material, or of a fibrous carbon reinforcement partially densified by a carbon matrix and protected against oxidation. For the manufacture of the ring, an annular preform is formed which constitutes the fibrous reinforcement. The preform is made of carbon fibers or ceramic fibers, for example fibers essentially of silicon carbide. By way of example, the fiber preform is produced by winding on a mandrel of a strip of fabric until the desired thickness is obtained. The superimposed layers of fabric can be linked together by needling or implantation of threads.

The preform is densified by gas or by liquid. In the first case, a matrix is produced by chemical vapor infiltration of ceramic material, for example silicon carbide, or carbon (for a protected C / C type material). In the second case, the preform is impregnated with a precursor of the matrix material, which is then obtained by heat treatment.

The duration of chemical vapor infiltration or the number of liquid-thermolysis impregnation cycles are chosen in order to obtain the desired final porosity taking into account the initial porosity of the preform. As an indication, an injection ring made of ceramic material C / SiC can be produced by manufacturing a carbon fiber preform having a fiber volume ratio of approximately 35% and densifying it by chemical vapor infiltration of silicon carbide until a residual porosity of about 40% is reached.

In the case of a C / C type material, a specific treatment will be carried out to protect the material against oxidation. Various anti-oxidation protection treatments for C / C composites are well known.

The ring 30 delimits by its outer surface a chamber 32 for injecting gaseous oxidant. This can consist of air taken from the surrounding medium or oxygen from a source (not shown).

The ring 30 is made in a single piece of porous composite material either with a ceramic matrix, for example in C / SiC material, or of C / C type protected against oxidation, in the same way as the ring 20. The porosity of the material constituting the ring 30 gives the latter the permeability necessary to allow the injection of a flow of gaseous oxidant by transpiration through the ring 30, the pressure in the injection chamber 32 being greater than that reigning in the ramjet chamber. The flow of gaseous oxidant into the chamber is therefore also carried out with a low radial velocity component.

The sections 12, 14, 16 of the ramjet chamber are preferably also made of a composite material with a ceramic or carbon matrix. Advantageously, a material having a reinforcement and a matrix of the same type as those of the injection rings 20 and 30 will be chosen. However, unlike the rings 20 and 30, the sections 12, 14 and 16 are sealed, the seal being obtained by densification sufficiently advanced to fill the porosity of the fibrous reinforcement until the material is impermeable.

Advantageously, the connection between the sections ons 12,14,16 of the wall of the chamber 10 and the injection rings 20, 30 is produced by co-densification. Actually, the sections 12, 14, 16 and the rings 20, 30 are produced separately while being incompletely densified with respect to the desired degree of final densification. The elements are then assembled end to end and placed in an infiltration oven to undergo a final co-densification by chemical vapor infiltration. During the final co-densification, the continuity of the matrix material at the interfaces between the sections 12, 14, 16 and the rings 20, 30 ensures the connection between these elements. This final co-densification is continued until the desired degree of porosity is obtained for the injection rings 20 and 30, the sections 12, 14, 16 having previously been sufficiently pre-densified to finally obtain the desired seal.

As shown schematically in the figure, the gas flow 34 of oxidant transpiring through the injection ring 30 forces the gas flow 24 of fuel to move away from the wall of the chamber 10 despite the supersonic air flow having tendency to press it against this wall. A satisfactory mixture is thus obtained between the combustible gas and the oxidizer constituted by the supersonic air and the flow 34. Complete combustion of the combustible gas can thus be carried out in a very short time, without creating violent interactions between the current d supersonic air and gas flows transpiring through the injection rings. This results in an increase in performance of the ramjet chamber, therefore better thrust and specific impulse of the propulsive system.

It has been envisaged above carrying out the injection of the gas flows into the chamber by transpiration through an injection ring of porous composite material with ceramic matrix.

Other types of porous materials, for example porous metallic structures, can be used in the case of a metallic chamber.

Claims (9)

1. Supersonic combustion ramjet comprising a combustion chamber (10) along which can flow longitudinally an airflux at supersonic speed, and a first injection means (20) for injecting into said chamber (10) a flux of combustible gas (24) flowing substantially tangentially along the wall thereof,
characterized in that a second injection means (30) is provided downstream of said first injection means along the direction of supersonic air flow to inject into said chamber (10) a flux of combustive gas (34) that serves to delaminate from the wall of the chamber (10) the flux of combustible gas (24) injected by the first injection means.

2. Ramjet according to claim 1, characterized in that the first injection means (20) comprises a first wall portion of the combustion chamber (10), said first wall portion being made of a material that is permeable to the flux of combustible gas to be injected into the chamber (10) and having a surface forming a part of the inner surface of the chamber, and an opposite surface that communicates with a source of combustible gas to be injected, so that the injection of said flux of combustible gas is obtained by transpiration through pores of a porous material forming said first injection means (20).

3. Ramjet according to claim 2, characterized in that the first wall portion of the chamber (10) is in the form of a ring of porous material.

4. Ramjet according to any one of claims 1 to 3, characterized in that the second injection means (30) comprises a second wall portion of the combustion chamber (10), said second wall portion being made of a material that is permeable to the flux of combustive gas to be injected into the chamber (10) and having a surface forming a part of the inner surface of the chamber, and an opposite surface that communicates with a source of combustive gas to be injected, so that the injection of the flux of combustive gas is obtained by transpiration through pores of a porous material forming the second injection means (30).

5. Ramjet according to claim 4, characterized in that the second wall portion of the chamber is in the form of a ring of porous material.

6. Ramjet according to any one of claims 2 to 5, characterized in that the porous material is a porous composite material selected from the ceramic matrix composites and the carbon/carbon type composites.

7. Ramjet according to claim 6, characterized in that the porous material is selected from a C/SiC type composite and a SiC/SiC type composite.

8. Ramjet according to any one of claims 6 and 7, characterized in that the wall portions of the chamber (12, 14, 16) adjacent to the injection means (20, 30) are made of an impermeable composite material selected from the ceramic matrix composites and the carbon/carbon type composites.

9. Ramjet according to claim 8, characterized in that the porous composite material forming the injection means (20, 30) and the impermeable composite material forming the wall portions (12,14,16) adjacent to said injection means (20, 30) are of the same type with different degrees of densification.

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