CA1341559C

CA1341559C - Thermal lining for jet engine combustion chamber

Info

Publication number: CA1341559C
Application number: CA000500256A
Authority: CA
Inventors: Bruno Gonthier; Jean Grignon; Jean-Michel Tauzia; Michel Hivert
Original assignee: Societe Nationale des Poudres et Explosifs
Current assignee: Societe Nationale des Poudres et Explosifs
Priority date: 1985-01-23
Filing date: 1986-01-22
Publication date: 2007-10-23
Anticipated expiration: 2024-10-23
Also published as: FR2898390A1; DE3601957B3; SE8600212D0; IT8667045A0; GB8601321D0

Abstract

The invention involves a thermal lining for the combustion chamber of an engine, especially a jet engine.

The thermal lining (1) consists of a three-dimensional, multidirectional heat-resistant fiber structure (2). This structure is self-supporting and permeable to gases. The thermal lining (1) also includes an elastic layer (3) of elastomer material which impregnates the structure (2) and can be in turn filled with fibers. At least one such elastic layer (3) is inserted between the structure (2) and the combustion chamber case (9).
The lining resists high temperatures and severe engine operating conditions, especially when high-frequency acoustic vibrations are generated.
The invention can especially be used in the power plants of missiles, rockets or similar vehicles.

Description

~3 4 1 Thermal lining for jet engine combustion chamber The invention pertains to a thermal lining for the combustion chamber of an engine, especially a jet engine.

More precisely, the invention involves a highly ablative-resistant thermal lining which, in a ramjet engine for instance, effectively protects the combustion chamber case during the operating phase of the engine, and during the acceleration phase if the accelerator is integrated to the engine.

A ramjet engine consists of a duct with an air intake, inside which solid or liquid fuel is burnt. Oxygen necessary for combustion is obtained from the air inlet. The gas flow resulting from the expansion of air and combustion gases is ejected at a speed higher than the inlet speed.

By reaction, the engine is submitted to a thrust in a direction opposite to the direction of the gas flow.

The combustion chamber case is therefore exposed to high temperatures and pressures, and to erosion due to the high-speed gas flow.

The case is generally protected by a coating of heat-resistant material which provides a thermal lining to the combustion chamber. As this lining is exposed to erosion by the gas flow, it should also be highly ablative-resistant.
In addition, the engine has to be in motion to capture air. Vehicles equipped with ramjet engines must therefore gain enough speed using, for instance, high-thrust boosters known as accelerator propellant charges. When the accelerator propellant charge is housed in the engine combustion chamber, it is called an integrated charge and the engine is an integrated-accelerator engine.

An improvement to this configuration consists in having the coating which inhibits the combustion of the accelerator charge (propellant grain), thermally protect the combustion chamber case not only during the acceleration phase but also during the effective operating phase of the engine.

The numerous types of thermal linings which have been suggested and used so far fall into two categories:

- rigid thermal linings made of thermosetting material, such as a phenolic resin - "elastic" thermal linings mostly consisting of a heat- and corrosion-resistant elastomer which can include carbon or similar fibers. The elastomer can be a silicone resin for instance.

The thermal linings of the first category, when used in an integrated-accelerator engine, can be cracked by the pressure increase in the combustion chamber. subsequent to the burning of the accelerator charge.
The cracks result from different strains in the case and the lining.
Therefore, such linings cannot protect the combustion chamber case during the operating phase of the ramjet engine. In addition, their thermal conductivity is generally too high to provide case protection for long periods of engine operation.

The thermal linings of the second category can be used without major trouble to protect combustion chambers when the engines do not operate under excessively severe conditions. However, problems arise when stresses become high. Especially, they cannot effectively protect the combustion chamber case of a ramjet engine subjected to acoustic vibrations, such as high-frequency vibrations (1000-3000 Hz) with a peak-to-peak amplitude about 20 to 30% of the nominal pressure in the chamber.

Under such conditions, elastomers are very soon ablated in successive layers-Ablation results from the generation of pyrolysis gases within the lining. The gases blow away the upper layer already pyrolyzed and made more or less airtight.

The purpose of the invention hereunder is to remedy all these problems by submitting a novel thermal lining which, even under severe operating conditions, including acoustic vibrations, does not ablate rapidly and effectively protects the combustion chamber case during ramjet engine operation, and resists the acceleration phase without major damage.

To this effect, the invention proooses a thermal lining designed for the combustion chamber of an engine, especially a jet engine, and composed of a three-dimensional, multidirectional, self-supporting, gas-permeable, heat-resistant fiber structure. Certain fibers in the structure are arranged along at least one direction not contained in the plane defined by at least two other fiber directions. The structure is impregnated with at least one layer of elastomer material over at least one of its sides.

A characteristic of the invention is the provision for preferred paths within the three-dimensional structure in order to improve its permeabi-lity to gases.

According to a first preferred manufacturing process, the three-dimensional structure consists of a layer of fibers arranged along at least two direc-tions. Bunches of fibers are embedded in this layer so that pins protrude from at least one of its sides. Structure integrity is obtained by weaving the fibers in the layer and inserting the bunches through the weft of the resulting fabric, or by impregnating the assembly with a thermosetting resin, such as a phenolic resin, or with a mineral binder such as silica or carbon.

Preferred gas paths are obtained either by holes provided in the fabric or in the fiber layer, or by loose weaving.

Also, the prefeied gas paths may be produced by low temperature decomposing fibers which are incorporating in the three-dimensional structure. These fibers are decomposed by melting or pyrolysis at a lower temperature than the decomposition temperature of other materials of the thermal lining.

Thus, according to a prefered embodiment of the invention, besides the branches of refractory fibers, bunches of low temperature decomposing fibers are inserted in the woven. Said decomposing fibers are made of material decomposable at low temperature, for example at a temperature above 200 C but low the neltinc; ~r decomposinc, ;:emperature of the is 1 ~ 4 1559 thermosetting resin impregnating the woven or of the materials of elastomer layer, more preferably at a temperature comprised between 200 C about and 300 C about.

These decomposing fibers may be elemental fibers which are impregnated as the refractory fibers in order to obtain bunches, or maybe rod or bar.
Convenable fibers are, for example, polyester, polyamide fibers, teflon rod or other materials having an appropriate decomposing temperature.

According to a second preferred manufacturing process, the three-dimensional, multidirectional structure is composed of at least two plies of woven or knitted fibers. The plies are superposed and loosely attached to each other by binding wires so as to make up a mattress-like structure.

According to a third preferred manufacturing process, the three-dimensional, multidirectional structure consists of a thick textile fabric made of at least two layers of weft threads which are superposed and attached by regularly undulating warp threads.

Thus, the invented thermal lining consists of a three-dimensional, multi-directional structure and an elastic layer of elastomer material. The high-integrity, multidirectional layer prevents excessive ablation of the elastomer layer, which assumes the form of the c anbustion chamber case strained by acoustic vibrations. Therefore the multidirectional structure does not burst and provides heat insulation to the casing.

In addition, due the permeability of the multidirectional structure, gases produced by elastomer pyrolysis can escape into the combustion chamber, which prevents the upper pyrolyzed layer and the structure itself from being blown away.

Another characteristic of the invention consists in installing the lining in an engine combustion chamber in such a way that the elastomer layer lies between the chamber case and the fiber layer of the multidirectional structure.

6' The multidirectional structure is made of suitably heat-resistant fibers, such as carbon, silicon carbide, silica, ceramic, metal or similar fibers, or a mixture thereof.

The multidirectional structure can also be mechanically reinforced by nonrefractory fibers, such as polyamide, aramide or polyaramide fibers.
A further characteristic of the invention is that the elastomer layer contains heat-resistant mineral fillers, such as fibers andJor fiber fillers (carbon, silicon carbide, boron carbide), or granular fillers (alumina, zirconium oxide, silicon carbide, boron carbide), or a mixture thereof.

The thermal conductivity of the lining is improved by adding to the elastomer some fillers able to have endothermic chemical reactions with each other and with the binder. They can consist of a carbon-silica combination for instance.

Another characteristic of the invention is the possibility of inserting, between the material described above and the combustion chamber case, an additional elastomer layer, preferably not containing any fiber fillers or other heat-conductive fillers.

Besides, when a propellant grain has to be cast in the combustion chamber (to serve as an accelerator charge in a ramjet engine, for instance), the inward side of the thermal lining is coated with a material inhibiting the combustion of the grain.

Elastomers suitable for use in this invention should offer, beside their intrinsic properties, adequate heat and corrosion resistance.
They can be silicone polymers for instance.

Further details, characteristics and advantages of the invention will be shown more clearly in the following description which refers to the attached figures_ These figures are mere examples and include:

13415~9 - Fig. 1 shows the longitudinal section of an engine combustion chamber fitted with a thermal lining in accordance with the invention - Fig. 2 is a scaled-up view of part II in Fig. 1, which illustrates the lining structure as per the invention - Fig. 3 is a scaled-up schematic perspective view showing a first manufacturing process for the three-dimensional structure of the invented lining - Fig. 4 is a scaled-up schematic perspective view showing a second manufacturing process for the three-dimensional structure of the invented lining - Fig. 5 is a scaled-up schematic perspective view showing a third manufacturing process for the three-dimensional structure of the invented lining.

Referring to Fig. 1, the case 9 of the combustion chamber of a jet engine, such as a rocket or missile ramjet engine, is protected from heat and from etching and straining by combustion gases, by a protec-tive layer 1, called a thermal lining. The thermal lining 1 is bonded to the case 9 , for instance by coating the inner side of the case 9 with an adhesive compound, such as a synthetic resin, which adheres to the case material and the thermal lining. The nature of this compound, which is known to the specialist, depends on the case material, which can be metal, ceramic, composite or laminate.

A combustion chamber means any enclosure where a combustion takes place, liberating a large amount of gases and heat.

However, the invention can also be used to protect any enclosure subjected to high temperatures and pressures, high-speed fluid flaw or severe stresses.

The following refers more specifically to Fig. 2 and describes the structure of the invented thermal lining.

According to the invention, the thermal lining 1 consists of a self-supporting structure 2 and at least one "elastic" layer 3.

The self-supporting structure 2 is a multidirectional, three-dimensional fiber structure, which is thick enough to provide mechanical attachment with the elastic layer 3.

Several examples of self-supporting structures suitable for use in the invention will be described more precisely below, with reference to Fig.
3, 4 and 5.

The "elastic" layer 3 is made of an elastomer such as room temperature vulcanizing silicone (RTV).

The elastomer is laid on one side of the self-supporting structure 2 so that it makes up an elastic layer 3 between the combustion chamber case 9 and the self-supporting structure 2 . Bonding between the structure 2 and the elastic layer 3 is obtained by partial impregnation of the structure 2 with the elastomer.

13 4155~

A preferred manufacturing process for the invention consists in impregnating the structure 2 with the elastomer throughout.

An improved elastic layer 3 is composed of an elastomer such as silicone, containing the heat-resistant mineral fillers described above, especially carbon or silicon carbide fibers, which increase mechanical and thermal properties.

In order to reduce the thermal conductivity of the elastic layer (3) and better protect the case 9 , fillers are added to the elastomer, such as a carbon-silica mixture which produces heat-absorbing reactions, or cooling fillers.

As shown in Fig. 2, the invention also allows the superposition of an additional elastomer layer 7 on the elastic layer 3 . This additional layer is preferrably made of the same elastomer material as the layer 3 However, to reduce the thermal conductivity of the lining, the material does not contain any heat--conductive or fiber filler. But it may contain cooling fillers or fillers causing an endothermic reaction, such as the carbon-silica combination mentioned above.

The additional layer 7 is inserted between the thermal lining 1 and the case 9 when the lining is installed in the combustion chamber.
Thus the elastomer material of the layer 7 fills possible gaps in the elastic layer 3 , which provides a homogeneous protective lining without trapped air.

In addition, when a propellant grain (not shown here) has to be cast in the combustion chamber, for instance to serve as the integrated accele-rator charge in a ramjet engine, the inner side of the thermal lining 1 and more precisely of the self-supporting structure 2 , is covered with 5 a layer 8 of material, which is preferrably the same elastomer as in the layers 3 or 7. The layer 8 is bonded to the thermal lining by its adherence to the elastomer of the layer 3 , which impregnates the self-supporting structure 2 .

10 The layer 8 is bonded to the propellant by means of a well-known process, i.e., by laying a primer of organic polyisocyanate, as described in the French patent No. 78 36 836, or directly by adding some compounds to the elastomer, as described in the French patents No. 82 21 644, 82 21 645 and 84 02 648. The invention also covers the installation, in the combustion chamber, of a "free", i.e., already inhibited, propellant grain, which is then merely positioned in the chamber and not bonded to the thermal lining.

After installing the thermal lining 1 in the combustion chamber (9), it is preferrable to vulcanize the material(s) composing the elastic layer 3 , and the layers 7 and 8 if applicable.

The self-supporting structure (2) is made of heat-resistant fibers arranged in three-dimensional, multidirectional fabric, which may be woven or not. The fabric should be permeable to gases and therefore include preferred gas paths.

The fabric can also include nonrefractory fibers, such as polyamide fibers, and especially the polyphenylene terephtalamide fibers marketed by Dupont de Nemours Inc. under the trademark "Kevlar".

13 4~5 59 Referring to Fig. 3, 4 and 5, three examples of manufacturing processes for this fabric are given below.

The first manufacturing process for the self-supporting structure 2 shown in Fig. 3, consists in embedding fiber bunches 5 in a fiber ply 4 so that pins protrude from at least one of the ply sides, as on a wire brush or a hedgehog's back.

The fiber ply may be woven or, as shown here, made of a first layer of fibers 4a arranged along a given direction, and a second layer of fibers 4b arranged along a direction preferrably orthogonal to the first one.
The pins (bunches) are embedded regularly and alternately in the resulting fabric. However, to provide paths for gases, the pins 5 are placed only every two wefts, for instance, so as to leave holes 6 . Integrity of the assembly is obtained by weaving the fibers 4a and 4b together, or by impregnating the whole with a thermosetting resin, such as a phenolic resin. The pins 5 are made of bunches of cut fibers, or of looped fibers.

A process for generating this structure, especially by revolution, is described in the French patents No. 2 408 676 and 2 480 261.

The elastomer of the layer 3 is then laid over the structure side fitted with the pins 5 , so as to embed them entirely. It is also preferrable to let the elastomer into the holes 5 , especially to improve bonding between an adhesive layer 8 and a propellant grain.
The pin length and density (i.e., the number of pins per surface unit of fabric) are not critical for the invention, although a minimum density of 4 pins per sq cm is advisable, with an equal, and preferrably greater, hole density 6 13 4155~

When a layer 4 is woven, a loose weaving is preferrable to make the fabric permeable to gases by means of paths similar to the holes 6 shown in Fig. 3.

Fig. 4 shows another manufacturing process suitable for the self-supporting structure of the invention. This structure consists of at least two layers of fabric 10 and 11 , superposed and loosely attached by a number of binding threads so as to make up a kind of mattress.

The weaving of the fabric layers 10 and 11 has to be loose so that the structure is permeable to gases and can also be infiltrated with the elastomer.

A third type of self-supporting structure, shown in Fig. 5, consists of a thick fabric including several laminations of weft threads 14a and 14b , attached to each other by warp threads 13 which undulate regularly between the weft threads 14 of each lamination. The directions of the weft threads 14 and the sine curve formed by the warp threads 13 do not have to be orthogonal. Such a structure is made permeable to gases by loose weaving.

Other three-dimensional structures are suitable for the invention, such as the structure described in the French patent No. 2 497 839.

The following examples of manufacturing processes for the invented thermal lining are given for information only.

13 4~J5~

Example 1 a) characteristics of the three-dimensional structure 2 (illustrated in fig 3) - T 300 carboii fibers marketed by Toray the structure was impregnated with a phenolic resin - thickness of fabric 4 : 3 mm - length of pins 5 7 mm - density of pins 5 about 6 pins per sq cm of fabric - density of holes 6 about 6 holes per sq cm of fabric b) characteristics of the "elastic" layer 3 - elastomer: RTV 630 silicone marketed by General Electrics 100 parts by weight - fillers: silicon carbide powder 25 parts by weight carbon fibers 8 parts by weight - cross-linking agent for RTV 630 silicone 10 parts by weight This thermal lining was tested on a bench simulating the flight of a vehicle powered by a ramjet engine, under operating conditions generating acoustic vibrations with a frequency of 1300 Hz at an effective pressure greater than one bar, or a frequency of 2500 Hz at an effective pressure near one bar.

The examination of the lining condition after a simulated flight of 10-40 seconds showed that integrity was preserved. However, elastomer pyrolysis had occurred, to a variable extent depending on the test duration.

Besides, a resistance test during a fast pressure increase in the combustion chamber, designed to simulate the ignition of an integrated accelerator charge, demonstrated the good behavior of the invented thermal lining.

134155~

Example 2 a) characteristics of the three-dimensional structure 2 (illustrated in fig 3) - silicon carbide fibers marketed under the trademark "Nicalon NIN1 102"
by Nippon Carbon - fabric thickness: 3 mm - pin density: 6 pins per sq cm - hole density: 6 holes per sq cm The three-dimensional structure was densified by impregnation with a phenolic resin.

b) characteristics of the elastic layer 3 same as Example 1 The tests described in Example 1 were conducted on this thermal lining, with identical results concerning resistance to a steep pressure increase and behavior during the simulated flight of a ramjet engine.

Example 3 a) characteristics of the three-dimensional structure .2 The structure has the texture shown in Fig. 5.
It is made of silicon carbide fibers marketed under the trademark "Nicalon NLM 102" by Nippon Carbon.
- number of warp threads per cm: 146 quadruple threads, 20 2 Texes - number of weft threads per cm: 27 quadruple threads, 20 2 Texes - number of weft laminations: 6 - bulk factor: 31.5 % (percentage of the structure volume occupied by fibers) - weft porosity: 50 %
- warp distribution: 61 %
- weft distribution: 39 %
- surface density: 6200 g per sQ m - apparent thic'kness: 8 mn 13 4155~

b) characteristics of the elastic layer 3 - elastomer: RTV 141 silicone marketed by Rhone-Poulenc 100 parts - fillers: silicone carbide powder 20 parts - cross-linking agent for RTV 141 silicone marketed by 10 parts 5 Rhone-Poulenc by weight Example 4 a) characteristics of the three-dimensional structure 2 10 The structure has the texture show in fig 3.
It is made of silicon carbide fibers marketed under trademark "Nicalon NLM102" by Nippon Carbon - fabric thickness : 3 mm - lenght of pins 5 : 7 mm 15 - density of pins 5 : about 5,35 pins per sq.cm of fabric.

Pins are inserted in holes 6 of the fabrics. These pins are made of polyimide aramide fibers marketed by Dupont de Nemours under trademark Kevlar , and have the same characteristics of refractory pins 5.

The density of kevlar fibers pins is about 5,35 pins per sp.cm of fabric.

The three-dimensional structure 2 is impregneted with a mineral binder, colloidal silica. The impregnating process is, for example, the process described in French patent n 2 526 785 which consists in successive impregnating steps in liquid phases, under vacuum and a thermal treatment at low temperature, about 150 C.
b) characteristics of the elastic layer 3: same as example 1.
The tests described in example 1 were conducted on this thermal lining.
The obtained results show an improved bonding between the several layers of the thermal lining, which leads to obtain very high integrity of the structure after the tests.

Resistance to heat, stresses and pressure is greatly improved compared with a nonreinforced equivalent structure.

The invented thermal lining offers high ablation resistance and preserves its integrity even under severe operating conditions, especially when acoustic vibrations are generated. Wear resistance and preserved integrity are obtained by means of the three-dimensional reinforcement structure of the layer 2 which retains the upper pyrolyzed layer. Therefore this thermal lining effectively protects the ccinbustion chamber of a ramjet engine, during both the sustainer phase and the booster phase, especially when an integrated accelerator is used. The lining can also be used for protecting the combustion chamber in a vane-type engine, as described in the French patent No. 82.02658.

Of course, any heat- and corrosion-resistant elastomer can be used in the layers 3 and 7 .

Besides, the layer 3 can be made of an elastomer without fillers, especially without refractory fibers.
Various compounds can also be added to the elastomer in order to improve its bonding to the propellant, its strength and its resistance to heat.

Claims

1. ~Thermal lining designed for the combustion chamber of an engine, especially a jet engine, and characterized in that it is composed of a three-dimensional, multidirectional, self-supporting, gas-permeable, heat-resistant fiber structure, certain fibers in the structure are arranged along at least one direction not contained in the plane defined by at least two other fiber directions, and at least one layer of elastomer material impregnating the said structure over at least one of its sides; said structure comprising preferred gas paths.

2. ~Thermal lining according to claim 1, characterized in that said structure (2) comprises fibers having a low temperature of decomposition in order to generate the preferred gas paths (6).

3. ~Thermal lining according to claim 1 or 2, characterized in that said structure (2) is reinforced by nonrefractory fibers.

4. ~Thermal lining according to anyone of claims 1, 2 or 3, characterized in that said elastomer layer (3) lies against the combustion chamber case (9) and said structure (2) lies towards the chamber inside.

5. ~Thermal lining according to anyone of claims 1 to 4, characterized in that said elastomer layer (3) includes heat-resistant. granular and/or fiber fillers.

6. ~Thermal lining according to claim 4, characterized in that said heat-resistant fillers are taken from a group including carbon fibers, silicon carbide fibers, boron carbide fibers, alumina powder, zirconium oxide powder, silicon carbide powder, boron carbide powder, silica powder and carbon powder.

7. ~Thermal lining according to claim 4 or 5, characterized in that the above-mentioned elastomer layer (3) contains fillers able to have endothermic reactions with each other and with the binder, such as a mixture of carbon and silica powder.

8. ~Thermal lining according to anyone of claims 1 to 7, characterized in that said structure (2) consists of a layer of fibers (4) arranged along at least two directions, in which fiber bunches (5) are embedded so that pins protrude from at least one side of the layer (4).

9. ~Thermal lining according to claim 8, characterized in that the fiber layer (4) includes holes (6) serving as the above-mentioned preferred gas paths.

10. ~Thermal lining according to claim 9, characterized in that said structure (2) comprises fibers or rod forming pins made of a material having a low temperature of decomposition, said pins being inserted in holes (6) of fabric.

11. ~Thermal lining according to claim 10, characterized in that the decomposition temperature of pins inserted in holes (6) of fabric is range to 200°C and 300°C.

12. ~Thermal lining according to claims 8 to 11, characterized in that the pin density on the above-mentioned structure (2) is at least 4 pins per square centimeter.

13. ~Thermal lining according to anyone of the claims 8 through 12, characterized in that the hole density in the above-mentioned structure (2) is at least 4 holes per square centimeter.

14. ~Thermal lining according to anyone of claims 1 through 7, characterized in that said structure (2) consists of at lest two plies (10) and (11) made of woven or knitted fibers, and superposed and attached to each other by binding threads (12) so as to make up a mattress-like structure.

15. ~Thermal lining according to anyone of claims 1 through 7, characterized in that said structure (2) consists of a thick textile structure with at lest two superposed weft thread layers (14a) and (14b), attached together by regularly undulating warp threads.

16. ~Thermal lining according to anyone of claims 1 to 15, characterized in that it includes a layer (7) of elastomer material without refractory or fiber fillers, which covers said elastomer layer (3).

17. ~Thermal lining according to anyone of claims 1 to 16, characterized in that said elastomer material is a silicone elastomer.

18. ~Thermal lining according to anyone of claims 1 to 17, used in the combustion chamber of a ramjet engine with an integrated accelerator propellant charge and characterized in that it includes a layer (8) inhibiting the charge combustion and lying on the side of said structure (2) towards the chamber inside.