Nozzle having a movable divergent section with a thermal protection system

Abstract

A nozzle having a movable diverging section, the nozzle including a stationary throat forming a ball joint and a diverging section having a top portion that is movably mounted around the throat; an annular lubrication chamber being interposed between the stationary throat and the top portion of the diverging section, the annular lubrication chamber containing a grease seal; an annular throttling element arranged between the stationary throat and the diverging section downstream from the annular lubrication chamber, the annular throttling element being made of refractory material; and an annular thermal protection element arranged between the stationary throat and the diverging section downstream from the annular lubrication chamber and upstream from the annular throttling element, the annular thermal protection element closing the lubrication chamber in its bottom portion.

Claims

1. A nozzle having a movable diverging section, the nozzle comprising: a stationary throat having an exterior spherical surface forming a ball of a ball joint; the movable diverging section having a top portion with an interior spherical surface forming a socket of the ball joint, the interior spherical surface in contact with and movably mounted around the exterior spherical surface; an annular lubrication chamber interposed between the exterior spherical surface and the interior spherical surface of the top portion of the movable diverging section, said annular lubrication chamber containing a grease seal; an annular throttling element arranged between the exterior spherical surface and the movable diverging section downstream from the annular lubrication chamber, said annular throttling element being made of refractory material; and an annular thermal protection element arranged between the exterior spherical surface and the movable diverging section downstream from the annular lubrication chamber and upstream from the annular throttling element, said annular thermal protection element closing a bottom portion of the lubrication chamber, wherein downstream is the direction of a combustion gas flow through the stationary throat towards the movable diverging section.

2. A nozzle according to claim 1, wherein the annular throttling element comprises a gland made of carbon fibers.

3. A nozzle according to claim 1, wherein the annular throttling element comprises a ring of thermostructural composite material selected from at least: carbon/carbon composite material and ceramic matrix composite material.

4. A nozzle according to claim 1, wherein the annular thermal protection element comprises an annular gasket made of graphite or of graphite-filled polytetrafluoroethylene (PTFE).

5. A nozzle according to claim 1, wherein the stationary throat is made at least in part out of a metal material.

6. A nozzle according to claim 1, wherein portions of the stationary throat and of the movable diverging section that are in contact with the annular throttling element comprise a rigidimer thermal protection material.

7. A thruster, comprising a nozzle with a movable diverging section according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention can be better understood on reading the following description given by way of non-limiting indication and with reference to the sole FIGURE, which shows a nozzle with a movable diverging section in an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENT OF THE INVENTION

(2) The sole FIGURE is a diagram showing the rear portion of a rocket engine having a casing 10 surrounding a combustion chamber 11 that receives a block of solid propellant (not shown). The chamber 11 opens out through the rear end wall 110 of the casing, upstream from a nozzle 200 having a throat 210 and a diverging section 220, with the upstream to downstream direction in the nozzles being indicated in FIG. 1 by arrow S.sub.A corresponding to the flow direction of the combustion gas.

(3) The throat 210, which defines not only the throat of the nozzle proper but also the converging section and a beginning of the diverging section, is fastened to the end wall 110 of the casing 10 so as to be secured thereto, e.g. by screw fastening. In the presently-described example, the throat part is constituted mainly by a first portion or throat part 211 made of a thermostructural material or of a thermally insulating composite material of rigidimer type, a second portion 212 made of a metal material, and a third portion 213 made of a thermally insulating material, such as a composite of rigidimer type (e.g. a material comprising carbon or silica reinforcement and a matrix made of phenolic resin), the third portion 213 being fastened to the downstream end of the second portion 212. In a variant embodiment, the throat portion 211 may be made of a metal material such as tungsten or molybdenum.

(4) The diverging section 220 is movably mounted via its top portion 221a on the throat 210 which is stationary and secured to the casing 10. In the presently-described example, the part constituting the movable diverging section comprises a casing 221 that may be made for example out of metal that is provided on its inside portion with a coating 222 of thermally insulating material such as a composite of rigidimer type (e.g. a material formed by carbon or silica reinforcement and a matrix made of phenolic resin).

(5) The throat 210 and the diverging section 220 are mutually in contact via respective spherical surfaces 210a, 220a centered on the axis 201 of the nozzle and thus form a hinged connection of the ball joint or sphere/sphere type. The diverging section 220 is then movable on the throat 210 in several directions. Thus, by tilting the diverging section, thrust is steered as a function of the angle formed between the axis 223 of the diverging section and the axis 201 of the nozzle.

(6) The movable diverging section is connected to the stationary portion of the nozzle (not shown) via a ring 30 and actuators 40 that serve to control the tilting of the diverging section. This type of assembly forming a nozzle having a movable diverging section is itself well known and is not described in greater detail. An embodiment of such a nozzle is described in particular in Document U.S. Pat. No. 6,948,307.

(7) Naturally, other known types of mounting and actuation for a movable diverging section on a stationary portion of a nozzle could naturally be envisaged.

(8) An annular lubrication chamber 230 containing a grease seal 231 is formed in a gap present between the throat 210 and the top portion 221a of the diverging section 220. The lubrication chamber 230 is closed at its top portion 230a, i.e. downstream, by a shoulder 2210 formed in the casing 221 of the diverging section, and it is open in its bottom portion 230b, i.e. upstream, situated closest to the combustion gas ejected by the throat portion 210 and the diverging section 220. The grease seal serves both to facilitate moving the ball joint connection between the diverging section and the throat, and to provide sealing between those two parts.

(9) In accordance with the invention, the nozzle is also provided with a thermal protection and sealing system that comprises a throttling element constituted in this example by a carbon fiber gland 310 housed in an annular groove 224 formed in the inside surface of the coating 222 of the diverging section 220, and a thermal barrier formed in this example by a gasket 320 made of graphite (Sigraflex) and situated between the lubrication chamber 230 and the throttling element.

(10) The gland 310 is arranged between the throat 210 and the top portion 221a of the diverging section 220 downstream from the lubrication chamber 230. The graphite gasket 320 is arranged between the throat and the diverging section upstream from the gland 310. The gasket 320 closes the bottom portion 230b of the lubrication chamber 230 against which it is placed, thereby serving to hold the grease seal 231 in position.

(11) The gland 310 serves to throttle the combustion gas that, in this location of the nozzle and in certain tilting configurations of the diverging section, can present a circumferential speed that is high (potentially sonic) that might damage the integrity of the gasket 320, and consequently the integrity of the grease seal 231. The gasket 320 acts as a thermal barrier against any combustion gas that passes the first level formed by the gland but that then presents a thermal convection effect only at this level, since its circumferential speed has been considerably reduced by the gland 310. The grease seal is thus well protected against thermal-erosion effects of the combustion gas.

(12) By using a thermal protection system having two levels of protection (throttling closer to the combustion gas and thermal barrier upstream), the temperature of the parts constituting the ball joint, namely the throat and the top portion of the diverging section that is in sliding contact therewith, does not increase while the nozzle is in operation, even when it is in operation for durations that are relatively long (several minutes). A so-called cold ball joint connection is thus made that enables the connection parts to be made of low-cost materials such as metal materials that are less expensive than composite materials suitable for withstanding very high temperatures.

(13) In the presently-described example, the thermal protection system is reinforced by making an additional thermal protection barrier at the portions of the throat and of the diverging section that are directly exposed to the combustion gas, namely the portion 213 of the throat and the internal coating 222 of the diverging section, which are made of thermally insulating material.

(14) The movable diverging nozzle of the invention may be used in thrusters or rocket engines using solid propellants, liquid propellants, or that are hybrid (using both solid and liquid propellants).