THRUST CHAMBERS

Abstract: There is described a film cooled thrust chamber of a liquid propellant rocket engine, the thrust chamber having at least a surface lining within which bipropellant combustion occurs, the lining comprising a first portion of a material including rhodium from a position at least where, in use, corrosive species formed by decomposition of fuel being used for film cooling, said first portion extending downstream to a position in the region of which said corrosive decomposition products of said film cooling layer cease, said lining continuing with a second portion of a material comprising iridium to a position extending at least beyond a nozzle throat of said chamber.

Description: THRUST CHAMBERS The present invention relates to thrust chambers for bipropellant liquid rocket engines Conventional bipropellant liquid fuel rocket engines have thrust chambers in which fuel and oxidiscr arc reacted together. The reaction between the two constituents generates thrust and exceed the melting temperature of the material from which the chamber is constructed or cause attack by corrosion of the chamber metal o\cr a period of use. In order to reduce the peak temperature reached by the chamber wall, the technique of film cooling is frequently employed. In this technique, the two bipropellant constituents arc fed into the thrust chamber in a predetermined manner. To generate a combustion reaction, fuel and oxidiscr arc both fed through a plurality of pairs of icts in an injector into the thrust chamber where they react together to generate thrust. Simultaneously, one constituent, usually the fuel, is fed through a ring of icts adjacent the thrust chamber wall so as to form a thermally insulating film along the chamber wall and separate the burning bipropellant therefrom by a cooler liquid and gaseous layer. The problem caused by film cooling is that as the distance from the injector jets increases downstream therefrom, the fuel component decomposes into uncombusted but very corrosive species which cause attack by pitting of the combustion chamber wall up to about shortly about before the throat of the nozzle at which point such pitting tends to stop The reason for this cessation of attack is that the corrosive species produced by decomposition of the fuel may become fully burnt at this point probably due to the rising temperature which occurs along the length of the chamber. However, the pitting corrosion problem is very serious in that rocket thrustcrs used for positioning and spatial adjustment of space vehicles such as satellites, for example, need a relatively long life and pitting corrosion can result in premature failure of the thrust chamber. A further disadvantage of the technique of film cooling is that it is an inefficient use of the fuel constituent. The ability to reduce or eliminate the quantity of the fuel constituent used in this way would enable an increase in the duration of a satellite, for example, on-station through more of the fuel being available for manoeuvring, or an increase in the launch vehicle payload through the need to carry less fuel or the ability to build smaller, less costly but improved performance thrustcr motors. US-A-4 882 904 describes a rocket motor employing a baffle in the thrust chamber to deflect the uncombusted fuel film cooling constituent into the high temperature burning core of fuel and oxidiscr before it can decompose to form corrosive species. However, disadvantages of this approach arc that cooling of the chamber downstream of the baffle may be inadequate, the presence of the baffle itself impairs motor performance and a consequence of disrupting the film cooling is that more heat is conducted into the rocket engine body causing problems with vapour locks in the propcllant supply to the injector and degradation of mechanical components such as plastics material value scats for example. US-A-4 917 968 seeks to provide a chamber liner by chemical vapour deposition of a corrosion resistant layer such as iridium onto a highly temperature resistant material such as rhenium. Other materials such as refractory oxides of hafnium or zirconium may also be employed as surface layers. However, although the rhenium layer is mechanically very strong at elevated temperatures, it is very susceptible to oxidation. Furthermore, the iridium surface layer exposed to the film cooling fuel layer has been found to be susceptible to grain boundary corrosion by the fuel decomposition products, as described above, causing the loss of surface grains of iridium producing pitting and allowing attack of the underlying rhenium layer. It is an object of the present invention to provide at least a chamber liner able to withstand the corrosive effects of the decomposition species of the fuel film cooling layer and to withstand the high temperatures of bipropellant combustion. It is a further objective to improve the performance of thrust chambers. According to the present invention there is provided a thrust chamber for a liquid propcllant rocket engine characterised in that at least the surface of the inner wall of the chamber is lined in a first zone with a material including rhodium and in a second zone, downstream of the first zone, with a material including iridium. Preferably, the first zone extends from a position where in use the production of corrosive species formed by decomposition of a cooling layer of fuel injected along the surface of the thrust chamber begins to a position where the formation of such corrosive species ends and said second zone extends from the end of the said first zone. The second zone preferably extends beyond the nozzle throat at the downstream end of the thrust chamber. Preferably, the first zone comprises substantially pure rhodium. It has been found that rhodium is resistant to the corrosive effects of the decomposed fuel species generated during film cooling. Preferably, the rhodium is in the form of a lining to a backing layer or a liner provided within a backing layer or main body; the backing layer or the main body of the thrust chamber may comprise a refractory metal or metal alloy. Although the corrosion resistance of rhodium is exceptionally high, the high temperature strength of rhodium may be inadequate . The first zone is also preferably prov ided in the form of a lining or a liner in view of the high cost of rhodium. Preferably, the second zone downstream of said first zone comprises substantially pure iridium. Again, the second portion is preferably provided in the form of a lining or a liner to a backing layer or within a main body as in the case of the first zone. A further reason for preferring the first and second zone to be provided in the form of linings or liners to a main body or backing layer is that refractory alloys used for such applications arc well characterised in terms of their mechanical and material properties. Thus, rocket engine thrust chambers according to the present invention may be produced with a greater degree of certainty with regard to materials and may require less resources for testing and certification. According to a second aspect of the present invention the first and second zones of the thrust chamber may comprise an alloy including rhodium and iridium. The alloy of rhodium and iridium preferably has a composition of from about 25wt rhodium/ 75wt% iridium to about 75wt% rhodium/ 25wt% iridium, and more preferably, the composition of the alloy may lie in the range from about 4()wt% rhodium/ 6()wt% iridium to about 60wt% rhodium/ 4()wt% iridium. One example of an alloy liner for a thrust chamber according to the present invention includes about 55wt%/ rhodium and about 45wt% iridium. In this second aspect of the present invention it is again preferred that the first and second zones are provided in the form of a liner composed of the rhodium and iridium alloy on a backing layer or within the main body of the thrust chamber, the backing layer or main body preferably being of a refractory metal or metal alloy. A lining or liner may be produced by various physical and/or chemical vapour deposition methods. Alternatively, a liner may be produced by fabrication from sheet materials and applied to the inner wall surface of a main body or backing member by employing metal working and joining techniques known in the metallurgical art. In order the present invention may be more fully understood, examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a schematic representation of a thrust chamber of a first embodiment of a rocket engine according to the present invention; and Figure 2 which shows a schematic graph of temperature against position within the thrust chamber of Figure 1. Referring now to the Figures and where the same features arc denoted by common reference numerals. A schematic cross section of a rocket engine thrust chamber is shown generally at 10. The chamber has an injector 12 at one end of the chamber, the injector having jets 14 in a central region through which bipropellant comprising fuel and oxidiscr is introduced for combustion and icts 1 around the outer pcπphcrv of the lnicctor for the introduction of a peripheral curtain of fuel alone adiaccnt the inner wall for the purpose of film cooling of the inside surface 18 of the chamber The chamber comprises a mam body member 20 formed from a refractor) metal alloy and a liner 22 bonded to the inner surface 24 of the mam body The liner 22 comprises two principal elements, a first portion 28 of rhodium extending from adjacent the injector 12 through a parallel portion of the chamber to a region 30 at which the liner material changes to a second portion 32 comprising indium and which extends through the throat 34 of the chamber to the end of the divergent nozzle 36 In operation the temperature of the inner wall 18 rises from the injector end towards the nozzle 36 as represented schcmaticallv in Figure 2 The temperature of the inner wall is prev ented from becoming as hot as would otherwise have been the case by the action of the film cooling of the curtain of raw fuel prov ldcd through the injector jets 16 The fuel coolant decomposes under the action of the heat of the combusting bipropellant in the core of the chamber and at a region, indicated by the arrow at 40, a distance downstream of the injector 12. the decomposition species from the fuel begin to attack the iridium liners used in prior art thrust chambers In the present invention, the use of rhodium from at least the region 40 has been found to prev ent such attack of the surface The corrosiv e species generated bv the coolant fuel decomposition exist in the thrust chamber during operation until about shortlv before the region indicated at 30 where the joint between the first portion of rhodium and the second portion of indium occurs At this region the temperature has nsen significantly, as indicated in Figure 2, but the corrosive species from the decomposed fuel have themselves been combusted due to the higher temperature in this region In the absence of the corrosive species but under the influence of the higher temperature, the material of the liner from the region 30 downstream thereof changes to indium which has a greater temperature capability than rhodium In the embodiment described abov e, the first portion of the liner 22 comprises rhodium from adjacent the injector 12 to the region 30 In a second embodiment of the present inv ention the liner 22 is composed entirely of an alloy of rhodium and iridium from adiacent the injector 12 to the end of the nozzle 36 One alloy used with particular ad antage for the liner comprises 55wt% rhodium/ 45wt% iridium. The manufacturing procedure is substantially the same as that described with reference to Figure 1, except that the joint at the region 30 docs not exist. Alloys comprising rhodium and indium of the type described have sufficient resistance to attack by the decomposition species of the fuel coolant and adequate thermal resistance to the temperatures reached m use.

Claims: CLAIMS 1. A thrust chamber for a liquid propcllant rocket engine characterised in that at least the surface of the inner wall of the chamber is lined in a first zone with a material including rhodium and in a second zone, downstream of the first zone, with a material including iridium. 2. A thrust chamber according to claim 1 where the first zone extends from a position where in use the production of corrosive species formed by decomposition of a cooling layer of fuel injected along the surface of the thrust chamber begins to a position where the production of such corrosive species ends and the second zone extends downstream from the end of the first zone. 3. A thrust chamber according to claim 2 wherein the second zone extends beyond a nozzle throat located at the downstream end of the chamber. 4. A thrust chamber according to any one of the preceding claims wherein the first zone comprises substantially pure rhodium. 5. A thrust chamber according to any one of the preceding claims wherein the second zone comprises substantially pure iridium. 6. A thrust chamber according to any one of claims 1. 2 or 3 wherein the first and second zones comprise an alloy of rhodium and iridium. 7. A thrust chamber according to claim 6 wherein the alloy has a composition of from about 25wt% rhodium/ 75wt% iridium to about 75wt r ό rhodium/ 25wt iridium. 8. A thrust chamber according to claim 7 wherein the alloy composition lies in the range of from about 4()wt% rhodium/ 60wt% iridium to about 60wt% rhodium / 4()wi r o iridium. 9. A thrust chamber according to claim 8 wherein the alloy composition comprises about 55wt% rhodium and about 45wt% iridium. 10. A thrust chamber according to any one of the preceding claim wherein the said first and second zones arc in the form of a liner vvithin a suppoπing structural body forming the outer walls of the chamber. 11. A thrust chamber according to claim 10 wherein the structural body comprises a refractory metal or metal alloy 12. A thrust chamber substantially as hereinbefore described with reference to the accompanying description and Figure 1 of the drawings. 13. A bipropellant rocket engine having a thrust chamber substantially as hereinbefore described with reference to the accompanying description and Figure 1 of the drawings.

Inventors: WOOD ROBERT STEPHEN, WOOD, ROBERT, STEPHEN
Applicants: ROYAL ORDNANCE PLC, WOOD ROBERT STEPHEN, WOOD, ROBERT, STEPHEN
Application year: 1996
Main classification: F02K9
IPC codes: C22C5, F02K9