turbopump

Abstract

There is disclosed a turbopump for use in an engine, such as a reaction engine, the engine having an engine passage within which combustion of a propellant takes place so as to provide thrust (for example motive thrust), and having a cooling system to extract heat from the engine passage. The described turbopump comprises: a rotatable shaft; an impeller for pumping propellant from a propellant supply to the cooling system, and a turbine for being driven by propellant subsequently flowing from the cooling system to the engine passage for combustion, the impeller and the turbine being coupled to opposing ends of the shaft; an electrical machine disposed between the impeller and the turbine, the electrical machine comprising a rotor and a stator surrounding the rotor, the rotor forming part of the shaft so as to corotate with the impeller and the turbine, the electrical machine being controllable to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

Description

[0001] Turbopump

[0002] The present invention relates to a turbopump for use in an engine, for example a reaction engine such as a ramjet, scramjet or rocket engine, and to an engine or a reaction engine incorporating such a turbopump.

[0003] Introduction

[0004] Reaction engines, and especially reaction engines which do not use rotating compressors or turbines within the main engine passage where with the fuel and / or propellant(s) are combusted, such as ramjets, scramjets and rocket motors, require reliable pumping of the fuel and / or propellant(s) to avoid engine failure or unwanted reductions in performance. Improved fuel and / or propellant handling systems can also assist in providing reaction engines which are reusable between flights, and may assist in improved engine efficiency and other factors.

[0005] Improved fuel and / or propellant handling systems can also assist in providing similar benefits in engines which may not necessarily be considered to be reaction engines, for example for use in power generation sets for industrial, military, domestic and other uses, whether in ocean going vessels, aircraft, land vehicles, fixed installations or various other scenarios.

[0006] Summary of the invention

[0007] We describe improved methods and apparatus for propellant (or fuel) delivery within engines such as reaction engines, propulsion systems, or other power generation equipment. These methods and apparatus are especially applicable within such engines which operate without rotating turbomachinery within the combustion chamber, or more broadly without rotating turbomachinery within an engine passage which includes the combustion chamber.

[0008] One particular application is to provide improved methods and apparatus for delivering propellant into ramjet and scramjet combustion chambers from one or more onboard tanks, without requiring storage of the propellant in those tanks at high pressures which would increase their structural mass. However, the described methods and apparatus can also be used to provide propellant delivery within rocket engines and other types of reaction engine, as well as within other types of engine.

[0009] More particularly, we describe a hybrid electric turbopump unit for pumping a propellant within an engine such as a reaction engine, and for being driven by regenerative

[0010] 17281426.JRP.JRP heat exchange of the propellant heated by the engine, the unit comprising a common shaft carrying both an impeller and a turbine at opposite ends of the shaft, and an electrical machine disposed between the impeller and the turbine for both extracting and inputting electrical power. The turbopump unit may further contain internal fluid channels used both for active cooling of the electrical machine including the rotor and stator, and also for feeding into fluid bearings (for example hydrostatic, hydrodynamic, or foil type fluid bearings) to support the shaft when operating at speed. The turbopump unit may be fully enclosed such that neither the shaft nor any associated rotating components protrude from the unit, thereby avoiding the requirement for rotary, dynamic, or shaft seals. The rotor of the electric machine may also be submerged in the propellant being pumped by the turbopump unit.

[0011] This hybrid electric turbopump unit may be used in a scramjet, ramjet, rocket engine, or other engine type cycle, with a cooling system providing regenerative cooling of a combustion chamber and / or other parts of the main engine passage such as the combustion chamber and / or intake and nozzle regions. In this cycle the pump output is fed into the inlet of cooling channels in the cooling system, and the output of this is then partly or wholly fed into the turbine side of the hybrid electric turbopump. The output after the turbine of the hybrid electric turbopump is then fed to one or more propellant injectors of the combustion chamber.

[0012] To this end, the invention provides an integrated hybrid electric turbopump unit with a rotor submerged fully in the propellant being pumped, the propellant being used as a feed for fluid bearings integrated into the casing of the turbopump unit, and also being used in cooling channels integrated into the unit which connect internally to the fluid bearings so as to improve cooling of the electrical machine and therefore the available electrical power density. The unit is also fully enclosed in the sense that there is no need for any rotary or dynamic shaft seals, since both impeller and turbine of the unit are combined into the same turbopump unit casing.

[0013] In more detail, the propellant flow from downstream of the impeller may be used to feed propellant to the fluid bearing supporting the shaft closest to the impeller, and then from this fluid bearing going both towards the back-face of the impeller, also providing cooling and lubrication for a rolling element bearing on the way, where it is pumped by the back-face of the impeller to match the pressure conditions at the impeller outlet, and also flowing through a gap between the rotor and stator of the electrical machine providing active cooling there. The propellant flow from downstream of the impeller may also be used to feed a fluid bearing supporting the shaft closest to the turbine, where this fluid then joins

[0014] 17281426.JRP.JRP the fluid that went through the gap between the rotor and stator and flows towards the back-face of the turbine, along the way also providing cooling and lubrication for another rolling element bearing. This propellant flow is then pumped by the turbine back-face up to match the pressure conditions at the turbine inlet, before making its way to the turbine output.

[0015] Advantages and benefits of the described arrangements include that: they can reduce or eliminate need for heavy, range limiting, high power output batteries to drive the pump system of a reaction engine such as a ramjet or scramjet, or other engine type; they can enable more precise control speed of the pump than is possible with a purely mechanical turbopump lacking the described electrical machine arrangements; they can use electrical power for engine startup, avoiding need to provide startup relying on propellant tank pressure or head; the lack of rotary, dynamic or shaft seals and use of fluid bearings simplifies mechanical assembly and leads to a high lifetime expected even when operating at high rotational speeds, resulting in longer flight ranges and / or more repeat flights of the vehicle; power can be generated in use or in flight for various other purposes such as to drive an oxidiser pump (especially in rocket engine applications), or other pumps or onboard systems in ramjet / scramjet applications, for example to power or control aerodynamic control surfaces, pumps for oil / lubricant, oxidiser pump in a multi-mode propulsion system and so forth.

[0016] More particularly, the invention provides a turbopump for use in an engine, or more particularly for use in a reaction engine (such as a ramjet, scramjet or rocket engine), where the engine or reaction engine has an engine passage within which combustion of a propellant takes place so as to provide motive or other thrust of the engine or reaction engine, and has a cooling system to extract heat from the engine passage. The cooling system may for example extract heat from one or more of a combustion chamber, air intake and nozzle region of the engine or reaction engine.

[0017] The turbopump then comprises: a rotatable shaft; an impeller for pumping propellant from a propellant supply to the cooling system, and a turbine for being driven by heated propellant subsequently flowing from the cooling system to the engine passage for combustion, the impeller and the turbine being coupled to opposing ends of the shaft; an electrical machine disposed between the impeller and the turbine, the electrical machine comprising a rotor and a stator surrounding the rotor, the rotor forming part of the shaft so as to corotate with the impeller and the turbine, the electrical machine being controllable to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

[0018] 17281426.JRP.JRP If the reaction engine is a scramjet or ramjet then the propellant may be described as a fuel which is combusted with air received at an air intake of the engine passage. If the reaction engine is a rocket engine then the propellant handled by the turbopump could be a fuel or an oxidiser for example. Generally, the propellant may be a cryogenic propellant such as liquid hydrogen, liquid methane, liquid oxygen and so forth, but non-cryogenic propellants may also or instead be used. If the propellant is a first propellant, and the rocket engine further comprises an additional impeller (typically separate to the main turbopump unit) to pump a second propellant to the combustion chamber for combustion with the first propellant, then the additional impeller may be at least partly driven using electrical power generated by the electrical machine of the turbopump, typically controllably supplied to the additional impeller as required.

[0019] The turbopump may comprise a first set of bearings supporting the shaft proximally to the impeller or towards the impeller end of the shaft, and a second set of bearings supporting the shaft proximally to the turbine or towards the turbine end of the shaft, and the turbopump may then be arranged so that portions of the propellant which are being pumped by or from the impeller, or more particularly by the impeller from the propellant supply, towards the cooling system, are redirected to, and more particularly into or through each of the first and second sets of bearings.

[0020] For example, the proportion of propellant being pumped by or from the impeller, or more particularly by the impeller from the propellant supply, towards the cooling system that is redirected in this way may be about from 1% to 25% or more preferably from about 5% to 20%.

[0021] In being redirected to, or more particularly into or through each of the first and second sets of bearings, the redirected portions of the propellent supply may perform one or more different roles within the bearings of each set of bearings, including providing a working fluid (especially for one or more bearing which are fluid bearings), a lubricant (especially for one or more bearings which are roller element or another type of mechanical bearing), and / or a coolant. Having passed through each bearing and / or each set of bearings to perform such roles, the redirected portions of the propellant supply may be directed onto various other parts of the turbopump as described below, and will not typically be fed directly back into the propellent flow from the impeller towards the cooling system, although that remains an option in some embodiments.

[0022] Additionally or alternatively, the turbopump may be constructed so that a first portion of the propellant which is pumped by or from the impeller, or more particularly by the impeller from the propellant supply, towards the cooling system, is redirected for use in

[0023] 17281426.JRP.JRP cooling the rotor and an adjacent portion of the stator by being passed between the rotor and the stator, and / or so that a second portion of this redirected propellant is used to cool a periphery of the stator, for example being passed through a stator cooling jacket or other stator peripheral cooling arrangement.

[0024] The use of redirected propellant at the sets of bearings (and particularly to pass through the bearings), and to provide cooling of the electrical machine, can be combined in various ways, for example as discussed below.

[0025] For example, the first and second sets of bearings may be constructed in various ways and may each include various combinations of one or more bearing types, but in some examples first set of bearings comprises a first fluid bearing, and a first rolling element or other mechanical bearing located between the first fluid bearing and the impeller. The portion (a) of the propellant redirected to / through the first set of bearings may then first be used as a working fluid to support the first fluid bearing, and may then be split into a flow from the first fluid bearing (i) through a gap between the rotor and the stator to / through the second set of bearings (thereby providing cooling of these components), and (ii) a flow from the first fluid bearing to / through the first rolling element bearing back to the impeller, for example providing lubrication and cooling of that first rolling element bearing.

[0026] The impeller may then comprise both an impeller main pumping surface, or front face, arranged to pump the propellant from the propellant supply towards the cooling system through an outlet volute of the impeller, and also an impeller secondary pumping surface which is typically (but not necessarily) on an opposite side of the impeller to the main or front face so may conveniently be described herein as an impeller back face. The turbopump is then arranged such that the flow of the propellant is directed from the first set of rolling element bearings to the impeller secondary pumping surface or back face which is arranged to pump the received propellant to the outlet volute of the impeller. For example, the impeller secondary pumping surface or back face may comprise one or more ridges or other structural features for assisting in this pumping action.

[0027] The turbopump may also comprise the above mentioned stator cooling jacket or other stator cooling arrangement arranged to cool the stator and especially an external or peripheral region of the stator, and the portion (b) of the propellant redirected to / through the second set of bearings may then be first passed through the stator cooling jacket for cooling an exterior or periphery of the stator before arriving at the second set of bearings.

[0028] Similar to the first set of bearings, the second set of bearings may comprise a second fluid bearing, and a second rolling element or other mechanical bearing, and the

[0029] 17281426.JRP.JRP portion of the propellant redirected to / through the second set of bearings may then first be used as a working fluid to support the second fluid bearing, before being directed on to / through the second rolling element bearing, and then from the second rolling element bearing to the turbine.

[0030] The flow of propellant (i) through the gap between the rotor and the stator as described above may also be directed through the second fluid bearing, typically axially between the opposing faces of the bearing rather than being injected radially through ports for supporting the bearing, and then through the second rolling element bearing to the turbine. However, in some embodiments, this flow of propellant could instead be injected radially into the second fluid bearing along with the flow from the stator jacket to function as a working fluid supporting the bearing, or could largely be directed around the second fluid bearing to bypass the second fluid bearing altogether.

[0031] The turbine may comprise a turbine main face or front face for being driven by propellant flowing from the cooling system to the engine passage for combustion, and a turbine pumping face which is typically (but not necessarily) on an opposite side of the turbine to the main or front face, so may conveniently be described herein as a turbine back face, the turbopump then being arranged to direct the flow of propellant from the second set of rolling element bearings to the turbine pumping face or back face which is arranged to pump the received propellant to the inlet volute of the turbine. Similar to the back face or secondary pumping face of the impeller, the back face or pumping face of the turbine may comprise one or more ridges or other structural features for assisting in this pumping action.

[0032] The described turbopump may be arranged such that, in operation, the periphery of the rotor, and in particular portions of the rotor periphery in confrontation with the stator, are immersed in the propellant to assist in cooling the rotor and also cooling of the stator.

[0033] The rotor may be formed of a cylinder or core of one or more magnetic materials (that is, materials with suitable magnetic properties) such as various ferromagnetic materials if the electrical machine is to operate on an inductive basis, or permanent magnetic materials if the electrical machine is to operate on a synchronous basis, and an external structural sheath surrounding the core, without an additional structural shaft passing through the core or along the rotational axis of the rotor. This simplifies construction and allows more of the core magnetic material to be included in the rotor. The rotor core could for example be made of or comprise a PrFeB material, and the sheath could be made for example from an Inconel or Titanium material. Although the rotor itself is

[0034] 17281426.JRP.JRP preferably be solid, portions of the shaft extending from the rotor towards the impeller and / or turbine may be hollow.

[0035] The stator may be constructed using conductors located in slots within a stator body, the slots typically extending radially out from a central aperture extending axially along the centre of the stator. The conductors may then be electrically connected to each other using hairpin structures extending from, or out of, the ends of the stator body, optionally wherein the hairpin structures are additively manufactured using a 3D printing or similar technique. The stator may for example comprise between five and ten conductors arranged radially with respect to each other within each slot. Each conductor may be at least twice as wide azimuthally as it is thick radially, relative to a central axis of the stator, so as to improve electrical efficiency at high rotational speeds.

[0036] One or more of the innermost conductors in each slot, for example the first one, two or three conductions in a radial direction starting from closest to the central aperture, may comprise at least two radially stacked sub conductors which are insulated from each other within the slot, but electrically connected to each other externally to the slot. This helps reduce eddy currents within these conductors, again so as to improve electrical efficiency at high rotational speeds.

[0037] A stator liner may be provided at the inner circumference of the stator, for example extending along and covering the entire inner surface of the stator in confrontation with the rotor, so to provide the stator with protection against propellant flowing between the rotor and the stator. Such a stator liner may be formed of a fluoropolymer or other flexible, chemical inert material.

[0038] In order to provide an effective seal to the propellant flowing between the rotor and stator, the stator liner may comprise an outwardly extending radial flange at the end of the stator furthest from the connection or phase leads emerging from the stator, and / or at the end closest to the turbine, and the radial flange of the stator liner may then pressed against an internal wall of a casing of the turbopump by the stator assembly. However, to further improve seal of the stator liner under especially conditions of thermal expansion / contraction under large temperature changes, a compression plate may be located between the stator and the radial flange of the stator liner, and one or more compression springs may then be provided on the stator side of the compression plate to urge the compression plate against the radial flange of the stator liner so as to press the radial flange against the internal wall of the casing.

[0039] Comparable arrangements may also be made at the end of the stator where the connection or phase leads emerge from the stator, which will typically be at the impeller

[0040] 17281426.JRP.JRP end of the stator, to ensure a good seal to the propellant. For example, the stator liner may comprise a conical flange (expanding away from the stator) at the end of the stator closest to the connection leads or impeller, and the conical flange may then be compressed between a threaded compression seat of the stator and a bevelled compression ring urged against the conical flange by a threaded compression plug screwed into the compression seat.

[0041] The described turbopump may also comprise an electrical subsystem arranged to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft, and may further comprise a battery arranged to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft. The electrical subsystem may for example comprise a DC bus and an inverter arranged to couple power between the typically AC electrical machine and the DC bus. In some examples, one or more of these electrical elements may be considered to be part of the wider engine or reaction engine instead of as part of the turbopump.

[0042] The invention also provides an engine, or more particularly a reaction engine, incorporating the described turbopump, the engine or reaction engine comprising: a propellant supply arranged to supply a propellant; an engine passage within which combustion of or using the propellent takes place so as to provide thrust of the engine, or more particularly motive thrust of the reaction engine; a cooling system arranged to receive heat from the engine passage; and the turbopump as described above, wherein the impeller of the turbopump is arranged to pump propellant from the propellant supply to the cooling system, and the turbine is arranged to be driven by the pumped propellant subsequently flowing from the cooling system to the engine passage for combustion.

[0043] Such an engine or reaction engine may also comprise various propellant control valves such as a turbine bypass valve arranged to controllably permit a bypass flow of the propellant from the cooling system to the combustion chamber, where this bypass flow does not flow through the turbine. This permits control of the engine or reaction engine to include reducing flow of propellant to the turbine and therefore also to reduce the mechanical power delivered to the impeller and to reduce the amount of excess electrical power generated by the electrical machine of the turbopump when required.

[0044] The turbopump may comprise a casing within which the impeller, turbine and shaft are housed, and the rotation of the impeller, turbine and shaft may then be retained entirely within the casing so that no rotational seals are required to transmit mechanical rotation of the shaft into or out of the casing.

[0045] 17281426.JRP.JRP The invention also provides methods of manufacturing or making, and methods of operating the described turbopump and / or engine or reaction engine. For example, the invention provides a method of operating a turbopump within an engine or reaction engine having an engine passage within which combustion of a propellant takes place so as to provide thrust of the engine or motive thrust of the reaction engine, and having a cooling system to extract heat from the engine passage, the method comprising: using an impeller on a rotating shaft to pump propellant from a propellant supply to the cooling system, and driving a turbine on the same shaft using propellant subsequently flowing from the cooling system to the engine passage for combustion, the impeller and the turbine being coupled to opposing ends of the shaft; and using an electrical machine, disposed between the impeller and the turbine and comprising a rotor forming part of the shaft and a stator surrounding the rotor, to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

[0046] The turbopump may further comprise a first set of bearings supporting the shaft proximally to the impeller and a second set of bearings supporting the shaft proximally to the turbine, and the method may then further comprise redirecting portions of the propellant being pumped from the impeller towards the cooling system to / through each of the first and second sets of bearings.

[0047] The turbopump may further comprise a stator cooling jacket or other peripheral stator cooling arrangement and a gap between the rotor and the stator, the method further comprising using the redirected portions of the propellant through the stator cooling jacket and a gap between the rotor and the stator to provide cooling of the electrical machine.

[0048] The method may further comprise using a turbine bypass valve to controllably permit a bypass flow of the propellant from the cooling system to the combustion chamber avoiding the turbine, to thereby provide power balancing or throttling of the engine or reaction engine.

[0049] Brief summary of the drawings

[0050] Embodiments of the invention will now be described, by way of example only, and with reference to the drawings of which:

[0051] Figure 1 illustrates schematically an engine, or more particularly a reaction engine, in which a propellant is pumped by the impeller of a turbopump unit to a cooling unit for regenerative cooling of an engine passage, before the heated propellant is used to drive a

[0052] 17281426.JRP.JRP turbine of the turbopump before being delivered to a combustion chamber of the engine or reaction engine for combustion;

[0053] Figure 2 shows in cross section how the turbopump unit of figure 1 may be implemented in more detail;

[0054] Figure 3 shows in perspective view, and figure 4 in cross section, an example of how the stator of figures 1 and 2 may be implemented; and

[0055] Figures 5 and 6 show in cross sectional view how the stator of the previous figures may be protected from the propellant flowing between the rotor and stator using a stator liner which can be sealed in various ways.

[0056] Detailed description of embodiments

[0057] Referring now to figure 1 there is shown schematically a turbopump 10 forming part of an engine 20 having an engine passage 22 within which combustion of a fuel takes place so as to provide thrust of the engine. Although the described embodiments are applicable for use in a variety of engine types for example including for power generation in static installations, power generation on various vehicle or vessel types, or in other applications, in the text below the embodiments are primarily described as used in, or suitable for use in a reaction engine such as a scramjet, ramjet, or rocket engine, so as to provide motive thrust of such a the reaction engine 20. Moreover, embodiments of the invention particularly apply to engines and reaction engines which do not use any rotating turbomachinery within the engine passage itself such as rotary compressor and turbine elements.

[0058] The turbopump is arranged to pump a propellant from a propellant source 36 to a combustion chamber 24 of the engine passage 22 for use in combustion there. Products of the combustion are then typically delivered to a nozzle region 26 of the engine passage so as to provide thrust. In embodiments where the reaction engine 20 is a scramjet, ramjet or of another air breathing design, air is typically delivered to the combustion chamber 24 via an inlet region 28 of the engine passage. In other embodiments where the reaction engine 20 is a rocket engine or similar, there may be no such air inlet region.

[0059] A large amount of heat is generated within the engine passage 22 during operation of the reaction engine 20, and so as depicted in figure 1 a cooling system 30 is provided to remove some of this heat from one or more of the inlet region 28, combustion chamber 24 and nozzle region 26, depending on the design of the reaction engine. Most typically the cooling system will at least be arranged to remove heat from walls of the combustion chamber 24, but frequently also from walls of the nozzle region 26. If the reaction engine is

[0060] 17281426.JRP.JRP an air breathing engine, then a significant amount of heat may also be generated at the inlet region 28, so the cooling system 30 may also or instead be arranged to remove heat from this inlet region 28 and to this end the cooling system 30 may in some examples comprise a regenerative heat exchanger located within the engine passage 22 itself, for example within the inlet region 28.

[0061] The cooling system 30 comprises suitable channels proximal to and / or within one or more of the combustion chamber 24, inlet region 28 and nozzle region 26, for example within walls of one or more of these regions, and a impeller 32 of the turbopump 10 is used to drive a flow of the propellant through these channels, in which the propellant is heated. The resulting increase in enthalpy of the propellant is then in turn used to drive a turbine 34 of the turbopump 10.

[0062] The turbopump 10 and cooling system 30 are thereby arranged to work together to form a regenerative cooling system in which heat generated at the engine passage 22 can be used to drive the turbopump to pump the propellant at a sufficiently high pressure to the combustion chamber 24. However, as discussed below, the described turbopump and associated electrical subsystem 50 as depicted in figure 1 are additionally arranged to selectively either deliver additional electrical power to the turbopump to support pumping of the propellant to the combustion chamber, or to receive and optionally also store excess electrical power generated by the turbopump through the increase in enthalpy provided by heating of the propellant by the cooling system 30.

[0063] In some embodiments the propellant pumped by and driving the turbopump 10 may be a low temperature or cryogenic fuel such as liquid hydrogen or liquid methane, or a low temperature or cryogenic oxidant such as liquid oxygen. However, other propellants and combinations of propellants may be used with just one such example being kerosene. Moreover, the propellant may be in a variety of different thermodynamic states, for example including gas, vapour and / or supercritical fluid states especially at the turbine inlet following heating within the cooling system.

[0064] As also shown in figure 1 , the reaction engine 20 may typically comprise a turbine bypass valve 16 controllably allowing propellant to bypass the turbine 34 and pass directly from the cooling system 30 to the combustion chamber 24. This valve allows control of the amount of mechanical power the turbine generates, and therefore also to throttle up / down the overall propellant flow without otherwise needing to extract excess mechanical power using the electrical machine 40 discussed below, and therefore also makes implementing electrical aspects of the engine described below more straightforward. The reaction engine 20 may also comprise a main propellant valve 18 as illustrated in figure 1 .

[0065] 17281426.JRP.JRP If the reaction engine 20 is a rocket engine requiring two propellants, then a first of the propellants may be handled and pumped by the turbopump unit 10 of figure 1 , and additional components may be provided within the reaction engine to handle the second propellant. These additional components may comprise a second pump or impeller, (preferably not forming part of and being separate from the main turbopump unit 10), which is arranged to receive the second propellant from a second propellant source and to pump it via a second propellant valve to the combustion chamber 24. In some such embodiments of the invention, the second impeller is driven using electrical power provided by the electrical subsystem 50 and / or batteries 54 discussed below, and so this electrical power may be controllably delivered via these electrical components having first been generated at least in part using the main turbopump 10. Typically, the first propellant may be a fuel and the second propellant an oxidiser, for example a cryogenic fuel and oxidiser such as liquid hydrogen or methane and liquid oxygen, although other propellant combinations may of course be used.

[0066] In more detail, the illustrated turbopump 10 comprises a rotating or rotatable shaft 29, and an impeller 32 and a turbine 34 mounted on opposite ends of the shaft 29 so as to corotate with the shaft. Rotation of the shaft 29 then drives rotation of the impeller 32 which receives propellant from a propellant source 36 such as a tank, and pumps the propellant out of an outlet volute 33 of the impeller, from there to and through the cooling system 30, and from there on to the turbine 34 via an inlet volute 35 of the turbine. Heating of the propellant in the cooling system 30 leads to an increase in enthalpy of the propellant which therefore drives rotation of the turbine 34. Propellant leaving the turbine 34 is then delivered to the combustion chamber 24.

[0067] The turbopump 10 also comprises an electrical machine 40 disposed between the impeller 32 and the turbine 34. The electrical machine 40 comprises a rotor 42, and a stator 44 surrounding the rotor. The rotor forms part of the shaft so as to corotate with both the impeller and the turbine. In practice the rotor may be provided by one or more components added to a main shaft element, or more typically may be provided using a central core or body of material with suitable magnetic properties such as permanent or ferromagnetic material depending on whether the electrical machine is to operate on inductive or synchronous principles, surrounded by a structural sheath of a metal or alloy such as Inconel or Titanium. The electrical machine 40 may in particular be implemented using a permanent magnet synchronous machine architecture, so as to maximise power density.

[0068] Although the rotor core will preferably be solid with no axial aperture, the shaft 29 extending from the rotor in the directions of the impeller and turbine may be hollow as

[0069] 17281426.JRP.JRP depicted in figure 2 and as discussed below, thereby reducing both overall weight and angular inertia. The rotatable shaft 29 is supported on a first set of bearings 38 at the impeller end of the shaft and a second set of bearings 39 at the turbine end of the shaft. Each such set of bearings may comprise one or more distinct types of bearings, such as one or more of fluid bearings (for example hydrostatic or hydrodynamic bearings), mechanical bearings (such as rolling element bearings, or journal bearings), magnetic bearings, and so forth.

[0070] In some particular embodiments such as that of figure 2 each set of bearings comprises a fluid bearing closer to the centre of the shaft, and a rolling element bearing closer to the local end of the shaft. If rolling element bearings are used as discussed in more detail below, these are preferably of unsealed assembly, so that propellant flows can then be used as described to improve cooling and lubrication of the rolling element bearings. Self-lubricating bearing cages, typically comprising a fluoropolymer, may also be used to form lubricating films on the bearing rolling surfaces.

[0071] If rolling element bearings are paired with sufficiently stiff fluid bearings, the load taken by the mechanical elements of the rolling element bearings is reduced, noting that bearing lifetime tends to increase as a roughly inverse cubic function of load. Rolling element bearings provide stiffness through mechanical stress while producing minimal contact friction between stationary and rotating surfaces. However rolling element bearings may require cooling, and lubrication (which if implemented using propellant flows as discussed below leads to propellant pressure drops which need to be budgeted in the fluid flow design), and are made of physically moving parts which makes them vulnerable to damage. Fluid bearings provide stiffness through variations in working fluid pressure that result from shaft perturbations. These rely on working fluid pressure drop which needs to be budgeted.

[0072] The fluid bearings if used may be of various types including hydrodynamic, hydrostatic and hydrofoil types. Hydrodynamic bearings rely on fluid viscosity causing pressure differences at high rotation speeds. Hydrostatic bearings rely on fluid pressure drops across thin channels between cavities. Hydrofoil bearings rely on the hydrodynamic effect around solid thin films suspended in the flow near a rotating shaft. Any of these, or any combination of these, may be used as fluid bearings in embodiments of the present invention to support the shaft, which in the described embodiments is suspended in the propellant which may be a cryogenic fluid.

[0073] The reaction engine 20 of figure 1 also comprises an electrical subsystem 50 which is electrically coupled to the stator 44 and arranged to selectively either deliver electrical

[0074] 17281426.JRP.JRP power to electrical machine 40 so as to drive rotation of the shaft 29, or to receive electrical power from the electrical machine 40 which can then be described as electrical power generated by rotation of the shaft. If driving rotation of the shaft, this may be supplemental to torque already being provided by the turbine, or could sometimes be the sole source of torque for example when the reaction engine is starting up.

[0075] Whether the electrical subsystem operates to receive electrical power from, or deliver electrical power to, the electrical machine 40, may be automatically controlled by a control system 52 of the reaction engine 20, for example depending on a current operational mode or current operating conditions of the reaction engine as monitored, controlled or sensed by that control system 52. In particular, during some operating conditions such as during startup or increasing engine thrust from a low level, electrical power may be required to supplement the turbine in driving the impeller 32 to provide sufficient propellant pressure and flow, while during some other operating conditions, such as during periods of moderate to high thrust, the turbine 34 may generate sufficient torque to both drive the impeller and to generated excess electrical power which can be extracted by the electrical subsystem 50.

[0076] The electrical subsystem 50 may also be electrically connected to one or more batteries 54 for storing electrical power received from the electrical machine 40 for future use, and for delivering stored electrical power to the electrical machine when needed, under control of the control system 52 as outlined above.

[0077] The control system 52 may, for example, set targets for rotation speed of the shaft 29 and position for the turbine bypass valve 16 based on mission parameters and forecasts of load parameters such as thrust, mass flow rate and excess power requirements, in order to run the turbopump at operating points that produce the desired shaft speed and engine thrust as well as producing the power needed for operation of the reaction engine or indeed vehicle in which the engine is installed based on wider system demand. Within this context, the turbine bypass valve 16 may be actuated primarily by feed forward control, for example by anticipating changes in system demand such as variations in turbopump pumping requirements and other expected power draw, and adjusting the valve accordingly, as well as using feedback control to account for other real-time variations in conditions.

[0078] The electrical machine 40 may utilise field orientated control for regulation of shaft speed and torque. For dynamic power flow, the control system 52 may tolerate brief increases / decreases in DC bus voltage if an inverter is used within the electrical subsystem 40 to connect the AC of the electrical machine 40 to a DC bus, using inherent capacitance within the inverter as a buffer, as well as transiently speeding up / slowing down of the

[0079] 17281426.JRP.JRP shaft. However, the battery 54, which will typically be connected to the same DC bus, can also be used for slower transients, smoothing out fluctuations and preventing over / under voltage conditions on the DC bus. A braking resistor can also or instead be used to dissipate excess electrical energy when needed.

[0080] In addition to the impeller pumping propellant from the propellant supply 36 to the cooling system 30 and on via the turbine 34 to the combustion chamber 24, various flows of the propellant may be used to assist in the operation of the turbopump 10 in other ways. For example, flow of the propellant may be used to provide cooling of the electrical machine 40 and therefore permit higher electrical powers to be used, for example by fully submerging the rotor within flow of the propellant, and / or by using flow of the propellant to also cool the stator distally from the rotor. Flow of the propellant may also be used as the working fluid used to provide the required support in fluid bearings if included in either or both of the first and second sets of bearings 38, 39, and to provide cooling and lubrication of mechanical or rolling element bearings if included in either or both of the first and second sets of bearings 38, 39.

[0081] Some aspects of these uses of the propellant within the operation of the turbopump are illustrated in figure 1 , and more detailed implementation options are illustrated in figure 2. In figure 1 then, it can be seen that portions of the propellant being pumped from the impeller 32 to the cooling system 30 are redirected to (and through) each of the first and second bearings, and both through the gap 45 between the rotor and stator and through a stator cooling jacket 46 or other peripheral stator cooling arrangement.

[0082] This is achieved by directing a first portion (a) of the redirected propellent to (and through) the first set of bearings 38 where this portion supports operation of those bearings and is split into a flow in one direction through the gap between the rotor and stator to arrive at (and pass through) the second set of bearings, and a flow in the opposite direction to arrive back at the impeller 32 to rejoin the flow of propellant being pumped towards the cooling system.

[0083] A second portion (b) of the redirected propellant is directed through the stator cooling jacket 46 to also arrive at (and pass through) the second set of bearings, where the two portions (a) and (b) together support operation of those bearings before arriving at the turbine 34 where they join the flow of propellant flowing from the cooling system to the engine passage.

[0084] In figure 1 , the broken line surrounding components of the turbopump 10 may be considered to represent a casing of the turbopump. Notably the, the shaft 29 and associated rotating components including the impeller 32 and turbine 24 are contained

[0085] 17281426.JRP.JRP entirely within the casing, and no corresponding rotation needs to be transmitted to outside of the casing, meaning that no rotational seals are required in the casing wall leading to a more reliable turbopump which is also easier to construct and maintain.

[0086] Ways in which the turbopump 10 of figure 1 can be constructed and operated in more detail are illustrated in figure 2, where like reference numerals are used for corresponding features between the figures. In figure 2 the external casing of the turbopump is generally indicated by reference number 1 1 and contains within it the stator and rotor of the electrical machine, the bearing described below, the impeller and the turbine, so that the only functional connections needed through the casing are for propellant flows and electrical connections, with no mechanical seals such as rotational seals being needed.

[0087] In figure 2 it can be seen that the first set of bearings 38 which is at the impeller end of the shaft 29 comprises a first fluid bearing 38-1 located further from the impeller 32 and a first rolling element bearing 38-2 closer to the impeller 32. Similarly, the second set of bearings 39 which is at the turbine end of the shaft 29 comprises a second fluid bearing 39- 1 located further from the turbine 34 and a second rolling element bearing 39-2 closer to the turbine 34. Propellant entering the impeller from the propellant supply and being pumped towards the cooling system by the impeller is shown as solid black arrows.

[0088] A modest proportion of the propellant exiting the impeller 32 through the outlet volute 33 and being pumped towards the cooling element 30, say from about 5 to 20% or from about 1 to 25% of this flow, is redirected as a first portion (a) shown as broken arrows in figure 2, and a second portion (b) shown as fine arrows, both through suitable conduits as shown in the figure, for use in supporting operation of the bearings and providing other cooling functions as discussed in more detail below. These conduits may take the redirected flows directly from the volute itself, or from any point further downstream before the flow reaches the cooling unit.

[0089] The first portion (a) is directed to (and through) the first fluid bearing 38-1 where it provides the working fluid to support this bearing by being injected through injection ports or capillaries into the space between opposing surfaces of the bearing. Following this use in the first fluid bearing 38-1 the propellant flow is split in opposite directions out of the space between the opposing fluid bearing surfaces into a forward flow from the first fluid bearing which passes along the cylindrical gap 45 between the rotor 42 and the stator 44 so as to arrive at (and pass through) the second set of bearings, and into a backward flow from the first fluid bearing 38-1 through the first rolling element bearing 38-2 as to arrive at the impeller 32. These split flows of the first portion (a) thereby provide functions of cooling

[0090] 17281426.JRP.JRP the rotor and stator while passing through the gap 45, and of cooling and / or lubricating the first rolling element bearing 38-2.

[0091] The impeller comprises both a front face 32-1 which is arranged to pump the propellant from the propellant supply to the cooling system 30, and a back face 32-2. The back face 32-2 functions to pump the propellant flow received through the first rolling element bearing 38-2 back to the output volute 33 of the impeller 32 to rejoin the pumped flow in the direction of the cooling system.

[0092] The second portion (b) of propellant redirected from the flow pumped by the impeller towards the cooling system, shown in figure 2 using broken arrows, is injected into the stator cooling jacket 46 which is arranged to cool the stator 44, for example to cool an exterior portion of the stator. Although in figure 2 the stator cooling jacket 46 comprises one or more channels running in an axial direction of the turbopump along the outside of an exterior portion of the stator, a wide range of other configurations may be used. For helical or labyrinthine channels may be used, or the channels may be defined by a lattice, a gyroid pattern, or similar. Use of lattice or gyroid patterns may for example provide better thermal hydraulic efficiency of heat transfer, in providing a greater surface area for heat transfer for a given level of resistance to the flow. The channels of the cooling jacket structure may be located entirely at the peripheral surface of the stator, or at least some channel structure may be recessed into or embedded within the stator. In some examples, the cooling jacket channels are formed using additive manufacture, in particular if a lattice or gyroid channel structure is used..

[0093] Following passing through the cooling jacket, the second portion (b) of the flow is then directed to the second fluid bearing 39-1 where it is injected through injection ports or capillaries into the space between opposing bearing surfaces to provide the working fluid to support this bearing before being passed on to (and through) the second rolling element bearings 39-2 providing lubrication and cooling of those bearings to arrive at the turbine.

[0094] Notably, the second fluid bearing 39-1 and in particular the propellant injection into the space between the opposing bearing surfaces, may be designed so that the propellant feed enters the bearing both by injection radially from the side in a conventional manner, and axially from the upstream end, which is a departure from standard analytical theory on such bearings. This is desirable in the present case to permit flow of the first portion (a) of propellant from the gap between the rotor and stator to pass axially along the length of the fluid bearing between the opposing bearing surfaces, thereby mixing with the flow injected radially into the second fluid bearing from the stator jacket, and proceeding as a combined flow on to the second rolling element bearing 39-2.

[0095] 17281426.JRP.JRP To this end, the forward flow part of the first portion (a) which has passed through the gap between the rotor and stator may be combined with the second portion (b) of redirected flow within the second fluid bearing itself, for example with the forward flow part of the first portion (a) entering the space between the opposing bearing surfaces at the end distal from the turbine and flowing axially along the space to merge with the radially injected flow. Alternatively, some or most of the forward flow part of the first portion (a) could be combined with the second portion (b) downstream of the second fluid bearing.

[0096] The flow of propellant combining the forward flow part of the first portion (a) and the whole of the second portion (b), which together are shown as heavy arrows in figure 2, then passes through the second rolling element bearing before arriving at the turbine. The turbine comprises both a front face 34-1 which is arranged to be driven by the flow of propellant from the cooling system to the combustion chamber, and a back face 34-2. The back face 34-2 functions to pump the propellant flow received through the second rolling element bearing 39-2 to the input volute 35 of the turbine to join the propellant flow from the cooling system to the combustion chamber which is depicted in figure 2 using solid black arrows.

[0097] The above pumping actions of the back faces 32-2, 34-2 of each of the impeller and turbine raise the static pressure of the propellant at those locations to ensure that the flow matches the pressure of the associated volute immediately downstream of the relevant back face. These pumping actions can be achieved using flat or smoothly curved back faces, but features such as ridges, channels, vanes or similar may be used to enhance the pumping action if required. Typically the back face of the impeller may be arranged to raise the pressure of the propellant by around 5000 to 10000 kPa between leaving the first rolling element bearing and arriving at the outlet volute 33 of the impeller, and the back face of the turbine 34 may be arranged to raise the pressure of the propellant by around 2000 to 4000 kPa between leaving the second rolling element bearing and arriving at the inlet volute 35 of the turbine 34. Mass flow rates of the propellant each of these pumping mechanisms may for example be around 0.05 to 0.5 kg / s depending on detailed design requirements and operating conditions.

[0098] The impeller 32 and turbine 34 are preferably both of a radial type (although could instead either or both be of axial type) with the overall direction of propellant flow being radial to the shaft. Either or both of the impeller and turbine can also be shrouded to reduce volumetric losses, by enclosing vanes of the impeller or turbine (and in particular of the respective front faces, but optionally also the back faces) in a casing or cover which rotates with the respective impeller or turbine. Either or both of the impeller and turbine maybe

[0099] 17281426.JRP.JRP made additively, in which case the impeller or turbine may be constructed to be partly hollow for example with the internal ribs or an internal lattice structure to improve strength and rigidity. Such constructions would reduce the weight of either component and reduce dynamic loading of the shaft 29.

[0100] Some typical example values for flow rates and pressures in the described arrangement of figure 2 are now given, in a situation where the impeller is sized for a bulk front face flow rate towards the cooling system 30 of about 3.4 kg / s. About 0.13 kg / s of pumped propellant leaving the outlet volute of the impeller may then then redirected as portion (a) and injected through injection ports into the first fluid bearing 38-1 at around 11800 kPa, of which around 0.05 kg / s then flows in one direction through the first rolling element bearings to the back face 32-1 of the impeller arriving there at about 9300 kPa, and about 0.08 kg / s flows in the other direction through the gap 45 between the rotor and stator at a pressure of about 9000 kPa.

[0101] About 0.2 kg / s of propellant leaving the outlet volute of the impeller is redirected as portion (b) entering the stator cooling jacket 46 at about 11800 kPa and exiting the cooling jacket at about 11300 kPa, entering the second fluid bearing injection ports at about 111 kPa. This then combines between the opposing surfaces of the second fluid bearing 39-1 for a combined flow of about 0.28 kg / s on through the second rolling element bearing where pressure drops across the rolling element bearing from about 6800 to about 6500 kPa before being pumped by the turbine back face to the input volute and joining the main flow, which exits the turbine at about 6500 kPa.

[0102] In this scenario, about 10 to 15 % of the total flow at the front face of the impeller is redirected into portions (a) and (b) which are used as described above, although this fraction could vary significantly according to specific designs, for example from about 5 to 20% or from about 1 to 25%. Of this total redirected flow, about 10 to 20% returns within the turbopump through the first rolling element bearing to the back face of the impeller to rejoin the main pumped flow there, and about 80 to 90% flows through the second rolling element bearing to join the main flow through the turbine.

[0103] The overall result of the described redirected propellant flows (a) and (b) through the turbopump 10 is that a portion of the flow pumped by the impeller 32 is used to cool and stabilize the internal operation of the turbopump, with most of the redirected flow rejoining the main flow from the cooling system 30 at the turbine 34, and a smaller portion, for example around being immediately recirculated back into the pumped flow at the impeller side. The described fluid flow path directions rely on inherent pressure distributions inside the various channels, which budgeted in detailed design of the turbopump and wider

[0104] 17281426.JRP.JRP reaction engine by appropriate sizing of the various propellant channels, careful budgeting for pressure drops from fluid passing through and past fluid and rolling element bearings as well as the strengths of the pumping effects of the impeller and turbine back faces, and design adjustments to ensure the correct heat transfer characteristics.

[0105] The rotor 42 and shaft 29 may be constructed in various ways, but in the arrangement of figure 2 the rotor is formed as a solid cylinder core of one or more materials with suitable magnetic properties, such as ferromagnetic materials or permanent magnet materials, with a suitable core material being PrFeB, without an additional structural shaft component along the central rotational axis. Structural strength and rigidity of the shaft 29 is then ensured by encasing the more or more core materials within a casing made from a metal or alloy with suitable mechanical and magnetic properties such as Inconel or Titanium. Avoiding an axial structural shaft within the centre of the rotor in this way both maximises the power density of the rotor-stator electrical machine and simplifies manufacture. To this end it can be seen that beyond the rotor core towards both the impeller and turbine the rotor has a hollow construction which assists in significantly reducing overall weight of the turbopump as well as specifically reducing rotational inertia of the shaft.

[0106] The rotor may in particular be constructed to perform as a two pole rotor within the electrical machine formed in combination with the stator, for example with diametrical magnetisation of the rotor core and use of a two pole stator winding. As already discussed above and seen in figures 1 and 2, the rotor is fully immersed in the propellant when the turbopump is in operation, as the propellant flows between the rotor and stator from the first to the second set of bearings.

[0107] Figure 3 shows in perspective view aspects of how the stator 44 of figures 1 and 2 may be constructed. In this example, a hairpin construction is used in which the conductors lie in slots 64 within a cylindrical stator body 60 having a central axis X about which the rotor rotates within the stator, and are coupled between different slots 64 according to the desired winding pattern using hairpin structures 62 of the winding conductors 63 which protrude from or lie outside each end of the stator body 60. Typically, the slots 64 within the body run parallel to the axis of the stator and rotation of the rotor within the central aperture 66, but other forms such as helical slots may be used.

[0108] In the example of figure 3 the winding is a 2 pole 3 phase full pitch distributed winding, but other forms may be used such as a 2 pole short pitched distributed winding or a 6 phase winding. The hairpin structures 62 are suited to additive manufacturing, since the large coil span needed for the suggested 2 pole arrangement is quite difficult to form by

[0109] 17281426.JRP.JRP more conventional winding techniques. Aluminium or suitable aluminium alloys may be used as the material for the winding conductors 63 and / or the hairpin structures 62 to provide a lighter weight stator and good heat conductivity.

[0110] In the three phase configuration of figure 3, the three connection or phase leads 68 for interfacing with the electrical subsystem 50 of figure 1 are visible on the right. Although the hairpin structures 62 are visible in figure 3, these would be encased in a potting compound before or as the stator is assembled into the turbopump 10.

[0111] Figure 4 shows a cross section through the stator 44 of figure 3. Particular configuration options demonstrated in figure 3 may be used alone or in various combinations with each other to provide various different benefits in the context of the turbopump 10. For example, as shown in figure 4, each conductor 63 (or pair of sub conductors 67 discussed below) preferably has a width in the azimuthal direction which is greater than twice the thickness in the radial direction, for improved efficiency at high rotational speeds. The arrangement of figure 4 uses a 6 layer design in which each slot 64 contains six layers of conductor 63 to achieve a good power density, although more of fewer could be used, for example eight such layers.

[0112] Notably, one or more of the innermost conductors in each slot 64, in this case the two innermost conductors, is divided into two sub conductors 67 stacked in a radial direction with an electrically insulating layer such as using a potting insulation between. Although the two sub conductors 67 of any particular of each these innermost conductors occupy the same electrical position as each other in the overall winding, for example being electrically connected at each end of the stator within the hairpin configurations, this separation within the stator body reduces eddy currents and therefore reduces proximity losses in the stator, especially at high rotational speeds.

[0113] The stator body may typically be formed using axial laminations of a magnetically suitable material which is also suitable for cryogenic conditions if a cryogenic propellant is to be used, such as a cobalt iron based material. Each slot 64 in the stator body is then preferably insulated from the conductors 63 within the slot, for example using a slot liner which could be made of Nomex paper or similar, with remaining spaces filled with a suitable electrically insulating potting compound compatible with the chemistry and temperature of the propellant, but ideally also having high thermal conductivity. One such suitable potting compound is Kohesi KB 1039 CRLP-AO, which is a two component, heat curing epoxy formulated for use in cryogenic conditions, has a very high resistance to cryogenic shocks, is relatively thermally conductive compared to some other epoxy materials, and passes typical space craft standards for low out-gassing in vacuum

[0114] 17281426.JRP.JRP conditions. The potting compound may also or instead be used to pot around outer portions of the stator including around the hairpin configurations of the conductors so as to hold these in position and provide good electrical insulation.

[0115] Although the stator may be electrically insulated using a potting compound as discussed above, it may be desirably to better protect the stator from the propellant which may be thermally and / or chemically harsh and to which the interior diameter of the stator is exposed through the propellant flowing along the gap 45 between the rotor and the stator as discussed above in respect of figures 1 and 2.

[0116] To help achieve this, a stator liner 70 may be installed along the length of the inner circumference of the stator as illustrated in cross section in figures 5 and 6. Figure 5 corresponds to the subregion of figure 2 labelled A in that figure, and figure 6 to subregion B. Arrangements for ensuring the stator liner provides sufficient sealing against egress of the propellant may be different at each end of the stator, especially if, and if so partly because the connection or phase leads 68 will typically emerge from the stator only at one end, and these leads need to make effective electrical connections outside of the turbopump space in which propellant is circulating.

[0117] In figure 5 the hairpin configurations 62 of the conductors 63 can be seen in cross section, as a number of blocks located within the potting compound 74 used to insulate the stator including by embedding the hairpin configurations. Towards the top of the figure the propellent channel within the stator cooling jacket 46 is apparent, and towards the bottom the rotor 42 can seen encased within a structural sheath 76 of Inconel, Titanium or similar, and forming part of the shaft 29.

[0118] The stator liner 70 may be formed of a chemically inert material which is flexible or soft enough to deform against other surfaces to provide good seals, even in cryogenic conditions if a cryogenic propellant is being used, with fluoropolymers being good candidates. Good electrical insulation properties are also very desirable to avoid compromising electromagnetic performance of the electrical machine.

[0119] The stator liner 70 is preferably a largely cylindrical structure fitting snugly within the stator, but with the addition of a radially extending flange 72 at the end of the liner 70 distant from the stator connecting or phase leads 68, typically at the end of the stator closest to the turbine. This flange is then pressed against an adjacent internal wall 76 of a casing of the turbopump 10 by the stator so as to provide an improved seal between the stator and the internal wall using the liner. The internal wall may be essentially perpendicular to the axis of rotation of the rotor, or may be at some other angle, but will typically face the impeller and may be of essentially annular shape.

[0120] 17281426.JRP.JRP The seal between the stator 44 and the internal wall 76 of the casing of the turbopump may be further improved, in particular given the mechanical vibrations and stresses likely during use of the turbopump during operation of the reaction engine, as well as potentially large temperature changes, by providing a compression plate 78 between the stator 44 and the internal wall 76 which is urged against the internal wall by a one or more compression springs 80 which may be housed for example within one or more recesses 82 in the end of the stator facing the internal wall, for example in one or more recesses within the potting compound using to pot the stator as shown in figure 5.

[0121] Arrangements which may be used for sealing the stator liner 70 at the other end of the stator, proximally to the connection or phase leads 68 and typically also the end closest to the impeller, are illustrated in figure 6. Here, the hairpin configurations 62 of the conductors 63 of the stator are see at the left, and one of the connection or phase leads 68 is partially visible extending through the potting compound 74 of the stator to a volume within the turbopump which does not contain any propellant, for onward electrical connection to the electrical subsystem 50 at the visible right hand end.

[0122] Here in figure 6, it can be seen that the impeller end of the stator liner 70 comprises a widening conical flange 83 to assist with sealing the stator liner. A stator compression seat 84 is fixed to the impeller end of the stator at the inside diameter of the stator, for example by adhesion to or by the potting compound 74. The compression seat 84 has a widening conical surface onto which the conical flange 83 of the stator liner is bedded.

[0123] To ensure that the bedding of the stator line conical flange 83 onto the compression seat 84 is secure, the stator compression seat 84 comprises an inside thread into which an external thread of a compression plug 86 can be screwed. The stator compression seat 84 and compression plug 86 define between them a bevelled annular recess which is occupied by a bevelled compression ring 88 which extends around a portion of the turbopump casing, and tapers externally against both the stator compression seat 84 and the compression plug 86. Therefore, when the conical flange 83 of the stator liner is bedded against the stator compression seat, and the compression ring 88 is pushed against the conical flange, the compression plug can be screwed tightly into the compression seat to compress the conical flange 83 of the stator liner 70 and provide a secure seal.

[0124] The compression plug functions in this way to prevent the rotation of the compression plug 86 damaging the stator liner as it is screwed into the compression seat. Typically, the compression seat and compression plug may be formed of a suitable metal such as titanium or Inconel, and the compression ring of a more flexible material but with

[0125] 17281426.JRP.JRP adequate compressive strength to compress the conical flange of the liner such as a polythene or other plastics material.

[0126] Although the above sealing arrangements imply a relatively flexible and soft material for the stator liner, in some examples more rigid stator liner materials could be used, if necessary along with different sealing arrangements. For example a ceramic matrix composite material, which is electrically insulating and which would provide effective chemical and physical protection of the stator from the propellant could be used with somewhat different sealing arrangements to those depicted in figures 5 and 6.

[0127] Although particular embodiments have been described, a number of alternatives and variations will be apparent to the skilled person without departing from the scope of the invention for example as set out in the appended claims. For example, although the claims may refer to use in a reaction engine, the described embodiments may be used in various other types of engine to provide motive thrust, power generation, or other services as required by the particular application.

[0128] 17281426.JRP.JRP

Claims

- 25 -CLAIMS:1 . A turbopump for use in a reaction engine having an engine passage within which combustion of a propellant takes place so as to provide motive thrust of the reaction engine, and having a cooling system to extract heat from the engine passage, the turbopump comprising: a rotatable shaft; an impeller for pumping propellant from a propellant supply to the cooling system, and a turbine for being driven by propellant subsequently flowing from the cooling system to the engine passage for combustion, the impeller and the turbine being coupled to opposing ends of the shaft; an electrical machine disposed between the impeller and the turbine, the electrical machine comprising a rotor and a stator surrounding the rotor, the rotor forming part of the shaft so as to corotate with the impeller and the turbine, the electrical machine being controllable to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

2. The turbopump of claim 1 wherein the turbopump comprises a first set of bearings supporting the shaft proximally to the impeller and a second set of bearings supporting the shaft proximally to the turbine, and the turbopump is arranged to redirect, to each of the first and second sets of bearings, portions of the propellant being pumped from the impeller or from the propellant supply towards the cooling system.

3. The turbopump of claim 2 wherein the proportion of propellant being pumped from the impeller or from the propellant supply, towards the cooling system, that is redirected to form the redirected portions, is from 5 to 20%.

4. The turbopump of claim 2 or 3 wherein the first set of bearings comprises a first fluid bearing, and a first rolling element bearing located between the first fluid bearing and the impeller, wherein the portion of the propellant redirected to the first set of bearings is first used as a working fluid of the first fluid bearing, and is then split into a flow from the first fluid bearing through a gap between the rotor and the stator, to the second set of bearings, and a flow from the first fluid bearing through the first rolling element bearing to the impeller.17281426.JRP.JRP5. The turbopump of claim 4 wherein the impeller comprises an impeller front face arranged to pump the propellant from the propellant supply towards the cooling system through an outlet volute of the impeller, and an impeller back face, the turbopump being arranged to direct the flow of the propellant from the first set of rolling element bearings to the impeller back face which is arranged to pump the received propellant to the outlet volute of the impeller.

6. The turbopump of any of claims 2 to 5 wherein the turbopump comprises a stator cooling jacket arranged to cool the stator, and the portion of the propellant redirected to the second set of bearings is first passed through the stator cooling jacket for cooling an exterior of the stator before arriving at the second set of bearings.

7. The turbopump of any of claims 2 to 6 wherein the second set of bearings comprises a second fluid bearing and a second rolling element bearing, and the portion of the propellant redirected to the second set of bearings is first used as a working fluid of the second fluid bearing, before being directed on to the second rolling element bearing, and then from the second rolling element bearing to the turbine.

8. The turbopump of claim 7 when dependent on claim 4 or 5, wherein the flow of propellant through the gap between the rotor and the stator is also then directed through the second fluid bearing and then through the second rolling element bearing to the turbine.

9. The turbopump of claim 7 or 8 wherein the turbine comprises a turbine front face for being driven by propellant flowing from the cooling system to the engine passage for combustion, and a turbine back face, the turbopump being arranged to direct the flow of propellant from the second set of rolling element bearings to the turbine back face which is arranged to pump the received propellant to the inlet volute of the turbine.

10. The turbopump of any preceding claim wherein the turbopump is arranged such that, in operation, the periphery of the rotor is immersed in the propellant.1 1 . The turbopump of any preceding claim wherein the rotor is formed of a core of one or more materials with suitable magnetic properties and an external structural sheath surrounding the core, without an additional structural shaft passing along the rotational axis of the rotor.17281426.JRP.JRP12. The turbopump of any preceding claim wherein the stator is constructed using conductors located in slots within a stator body, the conductors being electrically connected to each other using hairpin structures extending from or out of the ends of the stator body, optionally wherein the hairpin structures are additively manufactured.

13. The turbopump of claim 12 wherein the stator comprises between five and ten conductors arranged radially within each slot, and / or each conductor is at least twice as wide azimuthally as it is thick radially, relative to a central axis of the stator.

14. The turbopump of claim 12 or 13 wherein one or more of the innermost conductors in each slot comprises at least two radially stacked sub conductors which are insulated from each other within the slot, but electrically connected to each other externally to the slot.

15. The turbopump of any preceding claim wherein a stator liner is provided at the inner circumference of the stator so to provide the stator with protection against propellant flowing between the rotor and the stator, optionally wherein the stator liner is formed of a fluoropolymer.

16. The turbopump of claim 15 wherein the stator liner comprises a radial flange at the end of the stator closest to the turbine, and the radial flange of the stator liner is pressed against an internal wall of a casing of the turbopump by the stator.

17. The turbopump of claim 16 wherein a compression plate is located between the stator and the radial flange of the stator liner, and one or more compression springs are provided to urge the compression plate against the radial flange of the stator liner so as to press the radial flange against the internal wall of the casing.

18. The turbopump of any of any preceding claim wherein the stator liner comprises a conical flange at the end of the stator closest to the impeller, and the conical flange is compressed between a threaded compression seat of the stator and a bevelled compression ring urged against the conical flange by a threaded compression plug screwed into the compression seat.17281426.JRP.JRP- 28 -19. The turbopump of any preceding claim further comprising an electrical subsystem arranged to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

20. The turbopump of any preceding claim further comprising a battery arranged to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.21 . A reaction engine, comprising: a propellant supply arranged to supply a propellant; an engine passage within which combustion using the propellent takes place so as to provide motive thrust of the reaction engine; a cooling system arranged to receive heat from the engine passage; the turbopump of any preceding claim wherein the impeller of the turbopump is arranged to pump propellant from the propellant supply to the cooling system, and the turbine is arranged to be driven by the pumped propellant subsequently flowing from the cooling system to the engine passage for combustion.

22. The reaction engine of claim 21 wherein the reaction engine further comprises a turbine bypass valve to controllably permit a bypass flow of the propellant from the cooling system to the combustion chamber which does not flow through the turbine.

23. The apparatus of any preceding claim wherein the propellant is at least one of: a cryogenic propellant; liquid hydrogen; liquid oxygen; and liquid methane.

24. The apparatus of any preceding claim wherein the reaction engine is a ramjet or a scramjet.

25. The apparatus of any preceding claim wherein the reaction engine is a rocket engine.

26. The apparatus of claim 25 wherein the propellant is a first propellant, and the rocket engine further comprises an additional impeller to pump a second propellant to the combustion chamber for combustion with the first propellant, wherein the additional17281426.JRP.JRP- 29 - impeller is at least partly driven using electrical power generated by the electrical machine of the turbopump.

27. The apparatus of any preceding claim wherein the turbopump comprises a casing within which the impeller, turbine and shaft are housed, and the rotation of the impeller, turbine and shaft is retained entirely within the casing.

28. A method of operating a turbopump within a reaction engine having an engine passage within which combustion of a propellant takes place so as to provide motive thrust of the reaction engine, and having a cooling system to extract heat from the engine passage, the method comprising: using an impeller on a rotating shaft to pump propellant from a propellant supply to the cooling system, and driving a turbine on the same shaft using propellant subsequently flowing from the cooling system to the engine passage for combustion, the impeller and the turbine being coupled to opposing ends of the shaft; and using an electrical machine, disposed between the impeller and the turbine and comprising a rotor forming part of the shaft and a stator surrounding the rotor, to selectively either deliver electrical power to the stator to drive rotation of the shaft, or to receive electrical power from the stator generated by rotation of the shaft.

29. The method of claim 28 further wherein the turbopump comprises a first set of bearings supporting the shaft proximally to the impeller and a second set of bearings supporting the shaft proximally to the turbine, and the method further comprises redirecting, to each of the first and second sets of bearings, portions of the propellant being pumped from the impeller towards the cooling system.

30. The method of claim 28 or 29 wherein the turbopump comprises a stator cooling jacket and a gap between the rotor and the stator, the method further comprising using the redirected portions of the propellant through the stator cooling jacket and a gap between the rotor and the stator to provide cooling of the electrical machine.31 . The method of any of claims 28 to 30 further comprising using a turbine bypass valve to controllably permit a bypass flow of the propellant from the cooling system to the combustion chamber avoiding the turbine.17281426.JRP.JRP

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