Patent ID: 12209536

DETAILED DESCRIPTION

A hydrogen-fueled airliner is illustrated inFIG.1. In this example, the airliner101is of substantially conventional tube-and-wing twinjet configuration with a central fuselage102and substantially identical underwing-mounted turbofan engines103. In the present embodiment, the turbofan engines103are geared turbofan engines.

A hydrogen storage tank104located in the fuselage102. In the present embodiment, the hydrogen storage tank104is a cryogenic hydrogen storage tank and thus stores the hydrogen fuel in a liquid state, in a specific example at 25 kelvin. In this example, the hydrogen fuel is pressurised to a pressure from around 1 bar to around 3 bar, in a specific example 4 bar. In other cases, the hydrogen could be stored as a cryogenically cooled, compressed gas or supercritical fluid.

A block diagram of one of the turbofan engines103is shown inFIG.2.

The turbofan engine103comprises a core gas turbine201.

The core gas turbine201comprises, in fluid flow series, a low-pressure compressor202, a high-pressure compressor204, a fuel injection system206, a combustor207, a high-pressure turbine208, a low-pressure turbine209, and a core nozzle210. The high-pressure compressor204is driven by the high-pressure turbine208via a first shaft211, and the low-pressure compressor203is driven by the low-pressure turbine209via a second shaft212. It will be appreciated that in alternative embodiments, the core gas turbine could be of three-shaft configuration.

The turbofan103also defines a fan213, which is driven by the low-pressure turbine209. The fan provides airflow to the core gas turbine201, and to a bypass duct227. As such, distinct bypass and core flows are provided through the bypass passage227and gas turbine engine core201respectively.

In operation, hydrogen fuel is pumped from the hydrogen storage tank104by a pump216and into a main fuel conduit217which ultimately delivers fuel to the fuel injection system206.

As will be appreciated, it is desirable to increase the temperature of the fuel from cryogenic storage condition to a temperature much closer to the firing temperature of the core gas turbine201; of course this is subject to the constraint of not exceeding the autoignition temperature of the hydrogen fuel prior to admission into the combustor207. In an example, the injection temperature is from 250 to 300 kelvin, for example 250 kelvin. In some cases, it may be desirable to increase the fuel temperature to above 10 an icing temperature, such as 273 kelvin.

A preheater218is therefore provided for heating of the hydrogen fuel. This takes place between the pump216and the fuel injection system206. In an embodiment, the preheater218is configured to raise the temperature of the hydrogen fuel to the required injection temperature. The heating may provide a phase change (for example from liquid to supercritical or to gas), or the fluid may remain in a supercritical state after heating by the preheater.

In another embodiment, the preheater218is configured to raise the temperature of the hydrogen fuel to an intermediate temperature less than the injection temperature. This could for example be from 60 to 200 kelvin, for example 150 kelvin.

The pre-heater218comprises a recuperator heat exchanger configured to exchange heat from the gas turbine engine core exhaust to the hydrogen fuel in the main fuel conduit217, prior to delivery to the fuel injector206. In some cases, at certain points in the operational envelope there will be insufficient heat output from the engine to raise the fuel temperature to the injection temperature using the recuperator alone. Such occasions may include, for example, ground start, in-flight relight, end of cruise idle, etc. An such cases, an additional auxiliary preheater (not shown) may be provided.

As will be appreciated, the provision of a recuperator heat exchanger increases the thermal efficiency of the engine, since waste heat that would normally be expelled from the exhaust is reintroduced into the engine cycle via the fuel. However, in studies conducted by the inventors, the advantages of a recuperated cycle are greatly (and in some cases, entirely) offset by reduced propulsive efficiency in view of the flow restriction provided by the recuperator. Additionally, the blockage of the recuperator may increase turbine back pressure, thereby reducing available pressure drop across the turbine, and so reducing turbine work and engine power density. A further disadvantage of recuperated designs is the presence of a relatively delicate heat exchanger in the core engine gas path. Foreign or domestic objects present in the exhaust flow may impinge on the heat exchanger, thereby damaging it. The present disclosure may solve some or all of these problems.

A first embodiment of the preheater218is shown in further detail inFIG.3which shows an aft part of the engine103.

The heat exchanger218comprises a heat exchange matrix301configured to flow hydrogen fuel through a first set of channels, and hot exhaust air through a second set of channels, to allow for heat exchange therebetween. The heat exchange matrix301is provided within a recuperator channel302arranged to guide a portion (i.e. less than the whole) of core gas turbine engine exhaust gas flow A. Typically, the recuperator channel is configured to accommodate between 10% and 25% of core mass flow, with the remainder of core mass flow being bypassed. In a particular example, the inventors have found that a preferred range of recuperator mass flow is between 15% and 20%. In engine modelling experiments, the inventors have found that 17% recuperator mass flow provides optimum heat exchange to the fuel without providing excessive blockage of the core exhaust.

The recuperator channel302is provided adjacent a radially inner side of the gas turbine engine core, and is mounted to a radially inner side wall303aft of the low-pressure turbine209. The radially inner side wall303extends annularly around the engine core to form a core centre body306, which projects from a rear of the engine201. The radially inner side wall303defines an inner extent of the recuperator channel302, while a radially outer recuperator duct wall304defines a radially outer wall of the recuperator channel. As such, a generally annular duct302is defined, which guides core flow generally axially through the duct302from an inlet, through the heat exchange matrix, and to an exhaust.

Radially outward of the duct302is a core bypass passage305through which the remainder of the core flow passes, without extending through the recuperator matrix. This core bypass passage305is distinct from the turbofan bypass duct227, and flows only core flow. The core bypass passage305is defined by an annulus between the recuperator channel outer wall304and a core outer wall307. The two flows mix aft of the core bypass passage, and are expelled through the exhaust nozzle210. As such, a portion of core bypass flow extends out of the exhaust without being restricted by the recuperator heat exchanger218. This may increase core outlet velocity relative to an engine in which all core flow extends through a recuperator, and may reduce backpressure, thereby increasing turbine effectiveness. These disadvantages may be reduced by employing heat exchanger designs with low pressure drop. However, such designs are typically large and bulky, and may require large diffusion ducts upstream of the heat exchanger. These design compromises may lead to increased overall weight, volume and cost of the propulsion system.

FIG.4shows a first alternative arrangement of a recuperator heat exchanger418in a gas turbine engine core. The arrangement is similar to that shown inFIG.3, but the recuperator heat exchanger418is provided radially relative to the arrangement shown inFIG.3. The recuperator heat exchanger418is provided within the core centre body406. A scoop408is provided, which extends into the core flow, to ingest a portion of the core flow aft of the turbine209, which is then redirected to the recuperator heat exchanger418through a recuperator channel402. The remainder of the core flow continues unabated out of the exhaust nozzle407.

The recuperator channel is divergent from an inlet to the front face of the heat exchanger418. Consequently, flow velocity is reduced, and pressure is increased. Consequently, heat exchanger effectiveness is increased. In addition, the probability of recuperator damage is reduced in view of the lower velocity, and the presence of the inlet at a low radial position, since particles in the exhaust are likely to be concentrated at the radially outer wall of the turbine. In some cases, a diverter (not shown) may be provided in the recuperator channel to further reduce the probability of debris damage.

Consequently, the recuperator is provided within a space that is normally empty, thereby improving engine packaging. Furthermore, engine core flows relatively uninterrupted through the gas turbine engine exhaust, thereby improving propulsive efficiency. Additionally, the recuperator is protected from damage.

FIG.5shows a second alternative arrangement of a recuperator heat exchanger518. In this arrangement, the recuperator heat exchanger518is again provided within a duct502within the centre body506. However, in this arrangement, the heat exchanger518and duct502are configured such that core flow flows generally axially from an inlet530toward the recuperator518before being turned generally radially inwardly and flowing through the recuperator218heat exchange matrix in a generally radially inward direction. Flow downstream of the recuperator518is again turned to a generally axial direction, where it flows out of the engine through a recuperator exhaust531the centre of the centre body506.

The recuperator518has a generally annular profile, and is arranged to flow core flow radially inward. Alternatively, the recuperator518may be part annular. As such, a relatively large area can be provided, since inlet flow area can be increased by increasing the axial extent of the recuperator518. The combination of large area and low velocity results in high heat exchange effectiveness for a given mass flow. Consequently, a relatively small quantity of air A can be drawn from the core flow, and decelerated to relatively slow velocities, before flowing through the recuperator heat exchanger518. As such, the impact on turbine backpressure and recuperator bypass flow B is still further reduced, while a high rate of heat transfer is maintained.

FIG.6shows a third alternative arrangement of the recuperator heat exchanger618. The arrangement is similar to that shown inFIG.4, but with the addition of a translating centre-body configured to control the outlet area of the recuperator channel602.

The upper half ofFIG.6shows the centre body translated aft, such that the outlet area of the recuperator channel602is reduced, whereas the lower half ofFIG.5shows the centre body translated forward such that the outlet area of the recuperator channel602is increased. By changing the outlet area, the mass flow and/or velocity through the channel602can be controlled, thereby controlling heat input to the fuel within the recuperator618. Consequently, fuel temperature can be controlled independently of engine core flow and temperature. For example, during operation at low power, fuel flow will typically be low, while core flow velocity will also be low, while core temperature may remain high. As such, the temperature rise of the fuel may be excessive under these conditions. Consequently, mass flow can be decreased by closing the nozzle, thereby reducing heat input. In some cases, the nozzle may be controlled completely, thereby halting heat input to the fuel. As will be appreciated, other flow control means could be employed, such as valves of various types.

FIGS.7aand7bshow a fourth alternative arrangement of the recuperator heat exchanger718.

In this arrangement, the recuperator channel702is provided at a radially outer portion of the engine core, adjacent a core outer wall707of the engine, with the recuperator heat exchanger718being provided within the recuperator channel702, and a core bypass being provided radially inwards. This arrangement provides the cooler, lower velocity air from the recuperator heat exchanger at the outer radius of the core exhaust, providing intermediate temperature and velocity airflow between the core and bypass flows, which may result in lower noise output from the engine.

As shown inFIG.7b, the recuperator channel comprises a valve arrangement comprising a plurality of rotatable covers, which can rotate in the directions shown by the arrows to cover or uncover the heat exchange matrix718. As such, the mass flow and/or velocity of air through the heat exchangers can be managed.

Various examples have been described, each of which comprise various combinations of features. It will be appreciated by those skilled in the art that, except where clearly mutually exclusive, any of the features may be employed separately or in combination with any other features and thus the disclosed subject-matter extends to and includes all such combinations and sub-combinations of the or more features described herein.