Integration of turbine engine and battery cooling system

Abstract

An aerial vehicle, comprising: - a battery pack for providing electrical power; - a primary electrical engine, powered by the battery pack, - a cooling system for cooling the battery pack and / or the primary electrical engine, comprising: o a circulation fluid in contact with the battery pack and / or the primary electrical engine, arranged for exchanging heat between the battery pack and / or primary electrical engine and the circulation fluid; o a heat exchanger, in contact with the ambient air, for exchanging heat between the circulation fluid and the ambient air; - a fuel storage system, for storing fuel; - a secondary turbine engine comprising a combustion chamber, an inlet duct and an exhaust nozzle, powered by the fuel; wherein the heat exchanger of the cooling system is positioned inside the inlet duct of the secondary turbine engine.

Description

[0001] Title: Integration of turbine engine and battery cooling system

[0002] Description:

[0003] Despite many people working on the subject very hard for many years, radical change in aircraft design has not come to life over the last 5 - 6 decades. When comparing the early examples of e.g. Airbus and Boeing aircraft with the state of the art aircraft, a lot of optimization has been effected but on a conceptual level the cigarshaped fuselage, with wings attached to it and kerosene-operated engines attached to the wings has proven too successful to change.

[0004] Whereas some companies are working on the return of a supersonic commercial plane as a replacement for the long-gone-but-not-forgotten Concorde aircraft, it cannot be denied that society is changing and that also the aviation industry needs to reduce its footprint. For this latter purpose, several alternative designs are explored by research groups around the world - both in academia and within companies. The Delft University of Technology is famous for having proposed several entirely different aircraft design, including the Prandtl Wing and the Flying Wing. The latter has become known as the Flying V concept, which has successfully flown as a scale model.

[0005] However, such radically different designs take many, many years before being commercially operative, and change is needed sooner in the aviation industry. For a more short-term footprint reduction, research groups are e.g. working on engines that combust more economically friendly fuel - examples being "green” kerosene and hydrogen. Electrically-powered aircraft are also proposed, with some smaller (trainer) aircraft having already been taken into operation successfully. Examples being the Velis Electro manufactured by the Slovenian company Pipistrel.

[0006] Such aircraft, which are fuelled by a non-traditional propulsion system, require alternative design strategies. Whereas the earliest models of e.g. battery-powered aircraft were converted aircraft, several companies are nowadays working on solutions that have electrical engines at the core of the design.

[0007] As engines operating on alternative energy sources are relatively new and unproven and as the aviation industry is heavily regulated (for good and obvious reasons), aviation regulations across the globe may require that aircraft having a main propulsion system that is of an “alternative” design, e.g. hydrogen- or battery-powered, in addition have a secondary, more traditional kerosene-powered propulsion system. This secondary propulsion system may be turned on to extend the range of the aircraft - for example when the aircraft cannot land at its planned location and / or at its planned time for whatever reason. Of course, the secondary propulsion system may also be turned on in case of failure of the primary propulsion system.

[0008] This is the reason that aircraft designed to operate on alternative propulsion systems, which are being developed nowadays, in fact are designed to have two types of propulsion system - a main propulsion system that is not being powered by traditional kerosene and a secondary propulsion system that is powered by traditional kerosene. As mentioned before, the secondary propulsion system is controlled to only become operational when the primary propulsion system runs out of energy.

[0009] Zooming in on the alternative propulsion systems, and electrical engines in particular, like traditional turbine engines, such engines (and their batteries) become hot during operation and need to be cooled. Conversely, in cold weather, the batteries need to be heated. However, conditioning systems designed and optimized for turbine engines may prove to be unsuitable for electrical engines and batteries. For that reason, a purposely designed conditioning system is typically associated with the electrical engines and batteries of a battery-powered aircraft. The conditioning system - which in fact ensures stable operating temperatures of the electrical engine and its batteries - comprises a circulation fluid that is in contact with the electrical engine and / or its batteries, as well as a heat exchanger which is in contact with the ambient air and which exchanges heat with the circulation fluid.

[0010] It is however felt by the present inventors that, from a systems integration point of view, presently-known solutions are suboptimal, and that efficiency gains can be achieved for an “as-such” designed electric aerial vehicle.

[0011] Accordingly, the present disclosure relates to an aerial vehicle comprising: one or more battery packs, for providing electrical power; one or more primary electrical engines, powered by the one or more battery packs,

[0012] - a cooling system for cooling the one or more battery packs and / or the one or more primary electrical engines, the cooling system comprising:

[0013] o a circulation fluid in thermal contact with the one or more battery packs and / or the one or more primary electrical engines, the circulation fluid arranged for exchanging heat between the one or more battery packs and / or the one or more primary electrical engines and the circulation fluid;

[0014] o a heat exchanger, in thermal contact with the ambient air, for exchanging heat between the circulation fluid and the ambient air; - a fuel storage system, for storing fuel;

[0015] - a secondary turbine engine comprising a combustion chamber, an inlet duct and an exhaust nozzle, powered by the fuel;

[0016] wherein the heat exchanger of the cooling system is positioned inside the inlet duct of the secondary turbine engine.

[0017] In known solutions, when the turbine engine forms a secondary propulsion system of an aerial vehicle, the inlet of the turbine engine may be closed during normal operation, i.e. when the primary propulsion system is active. This minimizes drag for the aerial vehicle. During normal operation, a second inlet duct may be associated with the heat exchanger of the electrical engine’s cooling system, the second inlet duct being variable in diameter to optimize the airflow through it depending on the needed exchange of heat between the ambient air and the circulation fluid.

[0018] Advantageously, by arranging the heat exchanger of the cooling system inside the inlet duct of the secondary turbine engine, the internal flow paths of the turbine engine on the one hand and the electrical engine on the other hand are integrated - instead of both propulsion systems having their own internal flow path. That is to say, the turbine engine has, as it usually does, an inlet duct as well as an exhaust. However, the inlet duct may be open even when the turbine engine itself is inoperative. The inlet duct contains the heat exchanger of the cooling system, so that air drawn through the inlet duct flows past the heat exchanger and may then, e.g., be bypassed from the turbine engine without fuel being combusted in the combustion chamber of the turbine engine.

[0019] The present disclosure relates to an aerial vehicle. As such, the present disclosure relates not only to aircraft, but also other forms or vehicles, typically heavier-than-air, flying through the air. To give some examples: unmanned aerial vehicles, helicopters, commercial aircraft, military aircraft, trainer aircraft, and other types of aerial vehicles.

[0020] According to the present disclosure, the aerial vehicle has a primary engine and a secondary engine. The secondary engine typically functions as a back-up engine. A traditional aircraft always carried an excess amount of fuel to divert from its original destination due to adverse weather conditions and / or to circle around its original destination due to the runways at the destination being crowded. The precise amount of excess fuel a traditional aircraft has to carry is closely regulated. However, it is relatively rare that this excess amount of fuel is actually used. For a battery-powered aircraft the weight penalty associated with such excess amount of “fuel”, i.e. battery power, for circling and / or diverting may be too much to make commercial operation possible. As such, a relatively small secondary engine may be carried instead - the secondary engine only kicking in when the flight route has to be changed compared to the planned flight route and when the batteries face the point of being drained. During normal operation, simultaneous operation of both the primary and the secondary engine is not envisaged. However, there may be a brief period of time, some minutes, in which the secondary engine system is warming up while the primary engine system is also being used - a transitional phase, so to say.

[0021] According to the present disclosure, the primary engine is an electrical engine that is powered by a battery. For that reason, the aerial vehicle comprises one or more battery packs. In principle, the batteries may be located at any position, e.g. the fuselage (if the aerial vehicle has a fuselage) and / or the wings (assuming the aerial vehicle comprises wings). The present disclosure is not limited to a certain type of battery, although it would be conceivable that an energy pack having a high energy to weight ratio would be chosen for aerial vehicles. For example, the electrical engine may power a propeller, the propeller displacing air providing a propulsive force to the aerial vehicle. According to the present disclosure, the secondary engine is a turbofan engine. In particular, the turbine engine may be a turbofan engine and / or a turboshaft engine, as is detailed further in the below.

[0022] As is quite conventional, according to the present disclosure the battery packs and / or electrical engines are cooled by a cooling system. As was already observed in the above, although the wording “cooling system” is conventional, one skilled in the art knows that there may be circumstances in which the batteries and / or electrical engines actually need to be warmed to have their desired operating window, in which case the cooling system may heat the battery / electrical engine. In normal operating conditions however, the cooling system ensures that a circulation fluid absorbs heat from the battery / electrical engine, by being in thermal contact with the components thereof. For example, the circulation fluid may be in direct contact with components thereof or the thermal contact may be established by means of heat radiation or convection. The circulation fluid itself becomes warmer in that process, and needs to be cooled for recirculation purposes. Therefore, in a heat exchanger the circulation fluid exchanges heat with the ambient air, typically by means of convection.

[0023] Hence, there must be contact between the heat exchanger of the cooling system and the ambient air. For reasons of drag reduction, having the heat exchanger protrude from the aerial vehicle does not make sense, so allowing air to enter the aerial vehicle would be the preferred option. As the secondary turbine engine also needs an inlet duct, according to the present disclosure a single inlet duct is used to allow air to reach both components of the aerial vehicle: the heat exchanger as well as the turbomachinery of the turbine engine. This combined inlet, compared to two inlet ducts for two propulsion systems designed in isolation from each other, reduces the number of parts needed for the aerial vehicle, reduces complexity, may reduce weight, may reduce drag and hence may be more efficient in terms of systems engineering.

[0024] In a preferred embodiment of the present disclosure, the inlet duct has an inlet area of variable size. For example, the inlet duct may comprise one or more hinge elements that may expand and / or decrease the size of the inlet area. The amount of ambient air needed to cool the heated circulation fluid may not always be the same - e.g. depending on the temperature of the ambient air, its density, the operating point of the electrical engines, and many more variables. In general, it may be desirable to minimize the amount of air that flows through the inlet duct, to keep the drag as low as possible. Besides that, the air requirements may differ quite substantially for operation of the aerial vehicle using its primary engine compared to operating the aerial vehicle using its secondary engine. In particular, when the secondary turbine engine is needed, one can imagine that as much air as possible may be desirable, calling for a requirement to increase the size of the inlet duct maximally. So, besides and / or in addition to incremental changes in the size of the inlet duct, a more step-like change may be desired as well.

[0025] In alternative embodiments, other mechanisms may, however, be deployed to vary the inlet area of the inlet duct. For example, one could use an axisymmetric nozzle or any other type of adjustable inlet.

[0026] In a preferred embodiment of the present disclosure, the inlet duct has a stationary portion and a variable-area portion. By allowing only a portion of the inlet duct to be variable in position, so that only a portion of the inlet duct has a variable area, the forces acting on the hinge may be limited so that the total weight of the system may be reduced compared to a more complex solution.

[0027] In a preferred embodiment of the present disclosure, the exhaust nozzle has an outlet area of variable size. For this purpose, a hinge may again be employed. However, also other types of exhaust nozzles may be used, such as an axisymmetric exhaust, louvres, or any other type of exhaust that allows to vary the area thereof.

[0028] According to the disclosure, during normal flight, either the primary electrical engine is used or the secondary turbine engine. There may, however, be situations in which both propulsion systems are operative at the same time. For example, if it is a priori known that the batteries of the electrical engine are about to run out of electrical energy, one may already start up and warm the turbine engine while still running on the primary engine. However, during ordinary operation, usually only one of the two propulsion systems will be active - in particular, the electrically powered engine.

[0029] In a preferred embodiment of the present disclosure, the heat exchanger is foldable about a hinge axis, wherein in a folded position, the heat exchanger is positioned substantially parallel to a wall of the inlet duct of the turbine engine, whereas, in an extended position, the heat exchanger extends away from said wall. As such, when the primary electrical engine is operational, the heat exchanger may be positioned in the flow channel formed by the inlet duct, to exchange heat with the ambient air flowing through the inlet duct. In this condition, some drag will be induced by the heat exchanger, but this drag is accepted as otherwise, the battery packs and / or the electrical engines may overheat. On the other hand, when the secondary turbine engine is in operation, the heat exchanger may be in its folded position. In this condition, it may be desirable that as much ambient air as possible reaches the turbine engine, in a flow state that is as good as possible. So, folding in the heat exchanger may result in a flow reaching the turbine with comparatively cleaner flow, i.e. less turbulence, and with less drag being induced. This results in a maximal total pressure recovery.

[0030] In a preferred embodiment of the present disclosure, the heat exchanger is positioned in the stationary portion of the inlet duct. Assuming that the heat exchanger can only fold out or retract, and not move along a plurality of extension positions, this ensures that the orientation of the heat exchanger to the incoming air flow is always the same, and hardly influenced by the area of the inlet.

[0031] In one embodiment according to the present disclosure, the turbine engine is a turbofan engine. In another embodiment according to the present disclosure, the turbine engine is a turboshaft engine.

[0032] In one embodiment according to the present disclosure, the fuel with which the secondary turbine engine is powered, is kerosene. As one skilled in the art knows, the general denomination “kerosene” includes both traditional kerosene as well as more environmentally friendly alternatives thereof. In another embodiment according to the present disclosure, the fuel may e.g. be hydrogen or another fuel suitable for combustion in a turbine engine.

[0033] In a preferred embodiment of the present disclosure, the heat exchanger is arranged in the same flow path as the turbine engine. This flow path may be characterized by an inlet duct first, followed by a heat exchanger (optionally foldable), then a turbine engine and finally an exhaust duct.

[0034] In a preferred embodiment of the present disclosure, the turbine engine is arranged in a windmilling condition when the primary electrical engine is operative during flight. This may minimize the total amount of drag induced by the turbine engine when inoperative.

[0035] In a preferred embodiment of the present disclosure, when the aerial vehicle is in contact with a ground surface the heat exchanger is in the extended position and the turbine engine is operative for generating a mass flow over the heat exchanger, the turbine engine in particular being operated by an electric starter motor thereof. As such, in contrast to when the aerial vehicle is in stationary flight, when the aerial vehicle is in contact with a ground surface both propulsion systems may be active.

[0036] These and other aspects of the present disclosure will now be elucidated further in the below, with reference to the attached Figures in which like elements are denominated with the same reference numerals. In these Figures:

[0037] Figure 1 schematically shows, in a cross-sectional view, an air duct associated with the aerial vehicle according to the present disclosure; and

[0038] Figure 2 schematically shows, in a cross-sectional view, a total propulsion system associated with the aerial vehicle according to the present disclosure.

[0039] In the below, Figures 1 and 2 will be discussed simultaneously. However, before discussing the figures that schematically show the inventive concept according to the present disclosure, first the state of the art is described. According to the state of the art, a battery-powered aerial vehicle may have a propeller driven by a number of batteries. The batteries power an electrical motor which in turn rotates the propeller, the propeller displaces a volume of air and, potentially, accelerates the same and as a result, thrust is generated. In operation, the batteries and the electrical motor are cooled using a cooling fluid. The cooling fluid is cooled by flowing it through a heat exchanger, the heat exchanger being in contact with the ambient air. For that reason, there is a flow channel inside of the aerial vehicle associated with the heat exchanger. Besides the battery-powered propeller aircraft, there is a (traditional) turbine engine which acts as a back-up propulsion system in case the electric energy from the batteries is depleted.

[0040] According to the present disclosure, the total propulsive system of such a battery-powered aerial vehicle, i.e. the system comprising the primary electrical engines and the components associated therewith, as well as the secondary turbine engine and the components associated therewith, is optimized by integrating the two systems that are normally designed in isolation from each other. According to the present disclosure, there is thus an aerial vehicle, e.g. an airplane of any sort. The aerial vehicle comprises an electrical engine, generally denominated by the reference number 163 as well as a turbine engine 13.

[0041] Zooming in on the electrical engine, it comprises in this case two electrical motors 163, which may e.g. comprise a stator and a rotor. In particular, the rotor may be connected to a propeller 162, so that the propeller 162 may be rotated by operating the electrical engine 163 thereby creating thrust. A spinner, with a governor, 161, may be associated with the propeller to keep the system in the desired balance. The electrical motors 163 are electrically powered by a set of batteries 164, which may e.g. be integrated with the wingbox of the aerial vehicle.

[0042] Zooming in on the turbine engine 13, it will typically have an air inlet duct, one or more compressor blades, a combustion chamber, one or more turbine blades, optionally, a bypass and a mixer 14, and an exhaust nozzle. All of these components are deemed known, at least to a basic level needed for understanding the present disclosure, to one skilled in the art. For example, the turbine engine 13 may be a turbofan engine or a turboshaft engine. For example, the turbine engine may be fuelled by kerosene.

[0043] Like a turbine engine 13 which typically needs cooling at the combustion chamber and the first turbine blade(s) behind the combustion chamber, an electrical engine 163 and a battery 164 need to be cooled as well (when used for propelling aerial vehicles). Cooling of electrical components such as electrical motors 163 and batteries 164 may take place by bringing them in thermal contact with a circulation fluid, the circulation fluid absorbing the heat generated by the electrical components 163, 164. As such, before the circulation fluid is brought in contact with the electrical components 163, 164 it is cold, after it is brought into contact with the electrical components 163, 164 it is hot. As the circulation fluid is being circulated, it must be cooled before it is returned to the electrical components 163, 164. For that purpose it is circulated through a heat exchanger 12, where it is in thermal contact with the ambient air. In the heat exchanger 12, the ambient air is heated and the circulation fluid is cooled. Depending on inter alia the intake of air, the flow rate of the circulation fluid through the heat exchanger 12, the inlet temperature of both media and the desired end temperature for the circulation fluid, a sufficient cooling of the circulation fluid can be obtained. In this way, a cooling system for the electrical components 163, 164 is provided.

[0044] According to the present disclosure, the total propulsive system is integrated by equipping the aerial vehicle with just a single inlet duct 11 per turbine engine 13. The single inlet duct 11 takes in a certain volume of air which is distributed towards the heat exchanger 12 of the electrical component’s 163, 164 cooling system and / or the turbine engine 13. As such, when considering the inlet duct 11 to be the inlet duct 11 associated with the turbine engine 13, the heat exchanger 12 of the cooling system is positioned inside the inlet duct 11 of the turbine engine. Vice versa, when considering the inlet duct 11 to be the inlet duct 11 associated with the cooling system / heat exchanger 12, the turbine engine 13 is placed inside the exhaust nozzle of the cooling system’s air duct. This is made possible because this heat exchanger 12 and this turbine engine 13 are arranged in the same flow path, behind each other (when seen in the flow path of the air).

[0045] As is shown, both the inlet duct 11 and the exhaust nozzle 15 have an inlet / outlet area of a variable size. In particular, each of the inlet duct 11 and the exhaust nozzle 15 comprise a hinge 111, 151. By manipulating the hinge 111, 151 a position of a variable-area portion 113, 152 of the inlet / exhaust can be manipulated, as is indicated by the respective arrows pointing upwards / downwards. A stationary portion 112, 153 of the inlet / outlet remains in a fixed position. In this way, the volume / mass of air that is introduced in the duct can be controlled. For every exhaust area, there exists an inlet area for which the total pressure recovery in the inlet duct is maximized.

[0046] As follows from a comparison of Figure 1 to Figure 2, it is not required that the inlet duct 11, or, for that matter, the outlet duct 15, is always symmetrical. For example, in the embodiment shown in Figure 2 the lower lip 113 of the inlet duct 11 may be moved and is variable in position, while the upper lip of the inlet duct 11 remains stationary and is non-variable. This is not a principal requirement, as both parts are variable in the embodiment of Figure 1.

[0047] When operating the turbine engine 13 the maximum amount of air may be desired. When operating the electrical engine 163 the relative opening of the inlet area may depend on the speed of the aerial vehicle, the height at which it flies (i.e. air density), the temperature of the outside air, the outlet area of the exhaust and other factors. In general it may be said that, when flying using the primary electrical engine, enough air should enter the inlet duct to sufficiently cool the circulation fluid, but not an unnecessary amount as this increases the drag of the vehicle.

[0048] Likewise, the outlet area of the exhaust nozzle 15 can be altered, in particular to control the speed with which the air leaves the exhaust 15. In this way, the thrust produced by the propulsion systems can be (slightly) improved and / or the time air spends around the heat exchanger can be changed.

[0049] Looking at the heat exchanger 12 now, also the position of the heat exchanger 12 in the duct 11 can preferably be changed. In particular, the heat exchanger 12 has a (shown) extended position, in which it is operational and inside the inlet duct 11 of the turbine engine 13. In the shown operational position, heat is exchanged between the ambient air and the circulation fluid inside the heat exchanger 12. As is evidenced by the arrow towards the end of the heat exchanger 12, the heat exchanger 12 can be retracted, or folded, towards a non-active position in which it is aligned with the stationary part 112 of the inlet duct 11. Of course, this may not be desirable when the aerial vehicle is operated in electrical engine 163 mode, as in this position of the heat exchanger 12 not much heat can be exchanged. However, when the electrical propulsion system is inactive, it may certainly be advantageous to allow the heat exchanger 12 to retract, as this vastly improved turbine 13 efficiency. For example, a hinge 121 may be associated with the heat exchanger 12 to allow this retractability.

[0050] Moving now to the different operational modes of the aerial vehicle, the electrical engines 163 may define the primary propulsion system, i.e. the propulsion system that is used by default. Preferably, when in flight, only one of the two propulsion systems may be used – in the default mode only the electrical propulsion system 161, 162, 163, 164. In this mode, the blades of the turbine engine 13 may be arranged in a windmilling condition to minimize the drag penalty of this component. When the primary, i.e. the electrical, engine fails, the secondary, i.e. turbine, engine may kick in. In starting up the turbine engine 13 the heat exchanger 12 may be folded in, to get the air towards the first compressor stage of the turbine engine 13 as clean as possible. In starting up the turbine engine 13, there may be a transitional phase, a brief period in which both propulsion systems 13, 16 are active. After the transitional phase, it will however typically be only the turbine engine 13 which is active, with the electrical engine 163 no longer providing thrust to the aerial vehicle. The exception to only one of the engines being operational may be when the aerial vehicle is on the ground, in particular when the aerial vehicle is parked. In this position, an electrical current may be desired inside the aerial vehicle, so that in this position especially the batteries 164 may be active and / or the electrical engines 163 may be active. The batteries 164 and / or electrical engines 163 being active means that they need to be cooled, but no ambient air is naturally flowing through the duct when the aerial vehicle is standing still. Hence, the turbofan engine 13 may be operated, by a starter thereof, to induce some air flow through the duct and have ambient air in contact with the heat exchanger 12 to cool the operational electrical engines 163 and / or batteries 164.

Claims

CLAIMS1. An aerial vehicle, comprising:one or more battery packs, for providing electrical power;- one or more primary electrical engines, powered by the one or more battery packs,a cooling system for cooling the one or more battery packs and / or the one or more primary electrical engines, the cooling system comprising:o a circulation fluid in thermal contact with the one or more battery packs and / or the one or more primary electrical engines, the circulation fluid arranged for exchanging heat between the one or more battery packs and / or the one or more primary electrical engines and the circulation fluid;o a heat exchanger, in thermal contact with the ambient air, for exchanging heat between the circulation fluid and the ambient air; a fuel storage system, for storing fuel;a secondary turbine engine comprising a combustion chamber, an inlet duct and an exhaust nozzle, powered by the fuel;wherein the heat exchanger of the cooling system is positioned inside the inlet duct of the secondary turbine engine.

2. The aerial vehicle according to claim 1, wherein the inlet duct has an inlet area of variable size.

3. The aerial vehicle according to claim 2, wherein the inlet duct has a stationary portion and a variable-area portion.

4. The aerial vehicle according to any one of the preceding claims, wherein the exhaust nozzle has an outlet area of variable size.

5. The aerial vehicle according to any one of the preceding claims, wherein the heat exchanger is foldable about a hinge axis, wherein in a folded position the heat exchanger is positioned substantially parallel to a wall of the inlet duct of the turbineengine whereas in an extended position the heat exchanger extends away from said wall.

6. The aerial vehicle according to claims 3 and 5, wherein the heat exchanger is positioned in the stationary portion of the inlet duct.

7. The aerial vehicle according to any one of the preceding claims, wherein the turbine engine is a turbofan engine.

8. The aerial vehicle according to any one of the claims 1 – 6, wherein the turbine engine is a turboshaft engine.

9. The aerial vehicle according to any one of the preceding claims, wherein the fuel is kerosene.

10. The aerial vehicle according to any one of the preceding claims, wherein the heat exchanger is arranged in the same flow path as the turbine engine.

11. The aerial vehicle according to any one of the preceding claims, wherein when the primary electrical engine is operative during flight, the turbine engine is arranged in a windmilling condition.

12. The aerial vehicle according to any one of the claims 6 - 11, wherein when the secondary turbine engine is operative during flight, the heat exchanger is arranged in the folded position.

13. The aerial vehicle according to any one of the preceding claims, wherein when the aerial vehicle is in contact with a ground surface, the heat exchanger is in the extended position and the turbine engine is operative for generating a mass flow over the heat exchanger, the turbine engine in particular being operated by an electric starter motor thereof.

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