HEAT RECOVERY DEVICE

Abstract

 The present invention relates to a heat recovery device particularly conceived for an internal combustion engine, and in particular for a vehicle including said internal combustion engine. The heat recovery device is based on a Rankine cycle in which the high-pressure stage has been modified. The invention is characterized by the use of a tank in the high-pressure region of the Rankine cycle for storing the fluid before entering the turbine or expander maintaining said fluid in the liquid phase so as to drastically reduce the specific volume, and an expansion valve arranged between the tank and the inlet of the turbine or expander for causing the liquid-to-vapor phase change of the fluid right at the inlet, which prevents that the high specific volume in the vapor phase leads to large-sized devices.

Description

Object of the Invention

[0001] The present invention relates to a heat recovery device particularly conceived for an internal combustion engine, and in particular for a vehicle including said internal combustion engine.

[0002] The heat recovery device is based on a Rankine cycle in which the high-pressure stage has been modified.

[0003] In a Rankine cycle like those known in the state of the art, the fluid on which the thermal cycle is carried out, or working fluid, is compressed in the liquid phase by the pump until it reaches the heat source causing the phase change. The phase change usually takes place in a boiler or in an evaporator, in such a manner that the fluid changes phase significantly increasing its specific volume in its transition inside the boiler or evaporator. The fluid in the vapor phase, having a high enthalpy provided by the heat source, enters the turbine or expander, where a large part of the enthalpy is transformed into mechanical energy.

[0004] The invention is characterized by the use of a tank in the high-pressure region of the Rankine cycle for storing the fluid before entering the turbine or expander, maintaining said fluid in the liquid phase so as to drastically reduce its specific volume, and an expansion valve arranged between the tank and the inlet of the turbine or expander for causing the liquid-to-vapor phase change of the fluid right at the inlet, which prevents that the high specific volume in the vapor phase leads to large-sized devices.

Background of the Invention

[0005] One of the most intensively developed fields of the art is the field of harnessing residual heat in combustion processes. In particular, this interest is even greater in relation to vehicles with internal combustion engines where the engine harnesses are, in a best-case scenario, between 15% and 20% of the energy stored in the fuel, more than 80% of the energy stored in said fuel therefore being lost. The rest of the energy is not used to generate mechanical power in the engine shaft, but rather is lost in the form of mechanical friction between the elements of the engine (the piston for example), the operation of auxiliary elements (such as refrigeration and lubrication pumps), or it is given off into the atmosphere in the form of heat (with the exhaust gases or with the energy absorbed by the coolant dissipated in a radiator for example).

[0006] Various solutions for harnessing residual heat have been sought, for example by means of heat exchangers that transfer this heat to a second fluid that is utilized for a number of uses, such as heating the interior of the vehicle or reducing the engine heating time to reach the nominal temperature by reducing, for example, the time in which the lubricant of the engine is not working under the best conditions.

[0007] Even in these cases, the heat flow given off into the atmosphere is constant while the internal combustion engine is operating, and the mentioned needs are often times isolated or limited over time, giving rise to wasting the exhaust gas energy.

[0008] One alternative used for harnessing the residual heat of the exhaust gases and of the cooling fluid is to include a Rankine cycle wherein said exhaust gases and cooling fluid are the heat source. Even though a Rankine cycle in an industrial plant can have enough space for the devices involved, in a vehicle, and in particular in the engine compartment, space is a scarce resource.

[0009] Evaporation devices or boilers in charge of providing energy to the Rankine cycle require a large volume since the phase change significantly increases the volume required for circulating the fluid in the liquid plus vapor phase or finally in the form of vapor.

[0010] When a Rankine cycle is used in a vehicle, the primary demand for energy occurs when a driving force of the vehicle is required, and is nil, with respect to this same force, when actuating with the brake of the vehicle. Under these circumstances, the Rankine cycle according to the state of the art does not have the capacity to almost instantaneously regulate the energy given off by the fluid in the turbine or expander and making use of the mechanical energy obtained, so as to provide that driving force at suitable times.

[0011] The present invention solves these problems by preventing the circulation of the fluid with high enthalpy in the vapor phase during the energy transfer from the hot source to the fluid, this objective being achieved by causing the phase change right before the fluid is introduced into the turbine or expander. The specific volume of the fluid with high enthalpy is thereby drastically reduced, and the components through which the fluid passes in this step are therefore also reduced. This allows reducing the size of the devices, thereby preventing the installation of extremely bulky evaporators.

[0012] The invention also solves specific problems according to various embodiments that will be described in detail below in relation to the figures.

Description of the Invention

[0013] The present invention is a heat recovery device suitable for an internal combustion engine. The device is based on a Rankine cycle and comprises at least:

• a turbine or an expander comprising a feed inlet for a fluid in the vapor phase and an outlet for the same fluid, wherein the turbine or expander is configured for transforming the thermal energy of the fluid in the vapor phase into mechanical energy;
• a condenser comprising an inlet for the fluid in fluid communication with the outlet of the turbine or expander and an outlet for the fluid in the liquid phase, wherein the condenser is configured for removing heat from the fluid, causing a vapor-to-liquid phase change of the fluid;
• a first pressure pump comprising an inlet for the fluid in fluid communication with the outlet of the condenser and an outlet for the fluid, wherein the first pump is configured for raising the pressure of the fluid in the liquid phase;
• a main heat exchanger configured for transferring heat from a hot fluid, preferably the exhaust gas of the internal combustion engine, to the high-pressure liquid fluid exiting the first pump;

wherein the outlet of the first pressure pump is in fluid communication with the turbine or expander.

[0014] In a particular example, the hot fluid is the cooling fluid.

[0015] The Rankine cycle is carried out on a fluid in a closed circuit. The turbine or expander is the component which transforms the energy stored in the working fluid, which has high enthalpy, into mechanical energy, for example driving a shaft. The inlet in the turbine or expander receives the fluid in the vapor phase with high enthalpy and at the outlet the same fluid continues in the vapor phase but with lower enthalpy and lower pressure.

[0016] The fluid at the outlet of the turbine or expander, now with lower enthalpy, enters the condenser for causing the vapor-to-liquid phase change. The condenser is a heat exchanger that cools the vapor by removing heat.

[0017] When the device of the invention is installed in an internal combustion engine, in a preferred embodiment the fluid coolant which removes the heat from the thermal fluid in the vapor phase is the liquid coolant of the internal combustion engine. If the heat to be removed is high, the engine may include a second cooling circuit for example with an independent radiator.

[0018] In a particular example, the fluid coolant which removes the heat from the thermal fluid in the vapor phase is the ambient air around the engine.

[0019] Once the fluid has exited the condenser, it is in the liquid phase and has a lower specific volume. The fluid is pumped by means of the pressure pump, again raising its pressure and maintaining the fluid in the liquid phase.

[0020] The fluid at high pressure again receives heat from the heat source, or main heat exchanger, to increase its enthalpy. When the device of the invention is installed in an internal combustion engine, the preferred way to provide heat is by means of one or several heat exchangers that transfer the heat of the exhaust gases to the thermal fluid following the Rankine cycle.

[0021] Preferably, the exhaust gases come from either the exhaust pipe circuit, from the exhaust gas recirculation circuit for recirculating said exhaust gas to the intake manifold, or from both.

[0022] In a particular example, the heat can be transferred from the hot cooling fluid of the engine to the thermal fluid following the Rankine cycle.

[0023] The invention modifies the elements normally arranged in the fluid communication existing between the pump and the turbine or expander. According to the invention, the device comprises:

• an expansion valve located in a position before the inlet of the turbine or expander for causing the liquid-to-vapor phase change of the fluid.

[0024] In a particular example, the device comprises a first tank (5) interposed in the fluid communication between the outlet (4.2) of the first pressure pump (4) and the inlet (1.1) of the turbine or expander (1) for storing the fluid at high pressure in the liquid phase heated by the main exchanger (7), and wherein the expansion valve (6) is located between the first tank (5) and the inlet (1.1) of the turbine or expander (1).

[0025] Normally and according to the state of the art, the liquid fluid exiting the pump enters a boiler or evaporator such that the phase change takes place inside this element. Inside the element where the phase change takes place, there is a first segment with the fluid in the liquid phase where its temperature gradually increases until reaching the boiling temperature, a second segment where a mixture of liquid plus vapor can be found, and finally a third segment where just vapor can be found. The second and third stages require the element used for causing the phase change to be very bulky, since the vapor gradually increases the specific volume in a very significant manner.

[0026] Elements of this type are furthermore oversized, since the point between the first and the second segment and the point between the second and the third segment constantly change position depending on operating conditions, and the positions thereof cannot be readily established. The element in charge of providing heat causing the phase change must therefore have a volume sufficient for storing all the vapor no matter where it is generated, in order not to become damaged.

[0027] However, the device according to the invention comprises an expansion valve causing in the fluid with high pressure and enthalpy the abrupt transitioning from the liquid phase to the vapor phase right before entering the turbine or expander. The highest specific volume of the vapor phase can be found right at the inlet of the turbine or expander, so no intermediate device is required to have a large volume for storing vapor.

[0028] Additionally, in the device that according to one example comprises a first tank instead of using a boiler or an evaporator, the tank is interposed in the fluid communication between the outlet of the first pressure pump and the inlet of the turbine or expander for storing the fluid at high pressure in the liquid phase and heated by the heat exchanger.

[0029] The heat exchanger according to a first embodiment raises the temperature by means of circulating the thermal fluid between the heat exchanger and the inside of the first tank. According to another embodiment, the first tank has more than one compartment such that the passage from one compartment to another is carried out through the heat exchanger. These and other embodiments will be described below in greater detail.

[0030] In any case, the first tank stores liquid at high pressure and high enthalpy, and the fluid also raises its temperature due to the transfer of heat either from the hot cooling fluid of the engine or else from the exhaust gases to the liquid fluid, or even from both.

[0031] The entire storage of the fluid at high pressure and high enthalpy takes place in the liquid phase such that the specific volume is low. Therefore, in a reduced volume there is a fluid with high enthalpy to be expanded by means of the turbine or by means of the expander.

[0032] The device combines the first tank with an expansion valve located between said first tank and the turbine or expander.

[0033] Various embodiments will be described based on the drawings.

Description of the Drawings

[0034] These and other features and advantages of the invention will be more clearly understood based on the following detailed description of a preferred embodiment given solely by way of nonlimiting illustrative example in reference to the attached drawings.

Figure 1 schematically shows the elements forming several embodiments. Discontinuous lines identify those elements that are optionally located in a given position in the diagram for configuring a specific embodiment.

Figure 2 shows the entropy-enthalpy graph for a fluid made up of one or more specific hydrocarbons showing at least one segment of the liquid plus vapor/vapor equilibrium curve (L2) for values of enthalpy that are lower than the critical point enthalpy such that an increase in entropy corresponds to an increase in enthalpy. This type of fluid will be used for a thermodynamic cycle particularly suitable for various examples of the invention.

Detailed Description of the Invention

[0035] According to the first inventive aspect, the present invention is a device for heat recovery that can be applied to recovering heat from any heat source with the suitable temperature so as to establish the thermodynamic cycle for the selected fluid. Nevertheless, all of the examples described in this section will refer to recovering heat from the residual heat coming from either a hot cooling fluid or else from the exhaust gases of an internal combustion engine, such as a stationary internal combustion engine, for example, used as an electricity generator; and more specifically for a vehicle with an internal combustion engine where space requirements are stricter.

[0036] Figure 1 shows a diagram where the components of a device according to several embodiments of the invention are identified.

[0037] Starting with what is shown on the right side of the drawing, a turbine or expander (1) is responsible for transforming part of the enthalpy (h) of the fluid in the vapor phase entering through an inlet (1.1) into mechanical energy, the fluid exiting also in the vapor phase through an outlet (1.2).

[0038] When the component transforming the enthalpy (h) of the fluid into mechanical energy is a turbine (1), then the mechanical energy that is obtained is provided in the rotating shaft of the turbine. When the component is an expander (1), said component can be a cylinder with axial displacement. One or more axial cylinders can for example drive a crankshaft transforming the axial displacement into rotation of the shaft also.

[0039] This shaft can provide its energy either directly to the driving of the vehicle with a kinematic coupling which is aggregated to the drive from the engine, or else indirectly for example by coupling the output shaft to a current generator feeding, with or without the intermediation of electric batteries, one or more electric motors, giving rise to a hybrid propulsion system or covering the electrical energy needs of the vehicle.

[0040] The vapor exiting the outlet (1.2) of the turbine or expander (1) is introduced in a condenser (2) for causing the phase change, from the vapor phase to the liquid phase, reducing its specific volume. The inlet (2.1) of the condenser (2) thereby receives vapor from the outlet of the turbine or expander (1) and through the outlet (2.2) of the condenser (2) itself it exits in the liquid state, ready for raising its pressure again.

[0041] In a particular embodiment, it is possible to intercalate a heat exchanger (12), or regenerator, between the outlet (1.2) of the turbine or expander (1) and the inlet (2.1) of the condenser (2). This exchanger (12) is normally used as a pre-heater for the fluid exiting the pump (4).

[0042] Continuing with the same diagram, the outlet (2.2) of the condenser (2) is fluidic communicated with a tank referred to as second tank (3) with a capacity for storing a variable volume of liquid. This second tank (3) is an optional element that will be used for a specific example that will be described below.

[0043] The outlet of the second tank (3) for storing liquid is fluidic connected with an inlet (4.1) of a first pump (4) at the outlet (4.2) of which the same liquid is obtained at a higher pressure.

[0044] According to one embodiment, the liquid fluid exiting the outlet (4.2) of the first pump (4) passes through a heat exchanger which will be identified as third heat exchanger (10). This third heat exchanger (10) is an optional component according to one embodiment in which the liquid fluid is pre-heated for example by means of the liquid coolant of the internal combustion engine or by means of the regenerator (12).

[0045] In a particular example, the liquid fluid exiting from either the outlet (4.2) of the first pump (4) or else from the third heat exchanger (10) enters a tank referred to as first tank (5). It is in this first tank (5) where, in combination with a heat exchanger (7, 8), its temperature is raised, based on the hot source of the thermal cycle. In the described embodiments, this hot source consists of the exhaust gases of the internal combustion engine from which heat is to be recovered. This heat of the exhaust gases may in turn have two sources: the exhaust gases circulating through the exhaust pipe out into the atmosphere, or the exhaust gases that are recirculated to the intake manifold of the engine.

[0046] In one embodiment, a main heat exchanger (7) has its inlet and its outlet in fluid communication with the first tank (5), the liquid fluid being exchanged between the first tank (5) and said main heat exchanger (7), raising its temperature.

[0047] One way to circulate the liquid fluid is by means of a hot fluid recirculation pump or drive pump, not depicted in Figure 1. Another way to circulate the liquid fluid is by means of pressure differences between the compartments of the tank.

[0048] According to another embodiment, the first tank (5) comprises a movable wall that allows the expansion of its internal volume such that the volume of liquid fluid to be stored is variable. According to one embodiment, this movable wall has a spring or elastic element that tends to recover its initial position such that it maintains the pressure in the variable inner volume.

[0049] According to this embodiment, it is possible to almost instantaneously manage the injection of fluid into the turbine or expander (1) since the mass flow at the outlet of the first tank (5) which changes phase in the expansion valve (6) does not have to be equal to the mass flow imposed by the first pump (4). When the application of this embodiment is a vehicle, the mechanical energy delivered by the turbine or expander (1) can be controlled in the event of drive demands of the vehicle or the energy needs of auxiliary devices.

[0050] Taking into consideration the configuration of the first tank (5), according to another embodiment that can be combined with the embodiments described up until now, this tank (5) comprises two compartments (5.1, 5.2), a low-temperature compartment (5.1) and another high-temperature compartment (5.2). According to this configuration, the liquid fluid either exiting the first pump (4) or else exiting the third heat exchanger (10) first enters the first low-temperature compartment (5.1) and from there it passes on to the second high-temperature compartment (5.2), passing through the main heat exchanger (7) which transfers heat from the exhaust gases to the thermal fluid. It is this second high-temperature compartment (5.2) that feeds the turbine or expander (1) with the intermediation of the expansion valve (6).

[0051] Given that the first tank (5) stores the liquid fluid with high enthalpy, the temperature of the fluid should be kept high when it is stored and is not yet being used by the turbine or expander (1). In this case, an exchanger:

• either the main exchanger (7)
• or else a second heat exchanger (8) configured for transferring heat from hot gases, preferably the exhaust gas of the internal combustion engine, to the high-pressure liquid fluid,

is in series with a second recirculation pump (9) for maintaining the high temperature of the fluid stored in the high-temperature compartment (5.2) of the first tank (5).

[0052] The possibility of almost instantaneously managing the generation of mechanical energy in the turbine (1) or in the expander (1) by combining the first tank (5) with a variable volume and the expansion valve (6) has been described. According to another embodiment, it is also possible to manage the thermal cycle according to the demands of the vehicle while braking.

[0053] According to this embodiment, which can be combined with the embodiments described above, the first pump (4) is actuated through a regenerative brake of the vehicle. In other words, the brake torque of the wheels of the vehicle is used as the drive torque of the first pump (4).

[0054] Another preferred embodiment of a regenerative brake is the one including the second tank (3) described above, since the first pump (4) has liquid to be pumped at any time, since the braking moments are not predictable. At the time of braking, the regenerative brake acts on the first pump (4) by raising the pressure of an amount of liquid fluid that is transferred from the second tank (3) to the first tank (5) regardless of the mass flow going through either the turbine or expander (1).

[0055] In a preferred embodiment, the device comprises a central processing unit (CPU) with an output for providing an actuation signal either in the expansion valve (6) or else in a flow control valve located before or after the expansion valve (6) for the opening or closing thereof, the processing unit (CPU) being configured for managing the expansion valve (6) or the flow control valve by injecting vapor into the turbine or expander (1) only when the vehicle requires driving power.

[0056] In another embodiment, the central processing unit (CPU) is additionally configured for sending an actuation signal to close the expansion valve (6) when the first pump (4) is driven by the regenerative brake. The cycle of the thermal fluid therefore adapts to the braking and drive demands of the vehicle, primarily when the mechanical energy obtained in the turbine or expander (1) is used in driving the vehicle.

[0057] In other words, the present embodiment allows controlling the expansion valve (6), located before the turbine or expander (1), by means of two options such that both the flow rate and the expansion are managed by the central processing unit (CPU):

a) this first option allows the electronically controlled flow control valve located before or after the expansion valve (6) to control the flow that is passed on to the turbine or expander (1), whereas the expansion valve (6) itself controls that said flow evaporates by means of flashing,

b) this second option allows, by means of the expansion valve (6), controlling both the passage section of the valve, where it is variable, such that control is applied on the passage of fluid and flashing and vaporization by means of this opening controlled by the outlet pressure. This regulation is performed electronically.

[0058] In both examples, the control of the expansion valve (6) requires reading the pressure difference with pressure sensors between the inlet and the outlet of said expansion valve (6) so that the central processing unit (CPU) can establish an opening of the expansion valve (6) that determines sufficient flashing for assuring the phase change of the entire flow.

[0059] One embodiment based on any of the examples described up until now includes a superheater (11) that raises the temperature of the vapor obtained in the expansion valve (6). It is thereby assured that the vapor does not transition to the liquid phase until after it exits the turbine or expander (1).

[0060] One embodiment that can be applied to any of the described examples in which the thermal fluid is such that the liquid plus vapor/vapor equilibrium curve (L2) in the entropy (S)/enthalpy (h) graph comprises at least one segment for values of enthalpy (h) that are lower than the critical point enthalpy in which the slope is such that an increase in entropy (S) corresponds to an increase in enthalpy (h) has been found to be of particular interest.

[0061] An example of an entropy (S)/enthalpy (h) graph showing this example is shown in Figure 2. The solid lines depict both the liquid/liquid plus vapor equilibrium curve (L1) and the liquid plus vapor/vapor equilibrium curve (L2). The discontinuous lines identify the path of the thermal cycle of the fluid according to a preferred example. The intersection of both continuous curves identifies the critical point (CR).

[0062] With respect to the path of the thermal cycle and starting from the point located farther to the left and in the lower part where the fluid is already in the liquid phase after having passed through the condenser (2), the first pump (4) raises the pressure and therefore the enthalpy (h) according to a process that would ideally be isentropic (D).

[0063] After the outlet of the first pump (4), the liquid raises the enthalpy and the entropy (E) thereof by raising the temperature by means of the heat given off from the hot cooling fluid of the engine and from the exhaust gases, for example through the main heat exchanger (7). In this entire path the fluid is kept to the left of the liquid/liquid plus vapor equilibrium curve (L1), so it is stored in the first tank (5) taking up a reduced volume.

[0064] At the upper end of the cycle, the liquid is expanded by means of the expansion valve (6) according to an isenthalpic process (A) causing all of the liquid to change phase to vapor phase. The vapor is introduced in the turbine or expander (1) continuing with a process which would ideally be isentropic (B), until reaching the lower point of the straight vertical segment.

[0065] In this embodiment, the isenthalpic process (A) takes place below the critical point (CR), although it may be possible for it to take place above it.

[0066] The fluid in the vapor phase is introduced in the condenser (2) going through two solid lines, given that it goes from vapor to liquid plus vapor and then all of the fluid is in the liquid phase, returning to the point from where the description of the path of the thermal cycle based on Figure 2 started.

[0067] According to this embodiment, the same drawing identifies, using a thicker segment located between two thick points, the at least one segment verifying the condition of having an inclination such that, for values of enthalpy (h) that are lower than the critical point enthalpy (CR), the slope is such that an increase in entropy (S) corresponds to an increase in enthalpy (h).

[0068] The use of a fluid characterized by this condition in its liquid plus vapor/vapor equilibrium line (L2) solves the problem of the occurrence of condensation drops in the fluid passing through the turbine or expander (1). Once the expansion valve has assured that the fluid enters the inlet of the turbine or expander (1) in vapor phase, the inclination of the liquid plus vapor/vapor equilibrium curve (L2) moves further away as the thermal cycle descends in its isentropic process, so there is no danger of crossing said equilibrium curve (L2), which would give rise to a thermodynamic state that would cause condensation.

[0069] In a preferred example the segment which is subject to the imposition of having an inclination such that the slope is such that an increase in entropy (S) corresponds to an increase in enthalpy (h) is a segment having its upper end at the critical point (CR).

[0070] One embodiment based on any of the examples described up until now includes a regenerator (12), which allows reducing the temperature of the gas after it passes through the turbine or expander (1) and reutilizing this heat to heat up the working fluid after it passes through the pump (4). Hence in Figure 1 the two stages of the heat exchanger (12) are shown to be connected by means of a dashed line, indicating that both stages can be configured in one and the same physical device.

Claims

1. A heat recovery device suitable for an internal combustion engine, wherein heat recovery takes place by means of a Rankine cycle, the device comprising:

- a turbine or an expander (1) comprising a feed inlet (1.1) for a fluid in the vapor phase and an outlet (1.2) for the same fluid, wherein the turbine or expander (1) is configured for transforming the thermal energy of the fluid in the vapor phase into mechanical energy;

- a condenser (2) comprising an inlet (2.1) for the fluid in fluid communication with the outlet (1.2) of the turbine or expander (1) and an outlet (2.2) for the fluid in the liquid phase, wherein the condenser (2) is configured for removing heat from the fluid causing a vapor-to-liquid phase change of the fluid;

- a first pressure pump (4) comprising an inlet (4.1) for the fluid in fluid communication with the outlet (2.2) of the condenser (2) and an outlet (4.2) for the fluid, wherein the first pump (4) is configured for raising the pressure of the fluid in the liquid phase;

- a main heat exchanger (7) configured for transferring heat from a hot fluid, preferably the exhaust gas of the internal combustion engine, to the high-pressure liquid fluid exiting the first pump (4);

wherein the outlet (4.2) of the first pressure pump (4) is in fluid communication with the turbine or expander (1) characterized in that the device additionally comprises

- an expansion valve (6) located in a position before the inlet (1.1) of the turbine or expander (1) for causing the liquid-to-vapor phase change of the fluid.

2. The device according to claim 1, additionally comprising a first tank (5) interposed in the fluid communication between the outlet (4.2) of the first pressure pump (4) and the inlet (1.1) of the turbine or expander (1) for storing the fluid at high pressure in the liquid phase heated by the main exchanger (7), and
wherein the expansion valve (6) is located between the first tank (5) and the inlet (1.1) of the turbine or expander (1).

3. The device according to claim 2, additionally comprising a superheater (11) interposed between the expansion valve (6) and the inlet (1.1) of the turbine or expander (1) for raising the temperature of the fluid in the vapor phase.

4. The device according to any of the preceding claims, wherein the fluid is such that the liquid plus vapor/vapor equilibrium curve (L2) in the entropy (S)/enthalpy (h) graph comprises at least one segment located in the vapor region for values of enthalpy (h) that are lower than the critical point enthalpy in which the slope is such that an increase in entropy (S) corresponds to an increase in enthalpy (h).

5. The device according to any of the preceding claims, wherein the first tank (5) is configured for the intake of a variable volume of liquid maintaining the pressure of the stored fluid.

6. The device according to the preceding claim, wherein the first tank (5) comprises a movable wall that allows the expansion of its internal volume.

7. The device according to any of the preceding claims, wherein the first tank (5) comprises two compartments (5.1, 5.2), a low-temperature compartment (5.1) and another high-temperature compartment (5.2).

8. The device according to claim 7, wherein the passage of fluid between the low-temperature compartment (5.1) and the high-temperature compartment (5.2) is carried out with the fluid passing through the main heat exchanger (7).

9. The device according to any of claims 7 or 8, wherein an exchanger:

- either the main exchanger (7)

- or a second heat exchanger (8) configured for transferring heat from hot gases, preferably the exhaust gas of the internal combustion engine, to the high-pressure liquid fluid,

is in series with a second recirculation pump (9) for maintaining the high temperature of the fluid stored in the high-temperature compartment (5.2) of the first tank (5).

10. The device according to any of the preceding claims, wherein a third heat exchanger (10) is located at the outlet (4.2) of the first pump (4) for raising the temperature of the liquid at high pressure in a pre-heating step from the heat of the liquid coolant of the internal combustion engine or from the enthalpy of the fluid at the outlet (1.2) of the turbine or expander (1) by means of a regenerator (12).

11. The device according to any of the preceding claims, wherein a second tank (3) with a capacity for storing a variable volume of liquid is intercalated between the condenser (2) and the first pump (4) for storing the liquid fluid before raising its pressure.

12. The device according to any of the preceding claims, wherein said device is installed in a vehicle and the first pump (4) is actuated through a regenerative brake of the vehicle, wherein a brake torque of the vehicle is used in operating the first pump (4).

13. The device according to claim 12, additionally comprising a central processing unit (CPU) with an output for providing an actuation signal either in the expansion valve (6) or else in a flow control valve located before or after the expansion valve (6), or else in both for the opening or closing thereof, the processing unit (CPU) being configured for managing the expansion valve (6) or the flow control valve by injecting vapor into the turbine or expander (1) only when the vehicle requires driving power.

14. The device according to claim 13, wherein the central processing unit (CPU) is additionally configured for sending an actuation signal to close the expansion valve (6) when the first pump (4) is driven by the regenerative brake.

15. A vehicle engine comprising a device according to any of the preceding claims.

16. A vehicle comprising an engine according to claim 15.

Drawing