Method for controlling a thermodynamic system for a motor vehicle

Abstract

The invention relates to a method for controlling a two-stage thermodynamic system comprising a first turbocharger (TC1), a second turbocharger (TC2), first (CC1) and second (CC2) combustion chambers and at least one fuel injector between the second turbocharger (TC2) and the second combustion chamber (CC2), the first turbocharger (TC1) comprising a first turbine (T2), the second turbocharger (TC2) comprising a second turbine (T1) and the second combustion chamber comprising an electrical heating resistor, the method comprising steps of: a) operating the electrical resistor of the second combustion chamber; b) reversing an operation of the first turbine (T2) in order to put the second turbine into compressor mode.

Description

DESCRIPTION TITLE: METHOD FOR CONTROLLING A THERMODYNAMIC SYSTEM IN A MOTOR VEHICLE The present invention claims priority from French application No. 2405891 filed on 05.06.2024, the content of which (text, drawings and claims) is incorporated herein by reference. TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the field of control methods for thermodynamic systems with gas turbine cycle with cooled compression, regeneration and intermediate heating during expansion, of the turbomachine type, equipping a powertrain of a motor vehicle. PREVIOUS STATE OF THE ART

[0002] Gas turbine-type power converters are currently being studied for highly electrified powertrains, particularly those known as range extenders in electric and / or hybrid vehicles. Such a converter operates as an Auxiliary Power Unit (APU), where its role is to recharge the batteries of an electric vehicle. It is thus mechanically decoupled from the powertrain and therefore operates at its maximum efficiency.

[0003] In particular, a thermodynamic system with a gas turbine cycle featuring cooled compression, regeneration, and reheating during expansion (a device known in English as an "Intercooled Regenerative Reheat Gas Turbine," or IRReGT) is a device with strong potential for applications in motor vehicles, especially those with an electric traction motor. This cycle allows for very high efficiency as well as very high power density (i.e., high net specific work).

[0004] Currently, in such a thermodynamic system, fuel is injected into a low-pressure combustion chamber when two turbochargers are spun. This injection and these rotations occur after the low-pressure combustion chamber has been electrically heated. However, there is no heating of the gas circulating between a low-pressure injector and the intake manifold (between the injector and the combustion chamber inlet). This works as long as the injected quantity of fuel is small enough to prevent condensation. Therefore, there is a risk of condensation of the injected fuel, and consequently, that this fuel, then in liquid form, could come into contact with an electrical resistor in the combustion chamber, potentially causing ignition. DESCRIPTION OF THE INVENTION

[0005] The invention aims to remedy all or part of the drawbacks of the prior art by proposing in particular a solution to reduce the risk of condensation and therefore the risk of ignition.

[0006] To this end, according to a first aspect of the invention, a method for controlling a two-stage thermodynamic system comprising a first turbocharger, a second turbocharger, first and second combustion chambers and at least one fuel injector between the second turbocharger and the second combustion chamber, the first turbocharger comprising a first turbine, the second turbocharger comprising a second turbine and the second combustion chamber comprising an electrical heating element, the thermodynamic system being configured such that at the outlet of the first combustion chamber, a first expansion occurs in the second turbine followed by a heating phase in the second combustion chamber before entering the first turbine to undergo a second expansion,The process comprises the steps of: a) Activating the electrical resistance of the second combustion chamber; b) Reversing the operation of the first turbine to switch the first turbine to compressor mode.

[0007] According to one embodiment, during the reversing step, the first turbine rotates in the opposite direction, circulating a flow of gas from the second combustion chamber to the fuel injector.

[0008] According to one embodiment, during the reversing step, the first turbine rotates by oscillating between opposite and normal operating directions, circulating a flow of gas between the second combustion chamber and the fuel injector in two flow directions.

[0009] According to one embodiment, during the reversing step, the second turbine is stopped.

[0010] According to one embodiment, during the reversing step, the second turbine is operating in a normal direction of operation.

[0011] According to one embodiment, during the reversing step, the first and second turbines rotate at predetermined speeds so as to circulate a flow of gas from the second combustion chamber to the fuel injector.

[0012] According to one embodiment, during the reversing step, the first and second turbines rotate at variable speeds so as to circulate a flow of gas between the second combustion chamber and the fuel injector in two flow directions.

[0013] According to one embodiment, at least the second turbine is a variable geometry turbine.

[0014] According to one embodiment, during the reversal step, the process modifies an opening of the second turbine.

[0015] According to another aspect of the invention, a motor vehicle is provided comprising a powertrain including an electric traction machine, a traction battery and a two-stage thermodynamic system, as well as a computer which is arranged to implement a control method according to the invention having at least one of the preceding technical characteristics. BRIEF DESCRIPTION OF THE FIGURES

[0016] Other features and advantages of the invention will become apparent from the following description, with reference to the attached figures, which illustrate: [Fig. 1]: a functional diagram of an example of a two-stage thermodynamic system, of the IRReGT type [Intercooled Recuperative Reheat Gas Turbine); [Fig. 2]: a schematic representation of an electrical energy production and storage circuit in a hybrid vehicle.

[0017] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DETAILED DESCRIPTION OF A METHOD OF IMPLEMENTATION

[0018] Figure 1 shows a functional diagram of an example of a two-stage thermodynamic system, of the IRReGT (Intercooled Recuperative Reheat Gas Turbine) type, on which a preferred embodiment of a method for controlling the thermodynamic system according to the invention is implemented.

[0019] With reference to Figure 2, we will describe here an example of the integration of such a gas turbine cycle thermodynamic system into the powertrain of a hybrid or electric vehicle, and more specifically within the electrical energy production and storage circuit of this vehicle. Such a thermodynamic system can notably operate as an auxiliary power unit (APU) in the case of an electric vehicle. When this thermodynamic system operates as an auxiliary power unit in a steady-state configuration, it recharges the traction battery(ies) B of the vehicle's powertrain via electric machines (EMG in Figure 2, or more specifically EMG1 and EMG2 in Figure 1).The battery is connected via AC-DC power converters (DC-AC blocks in Figure 2), on the one hand, to the thermodynamic system as an APU and, on the other hand, to an electric traction machine (ELM) of the motor vehicle's powertrain. A drive chain of a known type then connects the electric traction machine to the... wheels W of the motor vehicle. The APU further comprises a computer arranged so as to be able to implement a method of controlling the thermodynamic system, such as the method of controlling a thermodynamic system according to the invention which will be described later.

[0020] We will now detail a thermodynamic system of the aforementioned gas turbine cycle type with reference to Figure 1.

[0021] Such a thermodynamic system comprises a first turbocharger TCI and a second turbocharger TC2. The first turbocharger TCI includes a first compressor C1 and a first turbine T2. The second turbocharger TC2 includes a second compressor C2 and a second turbine T1. More specifically, the first turbocharger TCI forms a "low-pressure" stage, and the second turbocharger TC2 forms a "high-pressure" stage. Here, both turbines T1 and T2 are variable geometry turbines (VGTs).

[0022] The turbochargers here are electrified, that is to say they each include an electric machine EMG1, EMG2 operating both in motor and generator mode, that is to say as a motor to drive and start the system, and as a generator to recover the energy produced by combustion.

[0023] The thermodynamic system further comprises two combustion chambers, CCI and CC2, and a flow cooler IC (also called an air-to-air or air-to-water heat exchanger, or simply an intercooler). The flow cooler IC is positioned between and connected to the first compressor C1 and the second compressor C2. Both combustion chambers are catalytic. The second combustion chamber also includes an electric heating element. In an alternative embodiment, the first combustion chamber also includes an electric heating element.

[0024] The thermodynamic system also includes a heat recovery unit TR (or heat exchanger). The heat recovery unit TR is connected here to the second compressor C2 upstream and to the first chamber of CCI combustion downstream. The first CCI combustion chamber is then connected to the second turbine Tl.

[0025] The second combustion chamber CC2 is connected to both turbines, specifically to the second turbine T1 upstream and the first turbine T2 downstream. The thermodynamic system includes a fuel injector INJ upstream of the second combustion chamber CC2. This fuel injector injects fuel into the exhaust gas stream from the second turbine T1 before it enters the second combustion chamber CC2. Similarly, the thermodynamic system includes another fuel injector (not shown) upstream of the first combustion chamber CCI, which injects fuel into the exhaust gas stream from the heat recovery unit before it enters the first combustion chamber CCI.

[0026] The thermodynamic system further includes a recovery branch RB1 connecting the first turbine T2 to the heat recovery unit TR and passing through it. The side of the recuperator TR through which the recovery branch RB1 passes is called the hot side of the recuperator, since a gas flow comes directly from the first turbine T2 after undergoing a second combustion in the combustion chamber CC2. Conversely, the side of the recuperator TR receiving compressed air from the compressor C2, and from which the air is directed to the first combustion chamber CCI, is called the cold side of the recuperator.

[0027] The thermodynamic system is configured to be traversed by a gaseous flow Fl, described later, between the different elements composing it.

[0028] The use of a second CC2 combustion chamber (for reheat) between the turbines increases power density, which reduces the required airflow at the same power output and reduces the size of the device.

[0029] We will now briefly describe the gas flow Fl in the thermodynamic system that has just been described.

[0030] In general, the gas flow Fl follows the arrows illustrated in Figure 1, which connect the different components, and passes through these components. Air Ambient air is first drawn into an AF air filter by compressor C1. This filtered air then enters compressor C1. The air is compressed there before entering the IC flow cooler where it is cooled. It then enters compressor C2 where it is compressed a second time before entering the recuperator TR, specifically the cold side of the recuperator. In the recuperator TR, the air is preheated by hot gases from the RB1 recovery branch originating from the outlet of turbine T2. The air exiting the recuperator TR thus enters the first combustion chamber CCI. At the outlet of the first combustion chamber CCI, an initial expansion occurs in the second (high-pressure) turbine T1, followed by a reheating phase in the second combustion chamber CC2 before entering the first turbine T2 for a second expansion.At the outlet of the first turbine T2, the hot gases enter the hot side of the recuperator TR to preheat the air coming from the second compressor C2, i.e. the cold side of the recuperator TR.

[0031] We will now describe a method for controlling a thermodynamic system according to the invention.

[0032] In certain life situations, particularly at the time of a start-up, the components of the thermodynamic system are cold or at a temperature such that injected fuel may condense on the walls of a pipe, particularly at the fuel injector INJ upstream of the second combustion chamber CC2.

[0033] To prevent condensation, the method for controlling a thermodynamic system according to the invention includes a reversing step during which the low-pressure stage operates in the opposite direction to its normal operation. Specifically, this applies to the first turbine, T2. This allows heat from the heating element of the second combustion chamber, CC2, to be transferred to the fuel injector, INJ, upstream of said second combustion chamber. This transfer is achieved using an airflow produced by the first turbine, T2, and operating in the opposite direction to the normal operation of the turbocharger, TCI. The purpose of this is to heat the gas and the manifold between the second combustion chamber, CC2, and the fuel injector, INJ. The first turbine, T2, then functions as a compressor, generating a flow rate.

[0034] Therefore, prior to the aforementioned reversal step, the method of controlling a thermodynamic system according to the invention includes a step of starting up the heating resistance of the second combustion chamber CC2.

[0035] Several embodiments of the reversal step are conceivable for heating the gas between the fuel injector INJ and the second combustion chamber, including setting in oscillation a column of air present by playing, on the one hand, on the speeds and directions of rotation of one or both of the turbines T1 and T2, and, on the other hand, on a position of the VGT of one or both of the turbines T1 and T2.

[0036] In a first embodiment of the method for controlling a thermodynamic system according to the invention, the two turbines T1 and T2 are fully open (VGTTI = VGTT2 = 100%). One aim is to heat the gas by moving the gas column.

[0037] In a second embodiment of the method for controlling a thermodynamic system according to the invention, during the reversal step, the method for controlling a thermodynamic system according to the invention rotates the first turbine T2 in the opposite direction to transfer heat to the fuel injector INJ by means of an airflow exiting the first turbine T2 and going to the second turbine T1. The second turbine T1 does not rotate during this step. The position of the first turbine T2 is open (VGTT2=100%) and the position of the second turbine T1 is closed (VGTT2=0%). One objective is to heat the gas by increasing the pressure in the manifold.

[0038] In a third embodiment of the method for controlling a thermodynamic system according to the invention, during the reversal step, the method for controlling a thermodynamic system according to the invention causes the first turbine T2 to oscillate (first in the opposite direction, then in the normal direction) to transfer heat to the fuel injector INJ via the airflow exiting the first turbine T2 and going towards the second turbine T1. The gas column is then set into oscillation. As with the second embodiment of the method for controlling a thermodynamic system according to the invention, the second turbine T1 does not rotate during this step. The position of the first turbine T2 is open (VGTT2=100%) and the The position of the second turbine T1 is closed (VGTT2=0%). This results in both the second combustion chamber CC2 (which is the initial role of the electrical resistance of said second combustion chamber CC2) and the area at the fuel injector INJ being heated by the airflow (heated by the electrical resistance of the second combustion chamber CC2). One aim is to heat the gas by increasing the pressure in the manifold.

[0039] In a fourth embodiment of the method for controlling a thermodynamic system according to the invention, during the reversal step, the method for controlling a thermodynamic system according to the invention rotates the second turbine T1 in its normal direction and rotates the first turbine T2 in the opposite direction at fixed speeds. Both turbines T1 and T2 are open (VGTTI = VGTT2 = 100%). A predetermined rotation of the two turbines T1 and T2 is set to establish an airflow in the opposite direction to the normal flow when the thermodynamic system normally operates as a range extender. In this embodiment of the method for controlling a thermodynamic system according to the invention, the air column is not oscillating as before, but continuously rises from the exhaust to the intake. One purpose is to heat the gas by moving the gas column.

[0040] In a fifth embodiment of the method for controlling a thermodynamic system according to the invention, during the reversal step, the method for controlling a thermodynamic system according to the invention rotates the second turbine T1 in its normal direction and the first turbine T2 in the opposite direction by varying one or both of its rotational speeds (with or without reversing the direction) in order to create an oscillation in the gas flow to return heat to the fuel injector INJ. As in the third embodiment of the method for controlling a thermodynamic system according to the invention described above, this oscillation aims, on the one hand, to heat the gases between the fuel injector INJ and the second combustion chamber CC2, and, on the other hand, to continue heating the second combustion chamber CC2 itself.An advantage of this fifth embodiment of the method for controlling a thermodynamic system according to the invention is the fact that the two turbines T1 and T2 each rotate in one direction (the second turbine T1 in the normal direction and the first turbine T2 in the opposite direction). (conversely) without needing to change direction to set the gas column into oscillation. It is the control of the respective speeds of each of the two turbines T1 and T2 that allows oscillation, by varying them in a phased manner.

[0041] Implementing such a method for controlling a thermodynamic system according to the invention, in one of the embodiments described above, makes it possible to avoid modifying the initial architecture of the thermodynamic system, for example by introducing additional resistors, to heat the gas column between the fuel injector INJ and the second combustion chamber CC2. This therefore limits the cost of heating the gases, while minimizing (or even eliminating) the risks of fuel condensation and thus ignition.

[0042] Naturally, the invention described above is by way of example. It is understood that a person skilled in the art is capable of carrying out different embodiments of the invention without departing from its scope.

[0043] It is emphasized that all features, as they are apparent to a person skilled in the art from this description, the drawings and the attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances render such combinations impossible or meaningless.

Claims

DEMANDS 1. Method for controlling a two-stage thermodynamic system comprising a first turbocharger (TCI), a second turbocharger (TC2), first (CCI) and second (CC2) combustion chambers and at least one fuel injector between the second turbocharger (TC2) and the second combustion chamber (CC2), the first turbocharger (TCI) comprising a first turbine (T2), the second turbocharger (TC2) comprising a second turbine (T1) and the second combustion chamber comprising an electrical heating element, the thermodynamic system being configured such that at the outlet of the first combustion chamber (CCI), a first expansion occurs in the second turbine (T1) then a heating phase in the second combustion chamber (CC2) before entering the first turbine (T2) to undergo a second expansion,characterized in that the process comprises the steps of: a) Activating the electrical resistance of the second combustion chamber; b) Reversing the operation of the first turbine (T2) to switch the first turbine to compressor mode.

2. Method according to claim 1, characterized in that during the reversing step, the first turbine rotates in the opposite direction, circulating a flow of gas from the second combustion chamber to the fuel injector.

3. Method according to claim 1, characterized in that during the reversing step, the first turbine rotates by oscillating between opposite and normal directions of operation, circulating a flow of gas between the second combustion chamber towards the fuel injector in two flow directions.

4. A method according to any one of claims 1 to 3, characterized in that during the reversal step, the second turbine is stopped.

5. A method according to any one of claims 1 to 3, characterized in that during the reversing step, the second turbine is operating in a normal direction of operation.

6. A method according to one of claims 1 or 2 and claim 5, characterized in that during the reversal step, the first and second turbines rotate at predetermined speeds so as to circulate a flow of gas from the second combustion chamber to the fuel injector.

7. Method according to claims 1 or 3 and claim 5, characterized in that during the reversing step, the first and second turbines rotate at variable speeds so as to circulate a flow of gas between the second combustion chamber and the fuel injector in two flow directions.

8. A method according to any one of claims 1 to 7, characterized in that at least the second turbine is a variable geometry turbine.

9. Method according to claim 8, characterized in that during the reversal step, the method modifies an opening of the second turbine.

10. Motor vehicle comprising a powertrain including an electric traction machine (ELM), a traction battery (B) and a two-stage thermodynamic system, characterized in that it further comprises an autopilot (APU) which is arranged to implement a control method according to any one of claims 1 to 9.

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