Cold start method of a thermodynamic system with a gas turbine cycle type with cooled compression, regeneration and reheating during expansion.

Abstract

The present invention relates to a cold start method for a thermodynamic system comprising two turbochargers (TC1, TC2), two catalytic combustion chambers (CCC1, CCC2), the second catalytic combustion chamber (CCC2) being equipped with electric heating means (RE), two electric machines (MEL1, MEL2) each connected to one of the turbochargers (TC1, TC2), fuel injection means (FI1, FI2), a heat recovery unit (REC) characterized in that it successively comprises a step (10) of activating the electric heater (RE) until reaching a first determined temperature of the second catalytic combustion chamber (CCC2), a step of rotating the two turbochargers (TC1, TC2) by their electric machine (MEL1, MEL2) at minimum rotation speeds, a step (20) of starting fuel injection in the second catalytic combustion chamber (CCC2),a step (30) of starting fuel injection into the first combustion chamber (CCC1) when it reaches a second determined temperature. Figure 2,

Description

Title of the invention: Cold start method of a gas turbine type cycle thermodynamic system with cooled compression, regeneration and reheating during expansion.

[0001] The present invention relates to the field of gas turbines. More particularly, the invention relates to a method for cold starting a thermodynamic system with a gas turbine cycle, with cooled compression, regeneration and reheating during expansion.

[0002] Gas turbine-type energy converters are known in electricity generation. These machines comprise a compressor that compresses air and increases its pressure, a combustion chamber that uses fuel and produces thermal energy, and a turbine that recovers the work from the gases. Part of the power produced by the turbine is used to drive the compressor, and another part to drive an electric generator and produce electrical power. In an automotive application, this electricity can be used to recharge the traction battery of an electric or hybrid vehicle.

[0003] In particular, the thermodynamic system with a gas turbine cycle of the type with cooled compression, regeneration and reheating during expansion (i.e. a device called in English "Intercooled Recuperative Reheat Gas Turbine", or IRReGT) is a device with high potential for automotive applications. This cycle makes it possible to achieve very high efficiency but also a very high power density (i.e. a high net specific work).

[0004] Such a thermodynamic system is known, for example, from document FR3124847A1. The thermodynamic system of document FR3124847A1 comprises two combustion chambers and proposes a method for controlling this system during startup by combining the operation of the electric generator in engine mode and the injection of fuel into the second combustion chamber. Indeed, startup is a polluting phase because the system components are cold. However, injecting this fuel into the second combustion chamber during the startup phase reduces pollutant emissions.

[0005] There is therefore a need to improve the start-up of such thermodynamic systems, which is the most polluting phase, in order to reduce polluting emissions.

[0006] The invention aims to solve this problem. To achieve this objective, the invention provides a cold start method for a thermodynamic system comprising: - a first turbocharger comprising: - a first compressor and a first turbine - a second turbocharger comprising: - a second compressor and a second turbine - two catalytic combustion chambers, the second catalytic combustion chamber being equipped with electrical heating means for this second combustion chamber, - a first electric machine connected in rotation to the first turbocharger and a second electric machine connected in rotation to the second turbocharger, - fuel injection means for each combustion chamber, - a heat recovery unit connected to the second compressor and the first combustion chamber, this first combustion chamber being connected to the second turbine, this second turbine being connected to the second combustion chamber, this second combustion chamber being connected to the first turbine, characterized in that it comprises successively: - an activation stage of the electric heater until a first determined temperature is reached in the second catalytic combustion chamber, - a stage of rotating the two turbochargers by their electric machine at minimum rotation speeds, - a fuel injection start-up stage in the second catalytic combustion chamber, - a fuel injection start-up step in the first combustion chamber when it reaches a second determined temperature.

[0007] The technical effect is to allow rapid implementation of the catalytic combustion chambers, the first combustion chamber being heated by air preheated by the recuperator.

[0008] Various additional features may be provided, alone or in combination.

[0009] In one embodiment, the first determined temperature corresponds to a so-called initiation temperature of the second catalytic combustion chamber.

[0010] In one embodiment, the second determined temperature corresponds to a so-called initiation temperature of the first catalytic combustion chamber.

[0011] In one embodiment, the thermodynamic system includes a step of increasing the rotational speed of the turbochargers to intermediate rotational speeds when the second combustion chamber reaches its nominal operating temperature.

[0012] In one embodiment, the thermodynamic system includes a step of increasing the fuel injection flow rate in the two combustion chambers to intermediate fuel flow rates when the second combustion chamber reaches its nominal operating temperature.

[0013] In one embodiment, the thermodynamic system includes a step of increasing the fuel injection flow rate in the first combustion chamber to an intermediate fuel flow rate when the second combustion chamber reaches its nominal operating temperature, the increase in the fuel injection flow rate in the second combustion chamber taking place for an intermediate temperature of the second combustion chamber between the ignition temperature and the nominal operating temperature.

[0014] In one embodiment, the thermodynamic system includes a step of increasing the fuel flow rates injected into the two combustion chambers to nominal fuel flow rates, when both combustion chambers have reached their nominal operating temperature.

[0015] The invention also relates to a thermodynamic system comprising: - a first turbocharger comprising: - a first compressor and a first turbine - a second turbocharger comprising: - a second compressor and a second turbine - a first electric machine connected in rotation to the first turbocharger and a second electric machine connected in rotation to the second turbocharger, - two combustion chambers, - fuel injection means for each combustion chamber, - a heat recovery unit connected to the second compressor and to a first combustion chamber, this first combustion chamber being connected to the second turbine, this second turbine being connected to the second combustion chamber, this second combustion chamber being connected to the first turbine, characterized in that the two combustion chambers are catalytic combustion chambers, the second catalytic combustion chamber only being equipped with means for electrically heating this second combustion chamber, and in that the system further comprises control means configured to implement a starting method according to one of the variants previously described.

[0016] In one embodiment, the electrical machines are electric motor-generators.

[0017] The invention also relates to a motor vehicle comprising a thermodynamic system according to one of the variants described above, the electric machines powering a traction battery of the vehicle.

[0018] Other features and advantages will become apparent from the following description of a particular, non-limiting embodiment of the invention, made with reference to the figures in which:

[0019] [Fig.1]: This figure schematically represents a motor vehicle according to the invention.

[0020] [Fig.2]: This figure schematically represents an embodiment of the thermodynamic system according to the invention.

[0021] [Fig.3]: This figure schematically represents an example of the realization of a catalytic combustion chamber.

[0022] [Fig.4] This figure schematically represents the steps of a cold start phase of the thermodynamic system of [Fig.2].

[0023] Figure 1 shows a motor vehicle comprising, within the dotted outline, a thermodynamic system 1 of the invention. As illustrated in Figure 2, the thermodynamic system 1 comprises electrical machines MEL1, MEL2 so as to convert the mechanical energy produced by this thermodynamic system 1 into electrical current.

[0024] The electric machines MEL1 and MEL2 are connected to an electrical network comprising a battery B and an electric motor MEL used to power the vehicle. AC / DC converters may be provided for managing the electrical current in the network. Thus, the electric machines MEL1 and MEL2 can recharge battery B. Battery B is used to power the traction electric motor MEL. The thermodynamic system 1 is thus mechanically decoupled from the traction system and can operate at its maximum efficiency point.

[0025] As illustrated in [Fig.2], the thermodynamic system comprises a first turbocharger TCI and a second turbocharger TC2.

[0026] The first turbocharger TCI comprises a first compressor Cl and a first turbine TU2. The second turbocharger TC2 comprises a second compressor C2 and a second turbine TU1. More specifically, the first turbocharger TCI forms a "low pressure" stage, and the second turbocharger TC2 forms a "high pressure" stage.

[0027] The turbochargers TCI, TC2, are electrified here, that is to say, each comprises an electric machine MEL1, MEL2 respectively. Each of the turbochargers TCI, TC2, is rotationally connected to its electric machine MEL1, MEL2. The electric machines MEL1, MEL2 can operate in motor mode. and generator, that is to say as a motor to drive the system as needed and as a generator to recover the energy produced by combustion via the rotation of the turbocharger.

[0028] The thermodynamic system includes an air cooler IC for the air exiting the first compressor Cl. This air cooler IC can be an air-to-air heat exchanger or an air-to-water heat exchanger. The inlet of the air cooler IC is connected between the compressed air outlet of the first compressor Cl and the air inlet of the second compressor C2.

[0029] The thermodynamic system further comprises two catalytic combustion chambers CCC1 and CCC2.

[0030] The thermodynamic system further includes a REC recuperator. This recuperator is a heat exchanger connected between the outlet of the compressed air from the second compressor C2 and the inlet of this compressed air into the first combustion chamber CCC1. The outlet of the first combustion chamber CCC1 is then connected to the inlet of the second turbine TU1.

[0031] The outlet of the second turbine TU1 is connected to the inlet of the second catalytic combustion chamber CCC2 and the outlet of the second catalytic combustion chamber CCC2 is connected to the inlet of the first turbine TU2.

[0032] The thermodynamic system further comprises a recovery branch BR connecting the outlet of the first turbine TU2 to an inlet of the heat recovery unit REC and passing through it. The side of the REC through which the recovery branch BR passes is called the hot side of the recuperator, since the gas flow comes directly from the first turbine TU2 after undergoing a second catalytic combustion in the catalytic combustion chamber CCC2. In contrast, the side of the REC receiving compressed air from the second compressor C2, and from which the air is directed to the first catalytic combustion chamber CCC1, is called the cold side of the recuperator.

[0033] The thermodynamic system is configured to be traversed by a gaseous flow FG, described later, between the different elements composing it.

[0034] The use of a second catalytic combustion chamber CCC2 for heating between the turbines makes it possible to increase the power density, which makes it possible to reduce the air flow required at the same power and to reduce the size of the device.

[0035] The thermodynamic system can be equipped with an air filter FA positioned upstream of the first compressor to filter the air admitted into this first compressor CL

[0036] The system is also equipped with a first fuel injection system Fil in the first catalytic combustion chamber CCC1 and a second fuel injection system FI2 in the second catalytic combustion chamber CCC2.

[0037] The two combustion chambers CCC1 and CCC2 are catalytic combustion chambers. Having two catalytic combustion chambers allows for greater flexibility in the system's operation. These catalytic combustion chambers function to oxidize the injected fuel through catalysis and to generate heat.

[0038] With catalytic combustion chambers, outlet gas temperatures of around 950°C are obtained. In the case of lean mixture operation, in other words with an excess of oxygen, since the temperature is below 1200°C (according to the Pischinger diagram), the formation of nitrogen oxides at the source is avoided.

[0039] The catalytic combustion chambers CCC1 and CCC2 each comprise a catalytic substrate or bread, which may be ceramic or metallic, through which the fuel mixture can pass. The catalytic bread is provided with a catalytic coating adapted to the oxidation of the fuel. This catalytic coating may comprise materials with catalytic properties such as platinum, rhodium, or palladium.

[0040] The gas flow FG in the system is now described. Generally, the gas flow FG follows the arrows shown in [Fig. 2] which connect the various components and passes through these components. Ambient air is first drawn into the air filter FA by the first compressor CL. This air then passes through the filter. The air is compressed in this first compressor CL before entering the cooler IC where it is cooled. The air exiting the cooler IC then enters the second compressor C2 where it is compressed a second time before entering the recuperator REC, specifically the cold side of the recuperator. In the recuperator REC, the air is heated by the hot gases from the recovery branch BR coming from the outlet of the turbine TU2. The air exiting the recuperator REC thus enters the first catalytic combustion chamber CCC1.At the outlet of the first catalytic combustion chamber CCC1, a first expansion occurs in the high-pressure turbine TU1 followed by a reheating phase in the second catalytic combustion chamber CCC2 before entering the low-pressure turbine TU2 to undergo a second expansion. At the outlet of the first turbine TU2, the hot gases enter the hot side of the recuperator REC to heat the air coming from the second compressor C2, i.e. the cold side of the recuperator REC.

[0041] These catalytic combustion chambers are active when the temperature of the catalytic block exceeds a certain ignition temperature. This ignition temperature can, for example, be between 300°C and 350°C. This ignition temperature varies depending on the type and quantity of materials with catalytic properties. used in catalytic bread. If the catalyst has not yet reached at least its ignition temperature, the catalyst is not active and its efficiency is reduced.

[0042] To facilitate the ignition of the catalytic combustion chamber, an electric heater RE is provided, as illustrated in [Fig. 3], in the second catalytic combustion chamber CCC2, upstream of the catalytic block PC. Upstream and downstream are defined here relative to the direction of flow of the gas stream FG.

[0043] In a preferred embodiment, an electric heater RE is used only for the second catalytic combustion chamber CCC2. The REC heat recovery unit of the thermodynamic system is designed to preheat the air entering the first catalytic combustion chamber using the hot gases from the turbine TU2. Thus, during the start-up phase, the REC heat recovery unit recovers some of the heat energy exiting the turbine TU2 to preheat the air entering the first catalytic combustion chamber CCC1. Therefore, there is no need for an electric heating element on the first catalytic combustion chamber CCC1. The REC heat recovery unit acts as the electric heating element. This reduces mass and cost, facilitates integration, and improves durability.

[0044] The thermodynamic system 1 further includes control means UC, arranged to control the fuel injection means, Fil, FI2, the electric heater RE, the electric machines MEL1, MEL2, as well as to implement the cold start method of the thermodynamic system 1 which is now described.

[0045] To control the operation of the thermodynamic system 1, temperature sensors can be used to determine the temperatures used in the process. The temperature sensors are preferably thermocouples.

[0046] With reference to [Fig.4], the cold start procedure of the thermodynamic system 1 comprises the following steps:

[0047] In step 10, the electric heater RE is activated until a predetermined first temperature Tl is reached in the second catalytic combustion chamber CCC2. This first temperature Tl preferably corresponds to the ignition temperature of the second catalytic combustion chamber CCC2. At this stage, the electric machines are not activated and the rotational speed of the turbochargers TCI, TC2 is zero. Fuel injection is also not activated at this stage.

[0048] Once the first temperature Tl is reached, in step 20 the two electric machines MEL1, MEL2 are activated in motor mode so as to drive the two turbochargers TCI, TC2 in rotation at a minimum speed Rmintcl, Rmintc2. This generates a gas flow in the thermodynamic system 1. These minimum speeds of The rotation speeds can be identical. For example, the minimum speed can be between 5000 and 10000 rpm. At this stage, fuel injection into the second combustion chamber CCC2 also begins. This fuel injection is performed according to an initial minimum fuel flow rate Qminccc2. At this stage, no injection is carried out into the first combustion chamber CCC1. The electric heater RE remains active at this stage.

[0049] Fuel injection into the second combustion chamber CCC2 further increases its temperature and increases the temperature of the first combustion chamber CCC1, via the recuperator REC.

[0050] When the temperature of the first combustion chamber CCC1 reaches a second predetermined temperature T2, fuel injection into the first combustion chamber CCC1 is initiated in step 30. This second temperature T2 preferably corresponds to the start-up temperature of the first catalytic combustion chamber CCC1. This fuel injection is carried out according to a second minimum fuel flow rate Qmincccl. It may be planned at this step to maintain the speed of the two turbochargers TCI, TC2 at the minimum speed Rmintcl, Rmintc2. The electrical resistance RE may be deactivated during this step.

[0051] When the second combustion chamber CCC2 reaches its nominal operating temperature (for example, approximately 950°C), in step 40 the rotational speed of the turbochargers TCI, TC2 is increased to intermediate rotational speeds Rinttcl, Rinttc2. These intermediate rotational speeds may be the same, but higher than the minimum speed Rminl, Rmin2. For example, the intermediate speed may be between 10,000 and 100,000 rpm. Also in step 40, the fuel injection rate in both combustion chambers is increased to intermediate fuel flow rates, Qintcccl, Qintccc2, higher than the minimum fuel flow rates. The intermediate fuel flow rates injected into combustion chambers CCC1, CCC2 may be the same.

[0052] Alternatively, the fuel injection flow rate in the second combustion chamber CCC2 can be increased to the intermediate fuel flow rate Qintccc2 before it has reached its nominal operating temperature, i.e. when the second combustion chamber CCC2 has reached an intermediate temperature between its ignition temperature and its operating temperature, for example between 650 and 750°C.

[0053] When both combustion chambers CCC1 and CCC2 have reached their nominal operating temperature, in step 50 the fuel flow rate injected into both combustion chambers CCC1 and CCC2 is increased to nominal fuel flow rates, Qnomcccl and Qnomccc2, which are higher than the intermediate fuel flow rates. The turbochargers Cl and C2 also reach their operating speed. nominal speeds, Rnomcl, Rnomc2, are higher than the intermediate rotational speeds. For example, the nominal speed can be greater than 100,000 rpm.

[0054] During this process the electrical machines MEL1, MEL2 switch from motor mode to generator mode when the turbine to which they are connected produces more power than the associated compressor consumes.

[0055] The invention is not limited to the embodiments described. Alternatively, a glow plug can be added upstream of each combustion chamber and downstream of each fuel injection device, the activation of which ensures complete evaporation of the injected fuel before it enters its combustion chamber.

[0056] The invention makes it possible to reduce start-up time and emissions at the source. It allows for a reduction in the electrical energy required during the start-up phase.

Claims

Demands

1. A cold start method for a thermodynamic system comprising: - a first turbocharger (TCI) including: - a first compressor (C1) and a first turbine (TU2) - a second turbocharger (TC2) including: - a second compressor (C2) and a second turbine (TU1) - two catalytic combustion chambers (CCC1, CCC2), the second catalytic combustion chamber (CCC2) being equipped with electrical heating means (RE) for this second combustion chamber (CCC2), - a first electric machine (MEL1) rotationally connected to the first turbocharger (TCI) and a second electric machine (MEL2) rotationally connected to the second turbocharger (TC2), - fuel injection means (Fil, FI2) for each combustion chamber (CCC1, CCC2), - a heat recovery unit (REC) connected to the second compressor (C2) and to the first combustion chamber (CCC1),this first combustion chamber (CCC1) being connected to the second turbine (TU1), this second turbine (TU1) being connected to the second combustion chamber (CCC2), this second combustion chamber (CCC2) being connected to the first turbine (TU2), characterized in that it successively comprises: - a step (10) of activation of the electric heater (RE) until a first determined temperature (T1) of the second catalytic combustion chamber (CCC2) is reached, - a step of rotation of the two turbochargers (TC1, TC2) by their electric machine (MEL1, MEL2) at minimum rotation speeds (Rmint1, Rmint2), - a step (20) of starting fuel injection into the second catalytic combustion chamber (CCC2), - a step (30) of starting fuel injection into the first combustion chamber (CCC1) when it reaches a second determined temperature (T2).

2. A method according to claim 1, characterized in that the first temperature (Tl) determined corresponds to a temperature called priming of the second catalytic combustion chamber (CCC2).

3. A method according to claim 1 or claim 2, characterized in that the second temperature (T2) determined corresponds to a so-called initiation temperature of the first catalytic combustion chamber (CCC1).

4. A method according to any one of claims 1 to 3, characterized in that it comprises a step (40) of increasing the rotational speed of the turbochargers (TCI, TC2) to intermediate rotational speeds (RinttCCCl, Rinttc2) when the second combustion chamber (CCC2) reaches its nominal operating temperature.

5. A method according to any one of claims 1 to 4, characterized in that it comprises a step (40) of increasing the fuel injection flow rate in both combustion chambers (CCC1, CCC2) to intermediate fuel flow rates (QintCCCl, QintCCC2) when the second combustion chamber (CCC2) reaches its nominal operating temperature.

6. A method according to any one of claims 1 to 4, characterized in that it comprises a step (40) of increasing the fuel injection flow rate in the first combustion chamber (CCC1) to an intermediate fuel flow rate (QintCCCl) when the second combustion chamber (CCC2) reaches its nominal operating temperature, the increase in the fuel injection flow rate in the second combustion chamber (CCC2) taking place for an intermediate temperature of the second combustion chamber (CCC2) between the ignition temperature and the nominal operating temperature.

7. A method according to any one of claims 4 to 6, characterized in that it comprises a step (50) of increasing the fuel flow rates injected into the two combustion chambers (CCC1, CCC2) to nominal fuel flow rates (QnomCCCl, QnomCCC2), when both combustion chambers (CCC1, CCC2) have reached their nominal operating temperature.

8. Thermodynamic system (1) comprising: - a first turbocharger (TCI) comprising: - a first compressor (Cl) and a first turbine (TU2) - a second turbocharger (TC2) comprising: - a second compressor (C2) and a second turbine (TU1) - a first electric machine (MEL1) rotationally connected to the first turbocharger (TCI) and a second electric machine (MEL2) rotationally connected to the second turbocharger (TC2), - two combustion chambers (CCC1, CCC2), - fuel injection means (Fil, F2) for each combustion chamber (CCC1, CCC2), - a heat recovery unit (REC) connected to the second compressor (C2) and to a first combustion chamber (CCC1), this first combustion chamber (CCC1) being connected to the second turbine (TU1), this second turbine (TU1) being connected to the second combustion chamber (CCC2), this second combustion chamber (CCC2) being connected to the first turbine (TU2), characterized in that the two combustion chambers (CCC1, CCC2) are catalytic combustion chambers,the second catalytic combustion chamber (CCC2) only being equipped with means for electrically heating this second combustion chamber (CCC2), and in that the system further comprises control means (UC) configured to implement a starting method according to one of the preceding claims.

9. System (1) according to the preceding claim, characterized in that the electric machines (MEL1, MEL2) are electric motor-generators.

10. Motor vehicle comprising a thermodynamic system (1) according to any one of claims 8 or 9, the electric machines (MEL1, MEL2) powering a traction battery (B) of the vehicle.