JP7794084B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

A fuel cell system includes a fuel cell stack. The fuel cell stack generates electricity by chemically reacting fuel gas with oxygen in the air. The fuel cell system may also include an electric compressor and a turbine. The electric compressor includes a compression section and a motor. The compression section compresses the air supplied to the fuel cell stack. The motor drives the compression section. The turbine has a turbine wheel. The turbine wheel rotates due to exhaust gas discharged from the fuel cell stack, assisting in driving the motor. Specifically, the turbine wheel rotates when exhaust gas discharged from the fuel cell stack is supplied to the turbine. The exhaust gas supplied to the turbine expands due to the rotation of the turbine wheel. The expansion of the exhaust gas converts the energy of the exhaust gas into rotational energy. In this way, the energy of the exhaust gas is converted into rotational energy, generating regenerative power in the turbine. The regenerative power generated by the turbine assists in driving the motor.

For example, the fuel cell system described in Patent Document 1 is equipped with a heat exchanger that exchanges heat between air compressed in the compression section of the electric compressor and exhaust gas discharged from the fuel cell stack. The exhaust gas discharged from the fuel cell stack is then heated in the heat exchanger by the air compressed in the compression section. This increases the energy of the exhaust gas, and therefore the rotational energy converted by the exhaust gas expanding due to the rotation of the turbine wheel in the turbine. As a result, the regenerative power generated by the turbine increases, efficiently assisting in driving the motor.

JP 2013-168308 A

However, for example, pressure loss that occurs when exhaust gas passes through a heat exchanger can hinder an increase in the regenerative power generated by the turbine. Therefore, it is desirable to efficiently increase the regenerative power generated by the turbine.

A fuel cell system that solves the above problem includes a fuel cell stack that generates electricity by chemically reacting fuel gas with oxygen in the air, an electric compressor that includes a compressor unit that compresses air supplied to the fuel cell stack and a motor that drives the compressor unit, and a turbine that has a turbine wheel that rotates with exhaust gas discharged from the fuel cell stack to assist in driving the motor. The system also includes a storage tank that stores water contained in exhaust gas discharged from the fuel cell stack. The storage tank has a supply port connected to an air layer within the storage tank and that supplies exhaust gas discharged from the fuel cell stack into the storage tank, a gas-liquid separation unit that separates water from the exhaust gas supplied from the supply port, a storage unit that stores the water separated by the gas-liquid separation unit, a heat exchange unit that exchanges heat between the water stored in the storage unit and air discharged from the electric compressor, and an outlet connected to the air layer and that discharges the exhaust gas from which water has been separated by the gas-liquid separation unit to the turbine.

According to this system, exhaust gas discharged from the fuel cell stack is supplied to an air layer in a storage tank through a supply port. The gas-liquid separator separates water from the exhaust gas supplied through the supply port. The water separated by the gas-liquid separator is then stored in a storage tank. The water stored in the storage tank is evaporated into water vapor through heat exchange with air discharged from the electric compressor via a heat exchanger. The water vapor is discharged to the turbine through an outlet as exhaust gas together with the exhaust gas from which the water has been separated in the gas-liquid separator. In this way, the mass of the exhaust gas supplied to the turbine increases by the amount of water vapor added. As a result, the mass of the exhaust gas expanding due to the rotation of the turbine wheel increases, increasing the amount of work the turbine wheel must do. This increases the regenerative power generated by the turbine. Furthermore, the exhaust gas from which the water has been separated in the gas-liquid separator passes through the air layer in the storage tank and is discharged to the turbine through an outlet. This reduces exhaust gas pressure loss within the storage tank, thereby avoiding interference with the increase in regenerative power generated by the turbine. As a result, the regenerative power generated by the turbine can be efficiently increased.

In the above fuel cell system, the storage tank may have a water storage volume control unit that controls the amount of water stored in the storage unit so that the liquid level of the water stored in the storage unit does not exceed a predetermined height, and the heat exchange unit may have a heat exchange main body that is positioned vertically below the predetermined height, and a protrusion that extends from the heat exchange main body and protrudes beyond the predetermined height into the air layer.

This allows the protrusion to create a capillary phenomenon that draws up the liquid surface of the water stored in the storage section, thereby increasing the surface area between the gas and liquid phases in the storage tank. As a result, the water stored in the storage section can be evaporated efficiently.

In the above fuel cell system, the turbine preferably has a turbine chamber that houses the turbine wheel and a fixed nozzle that throttles the flow rate of exhaust gas supplied to the turbine chamber. It also preferably has an inlet flow path that introduces air discharged from the electric compressor into the heat exchanger, a bypass flow path that branches off from the inlet flow path and supplies the air flowing through the inlet flow path to the fuel cell stack, bypassing the heat exchanger, and a flow rate adjustment unit that adjusts the flow rate of air that branches off from the inlet flow path and flows into the bypass flow path, thereby adjusting the flow rate of air introduced from the electric compressor via the inlet flow path to the heat exchanger.

This allows the amount of water vapor generated by heat exchange between the water stored in the storage unit and the air discharged from the electric compressor via the heat exchange unit to be adjusted. Therefore, even if the flow rate of exhaust gas supplied to the turbine chamber is uniquely determined, such as when the turbine has a fixed nozzle, it is possible to adjust the flow rate of exhaust gas that expands due to the rotation of the turbine wheel. As a result, the expansion ratio of the turbine can be adjusted, allowing the turbine to operate at high turbine efficiency.

In the above fuel cell system, the heat exchange unit may have a plurality of piping sections arranged vertically in the storage tank, and the air discharged from the electric compressor may flow through each of the piping sections, and each of the piping sections may exchange heat between the water stored in the storage section and the air discharged from the electric compressor.

For example, as the liquid level of the water stored in the storage section drops, one of the multiple piping sections located vertically at the top may become exposed to the air layer within the storage tank. In piping sections exposed to the air layer within the storage tank, heat exchange between the water stored in the storage section and the air discharged from the electric compressor becomes more difficult. In this way, fluctuations in the liquid level of the water stored in the storage section can fine-tune the amount of water vapor generated by heat exchange between the water stored in the storage section and the air discharged from the electric compressor via the heat exchange section.

In the above fuel cell system, the heat exchange unit may include a porous material that is thermally coupled to the heat exchange body and is positioned vertically below the predetermined height.

By doing this, heat exchange occurs between the water stored in the storage section and the porous material, causing the water stored in the storage section to evaporate and become water vapor. Therefore, the water stored in the storage section can be evaporated efficiently.

This invention makes it possible to efficiently increase the regenerative power generated by the turbine.

FIG. 1 is a diagram illustrating a fuel cell system according to an embodiment. FIG. 2 is a cross-sectional view illustrating the water storage tank. FIG. 2 is a cross-sectional view illustrating the water storage tank. 4 is a graph showing the relationship between the expansion ratio of a turbine and turbine efficiency. 4 is a graph showing the relationship between the expansion ratio of the turbine and the corrected flow rate of the exhaust gas.

An embodiment of a fuel cell system will now be described with reference to Figures 1 to 5. The fuel cell system of this embodiment is mounted on a fuel cell vehicle.
<Overall Configuration of Fuel Cell System 10>
As shown in Fig. 1, a fuel cell system 10 includes a fuel cell stack 11, an electric compressor 12, and a turbine 13. The fuel cell stack 11 includes, for example, a plurality of cells. Each cell is configured by stacking an oxygen electrode, a hydrogen electrode, and an electrolyte membrane disposed between the two electrodes. The fuel cell stack 11 generates electricity by chemically reacting hydrogen, which is a fuel gas, with oxygen in the air.

Only about 20% of the air contains oxygen, which contributes to the power generation of the fuel cell stack 11. Therefore, about 80% of the air supplied to the fuel cell stack 11 is discharged from the fuel cell stack 11 as exhaust gas without contributing to the power generation of the fuel cell stack 11. The exhaust gas discharged from the fuel cell stack 11 contains water that is produced when the fuel cell stack 11 generates power.

The fuel cell stack 11 is electrically connected to a traction motor (not shown). The traction motor is powered by electricity generated by the fuel cell stack 11. The power of the traction motor is transmitted to the axle via a power transmission mechanism (not shown). The fuel cell vehicle travels at a speed that corresponds to the accelerator pedal depression.

<Electric compressor 12>
The electric compressor 12 includes a compression unit 14 and a motor 15. The electric compressor 12 also includes a rotary shaft 16. The compression unit 14 is connected to a first end of the rotary shaft 16. The compression unit 14 is, for example, an impeller. The compression unit 14 is rotatable integrally with the rotary shaft 16. The compression unit 14 compresses air supplied to the fuel cell stack 11. The motor 15 rotates the rotary shaft 16. The rotation of the rotary shaft 16 drives the compression unit 14. Therefore, the motor 15 drives the compression unit 14.

<Turbine 13>
The turbine 13 has a turbine wheel 17 and a turbine housing 18. The turbine wheel 17 is connected to a second end of the rotary shaft 16. The turbine wheel 17 is rotatable integrally with the rotary shaft 16.

The turbine housing 18 is cylindrical and has a circular discharge port 19. The turbine housing 18 is fixed to the electric compressor 12. Therefore, the turbine 13 is integrated with the electric compressor 12.

The turbine 13 has a turbine chamber 20 and a fixed nozzle 21. The turbine chamber 20 is formed in the turbine housing 18. The turbine chamber 20 houses the turbine wheel 17. The discharge port 19 is connected to the turbine chamber 20. The turbine 13 has a suction chamber 22. The suction chamber 22 is formed in the turbine housing 18. The suction chamber 22 extends around the axis of the discharge port 19 around the periphery of the turbine chamber 20. Exhaust gas discharged from the fuel cell stack 11 is drawn into the suction chamber 22.

The fixed nozzle 21 is a passage formed in the turbine housing 18 that connects the turbine chamber 20 and the suction chamber 22. The fixed nozzle 21 extends radially from the rotating shaft 16. The fixed nozzle 21 supplies exhaust gas drawn into the suction chamber 22 to the turbine chamber 20 from the radial direction of the rotating shaft 16. The fixed nozzle 21 throttles the flow rate of exhaust gas supplied to the turbine chamber 20. The turbine wheel 17 is rotated by the exhaust gas supplied to the turbine chamber 20. Therefore, the turbine wheel 17 is rotated by the exhaust gas discharged from the fuel cell stack 11. The turbine wheel 17 is then rotated by the exhaust gas to assist in driving the motor 15.

<Storage tank 30>
As shown in Figures 2 and 3, the fuel cell system 10 includes a storage tank 30. The storage tank 30 stores water contained in exhaust gas discharged from the fuel cell stack 11. The storage tank 30 is, for example, in the shape of a rectangular box. The storage tank 30 has an upper wall 31, a lower wall 32, a first side wall 33, and a second side wall 34. The upper wall 31 and the lower wall 32 face each other in the vertical direction. The first side wall 33 and the second side wall 34 face each other in the horizontal direction.

The storage tank 30 has a supply port 35. The supply port 35 is provided in a portion of the top wall 31 of the storage tank 30 near the first side wall 33. The supply port 35 supplies exhaust gas discharged from the fuel cell stack 11 into the storage tank 30.

The storage tank 30 has a gas-liquid separation section 36. The gas-liquid separation section 36 is a cylindrical section that protrudes from the inner surface of the upper wall 31. The gas-liquid separation section 36 protrudes from the inner surface of the upper wall 31, surrounding the opening of the supply port 35 to the interior of the storage tank 30. The exhaust gas supplied into the storage tank 30 from the supply port 35 passes inside the gas-liquid separation section 36. Water contained in the exhaust gas is separated from the exhaust gas by centrifugation as it passes inside the gas-liquid separation section 36. The water contained in the exhaust gas is also separated from the exhaust gas by the exhaust gas colliding with the inner surface of the gas-liquid separation section 36. Therefore, the gas-liquid separation section 36 separates water from the exhaust gas supplied from the supply port 35.

The water separated from the exhaust gas by the gas-liquid separator 36 is stored in the storage tank 30. Therefore, the storage tank 30 has a storage section 37 in which the water separated by the gas-liquid separator 36 is stored. Inside the storage tank 30, the space other than the storage section 37 in which the water is stored forms an air layer 38. Therefore, the upper part of the storage tank 30 forms the air layer 38. The supply port 35 is connected to the air layer 38 inside the storage tank 30.

The storage tank 30 has an outlet 39. The outlet 39 is provided in a portion of the upper wall 31 of the storage tank 30 near the second side wall 34. The outlet 39 is connected to the air space 38. The outlet 39 discharges the exhaust gas from which water has been separated in the gas-liquid separation section 36 to the turbine 13.

The storage tank 30 has a water storage volume control unit 40. The water storage volume control unit 40 controls the amount of water stored in the storage unit 37 so that the liquid level of the water stored in the storage unit 37 does not exceed a predetermined height H1. The predetermined height H1 is a preset height of the water liquid level. The predetermined height H1 is lower than the bottom end of the gas-liquid separation unit 36 within the storage tank 30. Therefore, the gas-liquid separation unit 36 is positioned higher than the predetermined height H1 within the storage tank 30.

The water storage volume control unit 40 has a drain pipe 41 and a drain valve 42. The drain pipe 41 is provided on the first side wall 33 of the storage tank 30. The inside of the drain pipe 41 is connected to the inside of the storage tank 30. The drain pipe 41 is provided at a portion of the first side wall 33 corresponding to a predetermined height H1. Therefore, the opening position of the drain pipe 41 to the interior of the storage tank 30 is a position within the storage tank 30 corresponding to the predetermined height H1. When the liquid level of the water stored in the storage section 37 reaches the predetermined height H1, the water stored in the storage section 37 flows into the drain pipe 41.

The drain valve 42 is configured to open when a preset amount of water stored in the storage section 37 flows into the drain valve 42 via the drain pipe 41. Therefore, the drain valve 42 is configured to close until a preset amount of water stored in the storage section 37 flows into the drain valve 42 via the drain pipe 41. When the drain valve 42 opens, the water flowing through the drain pipe 41 is discharged to the outside. In this way, the water storage volume control unit 40 controls the amount of water stored in the storage section 37 so that the liquid level of the water stored in the storage section 37 does not exceed a predetermined height H1.

The storage tank 30 has a heat exchanger 50. The heat exchanger 50 has a heat exchanger main body 51, an upstream header 52, and a downstream header 53. The heat exchanger main body 51 has multiple piping sections 54. Therefore, the heat exchanger 50 has multiple piping sections 54.

Each piping section 54 is, for example, a rectangular tubular shape. Each piping section 54 is, for example, a flat tube. Each piping section 54 is made of, for example, a metal with excellent thermal conductivity. Each piping section 54 spans the inside of the storage tank 30, spanning between the first side wall 33 and the second side wall 34. Multiple piping sections 54 are arranged vertically side by side within the storage tank 30. The thickness direction of each piping section 54 coincides with the vertical direction. Each piping section 54 is arranged vertically below a predetermined height H1. Therefore, the heat exchanger main body 51 is arranged vertically below the predetermined height H1.

The upstream header 52 is connected to a first end of each piping section 54. The first end of each piping section 54 is the end of the piping section 54 located on the second side wall 34 side. The upstream header 52 distributes the air discharged from the electric compressor 12 into each piping section 54. The air distributed from the upstream header 52 into each piping section 54 flows through each piping section 54. Therefore, the air discharged from the electric compressor 12 flows through each piping section 54. Each piping section 54 exchanges heat between the water stored in the storage section 37 and the air discharged from the electric compressor 12. Therefore, the heat exchange section 50 exchanges heat between the water stored in the storage section 37 and the air discharged from the electric compressor 12.

The downstream header 53 is connected to the second end of each piping section 54. The second end of each piping section 54 is the end of each piping section 54 located on the first side wall 33 side. The air that has passed through each piping section 54 joins the downstream header 53. The downstream header 53 then directs the air from each piping section 54 toward the fuel cell stack 11.

The heat exchange unit 50 has a plurality of protrusions 55. Each protrusion 55 is thin and flat. Each protrusion 55 is made of, for example, a metal with excellent thermal conductivity. Each protrusion 55 is arranged within the storage tank 30 with the thickness direction of each protrusion 55 aligned horizontally. The multiple protrusions 55 are arranged at intervals in the horizontal direction within the storage tank 30. The multiple protrusions 55 are arranged side by side at equal intervals in the horizontal direction.

Each protrusion 55 extends from the heat exchanger main body 51. Specifically, each protrusion 55 is supported by a corresponding piping section 54. Each piping section 54 penetrates each protrusion 55 in the thickness direction of the protrusion 55. Each protrusion 55 extends from each piping section 54 upward within the storage tank 30. Each protrusion 55 extends from each piping section 54 to a position exceeding a predetermined height H1. Therefore, each protrusion 55 extends from the heat exchanger main body 51 and protrudes into the air layer 38 exceeding the predetermined height H1. Each protrusion 55 is thermally coupled to each piping section 54. Each protrusion 55 causes capillary action, which draws up the liquid level of the water stored in the storage section 37.

The heat exchanger 50 includes a porous material 56. The porous material 56 is thermally coupled to the heat exchanger body 51. The porous material 56 is disposed within the storage tank 30 in close contact with the lowest of the multiple pipe sections 54. Therefore, the porous material 56 is thermally coupled to the heat exchanger body 51 and is disposed vertically below a predetermined height H1.

<Each flow path>
1 , the fuel cell system 10 includes an inlet flow path 61. A first end of the inlet flow path 61 is connected to a discharge chamber (not shown) of the electric compressor 12. A second end of the inlet flow path 61 is connected to an upstream header 52 of the heat exchanger 50. The inlet flow path 61 connects the electric compressor 12 and the heat exchanger 50. The inlet flow path 61 introduces air discharged from the electric compressor 12 into the upstream header 52. Therefore, the inlet flow path 61 introduces the air discharged from the electric compressor 12 into the heat exchanger 50.

The fuel cell system 10 has an air supply passage 62. A first end of the air supply passage 62 is connected to the downstream header 53 of the heat exchanger 50. A second end of the air supply passage 62 is connected to the fuel cell stack 11. The air supply passage 62 connects the heat exchanger 50 and the fuel cell stack 11. The air supply passage 62 supplies air that has passed through the heat exchanger 50 to the fuel cell stack 11.

The fuel cell system 10 is equipped with an exhaust flow path 63. A first end of the exhaust flow path 63 is connected to the fuel cell stack 11. A second end of the exhaust flow path 63 is connected to the supply port 35 of the storage tank 30. The exhaust flow path 63 connects the fuel cell stack 11 to the supply port 35 of the storage tank 30. The exhaust flow path 63 directs exhaust gas discharged from the fuel cell stack 11 toward the supply port 35. The exhaust gas flowing through the exhaust flow path 63 is supplied to the supply port 35.

The fuel cell system 10 is equipped with a gas supply passage 64. A first end of the gas supply passage 64 is connected to the discharge port 39 of the storage tank 30. A second end of the gas supply passage 64 is connected to the suction chamber 22 of the turbine 13. The gas supply passage 64 connects the discharge port 39 of the storage tank 30 to the suction chamber 22 of the turbine 13. The gas supply passage 64 directs exhaust gas discharged from the discharge port 39 toward the suction chamber 22. The exhaust gas flowing through the gas supply passage 64 is supplied to the suction chamber 22.

The fuel cell system 10 is equipped with a bypass flow path 65. A first end of the bypass flow path 65 is connected to the intake flow path 61. Therefore, the bypass flow path 65 branches off from the intake flow path 61. A second end of the bypass flow path 65 is connected to the air supply flow path 62. The air that branches off from the intake flow path 61 and flows into the bypass flow path 65 merges with the air supply flow path 62 via the bypass flow path 65 and is then supplied to the fuel cell stack 11 via the air supply flow path 62. Therefore, the bypass flow path 65 supplies the air flowing through the intake flow path 61 to the fuel cell stack 11, bypassing the heat exchanger 50. An intercooler 66 is provided in the bypass flow path 65. The air flowing through the bypass flow path 65 is cooled by the intercooler 66.

<Flow rate adjustment section 67>
The fuel cell system 10 includes a flow rate adjuster 67. The flow rate adjuster 67 is, for example, a flow rate control valve provided at a connection point between the inlet flow path 61 and the bypass flow path 65. The fuel cell system 10 also includes a controller 70. The controller 70 is electrically connected to the flow rate adjuster 67. The controller 70 controls the valve opening of the flow rate adjuster 67. The flow rate adjuster 67 adjusts the flow rate of air branching from the inlet flow path 61 to the bypass flow path 65 by having the valve opening controlled by the controller 70. The flow rate adjuster 67 adjusts the flow rate of air branching from the inlet flow path 61 to the bypass flow path 65, thereby adjusting the flow rate of air introduced from the electric compressor 12 to the heat exchanger 50 via the inlet flow path 61.

The fuel cell system 10 is equipped with a rotation speed sensor 71, a flow rate sensor 72, a pressure sensor 73, and a temperature sensor 74. The rotation speed sensor 71, the flow rate sensor 72, the pressure sensor 73, and the temperature sensor 74 are electrically connected to the controller 70.

The rotation speed sensor 71 detects the rotation speed of the turbine wheel 17. The rotation speed sensor 71 outputs a detection signal related to the rotation speed of the turbine wheel 17 to the control controller 70. The flow rate sensor 72 detects the flow rate of air drawn in from the outside by the electric compressor 12. The flow rate sensor 72 outputs a detection signal related to the air flow rate to the control controller 70. The pressure sensor 73 detects the pressure of exhaust gas discharged from the fuel cell stack 11. The pressure sensor 73 outputs a detection signal related to the exhaust gas pressure to the control controller 70. The temperature sensor 74 detects the temperature of exhaust gas drawn into the suction chamber 22 of the turbine 13. The temperature sensor 74 outputs a detection signal related to the exhaust gas temperature to the control controller 70.

Figure 4 shows the relationship between the expansion ratio and turbine efficiency of the turbine 13. A map correlating the expansion ratio and turbine efficiency of the turbine 13 is pre-stored in the control controller 70. The relationship between the expansion ratio and turbine efficiency of the turbine 13 is shown, for example, as characteristic line L1 in Figure 4. Characteristic line L1 showing the relationship between the expansion ratio and turbine efficiency of the turbine 13 is determined by the rotation speed of the turbine wheel 17. Note that Figure 4 shows, as an example, characteristic line L1 determined by the rotation speed of the turbine wheel 17 under specified operating conditions. A program is pre-stored in the control controller 70 that derives characteristic line L1 showing the relationship between the expansion ratio and turbine efficiency of the turbine 13 based on the rotation speed of the turbine wheel 17 detected by the rotation speed sensor 71. Note that a program is pre-stored in the control controller 70 that calculates the expansion ratio of the turbine 13 based on the pressure detected by the pressure sensor 73.

Figure 5 shows the relationship between the expansion ratio of the turbine 13 and the corrected flow rate of the exhaust gas. Here, the "corrected flow rate of the exhaust gas" is the mass flow rate of the exhaust gas flowing into the turbine 13 corrected by the exhaust gas pressure and exhaust gas temperature. The corrected flow rate of the exhaust gas is the flow rate before passing through the turbine wheel 17. As shown by the solid line L2 in Figure 5, the corrected flow rate of the exhaust gas increases as the expansion ratio of the turbine 13 increases. A correction program is pre-stored in the control controller 70, which corrects the flow rate detected by the flow sensor 72 to the corrected flow rate based on the pressure detected by the pressure sensor 73 and the pressure detected by the temperature sensor 74.

The control controller 70 is pre-stored with a program that adjusts the valve opening of the flow rate adjustment unit 67 so that the turbine efficiency approaches the peak value ηmax. Consider, for example, a case where the expansion ratio of the turbine 13 calculated by the control controller 70 is lower than the expansion ratio corresponding to the peak value ηmax, as shown at state point P1 in Figure 4. In such a case, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to increase the flow rate of air introduced from the electric compressor 12 to the heat exchange unit 50 via the introduction flow path 61. In other words, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to reduce the flow rate of air branching from the introduction flow path 61 and flowing into the bypass flow path 65.

On the other hand, consider a case where the expansion ratio of the turbine 13 calculated by the control controller 70 is higher than the expansion ratio corresponding to the peak value ηmax, as in state point P2 shown in Figure 4. In such a case, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to reduce the flow rate of air introduced from the electric compressor 12 to the heat exchange unit 50 via the introduction flow path 61. In other words, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to increase the flow rate of air branching from the introduction flow path 61 and flowing into the bypass flow path 65.

[Operation of the embodiment]
Next, the operation of this embodiment will be described.
Exhaust gas discharged from the fuel cell stack 11 is supplied to an air layer 38 in the storage tank 30 via a supply port 35. A gas-liquid separator 36 separates water from the exhaust gas supplied from the supply port 35. The water separated by the gas-liquid separator 36 is then stored in a storage section 37. The water stored in the storage section 37 is evaporated into water vapor by heat exchange with air discharged from the electric compressor 12 via a heat exchanger 50.

Here, each protrusion 55 causes capillary action, which draws up the liquid surface of the water stored in the storage section 37. Therefore, the surface area between the gas phase and the liquid phase in the storage tank 30 is increased, allowing the water stored in the storage section 37 to evaporate efficiently. Furthermore, heat exchange occurs between the water stored in the storage section 37 and the porous material 56, causing the water stored in the storage section 37 to evaporate and become water vapor. Therefore, the water stored in the storage section 37 is evaporated efficiently.

The water vapor is discharged as exhaust gas to the turbine 13 via the outlet 39 together with the exhaust gas from which water has been separated in the gas-liquid separator 36. In this way, the mass of the exhaust gas supplied to the turbine 13 increases by the amount of water vapor added. As a result, the mass of the exhaust gas expanding due to the rotation of the turbine wheel 17 increases, increasing the amount of work done by the turbine wheel 17. This increases the regenerative power generated by the turbine 13. In addition, the exhaust gas from which water has been separated in the gas-liquid separator 36 passes through the air layer 38 in the storage tank 30 and is discharged to the turbine 13 via the outlet 39. Therefore, pressure loss of the exhaust gas within the storage tank 30 is unlikely to occur, avoiding any hindrance to the increase in regenerative power generated by the turbine 13.

For example, consider a case where the expansion ratio of the turbine 13 calculated by the controller 70 is lower than the expansion ratio corresponding to the peak value ηmax, as shown in state point P1 in Figure 4. In such a case, the controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to increase the flow rate of air introduced from the electric compressor 12 to the heat exchange unit 50 via the introduction flow path 61. In other words, the controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to reduce the flow rate of air branching from the introduction flow path 61 and flowing into the bypass flow path 65.

This increases the amount of water vapor generated by heat exchange via the heat exchange section 50 between the water stored in the storage section 37 and the air discharged from the electric compressor 12. Therefore, the corrected flow rate of the exhaust gas increases, and the flow rate of the exhaust gas expanded by the rotation of the turbine wheel 17 increases. This increases the expansion ratio of the turbine 13, and the expansion ratio of the turbine 13 approaches the expansion ratio corresponding to the peak value ηmax. As a result, the turbine efficiency approaches the peak value ηmax.

On the other hand, consider a case where the expansion ratio of the turbine 13 calculated by the control controller 70 is higher than the expansion ratio corresponding to the peak value ηmax, as in state point P2 shown in Figure 4. In such a case, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to reduce the flow rate of air introduced from the electric compressor 12 to the heat exchange unit 50 via the introduction flow path 61. In other words, the control controller 70 adjusts the valve opening of the flow rate adjustment unit 67 so as to increase the flow rate of air branching from the introduction flow path 61 and flowing into the bypass flow path 65.

This reduces the amount of water vapor generated by heat exchange via the heat exchange section 50 between the water stored in the storage section 37 and the air discharged from the electric compressor 12. Therefore, the corrected flow rate of the exhaust gas decreases, and the flow rate of the exhaust gas expanded by the rotation of the turbine wheel 17 decreases. This reduces the expansion ratio of the turbine 13, and the expansion ratio of the turbine 13 approaches the expansion ratio corresponding to the peak value ηmax. As a result, the turbine efficiency approaches the peak value ηmax.

In this way, by adjusting the amount of water vapor generated by heat exchange via the heat exchange section 50 between the water stored in the storage section 37 and the air discharged from the electric compressor 12, the flow rate of the exhaust gas expanded by the rotation of the turbine wheel 17 is adjusted. As a result, the expansion ratio of the turbine 13 is adjusted, allowing the turbine 13 to operate at high turbine efficiency.

As shown in FIG. 3 , suppose the amount of water vapor generated by heat exchange between the water stored in the storage section 37 and the air discharged from the electric compressor 12 via the heat exchanger 50 increases, causing the liquid level of the water stored in the storage section 37 to drop. As a result of this drop in the liquid level of the water stored in the storage section 37, the uppermost pipe section 54 in the vertical direction may become exposed to the air layer 38 within the storage tank 30. In the pipe section 54 exposed to the air layer 38 within the storage tank 30, heat exchange between the water stored in the storage section 37 and the air discharged from the electric compressor 12 becomes more difficult. In this way, fluctuations in the liquid level of the water stored in the storage section 37 fine-tune the amount of water vapor generated by heat exchange between the water stored in the storage section 37 and the air discharged from the electric compressor 12 via the heat exchanger 50.

[Effects of the embodiment]
The above embodiment can provide the following effects.
(1) Exhaust gas discharged from the fuel cell stack 11 is supplied to the air layer 38 in the storage tank 30 via the supply port 35. The gas-liquid separator 36 separates water from the exhaust gas supplied via the supply port 35. The water separated by the gas-liquid separator 36 is then stored in the storage portion 37. The water stored in the storage portion 37 is evaporated into water vapor through heat exchange with air discharged from the electric compressor 12 via the heat exchanger 50. The water vapor is discharged as exhaust gas to the turbine 13 via the discharge port 39 together with the exhaust gas from which water has been separated by the gas-liquid separator 36. In this way, the mass of the exhaust gas supplied to the turbine 13 increases by the amount of water vapor. As a result, the mass of the exhaust gas expanding due to the rotation of the turbine wheel 17 increases, thereby increasing the workload of the turbine wheel 17. This increases the regenerative power generated by the turbine 13. Furthermore, the exhaust gas from which water has been separated in the gas-liquid separator 36 passes through an air layer 38 in the storage tank 30 and is discharged from an outlet 39 to the turbine 13. Therefore, pressure loss of the exhaust gas is unlikely to occur in the storage tank 30, and the increase in regenerative power generated in the turbine 13 is not hindered. As a result, the regenerative power generated in the turbine 13 can be efficiently increased.

(2) The protrusion 55 can induce capillary action, which draws up the liquid surface of the water stored in the storage section 37, thereby increasing the surface area between the gas phase and the liquid phase in the storage tank 30. As a result, the water stored in the storage section 37 can be evaporated efficiently.

(3) The fuel cell system 10 includes an inlet flow path 61, a bypass flow path 65, and a flow rate adjustment unit 67. The flow rate adjustment unit 67 adjusts the flow rate of air branching from the inlet flow path 61 to the bypass flow path 65, thereby adjusting the flow rate of air introduced from the electric compressor 12 to the heat exchange unit 50 via the inlet flow path 61. This makes it possible to adjust the amount of water vapor generated by heat exchange between water stored in the reservoir 37 and air discharged from the electric compressor 12 via the heat exchange unit 50. Therefore, even if the flow rate of exhaust gas supplied to the turbine chamber 20 is uniquely determined, such as when the turbine 13 has a fixed nozzle 21, it is possible to adjust the flow rate of exhaust gas expanded by the rotation of the turbine wheel 17. As a result, the expansion ratio of the turbine 13 can be adjusted, allowing the turbine 13 to operate with high turbine efficiency.

(4) For example, if the liquid level of the water stored in the storage section 37 drops, one of the multiple pipe sections 54 located at the top in the vertical direction may become exposed to the air layer 38 within the storage tank 30. In the pipe section 54 exposed to the air layer 38 within the storage tank 30, heat exchange between the water stored in the storage section 37 and the air discharged from the electric compressor 12 becomes difficult. In this way, fluctuations in the liquid level of the water stored in the storage section 37 can fine-tune the amount of water vapor generated by heat exchange between the water stored in the storage section 37 and the air discharged from the electric compressor 12 via the heat exchange section 50.

(5) The heat exchange unit 50 has a porous material 56 that is thermally coupled to the heat exchange body 51 and is positioned vertically below a predetermined height H1. As a result, heat exchange occurs between the water stored in the storage unit 37 and the porous material 56, causing the water stored in the storage unit 37 to evaporate and become water vapor. Therefore, the water stored in the storage unit 37 can be efficiently evaporated.

[Example of change]
The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

In the above-described embodiment, the heat exchanger 50 does not have to have a plurality of protrusions 55. For example, the heat exchanger 50 may have only one protrusion 55.
In the embodiment, the protruding portion 55 does not have to be thin and flat, and may be, for example, columnar. The protruding portion 55 may also be made of, for example, a lattice material or a mesh material. The key is that the protruding portion 55 needs only to extend from the heat exchanger body 51 and protrude beyond the predetermined height H1 into the air layer 38. The protruding portion 55 needs only to be configured to cause capillary action that draws up the liquid surface of the water stored in the storage portion 37.

In the above embodiment, the heat exchanger 50 does not have to have the protrusion 55 .
In the above-described embodiment, the fuel cell system 10 may not include the bypass flow path 65 and the flow rate regulator 67 .

In an embodiment, the turbine 13 may be configured to have a variable nozzle, instead of a fixed nozzle 21, that can vary the flow rate of exhaust gas supplied to the turbine chamber 20.

In the above-described embodiment, the heat exchange unit 50 does not have to include a plurality of pipes 54. For example, the heat exchange unit 50 may include only one pipe 54.
In the above-described embodiment, the pipes 54 do not have to be flat tubes and may be, for example, cylindrical tubes. In other words, the shape of the pipes 54 is not particularly limited.

In the above embodiment, the heat exchange unit 50 does not have to include the porous material 56 .
In the above embodiment, the fuel cell system 10 does not necessarily have to include the temperature sensor 74 that detects the temperature of the exhaust gas taken into the intake chamber 22 of the turbine 13. In this case, the temperature of the exhaust gas may be estimated from the temperature of the cooling water that adjusts the temperature of the fuel cell stack 11, for example.

- In an embodiment, the storage tank 30 may have, for example, a water level sensor that measures the height of the water level stored in the storage section 37. The drain valve 42 may also be configured so that its opening and closing are controlled by the control controller 70. The control controller 70 may then control the operation of the drain valve 42 to open it when a detection signal indicating that the water level has reached a predetermined height H1 is transmitted from the water level sensor.

In the embodiment, the gas-liquid separation section 36 was a cylindrical section protruding from the inner surface of the upper wall 31, but this is not limited to this. In short, the specific configuration of the gas-liquid separation section 36 is not particularly limited as long as it is capable of separating water from the exhaust gas supplied from the supply port 35.

In this embodiment, the fuel cell system 10 does not have to be installed in a fuel cell vehicle. In other words, the fuel cell system 10 is not limited to being installed in a vehicle.

[Note]
The above embodiment includes the configurations described in the following supplementary notes.
<Appendix 1>
a fuel cell stack that generates electricity by chemically reacting fuel gas with oxygen in the air;
an electric compressor including a compression unit that compresses air supplied to the fuel cell stack and a motor that drives the compression unit;
a turbine having a turbine wheel that is rotated by exhaust gas discharged from the fuel cell stack to assist in driving the motor,
a storage tank for storing water contained in exhaust gas discharged from the fuel cell stack;
The storage tank comprises:
a supply port connected to an air space in the storage tank and configured to supply exhaust gas discharged from the fuel cell stack into the storage tank;
a gas-liquid separation unit that separates water from the exhaust gas supplied from the supply port;
a storage section in which the water separated by the gas-liquid separation section is stored;
a heat exchange unit that exchanges heat between the water stored in the storage unit and the air discharged from the electric compressor;
an outlet connected to the air layer and for discharging the exhaust gas from which water has been separated in the gas-liquid separator to the turbine.

<Appendix 2>
the storage tank has a water storage amount control unit that controls the amount of water stored in the storage unit so that the liquid level of the water stored in the storage unit does not exceed a predetermined height,
The heat exchange unit is
a heat exchange body disposed vertically below the predetermined height;
and a protrusion extending from the heat exchange body and protruding beyond the predetermined height into the air layer.

<Appendix 3>
The turbine is
a turbine chamber that houses the turbine wheel;
a fixed nozzle that throttles the flow rate of exhaust gas supplied to the turbine chamber,
an introduction flow path that introduces air discharged from the electric compressor into the heat exchanger;
a bypass flow path that branches off from the inlet flow path and supplies the air flowing through the inlet flow path to the fuel cell stack, bypassing the heat exchanger;
a flow rate adjusting unit that adjusts the flow rate of air that branches off from the inlet flow path and flows into the bypass flow path, thereby adjusting the flow rate of air that is introduced from the electric compressor through the inlet flow path to the heat exchange unit.

<Appendix 4>
the heat exchange unit has a plurality of piping units arranged side by side in a vertical direction within the storage tank,
The air discharged from the electric compressor flows through the piping sections,
The fuel cell system described in any one of <Appendix 1> to <Appendix 3>, characterized in that each of the piping sections performs heat exchange between the water stored in the storage section and the air discharged from the electric compressor.

<Appendix 5>
The fuel cell system described in <Appendix 2> is characterized in that the heat exchange unit has a porous material that is thermally coupled to the heat exchange main body and is positioned vertically below the specified height.

10...Fuel cell system, 11...Fuel cell stack, 12...Electric compressor, 13...Turbine, 14...Compression section, 15...Motor, 17...Turbine wheel, 20...Turbine chamber, 21...Fixed nozzle, 30...Storage tank, 35...Supply port, 36...Gas-liquid separation section, 37...Storage section, 38...Air layer, 39...Outlet, 40...Storage volume control section, 50...Heat exchange section, 51...Heat exchange main body, 54...Piping section, 55...Protrusion, 56...Porous material, 61...Inlet flow path, 65...Bypass flow path, 67...Flow rate adjustment section.

Claims (5)

a fuel cell stack that generates electricity by chemically reacting fuel gas with oxygen in the air;
an electric compressor including a compression unit that compresses air supplied to the fuel cell stack and a motor that drives the compression unit;
a turbine having a turbine wheel that is rotated by exhaust gas discharged from the fuel cell stack to assist in driving the motor,
a storage tank for storing water contained in exhaust gas discharged from the fuel cell stack;
The storage tank comprises:
a supply port connected to an air space in the storage tank and configured to supply exhaust gas discharged from the fuel cell stack into the storage tank;
a gas-liquid separation unit that separates water from the exhaust gas supplied from the supply port;
a storage section in which the water separated by the gas-liquid separation section is stored;
a heat exchange unit that exchanges heat between the water stored in the storage unit and the air discharged from the electric compressor;
an outlet connected to the air layer and for discharging the exhaust gas from which water has been separated in the gas-liquid separator to the turbine. the storage tank has a water storage amount control unit that controls the amount of water stored in the storage unit so that the liquid level of the water stored in the storage unit does not exceed a predetermined height,
The heat exchange unit is
a heat exchange body disposed vertically below the predetermined height;
2. The fuel cell system according to claim 1, further comprising: a protrusion extending from said heat exchange body and protruding beyond said predetermined height into said air layer. The turbine is
a turbine chamber that houses the turbine wheel;
a fixed nozzle that throttles the flow rate of exhaust gas supplied to the turbine chamber,
an introduction flow path that introduces air discharged from the electric compressor into the heat exchanger;
a bypass flow path that branches off from the inlet flow path and supplies the air flowing through the inlet flow path to the fuel cell stack, bypassing the heat exchanger;
a flow rate adjusting unit that adjusts the flow rate of air that branches off from the inlet flow path and flows into the bypass flow path, thereby adjusting the flow rate of air that is introduced from the electric compressor through the inlet flow path to the heat exchanger. the heat exchange unit has a plurality of piping units arranged side by side in a vertical direction within the storage tank,
The air discharged from the electric compressor flows through the piping sections,
2. The fuel cell system according to claim 1, wherein each of the piping sections exchanges heat between the water stored in the storage section and the air discharged from the electric compressor. The fuel cell system described in claim 2, characterized in that the heat exchange unit has a porous material that is thermally coupled to the heat exchange body and is positioned vertically below the predetermined height.