EVAPORATIVE COOLING FOR A MOTOR VEHICLE WITH FUEL-CELL DRIVE

Abstract

A fuel cell system for a vehicle, comprising a fuel cell and a water collection device for collecting liquid water from exhaust gas of the fuel cell, comprising an exhaust gas cooler including a heat exchanger which cools the exhaust gas by transferring heat from the exhaust gas to a flow of a cooling medium and condenses water contained in the exhaust gas and comprising a water tank for storing the collected water, a cooling device for cooling the fuel cell comprising a cooler, and a water ejection device for ejecting and distributing water. The water tank may be pressurized. A control means may choose operating modes for the fuel cell system that comprise an operating mode for water collection and an operating mode for water ejection based on a power schedule that comprises a sequence of scheduled operating phases with varying power requirements for the fuel cell system.

Claims

1. A fuel cell system for a vehicle, including: a fuel cell; an exhaust line for exhausting exhaust gas containing water from the fuel cell; and a water collection device for collecting liquid water from the exhaust gas, the water collection device including an exhaust gas cooler, wherein the exhaust gas cooler comprises a heat exchanger disposed on the exhaust line and adapted to, by transferring heat from the exhaust gas to a flow of a cooling medium, cool the exhaust gas passed in the exhaust line via the heat exchanger and condense water contained in the exhaust gas, wherein the water supplied to the heat exchanger with the exhaust gas, including the water condensed therefrom, is discharged from the heat exchanger via the exhaust line; a water tank coupled to the water collection device downstream of the heat exchanger and adapted to store collected water; a cooling device for cooling the fuel cell, comprising a cooler; a water ejection device for ejecting and distributing water on the cooler or in a supply air stream of the cooler; and a water line for supplying water from the water tank to the water ejection device.

2. The fuel cell system of claim 1, wherein the cooling device for cooling the fuel cell comprises a cooling circuit comprising a cooling medium, the cooling circuit comprising a cooling path that passes over the heat exchanger and that is adapted to provide the flow of the cooling medium over the heat exchanger.

3. The fuel cell system of claim 1, wherein the flow of the cooling medium via the heat exchanger is a flow of air from environment of the vehicle.

4. The fuel cell system of claim 1, wherein the water tank is pressurizable by a pressure source, wherein the water line includes a valve via which the water tank is connectable to the water ejection device, wherein the water ejection device is arranged to eject water from the water tank connected by the valve by the pressure applied to the water tank and to distribute it on the cooler or in a supply air flow of the cooler.

5. The fuel cell system of claim 1, further comprising a pump adapted to feed water discharged from the heat exchanger via the exhaust line into the water tank against pressure applied to the water tank.

6. The fuel cell system of claim 1, further comprising a control means which is arranged for an operating method of the fuel cell system in which: by the control means, based on a power schedule comprising a sequence of planned operating phases with different power requirements for the fuel cell, operating modes for the fuel cell system are selectively chosen according to the planned operating phases, which operating modes comprise at least one operating mode for water collection and at least one operating mode for water ejection, wherein in the at least one operating mode for water collection, the water collection device is operated to collect liquid water from the exhaust gas and supply it to the water tank, and wherein, in the at least one operating mode for water ejection, water is supplied from the water tank to the water ejection device and ejected from the water ejection device and distributed on the cooler or in a supply air stream of the cooler.

7. The fuel cell system of claim 6, wherein the power schedule determines a power requirement for the fuel cell as a function of a location history of the vehicle and/or a time history.

8. The fuel cell system of claim 6, wherein the at least one operating mode for water ejection comprises an operating mode for water ejection in which the water collection device is not actively operated.

9. The fuel cell system of claim 6, wherein the control means is adapted to adjust the power schedule during travel of the vehicle based on a current movement of the vehicle.

10. The fuel cell system of claim 1, wherein the cooler includes a fan drive, the fuel cell system comprising one or more control means adapted for a water ejection operation mode, wherein the water ejection device ejects and distributes water on the cooler or in a supply air stream of the cooler, and wherein the control means controls a power of the fan drive of the cooler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The invention is described in detail below with reference to figures. In the figures shows:

[0065] FIG. 1 a schematic representation of a fuel cell system according to embodiments of the present disclosure;

[0066] FIG. 2 a schematic representation of a schematic example of an exhaust gas cooler according to embodiments of the invention;

[0067] FIG. 3 a schematic representation of another example of an exhaust gas cooler according to embodiments of the invention;

[0068] FIG. 4 a schematic representation of a water spray device according to embodiments of the invention;

[0069] FIG. 5 an operating method of the fuel cell system according to embodiments of the invention; and

[0070] FIG. 6 a graph schematically indicating a condensation rate as a function of an exhaust gas temperature.

DETAILED DESCRIPTION

[0071] In the following, unless otherwise noted, the same reference signs are used for the same elements and elements having the same effect.

[0072] FIG. 1 shows a schematic diagram of a fuel cell system 10 for a vehicle according to embodiments of the present disclosure. The fuel cell system 10 comprises a fuel cell 20 and a cooling device 30 for the fuel cell 20. The cooling device 30 comprises a cooling circuit 32 with a pump 33, a cooler 35 and a fan 34 arranged on the cooler 35. The pump 33 is arranged to pump a cooling medium contained in the cooling circuit 32 through the fuel cell 20 and the cooler 35.

[0073] The fan 34 comprises a fan drive 36, and the fan 34 is configured to generate a cooling air stream 38 over or through the cooler 35 to cool the cooling medium by heat exchange with the cooling medium to dissipate waste heat from the fuel cell 20 to the ambient air in the cooling air stream 38 via the cooling circuit 32.

[0074] The fuel cell system 10 comprises a water collection device 100 having an exhaust line 102 for exhausting exhaust gas containing water from the fuel cell 20, an exhaust gas cooler 105, a gas-liquid separator 106, a water reservoir 109, and a high pressure pump 111, which are coupled together in this order. Via a switchable branch valve 103, the exhaust gas flow from the fuel cell 20 can be supplied to the exhaust gas cooler 105 through the exhaust line 102. Depending on the switch position of the branch valve 103, a portion of the exhaust gas flow may be vented to the environment through an exhaust line 104.

[0075] The exhaust gas cooler 105 comprises a heat exchanger 150 arranged on the exhaust line 102. The exhaust line 102 is routed through the heat exchanger 150. Further, a secondary path 101 of the cooling circuit 32 is passed through the heat exchanger 150. The cooling medium of the cooling circuit 32 and the exhaust gas of the fuel cell 20 conducted through the exhaust line 102 are in heat exchange with each other via a heat permeable wall 152 of the heat exchanger 150. The cooling circuit 32 comprises a controllable, for example continuously variable, valve 130 at which the secondary path 101 branches off from the main path or primary path 40 of the cooling circuit 32. The operation of the heat exchanger 150, and thus the exhaust gas cooler 105, is thus controllable by the controllable valve 130.

[0076] The gas-liquid separator 106 is connected to the water reservoir 109 via a pipeline 108. Any remaining water vapor can be discharged to the environment via an outlet line 107.

[0077] The high-pressure pump 111 is connected to the water reservoir 109 via a pipeline 110. It is part of an evaporative cooling system 124 for cooling the cooler 35 of the cooling circuit 32. The evaporative cooling system 124 further comprises a pressurizable water tank 113 and a water ejection device 120 connectable thereto. The water tank 113 is pressurizable by means of compressed air via a pipeline 114 and a valve 115 arranged on the pipeline 114 by means of a pressure source 116 in the form of an air compressor or air presser. The high-pressure pump 111 is connected to the water tank 113 via a check valve 112, and is adapted to supply water from the water reservoir 109 to the water tank 113 through the check valve 112 while overcoming the pressure applied to the water tank 113.

[0078] An outlet of the water tank 113 is connected to the water ejection device 120 via a water line 117 and a switchable valve 118, which is arranged on the water line 117. Further, the water tank 113 is connected at a drain port 121 to a drain valve 122 for draining water contained in the water tank 113 when required. A pressure release valve 131 for releasing compressed air and a closure 132 for manually filling the water tank 113 are further arranged at the water tank 113.

[0079] A control means 180 for controlling the fuel cell system 10 is particularly connected to the controllable valves 103, 130, 115, 118, 122, 130 for controlling the same and is adapted to control the high pressure pump 111 and the fan drive 36. The control means 180 may be further connected to sensors 193 for detecting a level in the water reservoir 109 and/or in the water tank 113.

[0080] FIG. 2 schematically shows an embodiment example in which the exhaust gas cooler 105 comprises a heat exchanger 150 connected to a secondary path 200 of a second cooling or refrigeration circuit 201 of the vehicle (for example, an air conditioning system, a battery cooling system, or a cooling system of an auxiliary unit such as a DC-DC converter, vehicle electrical system intermediate converter, electrical machines, inverters) instead of the secondary path 101. The secondary path 200 can in turn be connected to the second cooling or refrigeration circuit 201 by a controllable valve 130, in particular one that can be switched continuously. Incidentally, the fuel cell system can be constructed in the same way as the fuel cell system 10 of FIG. 1.

[0081] FIG. 3 schematically shows an embodiment example in which the exhaust gas cooler 105 comprises a heat exchanger 300 arranged to transfer heat from the exhaust gas of the fuel cell 20 flowing through the exhaust line 102 via a wall 152 to a flow of ambient air, which is used here as a cooling medium for the heat exchanger 300. For example, the heat exchanger 300 may be disposed in or on an air duct 301. A forced air flow may be generated in the air duct 301, for example, by a fan 303. The heat exchanger 300 may also be cooled, for example, by an airstream, and the heat exchanger 300 may be arranged freely on the vehicle, for example, that is, without an air duct 301, such as on the underbody of the vehicle. In the case of an air duct 301 or fan 303, control of the exhaust gas cooler 105 by the control means 180 may be accomplished, for example, by controlling the fan 303 and/or by controlling air dampers. The fuel cell system may otherwise be structured like the fuel cell system 10 of FIG. 1.

[0082] In the embodiment examples described, a control of the exhaust gas cooler 105 may also be performed by controlling the branch valve 103, for example by supplying the exhaust gas flow to the exhaust gas cooler 105 completely, partially and/or not at all. Control of the water collection device 100 may be accomplished, for example, by controlling the operation of the exhaust gas cooler 105 and/or, for example, by controlling the operation of the high pressure pump 111. Excess exhaust gas or excess water in the exhaust gas may be discharged, for example, through the outlet line 107 from the gas-liquid separator 106.

[0083] FIG. 4 schematically illustrates the water ejection device 120 according to embodiments of the invention. The water ejection device 120 is designed, for example, as a water spraying device and comprises one or more nozzles 220 for spraying the water onto the cooler 35, for example onto cooling fins or a surface of the cooler 35, and into the supply air stream of the cooler 35. The supply air stream is the inlet-side part of the cooling air stream 38. As shown schematically in FIG. 4, the cooling medium flows through the cooler 35 as part of the cooling circuit 32. The cooling medium thereby transfers heat to the cooling air stream 38 by heat exchanger. The sprayed-on or sprayed-in water can cause the following physical mechanisms to increase the cooling capacity of the cooler 35: an evaporation (non-adiabatic) of water on the cooler surface, concurrent with a transfer of heat from the cooler 35 to the water; an evaporation (adiabatic) in the air stream 38, decreasing the air inlet temperature of the cooling air stream 38 at the cooler 35; and an increase in the heat capacity of the water-enriched cooling air stream 38 entering the cooler.

[0084] FIG. 5 schematically illustrates an operating method of the fuel cell system according to embodiments of the invention, controlled by the control means 180.

[0085] Based on a predetermined route or a route usually traveled by the vehicle, a current route is determined that has a high probability of being traveled. Based on this route plan (S10) and based on vehicle data such as a vehicle mass and a current and/or expected ambient temperature, a route plan is determined (S12). The route plan comprises route data as a function of a location s and a time t of the vehicle, for example, the expected slope of the roadway at location s and time t and/or an expected driving speed at location s and time t. The route data can also be adjusted using, for example, weather data or weather data, such as ambient temperature, and data about the traffic situation on the planned route. This data can be obtained, for example, from cloud-based services or an infotainment system of the vehicle. Steps S10 and S12 can be combined by determining the route plan during route planning.

[0086] Based on the determined route plan, and for example additionally based on an expected ambient temperature T.sub.amb(t) as a function of time t, or an expected ambient temperature T.sub.amb(s, t) as a function of time t and location s, and based on the vehicle data, a predictive determination (S14) of a power schedule is performed. The power schedule can be specified, for example, as the expected target power of the fuel cell as a function of the vehicle location s and time t as P.sub.BZ,soll(s,t), for example as a sequence of planned operating phases at specific times t and associated locations s with different high power requirements P.sub.BZ,soll on the fuel cell.

[0087] Based on the power schedule, a cooling power schedule (S16) is determined that correspondingly comprises a sequence of planned operating phases of different high cooling target powers of the cooling device 30 for the fuel cell 20. The target cooling power can be specified as P.sub.kühl,soll(s,t). From the cooling power schedule, depending on the expected ambient temperature, an amount of water required by the water ejection device 120 up to a location s and time t is determined, for example as an integral over the required water mass flow {dot over (m)}, which can be described as ∫{dot over (m)}(s,t).sub.Aufdüsen,soll (S18). From this, or in a corresponding manner, an amount of water to be collected or generated by the water collection device 100 is determined as a function of location s and time t as ∫{dot over (m)}(s,t).sub.Generierung,soll (S20). For example, the evaporative cooling device 124 may be configured to generate a water ejection of the water ejection device 120 of, for example, 50 ml/s for maximum cooling performance by evaporative cooling. The water tank 113 may include a water capacity of 200 liters, for example.

[0088] While the vehicle is moving, a check may additionally be made to determine whether the cooling circuit 32 or cooling or refrigeration circuit 201 used by the exhaust gas cooler 105 in the heat exchanger for cooling has current remaining capacity for cooling (S22), and based on the result, an adjustment may be made to the determined amounts of water required for ejecting and/or generating.

[0089] Depending on the determined value of the current amount of water to be generated, and possibly adjusted based on the determined residual capacity of the respective cooling circuit, a selective choice (S24) of an operating mode for the fuel cell system 10 is performed by the control means 180. In particular, the following operating modes can be chosen in accordance with the required water quantity, and thus in accordance with the model-predictively determined power requirements for the fuel cell in accordance with the power schedule: a first operating mode corresponding to a deactivated water collection device 100; a second operating mode corresponding to an active operation of the water collection device 100 for collecting liquid water from the exhaust gas of the fuel cell and supplying the collected water to the water tank 113; and a third operating mode for water ejection in which water is ejected by the water ejection device 120, thereby increasing the cooling capacity of the cooler 35 for the cooling device for cooling the fuel cell 20.

[0090] The control means 180 controls the fuel cell system 10 according to the selected operating mode (S26). In particular, the control means 180 may control the water collection device 100 according to the formed operating mode, in particular the exhaust gas cooler 105 and/or the high pressure pump 111, and the control means 180 may control the water ejection device 120 for example by controlling the valve 118. For checking the current operating phase and selecting the next operating phase, a return is made to step S22 or before step S24.

[0091] While the vehicle is moving, an adjustment of the predictive determination of the power schedule can be made based on a current driving situation, current vehicle data, and in particular a current ambient temperature (S14). In this case, the steps following step S14 can also be adjusted.

[0092] In addition, an adjustment of the route planning (S10) can take place during the journey due to current route influences, such as traffic conditions (congestion, etc.), current weather conditions and current ambient temperature, whereby the steps following step S10 are also adjusted.

[0093] In embodiments, the fuel cell system may comprise an external data unit 500, and the control means may be arranged to communicate with the external data unit 500, for example via mobile communications. The external data unit 500 may, for example, perform steps S10 (route planning) and/or S12 (route planning). Vehicle data may be communicated from the control means 180 to the external data unit 500. For example, the power schedule, the cooling power schedule, and the data on the amount of water required and the amount of water to be collected may be communicated from the external data unit 500 to the control means 180 when determined by the external data unit 500. Preferably, the residual capacity check is performed by the control means 180, i.e., on the vehicle side. Of the described method steps, some may be performed by the external data unit 500 in advance of the trip or during the trip away from the vehicle, for example by a cloud-based system or other server. Both the power schedule described at step S14 and the cooling power schedule described at step S16 may be used by the control means 180 as the power schedule for selecting the corresponding operating modes.

[0094] As an alternative to the pressurized water tank 113 of the embodiments described, which is filled by the high pressure pump 111, a non-pressurized water tank 113 may be provided, and instead of or in addition to the high pressure pump 111, a pump 411 may be provided to supply water from the water tank 113 to the water ejection device 120. The water ejection device 120 may be controlled by actuating the optional valve 118 and/or said pump 411.

[0095] FIG. 6 schematically shows an example of the relative condensation rate R of the gaseous product water in the exhaust gas of the fuel cell 20 as a function of the exhaust gas temperature or the temperature T of the exhaust gas reached in the exhaust gas cooler 105. The figure shows an approximately exponential course of the function. From the curve of the condensation rate R, it can be seen that a large amount of liquid water can be generated from the exhaust gas even when the exhaust gas is cooled by a relatively small temperature difference. Together with the water tank 113, a supply of water can thus be efficiently created for cooling the cooler 35 in later operating phases of the fuel cell 20 with higher fuel cell power.

REFERENCE NUMERALS

[0096] 10 fuel cell system [0097] 20 fuel cell [0098] 30 cooling device [0099] 32 cooling circuit [0100] 33 pump [0101] 34 fan [0102] 35 cooler [0103] 36 fan drive [0104] 38 cooling air flow [0105] 40 primary path [0106] 100 water collection device [0107] 101 secondary path [0108] 102 exhaust line [0109] 103 branch valve [0110] 104 exhaust line [0111] 105 exhaust gas cooler [0112] 106 liquid separator [0113] 107 outlet line [0114] 108 pipeline [0115] 109 water reservoir [0116] 110 pipeline [0117] 111 high pressure pump [0118] 112 check valve [0119] 113 water tank [0120] 114 pipeline [0121] 115 valve [0122] 116 pressure source [0123] 117 water line [0124] 118 valve [0125] 120 water ejection device [0126] 121 drain opening [0127] 122 drain valve [0128] 124 evaporative cooling system [0129] 130 valve [0130] 131 pressure release valve [0131] 132 closure [0132] 150 heat exchanger [0133] 152 wall [0134] 180 control means [0135] 193 sensors [0136] 200 secondary path [0137] 201 refrigeration circuit [0138] 220 nozzles [0139] 300 heat exchanger [0140] 301 air duct [0141] 303 fan [0142] 411 pump [0143] 500 data unit