METHOD FOR STARTING A FUEL CELL AT LOW TEMPERATURES

Abstract

A method and a system for starting a fuel cell at temperatures below 0 Celsius with a two-phase cooling system are indicated, whereby the two-phase cooling system has a pump to convey a coolant present in the two-phase cooling system, whereby the coolant is present at least partially in a gas phase in the two-phase cooling system, including steps of starting the fuel cell, and activating the pump after a defined period of time, whereby the coolant is present substantially in the gas phase within the fuel cell during the defined period of time.

Claims

1. A method for starting a fuel cell at temperatures below 0 Celsius with a two-phase cooling system, the two-phase cooling system comprising a pump for conveying a coolant present in the two-phase cooling system, wherein the coolant is present in the two-phase cooling system at least partially in a gas phase, the method comprising: starting the fuel cell; and activating the pump after a defined period of time, whereby the coolant is present substantially in the gas phase within the fuel cell during the defined period of time.

2. The method of claim 1, whereby, 100% of the coolant is present in the gas phase in the fuel cell in starting the fuel cell.

3. The method of claim 1, whereby the defined period of time is at least 60 seconds, or at least 30 seconds, or at least 20 seconds.

4. The method of claim 1, wherein the coolant comprises methanol and/or ethanol.

5. The method of claim 1, whereby the pump operates intermittently in order to keep a thermal mass of a mass flow of the coolant in the fuel cell low.

6. A system for starting a fuel cell at temperatures below 0 Celsius with a two-phase cooling system, wherein the system is configured to perform the method of claim 1, the system comprising: at least one fuel cell; a pump; a coolant circuit; wherein the coolant circuit is configured to cool the fuel cell by two-phase cooling, and wherein the pump is configured to be activatable after a defined period of time.

7. The system of claim 5, whereby comprising a condenser bypass to keep a thermal mass of a mass flow to and/or from a condenser low.

8. An aircraft comprising the system of claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Example embodiments of the disclosure herein are discussed in greater detail below on the basis of the enclosed drawings. The representations are schematic and not true-to-scale. Identical reference signs relate to identical or similar elements. In the drawings:

[0048] FIG. 1 shows a flowchart of a method for starting a fuel cell at temperatures below 0 C.;

[0049] FIG. 2A shows a system for operating a fuel cell with a two-phase cooling system according to a first embodiment;

[0050] FIG. 2B shows a system for operating a fuel cell with a two-phase cooling system according to a second embodiment;

[0051] FIG. 3 shows an aircraft with a system for starting a fuel cell at temperatures below 0 C.; and

[0052] FIG. 4 shows a graphic representation of a temperature profile over time.

DETAILED DESCRIPTION

[0053] FIG. 1 shows a method 100 for starting a fuel cell at temperatures below 0 C. with a two-phase cooling system includes various steps in order to ensure a frictionless starting process. In the case of this method, a two-phase cooling system is used which contains a pump 20 in order to convey the coolant in the system 10. In this case, the coolant is located at least partially in a gas phase within the two-phase cooling system.

[0054] The first step of the method is starting 102 the fuel cell 12. In the case of temperatures below freezing point, it is particularly important that the starting process is carried out properly. Once the fuel cell has been started, the process continues to the next step.

[0055] In the next step, activation 104 of the pump 20 is performed, and indeed after a defined period of time. During this period of time, the coolant is substantially in the gas phase within the fuel cell 12. This is a decisive step in order to effectively ensure cooling. As a result of the activation of the pump, the coolant is moved through the two-phase cooling system, as a result of which the heat is discharged and the temperature of the fuel cell is stabilized.

[0056] The method makes it possible to successfully start the fuel cell even in the case of extremely low temperatures. The cooling is optimized as a result of the two-phase cooling system and the targeted activation of the pump. This helps to extend the life span of the fuel cell and increases operational reliability.

[0057] FIGS. 2A and 2B show in each case a system 10 for starting a fuel cell at temperatures below 0 C. with a two-phase cooling system which is configured to carry out the method 100 described. The system 10 is composed of several components which work together to enable a successful starting process.

[0058] The central component of the system is the fuel cell 12 which converts chemical energy into electrical energy. A two-phase cooling system is used in order to ensure effective cooling. This system uses a combination of liquid and gas phase of the coolant in order to discharge the heat and regulate the temperature of the fuel cell.

[0059] A pump 20 is present in order to move the coolant in the cooling system. This pump is designed so that it can be activated after a defined period of time. This period of time is vital to ensure that the coolant is in the correct state to ensure optimum cooling of the fuel cell.

[0060] In addition to the two-phase cooling system and the pump 20, a coolant circuit 16 and a heat exchanger 18 are integrated in the system 10. This circuit enables the continuous flow of the coolant through the fuel cell and the cooling system. It is ensured by the coolant circuit that the coolant is efficiently circulated and the discharge of heat is optimized.

[0061] The key difference between the embodiments of FIGS. 2A and 2B can be seen in the fact that the accumulator/collector 14 is connected to the return line and as a result of this the gas phase can mix with the liquid phase. In this embodiment, a condenser bypass is used to keep the thermal mass of a mass flow circulating through the fuel cell low. A condenser bypass is a device or an arrangement which makes it possible to conduct part of the mass flow or the coolant around the condenser, instead of guiding it through the condenser. The condenser bypass thus conducts the coolant past the condenser. As a result of this, the thermal mass of the circulating coolant in the circuit is reduced and no unnecessary discharge of heat to the surroundings occurs during the starting process.

[0062] The system 10 for operating a fuel cell with a two-phase cooling system offers efficient cooling, improved performance and a longer service life of the fuel cell 12. It enables reliable operation even in the case of extreme temperatures and ensures stable and effective energy generation.

[0063] FIG. 3 shows an aircraft 200 which is equipped with a system 10 which was developed for the operation of a fuel cell. The system 10 operates in combination with a fuel cell in order to enable efficient energy generation.

[0064] In addition to the cooling system 10 and the pump 20, the system 10 also contains a coolant circuit 16. This coolant circuit 16 enables a continuous flow of the coolant through the system in order to ensure a constant cooling of the fuel cell. The coolant circuit plays a vital role in maintaining the optimum operating temperature of the fuel cell, and can be started with the described method even at temperatures below 0 Celsius.

[0065] FIG. 4 shows in each case a graphic representation of two temperature profiles over time. Both graphs begin below 0 Celsius, T.sub.0, and approach the operating temperature T.sub.B. It is clearly apparent that the left-hand graph (continuous line) reaches the operating temperature T.sub.B quicker than the right-hand graph (dashed line). This is due to the fact that the pump is only activated after a defined period of time t.sub.P and the described effects come about. In contrast, the right-hand graph which represents a profile in which the pump is activated right at the start is significantly flatter at the start and the operating temperature T.sub.B is reached later relative to this. The described method thus makes it possible to speed up the starting process of the fuel cell at temperatures below freezing point.

[0066] It should additionally be pointed out that comprising or having does not rule out any other elements or steps and one or a does not rule out a plurality. It should furthermore be pointed out that features or steps which have been described with reference to one of the above example embodiments can also be used in combination with other features or steps of other example embodiments described above. Reference signs in the claims should not be regarded as a restriction.

[0067] While at least one example embodiment of the invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a, an or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

LIST OF REFERENCE SIGNS

[0068] 10 System [0069] 12 Fuel cell [0070] 14 Accumulator [0071] 16 Coolant circuit [0072] 18 Heat exchanger [0073] 20 Pump [0074] 100 Method for starting a fuel cell at temperatures below 0 102 Starting the fuel cell [0075] 104 Activating the pump after a defined period of time [0076] 200 Aircraft [0077] T.sub.0 Freezing point of water [0078] T.sub.B Operating temperature [0079] t.sub.P Defined period of time