Fuel cell system and operating method therefor - Patent application

Abstract

The fuel cell system 100 includes a fuel cell stack 101, an anode section 103 for supplying fuel to the fuel cell stack 101, a discharge valve 105 for discharging anode gas from the anode section 103, a metering valve 107 for metering fuel into the anode section 103, and a computing unit 109. The computing unit 109 clocks the metering valve 107 and also clocks the discharge valve 105 depending on the activation of the metering valve 107.

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system and an operating method for a fuel cell system according to the appended claims. [Background technology]

[0002] Hydrogen-based fuel cell systems are seen as a mobility concept of the future, as they emit only water as an exhaust gas and enable quick refueling times.

[0003] During operation of a fuel cell system, it is known to recirculate anode gas to keep hydrogen losses low and maximize inlet humidity.

[0004] For recirculation, so-called "jet pumps", recirculation fans or a combination of both concepts can be used.

[0005] During operation of the fuel cell system, water and nitrogen accumulate in the anode circuit, and the water gradually displaces the hydrogen. Therefore, to avoid the hydrogen concentration becoming too low and to reduce the energy costs for recirculation, the anode circuit is regularly cleaned with fresh hydrogen in a so-called "purging." For this purpose, a discharge valve, or so-called "purge valve," is briefly opened to direct part of the gas mixture into the cathode exhaust gas channel.

[0006] From a cost and construction space standpoint, it is advantageous to use only one jet pump.

[0007] For correct operation of the jet pump, a minimum initial mass flow is required, below which the throughflow rate becomes subcritical and the recirculation mass flow collapses.

[0008] A known possibility for extending the operating range of a fuel cell system is the clocked activation of the metering valve or so-called hydrogen gas injector (HGI), thereby gradually operating the jet pump above the minimum mass flow while simultaneously supplying not much more hydrogen than is consumed in the fuel cell stack on a time average.

[0009] Clock actuation of the metering valve is known in many fuel cell systems, regardless of the interaction between the metering valve and the jet pump. Summary of the Invention

[0010] Within the framework of the present invention, a fuel cell system and an operating method for operating a fuel cell system are presented. Further features and details of the invention are evident from the respective dependent claims, the description and the drawings. It should be noted that features and details described in the context of the operating method according to the invention also naturally apply in the context of the fuel cell system according to the invention and vice versa, so that the disclosures of the individual aspects of the invention are or can always be linked to one another.

[0011] The present invention is particularly useful for providing fuel efficient fuel cell systems.

[0012] Thus, according to a first aspect of the present invention, a fuel cell system for exchanging energy is presented.

[0013] The fuel cell system provided includes a fuel cell stack, an anode section for supplying fuel to the fuel cell stack, a discharge valve for discharging anode gas from the anode section, a metering valve for metering fuel into the anode section, and a computing unit, wherein the computing unit is configured to clock-activate the metering valve, and the computing unit is further configured to clock-activate the discharge valve depending on the activation of the metering valve.

[0014] A computing unit should be understood in the context of the presented invention to be a computer, controller, processor or any other programmable circuit.

[0015] By metering valve, in the context of the presented invention, is to be understood a valve for metering fuel into the anode section, such as a proportional valve.

[0016] By exhaust valve, in the context of the presented invention, is to be understood a valve for exhausting the anode gas from the anode section, such as a so-called "purge valve".

[0017] Clock activation is to be understood in the context of the presented invention as an actuation of the valve such that the valve is repeatedly opened and closed, for example regularly, at a predetermined frequency, for example between 0.1 Hz and 50 Hz.

[0018] The presented invention is based on the principle that both the metering valves and the exhaust valves of the presented fuel cell system are clocked, resulting in minimum fuel losses and maximum fuel efficiency of the fuel cell system, which in turn results in minimum fuel concentration in the exhaust gas of the fuel cell system and maximum safety during operation of the fuel cell system.

[0019] Furthermore, minimizing water evaporation losses avoids very dry conditions in the anode section, thereby maximizing membrane conductivity and therefore the service life of the fuel cell system. Correspondingly, the presented invention allows for improved lifespan due to the avoidance of dry conditions and the efficiency gains from high membrane conductivity.

[0020] By activating the discharge valve depending on the activation of the metering valve, it is possible to discharge, for example, a nitrogen phase, i.e., a certain amount of anode gas containing a relatively smaller amount of fuel than the other amount of anode gas, by activating the discharge valve before the amount of fuel dispensed into the anode section through the metering valve approaches the vicinity of the discharge valve.

[0021] Alternatively, the relative air humidity in the anode section can be maximized by activating the discharge valve depending on the activation of the metering valve, for example by discharging the fuel phase, i.e., by discharging a certain amount of anode gas that contains a relatively larger amount of fuel than the other amounts of anode gas.

[0022] By determining the time that has elapsed since actuation of the metering valve, the composition of the gas present at the discharge valve can be inferred and the discharge valve actuated accordingly.

[0023] It may be considered that the computing unit is configured to activate the discharge valve within a time range between a first time point at which the metering valve is activated to meter fuel into the anode section at the anode inlet and a second time point at which the fuel concentration increases at the anode outlet in response to the metering of fuel by the metering valve.

[0024] Activating the discharge valve between a first time point when the metering valve is activated to dispense fuel into the anode section at the anode inlet and a second time point when the fuel concentration at the anode outlet increases in response to the dispensing of fuel by the metering valve minimizes fuel transport by activating the discharge valve, utilizing the gas transit time of the fuel within the anode section to activate the discharge valve to discharge anode gas, which is transiting through the anode section ahead of the gas phase dispensed through the metering valve, from the anode section for the cleaning process.

[0025] It may further be considered that the computing unit is configured to determine the second point in time based on a gas transit time between the anode inlet and the anode outlet to minimize fuel loss due to activation of the exhaust valve.

[0026] The second point in time can be dynamically determined via the gas transit time, since the gas transit time can vary depending on the operating point.

[0027] It may be considered that the calculation unit is configured to determine the second point in time using the length of the distance between the metering valve and the discharge valve and the flow rate of the fuel flowing into the anode section, and is configured to determine the flow rate using a mathematical model of the fuel cell system for a current operating point of the fuel cell system.

[0028] In the case of the presented mathematical model of the fuel cell system, for example, the temperature and pressure are mathematically derived depending on the operating point, but such a mathematical model makes it possible to determine the gas transfer time particularly accurately and therefore to accurately determine the second point in time at which the exhaust valve is, for example, deactivated.

[0029] It may further be considered that the computing unit is configured to determine the second point in time depending on measurements determined by a lambda sensor at the anode outlet and / or depending on measurements determined by a hydrogen concentration sensor in the cathode section of the fuel cell system.

[0030] Because the lambda sensor quantifies the mass flow at the anode outlet, the lambda sensor measurement provides a direct estimate of the gas transit time through the anode section.

[0031] A hydrogen concentration sensor installed in the cathode section of the fuel cell system determines the composition of the gas discharged through the exhaust valve, so that the fuel discharge can be increased or decreased by, for example, adjusting the opening time of the exhaust valve based on the measurement value of the hydrogen concentration sensor.

[0032] It may further be considered that the arithmetic unit includes a memory, in which an allocation diagram is filed that assigns an activation point for activating the exhaust valve to a current operating point of the fuel cell system, and the arithmetic unit is configured to activate the exhaust valve at a time point that is assigned to the current operating point of the fuel cell system.

[0033] The allocation diagram filed in the memory allows the computation load of the computing unit of the proposed fuel cell system to be minimized.

[0034] It may further be considered that the computing unit is configured to activate the metering valve in such a way that the time range in which the discharge valve is activated partially overlaps with the time range in which the metering valve is activated.

[0035] The overlapping actuation of the discharge and metering valves allows for very short gas transfer times or very little nitrogen phase filling.

[0036] It may further be considered that the computing unit is configured to activate the discharge valve in a time range beginning when the fuel concentration at the anode outlet increases in response to activation of the metering valve and then decreases again, in order to minimize water evaporation loss due to activation of the discharge valve.

[0037] By activating the discharge valve in a time range beginning when the fuel concentration at the anode outlet increases in response to activation of the metering valve and then decreases again, the dry fuel phase for the cleaning process dispensed by the metering valve is discharged, thereby maximizing the wet nitrogen phase in the anode section.

[0038] Furthermore, it may be provided that the period for activating the metering valve is different from the period for activating the discharge valve.

[0039] By varying the length of the start-up period, for example, more gas can be discharged from the anode section than is dispensed into the anode section, or less gas can be discharged than is dispensed, for example, only the nitrogen phase flowing in front of the dispensed fuel phase can be discharged.

[0040] Furthermore, it may be provided that the computing unit is configured to activate the discharge valve only when operation requires the discharge of the anode gas.

[0041] To avoid unnecessary discharge of fuel, the discharge valve can be activated only when necessary for the operation of the fuel cell system, but dependent on the activation of the metering valve.

[0042] According to a second aspect, the invention presented relates to an operating method for a fuel cell system, in which the discharge valve of a possible configuration of the presented fuel cell system is clocked depending on the activation of the metering valve of said fuel cell system.

[0043] Further advantages, features and details of the invention will become apparent from the following description, in which several embodiments of the invention are individually described with reference to the drawings, whereby the features set out in the claims and in the following description may each be essential to the invention individually or in any combination. [Brief explanation of the drawings]

[0044] [Figure 1] 1 is a schematic diagram of one possible configuration of the presented fuel cell system. [Figure 2] FIG. 1 illustrates one possible configuration of the presented method. [Figure 3] 10A-10C illustrate other possible configurations of the presented method. DETAILED DESCRIPTION OF THE INVENTION

[0045] 1 illustrates a fuel cell system 100. The fuel cell system 100 includes a fuel cell stack 101, an anode section 103 for supplying fuel to the fuel cell stack 101, a discharge valve 105 for discharging anode gas from the anode section 103, a metering valve 107 for metering fuel into the anode section 103, and a computing unit 109.

[0046] The arithmetic unit 109 is configured to clock the metering valve 107, for example to activate it at a predetermined frequency, and to clock the discharge valve 105, for example to activate it at a predetermined frequency, depending on the activation of the metering valve 107.

[0047] A method of operation 200 is illustrated in Figure 2. A graph 201 has time plotted on the horizontal axis and mass fraction of the substance in the anode gas plotted on the vertical axis.

[0048] The first progression 203 shows the mass fraction of the fuel as measured at the anode inlet.

[0049] A second progression 205 shows the mass fraction of the fuel as measured at the anode outlet.

[0050] A third progression 207 shows the mass fraction of water measured at the anode inlet.

[0051] A fourth progression 209 shows the mass fraction of water measured at the anode outlet.

[0052] A fifth progression 211 shows the nitrogen mass fraction measured at the anode inlet.

[0053] A sixth progression 213 shows the nitrogen mass fraction measured at the anode outlet.

[0054] Bar 215 indicates the activation period for activating the metering valve 107 .

[0055] Bar 217 indicates the activation period during which the drain valve 105 is activated.

[0056] The interval Δt represents the interval between a first time T1 at which the metering valve 107 is activated to meter fuel into the anode section at the anode inlet and a second time T2 at which the fuel concentration at the anode outlet increases in response to the metering of fuel by the metering valve 107.

[0057] Comparing bars 215 and 217, it can be seen that the activation period for activating the discharge valve 105 is extended until the second time T2 in order to minimize the discharge of fuel-containing gases. By deactivating the discharge valve 105 at the turning point of transition 205, the transport of fuel-rich gases is avoided, or so-called "purged" before the fuel dispensed by the metering valve 107 reaches the discharge valve 105.

[0058] Correspondingly, by actuating the discharge valve 105 within the time range of bar 217, the export of water and nitrogen is maximized.

[0059] A method of operation 300 is illustrated in Figure 3. A graph 301 has time plotted on the horizontal axis and mass fraction of the substance in the anode gas plotted on the vertical axis.

[0060] The first progression 303 shows the mass fraction of the fuel as measured at the anode inlet.

[0061] A second progression 305 shows the mass fraction of the fuel as measured at the anode outlet.

[0062] A third progression 307 shows the mass fraction of water measured at the anode inlet.

[0063] A fourth progression 309 shows the mass fraction of water measured at the anode outlet.

[0064] A fifth progression 311 shows the nitrogen mass fraction measured at the anode inlet.

[0065] A sixth progression 313 shows the nitrogen mass fraction measured at the anode outlet.

[0066] Bar 315 indicates the activation period during which the metering valve 107 is activated.

[0067] Bar 317 indicates the activation period during which the exhaust valve 105 is activated.

[0068] By actuating the exhaust valve 105 during the time period in which the transition 305 rises and then falls again at its turning point, beginning after the metering valve 107 is activated, the discharge of water and nitrogen from the anode section is minimized and membrane wetness of the fuel cell system is maximized. [Explanation of symbols]

[0069] 100 Fuel Cell System 101 Fuel Cell Stack 103 Anode Section 105 Discharge valve 107 Dosing valve 109 arithmetic unit

Claims

1. A fuel cell system (100) for converting energy, comprising: The fuel cell system (100) a fuel cell stack (101), an anode section (103) for supplying fuel to said fuel cell stack (101); - a discharge valve (105) for discharging the anode gas from said anode section (103); a metering valve (107) for metering fuel into said anode section (103); a calculation unit (109), Including, the computing unit (109) is configured to clock-activate the metering valve (107); The computing unit (109) is further configured to clock actuation of the discharge valve (105) depending on actuation of the metering valve (107). A fuel cell system (100).

2. 2. The fuel cell system of claim 1, wherein the computing unit is configured to activate the exhaust valve within a time range between a first time point at which the metering valve is activated to meter fuel into the anode section at the anode inlet and a second time point at which fuel concentration increases at the anode outlet in response to the metering of fuel by the metering valve.

3. 3. The fuel cell system (100) of claim 2, wherein the computing unit (109) is configured to determine the second point in time based on gas transit time between the anode inlet and the anode outlet to minimize fuel loss due to activation of the exhaust valve (105).

4. 4. The fuel cell system (100) of claim 2 or 3, wherein the calculation unit (109) is configured to determine the second point in time using the length of the distance between the metering valve (107) and the discharge valve (105) and the flow rate of the fuel flowing into the anode section (103), and to determine the flow rate using a mathematical model of the fuel cell system (100) for a current operating point of the fuel cell system (100).

5. 5. The fuel cell system (100) of claim 2, wherein the computing unit (109) is configured to determine the second point in time depending on measurements determined by a lambda sensor at the anode outlet and / or depending on measurements determined by a hydrogen concentration sensor in the cathode section of the fuel cell system (100).

6. The computing unit (109) includes a memory, and an allocation diagram is stored in the memory, which allocates a trigger point for activating the exhaust valve (105) to a current operating point of the fuel cell system (100); and the computing unit (109) is configured to activate the exhaust valve (105) at a time point assigned to the current operating point of the fuel cell system (100); A fuel cell system (100) according to any one of claims 1 to 5, characterized in that

7. 7. The fuel cell system (100) according to claim 1, wherein the computing unit (109) is configured to activate the metering valve (107) so that the time range in which the discharge valve (105) is activated partially overlaps with the time range in which the metering valve (107) is activated.

8. 8. The fuel cell system (100) of claim 1, wherein the computing unit (109) is configured to activate the exhaust valve (105) in a time range beginning when the fuel concentration at the anode outlet increases in response to activation of the metering valve (107) and then decreases again, in order to minimize water evaporation loss due to activation of the exhaust valve (105).

9. 9. The fuel cell system (100) according to claim 1, wherein the period during which the metering valve (107) is activated is different from the period during which the discharge valve (105) is activated.

10. 10. The fuel cell system (100) according to claim 1, wherein the computing unit (109) is configured to activate the exhaust valve (105) only when operation requires the exhaust of anode gas.

11. 11. A method (200, 300) for operating a fuel cell system (100) according to any one of claims 1 to 10, in which a discharge valve (105) of the fuel cell system (100) is clock-activated depending on activation of a metering valve (107) of the fuel cell system (100).

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