WO2022271830A1

WO2022271830A1 - Fuel cell systems and methods for integrating and sizing a recirculation blower and an ejector

Info

Publication number: WO2022271830A1
Application number: PCT/US2022/034530
Authority: WO
Inventors: Richard J. Ancimer; Eero Teene; Paolo Forte; Sumit TRIPATHI
Original assignee: Cummins Inc.; Hydrogenics Corporation
Priority date: 2021-06-25
Filing date: 2022-06-22
Publication date: 2022-12-29

Abstract

The present disclosure generally relates to fuel cell systems and methods for sizing and/or integrating a recirculation blower with a venturi or an ejector in a fuel cell or fuel cell stack.

Description

FUEL CELL SYSTEMS AND METHODS FOR INTEGRATING AND SIZING A RECIRCULATION BLOWER AND AN EJECTOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This nonprovisional application claims the benefit and priority, under 35 U.S.C. § 119(e) and any other applicable laws or statutes, to U.S. Provisional Patent Application Serial No. 63/215,083 filed on June 25, 2021, the entire disclosure of which is hereby expressly incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to fuel cell systems and methods for sizing and/or integrating a recirculation blower with a venturi or an ejector.

BACKGROUND

[0003] Vehicles and/or powertrains use fuel cells, fuel cell stacks, and/or fuel cell systems for their power needs. A minimum excess fuel target for a fuel cell system may be specified as a minimum level of an excess fuel target required by the fuel cell or fuel cell stack based on the operating conditions of the fuel cell, stack or system. A fuel cell or fuel cell stack may have an excess fuel level higher than the minimum excess fuel target, but achieving that higher level may result in a high parasitic load on the fuel cell or fuel cell stack. For example, the excess fuel level higher than the minimum excess fuel target may be achieved by maintaining high fuel flow rates at the anode, which may lead to a pressure loss in the fuel cell, stack, or system.

[0004] A blower and/or a pump (e.g., a recirculation pump) may function at a capacity proportional to the pressure loss in the fuel cell or fuel cell stack. The blower and/or the pump may also function at a capacity proportional to a volumetric flow rate through the blower and/or the pump. A blower and/or a pump may use additional power to compensate for the pressure loss. However, use of additional power by the blower and/or the pump may result in a high parasitic load on the fuel cell, fuel cell stack and/or fuel cell system. The present disclosure related to systems and methods for operating and/or integrating a fuel cell system to enable the blower or pump to boost ejector performance, optimally sizing the blower or pump based on ejector performance and/or system transient state, and optimally using one or more by-pass valve(s) based on system requirements. SUMMARY

[0005] Embodiments of the present disclosure are included to meet these and other needs.

[0006] In one aspect of the present disclosure, described herein, a system for monitoring or controlling operation of a fuel cell system includes a first fuel entering an ejector, a second fuel entering a blower or the ejector, and a controller that communicates with the blower or the ejector to monitor or control flow of the first fuel or the second fuel in the fuel cell system. The ejector has a primary inlet pressure and a secondary inlet pressure.

[0007] In some embodiments, the fuel cell system may operate in a system operating state including a steady state or a transient state. The fuel cell system may include a target excess fuel ratio or an anode gas inlet humidity. In some embodiments, the blower may operate in a blower operating state including idle state, ejector support state, or prime state. The controller may determine the blower operating state. In some embodiments, a by-pass valve may be positioned across the blower to allow the second fuel to flow around the blower. In some embodiments, the controller may communicate with the by-pass valve positioned across the blower. In some embodiments, the controller may determine a pressure drop at the system operating state, a pressure lift that can be delivered by the ejector, and may determine if the pressure drop is greater or lesser than the pressure lift that can be delivered by the ejector.

[0008] In some embodiments, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the blower may operate in the idle state. In some embodiments, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the by pass valve positioned across the blower may be opened. In some embodiments, if the pressure drop is more than the pressure lift that can be delivered by the ejector, the blower may operate in the ejector support state.

[0009] In some embodiments, the controller may determine a blower operating state based on a target entrainment ratio of the fuel cell system, efficiency of the blower, choked or unchoked condition of the ejector, or transient or steady state of the fuel cell system.

[0010] In a second aspect of the present disclosure, a method for monitoring or controlling operation of a fuel cell system includes the steps of flowing a first fuel into an ejector, flowing a second fuel into a blower or the ejector, communicating with the blower or the ejector through a controller, and monitoring or controlling flow of the first fuel or flow of the second fuel in the fuel cell system. The ejector has a primary inlet pressure and a secondary inlet pressure.

[0011] In some embodiments, the method may include operating the fuel cell system in a system operating state including a steady state or a transient state. The fuel cell system may include a target excess fuel ratio or an anode gas inlet humidity. In some embodiments, the method may further include the blower operating in a blower operating state including idle state, ejector support state, or prime state. In some embodiments, the fuel cell system may include a by-pass valve positioned across the blower to allow the second fuel to flow around the blower. In some embodiments, the method may include the controller communicating with the by-pass valve positioned across blower. In some embodiments, the method may further include the controller determining the blower operating state. In some embodiments, the method may further include the controller determining a pressure drop at the system operating state, a pressure lift that can be delivered by the ejector, and may determine if the pressure drop is greater or lesser than the pressure lift that can be delivered by the ejector.

[0012] In some embodiments, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the method may include the controller operating the blower in the idle state. In some embodiments, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the method may further include opening the by-pass valve positioned across the blower. In some embodiments, if the pressure drop is more than the pressure lift that can be delivered by the ejector, the method may further include operating the blower in the ejector support state.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout the drawings, wherein:

[0014] FIG. 1A is an illustration of a fuel cell system including one or more fuel cell stacks connected to a balance of plant. [0015] FIG. IB is an illustration showing a fuel cell system having fuel cell modules, each fuel cell module having fuel cell stacks and/or fuel cells.

[0016] FIG. 1C is an illustration of components of a fuel cell in the fuel cell stack.

[0017] FIG. 2 is a graph showing the operating curves of as system comprising a fuel cell or fuel cell stack.

[0018] FIG. 3is a schematic showing a mechanical regulator used along with a venturi or an ejector in a fuel cell system.

[0019] FIG. 4 is a schematic showing a proportional control valve used along with a venturi or an ejector in a fuel cell system.

[0020] FIG. 5A is a graph showing the operating curves of as system comprising a venturi or an ejector under choked conditions.

[0021] FIG. 5B is a graph showing the operating curves of as system comprising a venturi or an ejector under choked and unchoked conditions.

[0022] FIG. 6 a graph showing the operating curves of as system comprising a blower in different operating states when the system is in a transient state.

[0023] FIG. 7 is a schematic showing by-pass valves across a blower and/or venturi or an ejector in a fuel cell system.

[0024] FIG. 8 is a block diagram showing one embodiment of a controller in communication with various components of a fuel cell stack system for monitoring and controlling the various components of the fuel cell stack.

DETAILED DESCRIPTION

[0025] The present disclosure relates to fuel cell systems and methods for sizing and/or integrating a recirculation blower and/or pump with an ejector in a fuel cell system. The present disclosure describes different system operating states such as idle state, boosted by a blower in an ejector support state, prime state, and load shedding state. The present disclosure also relates to methods of operating and/or integrating a system to enable blower to boost ejector performance, optimally sizing the blower based on ejector performance and/or system transient state, and optimally using one or more by-pass valve(s) around the blower based on the fuel cell system requirement.

[0026] As shown in FIG. 1A, fuel cell systems 10 often include one or more fuel cell stacks 12 or fuel cell modules 14 connected to a balance of plant (BOP) 16, including various components, to create, generate, and/or distribute electrical power for meet modern day industrial and commercial needs in an environmentally friendly way. As shown in FIGS. IB and 1C, fuel cell systems 10 may include fuel cell stacks 12 comprising a plurality of individual fuel cells 20. Each fuel cell stack 12 may house a plurality of fuel cells 20 connected together in series and/or in parallel. The fuel cell system 10 may include one or more fuel cell modules 14 as shown in FIGS. 1A and IB. Each fuel cell module 14 may include a plurality of fuel cell stacks 12 and/or a plurality of fuel cells 20.

[0027] The fuel cells 20 in the fuel cell stacks 12 may be stacked together to multiply and increase the voltage output of a single fuel cell stack 12. The number of fuel cell stacks 12 in a fuel cell system 10 can vary depending on the amount of power required to operate the fuel cell system 10 and meet the power need of any load. The number of fuel cells 20 in a fuel cell stack 12 can vary depending on the amount of power required to operate the fuel cell system 10 including the fuel cell stacks 12.

[0028] The number of fuel cells 20 in each fuel cell stack 12 or fuel cell system 10 can be any number. For example, the number of fuel cells 20 in each fuel cell stack 12 may range from about 100 fuel cells to about 1000 fuel cells, including any specific number or range of number of fuel cells 20 comprised therein (e.g., about 200 to about 800). In an embodiment, the fuel cell system 10 may include about 20 to about 1000 fuel cells stacks 12, including any specific number or range of number of fuel cell stacks 12 comprised therein (e.g., about 200 to about 800). The fuel cells 20 in the fuel cell stacks 12 within the fuel cell module 14 may be oriented in any direction to optimize the operational efficiency and functionality of the fuel cell system 10.

[0029] The fuel cells 20 in the fuel cell stacks 12 may be any type of fuel cell 20. The fuel cell 20 may be a polymer electrolyte membrane or proton exchange membrane (PEM) fuel cell, an anion exchange membrane fuel cell (AEMFC), an alkaline fuel cell (AFC), a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), or a solid oxide fuel cell (SOFC). In an exemplary embodiment, the fuel cells 20 may be a polymer electrolyte membrane or proton exchange membrane (PEM) fuel cell or a solid oxide fuel cell (SOFC).

[0030] In an embodiment shown in FIG. 1C, the fuel cell stack 12 includes a plurality of proton exchange membrane (PEM) fuel cells 20. Each fuel cell 20 includes a single membrane electrode assembly (MEA) 22 and a gas diffusion layer (GDL) 24, 26 on either or both sides of the membrane electrode assembly (MEA) 22 (see FIG. 1C). The fuel cell 20 further includes a bipolar plate (BPP) 28, 30 on the external side of each gas diffusion layers (GDL) 24, 26.

The above mentioned components, 22, 24, 26, 30 comprise a single repeating unit 50.

[0031] The bipolar plates (BPP) 28, 30 are responsible for the transport of reactants, such as fuel 32 (e.g., hydrogen) or oxidant 34 (e.g., oxygen, air), and cooling fluid 36 (e.g., coolant and/or water) in a fuel cell 20. The bipolar plate (BPP) 28, 30 can uniformly distribute reactants 32, 34 to an active area 40 of each fuel cell 20 through oxidant flow fields 42 and/or fuel flow fields 44. The active area 40, where the electrochemical reactions occur to generate electrical power produced by the fuel cell 20, is centered within the gas diffusion layer (GDL) 24, 26 and the bipolar plate (BPP) 28, 30 at the membrane electrode assembly (MEA) 22. The bipolar plate (BPP) 28, 30 are compressed together to isolate and/or seal one or more reactants 32 within their respective pathways, channels, and/or flow fields 42, 44 to maintain electrical conductivity, which is required for robust during fuel cell 20 operation.

[0032] The fuel cell system 10 described herein, may be used in stationary and/or immovable power system, such as industrial applications and power generation plants. The fuel cell system 10 may also be implemented in conjunction with electrolyzers 18 and/or other electrolysis system 18. In one embodiment, the fuel cell system 10 is connected and/or attached in series or parallel to an electrolysis system 18, such as one or more electrolyzers 18 in the BOP 16. In one embodiment, the fuel cell system 10 is not connected and/or attached in series or parallel to an electrolysis system 18, such as one or more electrolyzers 18 in the BOP 16.

[0033] The present fuel cell system 10 may also be comprised in mobile applications.

In an exemplary embodiment, the fuel cell system 10 is in a vehicle and/or a powertrain 100. A vehicle 100 comprising the present fuel cell system 10 may be an automobile, a pass car, a bus, a truck, a train, a locomotive, an aircraft, a light duty vehicle, a medium duty vehicle, or a heavy duty vehicle.

[0034] The vehicle and/or a powertrain 100 may be used on roadways, highways, railways, airways, and/or waterways. The vehicle 100 may be used in applications including but not limited to off highway transit, bobtails, and/or mining equipment. For example, an exemplary embodiment of mining equipment vehicle 100 is a mining truck or a mine haul truck.

[0035] One embodiment of the operating characteristics of a fuel cell system 10 comprising a fuel cell 20 or fuel cell stack 12 is illustrated in graph 101 in FIG. 2.

Operating pressures and the associated operating temperatures are shown as a function of current density 108. The fuel cell 20 or fuel cell stack 12 may be required to operate within a pressure range known as anode inlet manifold pressure (PAIM) measured at the anode inlet manifold 404 as shown in FIGS. 3 and 4.

[0036] A highest anode inlet manifold pressure (PAHVLHI) of a fuel cell 20 or fuel cell stack 12 is denoted by 110. A lowest anode inlet manifold pressure (PAHVLHI) of a fuel cell 20 or fuel cell stack 12 is denoted by 120. The range 160 between the highest anode inlet manifold pressure (PAHVLHI) HO and the lowest anode inlet manifold pressure (PAEVLLO) 120 indicates a target anode inlet manifold pressure range or operating pressure. A target temperature of the fuel cell system 10 may range from a low fuel supply operating temperature (TCV_LO) 102 to a high fuel supply operating temperature (Tcvjn) 104.

[0037] It is critical to operate the fuel cell 20 or fuel cell stack 12 at a pressure that ranges from about or approximately the highest anode inlet manifold pressure (PAHVLHI) HO to about or approximately the lowest anode inlet manifold pressure (PAIM_LO) 120 when the fuel cell 20 or fuel cell stack 12 is operating above a critical current density (i LO_CR) 130.

In some embodiments, the critical current density (i LO_CR) 130 may be at about 0.7 A/cm². In other embodiments, the critical current density (i LO _CR) 130 may be at about 0.6 A/cm². In some further embodiments, the critical current density (i LO_CR) 130 may be higher or lower than 0.7 A/cm², such as ranging from about 0.5 A/cm² to about 0.9 A/cm², including every current density 108 or range of current density 108 comprised therein.

[0038] The fuel cell 20 or fuel cell stack 12 may operate at a high current density 138, which may be higher than the critical current density (i LO_CR) 130. The high current density 138 may range from about 1.3 A/cm² to about 2.0 A/cm², or about 1.3 A/cm² to about 1.6 A/cm², or about 1.0 A/cm² to about 1.6 A/cm², including every current density 108 or range of current density 108 comprised therein.

[0039] In some embodiments, operating the fuel cell 20 or fuel cell stack 12 at such high current density 138 (e.g., at about 1.6 A/cm²) will result in operating the fuel cell 20 or fuel cell stack 12 at pressures and temperatures different from optimal target operating pressures and operating temperatures. Operating the fuel cell 20 or fuel cell stack 12 at pressures and temperatures different from the optimal target operating pressures and operating temperatures may lower the efficiency of the fuel cell 20 or fuel cell stack 12. Such operation may also result in damage to the fuel cell 20 or fuel cell stack 12 because of MEA 22 degradation (e.g., due to starvation, flooding and/or relative humidity effects). [0040] In some embodiments, there may be more flexibility in the fuel cell 20 or fuel cell stack 12 operating pressure and operating temperature when the fuel cell 20 or fuel cell stack 12 is operating below the critical current density (i LO_CR) 130. The present operating system comprising the fuel cell or fuel cell stack can operate at a minimum current density (IMIN) 132 and/or a maximum current density (IMAX) 134.

[0041] In one embodiment, the fuel cell system 10 comprising the fuel cell 20 or fuel cell stack 12 may operate in a functional range that may be different than that indicated by the curve 160 in FIG. 2. The fuel cell system 10 may operate at higher pressures (e.g., the highest anode inlet manifold pressure (PAHVLHI) HO) or at a current density 108 as low as the critical current density (i LO_CR) 130. For example, the fuel cell system 10 may extend steady state operation at about 2.5 bara down to about the critical current density (i LO_CR) 130. Pressure measurements in bara refer to the absolute pressure in bar.

[0042] FIG. 3 illustrates one embodiment of a fuel cell system 10 comprising a fuel cell stack 12, a mechanical regulator 250, a recirculation pump or blower 220 in series or in parallel to the fuel cell stack 12, an exhaust valve 280, a shut off valve 270, a pressure transfer valve 290, one or more pressure transducers 240/260, and a venturi or an ejector 230. In some embodiments, the fuel cell system 10 may comprise one or more fuel cell stacks 12 and/or one or more fuel cells 20. In other embodiments, there may also be one or multiple valves, sensors, compressors, regulators, blowers, injectors, ejectors, and/or other devices in series or in parallel with the fuel cell stack 12.

[0043] In one embodiment of the fuel cell system 10, an anode inlet stream 222, flows through an anode 204 end of the fuel cell stack 12. Typically, the anode inlet stream 222 may be a mixture of fresh fuel (e.g., Fb) and anode exhaust (e.g., Fb fuel and/or water). Conversely, oxidant 206 (e.g., air, oxygen, or humidified air) may flow through the cathode 208 end of the fuel cell stack 12.

[0044] Excess fuel may be provided at the anode inlet 212 to avoid fuel starvation towards the anode outlet 214. Water content of the anode inlet stream 222 or the relative humidity of the anode inlet stream 222 may impact the performance and health of the fuel cell stack 12. For example, low inlet humidity may lead to a drier membrane electrode assembly (MEA) 22, resulting in reduced performance.

[0045] Low inlet humidity may also induce stresses that can lead to permanent damage to the membrane electrode assembly (MEA) 22. High humidity levels may lead to flooding within the fuel cell 20 or fuel cell stack 12, which can induce local starvation and/or other effects that may reduce fuel cell performance and/or damage the membrane electrode assembly (MEA) 22. In some embodiments, there may be an optimal inlet relative humidity range in which fuel cell performance is improved and membrane electrode assembly (MEA) 22 degradation rate is minimized. For example, the fuel cell 20 or fuel cell stack 12 may achieve optimal performance when the relative humidity level of the anode inlet stream 222 is in the range of about 30% to about 35%, including any percentage or range comprised therein.

[0046] The source of the excess fuel and water content in a fuel cell 20 may be from a secondary or recirculated flow 226. Composition of the secondary flow 226 in the fuel cell system 10 is dependent on its composition of anode outlet stream 225. In some embodiments, the anode outlet stream 225 may be saturated with water at a given anode gas outlet temperature and pressure. Thus, the variation in the composition of the secondary flow 226 may be taken into account when determining a required secondary flow 226 to meet the excess fuel or relative humidity targets of the anode inlet stream 222.

[0047] The required flow rate of the secondary flow 226 can be determined by either the need for excess fuel, or by the need for increased water content, whichever calls for a higher flow of the secondary flow 226. The required flow of the secondary flow 226 can be expressed as the target entrainment ratio (ER). The entrainment ratio (ER) is defined as the ratio of mass flow rate of the low pressure stream (e.g., the secondary mass flow rate) to the mass flow rate of the high pressure stream (e.g., the primary mass flow rate). Alternatively, a target effective excess fuel ratio or a minimum required fuel ratio may account for either the need for excess fuel, or for the increased water content of the anode inlet stream 222.

[0048] Excess fuel ratio (l) or the anode stoichiometry ratio is defined as the ratio of anode inlet stream 222 flow rate to the fuel consumed in the fuel cell 20 or fuel cell stack 12. Excess fuel ratio (l) may be used to represent the required composition of the secondary flow 226 to meet the required anode inlet stream 222 characteristics. The required anode inlet stream 222 characteristics may be the more stringent of excess fuel ratio or relative humidity requirements of the fuel cell system 10. Minimum required excess fuel ratio (l) 140 as a function of current density 108 is shown in FIG. 2. In some embodiments, the fuel cell system 10 requires or may require a fuel amount at or above the minimum required excess fuel ratio (l) 140.

[0049] In other embodiments, the fuel cell system 10 may require a target water or humidity level, which may affect the excess fuel ratio (l) 140. The excess fuel ratio (l) 140 may be flat across the fuel cell system 10 operating range except at low current densities 108, such as at a current density 108 at or below an excess fuel ratio current density threshold (i J,_THV) 150. Alternatively, or additionally, the excess fuel ratio (l) 140 may change with a change in current density 108.

[0050] In some embodiments, the excess fuel ratio (l) 140 above the excess fuel ratio current density threshold (i

TIIV ) 150 may be in the range from about 1.3 to about 1.9, including any ratio comprised therein. In one preferable embodiment, the excess fuel ratio (l) 140 above the excess fuel ratio current density threshold (i J,_THV) 150 may be in the range of about 1.4 to about 1.6, including any ratio or range of ratio comprised therein.

[0051] In some embodiments, the excess fuel ratio current density threshold (i J,_THV) 150 of the fuel cell system 10 may be at or about 0.2 A/cm². In other embodiments, the excess fuel ratio current density threshold (i J,_THV) 150 may be at a different current density 108. For example, the excess fuel ratio current density threshold (i TIIV) 150 may be at a current density 108 in the range of about 0.05 A/cm² to about 0.4 A/cm², including any current density 108 or range of current density 108 comprised therein. In one preferable embodiment, the excess fuel ratio current density threshold (i J,_THV) 150 may be about 0.1 A/cm² or about 0.2 A/cm². The excess fuel ratio current density threshold (i J,_THV) 150 may depend on the operating conditions of the fuel cell 20 or fuel cell stack 12.

[0052] In one embodiment, if the fuel cell 20 or fuel cell stack 12 is operating below the excess fuel ratio current density threshold (i J,_THV) 150, a minimum volumetric flow rate may be maintained through the anode 204 to flush out any liquid water that might form in the fuel cell 20 or fuel cell stack 12. At low flow rates (e.g., below about 0.2 A/cm² or below about 0.1 A/cm²), there may be flooding in the fuel cell 20 or fuel cell stack 12. If the minimum volumetric flow rate is below the excess fuel ratio current density threshold (i J,_THV) 150, the rate of fuel cell 20 or fuel cell stack 12 degradation may increase and the performance of the fuel cell or fuel cell stack may be adversely affected.

[0053] A venturi or an ejector 230 may be used in the fuel cell system 10. The venturi or ejector 230 may be sized, such that the fuel cell system 10 may not require the assistance of a recirculation pump 220, such as a blower, at certain current densities 108. Absence of usage of the recirculation pump or blower 220 may result in a decrease in parasitic load, as shown by the curves 170 and 180 of FIG. 2.

[0054] The curve 170 shows a fraction of flow that is delivered by the recirculation pump or blower 220 in the absence of a venturi or ejector 230. The curve 180 shows the corresponding parasitic load. The parasitic load may increase with an increase in current density, as shown by the curve 180. This is because recirculation pump or blower 220 may function at a capacity proportional to pressure loss in the fuel cell 20 or fuel cell stack 12 and/or proportional to the required flow rate of the secondary flow 226 in the fuel cell 20 or fuel cell stack 12.

[0055] The fuel cell 20 or fuel cell stack 12 may be initially operating at high current density 138 and/or at high operating temperatures and pressures such that the fuel cell load under this initial operating condition is high. The fuel cell load is defined as:

Load = stack power = current x fuel cell or fuel cell stack voltage = current density x fuel cell area x fuel cell or fuel cell stack voltage.

The fuel cell 20 or fuel cell stack 12 may be in a load shedding state when the load demand for power is rapidly reduced or shed requiring the fuel cell 20 or fuel cell stack 12 to reduce the current delivered.

[0056] During transient operations in the fuel cell 20 or fuel cell stack 12, the operating pressure in the fuel cell 20 or fuel cell stack 12 may change based on the changes in the fuel cell 20 or fuel cell stack 12 operating temperature. For example, during load shedding, the fuel cell system 10 may have an operating pressure that corresponds to a transient operating pressure (P AM TRS ) that may be greater than its steady state operating pressure (P AIM SS ). In some embodiments, the transient operating pressure (P AIM_TRS) may equal the highest anode inlet manifold pressure (PAHVLHI) HO even at low current densities 108. During load acceptance, the rate of increase in current density 108 is limited, and the steady state operating pressure (P AIM ss) may equal the anode inlet manifold pressure (PAIM).

[0057] In one embodiment, the operating pressure of the fuel cell 20 or fuel cell stack 12 may optimize the balance between enabling efficient fuel cell 20 or fuel cell stack 12 operation and the parasitic load required to operate at the chosen operating pressure (e.g., the parasitic load of an air compressor, a blower, and/or a pump). In some embodiments, the operating temperature, operating pressure, and/or excess air ratio 140 may maintain a target relative humidity (RH) for the fuel cell 20 or fuel cell stack 12 operation. The operating temperature, operating pressure, and/or excess air ratio 140 may be determined by targeting a specific value for the relative humidity (RH) at the cathode 208.

[0058] The excess air ratio is defined similarly to excess fuel ratio 140, but refers to the cathode 208 side flow (i.e., excess Chin the air). The combination of excess air ratio, pressure and temperature are used together to control humidity on the cathode 208 side, which in turn impacts water content on the anode 204 (¾) side. In one embodiment, temperature, pressure, and excess air ratio that vary with current density may be used to control humidity on the cathode 208 side. In some embodiments, excess air ratio may be about 2.0. In other embodiments, excess air ratio may be in the range of about 1.7 to about 2.1, including any ratio or range of ratio comprised therein. In some other embodiments, excess air ratio may be in the range of about 1.8 to about 1.9, including any ratio or range of ratio comprised therein, under pressurized operation. Excess air ratio may increase to below an air threshold current to keep volumetric flow rate high enough to prevent flooding in the fuel cell 20 or fuel cell stack 12 on the cathode 208 side.

[0059] The target relative humidity (RH) may be maintained by using a humidification device in combination with the operating pressure and operating temperature. For example, a humidification device may be used on the cathode 208 side of the fuel cell 20 or fuel cell stack 12. If the target relative humidity (RH) and the target operating pressure of the fuel cell 20 or fuel cell stack 12 are specified, the target temperature for the fuel cell 20 or fuel cell stack 12 operation may be determined.

[0060] The mechanical regulator 250 is a control valve 254 that may be used to control the flow of fresh fuel 202 also referred to as primary flow, primary mass flow, primary fuel, or motive flow to the anode 204. Pressure differential between the gas streams (e.g. anode inlet stream 222 and air 206) at the anode 204 and the cathode 208 may provide an input signal 256 to a controller 252 in the mechanical regulator 250.

[0061] The controller 252 of the mechanical regulator 250 may determine the flow of the anode inlet stream 222 through an anode inlet 212 at the anode 204. The control valve 254 may be a proportional control valve, or an injector. In other embodiments, the control valve 256 may comprise an inner valve 258, coil 255, or solenoid 257 that controls the opening or closing of the control valve 254. The input signal 256 from the anode 204 and/or cathode 208 of the fuel cell 20 or fuel cell stack 12 may be a physical signal 256 or a virtual (e.g., an electronic) signal 256. The signal may be any type of communicative or computer signal 256 known in the art.

[0062] Flow rate of the primary flow 202, or a primary flow rate, may be controlled to match the fuel consumption in the fuel cell stack 12 based on the operating pressure (e.g., anode pressure). In some embodiments, the pressure in the anode 204 may stabilize when fuel consumption matches the fresh fuel feed at the anode 204 assuming that all other parameters are equal. Since the functioning of the mechanical regulator 250 is based on the pressure differential between the anode 204 and cathode 208, a target pressure differential needs to be maintained when using the mechanical regulator 250. In some embodiments, pressure at the cathode 208 is controlled and/or maintained at a target level via cathode side controls 282.

[0063] A mechanically regulated approach, such as by employing actuators 282, may use pressure signals 281 from a cathode/air inlet 216 to control mass flow and maintain an appropriate pressure on the cathode 208 side of the fuel cell stack 12. In some embodiments, pressure signals 218 from cathode 208 side are inputs to the mechanical regulator 250. In some embodiments, the anode 204 side mass flow and anode 204 side pressure may be controlled by using the pressure signals 281 from cathode 208 side and measuring one or more anode 204 side conditions.

[0064] The pressure signals 281 from cathode 208 side may change the position of an inner valve 258 in the mechanical regulator 250 to control mass flow through the mechanical regulator 250 and maintain the target pressure differential between the anode 204 and the cathode 208. The input signal 256 that acts on the mechanical regulator 250 is effectively a pressure differential that acts on a diaphragm 257 or other parts of the mechanical regulator 250. No other direct measurement of the pressure differential may be undertaken. A single point pressure at the anode 204 may be calculated to be the cathode 208 side pressure plus the pressure differential between the gas streams (e.g., 222) at the anode 204 and the gas streams (e.g., 206) at the cathode 208. Single point pressure may be absolute pressure or gauge pressure.

[0065] The venturi or ejector 230 may draw the secondary flow 226, also referred to as secondary mass flow, entrainment flow, or recirculation flow, using a flow pressure across an anode gas recirculation (AGR) loop 224. As discussed later, the venturi or ejector 230 may take advantage of the available excess enthalpy from the higher pressure primary flow to draw in the secondary flow 226, working against the pressure losses through the AGR loop 224. The anode gas recirculation loop 224 may include the venturi or ejector 230, the fuel cell stack 12, and a secondary inlet 232, such as one comprised in a suction chamber 620 in the venturi or ejector 230, and/or other piping, valves, channels, manifolds associated with the venturi or ejector 230 and/or fuel cell stack 12. The recirculation pump or blower 220 may increase or decrease the differential pressure across the AGR loop 224.

[0066] The fuel cell system 10 may require a target water or humidity level, which may drive the flow of saturated secondary flow 226. The saturated secondary flow 226 may then drive the primary flow 202, such that the target excess fuel ratio (l) 140 may be dependant on the target water or humidity level.

[0067] In one embodiment, the recirculation pump or blower 220 may be used to achieve the excess fuel ratio. The recirculation pump or blower 220 may operate across the entire operating range (current density) of the fuel cell stack 12. The parasitic load of the recirculation pump or blower 220 may be substantial. In one embodiment, a large recirculation pump or blower 220 may be required to provide the power to achieve the target excess fuel ratio (l) 140. In some embodiments the use of the recirculation pump or blower 220 may be inefficient and expensive. The operating characteristics of a recirculation pump or blower 220 may be distinct from the operating conditions of the venturi or ejector 230.

[0068] The pressure lift capability of the recirculation pump or blower 220 (DR BLWR) is a function of the flow through the recirculation pump or blower 220 (Q), the blower speed (N), and the density of the flow composition (p). The pressure lift of the recirculation pump or blower 220 (DR BLWR) may be limited by power draw limits and/or speed limit of the fuel cell system 10. When the recirculation pump or blower 220 is not spinning or is operating under other fuel cell system 10 stall conditions, the recirculation pump or blower 220 may act as a restriction in the AGR loop 224.

DR BLWR = ./(Q, N, p) (1)

[0069] As illustrated in the operating fuel cell system 11 shown in FIG. 4, a proportional control valve 310 may be used instead of a mechanical regulator 250. A proportional control valve 310 is electronically controlled and may provide more flexibility in controlling single point pressure at the anode 204 than the mechanical regulator 250.

The proportional control valve 310 may be used to control the primary flow in the fuel cell system 11. In other embodiments, an injector (not shown) may be used instead of a proportional control valve 310.

[0070] The proportional control valve 310 may beneficially allow for active management of the differential pressure, may avoid droop issues, and/or provide flexibility in operating the fuel cell stack 12 under different operating conditions. Illustrative operating conditions may include, but are not limited to operating current density, operating pressure, operating temperature, operating relative humidity, fuel supply pressure, fuel supply temperature, required secondary flow, entrainment ratio, parasitic load limitations, power needs, pressure loses in the AGR loop 224, venturi or ejector 230 performance and/or efficiency, recirculation pump or blower 220 performance and/or efficiency, fuel density, purge flow, and choked or unchoked (e.g., not choked) flow conditions.

[0071] The turn down ratio of the fuel cell system 10/11 is defined as the ratio of the maximum capacity of the venturi or ejector 230 to the minimum capacity of the venturi or ejector 230. The venturi or ejector 230 may draw the recirculation flow 226 using a primary flow exergy. The turn down ratio characterizes the range over which the venturi or ejector 230 can deliver the required excess fuel ratio (l) 140 to the fuel cell stack 12. The fuel cell system 10/11 may be designed to maximize the venturi or ejector 230 turn down ratio. Consequently, maximizing the turn down ratio of the venturi or ejector 230 also works to minimize the size and parasitic load associated with the recirculation pump or blower 220. In some embodiments, the venturi or ejector 230 may be required to operate and/or perform robustly to deliver the required primary flow 202 at the required excess fuel ratio (l) 140.

[0072] In one embodiment, a fuel supply system 80 may supply fuel at a fuel supply pressure (Pcv) and a fuel supply temperature (Tcv). The primary flow 202 may pass through the control valve 256 and enter the venturi or ejector 230 through a primary nozzle 236 at a primary nozzle inlet pressure (Po) and a primary inlet temperature (To). The secondary flow 226 may enter the venturi or ejector 230 through a secondary inlet or entrance 232 in a suction chamber 620 at a secondary inlet pressure (Ps) and a secondary inlet temperature (Ts).

[0073] In some embodiments, the sizing pressure (P _CV_MIN) may be the minimum inlet pressure at a control valve such as the proportional control valve 310 or mechanical regulator 250 or injector. In other embodiments, fuel sizing pressure (P CV_MIN) may be the pressure at the inlet of a control valve under empty pressure conditions (PEMPTY).

[0074] The venturi or ejector 230 may have exergy available in primary flow to induce the anode gas recirculated flow as the secondary flow 226 in the venturi or ejector 230.

The stack pressure (APSTACK) is the pressure loss through the AGR loop 224. The secondary flow 226 may be lifted against the stack pressure (APSTACK).

[0075] The pressure lift (APLIFT) is the pressure required to overcome the pressure loses in the AGR loop 224 (APSTACK). In some embodiments, the pressure lift (APLIFT) may be dominated by the pressure losses through the fuel cell stack 12 or any other component of the AGR loop 224. In some embodiments, pressure losses may be proportional to volumetric flow rate through one or more manifolds and/or channels in the AGR loop 224. In other embodiments, the volumetric flow 222 at anode inlet 212 may include a mixture of fresh fuel (e.g., ¾) as the primary flow 202 and the recirculation flow 226.

[0076] The secondary inlet pressure (Ps) may depend on the anode inlet manifold pressure (PAIM) of the fuel cell or fuel cell stack 12 and the pressure loses in the AGR loop 224 (APSTACK) or the required pressure lift (APLIFT).

Ps = PAIM - APLIFT (2)

[0077] The amount of secondary flow 226 that can be entrained is dictated by the boundary conditions of the fuel cell system 10/11 and the efficiency of the venturi or ejector 230. In some embodiments, the boundary conditions may be the primary nozzle inlet pressure (Po), the secondary inlet pressure (Ps), the anode inlet manifold pressure (PAIM) of the fuel cell or fuel cell stack 12, and/or secondary flow 226 composition. In some embodiments, the secondary flow 226 from the anode outlet 214 to the venturi or ejector secondary inlet 232 is an adiabatic process. The primary inlet temperature (To) and the secondary inlet temperature (Ts) of the venturi or ejector 230 may affect secondary flow 226.

[0078] As described earlier, above a certain critical current density (i LO_CR) 130, the fuel cell system 10/11 is required to operate in the target anode inlet manifold pressure range indicated by the curve 160 in FIG. 2. The primary inlet pressure (Po) may decrease proportionally with primary fuel demand, until the primary nozzle 236 is no longer choked (i.e., unchoked). In other embodiments, if the primary nozzle 236 is unchoked, the rate of decrease of the primary inlet pressure (Po) may be non-linear and/or may be sensitive to downstream pressure, such as the secondary inlet pressure (Ps). In other embodiments, the primary inlet pressure (Po) may decrease as the primary inlet temperature (To) decreases.

[0079] The primary inlet temperature (To) may be equal to the fuel supply temperature (Tcv). The primary inlet temperature (To) may affect the primary flow 202. In some embodiments, the fuel cell system 10/11 may have a target mass flow rate. In other embodiments, the secondary inlet temperature (Ts) may influence the secondary flow 226 through geometric constraints of the secondary inlet 232 and/or the venturi or ejector 230. In some embodiments, the secondary inlet temperature (Ts) may be a geometric constraint. The thermodynamic constraints and/or venturi or ejector 230 efficiency may also influence the secondary flow 226.

[0080] The venturi or ejector 230 may be sensitive to the primary nozzle inlet pressure (Po), the backpressure, and the required pressure lift (APLIFT). The backpressure may be an exit pressure at an ejector exit 238 (Pc) or may be the anode inlet manifold pressure (PAIM). If there are no pressure losses to the anode inlet manifold from the venturi or ejector 230 outlet, the exit pressure at the ejector exit 238 (Pc) may be equal to the anode inlet manifold pressure (PAM). In some embodiment, the primary nozzle inlet pressure (Po) may be a function of the current density (i) in the fuel cell system 10/11.

Po =/( i) (3)

[0081] Entrainment ratio (ER), which is a measure of the performance and/or capability of the venturi or ejector 230 and may be sensitive to the primary nozzle inlet pressure (Po), the backpressure (e.g., Pc, PAM) and/or the pressure lift (APLIFT). In one embodiment, as backpressure (e.g., Pc, PAM) increases, the venturi or ejector 230 may change from being double choked (with a stable entrainment ratio), to being in a transitioning condition (with a decreasing entrainment ratio), to having a reverse flow. Reverse flow in the venturi or ejector 230 may be undesirable as reverse flow indicates no fuel recirculation through the AGR loop 224. In some embodiments, the venturi or ejector 230 may need to offset pressure losses through the fuel cell or fuel cell stack 12 (APSTACK), while operating against the backpressure (e.g., Pc, PAM).

[0082] In one embodiment, the reversible entrainment ratio (RER) or the reversible portion of the entrainment ratio (ER) based on the thermodynamic limits, is defined as:

RER = - Dc _M / Dc s

Dc _M is the motive flow exergy and Dc s is the entrained flow exergy.

[0083] In one embodiment, if the minimum and maximum anode inlet manifold pressures (PAM_LO 120 and PAM_HI 110, respectively) are known, the low break point (i.e. current density) at which the minimum anode inlet manifold pressure PAM_LO 120 0_LO_BRK) and the high break point (i.e. current density) at which the maximum anode inlet manifold pressure PAM_HI HO (i BRK) may be determined.

[0084] FIG. 5A illustrates the operating range for a venturi or ejector 230 under choked conditions, and FIG. 5B illustrates the operating range for the venturi or ejector 230 under choked and unchoked conditions. In one embodiment, as shown in FIGS. 5A and B, the curve 160 indicates the target anode inlet manifold pressure range as determined by fuel cell stack 12 design. Above a critical current density (i LO_CR) 130, it may be essential to operate the system 10/11 at the target anode inlet manifold pressure range which lies in the range indicated by 160. In the illustrated embodiment, the critical current density (i LO _CR) 130 is about 0.7 Amps/cm². The maximum anode inlet manifold pressure (PAIM) preferred by the venturi or ejector 230 i.e. maximum ejector pressure (P AIM_EJCT_MAX) preferred by the venturi or ejector 230 as a function of current density is shown by the curve 410. The maximum ejector pressure (P AIM_EJCT_MAX) preferred by the venturi or ejector 230 is sensitive to the primary inlet temperature (To) as shown by the curve 420.

[0085] The maximum ejector pressure (P AIM_EJCT_MAX) may vary according to the limits and ranges fuel supply system. In one embodiment, the current density at which the maximum ejector pressure (P AIM_EJCT_MAX) curve 410 intersects the maximum anode inlet manifold pressures (PAIMJII) HO is defined as the high current density ejector threshold (i__Hi-THv) 464. In one embodiment, the current density at which the maximum ejector pressure (P AIM_EJCT_MAX) curve 410 intersects the minimum anode inlet manifold pressures (PAIMJII) 120 is defined as the low current density ejector threshold (i LO_THV) 460.

[0086] In one embodiment, if the maximum ejector pressure (P AIM_EJCT_MAX) is greater than the anode inlet manifold pressure (PAIM), the venturi or ejector 230 may operate under primary nozzle 236 choked conditions, which is a robust ejector state. In some embodiments, though the venturi or ejector 230 can still entrain flow if the anode inlet manifold pressure (PAIM) is greater than the maximum ejector pressure (P AIM_EJCT_MAX), the venturi or ejector 230 may become more sensitive to the boundary conditions. In other embodiments, the ability of the venturi or ejector 230 to continue to meet the entrainment ratio (ER) requirements may become more sensitive to the pressure lift (DR LIFT) if the anode inlet manifold pressure (PAIM) is greater than the maximum ejector pressure

(P_AIM_EJCT_MAx) ·

[0087] In one embodiment, the venturi or ejector 230 configuration may be sized to fully deliver the recirculation flow 226 at the critical current density (i LO_CR) 130 taking into account the differential pressure across the AGR loop 224. In some embodiments, the venturi or ejector 230 configuration may be sized to fully deliver the recirculation flow 226 without the assistance of the recirculation pump or blower 220. Absence of usage of the recirculation pump or blower 220 may result in a decrease in parasitic load as shown by the curves 170 and 440. The curve 170 shows the fraction of the recirculated flow that is delivered by the recirculation pump or blower 220 and the curve 440 shows the corresponding parasitic savings. The curve 440 illustrating the parasitic savings 440 is inversely related to the curve 170 illustrating the fraction of the recirculated flow that is delivered by the recirculation pump or blower 220.

[0088] In one preferable embodiment, the venturi or ejector 230 is designed such that the venturi or ejector 230 can continue to robustly meet any entrainment ratio (ER) requirements at low current densities. In some embodiments, the venturi or ejector 230 can continue to meet entrainment ratio (ER) requirements at a current density as low as the excess fuel ratio current density threshold (i _l_thn) 150 in FIG. 5A and FIG. 5B. The benefits of a configuration where the venturi or ejector 230 can continue to meet entrainment ratio (ER) requirements at such low current densities is illustrated by the curve showing parasitic savings 440. In one embodiment, the venturi or ejector 230 and recirculation pump or blower 220 may be operated simultaneously. In other embodiments, the recirculation pump or blower 220 may be sized smaller to increase the parasitic savings and/or reduce system 10/11 cost, size, or weight.

[0089] In one embodiment, as shown in FIGS. 3 and 4, if the recirculation pump or blower 220 is upstream of the venturi or ejector 230, the flow rate (Q) through the recirculation pump or blower 220 corresponds to the recirculation flow through the anode recirculation loop 224. For example, if the entrainment ratio (ER) is equal to 2.0, then flow through the recirculation pump or blower 220 (Q) is 2/3 of the total fuel 222 flow (primary fuel flow 202 + recirculation fuel flow 226).

[0090] In one embodiment, the venturi or ejector 230 and the recirculation pump or blower 220 may be optimally integrated and/or sized to enhance the operation and/or performance of the venturi or ejector 230 in the fuel cell stack 12. In some embodiment, the recirculation pump or blower 220 may be sized to deliver pressure lift (APLIFT) to offset any pressure losses through the anode recirculation loop 224. In other embodiments, the recirculation pump or blower 220 may be sized to support the operation and/or performance of the venturi or ejector 230 in the fuel cell stack 12 under varying operating conditions. The operating conditions may include, but may not be limited to pseudo- steady state condition and transient conditions.

[0091] In one embodiment, the recirculation pump or blower 220 may exist in different states of operation. In one embodiment, the recirculation pump or blower 220 may be in an idle state 484 and the venturi or ejector 230 may operate without recirculation pump or blower 220 support.

[0092] In one embodiment, the recirculation pump or blower 220 may be in a blower prime state 480, i.e. the current density may be below excess fuel ratio current density threshold (i_r__THv). Under such conditions, the performance and/or operation of the venturi or ejector 230 may be challenged and the venturi or ejector 230 may operate with recirculation pump or blower 220 support. In one embodiment, the recirculation pump or blower 220 may primarily deliver the required recirculation flow through the recirculation anode loop 224. In other embodiments, the blower pressure (APBLWR) may adjust to provide sufficient recirculation flow fuel flow to match the fuel cell stack 12 excess fuel requirement in the system 10/11.

[0093] In one embodiment, the recirculation pump or blower 220 may be in a ejector support state 582 where the venturi or ejector 230 may be boosted by the recirculation pump or blower 220. The current density may be greater than excess fuel ratio current density threshold (ΐ_l__ΐΉn) but less than a low break point current density at which the minimum anode inlet manifold pressure (PAIM_LO) 120 may be set (i LO_BRK). The recirculation pump or blower 220 blower may be providing a part of the recirculating flow.

[0094] As shown in FIG. 6, the lowest current density at which the venturi or ejector 230 is choked at steady state operating pressure (P _AIM_SS) is known as the lowest choked current density (i LO_ACT) 520. The system 10/11 may operate in a pseudo-steady state condition when the recirculation pump or blower 220 is in an idle state 484 i.e. the operating current density is greater than lowest choked current density (i LO_ACT) 520, or the blower is in a prime state i.e., the operating current density is much lower than the excess fuel ratio current density threshold (i l_thn) 150, or the system 10/11 is boosted by the blower in a ejector support state 582. The system 10/11 may be operating at a current density that is greater than the excess fuel ratio current density threshold (i l_thn) 150 but less than lowest choked current density (i LO_ACT) 520 when it is in the ejector support state 582. In some embodiments, the lowest choked current density (i LO_ACT) 520 may be equal to the critical current density (i LO_CR) 130.

[0095] In one embodiment, the system 10/11 may operate in a transient condition such as load shedding support state, where the target operating pressure (PAIM) is greater than the steady state operating pressure (P AIMJSS) such that the primary inlet nozzle is not choked. In other embodiments, the system 10/11 may operate in a transient condition such as load accepting support state, where the rate of increase in current density (i) is greater than a certain threshold such as 0.2 Amps/cm². In some embodiments, the system 10/11 may operate in a transient condition such system 10/11 startup or system 10/11 shutdown. In one embodiment, the recirculation pump or blower 220 is sized such that the operation and/or performance of the venturi or ejector 230 may be increased if required. In some embodiments, this increased capability of the venturi or ejector 230 may impose higher cost and higher parasitic loads on the system 10/11.

[0096] In one embodiment, the recirculation pump or blower 220 is sized to be able to at a minimum support the system 10/11 when the recirculation pump or blower 220 is a prime state and during system 10/11 startup or system 10/11 shutdown states when the venturi or ejector 230 cannot deliver the required fuel flow rates. In other embodiments, the recirculation pump or blower 220 is sized to the differential pressure across the fuel cell stack 12 when the system 10/11 is under a transient condition such as load shedding support state.

[0097] In one embodiment, as shown in FIG. 6, the venturi or ejector 230 may operate without ejector support at and above a blower threshold current density (i BS_THV) 522, the turn down ratio (TDRATIO) that can be managed by the venturi or ejector 230 when the system 10/11 is not choked is equal is:

TDRATIO = I_BS_THV / I_LO_ACT

[0098] The lowest current density threshold at which the venturi or ejector 230 is choked when the operating pressure (PAIM) is the maximum operating pressure (P AM_HI) 110 is the high current ejector threshold (i HI_THV) 464. In one embodiment, if a venturi or ejector 230 needs to operate at the maximum operating pressure (P AM_HI) in ^a load shedding support state, then the venturi or ejector 230 may drop below a current density equal to the high current ejector threshold (i HI_THV) 464. The venturi or ejector 230 may not be choked at this current density. As this current density, the system 10/11 may need a recirculation pump or blower 220 to provide blower support if the operating pressure (PAIM) remains at the maximum operating pressure (P AIM_HI) HO· In some embodiments, for the same turndown ratio (TDRATIO), recirculation pump or blower 220 support may be needed starting at a current density equal to the transition blower threshold current density (i _Bs _TRNs THV) 524. In other embodiments, the upper limit of the ejector support state 582 is defined by the transition blower threshold current density (i BS_TRNS_THV) 524. I BS TRNS THV = i_BS_THV/ ί 1.0 ACT X i_HI_THV

[0099] In one embodiment, if the venturi or ejector 230 can operate without blower support at and above a blower threshold current (i BS_THV) 522 equal to the excess fuel ratio current density threshold (i mv) 150,

I BS TRNS THV = ί /. THv/ί 1.0 AC T X 1_HI_THV

[0100] A recirculation pump or blower 220 is sized to provide flow under conditions where the venturi or ejector 230 cannot provide all the fuel flow by itself. In one embodiment, during operation of the system 10/11 when support of the recirculation pump or blower 220 is not needed, the recirculation pump or blower 220 may act as a restriction and cause pressure loss in the anode recirculation loop 224. The recirculation pump or blower 220 may need to be oversized to support the venturi or ejector 230 by decreasing the pressure lift (DR LIFT) requirement under load shedding transient conditions when the system 10/11 is operating at a high primary anode inlet manifold pressure (e.g., (P AIM_HI) 110).

[0101] The recirculation pump or blower 220 may be sized porportional to the blower threshold current density (i BS_THV) 522 and/or the transition blower threshold current density (i BS_TRNS_THV) 524. In other embodiments, the sizing of the recirculation pump or blower 220 may not be linearly proportional to the blower threshold current density (i__Bs__THv) 522 and/or the transition blower threshold current density (i BS_TRNS_THV) 524. Alternatively, or additionally, the size of the recirculation pump or blower 220 may depend on the mass flow rate through the recirculation pump or blower 220.

[0102] The size of the recirculation pump or blower 220 may depend on variables including but not limited to the entrainment ratio (ER) of the system 10/11, the excess fuel ratio (l) of the system 10/11, the density of fuel composition flowing through the recirculation pump or blower 220, the density of fuel composition flowing through the fuel cell or fuel cell stack 12, the anode inlet manifold pressure (PAIM) of the system 10/11, the operating temperature of the system 10/11, the mass flow through the system 10/11, and/or the entrained flow through the recirculation pump or blower 220.

[0103] A blower by-pass valve may be employed to lower the restriction imposed by the recirculation pump or blower 220 when the system 10/11 is in a blower idle state 584/484. A by-pass valve provides flexibility to avoid pressure losses due to the presence of a recirculation pump or blower 220, and allows for robust interaction between the recirculation pump or blower 220 and the venturi or ejector 230.

[0104] As illustrated in fuel cell system 13 in FIG. 7, a by-pass valve 620 may be located around the recirculation pump or blower 220. In one embodiment, the by-pass valve 620 may be electronically controlled, and/or mechanically controlled. In other embodiments, when the recirculation pump or blower 220 cause a restriction under idle state conditions 584/484, a by-pass valve 620 may open.

[0105] The recirculation pump or blower 220 in the system 13 may be in an idle state 584/484. The by-pass valve 620 may be open when the recirculation pump or blower 220 is in the idle state 584/484. The recirculation pump or blower 220 in the system 13 may be in a prime state 580/480. The by-pass valve 620 may be fully closed when the recirculation pump or blower 220 is in the prime state 580/480. Alternatively, the recirculation pump or blower 220 blower may be providing all of the recirculation flow 226. The blower pressure (APBLWR) may adjust to provide sufficient recirculation flow fuel flow to match the fuel cell stack 12 excess fuel requirement in the system 13.

[0106] The recirculation pump or blower 220 in the system 13 may be in a ejector support state 582/482. The by-pass valve 620 may be fully closed, fully open, or partially open, depending on the system 13 need in the ejector support state 582/482. The system 13 may be in an ejector support state 582/482 when transitioning from the blower prime state 480/580 to the blower idle state 484/584. The blower by-pass valve 620 may be opened while the recirculation pump or blower 220 is operating to smooth this transition.

[0107] The recirculation pump or blower 220 may be configured or implemented to target a total recirculation volumetric flow rate. If the recirculation pump or blower 220 cannot meet the required total recirculation volumetric flow rate, or if the recirculation pump or blower 220 transiently cannot meet the required total recirculation volumetric flow rate, a by-pass valve 620 may be opened to allow by-pass or recirculation flow.

[0108] The recirculation pump or blower 220 may be in a blower idle state 584/484 i.e. in a high load pseudo-steady state such that the current density is above the low current ejector threshold (i LO_THV) 460. When the system 10/11/13 is operating at a current density above the low current ejector threshold (i LO_THV) 460, the venturi or ejector 230 may be capable of delivering the required entrainment ratio (ER). [0109] The venturi or ejector 230 may have a robust entrainment ratio (ER) because of one or more controllers 790 of the venturi or ejector 230 and of the recirculation pump or blower 220. One or more controllers 790 of the venturi or ejector 230 and the recirculation pump or blower 220 may allow for the system 10/11/13 to monitor the state of the venturi or ejector 230 and start initiating and/or increasing speed of the recirculation pump or blower 220 when support is needed.

[0110] In one embodiment, there may be a mismatch between the pressure provided by the recirculation pump or blower 220 and the pressure needed by the venturi or ejector 230 during recirculation pump or blower 220 start up and/or shut down. In some embodiments, the by-pass valve 620 may be used for a smooth transition during recirculation pump or blower 220 start up and/or shut down.

[0111] In one embodiment, the by-pass valve 620, the venturi or ejector 230, and/or the recirculation pump or blower 220 may be controlled by one or more controllers 790 internal to the system 10/11/13. In other embodiments, the by-pass valve 620, the venturi or ejector 230, and/or the recirculation pump or blower 220 may be remotely monitored and/or controlled by one or more controllers 790. In some embodiments, the one or more controller 790 may be in communication with the fuel cell or fuel cell stack 12 in the system 10/11/13, and/or the fuel management system in the fuel cell or fuel cell stack power module.

[0112] In one embodiment, the one or more controllers 790 may measure/ monitor the excess fuel ratio (l) of the system 10/11/13. In some embodiments, the one or more controllers 790 may determine if the system 10/11/13 is operating in a steady state (nominal) condition or a transient (non-nominal) condition. In some embodiments, the one or more controllers 790 may determine the state of the recirculation pump or blower 220 and/or the by-pass valve 620 depending on the excess fuel ratio (l) and/or operating state of the system 10/11/13.

[0113] In one embodiment, the one or more controller 790 for monitoring and/or controlling the operation of the proportional control valve 310 or mechanical regulator 250, by-pass valve 620, the venturi or ejector 230, and/or the recirculation pump or blower 220 in a system 10/11/13 may be implemented, in some cases, in communication with hardware, firmware, software, or any combination thereof present on or outside the in a system 10/11/13 comprising the fuel cell or fuel cell stack 12. Information may be transferred to the one or more controllers 790 using any one or more communication technology (e.g., wired or wireless communications) and associated protocols (e.g., Ethernet, InfiniBand®, Wi-Fi®, Bluetooth®, WiMAX, 3G, 4G LTE, 5G, etc.) to effect such communication.

[0114] The one or more controller 790 may decipher, interpret, monitor, or read one or more sensors in the various components of the system 10/11/13. The one or more controller 790 may actuate a change in one or more components of the system 10/11/13. In other embodiments, the one or more controller 790 may control the function, operation, initiation, or stoppage of one or more components of the system 10/11/13.

[0115] In one embodiment, as shown in FIG. 8, the one or more controller 790 may be in a computing device 710. The computing device 710 may be embodied as any type of computation or computer device capable of performing the functions described herein, including, but not limited to, a server (e.g., stand-alone, rack-mounted, blade, etc.), a network appliance (e.g., physical or virtual), a high-performance computing device, a web appliance, a distributed computing system, a computer, a processor-based system, a multiprocessor system, a smartphone, a tablet computer, a laptop computer, a notebook computer, and a mobile computing device.

[0116] The computing device 710 may include an input/output (I/O) subsystem 702, a memory 704, a processor 706, a data storage device 708, a communication subsystem 712, a controller 790, and a display 714. The computing device 710 may include additional and/or alternative components, such as those commonly found in a computer (e.g., various input/output devices), in other embodiments. In other embodiments, one or more of the illustrative components may be incorporated in, or otherwise form a portion of, another component. For example, the memory 704, or portions thereof, may be incorporated in the processor 706.

[0117] The following described aspects of the present invention are contemplated and non-limiting:

[0118] A first aspect of the present invention relates to a system for monitoring or controlling operation of a fuel cell system. The system includes a first fuel entering an ejector, a second fuel entering a blower or the ejector, and a controller that communicates with the blower or the ejector to monitor or control flow of the first fuel or the second fuel in the fuel cell system. The ejector has a primary inlet pressure and a secondary inlet pressure. [0119] A second aspect of the present invention relates to a method for monitoring or controlling operation of a fuel cell system. The method includes the steps of flowing a first fuel into an ejector, flowing a second fuel into a blower or the ejector, communicating with the blower or the ejector through a controller, and monitoring or controlling flow of the first fuel or flow of the second fuel in the fuel cell system. The ejector has a primary inlet pressure and a secondary inlet pressure.

[0120] In the first or second aspect of the present invention, the fuel cell system may operate and/or the method may include operating the fuel cell system in a system operating state including a steady state or a transient state. The fuel cell system may include a target excess fuel ratio or an anode gas inlet humidity. In the first and second aspect of the present invention, the blower may operate and/or the method may further include the blower operating in a blower operating state including idle state, ejector support state, or prime state. The controller may determine the blower operating state. In the first and second aspect of the present invention, a by-pass valve may be positioned across the blower to allow the second fuel to flow around the blower. The by-pass valve may be included in the fuel cell system. In the first and second aspect of the present invention, the controller may communicate with and/or the method may include the controller communicating with the by-pass valve positioned across the blower. In the first and second aspect of the present invention, the controller may determine and/or the method may further include the controller determining the blower operating state. In the first and second aspect of the present invention, the controller may determine and/or the method may further include the controller determining a pressure drop at the system operating state, a pressure lift that can be delivered by the ejector, and may determine if the pressure drop is greater or lesser than the pressure lift that can be delivered by the ejector.

[0121] In the first and second aspect of the present invention, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the blower may operate in the idle state and/or the method may include the controller operating the blower in the idle state. In the first and second aspect of the present invention, if the pressure drop is less than the pressure lift that can be delivered by the ejector, the by-pass valve positioned across the blower may be opened and/or the method may further include opening the by-pass valve positioned across the blower. In the first and second aspect of the present invention, if the pressure drop is more than the pressure lift that can be delivered by the ejector, the blower may operate in the ejector support state and/or the method may further include operating the blower in the ejector support state.

[0122] In the first and second aspect of the present invention, the controller may determine and/or the method may further include the controller determining a blower operating state based on a target entrainment ratio of the fuel cell system, efficiency of the blower, choked or unchoked condition of the ejector, or transient or steady state of the fuel cell system.

[0123] The features illustrated or described in connection with one exemplary embodiment may be combined with any other feature or element of any other embodiment described herein. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, a person skilled in the art will recognize that terms commonly known to those skilled in the art may be used interchangeably herein.

[0124] The above embodiments are described in sufficient detail to enable those skilled in the art to practice what is claimed and it is to be understood that logical, mechanical, and electrical changes may be made without departing from the spirit and scope of the claims. The detailed description is, therefore, not to be taken in a limiting sense.

[0125] As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated.

[0126] Furthermore, references to “one embodiment” of the presently described subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Specified numerical ranges of units, measurements, and/or values include, consist essentially or, or consist of all the numerical values, units, measurements, and/or ranges including or within those ranges and/or endpoints, whether those numerical values, units, measurements, and/or ranges are explicitly specified in the present disclosure or not.

[0127] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms “first”, “second”, “third”, and the like, as used herein do not denote any order or importance, but rather are used to distinguish one element from another. The term “or” and “and/or” is meant to be inclusive and mean either or all of the listed items. In addition, the terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect.

[0128] Moreover, unless explicitly stated to the contrary, embodiments “comprising”, “including”, or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. The term “comprising” or “comprises” refers to a composition, compound, formulation, or method that is inclusive and does not exclude additional elements, components, and/or method steps. The term “comprising” also refers to a composition, compound, formulation, or method embodiment of the present disclosure that is inclusive and does not exclude additional elements, components, or method steps. The phrase “consisting of’ or “consists of’ refers to a compound, composition, formulation, or method that excludes the presence of any additional elements, components, or method steps.

[0129] The term “consisting of’ also refers to a compound, composition, formulation, or method of the present disclosure that excludes the presence of any additional elements, components, or method steps. The phrase “consisting essentially of’ or “consists essentially of’ refers to a composition, compound, formulation, or method that is inclusive of additional elements, components, or method steps that do not materially affect the characteristic(s) of the composition, compound, formulation, or method. The phrase “consisting essentially of’ also refers to a composition, compound, formulation, or method of the present disclosure that is inclusive of additional elements, components, or method steps that do not materially affect the characteristic(s) of the composition, compound, formulation, or method steps.

[0130] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, and “substantially” is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged.

Such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. [0131] As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.

[0132] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used individually, together, or in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the subject matter set forth herein without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the disclosed subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the subject matter described herein should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0133] This written description uses examples to disclose several embodiments of the subject matter set forth herein, including the best mode, and also to enable a person of ordinary skill in the art to practice the embodiments of disclosed subject matter, including making and using the devices or systems and performing the methods. The patentable scope of the subject matter described herein is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0134] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

WHAT IS CLAIMED IS:

1. A system for monitoring or controlling operation of a fuel cell system, comprising: a first fuel entering an ejector having a primary inlet pressure and a secondary inlet pressure, a second fuel entering a blower or the ejector, and a controller that communicates with the blower or the ejector to monitor or control flow of the first fuel or the second fuel in the fuel cell system.

2. The system of claim 1, wherein the fuel cell system operates in a system operating state comprising a steady state or a transient state, and wherein the fuel cell system comprises a target excess fuel ratio or an anode gas inlet humidity.

3. The system of claim 2, wherein the blower operates in a blower operating state comprising idle state, ejector support state, or prime state, and wherein the controller determines the blower operating state.

4. The system of claim 3, wherein a by-pass valve is positioned across the blower to allow the second fuel to flow around the blower.

5. The system of claim 4, wherein the controller communicates with the by-pass valve positioned across the blower.

6. The system of claim 5, wherein the controller determines a pressure drop at the system operating state, a pressure lift that can be delivered by the ejector, and determines if the pressure drop is greater or lesser than the pressure lift that can be delivered by the ejector.

7. The system of claim 6, wherein if the pressure drop is less than the pressure lift that can be delivered by the ejector, the blower operates in the idle state.

8. The system of claim 6, wherein if the pressure drop is less than the pressure lift that can be delivered by the ejector, the by-pass valve positioned across the blower is opened.

9. The system of claim 6, wherein if the pressure drop is more than the pressure lift that can be delivered by the ejector, the blower operates in the ejector support state.

10. The system of claim 1, wherein the controller determines a blower operating state based on a target entrainment ratio of the fuel cell system, efficiency of the blower, choked or unchoked condition of the ejector, or transient or steady state of the fuel cell system.

11. A method for monitoring or controlling operation of a fuel cell system, comprising: flowing a first fuel into an ejector having a primary inlet pressure and a secondary inlet pressure, flowing a second fuel into a blower or the ejector, communicating with the blower or the ejector through a controller, and monitoring or controlling flow of the first fuel or flow of the second fuel in the fuel cell system.

12. The method of claim 11, wherein the method comprises operating the fuel cell system in a system operating state comprising a steady state or a transient state, and wherein the fuel cell system comprises a target excess fuel ratio or an anode gas inlet humidity.

13. The method of claim 12, wherein the method comprises the blower operating in a blower operating state comprising an idle state, ejector support state, or prime state.

14. The method of claim 13, wherein the fuel cell system comprises a by-pass valve positioned across the blower to allow the second fuel to flow around the blower.

15. The method of claim 14, wherein the method further comprises the controller communicating with the by-pass valve positioned across the blower.

16. The method of claim 15, wherein the method further comprises the controller determining the blower operating state.

17. The method of claim 16, wherein the method further comprises the controller determining a pressure drop at the operating state, determining a pressure lift that can be delivered by the ejector, and determining if the pressure drop is greater or lesser than the pressure lift that can be delivered by the ejector.

18. The method of claim 17, wherein the method comprises the controller operating the blower in the idle state if the pressure drop is less than the pressure lift that can be delivered the ejector.

19. The method of claim 17, wherein if the pressure drop is less than the pressure lift that can be delivered by the ejector, the method comprises opening the by pass valve positioned across the blower.

20. The method of claim 17, wherein if the pressure drop is more than the pressure lift that can be delivered by the ejector, the method comprises operating the blower in the ejector support state.