FI20195159A1

FI20195159A1 - A system for controlling a primary fuel flow in proton exchange membrane fuel cells and a fuel ejector

Info

Publication number: FI20195159A1
Application number: FI20195159A
Authority: FI
Inventors: Kaj Nikiforow; Jari Ihonen; Pauli Koski
Original assignee: Teknologian Tutkimuskeskus Vtt Oy
Priority date: 2019-03-05
Filing date: 2019-03-05
Publication date: 2020-09-06
Also published as: WO2020178485A1

Abstract

The invention concerns a fuel injector (20) and a system for controlling a primary fuel flow in proton exchange membrane fuel cells (PEMFC). The inventive fuel injector comprises an elongate nozzle (23) receiving pressurized fuel from a first inlet (24) into the ejector and including a hollow cavity (25) and a pressure-sensing needle (26) sliding in the cavity and having a pointed end and an opposite end with a pressure-sensing surface (30), and further a second inlet (29) for receiving recirculated fuel from a proton exchange membrane fuel cell. A mixing section (27) for receiving fuel from said nozzle and said second inlet is also provided and a diffuser (28) receiving fuel from the mixing section. An ejector outlet (33) is connected to the diffuser for delivering fuel to the anode system of said proton exchange membrane fuel cell. A first side of the pressure-sensing surface (30) is biased by a pressure sensed at the ejector outlet (33) and a second and opposite side of the pressure-sensing surface is under a pilot pressure (PP) taken from the cathode air inlet pressure of the proton exchange membrane fuel cell. The pilot pressure is acting as a passive compensating force counteracting said bias pressure.

Description

Title of the Invention

A SYSTEM FOR CONTROLLING A PRIMARY FUEL FLOW IN PROTON

EXCHANGE MEMBRANE FUEL CELLS AND A FUEL EJECTOR Field of the Invention The invention relates to proton exchange membrane fuel cell (PEMFC) systems. More specifically, it relates to the control of fuel ejectors in anode gas recirculation systems in such fuel cell systems. Background of the Invention Ejectors can be employed for anode gas recirculation in proton exchange membrane fuel cell (PEMFC) systems. In such systems, the hydrogen to be consumed by the fuel cell is the high pressure primary flow (i.e. the ejector motive flow), and the recirculated flow is the low pressure secondary flow (i.e. the entrained flow in ejector). The flows are combined in an ejector from which the outlet flow then enters the anode(s) of the fuel cell.

The primary flow is controlled to match the fuel consumption rate in the PEMFC, or otherwise under- or over-pressurization of the fuel cell anode compartment will result. The anode compartment pressure should be kept as to close to cathode compartment pressure (which depends on fuel cell system design and fuel cell output power level) as possible to avoid mechanical stress on the membrane that separate the anode and cathode compartments. The control of the primary flow can be made either by varying the ejector primary flow pressure as such, or by varying the ejector primary flow opening (i.e. the = ejector primary nozzle).

N 3 The ejector primary flow pressure control can be implemented by using electronically 2 controlled flow restrictions, such as solenoid valves, proportional valves, mass flow = 25 controllers, etc., or by using a passively operated pressure reducer.

a D The ejector primary flow opening can be controlled with a motive needle which position is 3 adjusted with a stepper motor. The approach resembles that of a needle valve, where the needle is pushed into a nozzle to restrict the flow and pulled out to allow more flow.

The latter approach comprising control of the opening, has the advantage of a better ejector recirculation performance throughout the ejector working range, and is therefore, as a principle, preferred over the supply pressure control approach in this context. A stepper motor may adjust the position of a motive needle accurately. Also a spring loaded needle that changes position based on sensing the anode pressure can be employed/have been suggested. Controlling the flow opening in an ejector is usually done with a stepper motor. The stepper motor together with its control electronics and a pressure transducer adjusts the position of the motive needle to provide the correct amount of fuel to the fuel cell anode. These components are expensive and the control does not work if power is lost. This introduces a safety issue. Failing of any of the three components will also prevent the control from functioning. Another issue with known control systems is that the fuel consumption in the fuel cell may vary sharply with e.g. a load current change applied on the fuel cell. This will result in a temporary under- or over-pressurization of the fuel cell, unless the primary flow control reacts instantly. In prior art solutions, where the anode compartment pressure is sensed and controlled with a spring loaded needle position approach, a higher primary flow rate results in lower ejector outlet pressure, because a larger flow opening will lower the ejector outlet pressure. This is in reverse to desired operation in a PEMFC system where the cathode compartment pressure (and hence the targeted anode compartment pressure) is expected to increase with increasing > PEMFC output power and ejector primary flow rate. N Object of the Invention

S O It is an object of the present invention to create a new type of opening control for an ejector z 25 primary flow, which is based on passive control of the primary flow without electronic > control system and sensor circuitry for a stepper motor. Thus a better and more reliable = control is achieved. >

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Summary of the Invention According to the invention, the pressure from the ejector outlet is taken through a passive pressure sense line as feedback to provide a force that strives to move a motive needle in one direction in the ejector’s primary nozzle throat area. The position of the needle varies the flow opening of the nozzle. A counter-force is, according to the invention, provided by a pilot pressure. The invention is based on the insight that the pressure at the outlet of the ejector, i.e. the anode inlet pressure, would then follow the pilot pressure, which corresponds to the cathode inlet pressure. The cathode pressure is again determined by the amount of air to be fed to the fuel cell, i.e. the current power level of the cell. This ensures that only a small pressure difference occur at the proton exchange membrane in all situations, which ensures that the membrane will not be damaged by excess pressure differences. According to one aspect of the invention, a fuel ejector for controlling a primary fuel flow in proton exchange membrane fuel cells (PEMFC) is provided. The inventive ejector comprises: — an elongate nozzle receiving pressurized fuel from a first inlet into said ejector and including a hollow cavity, — a pressure-sensing needle sliding in said cavity and having a pointed end and an opposite end with a pressure-sensing surface, — a second inlet for receiving recirculated fuel from a proton exchange membrane fuel cell, — a mixing section receiving fuel from said nozzle and said second inlet, and — a diffuser receiving fuel from said mixing section, and — an ejector outlet connected to said diffuser for delivering fuel to the anode system of said o proton exchange membrane fuel cell. S A first side of the pressure-sensing surface is biased by a pressure sensed at the ejector g 25 outlet, and a second and opposite side of said pressure-sensing surface is under a pilot 3 pressure taken from the cathode air inlet pressure of the proton exchange membrane fuel cell E acting as a passive compensating force counteracting said bias pressure. 3 According to some embodiments, the bias pressure sensed at said ejector outlet is led with a 3 pressure line to said first side of said pressure-sensing surface.

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According to some embodiments, the pilot pressure is led from the cathode air inlet pressure of said proton exchange membrane fuel cell with a pressure line to the second and opposite side of the pressure-sensing surface. According to some embodiments, the inventive fuel ejector may further comprise a passive spring-loaded moving wall facing at least part of the primary fuel flow from said ejector, said wall having a lever and link system connected to said pressure-sensing needle. According to a second aspect of the invention, a system for controlling a primary fuel flow in proton exchange membrane fuel cells (PEMFC) is provided. The inventive system comprises — a fuel ejector; — a proton exchange membrane fuel cell connected to the ejector; — alow pressure secondary fuel feed recirculating unused fuel from the proton exchange membrane fuel cell to a second inlet of the fuel ejector; wherein the fuel ejector comprises: — afirstinlet for receiving pressurized primary fuel and an elongate nozzle receiving the pressurized fuel and including a hollow cavity, — a pressure-sensing needle sliding in the cavity and having a pointed end and an opposite end with a pressure-sensing surface, — a second inlet for receiving recirculated fuel from a proton exchange membrane fuel cell, — a mixing section receiving fuel from the nozzle and the second inlet, and — a diffuser receiving fuel from the mixing section, and — an ejector outlet connected to the diffuser for delivering fuel to the anode system of the O proton exchange membrane fuel cell, and N wherein the a first side of the pressure-sensing surface is biased by a pressure sensed at the 3 25 ejector outlet, and a second and opposite side of the pressure-sensing surface is under a pilot 3 pressure taken from the cathode air inlet pressure of the proton exchange membrane fuel cell E acting as a passive compensating force counteracting the bias pressure. 3 Further embodiments of the inventive system are characterized by what is stated in the > appended claims.

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Brief description of the Drawings Fig. 1 shows an overall outline of a system for controlling a primary fuel flow in PEMFC cells, according to at least some embodiments of the invention; Fig. 2 shows an exemplary fuel ejector capable of controlling a primary hydrogen fuel flow 5 in PEMFC systems according to at least some embodiments of the present invention; Fig. 3 shows another exemplary fuel ejector capable of controlling a primary hydrogen fuel flow in PEMFC systems according to at least some embodiments of the present invention.

Detailed Description of Embodiments Reference is made to Fig. 1, which provides an overview of a system 10 for controlling a primary fuel flow in a proton exchange membrane fuel cell (PEMFC) 13 connected to a load M.

On the cathode side, an air compressor 11 is coupled to an air intake and feeds pressurized air into membrane humidifier 12. Humidified air is fed through the cathode compartment C of the fuel cell 13 via a cathode inlet, and returns from the cathode outlet to the humidifier 12, as shown.

On the anode side, a high pressure primary fuel feed from a fuel supply 14 is fed to a fuel ejector 18. The ejector outlet/anode inlet 15 delivers fuel (hydrogen) to the anode compartment A of the PEMFC 13, driving the load M.

From the anode outlet, a portion of fluid mixture (consisting mainly of hydrogen, nitrogen and water) is discharged from the system through a purge valve 17, while the rest is recirculated back to a second inlet of the fuel ejector 18 via a low pressure secondary fuel feed line 19. Discharging a portion of the anode outlet fluid prevents fuel impurity build-up in the recirculation line and hence ensures stable operation and high performance of the PEMFC. oO > The inlet pressure at the anode compartment A may be 2 bar gauge or less.

The pressure loss 0 across the anode may be tens or a few hundred mbar, for example.

Thus the pressure in the 2 recirculation line 19 may only be slightly less than the anode fuel inlet pressure. = 25 According to the invention, a passive force element is provided by the pilot pressure taken 2 via line 16 from the cathode air inlet of the proton exchange membrane fuel cell.

This io ensures the anode inlet pressure follows the cathode inlet pressure, as the pilot pressure > provides a counter-force to the needle bias of the ejector, as explained below.

In Fig. 2 is shown an inventive fuel ejector 20 for controlling a primary hydrogen fuel flow in proton exchange membrane fuel cell (PEMFC) systems. The ejector comprises an elongate nozzle portion 23 receiving pressurized fuel from a first inlet 24 into the ejector which includes a hollow cavity 25. A pressure-sensing needle 26 having a pointed end is sliding in said cavity, with the pointed end pointing in the direction of a mixing region 27, a diffuser 28 and an outlet 33 of the ejector 20. A second inlet 29 is provided for receiving recirculated fuel from a fuel recirculation line system in the proton exchange membrane fuel cell (not shown). Momentum of the primary gas delivered at high velocity from nozzle 23 is transferred to secondary gas when the two gases come in contact in mixing section 27 and upstream of mixing section 27. The gas mixture is decelerated in diffuser 28 whereupon the pressure increases at the outlet 33 to a higher level than at inlet 29. The gas mixture is delivered (arrow 22) to the anode compartment of the proton exchange membrane fuel cell. According to the invention, the needle is connected to a sensing element, which may be a piston consisting of a needle sensing plate 30 combined with a diaphragm 32, which is subjected to two counteracting forces, on each side of the surface of the combined pressure sensing element consisting of the plate 30 and diaphragm 32. On one side of the surface, to the left in Fig. 2, a bias pressure force from the ejector outlet (which is the pressure one wants have control over) is applied. On the opposite side to the right, a load force created by a pilot pressure. The needle 26 has the pressure-sensing plate 30 attached to its opposite end, which is biased by a pressure sensing means, here pressure line 31 and the diaphragm 32, connected between the plate 30 and the ejector outlet 33. The pressure sensing means may > consist of the pressure line 31 and any pressure-sensing components that acts in a manner > like the combined sensing plate 30 and diaphragm 32. S 25 The pressure is sensed from an opening 31a of the pressure sensing line 31 residing in the S ejector outlet 33. The bias force 21 presses the plate 30 and the needle 26 to the right in Fig. E: 2. The bias force 21, as sensed at ejector outlet 33, makes the flow opening at nozzle tip 23a 2 smaller when the pressure at ejector outlet 33 increases. The ejector primary flow then io decreases and the ejector outlet pressure decreases.

N The bias force 21 is according to the invention counteracted by a pilot pressure PP entering the chamber 34 formed around the needle sensing plate 30. The pilot pressure then provides the counter-force P against the biased plate 30. The force P compensates for variations in the pressure sensed at the ejector outlet 33 and conveyed to the pressure plate as bias force 21. The pilot pressure PP works towards making the flow area larger at nozzle tip 23a, so that when the ejector outlet 33 pressure decreases, the pilot pressure PP pushes the needle 26 to the left in Fig. 2 and away from the nozzle tip 23a, thus making the flow opening larger which results in higher primary flow rate and increased ejector outlet pressure. In this way the position of the needle 26 and thus the ejector outlet pressure always approaches an equilibrium state, where the two forces 21 and P cancel out each other. The pilot pressure may be the same as the cathode air supply pressure to the proton exchange membrane fuel cell, which brings the benefit of that the ejector outlet pressure then follows the air supply pressure, which is usually a preferred condition in a PEMFC fuel cell. As the cathode pressure is determined by the amount of air to be fed to the fuel cell, i.e. the current power level of the fuel cell, the inventive arrangement ensures that only a small pressure difference occur at the proton exchange membrane in all situations, which ensures that the membrane will not be damaged by excess pressure differences. With the present invention a high ejector performance on a wide operating range is achievable, without using expensive and potentially failing electronic equipment. The pressure decrease that follows an increasing flow rate can be kept low, and thus pressure variations at the ejector outlet may be minimized. > In a third embodiment shown in Fig. 3, the ejector outlet flow 22 may be directed towards a > spring-loaded moving wall 36, that is connected to the needle shaft 26 by a linkage 35 and a O lever/link system 37, 38. The pressure of the dynamic flow exerted against the wall 36 0 forces the needle 26 to close and open, thus affecting the force P. As the wall 36 moves to I 25 the right due to a sensed pressure increase, the mechanism 25, 37, 38 force the needle to > open. This will further minimize, or totally prevent, an ejector outlet pressure decrease = associated with increased primary flow rate.

O > It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to eguivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a > thorough understanding of embodiments of the invention. One skilled in the relevant art will N recognize, however, that the invention can be practiced without one or more of the specific S 25 details, or with other methods, components, materials, etc. In other instances, well-known S structures, materials, or operations are not shown or described in detail to avoid obscuring = aspects of the invention. e While the forgoing examples are illustrative of the principles of the present invention in one 2 or more particular applications, it will be apparent to those of ordinary skill in the art that N 30 numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below. The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality. Industrial Applicability At least some embodiments of the present invention find industrial application in systems for controlling primary fuel flow in proton exchange membrane fuel cells.

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Claims

1. A fuel ejector for controlling a primary fuel flow in proton exchange membrane fuel cells (PEMFC), wherein the ejector comprises: — an elongate nozzle receiving pressurized fuel from a first inlet into said ejector and including a hollow cavity, — a pressure-sensing needle sliding in said cavity and having a pointed end and an opposite end with a pressure-sensing surface, — a second inlet for receiving recirculated fuel from a proton exchange membrane fuel cell, — a mixing section receiving fuel from said nozzle and said second inlet, and — adiffuser receiving fuel from said mixing section, and — an ejector outlet connected to said diffuser for delivering fuel to the anode system of said proton exchange membrane fuel cell, wherein a first side of said pressure-sensing surface is biased by a pressure sensed at said ejector outlet, and a second and opposite side of said pressure-sensing surface is under a pilot pressure taken from the cathode air inlet pressure of said proton exchange membrane fuel cell acting as a passive compensating force counteracting said bias pressure.

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2. A fuel ejector according to claim 1, wherein said bias pressure sensed at said ejector > 20 outlet is led with a pressure line to said first side of said pressure-sensing surface.

O T

3. A fuel ejector according to claim 1 or 2, wherein said pilot pressure is led from the

LO 9 cathode air inlet pressure of said proton exchange membrane fuel cell with a pressure line to

I T said second and opposite side of said pressure-sensing surface.

D 5

4. A fuel ejector according to claims 1, 2 or 3, wherein the fuel ejector further comprises a

O S 25 passive spring-loaded moving wall facing at least part of the primary fuel flow from said ejector, said wall having a lever and link system connected to said pressure-sensing needle.

5. A system for controlling a primary fuel flow in proton exchange membrane fuel cells (PEMFC), comprising: — a fuel ejector; — a proton exchange membrane fuel cell connected to said ejector; — alow pressure secondary fuel feed recirculating unused fuel from said proton exchange membrane fuel cell to a second inlet of said fuel ejector; wherein said fuel ejector comprises: — a first inlet for receiving pressurized primary fuel and an elongate nozzle receiving said pressurized fuel and including a hollow cavity, — a pressure-sensing needle sliding in said cavity and having a pointed end and an opposite end with a pressure-sensing surface, — a second inlet for receiving recirculated fuel from a proton exchange membrane fuel cell, — a mixing section receiving fuel from said nozzle and said second inlet, and — a diffuser receiving fuel from said mixing section, and — an ejector outlet connected to said diffuser for delivering fuel to the anode system of said proton exchange membrane fuel cell, and wherein said a first side of said pressure-sensing surface is biased by a pressure sensed at S said ejector outlet, and a second and opposite side of said pressure-sensing surface is under a N . . . v 20 pilot pressure taken from the cathode air inlet pressure of said proton exchange membrane O . . . . ad: Lo fuel cell acting as a passive compensating force counteracting said bias pressure.

O = 6. A system according to claim 5, wherein said bias pressure sensed at said ejector outlet is a o led with a pressure line to said first side of said pressure-sensing surface.

LO O 7. A system according to claim 7 or 8, wherein said pilot pressure is led from the cathode air OS . . . . N 25 inlet pressure of said proton exchange membrane fuel cell with a pressure line to said second and opposite side of said pressure-sensing surface.

8. A system according to any of claims 5 - 7, wherein the fuel ejector further comprises a passive spring-loaded moving wall facing at least part of the primary fuel flow from said ejector, said wall having a lever and link system connected to said pressure-sensing needle. oO

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