Fuel cell system including air inlet baffle and method of operating thereof

A fuel cell system includes a stack of fuel cells, a cathode recuperator configured to heat air using cathode exhaust output from the stack, and an air inlet baffle disposed between the cathode recuperator and the stack and containing at least two rows of apertures which are separated along a vertical direction and configured to provide the heated air output from the cathode recuperator to plural areas of the stack.

FIELD

Aspects of the present invention relate to electrochemical cell systems, and more particularly, to fuel cell systems including an air inlet baffle having apertures.

BACKGROUND

Fuel cells, such as solid oxide fuel cells, are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide regenerative fuel cells, that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input.

SUMMARY

According to various embodiments, a fuel cell system includes a stack of fuel cells, a cathode recuperator configured to heat air using cathode exhaust output from the stack, and an air inlet baffle disposed between the cathode recuperator and the stack and containing at least two rows of apertures which are separated along a vertical direction and configured to provide the heated air output from the cathode recuperator to plural areas of the stack.

According to various embodiments, a method of operating a fuel cell system comprises providing heated air and fuel to a stack of fuel cells, operating the stack in a steady-state mode to output a fuel exhaust and an air exhaust, providing the fuel exhaust and the air exhaust to an anode tail gas oxidizer to oxidize the fuel exhaust, providing an exhaust from the anode tail gas oxidizer to a cathode recuperator, providing air to the cathode recuperator, heating the air using the exhaust from the anode tail gas oxidizer to output the heated air from the cathode recuperator onto an air inlet baffle disposed between the cathode recuperator and the stack and comprising at least two rows of apertures which are separated along a vertical direction, and providing the heated air through the at least two rows of apertures to plural areas of the stack.

DETAILED DESCRIPTION

As set forth herein, various aspects of the disclosure are described with reference to the exemplary embodiments and/or the accompanying drawings in which exemplary embodiments of the invention are illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments shown in the drawings or described herein. It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations.

In a solid oxide fuel cell (SOFC) system, one or more fuel cell stacks may be provided with air and fuel in order to generate electricity. During operation, stacks may develop a vertical temperature gradient due to cell heat generation, convective cooling due to the incoming air, and/or radiative coupling between stacks and/or other system components. For example, fuel cells at the top and/or bottom of a stack may have a lower temperature than cells in the middle of the stack, and/or cells in the middle of the stack may be excessively cooled or heated. An excessive vertical temperature gradient may result in reduced voltage performance, thermal stress, cell degradation, and non-uniform fuel delivery, which may reduce overall system performance and/or efficiency. This may even lead to fuel starvation and associated failure of some fuel cells in the stack. Accordingly, embodiments of the present disclosure provide SOFC systems containing a perforated air inlet baffle that improves stack temperature variation and helps in optimizing the vertical stack temperature profile for uniform fuel flow to individual cells in a stack.

FIG.1is a schematic representation of a SOFC system10, according to various embodiments of the present disclosure. Referring toFIG.1, the system10includes a hotbox100and various components disposed therein or adjacent thereto. The hot box100may contain stacks102containing alternating fuel cells, such as solid oxide fuel cells, and interconnects. One solid oxide fuel cell of the stack102contains a ceramic electrolyte, such as yttria stabilized zirconia (YSZ), scandia stabilized zirconia (SSZ), scandia and ceria stabilized zirconia or scandia, yttria and ceria stabilized zirconia, an anode electrode, such as a nickel-YSZ, a nickel-SSZ or nickel-doped ceria cermet, and a cathode electrode, such as lanthanum strontium manganite (LSM). The interconnects may be metal alloy interconnects, such as chromium-iron alloy interconnects. The stacks102may be internally or externally manifolded for fuel.

The hot box100may also contain an anode recuperator heat exchanger110, a cathode recuperator heat exchanger500, an anode tail gas oxidizer (ATO)150, an anode exhaust cooler heat exchanger140, a splitter158, a vortex generator159, and a water injector160. The system10may also include a catalytic partial oxidation (CPOx) reactor200, a mixer210, a CPOx blower204(e.g., air blower), a main air blower208(e.g., system blower), and an anode recycle blower212, which may be disposed outside of the hotbox100. However, the present disclosure is not limited to any particular location for each of the components with respect to the hotbox100.

The CPOx reactor200receives a fuel inlet stream from a fuel inlet300, through fuel conduit300A. The fuel inlet300may be a fuel tank or a utility natural gas line including a valve to control an amount of fuel provided to the CPOx reactor200. The CPOx blower204may provide air to the CPOx reactor200during system start-up. The fuel and/or air may be provided to the mixer210by fuel conduit300B. Fuel (e.g., the fuel inlet stream) flows from the mixer210to the anode recuperator110through fuel conduit300C. The fuel is heated in the anode recuperator110by a portion of the fuel exhaust and the fuel then flows from the anode recuperator110to the stack102through fuel conduit300D.

The main air blower208may be configured to provide an air stream (e.g., air inlet stream) to the anode exhaust cooler140through air conduit302A. Air flows from the anode exhaust cooler140to the cathode recuperator500through air conduit302B. The air is heated by the ATO exhaust in the cathode recuperator500. The air flows from the cathode recuperator500to the stack102through air conduit302C.

An anode exhaust stream (e.g., the fuel exhaust stream) generated in the stack102is provided to the anode recuperator110through anode exhaust conduit308A. The anode exhaust may contain unreacted fuel and may also be referred to herein as fuel exhaust. The anode exhaust may be provided from the anode recuperator110to the splitter158by anode exhaust conduit308B. A first portion of the anode exhaust may be provided from the splitter158to the anode exhaust cooler140through the water injector160and the anode exhaust conduit308C. A second portion of the anode exhaust is provided from the splitter158to the ATO150through the anode exhaust conduit308D. The first portion of the anode exhaust heats the air inlet stream in the anode exhaust cooler140and may then be provided from the anode exhaust cooler140to the mixer210through the anode exhaust conduit308E. The anode recycle blower212may be configured to move anode exhaust though anode exhaust conduit308E, as discussed below.

Cathode exhaust generated in the stack102flows to the ATO150through exhaust conduit304A. The vortex generator159may be disposed in exhaust conduit304A and may be configured to swirl the cathode exhaust. The anode exhaust conduit308D may be fluidly connected to the vortex generator159or to the cathode exhaust conduit304A or the ATO150downstream of the vortex generator159. The swirled cathode exhaust may mix with the second portion of the anode exhaust provided by the splitter158before being provided to the ATO150. The mixture may be oxidized in the ATO150to generate an ATO exhaust. The ATO exhaust flows from the ATO150to the cathode recuperator500through exhaust conduit304B. Exhaust flows from the cathode recuperator and out of the hotbox100through exhaust conduit304C.

Water flows from a water source206, such as a water tank or a water pipe, to the water injector160through water conduit306. The water injector160injects water directly into first portion of the anode exhaust provided in anode exhaust conduit308C. Heat from the first portion of the anode exhaust (also referred to as a recycled anode exhaust stream) provided in anode exhaust conduit308C vaporizes the water to generate steam. The steam mixes with the anode exhaust, and the resultant mixture is provided to the anode exhaust cooler140. The mixture is then provided from the anode exhaust cooler140to the mixer210through the anode exhaust conduit308E. The mixer210is configured to mix the steam and first portion of the anode exhaust with fresh fuel (i.e., fuel inlet stream). This humidified fuel mixture may then be heated in the anode recuperator110by the anode exhaust, before being provided to the stack102. The system10may also include one or more fuel reforming catalysts112,114, and116located inside and/or downstream of the anode recuperator110. The reforming catalyst(s) reform the humidified fuel mixture before it is provided to the stack102.

The system10may further a system controller225configured to control various elements of the system10. The controller225may include a central processing unit configured to execute stored instructions. For example, the controller225may be configured to control fuel and/or air flow through the system10, according to fuel composition data.

FIG.2Ais a sectional view showing components of the hot box100of the system10ofFIG.1, andFIG.2Bshows an enlarged portion ofFIG.2A.FIG.2Cis a three-dimensional cut-away view of a central column400of the system10, according to various embodiments of the present disclosure, andFIG.2Dis a perspective view of an anode hub structure600disposed in a hot box base101on which the column400may be disposed.

Referring toFIGS.2A-2D, the fuel cell stacks102may be disposed around the central column400in the hot box100. For example, the stacks102may be disposed in a ring configuration around the central column400and may be positioned on the hot box base101. The column400may include the anode recuperator110, the ATO150, and the anode exhaust cooler140. In particular, the anode recuperator110is disposed radially inward of the ATO150, and the anode exhaust cooler140is mounted over the anode recuperator110and the ATO150. In one embodiment, an oxidation catalyst112and/or the hydrogenation catalyst114may be located in the anode recuperator110. A reforming catalyst116may also be located at the bottom of the anode recuperator110as a steam methane reformation (SMR) insert.

The ATO150comprises an outer cylinder152that is positioned around the outer wall of the anode recuperator110. Optionally, ATO insulation156may be enclosed by an ATO inner cylinder154. Thus, the insulation156may be located between the anode recuperator110and the ATO150. An ATO oxidation catalyst may be located in the space between the outer cylinder152and the ATO insulation156. A fuel inlet path bellows854may be located between the anode exhaust cooler140and the inner ATO cylinder154. An ATO thermocouple feed through1601extends through the anode exhaust cooler140, to the top of the ATO150. The temperature of the ATO150may thereby be monitored by inserting one or more thermocouples (not shown) through this feed through1601.

The anode hub structure600may be positioned under the anode recuperator110and ATO150and over the hot box base101. The anode hub structure600is covered by an ATO skirt1603. The vortex generator159and fuel exhaust splitter158are located over the anode recuperator110and ATO150and below the anode exhaust cooler140. An ATO glow plug1602, which initiates the oxidation of the stack fuel exhaust in the ATO during startup, may be located near the bottom of the ATO150.

The anode hub structure600is used to distribute fuel evenly from the central column to fuel cell stacks102disposed around the central column400. The anode flow hub structure600includes a grooved cast base602and a “spider” hub of fuel inlet conduits300D and anode exhaust conduits308A. Each pair of conduits300D,308A connects to a fuel cell stack102. Anode side cylinders (e.g., anode recuperator110inner and outer cylinders and ATO outer cylinder152) are then welded or brazed into the grooves in the base602, creating a uniform volume cross section for flow distribution as discussed below.

As shown by the arrows inFIGS.2A and2B, air enters the top of the hot box100and then flows into the cathode recuperator500where it is heated by ATO exhaust output from the ATO150. The heated air then flows through the cathode recuperator500and then exits the cathode recuperator500through an air outlet530. An air inlet baffle550may be disposed between the stacks102and the cathode recuperator500. As discussed in detail below, the air inlet baffle550may be configured to control air flow to the stacks102.

For solid oxide fuel cells, the air then flows through the stacks102, such that oxygen ions diffuse from the cathode electrodes through the fuel cell electrolytes to the anode electrodes and react with fuel (i.e., fuel inlet stream) provided from the anode hub structure600at the anode electrodes of the fuel cells. Air exhaust flows from the stacks102and then passes through vanes of the vortex generator159and is swirled before entering the ATO150.

The splitter158may direct the second portion of the fuel exhaust exiting the top of the anode recuperator100through openings (e.g., slits) in the splitter into the swirled air exhaust (e.g., in the vortex generator159or downstream of the vortex generator159in exhaust conduit304A or in the ATO150). At such the fuel and air exhaust may be mixed before entering the ATO150.

FIGS.3A and3Bare side cross-sectional views showing flow distribution through the central column400, and3C is top cross-sectional view taken through the anode recuperator110. Referring toFIGS.2A,2B,3A, and3C, the anode recuperator110includes an inner cylinder110A, a corrugated plate110B, and an outer cylinder110C that may be coated with the ATO insulation156. Fuel from fuel conduit300C enters the top of the central column400. The fuel then bypasses the anode exhaust cooler140by flowing through its hollow core and then flows through the anode recuperator110, between the outer cylinder110C and the and the corrugated plate110B. The fuel then flows through the hub base602and conduits300D of the anode hub structure600shown inFIG.3B, to the stacks102.

Referring toFIGS.2A,2B,2C,3A, and3B, the fuel exhaust flows from the stacks102through conduits308A into the hub base602, and from the hub base602through the anode recuperator110, between in inner cylinder110A and the corrugated plate110B, and through anode exhaust conduit308B into the splitter158. The first portion of the fuel exhaust flows from the splitter158to the anode exhaust cooler140through anode exhaust conduit308C, while the second portion flows from the splitter158to the ATO150through anode exhaust conduit308D, as shown inFIG.1. Anode exhaust cooler inner core insulation140A may be located between the fuel conduit300C and bellows852/supporting cylinder852A located between the anode exhaust cooler140and the vortex generator159, as shown inFIG.3A. This insulation minimizes heat transfer and loss from the first portion of the anode exhaust stream in anode exhaust conduit308C on the way to the anode exhaust cooler140. Insulation140A may also be located between fuel conduit300C and the anode exhaust cooler140to avoid heat transfer between the fuel inlet stream in conduit300C and the streams in the anode exhaust cooler140. In other embodiments, insulation140A may be omitted from inside the cylindrical anode exhaust cooler140.

FIG.3Balso shows air flowing from the air conduit302A to the anode exhaust cooler140(where it is heated by the first portion of the anode exhaust) and then from the anode exhaust cooler140through conduit302B to the cathode recuperator500. The first portion of the anode exhaust is cooled in the anode exhaust cooler140by the air flowing through the anode exhaust cooler140. The cooled first portion of the anode exhaust is then provided from the anode exhaust cooler140to the anode recycle blower212shown inFIG.1.

As will be described in more detail below and as shown inFIGS.2A and3B, the anode exhaust exits the anode recuperator110and is provided into splitter158through anode exhaust conduit308B. The splitter158splits the anode exhaust into first and second anode exhaust portions (i.e., streams). The first stream is provided into the anode exhaust cooler140through anode exhaust conduit308C. The second stream is provided to the ATO150through anode exhaust conduit308D.

The relative amounts of anode exhaust provided to the ATO150and the anode exhaust cooler140is controlled by the anode recycle blower212. The higher the blower212speed, the larger portion of the anode exhaust is provided into anode exhaust conduit308C and a smaller portion of the anode exhaust is provided to the ATO150via anode exhaust conduit308D, and vice-versa. The anode exhaust provided to the ATO150may be oxidized by the stack cathode (i.e., air) exhaust and provided to the cathode recuperator500through conduit304B.

FIG.4Ais a cross-sectional view showing the air inlet baffle550disposed inside of the cathode recuperator500,FIG.4Bis simplified partial cross-sectional view showing air and exhaust flow through the cathode recuperator500, stack102, and a central column400, andFIG.4Cis a side view of the air inlet baffle550.

Referring toFIGS.4A-4C, the cathode recuperator500may surround one or more of the stacks102and the central column400which is shown in more detail inFIG.2A. The cathode recuperator500may include a cover510including an air inlet510A and air exhaust outlets510B, an upper lid514, an optional fin assembly518, a lower cylinder524and an outer shell528. The fin assembly518may include a cylindrical corrugated plate520and an inner wall522disposed inside of the corrugated plate520. The corrugated plate520may be configured to transfer heat between incoming air and outgoing cathode exhaust. The inner surface of the inner wall522may be covered with heat shield insulation.

An annular air outlet530may be formed between the inner wall522and the lower cylinder524. In particular, the air outlet530may be formed where the lower cylinder524and the inner wall522overlap. An annular ATO exhaust inlet532may be formed between the outer shell528and the lower cylinder524.

As shown inFIGS.4A and4B, air may enter the cathode recuperator500through the air inlet510A, flow under the upper lid514, along an inner surface of the corrugated plate520, and then out of the air outlet530. The air may then pass through the air inlet baffle550and be provided to the fuel cell stacks102which are surrounded by the cathode recuperator500. Cathode exhaust output from the stack102may flow into the central column400, be mixed with anode exhaust (not shown) in the vortex generator159, and then provided to the ATO150. ATO exhaust (i.e., oxidized fuel exhaust) output from the ATO150may be provided to the ATO exhaust inlet532of the cathode recuperator500, flow along an outer surface of the corrugated plate520and over an upper surface of the upper lid514, before exiting through the exhaust outlets510B. Accordingly, the air is heated by heat extracted from the ATO exhaust.

The air inlet baffle550may be a cylindrical component disposed inside of the cathode recuperator500, and surrounding the fuel cell stacks102. The air inlet baffle may form a barrier between the fuel cell stacks102from the cathode recuperator500. The air inlet baffle550may be configured to control the flow of the heated air to the fuel cell stacks102, in order to limit the vertical temperature variations along the height of the fuel cell stacks102and also to optimize it to be favorable for uniform fuel utilization across the cells. For example, during steady-state operation of the system (which occurs after start-up operation of the system), the air inlet baffle550may be configured to provide a vertical cell-to-cell temperature variation in the fuel cell stack102of about 40° C. or less, such from about 30° C. to about 40° C. In some embodiments, during steady-state operation of the system, the air inlet baffle550may be configured to control the temperature of the fuel cell stacks102, such that a maximum fuel utilization of any fuel cell in the stack102is about 1% or less above the average fuel utilization of the entire fuel cell stack102, such as 0.1 to 1% above the average fuel utilization. In some embodiments, the air inlet baffle550may be configured to control the temperature of the stacks102, such that the fuel utilization of the fuel cells in the stack102ranges from about 86% to about 91%. Thus, the difference between the minimum and maximum fuel utilization between the two different fuel cells in the same stack is 10% or less, such as 5% or less, such as 4 to 6%.

The air inlet baffle550may include an array of apertures552configured to direct heated air towards particular portions of the stacks102. For example, in some embodiments, the apertures552may be arranged on the air inlet baffle550, such that the air inlet baffle directs more of the air output from the cathode recuperator500to a top portion of the stack102than to a bottom portion of the stack102.

In some embodiments the apertures552may be circular through holes, as shown inFIG.4C. However, in other embodiments the apertures552may have other shapes, such as horizontal or vertical slits, or the like. The location, size, and/or number of the apertures552may be set according to desired stack102and/or system characteristics influenced by air provided through the air inlet baffle550.

In one embodiment, the air inlet baffle550may lack any apertures552at the vertical level of the air outlet530. Thus, air exiting the air outlet530is incident on a solid plate portion553of the air inlet baffle550and is not provided directly to the fuel cell stacks102. Thus, portions of the fuel cell stacks102located at the vertical level of the air outlet530are not subjected to overcooling from a direct impact of the air stream provided from the air outlet530. Thus, the solid plate portion553of the air inlet baffle550spreads (i.e., deflects) the air exiting the air outlet530in the vertical direction (i.e., up and down) before the air reaches the fuel cell stacks102through the apertures552. Thus, the air achieves a more uniform temperature by flowing vertically before reaching the stacks102. Furthermore, since the air is incident on several vertical portions of the stacks102which are located at the vertical levels of the apertures, a single region of the stack102is not subject to overcooling from the air stream. This provides a more uniform vertical temperature distribution along the height of the stack102.

Fuel provided to the fuel cells flows from the bottom of the stack to the top of the stack102, and fuel exhaust from the fuel cells flows through the stack102in the opposite direction, either through riser tubes or through an integrated fuel channels within the fuel cell stack102. Fuel distribution may be governed by the geometry of the stack102, as well as variations in the properties of the fuel with the stack102, due to local temperature variations in the stack102. For example, higher fuel temperatures may result increased fuel flow resistance, which may result in reduced fuel flow rates. Vertical stack temperature variations may result from variations in fuel cell heat generation, convective cooling of a stack by incoming air, as well as radiation coupling between a stack and other heat generating components of a SOFC system.

For example,FIG.5is simplified cross-sectional view showing air distribution from cathode recuperator500to a stack102, in a comparative fuel cell system that does not include the air inlet baffle. As shown inFIG.5, air exits the cathode recuperator500through the air outlet530and is initially directed to fuel cells in a central portion CP of the stack102. As a result, the stack102may experience an uneven vertical temperature profile, due to cooling of the fuel cells in the central portion CP by the incoming air.

In contrast, as descried above with regard toFIGS.4A-4C, in one embodiment, portions of the fuel cell stacks102located at the vertical level of the air outlet530are not subjected to overcooling from a direct impact of the air stream provided from the air outlet530. Thus, the solid plate portion553of the air inlet baffle550spreads (i.e., deflects) the air exiting the air outlet530in the vertical direction (i.e., up and down) before the air reaches the fuel cell stacks102through the apertures552. Thus, the air achieves a more uniform temperature by flowing vertically before reaching the stacks102. Furthermore, even if there are apertures552at the vertical level of the air outlet5230, since the air is incident on several vertical portions of the stacks102which are located at the vertical levels of the apertures552, a single region of the stack102is not subject to overcooling from the air stream. This provides a more uniform vertical temperature distribution along the height of the stack102.

The present inventors determined that reducing vertical temperature variations within stacks may provide better cell temperature control, voltage performance, and voltage uniformity, and may reduce cell degradation and reduced thermal stress, over various operating conditions. Additionally, an optimum vertical stack temperature profile increases the uniformity of fuel flow to the fuel cells in a stack, in the vertical direction. Fuel cells may degrade and/or fail at excessively high fuel utilization rates, due to fuel cell starvation. The maximum fuel utilization in a cell within a stack may be a factor in determining the overall fuel utilization rate and system efficiency.

For example, referring again toFIG.4C, a high number of small-diameter apertures552may minimize a pressure drop and parasitic losses from the air blower providing air to the cathode recuperator500. A high number of small-diameter apertures552may also prevent and/or reduce high velocity air jets from impinging upon the stacks102directly, which may decrease damage to the stack and more smoothly distribute the incoming air into an air inlet plenum surrounding the stacks102.

Accordingly, the number, diameter, and/or spacing of the apertures552in each array554, and/or the arrangement of the arrays554, may be selected to provide desired stack characteristics, such as stack temperature profile and corresponding fuel utilization. For example, the apertures552of the air inlet baffle550may be arranged in one or more annular arrays554which are vertically separated from each other by a respective solid plate portion553which lacks any apertures. For example, the apertures552may be arranged in a first array554A, a second array554B, a third array554C, and a fourth array554D. However, the present disclosure is not limited to any particular number of arrays554. For example, each array554may include at least one row of apertures552, such as from 1 to 10 rows of apertures552, from 2 to 8 rows of apertures552, or from 2 to 5 rows of apertures552.

In some embodiments, the first and second arrays554A,554B are disposed below the annular air outlet530, while the third and fourth arrays554C,554D are disposed above the annular air outlet530. In some embodiments, the third and fourth arrays554C,554D may include more rows of apertures552than the first and second arrays554A,554B, and the third array554C may include more rows of apertures552than the fourth array554D. Accordingly, the air inlet baffle550may provide more air flow to an upper end of a stack than a lower end thereof.

The apertures552may have a diameter ranging from about 2 mm to about 20 mm, such as from about 5 mm to about 15 mm. The apertures552of each row may have a center-to-center horizontal spacing ranging from about 2 mm to about 20 mm, such as from about 5 mm to about 15 mm. The apertures552of adjacent rows may have a vertical center-to-center spacing ranging from about 2 mm to about 20 mm, such as from about 5 mm to about 14 mm.

In some embodiments, the first array554A may be disposed from about 130 mm to about 150 mm from the bottom of the air inlet baffle plate550. The second array554B may be disposed from about 240 mm to about 265 mm from the bottom of the air inlet baffle plate550. The third array554C may be disposed from about 410 mm to about 435 mm from the bottom of the air inlet baffle plate550. The fourth array554D may be disposed from about 500 mm to about 525 mm from the bottom of the air inlet baffle plate550.

Initial column/stack fuel distribution (CFD) modeling predicts that a linear temperature profile with a difference of about 20° C., with hotter temperatures at the bottom than at the top of the stack or column, would provide improved fuel delivery uniformity. In order to provide a high fuel cell fuel utilization rate, low cell-to-cell fuel utilization rate variations, and a high overall system efficiency, the maximum fuel utilization rate in any cell in a stack should preferably be maintained within about 1%, of the average stack fuel utilization rate. The air inlet baffle may be designed in order to obtain stack temperature profiles having a slight negative slope in the vertical direction (e.g., from the bottom to the top of the stack), to thereby provide an improved vertical fuel distribution along a stack.

For example, a larger volume of apertures552may be located in the upper portion of the air inlet baffle than in the lower portion of the air inlet baffle550such that a larger amount of the heated air is provided to an upper portion of the stack102located above the annular air outlet530than to a lower portion of the stack102located below the annular air outlet530, and such that the upper portion of the stack102is maintained at a lower temperature than the lower portion of the stack102and a middle portion of the stack102located at the level of the annular air outlet530. Furthermore, the lower portion of the stack102may be maintained at a lower temperature than a middle portion of the stack102located at the level of the annular air outlet530.

FIG.6is a graph showing average vertical temperature profiles for beginning-of-life (BOL) stacks operated at 51 Amps, when used in a fuel cell system including an air inlet baffle as shown inFIG.4C, and a predicted vertical temperature profile based on an optimal cell fuel distribution (CFD).

Referring toFIG.6, each tested stack included 256 sequentially numbered fuel cells, with cell1being disposed at the bottom of the stack and cell256disposed on the at the top of the stack. The temperatures of cells1through about cell32may gradually increase, such that cell1has the lowest temperature and cell32has the highest temperature. The temperatures of cells33-224may gradually decrease at a relatively constant rate, with cell33having the highest temperature and cell224having the lowest temperature, such that the vertical temperature gradient from cells33to224is has substantially linear, negative slope. The air inlet baffle plate was shown to provide a vertical stack temperature profile that closely matches the predicted temperature profile. As such, the air inlet baffle plate provides improved fuel distribution.

FIG.7is a graph showing the average vertical fuel utilization profile of the stacks tested under the 51 Amp BOL operating condition. Referring toFIG.7, the graph demonstrates that the maximum fuel utilization cells in the stacks was 91%, which is within 1% of the average stack fuel utilization of 90%. Thus, the air inlet baffle design was shown to maintain a tight vertical fuel utilization spread, as well as a tight thermal distribution.

FIG.8is a graph showing average vertical temperature profiles for beginning-of-life (BOL) stacks operated at 51 Amps, and for middle of life (MOL) stacks operated 66 Amps (e.g., degraded cell conditions), when used in a fuel cell system including an air inlet baffle as shown inFIG.4C. As can be seen inFIG.6, the air inlet baffle maintains a tight vertical thermal spread at higher currents and under degraded cell conditions. In addition, although the thermal profile shifted to lower temperatures for 66 Amp MOL operation, the slope and the nature of the temperature profile closely matches that of the 51 Amp BOL profile, and thus, is indicative of improved fuel distribution.

Fuel cell systems of the embodiments of the present disclosure are designed to reduce greenhouse gas emissions and have a positive impact on the climate.