Operation of a fuel cell stack to prevent low oxygen concentrations in a surrounding enclosed space

A method of operating a fuel cell stack that powers a vehicle includes determining when the vehicle is in a non-moving state, calculating an O2 concentration over time of an assumed enclosed space while the vehicle is in the non-moving state, establishing a set of O2 concentration concern levels that includes a first O2 concentration concern level being less than a standard atmospheric O2 concentration and a second O2 concentration concern level being less than the first O2 concentration concern level, comparing the O2 concentration of the assumed enclosed space over time with the set of O2 concentration concern levels, and operating the fuel cell stack without restriction when the vehicle is in the non-moving state so long as the O2 concentration of the assumed enclosed space remains greater than the first O2 concentration concern level.

INTRODUCTION

The present disclosure relates to operating a fuel cell stack (FCS) for a vehicle that may be enclosed by a surrounding structure such as a closed garage or other confined space. More specifically, the present disclosure provides methods to operate the FCS according to a conditional operating mode that assumes the vehicle is in an enclosed space when certain operating conditions of the vehicle are met. The conditional operating mode is designed so that, if the vehicle is actually contained within an enclosed space, the operation of the FCS will be modified so that the FCS does not overly deplete the available oxygen within that space beyond an acceptable level. The conditional operating mode also seeks to avoid unnecessary modifications to the operation of the FCS when the vehicle is not actually in an enclosed space but, nonetheless, the conditional operating mode is triggered.

A proton-exchange membrane (PEM) fuel cell is an electro-chemical device that includes a membrane-electrode-assembly having an anode catalyst layer and a cathode catalyst layer disposed on opposite sides of a proton-conducting solid polymer electrolyte. The anode catalyst layer receives hydrogen gas and the cathode catalyst layer receives oxygen or air. The hydrogen gas is dissociated at the anode catalyst layer to generate free protons and electrons. The protons migrate through the electrolyte and the electrons are directed through a load to perform work. The protons and electrode eventually reach the cathode catalyst layer where they react with oxygen to generate water. A FCS includes a plurality of similar PEM fuel cells that are separated by bipolar plates and connected to common supplies of hydrogen gas and oxygen or air.

The cathode catalyst layers of the FCS are supplied with oxygen from the surrounding ambient environment and consume that oxygen as needed to support the on-going operation of the FCS. If the vehicle is in an enclosed space when the FCS is running—such as when the vehicle is running in a closed garage to heat the passenger compartment—the amount of available oxygen within the enclosed space may be depleted faster than it can be replenished by the exchange of air from outside the enclosed space to inside the enclosed space. As such, under these circumstances, the oxygen concentration within the enclosed space may begin to drop. A conditional operating mode for a FCS is therefore needed that can address the issue of a falling oxygen concentration within an enclosed space whenever certain operating conditions of the vehicle suggest that the vehicle could be in an enclosed space without, of course, unnecessarily disrupting operation of the FCS when the vehicle is assumed to be, but is not actually in, such an enclosed space.

SUMMARY

A method of operating a fuel cell stack according to one embodiment may include several steps. One step involves determining when a vehicle that is powered by the fuel cell stack is in a non-moving state. In another step, an O2concentration of an assumed enclosed space is calculated over time while the vehicle is in the non-moving state. In yet another step, a set of O2concentration concern levels is established that includes a first O2concentration concern level being less than a standard atmospheric O2concentration and a second O2concentration concern level being less than the first O2concentration concern level. In still another step, the fuel cell stack is operated without restriction when the vehicle is in the non-moving state so long as the O2concentration of the assumed enclosed space remains greater than the first O2concentration concern level.

The method of the aforementioned embodiment may include several steps or be further defined. For example, the step of determining when the vehicle that is powered by the fuel cell stack is in a non-moving state may include determining that a speed of the vehicle is less than or equal to five kilometers/hour. As another example, the step of determining when the vehicle that is powered by a fuel cell stack is in a non-moving state may include determining that the vehicle is stationary. And, in yet another example, the step of determining when the vehicle that is powered by the fuel cell stack is in a non-moving state may include determining that the vehicle is stationary and that GPS coordinates of the vehicle indicate that the vehicle is not on a road.

Additionally, the step of calculating the O2concentration of the assumed enclosed space over time may include setting the O2concentration of the assumed enclosed space at standard atmospheric O2concentration when the vehicle is first determined to be in the non-moving state and thereafter adjusting the O2concentration of the assumed enclosed space based on an amount of O2consumed by the fuel cell stack over time and an amount of O2replenished to the assumed enclosed space over time. The amount of O2consumed by the fuel cell stack may include an amount of O2consumed due to generating a current of the fuel cell stack, an amount of O2consumed due to cathode catalytic heating (CCH), and an amount of O2consumed due to stack voltage recovery (SVR), and the amount of O2replenished to the enclosed space may be based on 0.03 air exchanges/hour.

Still further, the first O2concentration concern level may be less than 21 mol % and greater than 19 mol % and, separately, the second O2concentration concern level may be less than 20 mol % and greater than 18 mol %. More narrowly, the first O2concentration concern level may be 20 mol % and the second O2concentration concern level may be 19 mol %.

The step of operating the fuel cell stack without restriction in the aforementioned method may include operating the fuel cell stack with CCH and SVR processes enabled. Moreover, the aforementioned method may further comprise the additional step of operating the FCS in a low-power state when the O2concentration of the assumed enclosed space is equal to or less than the first O2concentration concern level yet greater than the second O2concentration concern level. The aforementioned method may also further comprise the step of shutting down the fuel cell stack when the O2concentration of the assumed enclosed space is equal to or less than the second O2concentration concern level.

A method of operating a fuel cell stack according to another embodiment may include several steps. One step involves determining when a vehicle that is powered by the fuel cell stack is in a non-moving state. In another step, an O2concentration of an assumed enclosed space is calculated over time while the vehicle is in the non-moving state. In yet another step, the O2concentration of the assumed enclosed space is compared over time with a set of O2concentration concern levels that includes a first O2concentration concern level and a second O2concentration concern level. The first O2concentration concern level is less than a standard atmospheric O2concentration and the second O2concentration concern level is less than the first O2concentration concern level. In still another step, the fuel cell stack is operated when the vehicle is in the non-moving state according to a conditional operating mode. The conditional operating mode includes (1) operating the fuel cell stack without restriction so long as the O2concentration of the assumed enclosed space remains greater than the first O2concentration concern level; (2) operating the fuel cell stack in a low-power state when the O2concentration of the assumed enclosed space is equal to or less than the first O2concentration concern level yet greater than the second O2concentration concern level; and (3) shutting down the fuel cell stack when the O2concentration of the assumed enclosed space is equal to or less than the second O2concentration concern level.

The method of the aforementioned embodiment may include several steps or be further defined. For example, the step of determining when the vehicle that is powered by the fuel cell stack is in a non-moving state may include determining that the vehicle is stationary. As another step, the step of determining when the vehicle that is powered by the fuel cell stack is in a non-moving state may include determining that the vehicle is stationary and that GPS coordinates of the vehicle indicate that the vehicle is not on a road.

Additionally, the step of calculating the O2concentration of the assumed enclosed space over time includes setting the O2concentration of the assumed enclosed space at standard atmospheric O2concentration when the vehicle is first determined to be in a non-moving state and thereafter adjusting the O2concentration of the assumed enclosed space based on an amount of O2consumed by the fuel cell stack over time and an amount of O2replenished to the assumed enclosed space over time. The amount of O2consumed by the fuel cell stack includes an amount of O2consumed due to generating a current of the fuel cell stack, an amount of O2consumed due to cathode catalytic heating (CCH), and an amount of O2consumed due to SVR, and the amount of O2replenished to the enclosed space is based on 0.03 air exchanges/hour

Still further, the first O2concentration concern level may be less than 21 mol % and greater than 19 mol %, and the second O2concentration concern level may be less than 20 mol % and greater than 18 mol %. Moreover, the step of operating the fuel cell stack in the low-power state may include disabling CCH and SVR of the fuel cell stack.

A method of operating a fuel cell stack according to yet another embodiment may include several steps. One step involves determining when a vehicle that is powered by a fuel cell stack is in a non-moving state. In another step, an O2concentration of an assumed enclosed space that encompasses the vehicle is calculated over time while the vehicle is in the non-moving state. In yet another step, the O2concentration of the assumed enclosed space is compared over time with a set of O2concentration concern levels that includes a first O2concentration concern level and a second O2concentration concern level. The first O2concentration concern level is less than 21 mol % and greater than 19 mol % and the second O2concentration concern level is less than 20 mol % and greater than 18 mol %. In another step, the fuel cell stack is operated when the vehicle is in the non-moving state according to a conditional operating mode. The conditional operating mode includes (1) operating the fuel cell stack without restriction so long as the O2concentration of the assumed enclosed space remains greater than the first O2concentration concern level; (2) idling the fuel cell stack when the O2concentration of the assumed enclosed space is equal to or less than the first O2concentration concern level yet greater than the second O2concentration concern level; and (3) shutting down the fuel cell stack when the O2concentration of the assumed enclosed space is equal to or less than the second O2concentration concern level.

DETAILED DESCRIPTION

Hydrogen is an attractive fuel for operating a vehicle because it is clean and can be used to efficiently produce electricity in a fuel cell. A number of individual PEM fuel cells that consume hydrogen as part of an electro-chemical reaction that produces electrical current are typically combined in a fuel cell stack (FCS) to generate the desired power for operating a vehicle. For example, a typical FCS for a vehicle may have two hundred or more stacked PEM fuel cells. The FCS typically receives a flow of hydrogen gas and a flow of an oxidant gas such as air or oxygen, and then distributes each of those reactant gasses to the anode catalyst layers and the cathode catalyst layers, respectively, of the various PEM fuel cells by way of bipolar plates that separate the PEM fuel cells. The FCS thus consumes both hydrogen and oxygen during normal operation.

In some types of enclosed spaces (e.g., a garage), oxygen from the air in the local environment may be consumed by the FCS faster than it is replenished. To address this issue, a method that includes a conditional operating mode of the FCS may be implemented when a vehicle10that is powered by a FCS12is in a non-moving state, as shown schematically inFIG. 1. Specifically, and as shown in the diagram ofFIG. 1, the conditional operating mode calls for the vehicle10to be treated as if it is contained within an enclosed spaced, referred to herein as an “assumed enclosed space” and identified by reference numeral14, whenever the vehicle10is determined to be in a non-moving state. The assumed enclosed space14is thus a virtual enclosure having a volume that may or may not be large enough to encompass the vehicle10. This space14is used to model the amount of O2in the volume of the assumed enclosed space14based on the operation of the FCS12and the pressure and temperature of the assumed enclosed space14, which can be estimated, measured, or simply assigned. In that regard, the assumed enclosed space14and the calculated amount of O2within that space14is designed to conservatively model what would happen if the vehicle10is actually contained within an enclosed space, such as a garage, even though it may not always be, and to take responsive action based on the O2concentration calculated within the assumed enclosed space14to help ensure that the O2concentration in an actual enclosed space is not excessively depleted.

FIG. 1schematically illustrates how oxygen may be consumed and replenished in the assumed enclosed space14, which may be designed to be just large enough to surround the vehicle10in accordance with the definition of a “small garage” as set forth in SAE J 2578, 3rd Edition (August 2014). The SAE J 2578, 3rd Edition (August 2014) (“the SAE J 2578 standard”) is incorporated herein by reference in its entirety. The size and volume of the assumed enclosed space14may vary depending on the size of the vehicle10. Other standards (e.g., ISO standard, JIS standard, local regulation, etc.) may also be used in lieu of the SAE J 2578 standard to define the size of the assumed enclosed space14, if desired, or the assumed enclosed space14may be an approximation of an actual surrounding enclosure whose dimensions can be assessed and estimated using vision systems or LIDAR. Still further, the assumed enclosed space14may simply be predefined. In many instances, however, regardless of how the assumed enclosed space14and its volume are ascertained, the assumed enclosed space14may have a volume that ranges from 5 m3to 200 m3or, more narrowly, from 20 m3to 50 m3. Additionally, to allow for the amount and concentration of O2to be modeled within the assumed enclosed space14, a temperature and pressure within the space14may be calibrated based on measured ambient atmospheric conditions, or those may be assigned. For instance, in one implementation, the temperature and pressure of the assumed enclosed space may be selected to be 60° C. and 1 atmosphere for simplification.

When the vehicle10containing the FCS12is in the non-moving state, the FCS12may consume oxygen in several ways, which can reduce the O2concentration in the assumed enclosed space14. In a first process16, the FCS12consumes O2from the volume of the assumed enclosed space14while simultaneously consuming H2to generate an electric current. The general cathode half-reaction for consuming O2and generating water, the general anode half-reaction for consuming H2and generating a flow of electrons, and the overall reaction of the fuel cells in the FCS12are depicted below:
2H2→H++4e−Anode:
O2+4H++4e−→2H2O  Cathode:
2H2+O2→2H2O  Overall:

To that end, the molar flow of O2({dot over (n)}O2) required to support the production of a given electrical current (I) by the FCS12for operation of the various vehicle systems can be calculated continuously with time while the vehicle10is in the non-moving state through the following equation:

In a second process18, the FCS12consumes O2from the volume of the assumed enclosed space14to support cathode catalytic heating (CCH) of the FCS12. During CCH, H2is routed around the polymer electrolytes and delivered to the cathode catalyst layers of the FCS12along with O2to facilitate the combustion of the H2. The heat generated at the cathode catalyst layers as a result of combusting H2is then used to heat the FCS12to its optimal operating temperature range and to also heat the passenger cabin of the vehicle10, if desired. CCH is thus useful when starting the vehicle10, especially at cold or freezing temperatures after the vehicle10has been in a non-operational state for an extended period. The molar flow rate of O2({dot over (n)}O2) required to support CCH can be calculated continuously with time while the vehicle10is in the non-moving state through the following equation:

In a third process20, the FCS12consumes O2from the volume of the assumed enclosed space14to support stack voltage recovery (SVR) of the FCS12. During SVR operation, the FCS12runs with a low voltage in order to remove contaminant build up and/or impurities from the catalyst layers and/or the solid polymer electrolytes within the stack (e.g., sulfate build-up). Subsequently, water washes away the contaminants. A SVR cycle is commonly implemented during vehicle start up, and the molar flow of O2({dot over (n)}O2) required to support a SVR cycle can be calculated continuously with time while the vehicle10is in the non-moving using the same equation as set forth above for drawing electrical current (I).

Other factors may also influence the amount of O2present within the assumed enclosed space14besides the direct consumption of O2. For example, in some cases, the O2concentration in the assumed enclosed space14can be further reduced based on the output of unreacted H2from the FCS12, which can dilute the O2and lower its concentration. The effect of O2dilution is generally negligible when compared to the direct consumption of O2through stack current generation, CCH, and SVR, and for that reason it can usually be ignored when calculating the O2of the assumed enclosed space14over time, although provisions can be made to take O2dilution into account if desired as part of the overall method.

The assumed enclosed space14is also replenished by air at an air/exchange rate22from outside of the assumed enclosed space14. The air/exchange rate22may be set to any value to adjust the modeling of the O2concentration within the assumed enclosed space14as desired. In one embodiment, according to the incorporated SAE J 2578 standard, the air/exchange rate22may be 0.03 air exchanges/hour, meaning that 3% of the air by volume in a designated space is replenished each hour. Of course, the air/exchange rate22is calibratable and may be set higher or lower than 0.03 air exchanges/hour. By knowing the volume, temperature, pressure, and original O2concentration of the assumed enclosed space14, as well as the amount of O2consumed by processes16,18,20and replenished by the air/exchange rate22, the amount and concentration of O2in the assumed enclosed space14can be calculated or modeled over time during the time the vehicle10is in the non-moving state and the FCS12is operating using the Ideal Gas Law or some other appropriate equation or algorithm. This information can be used to inform the conditional operating mode of the FCS12and to trigger certain actions with respect to the operation of the FCS12when the modeled O2concentration of the assumed enclosed space14eclipses certain predetermined O2concentration concern levels.

With reference, for the moment, toFIG. 2, a graph is shown in which several different operating scenarios of the FCS12are depicted with the y-axis representing a calculated O2concentration in mole percentage of the assumed enclosed space14and the x-axis representing time in seconds. The volume of assumed enclosed space14is that established in the SAE J 2578 standard. Additionally, the air/exchange rate22is set at 0.03 air exchanges/hour, the temperature and pressure within the assumed enclosed space14is set to be 60° C. and 1 atmosphere, respectively, and the O2concentration of the assumed enclosed space14is set at the standard atmospheric O2concentration of 21 mol % at the time the vehicle10that includes the FCS12is first determined to be in the non-moving state. Each of the current generating process16, the CCH process18, and the SVR process20are deemed to consume O2from the assumed enclosed space14as described above. The graph here is meant to show how certain operating scenarios of the FCS12can deplete the modeled O2concentration within the assumed enclosed space14and how quickly such depletion can occur.

Four specific operating scenarios of the FCS12are illustrated inFIG. 2. In a first scenario, identified by reference numeral30, a 200 second warm-up cycle32is performed using the CCH process18, followed by an idle period34of greater than 1200 seconds without running the CCH or SVR processes18,20. In this scenario30, the O2concentration of the assumed enclosed space14dropped by approximately 0.7 mol % during the warm-up cycle32, but then decreased only slightly by another 0.1 mol % to 0.2 mol % over the lengthier idle period34. In a second scenario, identified by reference numeral36, a 200 second warm-up cycle38is performed in the same way as the first scenario30, followed by an idle period40of 1200 seconds in which the CCH process18was used to provide 8 kW of cabin heating. In this scenario36, after 1400 seconds, the O2concentration of the assumed enclosed space14dropped by over 2.5 mol %.

In a third scenario, identified by reference numeral42, a 200 second warm-up cycle44is performed in the same way as the first and second scenarios30,36, followed by a 30 second SVR cycle46and then an idle period48of 820 seconds in which the CCH process18was used to provide 8 kW of cabin heating. Here, after 1100 seconds, O2concentration of the assumed enclosed space14dropped by over 3.0 mol %. Finally, in a fourth scenario, identified by reference numeral50, two 30 second SVR cycles52are performed followed by an idle period54of greater than 1100 seconds without running the CCH or SVR processes18,20. In this scenario50, the O2concentration of the assumed enclosed space14dropped by approximately 0.5 mol % during each SVR cycle20, but then decreased only slightly by another 0.1 mol % to 0.2 mol % over the lengthier idle period54.

In light of the various ways the FCS12may consume O2and actually affect the O2concentration within the assumed enclosed space14over time, the conditional operating mode relies on a set of programmed O2concentration concern levels to ensure that the calculated O2concentration of the space14does not drop too excessively. But first, in order to trigger the conditional operating mode, the vehicle10that is powered by the FCS12is first determined to be in a non-moving state. This can be accomplished by observing certain available parameters of the vehicle10, including its speed and/or location (using GPS coordinates), as well as utilizing proximity sensor(s), vision systems, and/or LIDAR to observe the surroundings of the vehicle10, to name a few options. After determining that the vehicle is in the non-moving state, an O2concentration of the assumed enclosed space14is calculated over time, as discussed above in connection withFIGS. 1-2, while the vehicle10is in the non-moving state. The calculated O2concentration of the assumed enclosed space14is then compared over time to a set of established O2concentration concern levels. Based on this ongoing comparison, the conditional operating mode may restrict certain operations of the FCS12, as will be further explained below.

Determining whether the vehicle10is in a non-moving state can be carried out by considering the speed of the vehicle10. For example, and referring now toFIG. 3, one approach60for determining when the vehicle10is in a non-moving state is shown in a flow diagram. The approach60starts in box62. In box64, the approach60involves determining whether the vehicle is moving at a speed indicative of a non-moving state. In one embodiment, a speed of less than or equal to 5 kilometers/hour may be programmed to be indicative of a non-moving state. In another narrower embodiment, the vehicle10may only be considered to be in a non-moving state when the vehicle is stationary (i.e., a speed of 0 kilometers/hour). If the speed condition for a non-moving state is not met, the approach60proceeds through arrow66to box68where the vehicle10is determined to not be a non-moving state and the conditional operating mode is therefore not initiated. If the speed condition for a non-moving state is met, the approach proceeds through arrow70to box72where the vehicle10is determined to be in a non-moving state and the conditional operating approach is initiated until the vehicle10in no longer in the non-moving state.

Another more robust approach74for determining when the vehicle10is in a non-moving state, which is shown inFIG. 4as a flow diagram, may be carried out by considering the speed and position of the vehicle10. This approach starts in box76. In box78, the approach involves determining whether the vehicle is moving at a speed indicative of a non-moving state in the same way as previously described in connection withFIG. 3. If the speed condition for a non-moving state is not met, the approach74proceeds through arrow80to box82where the vehicle10is determined to not be a non-moving state and the conditional operating mode is therefore not initiated. If, however, the speed condition for a non-moving state is met, the approach74proceeds through arrow84to box86where GPS coordinates of the vehicle10are referenced to ascertain whether the vehicle10is on a road (e.g., a highway). If the vehicle10is on a road, the approach proceeds through arrow88to box90where the vehicle10is determined to not be a non-moving state and the conditional operating mode is therefore not initiated. If the vehicle10is not on a road, the approach proceeds through arrow92to box94where the vehicle10is determined to be in a non-moving state and the conditional operating approach is initiated until the vehicle10in no longer in the non-moving state.

If the vehicle is determined to be in a non-moving state by either approach60,74described above, or some other approach, the O2concentration of the assumed enclosed space14is calculated over time while the vehicle10remains in the non-moving state. This may entail initially setting the O2concentration of the assumed enclosed space14at the standard atmospheric O2concentration of 21 mol % at the time the vehicle10that includes the FCS12is first determined to be in the non-moving state and then adjusting the O2concentration of the assumed enclosed space14based on the amount of O2consumed by the FCS12over time and the amount of O2replenished to the assumed enclosed space14over time. The amount of O2consumed by the FCS12over time and an amount of O2replenished to the assumed enclosed space14over time can be easily calculated using the O2consumption processes16,18,20and the air/exchange rate22discussed above, respectively, in connection withFIGS. 1-2. And by additionally knowing the volume, temperature, and pressure of assumed enclosed space14—each of which can be specified in a variety of ways as explained above—the O2concentration within the assumed enclosed space14can be continuously calculated.

Referring now toFIG. 5, the calculated O2concentration within the assumed enclosed space14is compared over time against a set of established O2concentration concern levels so long as the vehicle10remains in the non-moving state. Here, in this figure, the calculated O2concentration (y-axis) is identified by reference numeral96and is plotted against time in seconds (x-axis). The set of O2concentration concern levels are also shown in this figure and includes a first O2concentration concern level98and a second O2concentration concern level100. The first O2concentration concern level98is less than the standard atmospheric O2concentration (i.e., less than 21%) and the second O2concentration concern level100is less than the first O2concentration concern level98. For example, the first O2concentration concern level98may be less than 21 mol % and greater than 19 mol %, and the second O2concentration concern level100may be less than 20 mol % and greater than 18 mol %. In one particular example, as shown, the first O2concentration concern level98may be set at 20 mol % and the second O2concentration concern level100may be set at 19 mol %.

The conditional operating mode of the FCS12performs its function based on the comparison of the calculated O2concentration96within the assumed enclosed space14against the set of established O2concentration concern levels. So long as the calculated O2concentration96within the assumed enclosed space14remains above the first O2concentration concern level98, which is the case between 0 seconds and approximately 340 seconds inFIG. 5, the FCS12can operate without restriction, meaning that all of its oxygen consuming processes16,18,20are enabled and can be operated as called-upon either individually or in combination to support the demands of the vehicle10. In particular, the the current generating process16can run supply any necessary current (I) required by the vehicle10, warm-up and cabin heating as enabled by the CCH process18can be performed, and cycles of the SVR process20can be conducted however desired.

If at some point the calculated O2concentration96reaches the first O2concentration concern level98, which occurs at approximately 340 seconds inFIG. 5, the FCS12is restricted to operating in a low-power state in which the FCS12outputs no more than 15% of its maximum power output in order to slow the rate at which the calculated O2concentration96is dropping. This may entail restricting the FCS12to a maximum power output of 8 kW. In one particular example of a low-power state, the FCS12may be idled. When idled, the FCS12supplies current (I) to power its associated prime mover, typically an electric motor that may or may not be coupled to an internal combustion engine, and its accessories without any applied loads. Essentially, the current generating process16is operational so that the FCS12can supply enough current (I) to power the prime mover while the prime mover is not coupled to the drivetrain and the foot pedal is not depressed. Each of the CCH process18and the SVR process20may also be disabled. Running the FCS12in the low-power state, particular in idle mode with the CCH and SVR processes18,20disabled, results in a fairly constant and minimal reduction in the calculated O2concentration96over time and allows the calculated O2concentration96to remain above the second O2concentration concern level100for an extended period. For example, in the example ofFIG. 5, the calculated O2concentration96will not reach the second O2concentration concern level100for approximately another 9,000 seconds (˜2.6 hours or 9,350 seconds since the vehicle entered the non-moving state) when the vehicle10is idled and the CCH and SVR processes18,20are disabled.

Should the calculated O2concentration96reach the second O2concentration concern level100, which occurs at approximately 9,350 seconds in the example ofFIG. 5as mentioned above, the FCS12is shut down to halt all of the oxygen consuming processes16,18,20and thus prevent any further decrease in the calculated O2concentration96. In that regard, since only the air/exchange rate22is affecting the amount O2in the assumed enclosed space14, the calculated O2concentration96should begin to rise until it eventually arrives at the standard atmospheric O2concentration of 21 mol %. By operating the FCS12in a low-power state when the calculated O2concentration96is equal to or less than the first O2concentration concern level98, yet greater than the second O2concentration concern level100, and shutting down the FCS12when the calculated O2concentration96is equal to or less than the second O2concentration concern level100, the conditional operating mode of the FCS12provides an orderly and controlled procedure for ensuring the FCS12will not deplete the available O2too extensively in an actual enclosed space such as a garage, if and when the vehicle10is in such a space, while at the same time not burdening the use of the FCS12with nuisance actions when the vehicle10is not in an actual enclosed space but is nonetheless in a non-moving state.

The capacity of the conditional operational mode of the FCS12to avoid nuisance actions—most notably unnecessary shut downs of the FCS12—is demonstrated inFIG. 6. Here, the calculated O2concentration96of the assumed enclosed space14is plotted against time in circumstances when the vehicle10has been determined to be in a non-moving state, although, in actuality, the vehicle10is not parked in an actual enclosed space but instead is stuck in a traffic jam where a shutdown of the FCS12is not desired. And since the program that administers the overall method including the conditional operating mode of the FCS12may be unable to distinguish between being parked in an actual garage or being stuck in a traffic jam, as the speed of the vehicle10in both instances may be 0 km/hour, the FCS12is subjected to the conditional operating mode by default even though the rationale behind implementing the conditional operating mode is not present.

As can be seen, and still referring toFIG. 6, the vehicle10is determined to be in a non-moving state at about 60 seconds due to traffic congestion, which is more likely to occur if the determination of a non-moving state is based on the speed of the vehicle10as described in connection withFIG. 3. The FCS12operates without restriction while stuck in traffic form approximately another 190 seconds (just over three minutes) until the calculated O2concentration96of the assumed enclosed space14reaches the first O2concentration concern level98, which has been set at 20 mol %. At this point, and with the vehicle10still in the non-moving state due to traffic congestion, the FCS12is restricted to operating in the low-power state, and is preferably idled with the CCH and SVR processes18,20disabled, until such time that the vehicle10moves to negate its status as being in a non-moving state, which occurs after about another 400 seconds. Indeed, the idling of the FCS12during this 400 second period (just under 7 minutes) slowed the rate of decrease of the calculated O2concentration96to the extent that the FCS12was nowhere close to being shut down on account of the calculated O2concentration96reaching the second O2concentration concern level100, which has been set at 19 mol %. In fact, the FCS12could have idled for at least a few hours before the calculated O2concentration96approached the second O2concentration concern level100. Consequently, the use of the first O2concentration concern level98to trigger the restrictive operation of the FCS12in the low-power state should prevent nuisance shut down of the FCS12as the length of time the FCS12can operate in such a state before triggering a shutdown will almost assuredly outlast any amount of time the vehicle10may be in a non-moving state due to a traffic jam or otherwise.

The various operations needed to administer the overall method including the conditional operating mode of the FCS stack12can be programmed into a standard vehicle electronic control unit or another control system that controls the operation of the vehicle and/or the FCS12. Such programming, for example, may follow the flow diagram illustrated inFIG. 7. In the illustrated flow diagram, a program that performs the overall method starts in box102. In box104, the program calculates the volume of the assumed enclosed space14to be used for carrying out the method. Subsequently, the program determines in box106if the vehicle10is in a non-moving state, as discussed above, for instance, in connection withFIGS. 3-4. If the vehicle10is determined not to be in a non-moving state, the program proceeds through arrow108to box110. In box110, the program resets the O2concentration of the assumed enclosed space14to the standard atmospheric concentration of 21 mol %, thus avoiding the conditional operating mode, and then cycles through boxes106and110until the vehicle10is determined to be in a non-moving state.

If the vehicle10is determined to be in a non-moving state in box106, the program follows arrow112to box114where the calculated O2concentration96of the assumed enclosed space14is computed based on a series of sub-calculations including calculating the consumption of O2in the assumed enclosed space14due to the current generating process16, box116, calculating the consumption of O2in the assumed enclosed space14due to the CCH process18, box118, calculating the consumption of O2in the assumed enclosed space14due to the SVR process20, box120, and calculating the replenishment of O2in the assumed enclosed space14due to the air/exchange rate22, box122, all of which may be computed using a selected temperature (e.g., 60° C.) and pressure (e.g., 1 atmosphere) of the assumed enclosed space14and an initial O2concentration that equals the standard atmospheric O2concentration (e.g., 21 mol %). The program then follows arrow124to box126where the calculated O2concentration96of the assumed enclosed space14is compared against the first O2concentration concern level98. If the calculated O2concentration96of the assumed enclosed space14is greater than the first O2concentration concern level98, the program proceeds through arrow128and continues to cycle through boxes106,114, and126, thus operating the FCS12without restriction, until the program indicates in box124that the calculated O2concentration96has reached the first O2concentration concern level98.

When the calculated O2concentration96has reached the first O2concentration concern level98, as indicated in box124, the program proceeds through arrow130to box132. In box132, the FCS12operates in a low-power state as described above, which may include idling the FCS12and disabling both the CCH process18and the SVR process120. The program then proceeds through arrow134to box136where the calculated O2concentration96is compared against the second O2concentration concern level100. If the calculated O2concentration96of the assumed enclosed space14is greater than the second O2concentration concern level100, the program proceeds through arrow138and continues to cycle through boxes106,114,126, and136, thus continuing to restrict operation of the FCS12to the low-power state, until the program indicates in box136that the calculated O2concentration96has reached the second O2concentration concern level100. When the calculated O2concentration96has reached the second O2concentration concern level100, as indicated in box136, the program proceeds through arrow140to box142. In box142, the FCS12is shut down. Of course, if the program at any time determines in box106that the vehicle10is no longer in a non-moving state and the FCS12has not been shut down, full unrestricted operation of the FCS12is restored and the calculated O2concentration96of the assumed enclosed space14is reset to the standard atmospheric concentration of 21 mol %.

The system and method(s) discussed herein provide advantages over simple timing systems that take a particular action (e.g., shut off the FCS) after a set time. Computing the calculated O2concentration of the assumed enclosed space14over time and comparing that value against the set of O2concentration concern levels98,100corrective actions to be taken with respect to the operation of the FCS12that would not be available with a simple countdown-style, timing system. Additionally, a countdown-style, timing system can result in nuisance shutdowns of the FCS12that the presently disclosed method can avoid.

The above description of preferred exemplary embodiments and specific examples are merely descriptive in nature; they are not intended to limit the scope of the claims that follow. Each of the terms used in the appended claims should be given its ordinary and customary meaning unless specifically and unambiguously stated otherwise in the specification.