DE102020119137A1 - Method for the model-based humidity control of a fuel cell device, fuel cell device and fuel cell vehicle - Google Patents

Abstract

The invention relates to a method for model-based humidity control of a fuel cell having a fuel cell stack, comprising the steps: - measuring the air mass flow at the system inlet before a compressor (4), - measuring the water loading of the ambient air Xamb, - calculating an air mass balance, - determining a mass flow distribution between a humidifier bypass (8) and a humidifier (3), wherein the bypass proportion WBYP is determined depending on the position of a first control flap (9) and a second control flap (10), - determination of the mass transfer coefficient β of a humidifier characteristic map, - calculation the average humidifier temperature and determination of the efficiency of the humidifier (3), - calculation of the molar water concentration of the supply air at the exit from the humidifier (3), - measurement of the temperature T2 at a cathode inlet (11), - calculation of the water concentration at the cathode inlet (11), - Calculation of the partial pressure and thus de s saturation vapor pressure at a dew point temperature of the water at the cathode inlet (11), - conversion of the vapor pressure into a dew point temperature using an inverted vapor pressure curve, - use of the dew point temperature as a controlled variable. The invention also relates to a fuel cell device and a fuel cell fuel cell vehicle.

Description

• - Messen des Luftmassenstroms am Systemeintritt vor einem Verdichter,
• - Messen der Wasserbeladung der Umgebungsluft X_amb
• - Berechnung einer Luftmassenbilanz anhand der Gleichung ${\dot{\text{m}}}_{\text{air}\text{,dry}}=\frac{{\dot{\text{m}}}_{\text{air}\text{,wet}\text{,measured}}}{1+{\text{X}}_{\text{amb}}},$
  
• - Ermittlung einer Massenstromaufteilung zwischen einem Bypass und einem Befeuchter,
• - Bestimmung des Stoffdurchgangskoeffizienten β eines Befeuchter-Kennfelds mittels der Gleichung $\mathrm{\beta =}\frac{{\text{D}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{exp}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right],$
  
• - Berechnung der mittleren Befeuchtertemperatur anhand der Gleichung ${\text{T}}_{\text{m}}=\frac{\text{T1}+\text{T3}}{2}$
  
  und Bestimmung des Wirkungsgrads des Befeuchters,
• - Berechnung der molaren Wasserkonzentration der Zuluft beim Austritt aus dem Befeuchter anhand der Gleichung c_D,out = c_D,in + η(c_w,in - c_D,in),
• - Messen der Temperatur T₂ an einem Kathodeneintritt
• - Berechnung der Wasserkonzentration an dem Kathodeneintritt anhand der Gleichung C_FC,in = C_D,in ∗ W_BYP + c_D,out(1 - w_BYP),
• - Berechnung des Partialdrucks und somit des Sättigungsdampfdrucks bei einer Taupunkttemperatur des Wassers am Kathodeneintritt anhand der Gleichung p_w,Fc,in = C_D,FC,inR ∗ T_stackin = P_s(T_DP),
• - Umrechnung des Dampfdrucks in eine Taupunkttemperatur anhand einer invertierten Dampfdruckkurve,
• - Nutzung der Taupunkttemperatur als Regelgröße.

The invention relates to a method for the model-based humidity control of a fuel cell device, comprising the steps:

• - Measurement of the air mass flow at the system inlet in front of a compressor,
• - Measuring the water loading of the ambient _{air X amb}
• - Calculation of an air mass balance using the equation ${\dot{\text{m}}}_{\text{air}\text{,dry}}=\frac{{\dot{\text{m}}}_{\text{air}\text{,wet}\text{,measured}}}{1+{\text{X}}_{\text{amb}}},$
  
• - Determination of a mass flow distribution between a bypass and a humidifier,
• - Determination of the mass transfer coefficient β of a humidifier map using the equation $\mathrm{\beta =}\frac{{\text{<figure-callout id="0" label="D" filenames="DE102020119137A1\_0014.png" state="{{state}}">D</figure-callout>}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{ex}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right],$
  
• - Calculation of the mean humidifier temperature using the equation ${\text{T}}_{\text{m}}=\frac{\text{T1}+\text{<figure-callout id="2" label="T3" filenames="DE102020119137A1\_0014.png,DE102020119137A1\_0015.png" state="{{state}}">T3</figure-callout>}}{2}$
  
  and determination of the efficiency of the humidifier,
• - Calculation of the molar water concentration of the supply air when leaving the humidifier using the equation c _D,out = c _D,in + η(c _w,in - c _D,in ),
• - Measuring the temperature T ₂ at a cathode inlet
• - Calculation of the water concentration at the cathode _{inlet using the equation C FC,in} = C _D,in ∗ W BYP + c _D,out (1 - w _BYP ),
• - Calculation of the partial pressure and thus the saturation vapor pressure at a dew point temperature of the water at the cathode inlet using the equation p _w,Fc,in = C _D,FC,in R ∗ T _stackin = P _s (T _DP ),
• - Conversion of the vapor pressure into a dew point temperature using an inverted vapor pressure curve,
• - Use of the dew point temperature as a control variable.

The invention further relates to a fuel cell device and a fuel cell vehicle.

Fuel cell devices are used for the chemical conversion of a fuel with oxygen into water in order to generate electrical energy. For this purpose, fuel cells contain the so-called membrane electrode unit as a core component, which is a combination of a proton-conducting membrane and one electrode (anode and cathode) arranged on both sides of the membrane. In addition, gas diffusion layers can be arranged on both sides of the membrane electrode unit on the sides of the electrodes facing away from the membrane. During operation of the fuel cell device with a plurality of fuel cells combined to form a fuel cell stack, the fuel, in particular hydrogen (H ₂ ) or a hydrogen-containing gas mixture, is fed to the anode, where electrochemical oxidation of H ₂ to H ⁺ takes place with the release of electrons. ^{The protons H + are transported} from the anode compartment to the cathode compartment via the membrane, which separates the reaction compartments from one another in a gas-tight manner and insulates them electrically. The electrons provided at the anode are fed to the cathode via an electrical line. Oxygen or an oxygen-containing gas mixture is supplied to the cathode, so that a reduction of O ₂ to O ^2- takes place, taking up the electrons. At the same time, in the cathode compartment, these oxygen anions react with the protons transported across the membrane to form water.

In fuel cell devices, air with the oxygen contained therein is compressed in the cathode cycle to supply the cathode chambers of the fuel cell stack, so that relatively warm and dry compressed air is present, the humidity of which is not sufficient for use in the fuel cell stack for the membrane electrode unit. The dry air provided by the compressor for the fuel cell stack is humidified by means of a humidifier, which is generally used in order to be able to transfer the moisture to the drier medium in the case of two gaseous media with a different moisture content. In such gas/gas humidifiers, the dry air from the compressor is guided past a membrane permeable to water vapor, the other side of which is coated with the moist exhaust air from the fuel cell stack.

The amount of water supplied is regulated via a humidifier bypass line and a humidity sensor. However, the moisture sensors were not specially developed for use in a fuel cell vehicle, but for use in the industrial sector. As a result, such a sensor, together with its evaluation unit, requires a large amount of space and also causes high costs. The sensor must also be equipped with a heater that requires a supply voltage of 24 V. This voltage must be provided in the fuel cell vehicle via a voltage converter, which means that additional installation space is required and costs are incurred.

In the DE 10 2014 100 186 A1 a method for determining the relative humidity of a fuel cell system is described, the relative humidity not being determined via an independent humidity sensor, but the signals from sensors installed in the fuel cell stack or a stack-as-sensor procedure being used for the determination. A method with an algorithm for sensorless control of the relative humidity of the cathode inlet air flow in a fuel cell device is described in DE 10 2006 058 833 A1 described. In the DE 10 2009 005 647 A1 describes a method for controlling the relative humidity at the cathode inlet using both sensor input and component models to allow the cathode effluent to selectively bypass cathode effluent processing components, thereby allowing the relative humidity to be adjusted arbitrarily.

It is the object of the present invention to provide a method which makes the additional moisture sensor unnecessary. The object is also to provide an improved fuel cell device and an improved fuel cell vehicle.

This object is achieved by a method having the features of claim 1, by a fuel cell device having the features of claim 7 and by a fuel cell vehicle having the features of claim 8. Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

The method mentioned at the outset offers the advantage that it no longer regulates the cathode humidity on the basis of a humidity sensor, but rather through model-based humidity regulation. As a result, an essential prerequisite for the suitability for series production of a fuel cell vehicle is fulfilled. By using the dew point temperature as a target variable, the calculation of the relative humidity is avoided, which means that the determination of the relative humidity is no longer necessary, which is why the method is significantly more robust and simpler than previous methods. Furthermore, there is no need to install the moisture sensor, which means that more space is available for other components and costs are saved.

It is also preferred that the activation energy, which is necessary for the calculation of the mass transfer coefficient β, is determined experimentally. The use of the mass transfer coefficient β determines the state of the humidifier’s characteristic diagram and thus the transfer behavior. Therefore, there is no need to determine the water mass flow, which means that the method is easier to carry out and therefore more practical than previous methods.

Another advantage is that the efficiency of the humidifier is determined using the number-of-transfer-units method.

Furthermore, it is advantageous that with a closed system bypass, the air mass balance is calibrated with a reduced measurement inaccuracy. This procedure reduces the absolute error in the measurement, resulting in less error propagation and thus an improved result. The consequence of this is that the cathode air is humidified in an improved manner and the fuel cell device therefore operates more efficiently.

Since the molar water concentration at the humidifier inlet is determined with this method to determine the water input via the intake air, it is not necessary to determine the water mass flow via the intake air. It is therefore advantageous that the water _{loading of the ambient air X amb is} determined by a combined sensor for temperature, pressure and humidity arranged at the humidifier inlet.

It is also preferred if the bypass portion W _{BYP is determined} as a function of the position of a first control flap and a second control flap.

The advantages and effects mentioned above also apply analogously to a fuel cell device with a control device for carrying out the method mentioned above and to a fuel cell vehicle with a fuel cell device of this type.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention. Embodiments are therefore also to be regarded as included and disclosed by the invention which are not explicitly shown or explained in the figures, but which result from the explained embodiments and can be generated by means of separate combinations of features.

• 1 eine schematische Darstellung einer Brennstoffzellenvorrichtung,
• 2 eine Arrhenius-Gerade zur Bestimmung der Aktivierungsenergie,
• 3 eine vereinfachte schematische Darstellung der Brennstoffzellenvorrichtung mit dem Befeuchter und mit einem Befeuchter-Bypass, und
• 4 eine schematische Darstellung des erfindungsgemäßen Verfahrens zur modellbasierten Feuchteregelung einer Brennstoffzellenvorrichtung.

Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and with reference to the drawings. show:

• 1 a schematic representation of a fuel cell device,
• 2 an Arrhenius line to determine the activation energy,
• 3 a simplified schematic representation of the fuel cell device with the humidifier and with a humidifier bypass, and
• 4 a schematic representation of the method according to the invention for model-based humidity control of a fuel cell device.

In the 1 a fuel cell device 1 is shown schematically, this comprising a humidifier 3 for humidity regulation of a plurality of fuel cells combined in a fuel cell stack 2 .

Each of the fuel cells includes an anode, a cathode, and a proton-conductive membrane separating the anode from the cathode. The membrane is formed from an ionomer, preferably a sulfonated polytetrafluoroethylene polymer (PTFE) or a polymer of perfluorinated sulfonic acid (PFSA). Alternatively, the membrane can also be formed as a sulfonated hydrocarbon membrane.

The anode can be supplied with fuel (for example hydrogen) from a fuel tank via an anode space. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The PEM lets the protons through but is impermeable to the electrons. At the anode, for example, the reaction takes place: 2H ₂ →4H ⁺ + 4e ^- (oxidation/donation of electrons). While the protons pass through the PEM to the cathode, the electrons are conducted to the cathode or an energy storage device via an external circuit.

The cathode gas (for example oxygen or oxygen-containing air) can be supplied to the cathode via a cathode space, so that the following reaction takes place on the cathode side: O ₂ +4H ⁺ →2H ₂ O (reduction/electron acceptance).

Since several fuel cells are combined in the fuel cell stack 2, a sufficiently large quantity of cathode gas must be made available so that a large cathode gas mass flow or fresh gas flow is made available by a compressor 4, with the temperature of the cathode gas increasing sharply as a result of the compression of the cathode gas. The conditioning of the cathode gas or the fresh air gas flow, i.e. its adjustment with regard to the desired temperature and humidity in the fuel cell stack 2, takes place in the charge air cooler 7 downstream of the compressor 4 and in the humidifier 3, which causes moisture saturation of the membranes of the fuel cells to increase their efficiency, since this favors proton transport.

• - Messen des Luftmassenstroms am Systemeintritt vor einem Verdichter 4,
• - Messen der Wasserbeladung der Umgebungsluft X_amb
• - Berechnung einer Luftmassenbilanz anhand der Gleichung ${\dot{\text{m}}}_{\text{air}\text{,dry}}=\frac{{\dot{\text{m}}}_{\text{air}\text{,wet}\text{,measured}}}{1+{\text{X}}_{\text{amb}}},$
  
• - Ermittlung einer Massenstromaufteilung zwischen einem Befeuchter-Bypass 8 und einem Befeuchter 3, wobei der Bypassanteil W_BYP in Abhängigkeit der Position von einer ersten Regelklappe 9 und einer zweiten Regelklappe 10 bestimmt wird,
• - Bestimmung des Stoffdurchgangskoeffizienten β eines Befeuchter-Kennfelds mittels der Gleichung $\mathrm{\beta =}\frac{{\text{D}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{exp}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right],$
  
• - Berechnung der mittleren Befeuchtertemperatur anhand der Gleichung ${\text{T}}_{\text{m}}=\frac{\text{T1}+\text{<figure-callout id="2" label="T3" filenames="DE102020119137A1\_0014.png,DE102020119137A1\_0015.png" state="{{state}}">T3</figure-callout>}}{2}$
  
  und Bestimmung des Wirkungsgrads des Befeuchters 3,
• - Berechnung der molaren Wasserkonzentration der Zuluft beim Austritt aus dem Befeuchter 3 anhand der Gleichung c_D,out = C_D,in + η(c_w,in - c_D,in),
• - Messen der Temperatur T₂ an einem Kathodeneintritt 11
• - Berechnung der Wasserkonzentration an dem Kathodeneintritt 11 anhand der Gleichung C_FC,in = C_D,in ∗ W_BYP + C_D,Out(1 - w_BYP),
• - Berechnung des Partialdrucks und somit des Sättigungsdampfdrucks bei einer Taupunkttemperatur des Wassers am Kathodeneintritt 11 anhand der Gleichung p_w,Fc,in = c_D,FC,_inR ∗ T_stackin = P_s(T_DP),
• - Umrechnung des Dampfdrucks in eine Taupunkttemperatur anhand einer invertierten Dampfdruckkurve,
• - Nutzung der Taupunkttemperatur als Regelgröße.

The method according to the invention for the model-based humidity control of a fuel cell device enables the humidity control and thus the optimal setting of the humidity without a humidity sensor. The procedure includes the steps:

• - Measurement of the air mass flow at the system inlet in front of a compressor 4,
• - Measuring the water loading of the ambient _{air X amb}
• - Calculation of an air mass balance using the equation ${\dot{\text{m}}}_{\text{air}\text{,dry}}=\frac{{\dot{\text{m}}}_{\text{air}\text{,wet}\text{,measured}}}{1+{\text{X}}_{\text{amb}}},$
  
• - Determination of a mass flow distribution between a humidifier bypass 8 and a humidifier 3, the bypass component W _{BYP being determined} depending on the position of a first control flap 9 and a second control flap 10,
• - Determination of the mass transfer coefficient β of a humidifier map using the equation $\mathrm{\beta =}\frac{{\text{D}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{ex}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right],$
  
• - Calculation of the mean humidifier temperature using the equation ${\text{T}}_{\text{m}}=\frac{\text{T1}+\text{T3}}{2}$
  
  and determining the efficiency of the humidifier 3,
• - Calculation of the molar water concentration of the supply air when leaving the humidifier 3 using the equation c _D,out = _CD,in + η(c _w,in - c _D,in ),
• - Measuring the temperature T ₂ at a cathode inlet 11
• - Calculation of the water concentration at the cathode _{inlet 11 using the equation C FC,in} = C _D,in ∗ W BYP + C _D,Out (1 - w _BYP ),
• - Calculation of the partial pressure and thus the saturation vapor pressure at a dew point temperature of the water at the cathode inlet 11 using the equation p _w,Fc,in = c _D,FC , _in R ∗ T _stackin = P _s (T _DP ),
• - Conversion of the vapor pressure into a dew point temperature using an inverted vapor pressure curve,
• - Use of the dew point temperature as a control variable.

ermittelt, wobei die Feuchte φ₁, der Druck p₁ und die Temperatur T₁ messtechnisch bestimmt werden. Wenn bei einem geschlossenen Befeuchter-Bypass 3 die Luftmassenbilanz kalibriert wird, so folgt daraus eine Verringerung der Messungenauigkeit.The measured air mass flows are measured in the wet state, which is why the sensors installed as standard _{measure the air mass flow ṁ air,wet,measurect} including the humidity contained. Since the dry air mass flow must be determined without the air humidity contained in it for the method according to the invention, the pressure, temperature and humidity are measured using a combination sensor arranged at the humidifier inlet 12, as is shown in 3 is symbolized, and thus the water loading of the ambient _air X amb using the equation ${\text{X}}_{\text{amb}}=0.622\ast \frac{{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119137A1\_0014.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1\ast {\text{p}}_{\text{s}}\left({\text{T}}_1\right)}{{\text{<figure-callout id="1" label="p" filenames="DE102020119137A1\_0014.png" state="{{state}}">p</figure-callout>}}_1-{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119137A1\_0014.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1\ast {\text{p}}_{\text{s}}\left({\text{T}}_1\right)}$

determined, with the humidity φ ₁ , the pressure p ₁ and the temperature T _{1 being} determined by measurement. If the air mass balance is calibrated with a closed humidifier bypass 3, the measurement inaccuracy is reduced.

verwendet, wobei Do für den Diffusionskoeffizienten bei einer Referenztemperatur T₀, δ_mem für die Schichtdicke der Membran des Befeuchters 3, T_m für die mittlere Befeuchtertemperatur und R für die allgemeine Gaskonstante steht. Die Aktivierungsenergie E_A wird experimentell über eine Arrhenius-Gleichung mit der Gleichung E_A = -m ∗ R bestimmt, wobei m für die Steigung der Arrhenius-Gleichung und R für die allgemeine Gaskonstante steht. Die Ermittlung der Aktivierungsenergie wird beispielhaft in der 2 gezeigt.An Arrhenius approach is used when calculating the mass transfer coefficient β of a humidifier map using the equation $\mathrm{\beta =}\frac{{\text{<figure-callout id="0" label="D" filenames="DE102020119137A1\_0014.png" state="{{state}}">D</figure-callout>}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{ex}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right]$

used, where Do for the diffusion coefficient at a reference temperature T ₀ , δ _mem for the layer thickness of the membrane of the humidifier 3, T _m for the average humidifier temperature and R for the general gas constant. The activation energy E _A is determined experimentally using an Arrhenius equation with the equation E _A = -m ∗ R, where m stands for the slope of the Arrhenius equation and R for the general gas constant. The determination of the activation energy is exemplified in the 2 shown.

berechnet werden, wobei φ₁ für die Feuchte und p_s(T₁) für den Sättigungsdampfdruck bei der Temperatur T₁ steht.the 3 shows a schematic representation of the humidifier 3 with a humidifier bypass line. _{The temperature T 1} , which is essential for calculating the mean humidifier temperature, is measured upstream of the humidifier 3, the humidifier bypass 8 and upstream of the cathode in the cathode fresh gas line 5, while the temperature T _{3 is} measured downstream of the cathode and upstream of the humidifier 3 in the cathode exhaust gas line 6 will. By measuring the temperature T ₁ , the molar water concentration at the outlet of the intercooler 7 can also be determined using the formula ${\text{c}}_{\text{D}\text{,in}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102020119137A1\_0014.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1\ast {\text{p}}_{\text{s}}\left({\text{t}}_1\right)}{\text{R}\ast {\text{<figure-callout id="1" label="T" filenames="DE102020119137A1\_0014.png" state="{{state}}">T</figure-callout>}}_1}$

be calculated, where φ _{1 stands} for the humidity and p _s (T ₁ ) for the saturation vapor pressure at the temperature T ₁ .

wobei φ_wet,in für einen Anpassungsparameter, der die relative Feuchte der Luft am Kathodenaustritt abschätzt und experimentell an Messdaten angepasst wird, und p_s(T₃) für den Sättigungsdampfdruck bei der Temperatur T₃ steht, kann die molare Wasserkonzentration der Zuluft am Befeuchteraustritt über die Gleichung c_D,out = C_D,in + η(c_w,in - C_D,in) berechnet werden. Dabei steht η für den Wirkungsgrad des Befeuchters 3, berechnet nach der Number-of-Transfer-Units-Methode, und c_w,in für die molare Wasserkonzentration am Kathodenaustritt.By the molar water concentration at the outlet of the intercooler 7 and the calculation of the molar water concentration at the cathode outlet with the formula ${\text{c}}_{\text{w}\text{,in}}=\frac{{\mathrm{\phi }}_{\text{wet}\text{,in}}\ast {\text{p}}_{\text{s}}\left({\text{T}}_3\right)}{\text{R}\ast {\text{T}}_3},$

where φ _{wet,in is} an adjustment parameter that estimates the relative humidity of the air at the cathode outlet and is experimentally adjusted to measurement data, and p _s (T ₃ ) stands for the saturation vapor pressure at temperature T ₃ , the molar water concentration of the supply air at the humidifier outlet can be calculated using the equation c _D,out = C _D,in + η(c _w,in - C _{D,in ).} η stands for the efficiency of the humidifier 3, calculated according to the number-of-transfer-units method, and c _w,in for the molar water concentration at the cathode outlet.

The water concentration at the inlet of the cathode can be calculated using _{the equation C FC,in} = _{CD ,in} ∗ W BYP + _CD,out (1 - W _{BYP ) from the known distribution of the air mass flows.} From the temperature T2 at the cathode inlet, the partial pressure of water at the cathode _inlet can be calculated using _{the equation P w,FC,in} = c _D,FC,in R ∗ T stackin = p _s (T _{DP ), where T stack} in stands for the temperature of the fuel cell stack and p _s (T _DP ) is the saturation vapor pressure at the dew point temperature.

the 4 shows a schematic representation of the method according to the invention for model-based humidity control for further illustration.

Reference List

1

fuel cell device

2

fuel cell stack

3

humidifier

4

compressor

5

Cathode fresh gas line

6

cathode exhaust line

7

intercooler

8th

humidifier bypass

9

first control flap

10

second control flap

11

cathode entry

12

humidifier entry

13

fuel tank

T0

reference temperature

T1

Temperature of the supply air upstream of the humidifier

T2

Temperature of the supply air downstream of the humidifier before the cathode

T3

Temperature of the exhaust air upstream of the humidifier

tom

mean humidifier temperature

tstack

in temperature of the fuel cell stack

TDP

dew point temperature

Xamb

ambient air

WBYP

bypass portion

β

mass transfer coefficient

do

Diffusion coefficient at reference temperature To

EA

activation energy

R

general gas constant

CD out

molar water concentration humidifier supply air OFF

CD, in,

molar water concentration charge air cooler OFF

cw,in

molar water concentration cathode OFF

δmem

Layer thickness of the humidifier membrane

n

Efficiency humidifier

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102014100186 A1 [0006]
• DE 102006058833 A1 [0006]
• DE 102009005647 A1 [0006]

Claims (8)

Method for model-based humidity control of a fuel cell device (1) having a fuel cell, comprising the steps: - measuring the air mass flow at the system inlet before a compressor (4), - measuring the water loading of the ambient _{air X amb} - calculating an air mass balance using the equation ${\dot{\text{m}}}_{\text{air}\text{,dry}}=\frac{{\dot{\text{m}}}_{\text{air}\text{,wet}\text{,measured}}}{1+{\text{X}}_{\text{amb}}},$

- Determination of a mass flow distribution between a humidifier bypass (8) and a humidifier (3), - Determination of the mass transfer coefficient β of a humidifier map using the equation $\mathrm{\beta =}\frac{{\text{D}}_0}{{\mathrm{\delta }}_{\text{men}}}\ast \text{ex}\left[-\frac{{\text{E}}_{\text{A}}}{\text{R}}\left(\frac{1}{{\text{T}}_{\text{m}}}-\frac{1}{{\text{T}}_0}\right)\right],$

- Calculation of the mean humidifier temperature using the equation ${\text{T}}_{\text{m}}=\frac{\text{T1}+\text{T3}}{2}$

and determination of the efficiency of the humidifier (3), - Calculation of the molar water concentration of the supply air when leaving the humidifier (3) using the equation c _D,out = _CD,in + η(c _w,in - c _D,in ) , - measuring the temperature T ₂ at a cathode inlet (11) - calculating the water concentration at the cathode inlet (11) using the equation C _FC,in = C _D,in ∗ W _BYP + c _D,out (1 - W _BYP ), - Calculation of the partial pressure and thus the saturation vapor pressure at a dew point temperature of the water at the cathode inlet (11) using the equation p _w,FC,in = c _D,FC,in R ∗ T _{stack in} = P _s (T _DP ), - Conversion of the vapor pressure into a dew point temperature using an inverted vapor pressure curve, - use of the dew point temperature as a controlled variable. procedure after claim 1 , characterized in that the activation energy, which is necessary for the calculation of the mass transfer coefficient β, is determined experimentally. Procedure according to one of Claims 1 until 2 , characterized in that the efficiency of the humidifier (3) is determined using the number-of-transfer-units method. Procedure according to one of Claims 1 until 3 , characterized in that with a closed humidifier bypass (8), the air mass balance is calibrated with a reduced measurement inaccuracy. Procedure according to one of Claims 1 until 4 , characterized in that the water _{loading of the ambient air X amb is} determined by a combination sensor for temperature, pressure and humidity arranged at the humidifier inlet. Procedure according to one of Claims 1 until 5 , characterized in that the bypass component W _{BYP is determined} as a function of the position of a first control valve (9) and a second control valve (10). Fuel cell device (1) with a control unit for carrying out the method according to one of Claims 1 until 6 . Fuel cell vehicle with a fuel cell device (1). claim 7 .

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