A low temperature cold start method for a fuel cell engine

Abstract

The application provides a low-temperature cold start method of a fuel cell engine, and belongs to the technical field of fuel cells, and solves the problem that the prior art cannot self-adaptively adjust a cold start strategy to ensure the success of the cold start of the fuel cell engine. The method comprises the following steps: determining theoretical heat required for the engine to successfully start at different low temperatures; obtaining high-frequency impedance of the engine after last shutdown and purging, and predicting initial water content of a proton exchange membrane in the engine according to the high-frequency impedance; determining a set time of a current start strategy according to the predicted initial water content and design parameters of a membrane electrode of a stack in the engine; starting the engine, obtaining an output electric signal of the engine under the current start strategy and a current temperature in real time, and obtaining actual heat generated by the stack in the cold start process; and judging whether the actual heat generated by the stack in the cold start process is lower than the theoretical heat corresponding to the current temperature, if yes, replacing the current start strategy, and otherwise, completing the low-temperature cold start of the fuel cell.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a low-temperature cold start method for a fuel cell engine. Background Technology

[0002] Proton exchange membrane fuel cell engines are considered a major force in driving carbon peaking and carbon neutrality in the transportation sector due to their high efficiency and zero emissions. However, the difficulty of cold-starting fuel cell engines in low-temperature environments is currently one of the obstacles hindering their large-scale development.

[0003] Most existing cold start methods for fuel cell engines employ a single cold start strategy. For example, Chinese patent CN114256486A adjusts the operating parameters of the fuel cell engine based on the feasible range of the target voltage. Chinese patent CN111785992B divides the cold start into two stages. The first stage involves external heating elements, the power battery, and residual heat from the system working together to supply fuel. Once the fuel cell reaches its startable temperature, the second stage, the hybrid start stage, begins, during which the air supply unit and hydrogen supply unit start operating, and the fuel cell operates at low power.

[0004] However, the aforementioned cold start control strategy does not fully consider the heat required for cold start of the fuel cell stack in different low-temperature environments, and therefore cannot guarantee a successful cold start. Furthermore, once the fuel cell begins to degrade, the risk of start-up failure is further increased. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a low-temperature cold start method for fuel cell engines, in order to solve the problem that the existing technology cannot adaptively adjust the cold start strategy to ensure the successful cold start of fuel cell engines.

[0006] This invention provides a low-temperature cold start method for a fuel cell engine, comprising the following steps:

[0007] S1. Determine the theoretical heat required for a fuel cell engine to successfully start in different low-temperature environments;

[0008] S2. Obtain the high-frequency impedance after the last shutdown and purging of the fuel cell engine, and predict the initial water content of the proton exchange membrane inside the fuel cell engine based on the high-frequency impedance.

[0009] S3. Based on the predicted initial water content and the design parameters of the membrane electrode assembly in the fuel cell engine, the volume of solid ice that the fuel cell stack can store during cold start is determined, and the setting time of the current start-up strategy is then determined.

[0010] S4. Start the fuel cell engine within the above-set time, and acquire the output electrical signal of the fuel cell engine in real time under the current start-up strategy and current temperature to obtain the actual heat generated by the stack during the cold start process.

[0011] S5. Determine whether the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat generated at the current temperature. If so, change the current start-up strategy; otherwise, complete the low-temperature cold start of the fuel cell.

[0012] The beneficial effects of the above technical solution are as follows: It provides an adaptive low-temperature cold start method. By acquiring the output electrical signal of the fuel cell engine in actual operation, and comparing the actual heat generation with the theoretical heat required for a successful cold start through theoretical calculations, an adaptive cold start strategy is switched, thereby promoting the solution of the fuel cell engine cold start problem.

[0013] Based on further improvements to the above method, the low-temperature cold start method also includes the following steps:

[0014] S6. Acquire the output signal of the fuel cell engine at the rated operating point at set intervals;

[0015] S7. Determine the polarization curve of the fuel cell engine based on the output signal, and then obtain the attenuation factor of the fuel cell engine;

[0016] S8. Based on the above attenuation factor, the volume of solid ice that the stack can store during the cold start process in step S3 and the actual heat generated by the stack during the cold start process in step S4 are corrected.

[0017] Furthermore, the high-frequency impedance in step S2 is also the high-frequency impedance value used as the condition for stopping purging in the fuel cell engine shutdown purging strategy.

[0018] Furthermore, the design parameters of the membrane electrode assembly include the catalytic layer porosity ε. cl Catalyst layer thickness δ cl Proton exchange membrane area A m ;and,

[0019] Step S3 further calculates the volume V of solid ice that the fuel cell stack can store during cold start using the following formula:

[0020]

[0021] In the formula, M w n is the molar mass of water. d ρ is the coefficient for membrane water diffusion and electron dragging. ice This is the density of ice.

[0022] Furthermore, step S4 further calculates the actual heat generation P of the fuel cell stack during the cold start process using the following formula:

[0023]

[0024] In the formula, I is the output current of the fuel cell engine, V0 is the open-circuit voltage of a single cell, and V i This represents the real-time voltage of a single cell.

[0025] Furthermore, this low-temperature cold start method also includes:

[0026] S9. During the start-up process of the fuel cell engine, acquire the real-time temperature of the fuel cell engine;

[0027] S10. Based on the real-time temperature of the fuel cell engine, determine the real-time membrane water content of the fuel cell engine;

[0028] S11. Based on the real-time membrane water content of the fuel cell engine, the amount of water precipitated into the catalyst layer from the stack membrane electrode during the cold start process is obtained;

[0029] S12. Obtain the amount of water corresponding to the volume of solid ice that can be stored during the cold start process, and add the amount of water that is precipitated into the catalyst layer by the membrane electrode of the fuel cell stack during the cold start process to obtain the actual total water production under the current start-up strategy.

[0030] S13. Based on the actual total water production under the current startup strategy, it is preliminarily determined whether the current startup strategy can successfully start cold. If so, the current cold start water production rate is obtained based on the output current of the fuel cell engine at the current moment. Based on the volume of solid ice V that the stack can store during the cold start process and the current cold start water production rate, the duration of the cold start process is estimated.

[0031] Furthermore, step S10 further calculates the real-time membrane water content λ of the fuel cell engine using the following formula. sat :

[0032] λsat=6.775×10⁻⁵T0 3 -4.747×10⁻²T₀ 2 +11.22T0-888.8,

[0033] In the formula, T0 is the real-time temperature of the fuel cell engine.

[0034] Furthermore, step S11 further calculates the amount of water V that is deposited into the catalyst layer by the membrane electrode assembly during the cold start process using the following formula. water :

[0035]

[0036] In the formula, F is the Faraday constant, ρ m ε represents the dry membrane density of the proton exchange membrane.m λ is the volume fraction of the ionomer, λ0 is the initial water content of the proton exchange membrane, and E w This is the dry membrane equivalent of the proton exchange membrane.

[0037] Furthermore, in step S5, if the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat generated at the current temperature, a control method of gradually reducing the single cell voltage of the fuel cell engine is adopted based on the current start-up strategy to increase the actual heat generated by the fuel cell stack during the cold start process.

[0038] Furthermore, step S13 further includes:

[0039] S131. Compare the actual total water production under the current startup strategy with the theoretical value. If the actual total water production under the current startup strategy is lower than the theoretical value, it can be preliminarily determined that the current cold start strategy can be successful. Continue to steps S4-S5 and execute the next step. Otherwise, it is preliminarily determined that the current cold start strategy cannot be successful and the cold start strategy is changed.

[0040] S132. Obtain the current output current of the fuel cell engine;

[0041] S133. Based on the current output current of the fuel cell engine, obtain the current cold start water production rate;

[0042] S134. The estimated duration of the cold start process is obtained by dividing the volume of solid ice that the fuel cell stack can store during the cold start process by the current cold start water production rate.

[0043] The summary section is provided to present the chosen concepts in a simplified form, which will be further described in the detailed description below. The summary section is not intended to identify essential or essential features of the invention, nor is it intended to limit the scope of the invention. Attached Figure Description

[0044] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same parts.

[0045] Figure 1 A schematic diagram of the steps of the low-temperature cold start method for the fuel cell engine in Example 1 is shown;

[0046] Figure 2 The graph showing the relationship between high-frequency impedance and membrane water content in Example 2 is illustrated.

[0047] Figure 3 A schematic diagram of the cold start strategy replacement in Example 2 is shown;

[0048] Figure 4 A schematic diagram illustrating the estimation of fuel cell degradation using polarization curves from Example 2 is shown.

[0049] Figure 5 A schematic diagram of the execution flow of the low-temperature cold start method in Example 2 is shown. Detailed Implementation

[0050] Embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0051] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0052] Example 1

[0053] One embodiment of the present invention discloses a low-temperature cold start method for a fuel cell engine, such as... Figure 2 As shown, it includes the following steps:

[0054] S1. Determine the theoretical heat required for a fuel cell engine to successfully start in cold conditions under different low-temperature environments;

[0055] Specifically, step S1 involves storing the theoretical heat required for a successful cold start of the fuel cell engine at different low-temperature environments in a storage device. Optionally, during a cold start, an ambient temperature sensor is used to detect the ambient temperature, and the heat required for a successful cold start is determined by combining this with the design parameters of the membrane electrode assembly (MEA) in the fuel cell engine stack. This provides data support for comparison in step S5 below.

[0056] S2. Obtain the high-frequency impedance after the last shutdown and purging of the fuel cell engine, and predict the initial water content of the proton exchange membrane inside the fuel cell engine based on the high-frequency impedance.

[0057] Specifically, the high-frequency impedance of the fuel cell engine can be obtained through the high-frequency impedance monitoring system provided by CN202210980890.1. The high-frequency impedance can be input into a pre-calibrated deep learning network or physical model to obtain the predicted initial water content of the proton exchange membrane inside the fuel cell engine.

[0058] S3. Based on the predicted initial water content and the design parameters of the membrane electrode assembly in the fuel cell engine, the volume of solid ice that the fuel cell stack can store during cold start is determined, and the setting time of the current start-up strategy is then determined.

[0059] Specifically, the predicted initial water content, combined with the design parameters of the membrane electrode assembly in the fuel cell engine stack, is input into a pre-calibrated deep learning network or the physical model described in Example 2 to obtain the volume of solid ice that the stack can store during cold start-up. Then, the set time (including heating time) of the current start-up strategy is determined based on the pre-measured experimental data.

[0060] S4. Start the fuel cell engine within the above-set time, and acquire the output electrical signal of the fuel cell engine in real time under the current start-up strategy and current temperature to obtain the actual heat generated by the stack during the cold start process.

[0061] Specifically, the voltage and current data of the fuel cell engine under the current startup strategy and current temperature are acquired in real time and input into a pre-calibrated deep learning network or the physical model described in Example 2 to obtain the actual heat generated by the stack during the cold start process.

[0062] S5. Determine whether the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat corresponding to the current temperature. If so, change the current start-up strategy; otherwise, complete the low-temperature cold start of the fuel cell.

[0063] Specifically, when the heat generation is too low, auxiliary heating can be used, as well as increasing the heating temperature and extending the heating time, to improve the probability of a successful cold start.

[0064] It should be noted that the above cold start method is applicable to existing proton exchange membrane fuel cell engines. The structure of a proton exchange membrane fuel cell engine can be found in published Chinese patents CN202210647132.8 and CN201821664393.6, etc.

[0065] Compared with existing technologies, this embodiment provides an adaptive low-temperature cold start method. By acquiring the output electrical signal of a fuel cell engine in actual operation, and comparing the actual heat generation with the theoretical heat required for a successful cold start through theoretical calculations, an adaptive cold start strategy is switched, thereby promoting the solution of the fuel cell engine cold start problem.

[0066] Example 2

[0067] Based on Example 1, an improvement is made: the high-frequency impedance in step S2 is also the high-frequency impedance value used as the stop-purge condition in the fuel cell engine shutdown purging strategy. That is, the fuel cell engine performs purging each time it shuts down to reduce the water content in the fuel cell stack. Generally, a high-frequency impedance value is set to exit the purging process. Upon restarting, this high-frequency impedance value is directly read, thus eliminating the complex procedure of measuring the high-frequency impedance value.

[0068] The high-frequency impedance values ​​read are converted into the initial water content (initial membrane water content) of the proton exchange membrane inside the fuel cell engine. Figure 2 The relationship between the calibrated high-frequency impedance value and the membrane water content is given. x-1 is the value at which the purging state is exited. The initial membrane water content above x-1 can be approximated as λ-1.

[0069] Preferably, the design parameters of the fuel cell membrane electrode in step S3 include the catalytic layer porosity ε. cl Catalyst layer thickness δ cl Proton exchange membrane area A m .

[0070] Step S3 further calculates the volume V of solid ice that the fuel cell stack can store during cold start using the following formula:

[0071]

[0072] In the formula, M w n is the molar mass of water. d ρ is the coefficient for membrane water diffusion and electron dragging. ice This is the density of ice.

[0073] Preferably, step S4 further obtains the output current I of the fuel cell engine and the real-time voltage V of the single cell. i (Obtained via CVM), the actual heat generation P of the fuel cell stack during cold start-up is calculated using the following formula:

[0074]

[0075] In the formula, I is the output current of the fuel cell engine, V0 is the open-circuit voltage of a single cell, and V i This represents the real-time voltage of a single cell.

[0076] Preferably, in step S5, when it is determined that the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat generated at the current temperature, a control method of gradually reducing the single-cell voltage (also known as the fuel cell single-cell voltage) of the fuel cell engine is adopted based on the current start-up strategy to increase the actual heat generated by the fuel cell stack during the cold start process. Figure 3 Otherwise, complete the low-temperature cold start of the fuel cell.

[0077] Preferably, the low-temperature cold start method further includes the following steps:

[0078] S6. At set intervals (exemplarily 100h), acquire the output signal of the fuel cell engine at the rated operating point;

[0079] Specifically, the output signal is preferably the output current or output voltage data of the fuel cell engine at the rated operating point;

[0080] S7. Determine the polarization curve of the fuel cell engine based on the output signal, and then obtain the attenuation factor of the fuel cell engine;

[0081] Specifically, the plotting of polarization curves can be found in Chinese patent CN114487843A, etc. The aging factor α described in Chinese patent CN114994555A is prior art and will not be elaborated further. Polarization curves are compared every 100 hours, or only the rated current and voltage are compared. The fuel cell degradation is estimated based on the voltage drop. Figure 4 As shown.

[0082] S8. Based on the above attenuation factor, the volume of solid ice that the stack can store during the cold start process in step S3 and the actual heat generated by the stack during the cold start process in step S4 are corrected.

[0083] Specifically, the solid ice volume in step 3 is multiplied by the attenuation factor to obtain the corrected solid ice volume, and the actual heat generated by the fuel cell stack during the cold start process is multiplied by the attenuation factor to obtain the corrected actual heat generated by the fuel cell stack.

[0084] Preferably, the low-temperature cold start method further includes the following steps:

[0085] S9. During the start-up process of the fuel cell engine, obtain the real-time temperature T0 of the fuel cell engine;

[0086] S10. Based on the real-time temperature T0 of the fuel cell engine, the real-time membrane water content of the fuel cell engine is obtained;

[0087] Specifically, the real-time membrane water content λ of the fuel cell engine is further obtained using the following formula. sat :

[0088] λsat=6.775×10⁻⁵T0 3 -4.747×10⁻²T₀ 2 +11.22T0-888.8,

[0089] In the formula, T0 is the real-time temperature of the fuel cell engine.

[0090] S11. Based on the real-time membrane water content of the fuel cell engine, the amount of water precipitated into the catalyst layer from the stack membrane electrode during the cold start process is obtained;

[0091] Specifically, the amount of water V that is deposited into the catalyst layer by the membrane electrode assembly during the cold start process can be further calculated using the following formula. water :

[0092]

[0093] In the formula, F is the Faraday constant, ρ m ε represents the dry membrane density of the proton exchange membrane. m λ is the volume fraction of the ionomer, λ0 is the initial water content of the proton exchange membrane, and E w This is the dry membrane equivalent of the proton exchange membrane.

[0094] S12. Obtain the amount of water corresponding to the volume of solid ice that can be stored during the cold start process, and add the amount of water that is precipitated into the catalyst layer by the membrane electrode of the fuel cell stack during the cold start process to obtain the actual total water production under the current start-up strategy.

[0095] S13. Based on the actual total water production under the current startup strategy, make a preliminary judgment on whether the current startup strategy can successfully start cold. If so, further determine the current cold start water production rate based on the output current of the fuel cell engine at the current moment. Based on the volume of solid ice V that the stack can store during the cold start process and the current cold start water production rate, estimate the duration of the cold start process.

[0096] Specifically, the actual total water production under the current startup strategy is compared with the theoretical value. If the actual total water production under the current startup strategy is higher than the theoretical value, it can be preliminarily determined that the cold start strategy is successful, and steps S4-S5 are continued. Otherwise, it is preliminarily determined that the cold start strategy is unsuccessful, and the startup strategy is changed.

[0097] The engine output current at the current moment is obtained and input into the calibration model to calculate the current cold start water production rate. Then, the duration of the cold start process is estimated by dividing the volume of solid ice that the fuel cell stack can store by the current cold start water production rate.

[0098] During implementation, the controller's control strategy can be set as follows: Figure 5 As shown.

[0099] Compared with the prior art, the low-temperature cold start method for fuel cell engines provided in this embodiment has the following beneficial effects:

[0100] 1. By estimating and judging, an adaptive strategy is used for cold start, reducing the limitations of a single strategy.

[0101] 2. The estimation method is modified by combining fuel cell degradation to ensure the accuracy of the estimation.

[0102] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or improvements to the prior art of the embodiments, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A low-temperature cold start method for a fuel cell engine, characterized in that, include: S1. Determine the theoretical heat required for a fuel cell engine to successfully start in different low-temperature environments; S2. Obtain the high-frequency impedance after the last shutdown purging of the fuel cell engine, and predict the initial water content of the proton exchange membrane inside the fuel cell engine based on the high-frequency impedance; the high-frequency impedance in step S2 is also the high-frequency impedance value used as the stop purging condition in the shutdown purging strategy of the fuel cell engine. S3. Based on the predicted initial water content and the design parameters of the membrane electrode assembly in the fuel cell engine, the volume of solid ice that the fuel cell stack can store during cold start is determined, and the setting time of the current start-up strategy is then determined. The design parameters of the membrane electrode assembly include the catalyst layer porosity εcl, the catalyst layer thickness δcl, and the proton exchange membrane area Am; and, Step S3 further calculates the volume V of solid ice that the fuel cell stack can store during cold start using the following formula: In the formula, Mw is the molar mass of water, nd is the membrane water diffusion and electron drag coefficient, and ρice is the density of ice. S4. Start the fuel cell engine within the above-set time, and acquire the output electrical signal of the fuel cell engine in real time under the current start-up strategy and current temperature to obtain the actual heat generated by the stack during the cold start process. S5. Determine whether the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat corresponding to the current temperature. If so, change the current start-up strategy; otherwise, complete the low-temperature cold start of the fuel cell.

2. The low-temperature cold start method for a fuel cell engine according to claim 1, characterized in that, It also includes the following steps: S6. Acquire the output signal of the fuel cell engine at the rated operating point at set intervals; S7. Determine the polarization curve of the fuel cell engine based on the output signal, and then obtain the attenuation factor of the fuel cell engine; S8. Based on the above attenuation factor, the volume of solid ice that the stack can store during the cold start process in step S3 and the actual heat generated by the stack during the cold start process in step S4 are corrected.

3. The low-temperature cold start method for a fuel cell engine according to claim 1, characterized in that, Step S4 further calculates the actual heat generated by the fuel cell stack during the cold start process using the following formula. : In the formula, I is the output current of the fuel cell engine, V0 is the open-circuit voltage of a single cell, and Vi is the real-time voltage of a single cell.

4. The low-temperature cold start method for a fuel cell engine according to claim 3, characterized in that, Also includes: S9. During the start-up process of the fuel cell engine, acquire the real-time temperature of the fuel cell engine; S10. Based on the real-time temperature of the fuel cell engine, determine the real-time membrane water content of the fuel cell engine; S11. Based on the real-time membrane water content of the fuel cell engine, the amount of water precipitated into the catalyst layer from the stack membrane electrode during the cold start process is obtained; S12. Obtain the amount of water corresponding to the volume of solid ice that can be stored during the cold start process, and add the amount of water that is precipitated into the catalyst layer by the membrane electrode of the fuel cell stack during the cold start process to obtain the actual total water production under the current start-up strategy. S13. Based on the actual total water production under the current startup strategy, make a preliminary judgment on whether the current startup strategy can successfully start cold. If so, further determine the current cold start water production rate based on the output current of the fuel cell engine at the current moment. Based on the volume of solid ice V that the stack can store during the cold start process and the current cold start water production rate, estimate the duration of the cold start process.

5. The low-temperature cold start method for a fuel cell engine according to claim 4, characterized in that, Step S10 further calculates the real-time membrane water content λsat of the fuel cell engine using the following formula: In the formula, T0 is the real-time temperature of the fuel cell engine.

6. The low-temperature cold start method for a fuel cell engine according to claim 5, characterized in that, Step S11 further calculates the amount of water Vwater that is deposited into the catalyst layer from the membrane electrode assembly during the cold start process using the following formula: In the formula, F is the Faraday constant, ρm is the dry membrane density of the proton exchange membrane, εm is the volume fraction of the ionomer, λ0 is the initial water content of the proton exchange membrane, and Ew is the dry membrane equivalent of the proton exchange membrane.

7. The low-temperature cold start method for a fuel cell engine according to claim 1, characterized in that, When step S5 determines that the actual heat generated by the fuel cell stack during the cold start process is lower than the theoretical heat generated at the current temperature, a control method of gradually reducing the single cell voltage of the fuel cell engine is adopted based on the current start-up strategy to increase the actual heat generated by the fuel cell stack during the cold start process.

8. The low-temperature cold start method for a fuel cell engine according to claim 7, characterized in that, Step S13 further includes: S131. Compare the actual total water production under the current startup strategy with the theoretical value. If the actual total water production under the current startup strategy is lower than the theoretical value, it can be preliminarily determined that the current cold start strategy can be successful. Continue to steps S4-S5 and execute the next step. Otherwise, it is preliminarily determined that the current cold start strategy cannot be successful and the cold start strategy is changed. S132. Obtain the current output current of the fuel cell engine; S133. Based on the current output current of the fuel cell engine, obtain the current cold start water production rate; S134. The estimated duration of the cold start process is obtained by dividing the volume of solid ice that the fuel cell stack can store during the cold start process by the current cold start water production rate.

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