JP2019008896A - Fuel cell system - Google Patents

Abstract

To improve stability of a power generation state of a fuel cell in a fuel cell system.SOLUTION: A reformer 2 is interposed in an exhaust passage 14 of an engine 1. Hydrocarbon contained in exhaust gas is reformed by the reformer 2 so as to generate hydrogen gas. A fuel cell 3 is provided to generate power by using, as fuel, the hydrogen gas thus generated by the reformer 2. A mixture recirculation passage 5 is provided to recirculate, into an intake system of the engine 1, mixture of reformed gas discharged from the reformer 2 and off-gas from the fuel cell 3. A catalyst passage 17 is provided which is branched from the exhaust passage 14 between the engine 1 and the reformer 2, and is connected to the outside of a vehicle. An exhaust flow dividing valve 46 is provided to control an amount of the exhaust gas introduced from the exhaust passage 14 into the catalyst passage 17. The amount of the exhaust gas is adjusted by a control device 29 in accordance with a temperature in the reformer 2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell system using engine exhaust gas.

2. Description of the Related Art Conventionally, a technique for improving engine exhaust gas performance and combustion stability by mixing fuel cell off-gas with engine intake air is known. For example, a high-temperature off-gas discharged from the anode of a solid oxide fuel cell (SOFC) contains a large amount of carbon dioxide (CO ₂ ) and hardly contains oxygen (O ₂ ). The same applies to the off-gas component of a molten carbonate fuel cell (MCFC). By introducing these off-gases into the intake system of the engine, the combustion temperature in the engine cylinder can be lowered and knocking can be made difficult to occur (see Patent Documents 1 and 2).

  On the other hand, a technique for generating power by supplying engine exhaust gas to a fuel cell has also been proposed. Since the engine exhaust gas contains an unburned hydrocarbon component (HC), hydrogen gas can be generated by performing a process such as steam reforming or partial oxidation reforming. By using this hydrogen gas as fuel for the fuel cell, it is possible to generate power while purifying the exhaust gas of the engine (see Patent Document 3).

JP 2013-189880 JP JP 2011-171217 A JP 2016-178054 A

  In an existing recirculation system that introduces fuel cell off-gas into the engine intake system, the amount of off-gas introduced is controlled in accordance with the operating state of the engine. In the above-mentioned Patent Document 1, the required exhaust amount is set according to the engine speed and the engine load, and the introduction amount of the off gas is determined by comparing the actual exhaust amount and the required exhaust amount. On the other hand, the temperature of the exhaust gas discharged from the engine can vary depending on the amount of off-gas introduced. Therefore, when power is generated by a fuel cell using this exhaust gas, the temperature of the fuel cell or reformer tends to deviate from the desired operating temperature range depending on the operating state of the engine. As described above, in the power generation system in which the fuel cell off-gas and the engine exhaust gas are mutually used, there is room for improvement in stabilizing the power generation state.

  One of the objects of the present case was invented in view of the above problems, and is to provide a fuel cell system that improves the stability of the power generation state in the fuel cell. It should be noted that the present invention is not limited to this purpose, and is an operational effect that is derived from each configuration shown in “Mode for Carrying Out the Invention” to be described later. Can be positioned as a purpose.

  (1) A disclosed fuel cell system is provided in an exhaust passage of an engine, reforms a hydrocarbon contained in exhaust gas to generate hydrogen gas, and the above-described fuel cell system generated by the reformer And a fuel cell that generates power using hydrogen gas as a fuel. Also, an air-fuel mixture recirculation passage for recirculating an air-fuel mixture of the reformed gas discharged from the reformer and the off-gas of the fuel cell to the intake system of the engine, and between the engine and the reformer And a catalyst passage that branches off from the exhaust passage and bypasses the reformer and is connected to the outside of the vehicle. Further, an exhaust shunt valve that controls the amount of exhaust gas introduced from the exhaust passage into the catalyst passage, and a control device that adjusts the opening of the exhaust shunt valve according to the temperature of the reformer are provided.

(2) The control device may control the opening degree of the exhaust shunt valve so that the amount of exhaust gas introduced from the exhaust passage into the catalyst passage increases as the temperature of the reformer increases. preferable.
(3) An outside air passage for introducing outside air into the exhaust passage between the exhaust shunt valve and the reformer, and an outside air mixing valve for controlling the amount of outside air introduced from the outside air passage. preferable.

(4) It is preferable that the control device controls the opening degree of the outside air mixing valve so that the outside air amount increases as the temperature of the reformer increases.
(5) It is preferable to provide a mixing rate control valve that controls the mixing rate of the reformed gas and the off gas in the mixture.
(6) It is preferable that the control device controls the opening degree of the mixing rate control valve so that the proportion of the off gas increases as the temperature of the reformer increases.

(7) A heat exchanger that is interposed in the air-fuel mixture recirculation passage and cools the air-fuel mixture, a water tank that recovers moisture of the air-fuel mixture cooled by the heat exchanger, and a water tank that collects the water It is preferable that the water injection valve which supplies the said water | moisture content performed inside the said reformer is provided.
(8) It is preferable that the control device controls the mixing rate of the mixing rate control valve so that the proportion of the off-gas increases as the remaining amount of water collected in the water tank decreases.
(9) The control device opens the exhaust gas diversion valve so that the amount of exhaust gas introduced from the exhaust passage into the catalyst passage decreases as the remaining amount of water collected in the water tank decreases. It is preferable to control the degree.

  By controlling the opening of the exhaust control valve in accordance with the temperature of the reformer, the reformer and the fuel cell can be heated with high-temperature exhaust gas while the reformer is warmed up. On the other hand, after the reformer is warmed up, the exhaust gas flow path can be bypassed to suppress overheating of the reformer and the fuel cell. As described above, the operating temperatures of the reformer and the fuel cell can be easily maintained within an appropriate temperature range, and the stability of the power generation state in the fuel cell can be improved.

1 is a side view of a vehicle to which a fuel cell system is applied. It is a schematic diagram which shows the structure of a fuel cell system. (A)-(F) are the graphs for demonstrating the opening degree characteristic of a valve. It is a flowchart for demonstrating the control procedure of a fuel cell system.

  Hereinafter, a fuel cell system as an embodiment will be described with reference to the drawings. The following embodiments are merely examples, and there is no intention of excluding various modifications and technical applications that are not explicitly described in the following embodiments. Each configuration of the present embodiment can be implemented with various modifications without departing from the spirit thereof. Further, they can be selected as necessary, or can be appropriately combined.

[1. Device configuration]
FIG. 1 shows a vehicle 10 to which the fuel cell system of this embodiment is applied. This vehicle 10 is a series / parallel hybrid vehicle equipped with an engine 1 as a drive source and an electric motor 26 (traveling motor generator). The engine 1 is an internal combustion engine such as a diesel engine or a gasoline direct injection engine, and drives a rotating shaft by burning an air-fuel mixture containing fuel (gasoline, light oil, etc.) in a cylinder. The electric motor 26 is an AC motor generator that has both a function as a motor (vehicle drive function) and a function as a generator (regenerative power generation function). The engine 1 and the electric motor 26 are connected in parallel to the drive wheels, and are provided so that each can independently transmit a driving force.

  The engine 1 is connected with a generator 27 (a motor generator for power generation). The generator 27 is an AC motor generator that has both a function as a generator that generates electric power using the driving force of the engine 1 and a function as a starter that starts the engine 1. Each of the electric motor 26 and the generator 27 is connected to the driving battery 25. The driving battery 25 is a secondary battery such as a lithium ion secondary battery or a nickel hydride battery. The driving battery 25 can be charged with regenerative electric power from the electric motor 26 or generated electric power from the generator 27, and can be externally charged using an external charging facility.

  The vehicle 10 is equipped with a fuel cell 3 and a reformer 2 for generating the fuel gas. In the fuel cell system of this embodiment, mutual use of the exhaust gas of the engine 1 and the off gas of the fuel cell 3 (gas discharged from the anode side of the fuel cell 3) is performed. That is, the exhaust gas of the engine 1 is introduced into the anode of the fuel cell 3, and the off-gas on the anode side of the fuel cell 3 is introduced into the intake system of the engine 1. The electric power generated by the fuel cell 3 is charged in the driving battery 25.

  FIG. 2 is a configuration example of the fuel cell system of the present embodiment. Here, one of a plurality of cylinders provided in the engine 1 is illustrated. Each cylinder is provided with an in-cylinder injector 20 connected to the fuel tank 28. The engine 1 is also equipped with an exhaust gas recirculation system (EGR (Exhaust Gas Recirculation) system) that recirculates exhaust gas from the exhaust passage 14 to the intake passage 12. The exhaust gas recirculation passage 22 (EGR passage) is formed so as to communicate, for example, an exhaust manifold (exhaust manifold) and an intake manifold (intake manifold). On the path of the exhaust gas recirculation passage 22, an exhaust gas cooling device 23 (EGR cooler) and an exhaust gas recirculation valve 24 (EGR valve) are provided. The black arrow in the figure indicates the flow of exhaust gas, and the white arrow indicates the flow of outside air.

  The exhaust gas flowing through the exhaust gas recirculation passage 22 is cooled by the exhaust gas cooling device 23 and then flows back to the intake air passage 12 through the exhaust gas recirculation valve 24. Thus, the exhaust gas recirculated from the exhaust passage 14 to the intake passage 12 is referred to as EGR gas. The introduction position of the EGR gas is set on the downstream side (side closer to the cylinder) than the throttle valve 13 interposed in the intake passage 12. The amount of EGR gas introduced is an amount corresponding to the opening degree and pressure of the exhaust gas recirculation valve 24 (pressure difference and pressure ratio between the upstream side and the downstream side of the exhaust gas recirculation valve 24). The opening degree of the exhaust gas recirculation valve 24 is adjusted according to the operating state (engine speed or engine load) of the engine 1.

The reformer 2 and the fuel cell 3 are interposed downstream of the branch position to the exhaust gas recirculation passage 22 in the exhaust passage 14. The reformer 2 is a catalyst device that reforms unburned hydrocarbon components (HC) in the exhaust gas into hydrogen (H ₂ ). As the reforming catalyst, for example, a nickel (Ni) -based or ruthenium (Ru) -based catalytic metal is used. In an operating situation where the exhaust gas has a sufficiently large amount of unburned hydrocarbon components, the fuel cell 3 generates power using only hydrogen obtained by reforming the unburned hydrocarbon components. On the other hand, in an operating situation where the unburned hydrocarbon component in the exhaust gas is insufficient, fuel is injected into the exhaust gas to replenish the unburned hydrocarbon component, thereby increasing the amount of hydrogen produced.

  The reformer 2 is provided with a reformer injector 21, a reformer temperature sensor 7, and a water injector 45 that inject fuel to the reforming catalyst. The reformer injector 21 is an injection valve that is connected to the fuel tank 28 through the same piping path as the in-cylinder injector 20 and injects fuel into the reformer 2 at an arbitrary injection amount. The water injector 45 is an injection valve that injects water consumed in the reforming reaction into the reformer 2. The reformer temperature sensor 7 is a temperature sensor that detects the temperature of the reformer 2, and detects, for example, the temperature of the reforming catalyst and the temperature (atmosphere temperature) in the casing. The temperature information detected here is transmitted to the control device 29 described later.

  There are three main methods for producing hydrogen from petroleum liquid fuels: steam reforming, partial oxidation reforming, and autothermal reforming. While the steam reforming reaction is an endothermic reaction, the partial oxidation reforming reaction is an exothermic reaction. Therefore, in the partial oxidation reforming, it is not necessary to apply heat from the outside, but in terms of the amount of hydrogen generated, the steam reforming reaction is improved. Further, the autothermal reforming reaction can control the balance of endothermic heat according to the amount of oxygen. The reaction formulas in these reforming techniques are exemplified below. The reformer 2 of the present embodiment uses these techniques in combination to generate not only hydrogen but also carbon monoxide (CO) and supply it to the anode side of the fuel cell 3.

  The fuel cell 3 is a gas cell that converts a change in free energy associated with an oxidation reaction of hydrogen into electric energy. Specific examples of the fuel cell 3 include a solid oxide fuel cell (SOFC), a molten carbonate fuel cell (MCFC), a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell ( Examples include PAFC (Phosphoric Acid Fuel Cell) and alkaline electrolyte fuel cell (AFC). The fuel cell 3 of the present embodiment is a solid oxide fuel cell (SOFC), and generates power using an oxidation reaction of hydrogen or carbon monoxide. The electrode reaction formula of the fuel cell 3 is illustrated below.

The anode side of the fuel cell 3 and the reformer 2 are connected by a fuel gas passage 8 and the reformed gas supplied from the reformer 2 is introduced to the anode side. This reformed gas contains hydrogen and carbon monoxide. On the other hand, an oxygen gas passage 9 is connected to the cathode side of the fuel cell 3, and air containing oxygen (O ₂ ) (that is, normal outside air) is introduced to the cathode side. The electric power generated by the fuel cell 3 is charged in the driving battery 25 and used as driving electric power for the electric motor 26 and on-vehicle electrical components. The fuel cell 3 of the present embodiment generates power only when the engine 1 is operating (that is, when exhaust gas is flowing). However, even when the engine 1 is not operating, it is possible to generate power by supplying the hydrogen gas generated by the reformer 2 to the fuel cell 3.

  A catalyst passage 17 serving as a path that bypasses the reformer 2 is provided downstream of the branch position to the exhaust gas recirculation path 22 in the exhaust path 14. The catalyst passage 17 is a passage branched from the exhaust passage 14 between the engine 1 and the reformer 2 and is formed in a shape that joins the exhaust passage 14 again downstream of the reformer 2 and the fuel cell 3. The An exhaust catalyst device 18 is interposed on the catalyst passage 17. The exhaust catalyst device 18 is a purification device including a catalyst for purifying exhaust gas components and a filter for collecting particulate matter. An electric heater 19 for quickly raising the catalyst temperature to the activation temperature is built in the exhaust catalyst device 18.

The fuel gas passage 8 provided on the downstream side of the reformer 2 has a shape branched into a passage continuing to the anode side of the fuel cell 3 and a reformed gas passage 41. The reformed gas passage 41 is a passage for recirculating the reformed gas discharged from the reformer 2 to the intake passage 12 of the engine 1. A part of the reformed gas discharged from the reformer 2 is introduced into the intake system of the engine 1 from the mixed gas recirculation passage 5. Similarly, the muffler-side passage 6 provided downstream of the anode of the fuel cell 3 has a shape branched into a passage continuing to the outside of the vehicle and an off-gas passage 42. The off-gas passage 42 is a passage for recirculating off-gas (main component is carbon dioxide (CO ₂ )) of the fuel cell 3 to the intake passage 12 of the engine 1. A part of the off gas of the fuel cell 3 is introduced from the mixed gas recirculation passage 5 into the intake system of the engine 1. Further, other off-gas is discharged to the outside of the vehicle 10 through the muffler side passage 6.

  The reformed gas passage 41 and the off-gas passage 42 are joined by a mixing ratio control valve 43 and connected to the mixed gas recirculation passage 5. As a result, a gas (mixed gas) in which the reformed gas and the off gas are mixed flows through the mixed gas recirculation passage 5 and is introduced into the intake passage 12. The mixing rate control valve 43 is a three-way valve that controls the mixing rate of the reformed gas and the off gas and distributes the mixed gas to the mixed gas recirculation passage 5. The mixing ratio (mixing ratio) of the reformed gas and the off gas is controlled by the control device 29 according to the temperature of the reformer 2.

  A mixed gas control valve 4 and a mixed gas cooler 11 for cooling the mixed gas are interposed in the mixed gas recirculation passage 5. The mixed gas control valve 4 is a valve for controlling the amount of mixed gas flowing into the intake passage 12. The joining position of the mixed gas recirculation passage 5 and the intake passage 12 is set downstream of the throttle valve 13. The opening degree of the mixed gas control valve 4 is controlled by the control device 29 according to the operating state of the engine 1 (engine speed and engine load).

  The mixed gas cooler 11 is a heat exchanger for cooling the mixed gas. The mixed gas flowing through the mixed gas recirculation passage 5 is cooled by the exhaust cooling device 23 and then flows back to the intake passage 12 through the mixed gas control valve 4. A water tank 44 that collects moisture (condensed water) of the mixed gas cooled by the mixed gas cooler 11 is provided below the mixed gas cooler 11. The water tank 44 is provided with a water tank sensor 49 that detects the remaining amount of water present therein. The water collected here is used as water for jetting by the water injector 45.

  Regarding the structure of the exhaust passage 14 upstream of the reformer 2, the amount of exhaust gas introduced from the exhaust passage 14 to the catalyst passage 17 is controlled at a branch point between the exhaust passage 14 and the catalyst passage 17. Exhaust gas diversion valve 46 is interposed. The exhaust gas diversion valve 46 is a three-way valve that distributes the flow of exhaust gas flowing in from the engine 1 side into two paths (the path on the reformer 2 side and the path on the catalyst path 17 side). is there. The ratio of the exhaust gas flowing into the exhaust catalyst device 18 (or the division ratio when the exhaust gas is divided into two paths) is controlled by the control device 29 according to the temperature of the reformer 2. In addition, a muffler 50 is interposed downstream of the joining point of the muffler side passage 6 and the catalyst passage 17 on the downstream side of the fuel cell 3, and the exhaust passage 14 is opened outside the vehicle on the downstream side.

  An outside air mixing valve 47 is interposed between the joining position of the exhaust passage 14 and the catalyst passage 17 and the reformer 2. The outside air mixing valve 47 is a three-way valve for mixing outside air into the exhaust gas. The outside air is introduced into the outside air mixing valve 47 through the outside air passage 48 opened to the outside of the vehicle 10. The outside air passage 48 is provided with a pressure feed pump for pushing outside air into the exhaust passage 14. The mixing ratio of the outside air and the exhaust gas mixed by the outside air mixing valve 47 (outside air mixing ratio) is controlled by the control device 29 according to the operating state of the engine 1 and the temperature of the reformer 2.

[2. Control configuration]
The control device 29 is an electronic control device (ECU (Electronic Control Unit)) that controls the opening degree of the mixed gas control valve 4, the mixing rate control valve 43, the exhaust gas diversion valve 46, and the outside air mixing valve 47. The control device 29 incorporates a processor, a memory, an interface device, and the like that are connected to each other via an internal bus. The processor is a processing device including, for example, a control unit (control circuit), an arithmetic unit (arithmetic circuit), a cache memory (register), and the like. The memory is a storage device that stores a program and working data, and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a nonvolatile memory, and the like. The contents of the control performed by the control device 29 are recorded and stored in the memory as firmware or an application program. The contents of the program are expanded in the memory space when the program is executed and executed by the processor.

  Connected to the controller 29 are a reformer temperature sensor 7, an engine speed sensor 30, an intake manifold pressure sensor 31, an air flow sensor 32, an accelerator opening sensor 33, a vehicle speed sensor 34, a shift position sensor 35, a water tank sensor 49, and the like. The information detected by these various sensors is input. The control device 29 grasps the operating state of the engine 1 based on these pieces of information and controls the power generation state in the fuel cell 3, as well as the mixed gas control valve 4, the mixing rate control valve 43, the exhaust shunt valve 46, the outside air The opening degree of the mixing valve 47 is controlled.

  The control device 29 determines whether or not the power generation condition of the fuel cell 3 is satisfied, and executes the power generation by the fuel cell 3 when the condition is satisfied. The power generation condition is, for example, a state in which the engine 1 is operating stably, and the remaining amount of fuel in the fuel tank 28 is equal to or greater than a predetermined amount, and regardless of the operating state of the engine 1, For example, the charging rate is below a predetermined value. The operating state of the engine 1 is grasped based on the engine speed, intake manifold pressure, intake air flow rate, accelerator opening, vehicle speed, shift position (selector operation position), and the like. During power generation of the fuel cell 3, based on the temperature of the reformer 2 detected by the reformer temperature sensor 7, the mixed gas control valve 4, the mixing rate control valve 43, the exhaust gas diversion valve 46, the outside air mixing The opening degree of each of the valves 47 is controlled.

  The mixed gas control valve 4 is opened at least during the operation of the engine 1 under the condition that the power generation condition of the fuel cell 3 is satisfied, and is preferably opened under the situation where the engine 1 is stably operating. For example, when the operating environment of the engine 1 is not an extremely hot environment or an extremely cold environment, and the fuel cell 3 is generating power during the operation after the warm-up operation of the engine 1 is completed, the mixed gas control valve 4 is Opened. On the other hand, if these conditions are not satisfied, the valve is controlled to be closed, and recirculation of the off-gas and reformed gas of the fuel cell 3 is prevented. Note that the mixed gas control valve 4 is closed if the fuel cell 3 is not generating power even when the engine 1 is in operation.

The opening degree of the mixed gas control valve 4 is controlled so as to increase as the temperature of the reformer 2 increases. For example, as shown in FIG. 3A, when the temperature of the reformer 2 is lower than the first temperature T ₁ , the opening degree of the mixed gas control valve 4 is controlled to a predetermined opening degree R ₀ and the second temperature T _2. In the above case, it is controlled to 100% (fully open). Further, when the temperature is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the opening degree is set so that the amount of the mixed gas introduced into the intake passage 12 increases as the temperature of the reformer 2 increases. Be controlled. The first temperature T ₁ and the second temperature T ₂ are set in advance as temperatures corresponding to a lower limit value and an upper limit value of a temperature range (operation temperature range) suitable for generating hydrogen gas in the reformer 2. The In the present embodiment, the first temperature T ₁ is set to about 600 to 650 ° C., and the second temperature T _{2 is set} to about 700 to 900 ° C.

The degree of opening of the mixing rate control valve 43 is such that the proportion of off-gas increases as the temperature of the reformer 2 increases (that is, the proportion of reformed gas increases as the temperature of the reformer 2 decreases). Be controlled. For example, as shown in FIG. 3B, when the temperature of the reformer 2 is lower than the first temperature T _1, off-gas is contained in R ₁ % (R ₁ is a predetermined value less than 50%), and the remaining 100− The opening degree is controlled so that R ₁ % becomes reformed gas. When the second temperature T ₂ above, the off-gas is R _2% (R ₁ is a predetermined value of 50% or more) included, the remaining 100-R _2% opening degree is controlled so that the reformed gas. When the temperature is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the opening degree is controlled so that the off-gas ratio increases as the temperature of the reformer 2 increases.

  However, when the remaining amount of water in the water tank 44 is less than or equal to a predetermined remaining amount, the proportion of off gas in the entire mixed gas may be increased in order to increase the amount of water recovered from the off gas. For example, as shown in FIG. 3E, as the remaining amount of water is smaller, the proportion of off-gas is increased and the proportion of reformed gas is decreased. By increasing the proportion of off gas, the amount of water contained in the mixed gas increases, and the water recovered in the water tank 44 can be increased.

The degree of opening of the exhaust shunt valve 46 is such that the exhaust gas introduced into the catalyst passage 17 increases as the temperature of the reformer 2 is higher (that is, the lower the temperature of the reformer 2 is, the higher the temperature of the reformer 2 is. It is controlled so that the amount of exhaust gas sent directly increases. For example, as shown in FIG. 3 (C), the temperature of the reformer 2 is at the first less than a temperature T ₁ of is controlled in the catalyst passages 17 side of the opening is 0% (fully closed), the reformer 2 The side is fully open (100%). On the other hand, the opening degree of the catalyst passage 17 side when the second temperature T ₂ above is controlled to 100% (fully open), the passage of the reformer 2 side is fully closed (0%). When the temperature is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the exhaust gas that flows around the reformer 2 (flows into the exhaust catalyst device 18) as the temperature of the reformer 2 rises. The opening degree of the exhaust shunt valve 46 is controlled so that (exhaust gas) increases.

  However, when the remaining amount of water in the water tank 44 is equal to or less than the predetermined remaining amount, the amount of exhaust gas flowing to the reformer 2 side is increased in order to increase the amount of recovered water contained in the exhaust gas of the engine 1. It may be increased. For example, as shown in FIG. 3F, the amount of exhaust gas flowing to the reformer 2 side is increased as the remaining amount of water is smaller. As a result, it becomes easy to secure water consumed by the steam reforming reaction in the reformer 2, and the condensed water recovered by the mixed gas cooler 11 increases, increasing the water recovered in the water tank 44. It becomes possible.

  The opening degree of the outside air mixing valve 47 is controlled according to the operating state of the engine 1, the power generation state of the fuel cell 3, and the temperature of the reformer 2. First, when power generation is performed by the fuel cell 3 when the engine 1 is not operating, the outside air passage 48 side of the outside air mixing valve 47 is controlled to be fully open (100% open), and the exhaust passage 14 side is fully closed (0%). . On the other hand, when the fuel cell 3 performs power generation when the engine 1 is operating, the opening degree of the outside air mixing valve 47 is controlled so that the outside air introduction amount increases as the temperature of the reformer 2 rises.

For example, as shown in FIG. 3 (D), the temperature of the reformer 2 is at the first less than a temperature T ₁ of is controlled to the opening degree of the outside air passage 48 side of 0% (fully closed), the exhaust passage 14 side is Fully open. On the other hand, when the temperature is equal to or higher than the second temperature T _2, the opening degree on the outside air passage 48 side is controlled to a predetermined opening degree R ₃ %, and the opening degree on the exhaust passage 14 side is controlled to 100-R ₃ %. When the temperature is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the opening degree on the outside air passage 48 side is increased as the temperature of the reformer 2 increases. Thereby, the reformer 2 is easily cooled by the outside air, and the excessive temperature rise of the reformer 2 due to the high-temperature exhaust gas is suppressed.

[3. Action]
FIG. 4 illustrates a flow of opening degree control accompanying power generation in the fuel cell 3. Information detected by the various sensors is read into the control device 29 (step A1), and it is determined whether or not the power generation condition of the fuel cell 3 is satisfied (step A2). If the power generation condition is not satisfied, this flow ends. On the other hand, when the power generation condition is satisfied, it is determined whether or not the engine 1 is operating (step A3). If the engine 1 is operating, the reformed gas obtained by reforming the exhaust gas of the engine 1 is used for power generation in the fuel cell 3, and the off gas of the fuel cell 3 and the reformed gas of the reformer 2 are combined. Control for recirculation to the intake passage 12 of the engine 1 is performed. That is, the opening degree of the mixed gas control valve 4, the mixing rate control valve 43, the exhaust gas diversion valve 46, and the outside air mixing valve 47 is set and controlled according to the temperature of the reformer 2 (step A4). Power generation is performed (step A5).

On the other hand, if the engine 1 is not operated, the mixed gas control valve 4 is closed, and the recirculation of the mixed gas is shut off. Further, since exhaust gas does not flow into the exhaust passage 14, the outside air passage 48 side of the outside air mixing valve 47 is opened (step A6).
Regarding the operation of the mixed gas control valve 4, if the temperature of the reformer ₂ is equal to or higher than the second temperature T2, the mixed gas recirculation passage 5 is largely opened as shown in FIG. 1 is introduced into the intake system. At this time, as shown in FIG. 3B, the mixed gas contains a large amount of off-gas of the fuel cell 3, and the off-gas functions as a combustion inhibitor for the engine 1. Therefore, the temperature of the exhaust gas flowing into the reformer 2 is slightly lowered, and the temperature of the reformer 2 is easily maintained in the operating temperature range.

On the other hand, the temperature of the reformer 2 is if the first temperature T _1, less than a mixed gas recirculation passage 5 is narrowed. As a result, the temperature of the exhaust gas is less likely to decrease due to the effect of off-gas, and the temperature of the reformer 2 is easily maintained in the operating temperature range. At this time, since the ratio of the off gas contained in the mixed gas is also low, the temperature of the reformer 2 is stably maintained. When the temperature of the reformer 2 is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the amount of the mixed gas introduced into the intake passage 12 increases as the temperature of the reformer 2 increases. To do. That is, the magnitude of the temperature rise suppression effect by the mixed gas is automatically adjusted according to the state of the reformer 2. This temperature rise suppression effect is further promoted by the opening degree control of the mixing rate control valve 43. Therefore, a sudden change in the temperature of the reformer 2 is efficiently prevented, the power generation state of the fuel cell 3 is stabilized, and the combustion stability of the engine 1 is also improved.

Regarding the operation of the exhaust gas diversion valve 46, if the temperature of the reformer ₂ is equal to or higher than the second temperature T2, the exhaust gas is supplied to the catalyst passage 17 as shown in FIG. As a result, a situation in which the high-temperature exhaust gas further raises the temperature of the reformer 2 is avoided, and overheating of the reformer 2 is prevented. Therefore, the temperature of the reformer 2 is easily maintained in the operating temperature range. Further, since the unburned hydrocarbon component in the exhaust gas is burned and removed by the exhaust catalyst device 18, the exhaust environmental performance of the vehicle 10 is improved.

On the other hand, if the temperature of the reformer 2 is lower than the first temperature T ₁ , exhaust gas is supplied to the reformer 2. Thereby, the reformer 2 is quickly warmed up by the high-temperature exhaust gas. Therefore, the temperature of the reformer 2 is easily maintained in the operating temperature range, and the power generation state of the fuel cell 3 is stabilized. When the temperature of the reformer 2 is equal to or higher than the first temperature T ₁ and lower than the second temperature T ₂ , the amount of exhaust gas flowing into the catalyst passage 17 increases as the temperature of the reformer 2 increases. On the contrary, the amount of inflow to the reformer 2 is reduced. That is, the temperature of the exhaust gas flowing into the reformer 2 is automatically adjusted according to the state of the reformer 2. Therefore, a sudden change in the temperature of the reformer 2 is efficiently prevented, and the power generation state of the fuel cell 3 is stabilized.

Regarding the operation of the outside air mixing valve 47, if the temperature of the reformer ₂ is equal to or higher than the second temperature T2, the outside air is introduced into the exhaust gas as shown in FIG. As a result, the exhaust gas is cooled by the outside air, and the exhaust gas having an appropriate temperature is introduced into the reformer 2 and the fuel cell 3. Therefore, the temperatures of the reformer 2 and the fuel cell 3 are easily maintained in an appropriate operating temperature range. Meanwhile, since the temperature of the reformer 2 is introduced in the outside air, if the first temperature T less than ₁ is stopped, the reformer 2 and the fuel cell 3 is quickly warmed, the power generation state of the fuel cell 3 is stabilized .

[4. effect]
(1) In the fuel cell system described above, the opening degree of the mixing rate control valve 43 is controlled according to the temperature of the reformer 2, and the amount of exhaust gas flowing to the reformer 2 side and the exhaust that bypasses the reformer 2 The amount of gas is adjusted. Thereby, for example, during the warm-up of the reformer 2, the temperature of the reformer 2 and the fuel cell 3 can be quickly raised using the heat of the exhaust gas. On the other hand, after the reformer 2 is warmed up, the overheating of the reformer 2 and the fuel cell 3 can be suppressed by bypassing the exhaust gas. Thus, the temperature of the reformer 2 and the fuel cell 3 can be easily maintained within an appropriate operating temperature range, and the stability of the power generation state in the fuel cell 3 can be improved.

  (2) As shown in FIG. 3 (C), the higher the temperature of the reformer 2, the higher the amount of exhaust gas introduced from the exhaust passage 14 into the catalyst passage 17, thereby reforming with higher temperature exhaust gas. It is possible to avoid a situation in which the vessel 2 is excessively heated. On the other hand, when the temperature of the reformer 2 is decreasing, the temperature of the reformer 2 is prevented from decreasing because the high-temperature exhaust gas introduced into the reformer 2 increases. Therefore, the power generation state in the fuel cell 3 can be stabilized.

  (3) In the above fuel cell system, the outside air mixing valve 47 for introducing outside air to the upstream side of the reformer 2 is disposed. Thereby, it is possible to control the temperature of the reformer 2 using not only high-temperature exhaust gas but also low-temperature outside air. For example, when the temperature of the exhaust gas is excessively high, it can be introduced into the reformer 2 after the temperature is appropriately reduced using outside air. Therefore, the temperature of the reformer 2 and the fuel cell 3 can be easily maintained within an appropriate operating temperature range, and the stability of the power generation state in the fuel cell 3 can be improved.

  (4) As shown in FIG. 3D, the reformer 2 can be cooled with outside air by increasing the amount of outside air as the temperature of the reformer 2 is higher. An excessive temperature rise can be suppressed. Moreover, even if the flow rate of the exhaust gas introduced from the exhaust gas diversion valve 46 to the reformer 2 is insufficient, the shortage can be covered with outside air, and a constant flow rate can be secured. Therefore, the circulation of exhaust gas, reformed gas, off gas, etc. can be maintained.

  (5) Carbon dioxide contained in the off-gas of the fuel cell 3 functions as a combustion inhibitor for the engine 1 and acts to lower the exhaust gas temperature of the engine 1. On the other hand, the hydrogen gas contained in the reformed gas functions as a combustion accelerator for the engine 1 and acts to increase the exhaust gas temperature of the engine 1. Therefore, by adjusting the mixing ratio of the off gas and the reformed gas, the balance between the combustion promoting action and the combustion suppressing action for the engine 1 can be adjusted, and the exhaust gas discharged from the engine 1 (that is, the reformed gas) The temperature of the exhaust gas introduced into the vessel 2 can be controlled. For example, the temperature of the reformer 2 can be actively brought close to 600 ° C., and the temperature environment required for reforming can be easily maintained. Thereby, the power generation state in the fuel cell 3 can be stabilized.

  (6) In the fuel cell system described above, as shown in FIG. 3B, the mixing rate control valve 43 is controlled such that the higher the temperature of the reformer 2, the higher the off-gas ratio. By such control, when the temperature of the exhaust gas discharged from the engine 1 is too high, the temperature can be lowered efficiently, and the temperature of the reformer 2 is maintained within a predetermined operating temperature range. It can be made easier. On the other hand, when the temperature of the exhaust gas is too low, the ratio of the reformed gas increases, so that the exhaust gas temperature can be increased efficiently. Therefore, the temperature of the reformer 2 and the fuel cell 3 can be easily maintained within an appropriate operating temperature range, and the stability of the power generation state in the fuel cell 3 can be improved.

  (7) In the fuel cell system described above, the mixed gas cooler 11 is interposed in the mixed gas recirculation passage 5, and the condensed water generated by cooling the mixed gas is recovered by the water tank 44 and reformed. It is used for the reforming process in the vessel 2. In this way, by reducing the temperature of the mixed gas that is recirculated to the engine 1, the in-cylinder temperature can be reduced, and the engine output and knock resistance can be improved. In addition, by using the moisture contained in the off-gas and reformed gas as water for steam reforming, it is not necessary to separately prepare moisture for operating the reformer 2, and the simple apparatus configuration and low cost can be achieved. A practical fuel cell system can be realized.

  (8) In the fuel cell system described above, as shown in FIG. 3E, the degree of opening of the mixing rate control valve 43 is controlled so that the proportion of off-gas increases as the remaining amount of water in the water tank 44 decreases. Is done. By such control, it is possible to increase the recovered amount of moisture contained in the off gas (that is, water vapor generated on the anode side of the fuel cell 3), and keep the reformer 2 operating stably for a long time. It becomes possible.

  (9) In the fuel cell system described above, as shown in FIG. 3F, the amount of exhaust gas introduced from the exhaust passage 14 to the catalyst passage 17 decreases as the amount of water in the water tank 44 decreases. Thus, the opening degree of the exhaust gas diversion valve 46 is controlled. By such control, the steam reforming reaction in the reformer 2 using moisture contained in the exhaust gas can be promoted, and the generation efficiency of the reformed gas can be increased. Further, since the exhaust gas containing moisture is introduced into the reformer 2 and the fuel cell 3, the amount of moisture recovered from the reformed gas and off-gas can be increased, and the remaining water in the water tank 44 can be increased. The amount can be increased.

[5. Modified example]
In the above-described embodiment, the vehicle 10 to which the fuel cell system of the present embodiment is applied is illustrated, but the application target of the fuel cell system is not limited to this. For example, the present invention may be applied to household electrical appliances, railways, ships, aircraft, factories, emergency power supply facilities, and the like. As long as the apparatus can at least use the fuel cell off-gas and the engine exhaust gas, the same configuration as in the above-described embodiment can be applied to achieve the same effects as the above-described embodiment. Become.

  In the above-described embodiment, the engine 1 equipped with the exhaust gas recirculation system is illustrated. However, the exhaust gas recirculation system is an essential element for realizing the mutual use of the fuel cell off-gas and the engine exhaust gas. is not. Therefore, the mixed gas recirculation passage 5 may be formed by using an EGR structure (such as a low pressure EGR passage or a high pressure EGR passage) of the engine 1 having an existing EGR system.

DESCRIPTION OF SYMBOLS 1 Engine 2 Reformer 3 Fuel cell 4 Mixed gas control valve 5 Mixed gas recirculation passage 7 Reformer temperature sensor 10 Vehicle 11 Mixed gas cooler 14 Exhaust passage 17 Catalyst passage 18 Exhaust catalyst device 29 Control device 41 Reformed gas passage 42 Off-gas passage 43 Mixing rate control valve 44 Water tank 46 Exhaust gas diversion valve 47 Outside air mixing valve 49 Water tank sensor

Claims (9)

A reformer interposed in the exhaust passage of the engine and reforming hydrocarbons contained in the exhaust gas to generate hydrogen gas;
A fuel cell that generates electricity using the hydrogen gas generated in the reformer as a fuel;
An air-fuel mixture recirculation passage for recirculating the air-fuel mixture of the reformed gas discharged from the reformer and the off-gas of the fuel cell to the intake system of the engine;
A catalyst passage branched from the exhaust passage between the engine and the reformer, bypassing the reformer and connected to the outside of the vehicle;
An exhaust gas diversion valve for controlling the amount of exhaust gas introduced from the exhaust passage into the catalyst passage;
A fuel cell system comprising: a control device that adjusts an opening of the exhaust gas diversion valve according to a temperature of the reformer. The control device controls the opening of the exhaust shunt valve so that the amount of exhaust gas introduced from the exhaust passage into the catalyst passage increases as the temperature of the reformer increases. The fuel cell system according to claim 1. An outside air passage for introducing outside air into the exhaust passage between the exhaust diversion valve and the reformer;
The fuel cell system according to claim 1, further comprising an outside air mixing valve that controls an amount of outside air introduced from the outside air passage. 4. The fuel cell system according to claim 3, wherein the control device controls the opening degree of the outside air mixing valve so that the outside air amount increases as the temperature of the reformer increases. 5. The fuel cell system according to any one of claims 1 to 4, further comprising a mixing rate control valve that controls a mixing rate of the reformed gas and the off-gas in the air-fuel mixture. 6. The fuel cell system according to claim 5, wherein the control device controls the opening degree of the mixing rate control valve so that the proportion of the off gas increases as the temperature of the reformer increases. A heat exchanger interposed in the mixture recirculation passage for cooling the mixture;
A water tank for recovering the moisture of the air-fuel mixture cooled by the heat exchanger;
The fuel cell system according to any one of claims 1 to 6, further comprising a water injection valve that supplies the moisture recovered in the water tank to the inside of the reformer. The said control apparatus controls the said mixing rate of the said mixing rate control valve so that the ratio of the said off-gas may increase, so that the residual amount of the said water | moisture content collect | recovered by the said water tank is small. 8. The fuel cell system according to 7. The control device controls the opening of the exhaust gas diversion valve so that the amount of exhaust gas introduced from the exhaust passage into the catalyst passage decreases as the remaining amount of water collected in the water tank decreases. The fuel cell system according to claim 7 or 8, wherein

Images