JP2006343268A - Concentration detecting apparatus and concentration detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration detecting apparatus and a concentration detecting method, capable of accurately detecting the concentration of substances dissolved in a liquid, without using a large-size system. <P>SOLUTION: The concentration detecting apparatus 200 comprises a Peltier device 202 for cooling a methanol solution, a solution temperature sensor 208 for detecting a temperature of the methanol solution to be cooled, and a Peltier temperature sensor 210 for detecting the temperature of the Peltier device 202. The freezing point of the methanol solution is detected from the detection result of the solution temperature sensor 208 and a detecting result of the Peltier temperature sensor 210. Then, the methanol concentration of the methanol solution is detected from the detected freezing point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a concentration detection device and a concentration detection method, and more particularly to a concentration detection device and a concentration detection method used in a fuel cell system.

  In a fuel cell system of a type that supplies an aqueous fuel solution such as a direct methanol fuel cell system to a fuel cell stack, the polymer membrane may be damaged if the fuel concentration is low, while if the fuel concentration is too high, the fuel cell system may be damaged. Therefore, the fuel concentration is kept constant by replenishing the circulated aqueous solution with fuel. For this purpose, it is necessary to detect the concentration of the fuel dissolved in the circulated aqueous solution every predetermined time.

Here, as an example of a technique for detecting the fuel concentration, a technique using an ultrasonic sensor is disclosed in Patent Document 1.
An apparatus for controlling the temperature of crystal growth using a Peltier element is disclosed in Patent Document 2.
Japanese Patent Laying-Open No. 2005-30949 JP-A-10-29899

However, the ultrasonic sensor disclosed in Patent Document 1 has a problem that the apparatus becomes large because the transmitter and the receiver must be provided at a certain distance. Further, when bubbles are generated in the aqueous solution, the concentration cannot be detected accurately.
The technique of Patent Document 2 is a technique used for temperature control of crystal growth and is not used for concentration detection.
Therefore, a main object of the present invention is to provide a concentration detection device and a concentration detection method capable of accurately detecting the concentration of a substance dissolved in a liquid without using a large device.

  In order to achieve the above object, the concentration detection apparatus according to claim 1 includes a cooling means for cooling the liquid in which the substance is dissolved, a first temperature detection means for detecting the temperature of the liquid to be cooled, and a first temperature. A freezing point detecting means for detecting the freezing point of the liquid based on the temperature detected by the detecting means, and a concentration detecting means for detecting the concentration of the substance dissolved in the liquid based on the freezing point detected by the freezing point detecting means are provided.

  The concentration detection device according to claim 2 is the concentration detection device according to claim 1, further comprising: a detection unit that holds the liquid in a stopped state in order to detect the temperature of the liquid; and a liquid in the detection unit. The first temperature detecting means detects the temperature of the liquid in the detecting section.

  The concentration detection device according to claim 3 is the concentration detection device according to claim 1 or 2, further comprising heating means for heating the liquid.

  According to a fourth aspect of the present invention, there is provided the concentration detection apparatus according to the third aspect, further comprising a temperature changing unit that is also used as a cooling unit and a heating unit.

  The concentration detection device according to claim 5 further includes second temperature detection means for detecting the temperature of the cooling means in the concentration detection device according to any one of claims 1 to 4, wherein the freezing point detection means includes: The solidification point of the liquid is detected based on the detection result of the temperature detection means and the detection result of the second temperature detection means.

  The concentration detection device according to claim 6 is the concentration detection device according to any one of claims 1 to 5, further comprising a tank for storing the liquid and a first pipe for sending the liquid in the tank to the vicinity of the cooling means. And a second pipe for returning the liquid after concentration detection to the tank.

  A fuel cell system according to a seventh aspect includes the concentration detection device according to any one of the first to sixth aspects.

  A transportation device according to an eighth aspect includes the fuel cell system according to the seventh aspect.

  The concentration detection method according to claim 9 includes a step of introducing a liquid in which a substance is dissolved into the cooling space, a step of cooling the liquid introduced into the cooling space by the cooling means, a step of detecting the temperature of the cooling means, and cooling. Detecting the temperature of the liquid cooled in the space, detecting the freezing point of the liquid based on the detected temperature of the cooling means and the temperature of the liquid, and dissolving in the liquid based on the detected freezing point of the liquid Detecting the concentration of the substance.

  The concentration detection method according to claim 10 is the concentration detection method according to claim 9, wherein the step of cooling the liquid is based on the first step of cooling the liquid with the first cooling capacity and the first cooling capacity. And a second step of cooling the liquid with a low cooling capacity.

  A fuel cell system according to an eleventh aspect is a fuel cell system using an aqueous fuel solution, wherein the freezing point of the aqueous fuel solution is detected and the concentration of the aqueous fuel solution is adjusted based on the detected freezing point.

  There is a correlation between the freezing point of the liquid and the concentration of the substance dissolved in the liquid. In the concentration detection apparatus according to the first aspect, by using this correlation, the concentration of the substance dissolved in the liquid can be accurately detected based on the freezing point of the liquid. Moreover, it is not necessary to use a large device such as an ultrasonic sensor. The same applies to the concentration detection method according to the ninth aspect.

  In the concentration detection apparatus according to claim 2, since the temperature of the liquid is detected in a state where the liquid introduced into the detection unit is stopped, the temperature of the liquid and thus the freezing point of the liquid can be accurately detected. The concentration of dissolved substances can be detected accurately.

  In the concentration detection apparatus according to the third aspect, since the liquid solidified for concentration detection can be dissolved, replacement of the liquid whose concentration is detected is surely and easily performed.

  In the concentration detection apparatus according to the fourth aspect, since the temperature changing means can be used for both cooling and heating of the liquid, the configuration of the apparatus can be simplified and reduced in size.

  When the liquid is cooled and solidified by the cooling means, when the liquid starts to solidify, the temperature of the liquid temporarily rises due to heat generation, and at this time, the temperature difference between the liquid and the cooling means also temporarily increases. In the concentration detection apparatus according to claim 5, by detecting not only the liquid but also the temperature of the cooling means and utilizing the above characteristics when the liquid solidifies, the liquid is detected based on the temperature difference between the liquid and the cooling means. It is possible to know that the liquid has started to solidify and to detect the freezing point of the liquid more accurately.

  In the concentration detection apparatus according to the sixth aspect, by returning the liquid whose concentration is detected to the tank, it is possible to prevent the liquid from being wasted for detecting the concentration.

  Since it is important to accurately detect the fuel concentration in the fuel cell system, the present invention is used in the fuel cell system as described in claim 7, and as a result, the fuel cell system as described in claim 8 is used. It is effective to use for the used transportation equipment.

  In the concentration detection method according to the tenth aspect, the time to concentration detection can be shortened and the concentration detection accuracy can be improved by cooling at a relatively high speed first and then reducing the cooling capacity.

  As in the fuel cell system according to claim 11, if the concentration of the aqueous fuel solution is directly adjusted based on the detected freezing point, the fuel can be detected without detecting the concentration of the substance contained in the aqueous fuel solution. The concentration of the aqueous solution can be easily adjusted.

  According to the present invention, the concentration of a substance dissolved in a liquid can be accurately detected without using a large device.

  Embodiments of the present invention will be described below with reference to the drawings. Here, the case where the fuel cell system including the concentration detection device of the present invention is mounted on the two-wheeled vehicle 10 which is an example of the transportation device will be described. Here, the liquid (solution) whose concentration is to be detected is an aqueous methanol solution. Thus, the solvent is water and the solute is methanol. Then, the concentration of the solute in the solution in which the solute is dispersed in the solvent is measured.

  First, the motorcycle 10 will be described. Left and right, front and rear, and top and bottom in the embodiment of the present invention mean left and right, front and back, and top and bottom, based on a state where the driver is seated on the seat of the motorcycle 10 toward the handle 24 thereof.

  1 to 7, the two-wheeled vehicle 10 has a body frame 12. The vehicle body frame 12 includes a head pipe 14, a front frame 16 having an I-shaped longitudinal section extending obliquely downward from the head pipe 14, and a rear frame connected to a rear end portion of the front frame 16 and rising obliquely upward rearward. 18 and a seat rail 20 attached to the upper end of the rear frame 18. The rear end portion of the front frame 16 is connected to a position slightly closer to the lower end portion than the center portion of the rear frame 18, and the front frame 16 and the rear frame 18 as a whole have a substantially Y shape in side view.

  The front frame 16 has a plate-like member 16a having a width in the up-down direction, extending obliquely downward to the rear and orthogonal to the left-right direction, and formed at the upper and lower edges of the plate-like member 16a, respectively, and to the rear. Flange portions 16b and 16c extending obliquely downward and having a width in the left-right direction, reinforcing ribs 16d projecting on both surfaces of the plate-like member 16a, and the rear frame 18 are connected to each other by, for example, bolts provided at the rear end portion. Connecting portion 16e. The reinforcing ribs 16d together with the flange portions 16b and 16c partition both surfaces of the plate-like member 16a to form a storage space for storing components of the fuel cell system 100 described later.

  On the other hand, the rear frame 18 includes plate-like members 18a and 18b that extend obliquely upward to the rear and have a width in the front-rear direction and are arranged so as to sandwich the connecting portion 16e of the front frame 16.

  As shown mainly in FIG. 1, a steering shaft 22 for changing the vehicle body direction is rotatably inserted into the head pipe 14. A handle support portion 26 to which a handle 24 is fixed is attached to the upper end of the steering shaft 22, and grips 28 are attached to both ends of the handle 24. The right grip 28 constitutes a rotatable throttle grip.

  A display operation unit (hereinafter abbreviated as a meter) 30 is disposed in front of the handle 24 of the handle support unit 26. The meter 30 is formed by integrating a display unit configured with, for example, a liquid crystal display for providing various information such as a driving state for the driver, and an input unit for inputting various information from the driver. A head lamp 32 is fixed below the meter 30 in the handle support portion 26, and flasher lamps 34 are respectively provided on the left and right sides of the head lamp 32.

  A pair of left and right front forks 36 are attached to the lower end of the steering shaft 22, and a front wheel 38 is attached to the lower end of each front fork 36 via a front axle 40. The front wheel 38 is rotatably supported by the front axle 40 while being buffered and suspended by the front fork 36.

  On the other hand, a frame-like seat rail 20 is attached to the rear end portion of the rear frame 18. The seat rail 20 is fixed to the upper end portion of the rear frame 18 by welding, for example, and is disposed substantially in the front-rear direction. A seat (not shown) is provided on the seat rail 20 so as to be freely opened and closed. A mounting bracket 42 is fixed to the rear end portion of the seat rail 20, and a tail lamp 44 and a pair of left and right flasher lamps 46 are mounted on the mounting bracket 42, respectively.

  A rear arm 48 is swingably supported at the lower end of the rear frame 18 via a pivot shaft 50, and a rear wheel 52, which is a drive wheel, is rotatably supported at a rear end 48a of the rear arm 48. The rear arm 48 and the rear wheel 52 are buffered and suspended from the rear frame 18 by a rear cushion (not shown).

  Further, a footrest mounting bar 54 is fixed to the front side of the lower end portion of the rear frame 18 so as to protrude from the rear frame 18 in the left-right direction, and a footrest (not shown) is mounted on the footrest mounting bar 54. Behind the footrest mounting bar 54, a main stand 56 is rotatably supported by a rear arm 48, and the main stand 56 is urged toward the closing side by a return spring 58.

  On the inner side of the rear end portion 48 a of the rear arm 48, for example, an axial gap type electric motor 60 that is coupled to the rear wheel 52 and rotates the rear wheel 52, and a drive that is electrically connected to the electric motor 60. A unit 62 is disposed. The drive unit 62 includes a controller 64 for controlling the rotational drive of the electric motor 60.

  In such a motorcycle 10, the fuel cell system 100 is mounted along the body frame 12. The fuel cell system 100 generates electric energy for driving the electric motor 60 and other components.

Hereinafter, the fuel cell system 100 will be described.
The fuel cell system 100 is a direct methanol fuel cell system that directly uses methanol (aqueous methanol solution) for power generation without reforming.

  The fuel cell system 100 includes a fuel cell stack (hereinafter simply referred to as a cell stack) 102 disposed below the front frame 16.

  As shown in FIGS. 8 and 9, the cell stack 102 includes a plurality of fuel cells (fuel cell) 104 that can generate electric energy by an electrochemical reaction between hydrogen based on methanol and oxygen, with a separator 106 interposed therebetween. It is configured by stacking. Each fuel cell 104 constituting the cell stack 102 includes an electrolyte (electrolyte membrane) 104a composed of a solid polymer membrane and the like, an anode (fuel electrode) 104b and a cathode (air electrode) facing each other across the electrolyte 104a. 104c. Each of the anode 104b and the cathode 104c includes a platinum catalyst layer provided on the electrolyte 104a side.

  As shown in FIG. 4 and the like, the cell stack 102 is placed on a skid 108, and the skid 108 is supported by a stay stack 110 that is suspended from a flange portion 16 c of the front frame 16.

  As shown in FIG. 6, an aqueous solution radiator 112 and a gas-liquid separation radiator 114 are disposed below the front frame 16 and above the cell stack 102. The radiators 112 and 114 are integrally formed, and have a plurality of plate-like fins (not shown) whose front surfaces are disposed slightly forward of the vehicle and are orthogonal to the front surfaces. Such radiators 112 and 114 can sufficiently receive wind during traveling.

  As shown in FIG. 6 and the like, the radiator 112 includes a radiator pipe 116 that is formed to pivot. The radiator pipe 116 is formed as a single continuous pipe from the inlet 118a (see FIG. 5) to the outlet 118b (see FIG. 3) by welding a straight pipe made of stainless steel or the like and a U-shaped joint pipe. Is formed. A radiator cooling fan 120 is provided on the back side of the radiator 112 so as to face the radiator pipe 116.

  Similarly, the radiator 114 includes two radiator pipes 122 formed to meander. Each radiator pipe 122 is a single continuous pipe from the inlet 124a (see FIG. 3) to the outlet 124b (see FIG. 3) by welding a straight pipe made of stainless steel or the like and a U-shaped joint pipe. Is formed. A radiator cooling fan 126 is provided on the back surface side of the radiator 114 so as to face the radiator pipe 122.

  1 to 7 and mainly referring to FIG. 3, a fuel tank 128, an aqueous solution tank 130, and a water tank 132 are arranged in order from the top on the rear side of the connecting portion 16 e of the front frame 16. The fuel tank 128, the aqueous solution tank 130, and the water tank 132 are obtained by, for example, PE (polyethylene) blow molding.

  The fuel tank 128 is disposed below the seat rail 20 and is attached to the rear end portion of the seat rail 20. The fuel tank 128 contains methanol fuel (high-concentration aqueous methanol solution) with a high concentration (for example, containing about 50 wt% of methanol) that becomes a fuel for the electrochemical reaction of the cell stack 102. The fuel tank 128 has a lid 128a on its upper surface, and the lid 128a is removed to supply methanol fuel.

  The aqueous solution tank 130 is provided below the fuel tank 128 and attached to the rear frame 18. The aqueous solution tank 130 contains an aqueous methanol solution obtained by diluting the methanol fuel from the fuel tank 128 to a concentration suitable for the electrochemical reaction of the cell stack 102 (for example, containing about 3 wt% of methanol). That is, the aqueous solution tank 130 contains an aqueous methanol solution to be sent out toward the cell stack 102 by an aqueous solution pump 146 (described later).

  A level sensor 129 is attached to the fuel tank 128 to detect the level of the methanol fuel level in the fuel tank 128. A level sensor 131 is attached to the aqueous solution tank 130 to detect the level of the aqueous methanol solution in the aqueous solution tank 130. By detecting the liquid level height with the level sensors 129 and 131, the amount of liquid in the tank can be detected. The liquid level in the aqueous solution tank 130 is controlled, for example, within a range indicated by X in FIG.

  The water tank 132 is disposed between the plate-like members 18 a and 18 b of the rear frame 18 and on the rear side of the cell stack 102.

  A secondary battery 134 is disposed on the front side of the fuel tank 128 and on the upper side of the flange portion 16 b of the front frame 16. The secondary battery 134 stores the electrical energy generated in the cell stack 102 and supplies the electrical energy to the corresponding electrical component in accordance with a command from a controller 156 (described later). For example, the secondary battery 134 supplies electric energy to the auxiliary machines and the drive unit 62.

  A fuel pump 136 is disposed above the secondary battery 134 and below the seat rail 20.

  A catch tank 140 is disposed above the aqueous solution tank 130. The catch tank 140 is provided with a lid 140a on the upper surface thereof. For example, in a state where the fuel cell system 100 has never been activated (the aqueous solution tank 130 is empty), the aqueous methanol solution is supplied by removing the lid 140a. The catch tank 140 is obtained by PE (polyethylene) blow molding, for example.

  In addition, an air filter 142 is disposed in a space surrounded by the front frame 16, the cell stack 102, and the radiators 112 and 114, and an aqueous solution filter 144 is disposed obliquely below and behind the air filter 142.

  As shown in FIG. 4, an aqueous solution pump 146 and an air pump 147 are stored in the storage space on the left side of the front frame 16. On the left side of the air pump 147, an electromagnetic valve 148, a concentration sensor 149, and an air chamber 150 are arranged. The aqueous solution pump 146 is provided at a position higher than the aqueous solution tank 130.

  Further, as shown in FIG. 5, a main switch 152, a DC-DC converter 154, a controller 156, a rust prevention valve 158, and a water pump 160 are arranged in order from the front in the storage space on the right side of the front frame 16. The main switch 152 is provided so as to penetrate the storage space of the front frame 16 from the right side to the left side. A horn 162 is provided on the front surface of the cell stack 102.

The piping of the fuel cell system 100 arranged in this way will be described with reference to FIGS. 4 to 7 and FIG.
The fuel tank 128 and the fuel pump 136 are connected by a pipe P1, and the fuel pump 136 and the aqueous solution tank 130 are connected by a pipe P2. The pipe P1 connects the lower left end of the fuel tank 128 and the lower left end of the fuel pump 136, and the pipe P2 connects the lower left end of the fuel pump 136 and the lower left end of the aqueous solution tank 130. By driving the fuel pump 136, the methanol fuel in the fuel tank 128 is supplied to the aqueous solution tank 130 through the pipes P1 and P2.

  The aqueous solution tank 130 and the aqueous solution pump 146 are communicated by a pipe P3, the aqueous solution pump 146 and the aqueous solution filter 144 are communicated by a pipe P4, and the aqueous solution filter 144 and the cell stack 102 are communicated by a pipe P5. The pipe P3 connects the lower left side corner of the aqueous solution tank 130 and the rear portion of the aqueous solution pump 146, the pipe P4 connects the rear portion of the aqueous solution pump 146 and the left side surface of the aqueous solution filter 144, and the pipe P5 connects the aqueous solution filter 144. The right side is connected to the anode inlet I1 located at the lower right corner of the front surface of the cell stack 102. By driving the aqueous solution pump 146, the aqueous methanol solution from the aqueous solution tank 130 is sent from the pipe P3 side to the pipe P4 side, and after impurities are removed by the aqueous solution filter 144, the aqueous solution pump 146 enters the cell stack 102 via the pipe P5. Given. In this embodiment, pipes P4 and P5 constitute pipes for guiding the aqueous methanol solution sent out by the aqueous solution pump 146 to each fuel cell 104 of the cell stack 102.

  The cell stack 102 and the aqueous solution radiator 112 are connected by a pipe P6, and the radiator 112 and the aqueous solution tank 130 are connected by a pipe P7. The pipe P6 connects the anode outlet I2 located at the upper left corner of the rear surface of the cell stack 102 and the inlet 118a (see FIG. 5) of the radiator pipe 116 drawn from the lower right end of the radiator 112, and the pipe P7 is connected to the radiator 112. The outlet 118b of the radiator pipe 116 (see FIG. 3) drawn from a position slightly closer to the center from the lower left end of the lower surface of the aqueous solution tank 130 is connected to the upper left corner of the aqueous solution tank 130. The unreacted aqueous methanol solution and carbon dioxide discharged from the cell stack 102 are supplied to the radiator 112 via the pipe P6, the temperature is lowered, and returned to the aqueous solution tank 130 via the pipe P7. As a result, the temperature of the aqueous methanol solution in the aqueous solution tank 130 can be lowered.

  The pipes P1 to P7 described above mainly serve as fuel flow paths.

  Further, the air filter 142 and the air chamber 150 are communicated by a pipe P8, the air chamber 150 and the air pump 147 are communicated by a pipe P9, and the air pump 147 and the rust prevention valve 158 are connected by a pipe P10 and are used for rust prevention. The valve 158 and the cell stack 102 are connected by a pipe P11. The pipe P8 connects the rear part of the air filter 142 and a position slightly ahead of the center part of the air chamber 150, and the pipe P9 connects the lower side of the center part of the air chamber 150 and the rear part of the air pump 147. P10 connects the air pump 147 located on the left side of the plate member 16a of the front frame 16 and the rust prevention valve 158 located on the right side of the plate member 16a, and the pipe P11 is connected to the rust prevention valve 158 and the cell stack 102. To the cathode inlet I3 located at the upper right end of the rear surface. When the fuel cell system 100 is operated, the rust prevention valve 158 is opened, and the air pump 147 is driven in this state, whereby oxygen-containing air is sucked from the outside. The sucked air is purified by the air filter 142, and then flows into the air pump 147 through the pipe P8, the air chamber 150, and the pipe P9, and further passes through the pipe P10, the rust prevention valve 158, and the pipe P11. Is provided to the stack 102. The rust prevention valve 158 is closed when the fuel cell system 100 is stopped, and prevents the backflow of water vapor to the air pump 147 to prevent the air pump 147 from rusting.

  The cell stack 102 and the radiator 114 for gas-liquid separation are communicated with each other by two pipes P12. The radiator 114 and the water tank 132 are communicated by two pipes P13, and the water tank 132 is connected to a pipe (exhaust pipe) P14. Is provided. Each pipe P12 connects a cathode outlet I4 located at the lower left corner of the front surface of the cell stack 102 and an inlet 124a (see FIG. 3) of each radiator pipe 122 drawn from the lower left end of the radiator 114. The outlet 124b (see FIG. 3) of each radiator pipe 122 drawn from a position slightly on the left side of the lower surface of the radiator 114 is connected to the front upper part of the water tank 132, and the pipe P14 is an upper rear part of the water tank 132. It is formed in a U shape so that it rises once and then descends. Exhaust gas containing water (water and water vapor) and carbon dioxide discharged from the cathode outlet I4 of the cell stack 102 is given to the radiator 114 via the pipe P12, and the water vapor is liquefied. Exhaust gas from the radiator 114 is supplied to the water tank 132 together with water through the pipe P13, and is discharged to the outside through the pipe P14.

  The pipes P8 to P14 described above mainly serve as an exhaust passage.

  Further, the water tank 132 and the water pump 160 are communicated by a pipe P15, and the water pump 160 and the aqueous solution tank 130 are communicated by a pipe P16. The pipe P15 connects the lower right side of the water tank 132 and the central part of the water pump 160, and the pipe P16 connects the central part of the water pump 160 and the upper left corner of the aqueous solution tank 130. By driving the water pump 160, the water in the water tank 132 is returned to the aqueous solution tank 130 via the pipes P15 and P16.

  The pipes P15 and P16 described above serve as water flow paths.

  In addition, a pipe P17 is connected to the pipe P4 so that a part of the methanol aqueous solution sent out by the aqueous solution pump 146 and flowing through the pipe P4 flows. As shown in FIG. 4, an electromagnetic valve 148 is connected to the pipe P17. The electromagnetic valve 148 and the concentration sensor 149 are communicated with each other by a pipe P18. Further, the pipe P18 connects the concentration sensor 149 and the upper surface of the aqueous solution tank 130, and the concentration sensor 149 and the aqueous solution tank 130 are communicated with each other.

  The concentration sensor 149 is a sensor for detecting the methanol concentration of the methanol aqueous solution that has flowed in (ratio of methanol in the methanol aqueous solution). The controller 156 detects the methanol concentration of the aqueous methanol solution based on the detection signal from the concentration sensor 149.

  The pipes P17 and P18 described above serve as a concentration detection flow path. In this embodiment, a detection part and a cooling space are formed in the pipe P18.

  Further, the aqueous solution tank 130 and the catch tank 140 are communicated by a pipe P19, the catch tank 140 and the aqueous solution tank 130 are communicated by a pipe P20, and the catch tank 140 and the air chamber 150 are communicated by a pipe P21. The pipe P19 connects the upper left corner of the aqueous solution tank 130 and the upper left corner of the catch tank 140, and the pipe P20 connects the lower end of the catch tank 140 and the lower left corner of the aqueous solution tank 130. The pipe P21 connects the position near the upper left side of the catch tank 140 and the upper end surface of the air chamber 150. The gas (mainly carbon dioxide, vaporized methanol and water vapor) in the aqueous solution tank 130 is given to the catch tank 140 through the pipe P19. The vaporized methanol and water vapor are cooled and liquefied in the catch tank 140 and then returned to the aqueous solution tank 130 via the pipe P20. The gas (carbon dioxide, unliquefied methanol and water vapor) in the catch tank 140 is supplied to the air chamber 150 through the pipe P21.

  The pipes P19 to P21 described above mainly serve as fuel processing flow paths.

  Such a fuel cell system 100 is activated by turning on the main switch 152, controlled by the controller 156, and supplemented with electric energy by the secondary battery 134. The DC-DC converter 154 converts the voltage from 24V to 12V, and the fans 120 and 126 are driven by the converted 12V voltage.

Next, main operations during operation of the fuel cell system 100 will be described.
When the main switch 152 is turned on, the fuel cell system 100 drives auxiliary equipment such as the aqueous solution pump 146 and the air pump 147 and starts operation.

  By driving the aqueous solution pump 146, the aqueous methanol solution stored in the aqueous solution tank 130 is sent from the pipe P 3 side to the pipe P 4 side and supplied to the aqueous solution filter 144. The methanol aqueous solution from which impurities and the like have been removed by the aqueous solution filter 144 is directly supplied to the anode 104b of each fuel cell 104 constituting the cell stack 102 via the pipe P5 and the anode inlet I1.

  On the other hand, the air (air) drawn from the air filter 142 by driving the air pump 147 is silenced by flowing into the air chamber 150 via the pipe P8. Then, the sucked air and the gas from the catch tank 140 given to the air chamber 150 are supplied to the cathode 104c of each fuel cell 104 constituting the cell stack 102 via the pipes P9 to P11 and the cathode inlet I3. The

  In the anode 104b of each fuel cell 104, methanol and water in the supplied aqueous methanol solution chemically react to generate carbon dioxide and hydrogen ions. The generated hydrogen ions flow into the cathode 104c through the electrolyte 104a, and electrochemically react with oxygen in the air supplied to the cathode 104c side to generate water (water vapor) and electric energy. That is, power generation is performed in the cell stack 102. The generated electrical energy is sent to and stored in the secondary battery 134 and used for driving the motorcycle 10 and the like.

  On the other hand, the carbon dioxide and unreacted methanol aqueous solution generated at the anode 104b of each fuel cell 104 rise in temperature due to the heat generated by the electrochemical reaction (for example, about 65 ° C. to 70 ° C.), and unreacted methanol. A part of the aqueous solution is vaporized. The carbon dioxide and the unreacted aqueous methanol solution flow into the aqueous solution radiator 112 via the anode outlet I2 of the cell stack 102, and are cooled by the fan 120 while flowing through the radiator pipe 116 (for example, about 40 ° C.). . The cooled carbon dioxide and the unreacted methanol aqueous solution are returned to the aqueous solution tank 130 via the pipe P7.

  On the other hand, most of the water vapor generated at the cathode 104c of each fuel cell 104 is liquefied and converted into water and discharged from the cathode outlet I4 of the cell stack 102, but the saturated water vapor is discharged in a gas state. A part of the water vapor discharged from the cathode outlet I4 is cooled by the radiator 114 and liquefied by lowering the dew point. The water vapor liquefaction operation by the radiator 114 is performed by operating the fan 126. Water (water and water vapor) from the cathode outlet I4 is supplied to the water tank 132 through the pipe P12, the radiator 114 and the pipe P13 together with unreacted air. Further, at the cathode 104c of each fuel cell 104, the vaporized methanol from the catch tank 140 and the methanol moved to the cathode 104c due to crossover react with oxygen in the platinum catalyst layer and decompose into harmless moisture and carbon dioxide. The Moisture and carbon dioxide decomposed from methanol are discharged from the cathode outlet I4 and supplied to the water tank 132 via the radiator 114. Further, the water moved to the cathode 104c of each fuel cell 104 due to the water crossover is discharged from the cathode outlet I4 and supplied to the water tank 132 via the radiator 114.

  The water collected in the water tank 132 is appropriately refluxed to the aqueous solution tank 130 through the pipes P15 and P16 by driving the water pump 160, and used as water of the methanol aqueous solution.

  In the fuel cell system 100 in operation, the concentration detection process of the aqueous methanol solution is periodically executed in order to cause each fuel cell 104 to efficiently generate power while preventing the deterioration of each fuel cell 104. Based on the detection result, the methanol concentration of the aqueous methanol solution to be supplied to the cell stack 102 is adjusted. Specifically, the methanol fuel in the fuel tank 128 is supplied to the aqueous solution tank 130 and the water in the water tank 132 is returned to the aqueous solution tank 130 based on the detection result of the methanol concentration.

  11, such a fuel cell system 100 includes an aqueous solution tank 130, an aqueous solution pump 146, an electromagnetic valve 148, a concentration sensor 149, a controller 156, and pipes P3, P4, P17, and P18. Is configured.

  Referring to FIGS. 11 and 12, density sensor 149 includes a strip-shaped Peltier element 202 and a heat sink 204 provided on one main surface side thereof. A member 206 such as a silicon sheet having good thermal conductivity is interposed between the Peltier element 202 and the heat sink 204. Further, a part of the pipe P18 is also a constituent member of the concentration sensor 149. Pipe P18 includes pipe portions P181, P182, and P183, a pipe portion P184 that is interposed between pipe portions P181 and P182, and a pipe portion P185 that is interposed between pipe portions P182 and P183. Pipe portions P181, P182 and P183 are made of metal such as stainless steel having relatively good thermal conductivity. The pipe part P184 is made of a heat-insulating resin such as Teflon (registered trademark). The pipe part P185 is made of a rubber material such as EPDM having poor thermal conductivity. The pipe part P182 is provided in a U shape so as to contact the other main surface of the Peltier element 202, and the pipe part P183 is provided so as to penetrate the heat sink 204. The pipe part P182 functions as a chamber that substantially becomes a detection part.

  Further, an aqueous solution temperature sensor 208 for detecting the temperature of the aqueous solution is provided in the pipe portion P182, and a Peltier temperature sensor 210 for detecting the temperature of the Peltier element 202 is provided on the other main surface of the Peltier element 202. ing.

  Such Peltier element 202, a part of heat sink 204, member 206, pipe portions P182, P184 and P185, aqueous solution temperature sensor 208 and Peltier temperature sensor 210 are molded with resin 212.

  The pipes P3, a part of the pipe P4, and the pipe parts P181 and P184 of the pipe P17 and the pipe P18 function as a first pipe for sending the aqueous methanol solution in the aqueous solution tank 130 to the vicinity of the Peltier element 202. The pipe parts P185 and P183 function as a second pipe for returning the methanol aqueous solution whose concentration has been detected to the aqueous solution tank 130. Further, the combination of the Peltier element 202 and the heat sink 204 constitutes a temperature changing unit that also serves as a cooling unit and a heating unit. The cooling means and the heating means may be configured only by the Peltier element 202. The controller 156 constitutes freezing point detection means and concentration detection means. The electromagnetic valve 148 constitutes a replacement means, and the flow of the methanol aqueous solution whose concentration is detected is controlled. The aqueous solution temperature sensor 208 constitutes first temperature detection means, and the Peltier temperature sensor 210 constitutes second temperature detection means.

Next, the controller 156 will be described.
The controller 156 performs necessary calculations and controls the operation of the fuel cell system 100, and a memory 216 made of, for example, an EEPROM for storing programs, data, and the like for controlling the operation of the fuel cell system 100. including. Detection signals from the aqueous solution temperature sensor 208 and the Peltier temperature sensor 210 are A / D converted by A / D converters 218 and 220, respectively, and input to the CPU 214. Control signals from the CPU 214 to the aqueous solution pump 146, the electromagnetic valve 148, and the Peltier element 202 are given via interface circuits 222, 224, and 226, respectively.

Here, the principle used in the present invention will be described.
In general, the freezing point of a solution in which a solute is dissolved in a certain amount of solvent is lower than the freezing point of the solvent (pure solvent) by Δt as shown in FIG. This phenomenon is called freezing point depression, and the temperature difference Δt at this time is called the freezing point depression degree. In such a solution, the freezing point depression degree Δt is proportional to the amount of solute substance (molar concentration of solution) regardless of the type of solute.

  As shown in FIG. 13 (b), generally, when the solution is cooled, it remains in a liquid state for a while without solidifying even when the freezing point is reached (this state is called supercooling). Solidification begins at a point). The reaction in which the liquid becomes solid is an exothermic reaction, and since this occurs abruptly, a rapid increase in temperature such as AB is observed. In the case of an alcohol-based aqueous solution, since the solute contained in the solid phase (primary crystal) that precipitates first when the solution solidifies is very small, the solute concentration in the remaining liquid phase increases with the progress of solidification, Eventually, the temperature rise of the solution stops and the temperature change falls to the right like BC. At this time, the freezing point of the solution is the D point, but since the B point and the D point are substantially equal, the temperature of the B point can be regarded as the freezing point. And a density | concentration is detected based on the temperature of B point made into this freezing point.

Next, an example of main operations of the concentration detection apparatus 200 will be described with reference to FIGS.
Referring to FIG. 14, first, electromagnetic valve 148 is opened in accordance with an instruction from controller 156 (step S1), and electromagnetic valve 148 is operated until a predetermined time (for example, 2 seconds) elapses (step S3 becomes YES). The open state continues. As a result, a part of the methanol aqueous solution sent out by the aqueous solution pump 146 and flowing through the pipe P4 is introduced into the pipe P18 via the pipe P17, and the methanol aqueous solution filled in the pipe P18 is discharged. That is, by opening the electromagnetic valve 148, introduction of a new methanol aqueous solution whose methanol concentration should be detected into the pipe portion P182 constituting the detection portion and discharge of the methanol aqueous solution whose methanol concentration has been detected from the pipe portion P182 are performed. Is called. Since the aqueous methanol solution is pressurized by the aqueous solution pump 146, it is introduced into the pipe portion P182 simply by opening the electromagnetic valve 148. The methanol aqueous solution whose methanol concentration has been detected discharged from the pipe P18 is returned to the aqueous solution tank 130.

  The electromagnetic valve 148 is closed at the start of driving of the aqueous solution pump 146, and the pipe P18 is filled with air from the start of operation until before the first concentration detection. In this case, it goes without saying that the air filling the pipe P18 flows into the aqueous solution tank 130.

When a predetermined time has elapsed (YES in step S3), the electromagnetic valve 148 is closed (step S5), and the flow (flow velocity) of the aqueous methanol solution flowing into the pipe P18 is suppressed. Here, by completely closing the electromagnetic valve 148, the aqueous methanol solution can be held and retained (stopped) by the pipe portion P182.
Then, density detection which will be described later is performed (step S7).

  After completion of the concentration detection, the solidified methanol aqueous solution is heated by the Peltier element 202 according to an instruction from the controller 156 and is easily discharged from the pipe part P182. The electromagnetic valve 148 is opened and the concentration-detected methanol aqueous solution is supplied to the pipe part P182. The aqueous methanol solution to be detected next time is introduced into the pipe portion P182 (step S9). At this time, the electromagnetic valve 148 is opened for a predetermined time (for example, 40 seconds) while counting the time, and the aqueous methanol solution is replaced (step S11).

  After a predetermined time has elapsed, the heating of the aqueous methanol solution is stopped (step S13), the process returns to step S5, the electromagnetic valve 148 is closed, and the replacement of the aqueous methanol solution is completed. Thereafter, the processes in steps S5 to S13 are repeated.

  For confirmation of the replacement of the methanol aqueous solution, for example, the temperature in the pipe part P182 may be detected, and if the temperature satisfies a predetermined condition, the process may proceed to step S13. For example, if the detected temperature is the same as that of the fuel cell system, or if the detected temperature is equal to or higher than the freezing point of the detection target (in this embodiment, the detection target is an aqueous solution, 0 ° C. or higher), the process proceeds to step S13. .

Next, the density detection operation will be described with reference to FIGS. 15 and 16.
First, when the operation is started, the variable N = 0 is set (step S51), and the pipe portion P182 serving as the detection portion in the cooling mode in which the energization current to the Peltier element 202 is maximized is rapidly determined by an instruction from the controller 156. (Step S53). As a result, the required time to the freezing point can be shortened.

  Then, the surface temperature of the Peltier element 202 is detected by the Peltier temperature sensor 210 (step S55), and the temperature of the aqueous methanol solution in the pipe portion P182 serving as the detection unit is detected by the aqueous solution temperature sensor 208 (step S57). Instead of the surface temperature of the Peltier element 202, a temperature representative of the Peltier element 202 may be detected.

  Next, it is determined whether or not the difference between the temperature of the aqueous solution in the pipe portion 182 and the temperature of the Peltier element 202 has become less than 1 ° C., and the temperature of the aqueous solution in the pipe portion P182 indicates that the solvent containing no fuel (this implementation) It is determined whether or not the temperature is slightly lower than the freezing point (2 ° C. in this embodiment) in the form of “water” (step S59). Until the difference between the aqueous solution temperature in the pipe part 182 and the temperature of the Peltier element 202 is less than 1 ° C. and the aqueous solution temperature in the pipe part P 182 is lower than 2 ° C., the processes in steps S53 to S59 are repeated to perform rapid cooling. Will continue. If the difference between the aqueous solution temperature and the temperature of the Peltier element 202 is 1 ° C. or higher, or if the aqueous solution temperature is 2 ° C. or higher, the aqueous solution will not solidify, so there is no problem even if it is rapidly cooled.

  On the other hand, if the difference between the aqueous solution temperature in the pipe portion 182 and the temperature of the Peltier element 202 is less than 1 ° C. and the aqueous solution temperature in the pipe portion P 182 is lower than 2 ° C. in step S59, the freezing point is approaching. And the process proceeds to step S61. In step S61, the cooling capacity of the Peltier element 202 is lowered from the beginning in accordance with an instruction from the controller 156. That is, the current supplied to the Peltier element 202 is set to a medium level and cooling is continued. This is because if the rapid cooling is continued even though the freezing point is approaching, the heat generated when solidifying from the supercooling may be rapidly taken away, and the freezing point may not be detected accurately. This is because a delay occurs and affects the temperature difference detection process in subsequent steps.

  When the cooling performance is low in view of the heat capacity of the aqueous solution to be detected, this step is not necessary because the cooling performance can only be gradually reduced.

  Then, the surface temperature of the Peltier element 202 is detected (step S63), the aqueous solution temperature in the pipe part P182 is detected (step S65), and the difference between the aqueous solution temperature in the pipe part 182 and the surface temperature of the Peltier element 202 is calculated. (Step S67), and the temperature difference is stored in the memory 216 (Step S69).

  Then, it is determined whether or not a first predetermined time (for example, 10 minutes) has elapsed since step S51 (step S71). If not, it is determined whether or not the aqueous solution temperature in the pipe portion P182 is -20 ° C or lower. (Step S73), if it is not below -20 ° C., it is judged whether or not the variable N = 0 (Step S75). If the variable N = 0, it is determined whether or not the second predetermined time has elapsed (step S77), and if the second predetermined time (for example, 5 minutes) has elapsed, the variable N is incremented by 1 (step S79). Returning to step S63, the temperature of the aqueous solution in the Peltier element 202 and the pipe part P182 is detected.

  If the first predetermined time has elapsed in step S71, or if the aqueous solution temperature in the pipe portion P182 is -20 ° C or lower in step S73, it is determined that an abnormality has occurred and a detection error has occurred. Is notified (step S81), and the process ends. This is because the temperature detection usually does not take much time, and it is not normal that the temperature is considerably lower than the assumed freezing point.

  If step S75 is NO, the process proceeds to step S83 shown in FIG. 16, and the previous temperature difference (difference between the aqueous solution temperature in the pipe portion 182 and the surface temperature of the Peltier element 202) stored in the memory 216 is the current time. It is determined whether or not the temperature difference (the difference between the aqueous solution temperature in the pipe portion 182 and the surface temperature of the Peltier element 202) is larger. If the temperature difference this time becomes larger, it is determined that the temperature of the aqueous solution has started to rise. As a result, it is determined that coagulation has started. That is, when solidification starts, even if cooling by the Peltier element 202 is performed, the temperature of the aqueous solution does not decrease due to the heat of solidification, but rises conversely. Can know.

  Then, it is determined whether or not the second predetermined time has elapsed (step S85), and the process waits until the second predetermined time elapses. When the second predetermined time elapses, the aqueous solution temperature in the pipe portion P182 is detected (step S87), and the aqueous solution The temperature is stored in the memory 216 (step S89). Then, it is determined whether or not the aqueous solution temperature has exceeded 0 ° C. (step S91). If it does not exceed 0 ° C., it is determined whether or not the aqueous solution temperature has decreased (step S93). If the aqueous solution temperature has not dropped, the process returns to step S87. On the other hand, if the aqueous solution temperature has dropped, the highest temperature in the aqueous solution temperature stored in the memory 216 in the processing after step S89 is temporarily placed as the freezing point (step S95), it is determined whether or not the temporarily set freezing point is -8 ° C. or higher and 0 ° C. or lower (step S97), and if it is within the range, it is formally determined as the freezing point (step S99). Then, referring to the table data indicating the relationship between the theoretical freezing point and the converted molar concentration value stored in the memory 216 shown in FIG. 17, the molar concentration corresponding to the theoretical freezing point closest to the detected freezing point is acquired (step). S101), the process ends. On the other hand, when the aqueous solution temperature exceeds 0 ° C. in step S91, or when the temporary freezing point is not −8 ° C. or more and 0 ° C. or less in step S97, the error is determined as an error (step S103), and the process ends. To do.

  When the molar concentration is acquired in step S101, the amount of methanol fuel from the fuel tank 128 to be supplied to the aqueous methanol solution in the aqueous solution tank 130 and the amount of water from the water tank 132 are determined based on the concentration. The Then, the methanol aqueous solution in the aqueous solution tank 130 is adjusted to a desired concentration by supplying the determined amount of methanol fuel and water.

  According to such a concentration detection apparatus 200, the concentration of methanol dissolved in the aqueous solution can be accurately detected based on the freezing point of the aqueous methanol solution by utilizing the correlation between the freezing point of the aqueous methanol solution and the molar concentration. Moreover, it is not necessary to use a large device such as an ultrasonic sensor.

  Further, since the temperature of the methanol aqueous solution introduced into the pipe portion P182 that is the detection unit is stopped, the temperature of the methanol aqueous solution and thus the freezing point can be accurately detected, and as a result, it is dissolved in the methanol aqueous solution. The concentration of methanol can be detected accurately.

  Furthermore, since the methanol aqueous solution coagulated for concentration detection can be dissolved, the replacement of the methanol aqueous solution whose concentration is detected is ensured and easy.

  Further, since the combination of the Peltier element 202 and the heat sink 204 can be used for cooling and heating of the methanol aqueous solution, the configuration of the apparatus can be simplified and reduced in size.

  Furthermore, by utilizing the characteristics shown in FIG. 13B when the aqueous methanol solution is solidified, it can be known that the solidification of the aqueous methanol solution has started based on the temperature difference between the aqueous methanol solution and the Peltier element 202. And the freezing point of the aqueous methanol solution can be detected more accurately.

  Further, by returning the aqueous methanol solution whose concentration is detected to the aqueous solution tank 130, it is possible to prevent the aqueous methanol solution from being wasted for detecting the concentration.

  Further, at the time of density detection, the time until density detection can be shortened and the density detection accuracy can be improved by cooling at a relatively high speed first and then lowering the cooling capacity.

  Since it is important to accurately detect the fuel concentration in the fuel cell system 100, it is effective to use the present invention in the fuel cell system 100, and in turn, in transportation equipment such as the two-wheeled vehicle 10 equipped with the fuel cell system 100. is there.

  In the above-described embodiment, the case where the methanol aqueous solution whose methanol concentration has been detected is returned to the aqueous solution tank 130 has been described. However, the present invention is not limited to this. For example, the methanol aqueous solution whose methanol concentration has been detected in the pipe P18 may be pushed back to the pipe P4. Alternatively, the pipe P18 may be connected to the pipe P4 on the downstream side of the connecting portion between the pipe P4 and the pipe P17, and the methanol aqueous solution whose methanol concentration has been detected may be supplied to the cell stack 102.

  Further, when the freezing point of the methanol aqueous solution is detected in the fuel cell system 100, the concentration of the aqueous methanol solution in the aqueous solution tank 130 may be directly adjusted based on the freezing point without obtaining the molar concentration. In this case, a correspondence relationship between the replenishment amount of methanol fuel and / or water and the freezing point is set in advance, and an amount of methanol fuel and / or water corresponding to the detected freezing point is replenished to the aqueous methanol solution in the aqueous solution tank 130. do it.

  In this way, the concentration of the aqueous methanol solution can be easily adjusted without detecting the concentration of methanol contained in the aqueous methanol solution.

  Furthermore, in the above-described embodiment, methanol is used as the fuel, and an aqueous methanol solution is used as the aqueous fuel solution. However, the present invention is not limited to this. May be.

  The present invention can be used for detecting the concentration of an arbitrary liquid in which an arbitrary substance is dissolved as long as it is a liquid in which the substance is dissolved.

  The fuel cell system of the present invention can be suitably used not only for motorcycles but also for any transportation equipment such as automobiles and ships.

  The present invention can also be applied to a reformer-mounted fuel cell system. The present invention can also be applied to a small installation type fuel cell system.

It is a left view which shows the two-wheeled vehicle carrying the fuel cell system of this invention. It is the perspective view which looked at the arrangement state of the fuel cell system to the body frame of a two-wheeled vehicle from the diagonally left front. It is the perspective view which looked at the arrangement state of the fuel cell system to the body frame of a two-wheeled vehicle from diagonally left rear. It is a left view which shows the piping state of a fuel cell system. It is a right view which shows the piping state of a fuel cell system. It is the perspective view which looked at the piping state of the fuel cell system from diagonally left forward. It is the perspective view which looked at the piping state of the fuel cell system from diagonally right forward. It is an illustration figure which shows a fuel cell stack. It is an illustration figure which shows a fuel cell. It is a system diagram which shows piping of a fuel cell system. It is an illustration figure which shows an example of a density | concentration detection apparatus. (A) is a perspective view which shows a density | concentration sensor, (b) is the sectional drawing. (A) is a graph which shows the temperature change with respect to the cooling time of a solvent and a solution, (b) is a graph which shows the temperature change with respect to the cooling time of a solution and a Peltier device. It is a flowchart which shows an example of main operation | movement of this invention. It is a flowchart which shows an example of operation | movement of a density | concentration detection process. FIG. 16 is a flowchart showing a continuation of the operation of FIG. 15. It is a table which shows the correspondence of a freezing point and molar concentration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Two-wheeled vehicle 100 Fuel cell system 102 Fuel cell stack 130 Aqueous solution tank 146 Aqueous solution pump 148 Electromagnetic valve 149 Concentration sensor 156 Controller 200 Concentration detection device 202 Peltier element 204 Heat sink 208 Aqueous solution temperature sensor 210 Peltier temperature sensor 214 CPU
216 Memory P1-P21 Pipe P181-P185 Pipe part

Claims (11)

A cooling means for cooling the liquid in which the substance is dissolved,
First temperature detecting means for detecting the temperature of the liquid to be cooled;
A freezing point detecting means for detecting a freezing point of the liquid based on the temperature detected by the first temperature detecting means;
A concentration detection apparatus comprising concentration detection means for detecting the concentration of a substance dissolved in the liquid based on the freezing point detected by the freezing point detection means. Furthermore, a detection unit for holding the liquid in a stopped state in order to detect the temperature of the liquid, and a replacement unit for replacing the liquid in the detection unit,
The concentration detection apparatus according to claim 1, wherein the first temperature detection unit detects a temperature of the liquid in the detection unit.   The concentration detection apparatus according to claim 1, further comprising a heating unit that heats the liquid.   The density | concentration detection apparatus of Claim 3 provided with the temperature change means combined with the said cooling means and the said heating means. A second temperature detecting means for detecting the temperature of the cooling means;
5. The concentration detection according to claim 1, wherein the freezing point detection unit detects a freezing point of the liquid based on a detection result of the first temperature detection unit and a detection result of the second temperature detection unit. apparatus. Furthermore, a tank for storing the liquid,
6. The apparatus according to claim 1, comprising: a first pipe for sending the liquid in the tank to the vicinity of the cooling means; and a second pipe for returning the liquid after concentration detection to the tank. Concentration detector.   A fuel cell system comprising the concentration detection device according to claim 1.   A transportation device comprising the fuel cell system according to claim 7. Introducing a liquid in which the substance is dissolved into the cooling space;
Cooling the liquid introduced into the cooling space by a cooling means;
Detecting the temperature of the cooling means;
Detecting the temperature of the liquid cooled in the cooling space;
Detecting the freezing point of the liquid based on the detected temperature of the cooling means and the temperature of the liquid, and detecting the concentration of the substance dissolved in the liquid based on the detected freezing point of the liquid A concentration detection method comprising:   The step of cooling the liquid includes a first step of cooling the liquid with a first cooling capacity, and a second step of cooling the liquid with a cooling capacity lower than the first cooling capacity. 10. The concentration detection method according to 9. A fuel cell system using an aqueous fuel solution,
A fuel cell system for detecting a freezing point of the aqueous fuel solution and adjusting a concentration of the aqueous fuel solution based on the detected freezing point.

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