JP5001540B2 - Fuel cell system and operation method thereof - Google Patents

Description

  The present invention relates to a fuel cell system that maintains a fuel gas in a fuel cell at a predetermined concentration during purging and an operation method thereof.

In a fuel cell system mounted on a fuel cell vehicle, unreacted hydrogen discharged from the anode electrode of the fuel cell is returned to the fuel cell and circulated in order to increase the use efficiency of hydrogen gas (fuel gas). Has been done. However, in this type of fuel cell system, while hydrogen is circulated, water in the air (oxidant gas) supplied to the cathode electrode of the fuel cell and water generated by an electrochemical reaction between hydrogen and oxygen However, it permeates through the electrolyte membrane to the anode electrode, and the hydrogen concentration in the anode electrode decreases, thereby reducing the power generation performance of the fuel cell. For this reason, during the power generation process, the purge valve is opened and the nitrogen in the anode is discharged. At this time, hydrogen is also discharged together, so this hydrogen is mixed with air in a diluter to dilute the hydrogen. It is discharged into the atmosphere so that the concentration does not exceed the predetermined concentration. For example, in Patent Document 1, the purge amount (hydrogen discharge amount) when purging the fuel cell is limited based on the hydrogen concentration at the outlet of the diluter, and when the hydrogen concentration is high, the purge valve is opened. The amount of purge is limited by shortening the time to do so.
Japanese Patent Laying-Open No. 2004-55287 (paragraph 0023, FIGS. 2 and 4)

  However, in the conventional fuel cell system, the purge valve opening time is limited by calculating the purge amount based on the generated current so that the hydrogen concentration discharged into the atmosphere does not exceed a predetermined concentration. It was. When the purge amount is limited based on the generated current in this way, the responsiveness of the generated current is high. For example, when the purge is executed during power generation with a high load, the purge amount is immediately By changing to a smaller value, the emission of impurities was excessively suppressed. As a result, there is a problem that the hydrogen concentration in the fuel cell cannot be sufficiently recovered and the power generation stability is impaired.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a fuel cell system that can be purged with an appropriate purge amount even if the generated current fluctuates during the purge, and an operating method thereof. .

The fuel cell system of the present invention has a fuel cell that generates power by a reaction between a fuel gas supplied to the anode electrode and an oxidant gas supplied to the cathode electrode, and circulates the fuel gas to the anode electrode of the fuel cell. A fuel gas circulation pipe, a fuel gas discharge pipe connected to the fuel gas circulation pipe and through which the fuel off-gas discharged from the anode electrode of the fuel cell flows, and an oxidant gas supplied to the cathode electrode of the fuel cell Is connected to the oxidant gas supply pipe through which the oxygen gas flows, the oxidant gas discharge pipe through which the oxidant off-gas discharged from the cathode electrode of the fuel cell flows, and the oxidant gas supply pipe. The fuel pipe is connected to the dilution pipe through which the oxidant gas before being supplied to the electrode flows, the fuel gas discharge pipe, the dilution pipe and the oxidant gas discharge pipe. A diluter that mixes and discharges the fuel off-gas from the discharge pipe with the oxidant gas from the dilution pipe and the oxidant off-gas from the oxidant gas discharge pipe, and supplies to the fuel cell and the dilution pipe A purgeable amount determining means for calculating an upper limit value of the purge amount for the fuel cell based on the flow rate of the oxidant gas, and a purge request for calculating a purge amount necessary for maintaining the concentration of the fuel gas in the fuel cell An amount determining means; and a purge executing means for executing a purging process based on the purge amount calculated by the purgeable amount determining means or the purge request amount determining means , wherein the purgeable amount determining means comprises the oxidant A flow rate detecting means for detecting a flow rate of the gas; a temperature detecting means for detecting the temperature of the oxidant gas; and a flow of the oxidant gas detected by the flow rate detecting means. And it is characterized in that and a purge can amount calculating means for calculating a purge possible amount based on the temperature of the oxidant gas by the temperature detecting means has detected.
In the embodiment described later, the hydrogen discharge pipe 22 corresponds to a fuel gas discharge pipe, the air supply pipe 31 corresponds to an oxidant gas supply pipe, the air discharge pipe 32 corresponds to an oxidant gas discharge pipe, and the anode The off gas corresponds to the fuel off gas, and the cathode off gas corresponds to the oxidant off gas.

According to the present invention, by controlling the purge amount based on the flow rate of the oxidant gas, for example, even if the generated current decreases during the purge, the decrease rate of the flow rate of the oxidant gas is higher than the decrease rate of the generated current. Since it changes gradually, the upper limit value of the purge amount does not drop rapidly, and the upper limit value of the purge amount can be set higher than the conventional value.
Further, since the flow rate of the oxidant gas can be accurately detected by the flow rate detection means, the purgeable amount can be calculated appropriately.
Further, by calculating the purgeable amount in consideration of the temperature, the purgeable amount can be calculated with high accuracy.

In this case, the flow rate detecting means preferably detects the flow rate of the oxidant gas upstream of the branch of the dilution pipe and the oxidant gas supply pipe.

An operation method of a fuel cell system according to the present invention includes a fuel cell that generates electricity by a reaction between a fuel gas supplied to an anode electrode and an oxidant gas supplied to a cathode electrode, and a fuel gas to the anode electrode of the fuel cell. A fuel gas circulation pipe that circulates the fuel gas, a fuel gas discharge pipe that is connected to the fuel gas circulation pipe and through which the fuel off-gas discharged from the anode electrode of the fuel cell flows, and is supplied to the cathode electrode of the fuel cell An oxidant gas supply pipe through which an oxidant gas flows, an oxidant gas discharge pipe through which an oxidant off-gas discharged from the cathode of the fuel cell flows, and the oxidant gas supply pipe are connected to the fuel. The dilution pipe through which the oxidant gas before being supplied to the cathode electrode of the battery flows, and the fuel gas discharge pipe, the dilution pipe and the oxidant gas discharge pipe are connected, The fuel off-gas from the serial fuel gas discharge pipe, and a diluter for discharging mixed with the oxidant-off gas from the oxidant gas and the oxidizing gas discharge pipe from the dilution pipe, the flow rate of the oxidant gas a flow rate detecting means for detecting a temperature detecting means for detecting a temperature of the oxidant gas, and a control means and the operating method of the fuel cell system wherein the control means, the fuel cell and the dilution An upper limit value of the purge amount in the fuel cell is calculated based on the flow rate of the oxidant gas supplied to the pipe, and a purge process is executed based on the upper limit value, or the fuel gas in the fuel cell calculating the purge request amount required for concentration maintenance, performing a purge process based on the purge demand, the flow rate of the oxidant gas, wherein the flow rate detecting means detects Oyo It is characterized in that comprises the steps of: calculating a purge possible amount based on the temperature of the oxidant gas by the temperature detecting means has detected.

According to the present invention, by controlling the purge amount based on the flow rate of the oxidant gas, even if the generated current decreases during the purge, the rate of decrease in the flow rate of the oxidant gas is slower than the rate of decrease in the generated current. For this reason, the upper limit value of the purge amount can be set higher than the conventional value.
Further, since the flow rate of the oxidant gas can be accurately detected, the purgeable amount can be calculated appropriately.
Further, by calculating the purgeable amount in consideration of the temperature, the purgeable amount can be calculated with high accuracy.

In this case, the flow rate detecting means, it is preferable to detect the flow rate of the oxidant gas upstream of the branch of the dilution pipe and the oxidant gas supply pipe.

  According to the fuel cell system and the operation method of the present invention, even when the purge process and the timing of fluctuation of the generated current overlap, it is possible to purge with an appropriate amount without limiting the purge amount excessively. Become.

  1 is an overall configuration diagram showing the fuel cell system of the present embodiment, FIG. 2 is a flowchart showing a purge process, FIG. 3 is a map for determining a purgeable amount, and FIG. 4 is a map for determining a purge request amount. FIG. 5 is a time chart showing changes in the purgeable amount. In the following, a fuel cell system mounted on a vehicle such as a fuel cell electric vehicle will be described as an example. However, the present invention is not limited to this, and the fuel cell system mounted on a ship, an aircraft, etc. Applicable.

  As shown in FIG. 1, the fuel cell system 1 of the present embodiment includes a fuel cell FC, an anode system 20, a cathode system 30, a dilution system 40, an ECU 50, and the like.

  The fuel cell FC includes a monovalent cation exchange type polymer electrolyte membrane (hereinafter referred to as “electrolyte membrane”) 11 having one surface side sandwiched between an anode electrode 12 and the other surface side sandwiched between a cathode electrode 13. It has a structure in which a plurality of single cells each composed of an electrode assembly (MEA) and a conductive separator (not shown) sandwiching both surfaces of the membrane electrode assembly are stacked. In addition, in FIG. 1, although the structure of the single cell is shown in figure, it has the structure which connected this single cell in multiple numbers in series. By supplying hydrogen as a fuel gas to the anode electrode 12 of the fuel cell FC and air (oxygen) as an oxidant gas to the cathode electrode 13, electric power is generated by an electrochemical reaction between hydrogen and oxygen. . The current value of the generated current extracted by power generation is detected by the current sensor 51.

  The anode system 20 supplies hydrogen to the anode electrode 12 of the fuel cell FC and discharges hydrogen from the anode electrode 12, and includes a hydrogen supply pipe 21, a hydrogen discharge pipe 22, a high-pressure hydrogen tank 23, a shut-off valve 24, A hydrogen circulation system 25, a purge valve 28, a temperature sensor 29, and the like are provided.

  One end of the hydrogen supply pipe 21 is connected to the inlet side a <b> 1 of the anode electrode 12 of the fuel cell FC, and the other end is connected to the high-pressure hydrogen tank 23. One end of the hydrogen discharge pipe 22 is connected to the outlet side a <b> 2 of the anode 12, and the other end is connected to the dilution system 40.

  The high-pressure hydrogen tank 23 is a container that can be filled with high-purity hydrogen at a very high pressure (for example, 35 MPa≈350 atm). The shutoff valve 24 is a valve capable of shutting off the supply of hydrogen to the fuel cell FC, and is provided on the downstream side of the high pressure hydrogen tank 23. The shut-off valve 24 may be an in-tank type provided integrally with the high-pressure hydrogen tank 23.

  The hydrogen circulation system 25 circulates the hydrogen discharged from the outlet side a2 of the anode electrode 12 of the fuel cell FC back to the inlet side a1, and circulates the ejector 26 and the hydrogen circulation pipe (fuel gas circulation path) 27. It is comprised by. The ejector 26 is provided in the hydrogen supply pipe 21, and one end of the hydrogen circulation pipe 27 is connected to the ejector 26, and the other end is connected to the upstream side of the purge valve 28 of the hydrogen discharge pipe 22.

  The purge valve 28 is a valve that can shut off the flow path of the hydrogen discharge pipe 22, and its opening / closing operation is controlled by an ECU 50 described later.

  The temperature sensor 29 detects the temperature of the anode off gas discharged through the purge valve 28 and is provided in the hydrogen discharge pipe 22.

  Although not shown, the anode system 20 is provided with a regulator or the like for decompressing the high-pressure hydrogen released from the high-pressure hydrogen tank 23.

  The cathode system 30 supplies air to the cathode electrode 13 of the fuel cell FC and discharges air from the cathode electrode 13, and includes an air supply pipe 31, an air discharge pipe 32, an air compressor 33, a temperature sensor 34, a flow rate. It consists of a sensor 35 and the like.

  One end of the air supply pipe 31 is connected to the inlet c1 of the cathode electrode 13 of the fuel cell FC, and the other end is connected to the air compressor 33. One end of the air discharge pipe 32 is connected to the outlet side c <b> 2 of the cathode electrode 13, and the other end is connected to the dilution system 40.

The air compressor 33 is a supercharger or the like driven by a motor, and supplies compressed air (outside air) to the fuel cell FC via the air supply pipe 31. Incidentally, the air supply pipe 31, a humidifier for humidifying the air you supplied to the cathode 13 of the fuel cell FC (not shown), the air discharge pipe 32, controls the pressure of the cathode system 30 An air back pressure valve (not shown) or the like is provided.

  The temperature sensor 34 is provided in the air supply pipe 31 and detects the temperature of air (air) supplied from the air compressor 33. The flow rate sensor 35 is provided in the air supply pipe 31 and detects the flow rate of air supplied from the air compressor 33 (air flow rate).

  The dilution system 40 includes a dilution pipe 41, a diluter 42, and the like. One end of the dilution pipe 41 is connected to the upstream side of the humidifier (not shown) of the air supply pipe 31, and the other end is connected to the diluter 42. The diluter 42 dilutes the hydrogen discharged from the anode electrode 12 to a hydrogen concentration below a predetermined value and discharges it into the atmosphere. The diluter 42 discharges the anode off-gas (hydrogen + nitrogen +) discharged through the hydrogen discharge pipe 22. Water) and dry air discharged through the dilution pipe 41 are mixed, and the mixed gas is further mixed with the cathode off-gas discharged through the air discharge pipe 32 and discharged to the atmosphere. It is configured as follows.

  Although not shown, the fuel cell system 1 is provided with a cooling system that releases heat generated by the fuel cell FC during power generation to the atmosphere. This cooling system includes a cooling medium circulation pipe, a radiator, a circulation pump, and the like.

  The ECU 50 includes a CPU (Central Processing Unit), a memory, an input / output interface, and the like, and a purgeable amount calculation unit that calculates a purgeable amount (upper limit value of the purge amount) based on air (air) flow rate information, A purge request amount determining means for calculating a purge amount (purge request amount) necessary for maintaining the hydrogen concentration, and a purge execution means for executing a purge process are provided.

  The purgeable amount is determined based on the map shown in FIG. 3 and the air flow rate information input from the flow rate sensor 35. In the map of FIG. 3, the purgeable amount can be corrected based on the air temperature (T2) information input from the temperature sensor 34, as indicated by the alternate long and short dash line. Thus, by using the temperature (T2) information from the temperature sensor 34, the purgeable amount can be controlled with high accuracy.

  The purge request amount is determined based on the map shown in FIG. 4 and the generated current information input from the current sensor 51. Further, in the map of FIG. 4, the purge request amount can be corrected based on the temperature (T1) information of the anode off gas (hydrogen + nitrogen + water, etc.) input from the temperature sensor 29, as indicated by the alternate long and short dash line. it can. As described above, by using the temperature (T1) information from the temperature sensor 29, the purge request amount can be controlled with high accuracy.

  The ECU 50 is electrically connected to the shutoff valve 24, the purge valve 28, the temperature sensors 29 and 34, the air compressor 33, the flow sensor 35, and the current sensor 51, and opens and closes the shutoff valve 24 and the purge valve 28. The number of rotations (rotational speed) of the motor is controlled, and temperature information from the temperature sensors 29 and 34, air flow information from the flow sensor 35, and generated current information from the current sensor 51 are acquired.

Next, the operation of the fuel cell system 1 of the present embodiment will be described with reference to FIGS. 2 to 5.
When the driver turns on the ignition switch of the vehicle, the ECU 50 opens the shut-off valve 24 and drives the air compressor 33. Thereby, hydrogen in the high-pressure hydrogen tank 23 is supplied to the anode electrode 12 of the fuel cell FC through the hydrogen supply pipe 21, and a humidifier (not shown) is driven through the air supply pipe 31 by driving the air compressor 33. ) Is supplied to the cathode 13 of the fuel cell FC. As a result, electric power is generated by an electrochemical reaction between hydrogen and oxygen in the humidified air in the fuel cell FC, and electric power (generated current) is supplied to a load such as a travel motor (not shown).

  By the way, when the power generation of the fuel cell FC is continued in this way, the anode system 20 circulates and uses hydrogen, so that nitrogen contained in the air in the cathode electrode 13 and water generated in the cathode electrode 13 are used. Impurities such as are transmitted to the anode electrode 12 through the electrolyte membrane 11, and the hydrogen concentration in the anode electrode 12 is reduced. As a result, the power generation performance of the fuel cell FC decreases. For this reason, the purge valve 28 is opened as necessary to discharge impurities from the anode electrode 12, and hydrogen is newly sent from the high-pressure hydrogen tank 23 to the anode electrode 12, thereby reducing the hydrogen concentration in the anode electrode 12. The desired concentration is maintained.

  Hereinafter, the purge process of the fuel cell FC will be described. As shown in FIG. 2, first, the ECU 50 determines the air flow rate obtained from the flow rate sensor 35 and the temperature sensor 34 based on the map for obtaining the purgeable amount shown in FIG. The purge amount is calculated from the obtained temperature T2, and this is set as the purgeable amount. In step S2, the ECU 50 determines whether or not the purge valve 28 is open. If the purge valve 28 is not open (No), the ECU 50 proceeds to step S8 and sets the purge request amount to 0 (zero). ).

  If the ECU 50 determines in step S2 that the purge valve 28 is open (Yes), the ECU 50 determines the purge request amount shown in FIG. 4 in step S3 (purge request amount determination means). Thus, the purge amount is calculated from the current information (current value A) obtained from the current sensor 51 and the temperature T1 obtained from the temperature sensor 29, and this is set as the purge request amount.

  In step S4, the ECU 50 determines whether or not the purge request amount is larger than the purgeable amount. If the ECU 50 determines that the purge request amount is larger than the purgeable amount (Yes), the ECU 50 requests the purge request in step S5. The amount is replaced with a purgeable amount, and it is determined in step S6 whether or not the purge execution amount has reached the purgeable amount. If the ECU 50 determines in step S4 that the purge request amount is equal to or less than the purgeable amount (No), the ECU 50 proceeds to step S6 without replacing the purge request amount with the purgeable amount, and the purge execution amount is It is determined whether the purge request amount has been reached. That is, if the purge request amount is equal to or less than the purgeable amount in step S4 (No), a purge amount that does not exceed the purge request amount calculated in step S3 is set. In step S6, this process is repeated until the purge execution amount reaches the purgeable amount, or until the purge execution amount reaches the purge request amount. When the purge execution amount reaches the purgeable amount, or when the purge execution amount reaches If the required purge amount is reached, the purge valve 28 is closed in step S7.

  Furthermore, the operation of the fuel cell system 1 of the present embodiment will be described in detail with reference to the time chart of FIG. In addition, the comparative example (conventional control) of FIG. 5 is a case where the purge amount is controlled based on the generated current.

  First, a case where the generated current does not change during the purge will be described. Since the generated current is constant at times t1 to t2, the purgeable amount set by the air flow rate (Example) and the purgeable amount set by the generated current (Comparative Example) are both the same. The purge execution amount becomes the purge request amount set based on the generated current. That is, the purge valve 28 is opened for the same period of time, and when the purge execution amount reaches the purgeable amount, the purge valve 28 is closed and the purge process is terminated, so that the same amount of anode off gas as the purge request amount is discharged. Will be.

  On the other hand, at times t3 to t6 in FIG. 5, the generated current decreases simultaneously with the purge start timing. In the embodiment, the purgeable amount is limited based on the air flow rate, and in the comparative example, the purgeable amount is Limited based on generated current. In this way, by limiting the purgeable amount based on the air flow rate, the purgeable amount decreases slowly (small slope) compared to the decrease in generated current (large slope). It is possible to set the upper limit value higher than when limiting based on the generated current. That is, in the embodiment, the opening time of the purge valve 28 is Tm1 (time t3 to t5), and in the comparative example, the opening time of the purge valve 28 is Tm3 (time t3 to t4). The purge valve 28 can be kept open for a time longer than the difference Δ1. Therefore, in the embodiment, the purge execution amount can be made closer to the purge request amount, and as a result, the disadvantage that the purge amount is excessively limited can be solved.

  Further, at time t7 to t10 in FIG. 5, the generated current is reduced during the purge after a while after the purge is started, and the opening time of the purge valve 28 is Tm2 (time t7 to t9) as described above. In the comparative example, the opening time of the purge valve 28 is Tm4 (time t7 to t8). Therefore, in the embodiment, the purge valve 28 can be opened for a time longer than the comparative example by the difference Δ2. . Accordingly, in this case as well, the purge execution amount can be made closer to the purge request amount, and the purge amount can be prevented from being excessively limited.

  Contrary to the above, even when the generated current fluctuates from low load to high load during purging, the purgeable amount is calculated based on the air flow rate, so that a small purge amount can be quickly increased to a large purge amount. Therefore, it is possible to prevent the purge process from being performed excessively (the purge valve 28 is opened for a long time).

Note that the present invention is not limited to the above-described embodiment. For example, the temperature sensors 29 and 34 may be unified with one of the temperature sensors to perform control . Also, each map described above is an example, it may be used in place of the map function or table.

It is a whole lineblock diagram showing the fuel cell system of this embodiment. It is a flowchart which shows a purge process. It is a map for determining the purgeable amount. 6 is a map for determining a purge request amount. It is a time chart which shows the change of purgeable quantity.

Explanation of symbols

1 Fuel cell system 26 Ejector 27 Hydrogen circulation piping (fuel gas circulation flow path)
28 Purge valve 34 Temperature sensor (temperature detection means)
35 Flow rate sensor (flow rate detection means)
41 Dilution piping (dilution means)
42 Diluter (dilution means)
50 ECU
FC fuel cell

Claims (4)

A fuel cell that generates electricity by a reaction between a fuel gas supplied to the anode electrode and an oxidant gas supplied to the cathode electrode;
Fuel gas circulation piping for circulating fuel gas to the anode of the fuel cell;
A fuel gas discharge pipe connected to the fuel gas circulation pipe and through which the fuel off-gas discharged from the anode electrode of the fuel cell flows;
An oxidant gas supply pipe through which an oxidant gas supplied to the cathode of the fuel cell flows;
An oxidant gas discharge pipe through which an oxidant off-gas discharged from the cathode of the fuel cell flows;
A dilution pipe that is connected to the oxidant gas supply pipe and through which the oxidant gas flows before being supplied to the cathode of the fuel cell;
Connected to the fuel gas discharge pipe, the dilution pipe and the oxidant gas discharge pipe, the fuel off-gas from the fuel gas discharge pipe is supplied from the oxidant gas and the oxidant gas discharge pipe from the dilution pipe. A diluter for mixing and discharging with the oxidant off-gas;
A purgeable amount determining means for calculating an upper limit value of a purge amount for the fuel cell based on a flow rate of the oxidant gas supplied to the fuel cell and the dilution pipe;
A purge request amount determining means for calculating a purge amount necessary for maintaining the concentration of the fuel gas in the fuel cell;
Purge execution means for executing a purge process based on the purge amount calculated by the purgeable amount determination means or the purge request amount determination means ,
The purgeable amount determining means includes
Flow rate detection means for detecting the flow rate of the oxidant gas;
Temperature detecting means for detecting the temperature of the oxidant gas;
And a purgeable amount calculating means for calculating a purgeable amount based on the flow rate of the oxidant gas detected by the flow rate detection means and the temperature of the oxidant gas detected by the temperature detection means. Fuel cell system. 2. The fuel cell system according to claim 1 , wherein the flow rate detection unit detects a flow rate of the oxidant gas upstream of a branch between the oxidant gas supply pipe and the dilution pipe. A fuel cell that generates electric power by a reaction between a fuel gas supplied to the anode electrode and an oxidant gas supplied to the cathode electrode; a fuel gas circulation pipe that circulates the fuel gas to the anode electrode of the fuel cell; and the fuel A fuel gas discharge pipe connected to a gas circulation pipe through which fuel off-gas discharged from the anode electrode of the fuel cell flows, and an oxidant gas supply through which an oxidant gas supplied to the cathode electrode of the fuel cell flows A pipe, an oxidant gas discharge pipe through which an oxidant off-gas discharged from the cathode electrode of the fuel cell flows, and the oxidant gas supply pipe, and before being supplied to the cathode electrode of the fuel cell The dilution pipe through which the oxidant gas flows, the fuel gas discharge pipe, the dilution pipe, and the oxidant gas discharge pipe are connected, and the fuel off from the fuel gas discharge pipe is connected. A scan, the diluter for discharging mixed with the oxidant-off gas from the oxidant gas and the oxidizing gas discharge pipe from the dilution pipe, and the flow rate detecting means for detecting the flow rate of the oxidant gas, wherein A temperature detecting means for detecting the temperature of the oxidant gas, and a control means.
Wherein,
An upper limit value of a purge amount in the fuel cell is calculated based on the flow rate of the oxidant gas supplied to the fuel cell and the dilution pipe, and a purge process is executed based on the upper limit value, or the fuel Calculating a required purge amount necessary for maintaining the concentration of the fuel gas in the battery, and performing a purge process based on the purge required amount ;
And calculating a purgeable amount based on the flow rate of the oxidant gas detected by the flow rate detection means and the temperature of the oxidant gas detected by the temperature detection means . how to drive. The method of operating a fuel cell system according to claim 3 , wherein the flow rate detection means detects a flow rate of the oxidant gas upstream of a branch between the oxidant gas supply pipe and the dilution pipe. .

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