JP2012255349A - Fuel supply device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel supply device of an internal combustion engine which has a heat exchanger of engine cooling water and liquefied fuel, and can supply the liquefied fuel into a cylinder by favorably evaporating the fuel by the heat exchanger even if a temperature of the engine cooling water becomes high.SOLUTION: There can selectively be performed fair current control for making the liquefied fuel pass through a liquefied fuel passage along the heat exchanger, and making the engine cooling water pass through an engine cooling water passage along the heat exchanger in the same direction as that of the liquefied fuel, and adverse current control for making the engine cooling water pass through the engine cooling water passage along the heat exchanger in a direction opposite to the liquefied fuel, the fair current control is selected when a degree of superheat ΔTU at the inlet side of the liquefied fuel passage of a heat exchanging wall is not higher than a set degree of superheat ΔTS in a range in which the liquefied fuel is transient-boiled at the inlet side of the liquefied fuel passage (step 103), and when the degree of superheat at the inlet side of the liquefied fuel passage is higher than the set degree of superheat, the adverse current control is selected. (step 104).

Description

  The present invention relates to a fuel supply device for an internal combustion engine for vaporizing liquefied fuel and supplying it to an internal combustion engine.

  As a fuel for an internal combustion engine, it is known to use a gaseous fuel at room temperature and normal pressure such as LPG. Such gaseous fuel is liquefied by cooling and stored in the fuel tank. The liquefied fuel in the fuel tank is heated and vaporized and supplied into the cylinder of the internal combustion engine. Generally, a heat exchanger with engine cooling water is used for heating and vaporizing the liquefied fuel.

  In the fuel supply device including such a heat exchanger, when the engine coolant becomes high temperature, the liquefied fuel may not be vaporized well in the heat exchanger. In the carburetor that promotes the vaporization of liquid fuel using the heat of the engine cooling water, when the engine cooling water reaches a high temperature, the supply of the engine cooling water to the vaporizer is stopped to prevent excessive heating of the liquid fuel. Has been proposed (see Patent Document 1).

Japanese Utility Model Hei 01-74347 JP 07-293345 A

  In a fuel supply device equipped with a heat exchanger with engine cooling water for vaporizing liquefied fuel, when the engine cooling water becomes high temperature and the liquefied fuel cannot be vaporized well, the heat supply to the heat exchanger Even if the supply of engine cooling water is stopped, the liquefied fuel cannot be vaporized well.

  Accordingly, an object of the present invention is to provide a heat exchanger for engine cooling water and liquefied fuel, and even if the engine cooling water becomes high temperature, the liquefied fuel is vaporized well by the heat exchanger and supplied into the cylinder. It is an object to provide a fuel supply device for an internal combustion engine.

  According to a first aspect of the present invention, there is provided a fuel supply device for an internal combustion engine comprising a heat exchanger having a heat exchange wall between a liquefied fuel passage and an engine coolant passage, wherein the liquefied fuel passes through the liquefied fuel passage. A forward flow control for allowing the engine cooling water to pass along the heat exchange wall and the engine cooling water passage through the engine cooling water passage along the heat exchange wall in the same direction as the liquefied fuel; Backflow control for causing the liquefied fuel passage to pass along the heat exchange wall and for allowing engine cooling water to pass through the engine cooling water passage along the heat exchange wall in a direction opposite to the liquefied fuel; Can be selectively implemented, and the degree of superheat on the inlet side of the liquefied fuel passage of the heat exchange wall is equal to or lower than a set superheat degree within a range where the liquefied fuel transitions to boiling on the inlet side of the liquefied fuel passage. Select forward flow control It is, when higher than the set degree of superheat is characterized in that the back flow control is selected.

  The fuel supply device for an internal combustion engine according to claim 2 according to the present invention is the fuel supply device for internal combustion engine according to claim 1, wherein the degree of superheat on the inlet side of the liquefied fuel passage of the heat exchange wall is It is estimated based on the temperature of the engine cooling water flowing into the engine cooling water passage.

  According to the fuel supply device for an internal combustion engine according to claim 1 of the present invention, the heat supply apparatus includes a heat exchanger having a heat exchange wall between the liquefied fuel passage and the engine coolant passage, and the liquefied fuel passes through the liquefied fuel passage. The forward flow control allows the engine cooling water to pass along the heat exchange wall and the engine cooling water passage along the heat exchange wall in the same direction as the liquefied fuel, and the liquefied fuel passes through the liquefied fuel passage. It is possible to selectively implement reverse flow control that allows the engine cooling water to pass along the heat exchange wall and the engine cooling water passage along the heat exchange wall in the opposite direction to the liquefied fuel. The forward flow control is selected when the superheat degree on the inlet side of the liquefied fuel passage of the heat exchange wall is equal to or lower than the set superheat degree within the range where the liquefied fuel transitions and boiles on the inlet side of the liquefied fuel passage. Accordingly, at this time, the heat flux on the inlet side of the liquefied fuel passage on the heat exchange wall is set to the outlet side by setting the inlet side of the liquefied fuel passage on the heat exchange wall higher than the outlet side by the engine coolant of the forward flow control. The liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by nucleate boiling or transition boiling near the boundary with nucleate boiling.

  In addition, when the superheat degree on the inlet side of the liquefied fuel passage of the heat exchanger wall is higher than the set superheat degree, forward flow control is performed so that the inlet side of the liquefied fuel passage of the heat exchanger wall is higher than the outlet side. Then, in transition boiling, the higher the degree of superheat, the smaller the heat flux and the insufficient vaporization, so that the liquefied fuel on the inlet side of the liquefied fuel passage cannot be vaporized well. However, when the degree of superheat on the inlet side of the liquefied fuel passage on the heat exchange wall of the heat exchanger is higher than the set superheat degree, the outlet side of the liquefied fuel passage on the heat exchange wall is superheated higher than the inlet side by the engine cooling water for backflow control. Therefore, the heat flux on the inlet side of the liquefied fuel passage on the heat exchange wall can be made larger than the heat flux on the outlet side, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by transition boiling. Can do.

  Thus, in particular, when the engine coolant becomes high temperature and the degree of superheat increases, in the forward flow control, the liquefied fuel on the inlet side of the liquefied fuel passage of the heat exchanger may undergo transition boiling, and thus the heat flux may be reduced. However, by reducing the degree of superheat on the inlet side of the liquefied fuel passage of the heat exchanger by backflow control, the heat flux in the transition boiling of the liquefied fuel can be increased, and the liquefied fuel is vaporized well in the heat exchanger. Can be made.

  According to a second aspect of the present invention, there is provided the internal combustion engine fuel supply apparatus according to the first aspect, wherein the degree of superheat on the inlet side of the liquefied fuel passage of the heat exchange wall is determined by the engine coolant passage. It is estimated based on the temperature of the engine cooling water flowing into the engine, and the forward flow control and the reverse flow control can be easily switched.

It is the schematic which shows the fuel supply apparatus of the internal combustion engine by this invention. It is a graph which shows the relationship between the superheat degree at the time of boiling of a liquefied fuel, and a heat flux. It is a flowchart for switching between forward flow control and reverse flow control of a heat exchanger.

  FIG. 1 is a schematic view showing a fuel supply device for an internal combustion engine according to the present invention. The control of each member of the fuel supply device described below is performed by an electronic control device (not shown). In the figure, reference numeral 10 denotes a fuel tank, which stores LPG mainly composed of propane (boiling point −42.09 ° C.) and butane (boiling point −0.5 ° C.). Of course, the liquefied fuel targeted by the fuel supply apparatus according to the present invention is not limited to LPG, and can be any combustible substance that is gaseous at normal temperature and pressure. For example, a flammable substance having a boiling point similar to that of propane, a flammable substance having a boiling point comparable to that of butane, and a flammable substance having a boiling point between that of propane and that of butane can be used.

  Reference numeral 20 denotes a heat exchanger for vaporizing the liquefied fuel in the fuel tank 10, and includes an inner tube 20a that functions as a liquefied fuel passage and an outer tube 20b that functions as an engine cooling water passage. Thus, the tube wall of the inner tube 20a functions as a heat exchange wall between the liquefied fuel and the engine cooling water. A fuel inflow passage 30 for supplying the liquefied fuel in the fuel tank 10 is connected to the inlet 20c of the inner pipe 20a, and the outlet 20d of the inner pipe 20a is directly connected to the fuel injection valve of each cylinder or A fuel outflow passage 40 for supplying vaporized fuel is connected through a pressure accumulation chamber common to each cylinder.

  Further, one side 20e of the outer pipe 20b is heated in a cooling water passage in a cylinder block (not shown) via the switching valve CV and the first connection pipe 70 and cooled by a radiator (not shown). It is connected to a cooling water inflow passage 50 for supplying the previous engine cooling water. The other side 20f of the outer pipe 20b is a cooling water for returning the engine cooling water flowing out from the outer pipe 20b to the radiator (or the cooling water passage of the cylinder block) via the switching valve CV and the second connection pipe 80. It is connected to the outflow passage 60. A cooling water pump is provided in the cooling water inflow passage 50 as necessary.

  A fuel pump P for pumping liquefied fuel to the fuel inflow passage 30 is provided in the fuel tank 10. The fuel inflow passage 30 is provided with a fuel metering valve FV for metering the flow rate of the liquefied fuel pumped by the fuel pump P and supplying it to the inner pipe 20a of the heat exchanger 20. The cooling water inflow passage 50 is provided with a temperature sensor 90 for measuring the temperature of the cooling water.

  The switching valve CV is capable of switching the connection between the cooling water inflow passage 50 and the cooling water outflow passage 60, that is, the cooling water inflow passage communicating with the first connection pipe 70 in FIG. 50 can be communicated with the second connection pipe 80, and in FIG. 1, the cooling water outflow passage 60 communicated with the second connection pipe 80 can be communicated with the first connection pipe 70. As a result, at the first position of the switching valve CV shown in FIG. 1, the engine coolant is not supplied to the liquefied fuel passing through the inner pipe 20a in the direction of the arrow along the heat exchange wall (the pipe wall of the inner pipe). It passes through the outer tube 20b along the heat exchange wall as indicated by the arrow in the same direction as the liquefied fuel. Further, when the connection between the cooling water inflow passage 50 and the cooling water outflow passage 60 is switched by the switching valve CV as described above and the switching valve CV is set to the second position, the inside of the inner pipe 20a is heat exchange wall (the pipe of the inner pipe). The engine cooling water passes through the outer pipe 20b in the opposite direction to the liquefied fuel along the heat exchange wall with respect to the liquefied fuel passing in the direction of the arrow along the wall. Thus, forward flow control with the switching valve CV as the first position and reverse flow control with the switching valve CV as the second position can be selectively performed.

  In the heat exchanger 20 of the present embodiment, the inner pipe 20a functioning as a liquefied fuel passage is always positioned higher on the inlet side than the outlet side even when the vehicle travels on a slope. Thereby, the liquefied fuel supplied to the inlet 20c of the inner pipe 20a tends to move to the outlet 20d by gravity. At this time, the liquefied fuel is boiled and vaporized on the inlet side of the inner pipe 20a by heat exchange with the engine cooling water through the heat exchange wall, and is completely vaporized on the outlet side of the inner pipe 20a. Has been.

  FIG. 2 is a graph showing the relationship between the degree of superheat and heat flux when a specific liquefied fuel is boiled in the inner tube 20a of the heat exchanger. Here, the degree of superheat is the difference between the temperature of the heat transfer surface which is the inner surface of the tube wall (heat exchange wall) of the inner tube 20a and the boiling point of the liquefied fuel, and the heat flux is from the heat transfer surface of the unit area. This is the amount of heat transferred to the liquefied fuel per unit time. When the superheat degree is equal to or less than the boundary superheat degree ΔTB, the liquefied fuel boils by nucleate boiling that generates vapor bubbles from a specific point on the heat transfer surface. On the other hand, when the superheat degree is higher than the boundary superheat degree ΔTB, the liquefied fuel boils by transition boiling in which vapor bubbles from a specific point on the heat transfer surface are connected and a vapor film is partially formed on the heat transfer surface.

  For a specific liquefied fuel, a graph showing the relationship between the degree of superheat and heat flux as shown in FIG. 2 shows the temperature and flow rate of engine cooling water passing outside the inner pipe 20a and the inside of the inner pipe 20a. It is determined by fixing two of the three factors with the flow rate of the liquefied fuel and changing the remaining one factor. If one of the two fixed factors is the temperature of the engine cooling water, the higher the temperature of the engine cooling water, the larger the overall heat flux with respect to the degree of superheat. If one of the two fixed factors is the flow rate of the engine cooling water, the higher the flow rate of the engine cooling water, the larger the overall heat flux with respect to the degree of superheat. If one of the two fixed factors is the flow rate of the liquefied fuel, the higher the flow rate of the liquefied fuel, the smaller the overall heat flux for the degree of superheat.

  Further, when the factor to be changed is the temperature of the engine cooling water, the degree of superheat increases as the temperature of the engine cooling water increases. When the changing factor is the flow rate of engine cooling water, the degree of superheat increases as the flow rate of engine cooling water increases. When the change factor is the flow rate of the liquefied fuel, the degree of superheat decreases as the flow rate of the liquefied fuel increases. As described above, there are innumerable graphs showing the relationship between the degree of superheat and heat flux for a specific liquefied fuel. In any graph, the boundary superheat degree ΔTB between the nucleate boiling region and the transition boiling region is almost constant. Thus, the magnitude of the heat flux when the boundary superheat degree ΔTB is different for each graph, but the heat flux when the boundary superheat degree ΔTB is the maximum value in any graph.

  By the way, in the heat exchanger 20 of the present embodiment, when the forward flow control with the switching valve CV as the first position is performed, the engine cooling water is the tube wall of the inner tube 20a outside the inner tube 20a. The temperature of the engine cooling water gradually decreases along the heat exchange wall from the liquefied fuel inlet side to the outlet side of the inner pipe 20a. As a result, the degree of superheat on the liquefied fuel inlet side of the heat exchange wall (the difference between the temperature of the heat transfer surface that is the inner surface of the inner tube 20a heat exchange wall and the boiling point of the liquefied fuel) is higher than the degree of superheat on the outlet side. . When reverse flow control is performed with the switching valve CV at the second position, the engine cooling water flows outside the inner tube 20a along the heat exchange wall that is the tube wall of the inner tube 20a. The liquefied fuel passes from the outlet side to the inlet side, and the temperature of the engine cooling water gradually decreases. Thereby, the degree of superheat on the outlet side of the liquefied fuel on the heat exchange wall becomes higher than the degree of superheat on the inlet side.

  In the graph shown in FIG. 2, the flow rate of the engine coolant supplied to the heat exchanger 20 is fixed to the specific engine coolant flow rate, and the flow rate of the liquefied fuel supplied to the heat exchanger 20 is fixed to the specific liquefied fuel flow rate. The degree of superheat increases as the temperature of the engine cooling water increases. In FIG. 2, ΔTU1 is the degree of superheat of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water when the temperature of the engine cooling water is the first temperature, and ΔTD1 lower than ΔTU1 is the engine cooling water. Is the degree of superheat of the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water when the temperature of the engine is the first temperature. As the temperature of the engine cooling water passing along the heat exchange wall decreases, a difference in superheat between the inflow side and the outflow side of the engine cooling water occurs in this way. Similarly, ΔTU2 is the degree of superheat of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water when the temperature of the engine cooling water is the second temperature, and ΔTD2 lower than ΔTU2 is the engine cooling. This is the degree of superheat of the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water when the water temperature is the second temperature. Similarly, ΔTU3 is the degree of superheat of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water when the temperature of the engine cooling water is the third temperature, and ΔTD3 lower than ΔTU3 is the engine cooling. This is the degree of superheat of the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water when the water temperature is the third temperature.

  As shown in FIG. 2, in the nucleate boiling region, the higher the degree of superheat, the greater the heat flux. Therefore, the forward flow control is selected and implemented, for example, the heat exchange wall on the inflow side of the engine cooling water. The superheat degree ΔTU1 of the heat transfer surface is the superheat degree on the inlet side of the inner tube 20a of the heat exchange wall, and the superheat degree ΔTD1 of the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water is the inner tube of the heat exchange wall. The degree of superheat on the outlet side of 20a. Since it is intended that all of the liquefied fuel is vaporized on the outlet side of the liquefied fuel passage, it is meaningless to increase the heat flux. Thus, the heat flux on the inlet side of the liquefied fuel passage of the heat exchange wall is reduced. By making it larger than the heat flux on the outlet side, the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by nucleate boiling.

  On the other hand, in the transition boiling region, the higher the degree of superheat, the smaller the heat flux. Therefore, the reverse flow control is selected and executed, for example, the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water. The degree of superheat ΔTU3 is the degree of superheat on the outlet side of the inner pipe 20a of the heat exchanger 20, and the degree of superheat ΔTD3 on the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water is the inlet of the inner pipe 20a of the heat exchange wall. The degree of superheat on the side. Thereby, the heat flux on the inlet side of the liquefied fuel passage of the heat exchange wall can be made larger than the heat flux on the outlet side, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by transition boiling.

  Further, when the superheat degree ΔTU2 of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water is ΔTS in the transition boiling region near the boundary with nucleate boiling, the heat exchange wall on the outflow side of the engine cooling water The degree of superheating ΔTD2 of this becomes the nucleate boiling region, and the heat fluxes of both become substantially equal. Accordingly, the forward flow control is selected, the superheat degree ΔTU2 of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water is set as the superheat degree on the inlet side of the inner pipe 20a of the heat exchanger 20, and the engine cooling water Even if the superheat degree ΔTD2 of the heat transfer surface of the heat exchange wall on the outflow side of the engine is the superheat degree on the outlet side of the inner tube 20a of the heat exchange wall, the reverse flow control is selected and the inflow side of the engine cooling water The degree of superheat ΔTU2 on the heat transfer surface of the heat exchange wall is defined as the degree of superheat on the outlet side of the inner pipe 20a of the heat exchanger 20, and the degree of superheat ΔTD2 on the heat transfer surface of the heat exchange wall on the outflow side of the engine cooling water is heat. Even if the degree of superheat on the inlet side of the inner pipe 20a of the exchange wall is set, the heat flux on the inlet side and the heat flux on the outlet side of the liquefied fuel passage on the heat exchange wall are substantially equal.

  Therefore, at this time, even if the forward flow control is selected and the liquefied fuel on the inlet side of the liquefied fuel passage is vaporized by transition boiling, the reverse flow control is selected and the liquefied fuel on the inlet side of the liquefied fuel passage is caused by nucleate boiling. It may be vaporized. However, when the degree of superheat of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water is lower than ΔTS in the transition boiling region near the boundary with nucleate boiling, the heat exchange wall is selected by selecting the forward flow control. The heat flux on the inlet side of the liquefied fuel passage can be made larger than the heat flux on the outlet side, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by transition boiling. In addition, when the superheat degree of the heat transfer surface of the heat exchange wall on the inflow side of the engine cooling water is higher than ΔTS of the transition boiling region near the boundary with nucleate boiling, the heat exchange wall is selected by selecting the reverse flow control. The heat flux on the inlet side of the liquefied fuel passage can be made larger than the heat flux on the outlet side, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by nucleate boiling or transition boiling.

  FIG. 3 is a flowchart for switching between such forward flow control and reverse flow control. It is repeatedly executed every set time by the electronic control unit. First, in step 101, the liquefied fuel passage of the heat exchanger 20, that is, the inner pipe 20a, is realized in order to realize the fuel injection amount of each cylinder necessary for the current engine operating state based on the engine load and the engine speed. The flow rate of the liquefied fuel supplied to the engine is determined based on two factors: the flow rate of the liquefied fuel and the flow rate of the engine coolant supplied to the engine cooling water passage of the heat exchanger 20, that is, the outer pipe 20b. A graph as shown in FIG. 2 is set. In this graph, on the inlet side of the liquefied fuel passage on the heat exchange wall when the forward flow control is selected based on the current temperature of the engine cooling water detected by the temperature sensor 90. The degree of superheat ΔTU is calculated.

  Next, at step 102, it is determined whether or not the superheat degree ΔTU is equal to or less than a set superheat degree ΔTS within a range where the liquefied fuel transitions and boiles on the inlet side of the liquefied fuel passage. When this determination is affirmative, forward flow control is selected in step 103, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by nucleate boiling or transition boiling. When the determination in step 102 is negative, the reverse flow control is selected in step 104, and the liquefied fuel on the inlet side of the liquefied fuel passage can be vaporized well by transition boiling. Thus, in particular, when the engine coolant becomes high temperature and the superheat degree becomes high, in the forward flow control, the liquefied fuel on the inlet side of the liquefied fuel passage of the heat exchanger undergoes transition boiling, so that the heat flow to the liquefied fuel at this time Although the bundle may be smaller, the transition of the liquefied fuel at the inlet side of the liquefied fuel passage is reduced by making the superheat degree at the inlet side of the liquefied fuel passage of the heat exchanger lower than the superheat degree at the outlet side by backflow control. The heat flux in boiling can be increased, and the liquefied fuel can be vaporized well in the heat exchanger.

  In the fuel supply device shown in FIG. 1, the flow rate of engine cooling water that flows into the heat exchanger 20 may be controlled. For example, if a communication path that connects the cooling water inflow path 50 and the cooling water outflow path 60 is provided, and a cooling water metering valve is provided in this communication path, the cooling water metering valve passes through the communication path to generate heat. By adjusting the flow rate of the engine coolant that does not pass through the outer pipe 20b of the exchanger 20, the flow rate of the engine coolant that passes through the outer pipe 20b can be controlled.

  The heat exchanger 20 may have an arbitrary shape without being limited to the double tube shape as shown in FIG. Of course, the graph showing the relationship between the degree of superheat and the heat flux is different for each heat exchanger having a different size, shape, and material, and is different for each fuel having a different boiling point and heat of vaporization. For example, when LPG is used as the fuel, it is preferable to use a graph showing the relationship between the degree of superheat and the heat flux suitable for each mixing ratio by detecting the mixing ratio of propane and butane.

DESCRIPTION OF SYMBOLS 10 Fuel tank 20 Heat exchanger 20a Inner pipe 20b Outer pipe 30 Fuel inflow path 40 Fuel outflow path 50 Cooling water inflow path 60 Cooling water outflow path FV Fuel metering valve CV switching valve

Claims (2)

  A heat exchanger having a heat exchange wall between the liquefied fuel passage and the engine cooling water passage to allow the liquefied fuel to pass through the liquefied fuel passage along the heat exchange wall; Forward flow control for allowing the engine coolant passage to pass in the same direction as the liquefied fuel along the heat exchange wall, and for allowing the liquefied fuel to pass through the liquefied fuel passage along the heat exchange wall. Reverse flow control for allowing engine cooling water to pass through the engine cooling water passage along the heat exchange wall in a direction opposite to the liquefied fuel can be selectively performed, and the liquefied fuel on the heat exchange wall can be The forward flow control is selected when the superheat degree on the inlet side of the passage is equal to or lower than the set superheat degree within the range where the liquefied fuel transitions to boiling on the inlet side of the liquefied fuel passage, and the reverse flow control is selected when the superheat degree is higher than the set superheat degree. Is selected The fuel supply apparatus for an internal combustion engine, characterized in that it is.   2. The internal combustion engine according to claim 1, wherein the degree of superheat on the inlet side of the liquefied fuel passage of the heat exchange wall is estimated based on a temperature of engine cooling water flowing into the engine cooling water passage. Fuel supply device.

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