JP2017110581A - Rankine cycle system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Rankine cycle system using mixed cooling medium obtained by mixing two types of cooling media different in boiling point, for suppressing the freezing of the cooling medium inside a condenser.SOLUTION: The Rankine cycle system includes a boiler for imparting waste heat of an internal combustion engine to cooling medium having water and LLC mixed to vaporize the cooling medium, the gas-liquid separator for separating the gas-liquid two-phase cooling medium delivered from the boiler into gas phase fluid and liquid phase fluid, a superheater for superheating the gas phase fluid delivered from the gas-liquid separator, an expander for expanding the gas phase fluid passing through the superheater to take out task, and a condenser for condensing the gas phase fluid passing through the expander and restoring it into the liquid phase fluid. The Rankine cycle system further includes a cooling medium passage for introducing the liquid phase cooling medium from the inside of the gas-liquid separator into the condenser, and a control valve provided in the cooling medium passage. The control valve is opened when the occurrence of freezing inside the condenser is detected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Rankine cycle system.

  Patent Document 1 discloses a Rankine cycle system using a mixed refrigerant obtained by mixing two refrigerants having different boiling points. In this Rankine cycle system, the engine is used as a Rankine cycle boiling machine. When boiling cooling is performed using a mixed refrigerant in which water and LLC are mixed, water having a low boiling point boils and LLC having a high boiling point remains. As a result, the LLC concentration of the refrigerant in the engine increases, and conversely, the LLC concentration of the refrigerant (condensed water) condensed in the condenser (condenser) decreases. In the technique of Patent Document 1, the water pump is operated to recirculate the water stored in the condensed water tank to the engine in order to prevent the LLC concentration of the refrigerant in the engine from becoming high. Thereby, it is prevented that engine cooling efficiency falls.

JP 2012-102644 A

  As described above, in the Rankine cycle system using a mixed refrigerant obtained by mixing two kinds of refrigerants having different boiling points, the LLC concentration of the refrigerant in the engine is high, and conversely, the LLC concentration of the refrigerant in the condenser is low. Here, the freezing point increases as the LLC concentration decreases. For this reason, there exists a problem that the refrigerant | coolant in a condenser tends to freeze in low temperature environments, such as a cold region. In the technique of the above-mentioned Patent Document 1, no consideration is given to the problem caused by the low LLC concentration in the condenser, and there is still room for improvement.

  The present invention has been made in view of the problems as described above, and suppresses freezing of the refrigerant in the condenser in the Rankine cycle system using the mixed refrigerant obtained by mixing two kinds of refrigerants having different boiling points. It aims at providing the Rankine cycle system which can be performed.

In order to achieve the above object, the present invention
A boiling device that applies waste heat of the internal combustion engine to a refrigerant in which a first refrigerant and a second refrigerant having a boiling point higher than that of the first refrigerant are mixed, and vaporizes the refrigerant;
A gas-liquid separator that separates a gas-liquid two-phase refrigerant sent from the boiling device into a gas-phase refrigerant and a liquid-phase refrigerant;
A superheater that superheats the gas-phase refrigerant delivered from the gas-liquid separator by heat exchange with the exhaust of the internal combustion engine;
An expander that expands the gas-phase refrigerant that has passed through the superheater and extracts work;
In the Rankine cycle system, comprising a condenser that condenses the gas-phase refrigerant that has passed through the expander and returns it to the liquid-phase refrigerant,
A refrigerant passage for introducing the liquid-phase refrigerant inside the gas-liquid separator into the condenser or a refrigerant pipe connecting the condenser and the boiler;
A control valve for opening and closing the refrigerant passage;
Detecting means for detecting that freezing occurs inside the condenser;
Valve control means for opening the control valve when freezing is detected by the detection means;
It is characterized by having.

  According to the present invention, when it is detected that freezing occurs inside the condenser, the liquid-phase refrigerant stored in the gas-liquid separator is introduced into the condenser. Thereby, since the freezing point of the refrigerant | coolant inside a condenser can be lowered | hung, it becomes possible to suppress effectively the freezing of the refrigerant | coolant inside a condenser.

It is a figure which shows the structure of the Rankine cycle system of Embodiment 1 of this invention. It is the figure which compared the saturated vapor curve of water and ethylene glycol. It is a flowchart of the routine which the Rankine cycle system of Embodiment 1 of this invention performs. It is a time chart for demonstrating the effect at the time of performing operation of a control valve in a Rankine cycle system. It is a figure which shows the modification of a structure of the Rankine cycle system of Embodiment 1 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. However, in the embodiment shown below, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the reference However, the present invention is not limited to these numbers. Further, the structures, steps, and the like described in the embodiments below are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Embodiment 1 FIG.
1. Configuration of Rankine Cycle System FIG. 1 is a diagram illustrating a configuration of a Rankine cycle system 100 according to the first embodiment. The Rankine cycle system 100 according to Embodiment 1 includes an internal combustion engine (engine) 10 and is configured as a vehicle Rankine cycle system mounted on a vehicle. There is no limitation on the type and structure of the engine 10. However, the refrigerant block 12 through which the refrigerant circulating in the engine 10 flows is formed in the cylinder block and the cylinder head of the engine 10. The refrigerant flow path 12 includes a water jacket surrounding the cylinder. The engine 10 is cooled by heat exchange with the refrigerant flowing through the refrigerant flow path 12. In the present embodiment, a refrigerant adjusted to a prescribed LLC concentration by mixing water (first refrigerant) with LLC (ethylene glycol) (second refrigerant) is used.

  The engine 10 is cooled by boiling the refrigerant flowing through the refrigerant flow path 12 with the waste heat of the engine 10 and evaporating a part thereof. That is, the refrigerant flow path 12 functions as a boiling device that boiles the liquid-phase refrigerant flowing through the inside by the heat of the engine 10. The configuration of the coolant channel 12 is not particularly limited as long as the coolant channel 12 is a passage that can flow through the engine 10.

  The refrigerant flow path 12 of the engine 10 is connected to a gas-liquid separator 16 via a refrigerant pipe 14. When the refrigerant is boiled by the heat of the engine 10, the liquid phase refrigerant is discharged from the refrigerant flow path 12 together with the gas phase refrigerant. The gas-liquid separator 16 separates the gas-liquid two-phase refrigerant that has flowed into the gas-liquid separator 16 into a liquid-phase refrigerant and a gas-phase refrigerant. The lower part of the gas-liquid separator 16 is connected to the first water pump 20 via the refrigerant pipe 18. The liquid phase refrigerant separated by the gas-liquid separator 16 flows into the first water pump 20 via the refrigerant pipe 18 and is sent to the refrigerant flow path 12 by the first water pump 20.

  The Rankine cycle system 100 includes an evaporator 13. The evaporator 13 is provided in the exhaust passage 22 of the engine 10. The lower part of the gas-liquid separator 16 is also connected to the evaporator 13 via the refrigerant pipe 11. A liquid phase refrigerant is introduced into the evaporator 13 from the gas-liquid separator 16. The introduced liquid-phase refrigerant is superheated by heat exchange with the exhaust gas flowing through the exhaust passage 22 and boiled, and a part thereof becomes vapor. The vapor phase refrigerant that has become vapor is introduced again into the gas-liquid separator 16 via the refrigerant pipe 15.

  The gas-liquid separator 16 is connected to the superheater 30 via the refrigerant pipe 28. The superheater 30 is provided upstream of the evaporator 13 in the exhaust passage 22 of the engine 10. In the gas-liquid separator 16, since the gas-phase refrigerant and the liquid-phase refrigerant coexist, the gas-phase refrigerant is saturated vapor. The gas-phase refrigerant that has entered the superheater 30 becomes superheated steam by heat exchange with the exhaust gas flowing through the exhaust passage 22. Note that the superheater 30 is not necessarily provided separately in the middle of the exhaust passage 22 and may be integrated with the exhaust manifold as long as it can absorb the exhaust heat.

  The superheater 30 is connected to a turbine 34 that is an expander via a refrigerant pipe 32. In the turbine 34, work is taken out by expanding the gas-phase refrigerant (superheated steam) sent from the superheater 30. A supersonic nozzle 35 is provided at a connection portion between the refrigerant pipe 32 and the turbine 34. The gas-phase refrigerant is sprayed from the supersonic nozzle 35 to the turbine 34 to rotate the turbine 34. The rotation of the turbine 34 is transmitted to the output shaft of the engine 10 via a speed reducer (not shown). That is, the work taken out by the turbine 34 is used for assisting the engine 10. However, it is also possible to drive the generator by the turbine 34 and store the generated electricity in the storage battery.

  The gas phase refrigerant expanded by the turbine 34 is sent to a condenser (condenser) 40 through a refrigerant pipe 36. The gas-phase refrigerant sent to the condenser 40 is cooled and condensed by the condenser 40 and returned to the liquid-phase refrigerant. The liquid phase refrigerant generated by the condensation of the gas phase refrigerant is sent from the condenser 40 to the catch tank 44 via the refrigerant pipe 42 and temporarily stored in the catch tank 44. The catch tank 44 is connected to the middle of the refrigerant pipe 18 via the refrigerant pipe 46. A second water pump 48 is provided in the refrigerant pipe 46. The second water pump 48 is a pump for sending the liquid refrigerant stored in the catch tank 44 to the refrigerant pipe 18.

  The Rankine cycle system 100 further includes a control valve 50 and a refrigerant pipe 52 for introducing the liquid-phase refrigerant inside the gas-liquid separator 16 into the condenser 40. The control valve 50 is, for example, an on-off valve configured as an electromagnetic valve, and is provided in the middle of the refrigerant pipe 52 that connects the lower part of the gas-liquid separator 16 and the middle of the refrigerant pipe 36. The refrigerant pipe 52 constitutes a path for introducing the liquid-phase refrigerant separated by the gas-liquid separator 16 into the capacitor 40. Therefore, the connection destination is not limited to the middle of the refrigerant pipe 36, but directly. It may be connected to the capacitor 40. Further, since the connection source of the refrigerant pipe 52 may be a position where the liquid-phase refrigerant in the gas-liquid separator 16 is derived, so long as it is connected to a position below the liquid level in the gas-liquid separator 16. Good.

  The Rankine cycle system 100 includes various sensors and an ECU (Electronic Control Unit) 70. The sensor included in the Rankine cycle system 100 includes a temperature sensor 72 for measuring the refrigerant temperature T1 in the capacitor 40. The ECU 70 is a control device that controls the overall operation of the Rankine cycle system 100 including the engine 10. The ECU 70 includes at least an input / output interface, a memory, and an arithmetic processing unit (CPU). The input / output interface is provided to take in sensor signals from various sensors including the above-described temperature sensor 72 and to output an operation signal to the actuator. The actuator from which the ECU 70 outputs an operation signal includes the control valve 50 and the water pumps 20 and 48. The memory stores various control programs and maps. The CPU reads out and executes a control program or the like from the memory, and generates operation signals for various actuators based on the acquired sensor signals.

2. Operation of Rankine Cycle System As described in the above configuration, the Rankine cycle system 100 includes the control valve 50 in the middle of the refrigerant pipe 52, and the control valve 50 is operated by the ECU 70. Hereinafter, the operation of the control valve 50 which is a characteristic operation of the Rankine cycle system 100 will be described with reference to the drawings.

  In FIG. 1 described above, a thick solid line means a pipeline through which liquid phase refrigerant flows, and a thick dotted line means a pipeline through which gas phase refrigerant flows. In the Rankine cycle system 100, a gas-phase refrigerant path is formed from the refrigerant flow path 12 to the superheater 30 via the gas-liquid separator 16 and from the superheater 30 to the condenser 40 via the turbine 34. The liquid-phase refrigerant sent to the engine 10 by the first water pump 20 receives the waste heat of the engine 10 in the refrigerant flow path 12 and boils to become a high-temperature and high-pressure gas-phase refrigerant. The gas-phase refrigerant that has flowed out of the refrigerant flow path 12 is separated from the liquid-phase refrigerant by the gas-liquid separator 16 and is sent to the superheater 30, which further receives the waste heat of the engine 10 and becomes superheated steam. The superheated steam works as it expands in the turbine 34 and is returned to the liquid phase refrigerant again in the condenser 40. The liquid phase refrigerant generated in the capacitor 40 is stored in the catch tank 44. Then, when the liquid level of the liquid phase refrigerant stored in the gas-liquid separator 16 becomes lower than the lower limit, the second water pump 48 is activated to connect the refrigerant pipe 46 and the refrigerant pipe 18 from the catch tank 44. The liquid-phase refrigerant is sent to the gas-liquid separator 16 through this.

  Here, in the Rankine cycle system 100, a mixed refrigerant of water and ethylene glycol (LLC) is used. FIG. 2 shows a comparison of saturated vapor curves of water and ethylene glycol. As shown in this figure, the boiling point of ethylene glycol is higher than the boiling point of water. For this reason, when the mixed refrigerant boils, water preferentially evaporates and ethylene glycol hardly evaporates. That is, in the Rankine cycle system 100, the vaporized water flows through the above-described gas-phase refrigerant path, and ethylene glycol (LLC) remains as a liquid-phase refrigerant in the refrigerant flow path 12 or the gas-liquid separator 16. . Therefore, the liquid phase refrigerant in the refrigerant flow path 12 and the gas-liquid separator 16 has a high LLC concentration, and conversely, the liquid phase refrigerant in the condenser 40 and the catch tank 44 has a low LLC concentration.

  As the LLC concentration decreases, the freezing point increases accordingly. For this reason, when the Rankine cycle system 100 is operated in a cryogenic environment such as a cold region, the liquid-phase refrigerant is easily frozen in the capacitor 40. Therefore, in the Rankine cycle system 100 of the first embodiment, the freezing of the refrigerant in the capacitor 40 is suppressed by controlling the opening and closing of the control valve 50.

3. Details of Control Valve Operation FIG. 3 is a flowchart showing a control flow of control valve operation according to the first embodiment. A control program corresponding to this control flow is stored in the memory of the ECU 70. Operation | movement of the above-mentioned Rankine cycle system 100 is implement | achieved when ECU70 operates the control valve 50 according to this control flow. At this time, the ECU 70 functions as a valve control means.

  The control flow shown in FIG. 3 is repeatedly executed at a predetermined control cycle while the Rankine cycle system 100 is in operation. In the control flow shown in FIG. 3, it is first determined whether or not the refrigerant temperature T1 in the capacitor 40 is equal to or lower than a determination value (step S1). A value measured by the temperature sensor 72 is used as the refrigerant temperature T1. Moreover, since the refrigerant in the capacitor 40 is mainly composed of water, the determination value can use the freezing point of water. Since the freezing point also changes depending on the pressure, the pressure in the capacitor 40 may be measured and reflected in the determination value. As a result, when it is not recognized that the refrigerant temperature T1 ≦ determination value is established, it is determined that the refrigerant is not frozen in the capacitor 40, the process proceeds to the next step, and the control valve 50 is closed. (Step S2). On the other hand, if it is determined in step S1 that the refrigerant temperature T1 ≦ determination value is established, it is determined that the refrigerant is frozen in the capacitor 40, the process proceeds to the next step, and the control valve 50 is turned on. The valve is opened (step S3).

4). Effect of Rankine Cycle System FIG. 4 is a time chart for explaining the effect when the control valve 50 is operated in the Rankine cycle system 100. In addition, the 1st time chart in this figure has shown the time change of the refrigerant | coolant temperature in a capacitor | condenser in the Rankine cycle system which is not provided with the control valve 50 as a comparative example. Further, the second time chart shows the time change of the refrigerant temperature in the condenser in the Rankine cycle system including the control valve 50. The third time chart shows the open / close state of the control valve 50. As shown in the first chart, in the Rankine cycle of the comparative example, even if the refrigerant temperature in the capacitor 40 decreases to the freezing point at time t1, the freezing point does not change. For this reason, after the time t1, the refrigerant temperature in the capacitor 40 falls below the freezing point, and the refrigerant freezes in the capacitor 40.

  On the other hand, as shown in the second and third charts, in the Rankine cycle system 100 of the first embodiment, when the refrigerant temperature in the capacitor 40 decreases to the freezing point at time t1, the control valve 50 is opened. The When the control valve 50 is opened, the liquid phase refrigerant in the gas-liquid separator 16 is introduced into the capacitor 40 through the refrigerant pipe 52. Since the liquid phase refrigerant in the gas-liquid separator 16 has a high LLC concentration, the freezing point of the refrigerant in the condenser 40 is lowered by opening the control valve 50. This prevents the refrigerant temperature in the capacitor 40 from falling below the freezing point even after the time t1, so that freezing of the refrigerant in the capacitor 40 is suppressed.

  As described above, according to the Rankine cycle system 100 of the first embodiment, when the refrigerant freezes in the capacitor 40, the freezing point of the refrigerant in the capacitor 40 can be lowered. Freezing of the refrigerant is suppressed.

  By the way, in Rankine cycle system 100 of Embodiment 1 mentioned above, although the refrigerant which mixed water with ethylene glycol (LLC) was used, the refrigerant used is not restricted to this. That is, if two or more kinds of refrigerants having different boiling points are mixed, the LLC concentration of the refrigerant in the condenser 40 is lower than the LLC concentration of the refrigerant in the gas-liquid separator 16, and therefore the control valve 50 is opened. It is possible to obtain the effect of suppressing freezing by the valve.

  In the Rankine cycle system 100 of the first embodiment described above, it is determined that the refrigerant in the capacitor 40 is frozen by comparing the refrigerant temperature T1 in the capacitor 40 with the determination value. However, the method for determining the freezing of the refrigerant in the capacitor 40 is not limited to this. That is, the refrigerant temperature T1 may be the temperature of the refrigerant stored in the catch tank 44, or the internal pressure of the condenser 40, the internal pressure of the catch tank 44, the outlet pressure of the supersonic nozzle 35, the turbine 34 The refrigerant temperature T1 may be estimated based on other state quantities such as the outlet pressure and the outside air temperature. The determination value does not necessarily need to be an accurate freezing point, and may be set to a value slightly higher than the freezing point to detect freezing in advance.

  In the Rankine cycle system 100 according to the first embodiment described above, the control valve 50 is opened when the refrigerant in the condenser 40 freezes. However, when the control valve 50 that has been closed is opened, There is a possibility that the gas-liquid separator 16 is pulled by the negative pressure in the condenser 40 and boiled under reduced pressure. Therefore, Rankine cycle system 100 according to the first embodiment may be configured such that a separate throttle is provided in refrigerant pipe 52 to reduce the flow rate when control valve 50 is opened. Instead of providing a separate throttle, the control valve 50 may be configured to be adjustable in opening, and the opening of the valve may be throttled.

  Further, in the Rankine cycle system 100 of the first embodiment described above, when the refrigerant in the condenser 40 freezes, the refrigerant in the gas-liquid separator 16 is introduced into the condenser 40. The structure which introduce | transduces a refrigerant | coolant from a LLC tank may be sufficient. FIG. 5 is a diagram illustrating a modification of Rankine cycle system 100 according to the first embodiment. In this figure, elements common to the configuration shown in FIG.

  The Rankine cycle system 110 shown in FIG. 5 includes a control valve 62 and a refrigerant pipe 64 for introducing the liquid-phase refrigerant stored in the LLC tank 60 into the condenser 40. The LLC tank 60 functions as a refrigerant reserve tank, and stores a refrigerant having a prescribed LLC concentration. The control valve 62 is, for example, an on-off valve configured as an electromagnetic valve, and is provided in the middle of the refrigerant pipe 64 that connects the lower part of the LLC tank 60 and the condenser 40. The refrigerant pipe 52 is configured as a flow path that connects the lower part of the gas-liquid separator 16 and the upstream side of the control valve 62 in the refrigerant pipe 64. Since the refrigerant pipe 64 constitutes a path for introducing the liquid phase refrigerant of the LLC tank 60 into the capacitor 40, the connection destination is not limited to the capacitor 40 and is connected in the middle of the refrigerant pipe 36. May be. In such a configuration, if the control valve 62 and the control valve 50 are opened when freezing in the capacitor 40 is detected, the LLC tank 60 in addition to the liquid-phase refrigerant in the gas-liquid separator 16 is opened. The liquid refrigerant inside is also introduced into the capacitor 40. Thereby, since the LLC density | concentration in the capacitor | condenser 40 becomes high, the freezing of the refrigerant | coolant in the capacitor | condenser 40 is suppressed. It should be noted that the refrigerant pipe 64 and the refrigerant pipe 52 may be separately provided with a restriction for restricting the rapid circulation of the refrigerant.

  In Rankine cycle system 100 of the first embodiment described above, water as the refrigerant corresponds to the “first refrigerant” of the present invention, and LLC as the refrigerant corresponds to the “second refrigerant” of the present invention. In the Rankine cycle system 100 of the first embodiment described above, the refrigerant pipe 52 corresponds to the “refrigerant passage” of the present invention, the control valve 50 corresponds to the “control valve” of the present invention, and the ECU 70 performs step S1. By executing this process, the “detecting means” of the present invention is realized, and when the ECU 70 executes the process of step S3, the “valve control means” of the present invention is realized.

10 Engine 12 Refrigerant flow path (boiler)
13 Evaporator 11, 14, 15, 18, 28, 32, 36, 42, 46, 52 Refrigerant pipe 16 Gas-liquid separator 20, 48 Water pump 22 Exhaust passage 30 Superheater 34 Turbine (expander)
40 Condenser
44 Catch tank 100 Rankine cycle system 60 LLC tank 62 Control valve 64 Refrigerant pipe 110 Rankine cycle system

Claims (1)

A boiling device that applies waste heat of the internal combustion engine to a refrigerant in which a first refrigerant and a second refrigerant having a boiling point higher than that of the first refrigerant are mixed, and vaporizes the refrigerant;
A gas-liquid separator that separates a gas-liquid two-phase refrigerant sent from the boiling device into a gas-phase refrigerant and a liquid-phase refrigerant;
A superheater that superheats the gas-phase refrigerant delivered from the gas-liquid separator by heat exchange with the exhaust of the internal combustion engine;
An expander that expands the gas-phase refrigerant that has passed through the superheater and extracts work;
In the Rankine cycle system, comprising a condenser that condenses the gas-phase refrigerant that has passed through the expander and returns it to the liquid-phase refrigerant,
A refrigerant passage for introducing the liquid-phase refrigerant inside the gas-liquid separator into the condenser or a refrigerant pipe connecting the condenser and the boiler;
A control valve for opening and closing the refrigerant passage;
Detecting means for detecting that freezing occurs inside the condenser;
Valve control means for opening the control valve when freezing is detected by the detection means;
A Rankine cycle system comprising:

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