JP2003278598A - Exhaust heat recovery method and device for vehicle using rankine cycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve heat recovery efficiency from exhaust gas using a Rankine cycle device, and to enhance the degree of freedom for selecting a working fluid. <P>SOLUTION: In this exhaust heat recovery method and device for a vehicle which is provided with a combustion engine 10 taking as a fuel combustible gas (e.g. hydrogen) which is gaseous at the ordinary temperature to generate running motive power by combustion of the fuel, heat is recovered from exhaust gas discharged from the combustion engine by Rankine cycle. A working fluid (fluorocarbon) of Rankine cycle is condensed by isobaric cooling in a condenser 20 using heat of vaporization of combustible gas supplied from a tank 16 to the combustion engine 10, the working fluid is adiabatic compressed by a pump 32, the working fluid is isobaric heated to be evaporated using heat of exhaust gas by heat exchange in a heat exchanger 14, and the working fluid is adiabatically expanded by a turbine 26 to take exhaust heat in the exhaust gas as work. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for recovering exhaust heat of a vehicle such as an automobile, and more particularly to recovering exhaust heat of a vehicle that recovers heat from exhaust gas discharged from a combustion engine by Rankine cycle. A method and an apparatus.

[0002]

2. Description of the Related Art As one of exhaust heat recovery devices for vehicles such as automobiles, heat is recovered by a Rankine cycle device from exhaust gas exhausted from a combustion engine, as described in, for example, Japanese Patent Application Laid-Open No. 2001-182504. BACKGROUND ART Exhaust heat recovery devices that perform heat exchange have been conventionally known, and Rankine cycle devices generally perform heat exchange between exhaust gas and Rankine cycle working fluid and use heat of exhaust gas to evaporate the working fluid. And an expander that adiabatically expands the gaseous working fluid from the heat exchanger to output work, a condenser that condenses the working fluid from the expander, and adiabatic compression of the working fluid from the condenser. And a compressor that supplies the heat exchanger.

According to such an exhaust heat recovery device, a part of the heat of the exhaust gas discharged from the combustion engine is recovered by the Rankine cycle device, so that in the case of a general vehicle in which the Rankine cycle device is not provided. In comparison, the thermal efficiency of the vehicle as a whole can be improved and the fuel consumption can be improved.

[0004]

Generally, the heat recovery efficiency when the heat is recovered by the Rankine cycle device from the exhaust gas discharged from the combustion engine is higher as the temperature of the exhaust gas is higher, and the working fluid by the condenser is higher. The lower the condensation temperature of, the higher. However, since the temperature of the exhaust gas discharged from the combustion engine is determined by the type of combustion engine and fuel, it is not possible to raise the temperature of the exhaust gas, and the in-vehicle condenser is cooled by a cooling device such as a radiator. Therefore, the condensing temperature by the condenser cannot be made lower than the outside air temperature (normal temperature), and thus it is difficult to improve the heat recovery efficiency in the conventional heat recovery device as described above.

Further, in the conventional exhaust heat recovery system using the Rankine cycle, since the condensation temperature of the condenser cannot be lower than the ambient temperature as described above, the working fluid of the Rankine cycle is higher than the ambient temperature. It is limited to substances that condense at high temperatures, such as water, so the degree of freedom in selecting a working fluid for Rankine cycle is low, and a working fluid suitable for improving the heat recovery efficiency of Rankine cycle equipment is freely selected. There is a problem that you can not.

The present invention has been made in view of the above-mentioned problems in the conventional exhaust heat recovery device configured to recover heat from the exhaust gas discharged from the combustion engine by the Rankine cycle device, The main problem of the present invention is
In a vehicle equipped with a combustion engine that uses a combustible gas that forms a gas at room temperature as a fuel to generate traveling power by burning the fuel, the combustible gas is stored in a container in a high-pressure liquid state and is a gas. Since it is burned in the state of being converted to, it is possible to lower the condensation temperature of the working fluid by effectively utilizing the heat of vaporization, and improve the efficiency of heat recovery from exhaust gas by the Rankine cycle device. This is to increase the degree of freedom in selecting the working fluid.

[0007]

According to the present invention, the above-mentioned main problem is provided with a combustion engine which uses a combustible gas that forms a gas at room temperature as a fuel to generate traveling power by combustion of the fuel. In a vehicle, the exhaust heat recovery method of the vehicle recovers heat from exhaust gas discharged from the combustion engine by Rankine cycle, and uses the heat of the exhaust gas to evaporate working fluid of Rankine cycle. A method for recovering exhaust heat of a vehicle (constitution of claim 1), characterized in that the working fluid is condensed by utilizing heat of vaporization of the combustible gas,
Alternatively, a vehicle equipped with a tank that stores a combustible gas that is a gas at normal temperature in a high-pressure liquid state, and a combustion engine that uses the combustible gas as a fuel to generate traveling power by burning the fuel. A heat exchanger for exchanging heat between the exhaust gas discharged from the combustion engine and the working fluid of the Rankine cycle and evaporating the working fluid by utilizing the heat of the exhaust gas; and An expander for adiabatically expanding the gaseous working fluid to output work, a condenser for condensing the working fluid from the expander, and the adiabatic compression of the working fluid from the condenser for the heat A Rankine cycle device including a compressor for supplying to a exchanger, a vehicle exhaust heat recovery device for recovering heat from the exhaust gas discharged from the combustion engine by the Rankine cycle device, wherein the condenser is the Flammable An exhaust heat recovery system for a vehicle, which is disposed between the tank and the combustion engine when viewed in terms of gas flow, and uses the heat of vaporization of the combustible gas to condense the working fluid (claim The configuration of item 2) is achieved.

Further, according to the present invention, in order to effectively achieve the above-mentioned main problem, in the structure of the above-mentioned claim 2, the Rankine cycle device is characterized by a function of the working fluid circulating in the Rankine cycle device. It is configured to have a first flow rate control means for controlling the flow rate (configuration of claim 3).

Further, according to the present invention, in order to effectively achieve the above-mentioned main problem, in the structure of the above-mentioned claim 2, the Rankine cycle device is supplied from the combustion engine to the heat exchanger. It is configured to have a second flow rate control means for controlling the flow rate of the exhaust gas (configuration of claim 4).

[0010]

According to the first and second aspects of the present invention, since the working fluid is condensed by utilizing the heat of vaporization of the combustible gas, compared with the case where the condensation is performed by cooling by the outside air. By lowering the condensing temperature, it is possible to efficiently recover the exhaust heat from the exhaust gas, and it is possible to use a substance that has a lower condensing temperature than water etc. as a working fluid. The degree of freedom in selecting the fluid can be increased, and the optimum working fluid can be selected according to the combustion engine to which the present invention is applied. This also increases the exhaust heat recovery efficiency. it can.

According to the structures of claims 1 and 2,
The flammable gas, which forms a gas at room temperature, not only condenses the working fluid due to its heat of vaporization, but is also used as fuel and burns in the combustion engine to generate driving power, so the flammable gas evaporates. Both latent heat and combustion heat can be effectively used, and the energy efficiency of the entire vehicle can be increased.

According to the third aspect of the present invention, the Rankine cycle apparatus has the first flow rate control means for controlling the flow rate of the working fluid circulating in the Rankine cycle apparatus, so that the Rankine cycle apparatus is circulated in the Rankine cycle apparatus. The flow rate of the working fluid can be controlled to a flow rate suitable for exhaust heat recovery by Rankine cycle.

According to the fourth aspect of the present invention, the Rankine cycle system has the second flow rate control means for controlling the flow rate of the exhaust gas supplied from the combustion engine to the heat exchanger. The flow rate of the exhaust gas supplied from the combustion engine to the heat exchanger can be optimally controlled according to the flow rate of the circulating working fluid and the temperature of the exhaust gas.

[0014]

According to a preferred embodiment of the present invention, in the structure of claim 1 or 2,
The combustible gas is configured to be hydrogen (preferred aspect 1).

According to another preferred embodiment of the present invention, in the constitution of claim 1 or 2, the working fluid is a fluid selected from the group consisting of chlorofluorocarbon, alcohol and ammonia. (Preferred aspect 2).

According to another preferred aspect of the present invention, in the structure of claim 1, the working fluid is isobarically heated by heat exchange between the exhaust gas and the working fluid of the Rankine cycle. It is configured to vaporize the working fluid (preferred aspect 3).

According to another preferred aspect of the present invention, in the structure of claim 1, the working fluid is isobarically cooled by heat exchange between the working fluid and the combustible gas cooled by the heat of vaporization. Is configured to condense the working fluid (preferred aspect 4).

According to another preferred embodiment of the present invention, in the structure of the above-mentioned claim 3, the first flow rate control means is provided between the compressor and the heat exchanger, and the heat generated by the compressor is controlled by the compressor. It is configured to be a first flow rate control valve that controls the flow rate of the liquid working fluid supplied to the exchanger (preferred aspect 5).

According to another preferred embodiment of the present invention, in the configuration of the preferred embodiment 5, the first flow control valve compresses in accordance with the flow rate of the combustible gas supplied from the tank to the combustion engine. It is configured to control the flow rate of the liquid working fluid supplied from the machine to the heat exchanger (preferred aspect 6).

According to another preferred aspect of the present invention, in the structure of claim 3, the compressor is a variable discharge pump, and the variable discharge pump also functions as a first flow rate control means. However, the flow rate of the liquid working fluid supplied from the compressor to the heat exchanger is controlled (preferred aspect 7).

According to another preferred aspect of the present invention, in the configuration of the preferred aspect 7, the variable discharge amount pump changes the discharge amount according to the flow rate of the combustible gas supplied from the tank to the combustion engine. It is configured to control the flow rate of the liquid working fluid supplied to the heat exchanger by changing the temperature (preferred aspect 8).

According to another preferred embodiment of the present invention, in the structure of the above-mentioned claim 4, the second flow rate control means supplies the exhaust gas discharged from the combustion engine to the heat exchanger. And a second flow rate control valve for controlling the flow rate of the exhaust gas supplied to the heat exchanger, as well as branching to the flow discharged directly into the atmosphere (preferred aspect 9).

According to another preferred embodiment of the present invention, in the configuration of the preferred embodiment 9, the second flow control valve controls the flow rate of the working fluid circulating in the Rankine cycle system and the temperature of the exhaust gas. Accordingly, the flow rate of the exhaust gas supplied to the heat exchanger is controlled (preferred aspect 10).

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings, with reference to some preferred embodiments.

First Embodiment FIG. 1 is a schematic configuration diagram showing a first embodiment of an exhaust heat recovery apparatus by a Rankine cycle according to the present invention.

In FIG. 1, reference numeral 10 denotes an internal combustion engine that uses hydrogen as a fuel, and an exhaust pipe 12 of the internal combustion engine 10 extends into a heat exchanger 14 as a heating device at a midway portion thereof. is doing. Reference numeral 16 denotes a hydrogen tank which stores high-pressure liquid hydrogen therein, and a fuel supply pipe 18 which connects the internal combustion engine 10 and the hydrogen tank 16 extends into the condenser 20 at an intermediate portion thereof. ing.

Hydrogen in the hydrogen tank 16 is supplied to the fuel supply pipe 18
When it is supplied to the internal combustion engine 10 via the condenser 20, it passes through the condenser 20 and is vaporized into gas by being injected in the fuel supply pipe 18 extending into the condenser 20. Internal combustion engine 10
The amount of hydrogen supplied to is controlled by the electronic control unit 22 according to the amount of depression of the accelerator pedal, which is not shown in the figure. The internal combustion engine 10 burns hydrogen in the inside thereof to generate power for running the vehicle and also to generate steam as exhaust gas, and the exhaust gas is discharged into the atmosphere through the exhaust pipe 12 and the heat exchanger 14. To be done.

The heat exchanger 14 is connected to the inflow side of the turbine 26 functioning as an expander by a conduit 24, and the outflow side of the turbine 26 is connected to the inflow side of the condenser 20 by a conduit 28. The outflow side of the condenser 20 is connected to the suction side of the pump 32 by a conduit 30, and the discharge side of the pump 32 is connected to the inflow side of the heat exchanger 14 by a conduit 34.
In the illustrated first embodiment, a flow control valve 36 is provided in the middle of the conduit 34, and the valve opening amount is controlled by the electronic control unit 22 as described later.

The pump 32 is rotationally driven by an electric motor 38 controlled by the electronic control unit 22, but may be rotationally driven by the internal combustion engine 10. Although not shown in detail in FIG. 1, the turbine 2
6 has a rotary shaft 26a, and the rotary shaft 26a is rotationally driven by the steam of the working fluid passing through the turbine 26, and the rotational driving force may be used as auxiliary power for running the vehicle, and May be used as a drive source of the device of the above, and may be stored and used as other energy by driving a generator, for example.

Thus, the heat exchanger 14, the turbine 26, the condenser 20, and the pump 32 cooperate with each other to form a Rankine cycle device, and a freon is provided inside these devices and each conduit connecting these devices. , Rankine cycle working fluid such as alcohol, ammonia, or ammonia is enclosed, and the heat exchanger 14, the turbine 26, the condenser 20,
The pumps 32 perform Rankine cycle isobaric heating, adiabatic expansion, isobaric cooling, and adiabatic compression on the working fluid.

That is, as shown in FIG. 1, the point P1 is the point of the conduit 24 near the inlet side of the turbine 26, and the conduit point P
When 2, P3 and P4 are points in the middle of the conduits 28, 30 and 34, respectively, the pump 32 adiabatically compresses the liquid working fluid and sends it to the heat exchanger 14 (P3 to P4), and the heat exchanger 1
Reference numeral 4 heats the working fluid at a constant pressure by exchanging heat between the high-temperature exhaust gas flowing in the exhaust pipe 12 and the working fluid. The working fluid heated to equal pressure evaporates after reaching a saturation state, and is further heated to become a complete gas state.
Is supplied to (P4 to P1).

The turbine 26 adiabatically expands the working fluid in a high temperature gas state to generate work (rotational driving force of the rotating shaft 26a), the working fluid expands to near the wet state and then flows out from the turbine 26 to form a condenser. 20 (P1 to P
2). The condenser 20 adiabatically cools the working fluid by heat exchange between the hydrogen and the working fluid whose temperature is lowered by the heat of vaporization in the fuel supply pipe 18, and supplies the working fluid to the pump 32 in a completely liquid state ( P2 to P3).

The working fluid rises in temperature due to isobaric heating due to heat exchange with the exhaust gas in the heat exchanger 14 to change to gas, and adiabatically expands in the turbine 26 to lower the temperature, and the condenser It is cooled to a liquid by being cooled to a constant pressure by the heat of vaporization of hydrogen in 20, and the pump 32
Any substance such as water may be used as long as it can be adiabatically compressed by, but chlorofluorocarbon, alcohol, ammonia and the like, which have a condensation temperature lower than room temperature and a small latent heat of vaporization, are preferable.

In the Rankine cycle apparatus, the amount of working fluid that can flow in the loop is determined by the condenser 20.
The heat of vaporization of hydrogen in the condenser 20 is limited to the amount condensed into a complete liquid, and the heat of vaporization of hydrogen in the condenser 20 per unit time is determined by the flow rate of hydrogen supplied to the internal combustion engine 10. It Therefore, the flow rate control valve 36 calorimetrically matches the flow rate of the working fluid passing therethrough with the flow rate of hydrogen supplied from the hydrogen tank 16 to the internal combustion engine 10 via the fuel supply pipe 18, in other words, the working fluid is The electronic control unit 22 controls the amount of hydrogen supplied to the internal combustion engine 10 in accordance with the flow rate of hydrogen so that the heat of vaporization of hydrogen in the condenser 20 condenses it into a complete liquid.

Second Embodiment FIG. 2 is a schematic configuration diagram showing a second embodiment of the exhaust heat recovery apparatus by the Rankine cycle according to the present invention. In FIG. 2, the same members as those shown in FIG. 1 are designated by the same reference numerals as those shown in FIG.

In this embodiment, the flow control valve 36 in the above-mentioned first embodiment is not provided,
A branch type flow control valve 40 is provided in the exhaust pipe 12 between the internal combustion engine 10 and the heat exchanger 14. Flow control valve 40
A second exhaust pipe 42 is connected to the flow control valve 4
0 is controlled by the electronic control unit 22,
The flow rate of the exhaust gas supplied to the heat exchanger 14 via the exhaust pipe 12 on the downstream side is controlled to a predetermined flow rate, and the remaining exhaust gas is discharged into the atmosphere via the second exhaust pipe 42. To do. As can be seen from the comparison between FIG. 2 and FIG. 1, the exhaust heat recovery apparatus of this embodiment is configured in the same manner as the above-described first embodiment in other points, and therefore detailed description thereof will be omitted. To do.

In the illustrated Rankine cycle device,
The working fluid must be completely vaporized by the heat exchanger 14, and therefore the flow rate of the exhaust gas passing through the exhaust pipe 12 into the heat exchanger 14 is such that the working fluid is completely evaporated by the heat exchange inside the heat exchanger 14. While the flow rate must be vaporizable, it must be limited to a flow rate that can prevent overheating of the heat exchanger 14.

Therefore, the flow rate control valve 40 controls the flow rate of the exhaust gas supplied to the heat exchanger 14 via the exhaust pipe 12 to be equal to that of the heat exchanger 1.
So that the working fluid can be completely vaporized by the heat exchange in 4 and the flow rate is limited to prevent the excessive temperature rise of the heat exchanger 14, in other words, the heat exchange in the heat exchanger 14 operates from the exhaust gas. From the hydrogen tank 16 via the fuel supply pipe 18 so that the amount of heat given to the fluid matches the flow rate of the working fluid condensed in the liquid by the heat of vaporization of hydrogen in the condenser 20 and circulating in the loop of the Rankine cycle device. It is controlled by the electronic control unit 22 according to the flow rate of hydrogen supplied to the internal combustion engine 10 and the temperature of the exhaust gas.

FIG. 4 is a temperature-entropy diagram of the Rankine cycle achieved by the Rankine cycle apparatus in the above-mentioned first and second embodiments. The points P1 to P4 shown in the diagram of FIG. 4 correspond to the points P1 to P4 of the Rankine cycle device shown in FIGS. 1 and 2, respectively.
A shows a saturated liquid line of the working fluid, and B shows a saturated vapor line of the working fluid.

As is well known, in FIG. 4, points P1 and P2 are adiabatic expansion processes in the turbine 26, and points P2 and P2 are
P3 is an isobaric condensation process in the condenser 20, and the point P3
~ P4 is the adiabatic compression process by the pump 32, point P4 ~
P4 ', points P4' to P1 ', and points P1' to P1 are the isobaric heating process, isobaric evaporation process, and isobaric heating process in the heat exchanger 14, respectively.

Generally, since work is generated by the adiabatic expansion process of points P1 and P2, the larger the enthalpy drop of points P1 and P2 is, the more work amount is generated by the Rankine cycle device, that is, the heat energy recovered from the exhaust gas. The amount increases. Since the enthalpy drop is proportional to the temperature drop between points P1 and P2, the temperature drop between points P1 and P2 may be increased in order to increase the amount of heat energy recovered from the exhaust gas.

However, the temperature at the point P1 is determined by the heat exchange between the exhaust gas and the working fluid in the heat exchanger 14, and therefore is determined by the temperature Tg of the exhaust gas and the heat exchange efficiency of the heat exchanger 14. Therefore, the temperature difference between the points P1 and P2 cannot be increased by increasing the temperature at the point P1.

According to the first and second embodiments described above,
Condensation of the working fluid in the condenser 20 is not performed by cooling using the atmosphere and cooling water as in the radiator in the conventional vehicle-mounted Rankine cycle device, but by utilizing the latent heat of vaporization when liquid hydrogen is vaporized. Since this is achieved by cooling the working fluid, the temperatures T2 and T3 at the points P2 and P3 are made lower than in the conventional case, so that the points P1 to P3 are reduced.
It is possible to increase the temperature drop of 2 to increase the amount of heat energy recovered from the exhaust gas and improve the efficiency of exhaust heat recovery from the exhaust gas.

That is, the temperatures of the working fluids at the points P1 and P2 are set to T1 and T2, respectively, and the enthalpies are set to h1 and h2, respectively, and are generated by the adiabatic expansion process in the turbine 26 at the points P1 and P2. Assuming that the work amount is W, the temperature difference T1-T2 is proportional to the work amount W, as expressed by the following formula 1. T1−T2∝W = h1−h2 (1)

If the heat input amount given to the working fluid by heat exchange with the exhaust gas in the heat exchanger 14 is Q, the heat input amount Q is expressed by the following equation 2, and the theoretical thermal efficiency of the Rankine cycle device is shown. ηth is expressed by the following expression 3, and the larger the temperature difference T1−T2 from the expressions 1 to 3, the larger the work amount W, and if the heat input Q is constant, the temperature difference T
It can be seen that the larger the 1-T2, the higher the theoretical thermal efficiency ηth of the Rankine cycle system. Q = h1−h4 (2) ηth = W / Q (3)

Further, according to the first and second embodiments described above, the temperature T3 of the working fluid flowing out from the condenser 20 can be lowered as compared with the case of the conventional vehicle-mounted Rankine cycle device. Therefore, the temperature T4 of the working fluid flowing into the heat exchanger 14 can be made lower than that in the case of the conventional vehicle-mounted Rankine cycle device, whereby the working fluid in the heat exchanger 14 becomes exhaust gas. It is possible to further increase the amount of heat to be taken and increase the amount of exhaust heat recovered from the exhaust gas by the Rankine cycle device.

For example, the temperature Tg of the exhaust gas flowing into the heat exchanger 14 is set to 600 ° C., and the temperature efficiency of the heat exchanger 14 is set to 8
When the temperature is 0%, when the temperature of the working fluid flowing into the heat exchanger 14 is 80 ° C., the temperature of the exhaust gas flowing out from the heat exchanger 14 becomes 184 ° C., and the amount of heat taken by the working fluid from the exhaust gas is 10%. In contrast to 0.5 kW, when the temperature of the working fluid flowing into the heat exchanger 14 is −80 ° C., the heat exchanger 1
The temperature of the exhaust gas flowing out from No. 4 becomes 56 ° C., and the amount of heat taken by the working fluid from the exhaust gas becomes 13.7 kW.

Further, according to the first and second embodiments described above, the temperature T3 of the working fluid flowing out of the condenser 20 can be lowered as compared with the case of the conventional vehicle-mounted Rankine cycle device. If possible, the above points P4, P
Since the temperatures T4, T4 'and T1' of 4'and P1 'can also be lowered, the degree of freedom in selecting the working fluid of the Rankine cycle device can be increased and the exhaust heat recovery device of the present invention can be applied. The optimum working fluid can be selected according to the specifications of the vehicle, especially the internal combustion engine 10. This also improves the exhaust heat recovery efficiency.

The difference in the amount of work obtained will be described, for example, when conventional steam is used as the working fluid and when CFC R12 is used according to the present invention. The temperature Tg of the exhaust gas flowing into the heat exchanger 14 is set to 60
The temperature T when the temperature is 0 ° C. and the steam flows into the heat exchanger 14.
Regarding the heat input amount when 4 is 80 ° C. and the temperature efficiency of the heat exchanger 14 is 80%, the heat amount when the working fluid is changed from steam to Freon R12 is calculated.

When the working fluid is water vapor, the temperature T
4 '= T1' reaches 179.88 ° C. and temperature T1 is 496
℃. Also, the working fluid is Freon R12 and Freon R12
The temperature T4 when 12 flows into the heat exchanger 14 is -80 ° C.
Then, the temperature T4 '= T1' becomes 36.85 ° C and the temperature T1 becomes 63 ° C. However, the pressure of water vapor at the points P1 and P4 is 1 MPa, and the pressure of the fluorocarbon R12 at the points P1 and P4 is 0.9 MPa.

The amount of heat [kJ / kg] (points P4 to P4 ') obtained by the liquid of the working fluid and the latent heat of vaporization [kJ / kg] in such a situation
(Points P4 'to P1'), the amount of heat obtained by the working fluid gas [kJ /
kg] (points P1 'to P1), work W = h1-h2 [kJ / kg]
(Points P1 and P2) are as shown in Table 1 below.

As can be seen from Table 1, when the heat input amount (10.5 kW) to the working fluid in the heat exchanger 14 is the same, the flow rate (39.2 g / s) of CFC R12 is changed to the flow rate (3) of steam. It can be about 12 times the value of 0.4 g / s). Further, as shown by the following inequality with the flow rate of water vapor as Gs, the work amount Wf when CFC R12 is used as the working fluid becomes larger than the work amount Ws when water vapor is used as the working fluid, and accordingly the expansion The degree of freedom in selecting a device that can be used as a reactor can be increased, and this can also increase the amount of exhaust heat recovered from exhaust gas by the Rankine cycle device. Ws = 820 * Gs <Wf = 79 * 12Gs = 948Gs

In particular, according to the illustrated embodiments, the combustible gas that is the fuel is hydrogen, and the boiling point of hydrogen is -252.5.
Since the temperature is ℃ and the latent heat of vaporization is relatively large, the working fluid can be efficiently condensed in the condenser 20 as compared with the case where other combustible gas such as propane or liquefied natural gas is used as the fuel. And the temperatures T3 and T4 can be lowered.

Further, according to the first embodiment, the flow rate of the working fluid circulating in the Rankine cycle system is controlled by the internal combustion engine 10
Flow control valve 3 that controls according to the flow rate of hydrogen supplied to the
Since 6 is provided, the working fluid is surely provided by the heat of vaporization of hydrogen in the condenser 20 as compared with the case where the means for controlling the flow rate of the working fluid circulating in the Rankine cycle device is not provided. Can be condensed into a complete liquid, and the flow control valve 36 can be used for the pump 32 and the heat exchanger 14.
Is provided between the Rankine cycle device and the Rankine cycle device in order to control the flow rate of the working fluid in a liquid state. The flow rate of the fluid can be controlled accurately,
Further, it is possible to reduce the risk of cavitation occurring in the pump 32.

Further, according to the second embodiment, the heat exchanger 1
In order for the amount of heat given to the working fluid from the exhaust gas by heat exchange in 4 to match the flow rate of the working fluid circulating in the loop of the Rankine cycle device, the internal combustion is carried out by the split flow control valve 40 provided in the exhaust pipe 12. Since the flow rate of the exhaust gas supplied from the engine 10 to the heat exchanger 14 is controlled, the heat exchanger is compared with the case where the means for controlling the flow rate of the exhaust gas supplied to the heat exchanger is not provided. It is possible to surely prevent the excessive temperature rise of 14 and to surely change the working fluid into a perfect gas in the heat exchanger 14.

As shown in FIG. 3 as a modified example,
Both the flow rate control valve 36 in the first embodiment and the flow dividing type flow control valve 40 in the second embodiment described above may be provided in the Rankine cycle device, and in that case, it goes without saying. As a result, both the effects of the first and second embodiments described above can be obtained, and therefore exhaust heat can be recovered more preferably than exhaust gas.

In the first embodiment shown in FIG. 1 and the modification shown in FIG. 3, a flow rate control valve for controlling the flow rate of the working fluid supplied from the pump 32 to the heat exchanger 14. Although a pump 36 is provided, a variable discharge pump may be used as the pump, whereby the flow control valve 36 may be omitted.

Although the present invention has been described above in detail with respect to specific embodiments, the present invention is not limited to the above-mentioned embodiments, and various other embodiments within the scope of the present invention. It will be apparent to those skilled in the art that

For example, in each of the above embodiments, the combustible gas is hydrogen and the combustion engine is an internal combustion engine that uses hydrogen as a fuel, but the combustible gas may be propane or liquefied natural gas. The combustion engine may be an external combustion engine.

In each of the above-mentioned embodiments, the working fluid of the Rankine cycle device is Freon, alcohol,
Ammonia is illustrated, but other materials may be used as the working fluid in the context of combustible gases.

Further, in each of the above-described embodiments, the expander of the Rankine cycle system is the turbine 26, but as long as the expander can generate work by adiabatically expanding the gaseous working fluid. , May have any configuration known in the art.

Further, in the above-described first embodiment, the flow control valve is provided between the pump 32 and the heat exchanger 14, but the means for controlling the flow rate of the working fluid is the Rankine cycle device. It may be provided in other parts of the loop,
It may be omitted. Similarly, in the above-described second embodiment, the flow rate control valve 40 that controls the flow rate of the exhaust gas supplied from the internal combustion engine 10 to the heat exchanger 14 is provided, but it is supplied to the heat exchanger. The means for controlling the flow rate of the exhaust gas may be omitted, and other means for preventing the excessive temperature rise of the heat exchanger 14 may be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an exhaust heat recovery device by a Rankine cycle according to the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of an exhaust heat recovery device by a Rankine cycle according to the present invention.

FIG. 3 is a schematic configuration diagram showing a modified example of the exhaust heat recovery apparatus by the Rankine cycle according to the present invention.

FIG. 4 is a temperature-entropy diagram of the Rankine cycle achieved by the Rankine cycle device in the first and second embodiments.

[Explanation of symbols]

10 ... Internal combustion engine 14 ... Heat exchanger 20 ... condenser 22 ... Electronic control unit 26 ... Turbine 32 ... Pump 36, 40 ... Flow control valve

Claims (4)

[Claims] 1. A vehicle equipped with a combustion engine that uses a combustible gas that is a gas at normal temperature as a fuel to generate traveling power by combustion of the fuel, and rankines the exhaust gas discharged from the combustion engine. A vehicle exhaust heat recovery method for recovering heat by a cycle, wherein the working fluid of the Rankine cycle is vaporized by using the heat of the exhaust gas, and the working fluid is condensed by using the heat of vaporization of the combustible gas. A method for recovering exhaust heat from a vehicle characterized by: 2. A tank that stores a combustible gas that is a gas at room temperature in a high-pressure liquid state, and a combustion engine that uses the combustible gas as a fuel to generate traveling power by combustion of the fuel. In the vehicle, a heat exchanger for exchanging heat between the exhaust gas discharged from the combustion engine and the working fluid of Rankine cycle, and evaporating the working fluid by utilizing the heat of the exhaust gas; An expander that adiabatically expands the gaseous working fluid from the heat exchanger to output work, a condenser that condenses the working fluid from the expander, and an adiabatic compression of the working fluid from the condenser And a compressor for supplying the heat exchanger with a Rankine cycle device, wherein the Rankine cycle device recovers heat from exhaust gas discharged from the combustion engine, Condenser Exhaust heat recovery of a vehicle, which is arranged between the tank and the combustion engine as seen in the flow of combustible gas, and uses the heat of vaporization of the combustible gas to condense the working fluid. apparatus. 3. The Rankine cycle apparatus comprises first flow rate control means for controlling a flow rate of the working fluid circulating in the Rankine cycle apparatus.
Exhaust heat recovery device for vehicles as described in. 4. The vehicle according to claim 2, wherein the Rankine cycle apparatus has second flow rate control means for controlling a flow rate of the exhaust gas supplied from the combustion engine to the heat exchanger. Exhaust heat recovery device.