JP2006009710A - Thermoacoustic engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoacoustic engine constantly forming a sufficient temperature gradient between both end parts of a heat accumulation means, and surely generating thermoacoustic self-excited oscillation of working fluid. <P>SOLUTION: The thermoacoustic engine 20 comprises: a gas column pipe 21 into which the working fluid is sealed; a heat accumulator 25 disposed in the gas column pipe 21; and a high temperature heat exchanger 26 and a low temperature heat exchanger 27. The temperature gradient is formed between the both end parts of the heat accumulator 25 to generate the thermoacoustic self-excited oscillation of the working fluid. The low temperature heat exchanger 27 has a plurality of heat transfer pipes 271, 272. A coolant supply control valve 17 is controlled to be opened or closed so as to allow or stop supplying engine cooling water to the heat transfer pipe 272, and thereby to change a heat transfer area of the low temperature heat exchanger 27. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermoacoustic engine that forms a temperature gradient between both ends of a heat storage means arranged in an air column tube and generates thermoacoustic self-excited vibration of a working fluid in the air column tube.

  Conventionally, a refrigerator utilizing a thermoacoustic phenomenon has been proposed (see, for example, Patent Document 1). This refrigerator includes a pipe filled with gas, a stack disposed inside the pipe and sandwiched between a high temperature side heat exchanger and a low temperature side heat exchanger, and a high temperature side at a position asymmetric with the stack. And a regenerator arranged together with the heat exchanger and the low temperature side heat exchanger. This refrigerator generates a self-excited vibration of gas in the stack by forming a temperature gradient between both ends of the stack, and stores it in the regenerator by propagation of standing waves and traveling waves obtained thereby. It is.

  Conventionally, an apparatus for recovering exhaust heat of an internal combustion engine using a thermoacoustic phenomenon has been proposed (see, for example, Patent Document 2). This device includes a resonance pipe connected to an exhaust gas purification catalytic converter of an internal combustion engine, a stack provided at one end of the resonance pipe, and a transducer provided at the other end of the resonance pipe. In this apparatus, one end of the stack is heated by heat generated from the catalytic converter, and a temperature gradient is applied between both ends of the stack. Thereby, sound waves are generated in the stack, and the energy of the sound waves is converted into electric energy by the transducer.

  Furthermore, conventionally, a thermoacoustic generator that generates a pressure gradient in the gas in the loop pipe by forming a temperature gradient between both ends of the heat storage section in the loop pipe and generates electric power in accordance with a traveling wave generated by the pressure vibration. Has also been proposed (see, for example, Patent Document 3). This thermoacoustic generator has a starter / generator including a linear motor and a piston cylinder. The starter / generator functions as a starter motor when the thermoacoustic generator is activated, and reciprocally moves the piston cylinder to apply pressure vibration to the gas at an arbitrary frequency to generate self-oscillation of the gas in the loop tube. When pressure vibration due to self-excited oscillation occurs in the loop tube, the starter / generator functions as a generator that generates power in accordance with traveling waves generated by the pressure vibration.

Japanese Patent No. 3015786 JP 2002-122020 A Japanese Patent Laid-Open No. 2003-324932

  However, particularly when recovering the waste heat of the internal combustion engine using the thermoacoustic phenomenon, depending on the operation state of the internal combustion engine, a sufficient temperature gradient cannot be formed between both ends of the stack, and the working fluid itself It may be difficult to generate the excitation vibration, or the self-excitation vibration may be lost.

  Therefore, an object of the present invention is to provide a thermoacoustic engine that can always generate a sufficient thermoacoustic vibration of a working fluid by always forming a sufficient temperature gradient between both ends of the heat storage means.

  The thermoacoustic engine according to the present invention has an air column tube in which a working fluid is enclosed, and heat storage means disposed inside the air column tube, and operates by forming a temperature gradient between both ends of the heat storage unit. In a thermoacoustic engine that generates thermoacoustic self-excited vibration of a fluid, the thermoacoustic engine includes a heat exchanging means provided close to one end of the heat accumulating means to form a temperature gradient, and the heat exchanging means changes the heat transfer area. It is comprised so that it can be made to do.

  The present inventor has intensively studied to always form a sufficient temperature gradient between both ends of the heat storage means, and has found that the following phenomenon occurs in the process. That is, especially when the amount of heating to the heat storage means is insufficient, the heat exchange means (a heat medium that circulates the heat exchange means) particularly between the heat medium inlet and the outlet of the heat exchange means on the low temperature side. The temperature of the heat storage may change, thereby making it impossible to form a sufficient temperature gradient in the heat storage means. In order to eliminate such a phenomenon, the present inventor further researched this, and by changing the heat transfer area of the heat exchanging means, from the inlet of the heat medium to the outlet of the heat exchanging means. It has been found that temperature changes during the period can be suppressed. That is, if the heat transfer area of the heat exchange means that forms a temperature gradient between both ends of the heat storage means can be changed as in this thermoacoustic engine, a sufficient temperature gradient is always formed between the both ends of the heat storage means. Thus, the thermoacoustic self-excited vibration of the working fluid can be reliably generated.

  In the thermoacoustic engine according to the present invention, the heat exchange means is preferably a low-temperature heat exchanger for cooling one end of the heat storage means. In this case, the thermoacoustic engine heats the other end of the heat storage means. It is preferable to further include a high temperature heat exchanger for controlling the temperature and the control means for changing the heat transfer area of the low temperature heat exchanger according to the temperature of the high temperature heat exchanger.

  Further, the low temperature heat exchanger includes a plurality of heat transfer tubes, and a refrigerant supply setting unit that stops or allows supply of a cooling medium to a part of the plurality of heat transfer tubes, and the control unit is configured to control the temperature of the high temperature heat exchanger. It is preferable to control the refrigerant supply setting means according to the above. If such a configuration is employed, the heat transfer area of the low-temperature heat exchanger can be easily and reliably changed. Moreover, it is preferable that the high-temperature heat exchanger uses exhaust gas from the internal combustion engine as a heat source.

  According to the present invention, it is possible to realize a thermoacoustic engine that can always generate a sufficient temperature gradient between both ends of the heat storage means and reliably generate the thermoacoustic self-excited vibration of the working fluid.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a thermoacoustic engine according to the present invention. As shown in the figure, the thermoacoustic engine 20 is applied to, for example, an internal combustion engine 1 used as a travel drive source of a vehicle. First, the internal combustion engine 1 to which the thermoacoustic engine 20 is applied will be briefly described. The internal combustion engine 1 burns a mixture of fuel and air in a combustion chamber 3 formed in the cylinder block 2 and burns it. The piston 4 is reciprocated in the chamber 3 to generate power.

  The intake port of the combustion chamber 3 is connected to the intake manifold 5, and the exhaust port of the combustion chamber 3 is connected to the exhaust manifold 6. In addition, an intake valve Vi that opens and closes an intake port, an exhaust valve Ve that opens and closes an exhaust port, a spark plug 7, and an injector 8 are disposed for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. The intake manifold 5 is connected to a surge tank 9, and an air supply pipe L <b> 1 is connected to the surge tank 9. The air supply pipe L1 is connected to an air intake port (not shown) via the air cleaner 10. Further, a throttle valve 11 is incorporated in the middle of the supply pipe L1 (between the surge tank 9 and the air cleaner 10). On the other hand, the exhaust manifold 6 is connected to an exhaust pipe L2, and a front-stage catalyst device 12a and a rear-stage catalyst device 12b each including an exhaust purification catalyst are incorporated in the exhaust pipe L2.

  The thermoacoustic engine 20 of the present invention is used to recover the exhaust heat of the internal combustion engine 1 as described above. The thermoacoustic engine 20 has an air column tube 21 formed of stainless steel or the like so as to have a circular cross section, and inside the air column tube 21 is an operation such as nitrogen, helium, argon, a mixed gas of helium and argon. A fluid (inert gas) is enclosed. As shown in FIG. 1, the air column tube 21 includes a loop portion 22 formed in a substantially rectangular loop shape, and a resonance portion 23 connected to one corner portion of the loop portion 22. The resonance part 23 includes a tube part 23a having a circular cross section approximately the same diameter as the loop part 22, and a closed end part 23b connected to the tip of the tube part 23a, and functions as a resonator. The diameter of the closed end portion 23b is gradually increased from the distal end of the tube portion 23a toward the closed end, and a transducer (converting sound wave energy (acoustic energy) into electrical energy is provided at the closed end of the closed end portion 23b. (Sound / electrical conversion means) 24 is arranged.

  A heat accumulator (heat storage means) 25 is disposed inside the loop portion 22 of the air column tube 21. The heat accumulator 25 has a plurality of narrow flow paths extending in parallel with the axial direction of the air column tube 21 at the arrangement location. As the heat accumulator 25, a honeycomb structure made of ceramic or the like, a thin mesh made of stainless steel or the like arranged at a minute interval, a nonwoven fabric in which metal fibers such as stainless steel are gathered, or the like can be used. A high-temperature heat exchanger 26 is disposed adjacent to one end side (the lower end side in FIG. 1) of the heat accumulator 25, and a low-temperature heat is disposed on the other end side (the upper end side in FIG. 1) of the heat accumulator 25. An exchanger 27 is disposed adjacent to the exchanger 27. That is, the heat accumulator 25 is arranged in a state of being sandwiched between the high temperature heat exchanger 26 and the low temperature heat exchanger 27.

  Exhaust gas flowing through the exhaust pipe L2 of the internal combustion engine 1 is supplied to the heat transfer tubes constituting the high temperature heat exchanger 26, and the high temperature heat exchanger 26 uses the exhaust gas of the internal combustion engine 1 as a heat source. In the present embodiment, the high-temperature heat exchanger (its heat transfer pipe) 26 is incorporated in the exhaust pipe L2 between the front-stage catalyst apparatus 12a and the rear-stage catalyst apparatus 12b. The heat transfer tubes 271 and 272 constituting the low-temperature heat exchanger 27 are incorporated in the cooling system L3 of the internal combustion engine 1, and the low-temperature heat exchanger 27 uses cooling water flowing through the cooling system L3 as a heat source (cold heat source). ). The cooling system L3 includes a cooling water pump 14, a radiator 15 (see FIG. 4), an on-off valve 16, and the like. By closing the on-off valve 16, the low-temperature heat exchanger (its heat transfer pipe) 27 is connected. The supply of cooling water can be stopped.

  The thermoacoustic engine 20 includes an electronic control unit (hereinafter referred to as “ECU”) 40 that functions as control means. The ECU 40 includes a CPU, a ROM, a RAM, an input / output port, a storage device, etc., all not shown. The on-off valve 16 and the like of the cooling system L3 described above are connected to an input / output port of the ECU 40 and are controlled by the ECU 40. In addition, a temperature sensor T that detects a catalyst temperature (catalyst bed temperature) is installed in the pre-stage catalyst device 12a of the internal combustion engine 1. The temperature sensor T is connected to the input / output port of the ECU 40, and gives a signal indicating the detected value to the ECU 40.

  In the thermoacoustic engine 20 configured as described above, the internal combustion engine 1 is operated in a state where the on-off valve 16 of the cooling system L3 is opened, and the exhaust gas from the combustion chamber 3 passes through the pre-catalyst device 12a. The operation starts when it passes through the high-temperature heat exchanger 26 of the thermoacoustic engine 20. In this case, since the temperature of the exhaust gas that has passed through the pre-stage catalyst device 12a reaches about 900 ° C. at the maximum, one end of the heat accumulator 25 is heated by the exhaust gas flowing through the high-temperature heat exchanger 26. Raise the temperature. On the other hand, the low-temperature heat exchanger 27 of the thermoacoustic engine 20 has cooling water at a relatively low temperature (generally atmospheric temperature immediately after the cold start of the internal combustion engine 1 and approximately 80 to 90 ° C. after completion of warm-up). Therefore, the other end of the heat accumulator 25 is cooled by cooling water flowing through the low-temperature heat exchanger 27. As a result, a large temperature gradient is formed between both ends of the heat accumulator 25, and as a result, thermoacoustic self-excited vibration (sound wave) of the working fluid is generated.

  When the frequency of the self-excited vibration (sound wave) of the working fluid generated in this way matches the resonance frequency in the resonance part 23, a standing wave is formed in the resonance part 23. Further, a traveling wave traveling from the low temperature heat exchanger 27 to the high temperature heat exchanger 26 is formed in the loop portion 22. And the vibration part of the transducer 24 arrange | positioned at the closed end part 23b is vibrated by the standing wave formed in the resonance part 23. FIG. The transducer 24 converts standing wave energy (acoustic energy) in the resonance unit 23 into electric energy, and the obtained electric energy is supplied to a predetermined electric load via a controller (not shown). Thereby, according to the thermoacoustic engine 20 of this invention, the exhaust heat of the internal combustion engine 1 can be collect | recovered efficiently, and the electric power for predetermined | prescribed electric loads can be obtained. Instead of arranging the transducer 24 in the resonance unit 23, a unit of a heat accumulator, a high temperature heat exchanger, and a low temperature heat exchanger is arranged in the loop unit 22, and the exhaust heat energy recovered by the thermoacoustic engine 20 is used. Then, the unit may be operated as a refrigerator.

  As described above, in the thermoacoustic engine 20, it is possible to form a temperature gradient between both ends of the heat accumulator 25 using the exhaust heat (waste heat) of the internal combustion engine 1. However, when the temperature of the exhaust gas is lower than a predetermined temperature (for example, when the exhaust heat is low), such as when the internal combustion engine is started or idling, as shown by a broken line in FIG. The temperature of the exhaust gas flowing through the heat transfer tube does not change so much from the entrance of the heat transfer tube to the outlet of the heat transfer tube, whereas as shown by the broken line in FIG. The temperature Tc (the temperature of engine cooling water flowing through the heat transfer tube) may increase as it goes from the inlet of the heat medium to the outlet of the heat transfer tube. When such a phenomenon occurs, the temperature difference between the high-temperature heat exchanger and the low-temperature heat exchanger becomes small on the heat medium outlet side of the heat transfer tube, so that a sufficient temperature gradient cannot be formed in the heat accumulator. It becomes difficult to generate the thermoacoustic self-excited vibration satisfactorily.

  In this case, for example, it is conceivable to change the supply amount of the cooling medium to the heat transfer tubes of the low-temperature heat exchanger so that a sufficient temperature gradient is formed in the heat accumulator. However, according to the research of the present inventor, for example, when the temperature of the exhaust gas is lower than a predetermined temperature (when the exhaust heat is low), for example, at the time of starting the internal combustion engine or idling, cooling the heat transfer tube of the low-temperature heat exchanger When the supply amount of the medium is decreased, the temperature Tc of the low-temperature heat exchanger (the temperature of the engine cooling water flowing through the heat transfer tube) does not change the supply amount of the cooling medium, as indicated by a one-dot chain line in FIG. Compared to (see the broken line in FIG. 3), it further increases as it goes from the inlet of the heat transfer tube to the outlet. Further, when the temperature of the exhaust gas is lower than a predetermined temperature, for example, at the time of starting the engine or idling, even if the amount of the cooling medium supplied to the heat transfer tube of the low-temperature heat exchanger is increased, the two-dot chain line in FIG. As shown, it is difficult to form a sufficient temperature gradient in the regenerator.

  On the other hand, when the inventor further researched, the heat transfer area of the low-temperature heat exchanger 27 was maintained while the amount of the heat medium (engine cooling water) to the heat transfer tube of the low-temperature heat exchanger 27 was kept constant. (In the example of FIG. 2, the heat transfer area is reduced by 50%), as shown by the solid line in FIG. 2, the cooling medium (from the inlet to the outlet of the heat medium of the low-temperature heat exchanger 27 ( It has been found that the temperature change of the engine cooling water) can be suppressed. In view of such research results, the thermoacoustic engine 20 is configured such that the low-temperature heat exchanger 27 for forming a temperature gradient between both ends of the heat accumulator 25 can change its heat transfer area. Has been.

  As shown in FIG. 4, the low-temperature heat exchanger 27 includes a plurality of heat transfer tubes 271 and a plurality of heat transfer tubes 272. In this embodiment, the heat transfer tubes 271 and 272 are members having the same structure, and the number of heat transfer tubes 271 and the number of heat transfer tubes 272 are the same. The refrigerant inlet of each heat transfer pipe 271 is connected in parallel to the refrigerant supply pipe L4 connected to the on-off valve 16, and the refrigerant outlet of each heat transfer pipe 271 supplies engine cooling water as a cooling medium to the cooling system L3. Is connected in parallel to the refrigerant return pipe L5 for returning to the pipe. The refrigerant inlet of each heat transfer tube 272 is connected in parallel to the branch pipe L6 branched from the refrigerant supply pipe L4, and the refrigerant outlet of each heat transfer pipe 272 is connected to the above-described refrigerant return pipe L5. Connected in parallel.

  Further, a refrigerant supply control valve 17 is provided in the branch pipe L6. The refrigerant supply control valve 17 is controlled to be opened and closed by the ECU 40, and the refrigerant supply control valve 17 can be opened and closed to stop or allow the supply of the cooling medium to each heat transfer tube 272. That is, if the refrigerant supply control valve 17 is opened when the on-off valve 16 is opened, the refrigerant supply pipe L4 and the branch pipe L6 are connected to all the heat transfer pipes 271 and 272 of the low-temperature heat exchanger 27. Thus, engine cooling water as a cooling medium is supplied. On the other hand, if the refrigerant supply control valve 17 is closed when the on-off valve 16 is open, (all) of the heat transfer tubes 271 and 272 of the low-temperature heat exchanger 27 (all the heat transfer tubes 271 (the low-temperature heat exchanger 27). Only 50% of the total heat transfer pipes) are supplied with engine coolant as a cooling medium through the refrigerant supply pipe L4. As described above, in the thermoacoustic engine 20, the heat transfer area of the low-temperature heat exchanger 27 can be easily and reliably changed by controlling the refrigerant supply control valve 17 to open and close.

  In the thermoacoustic engine 20 including the low-temperature heat exchanger 27 described above, a sufficient temperature gradient is always formed between both ends of the heat accumulator 25 when the on-off valve 16 is operated in an open state. Thus, in order to reliably generate the thermoacoustic self-excited vibration of the working fluid, the ECU 40 repeatedly executes the heat transfer area control routine shown in FIG. 5 every predetermined time. In this case, the ECU 40 first obtains the temperature Te of the exhaust gas supplied to the high temperature heat exchanger 26 based on the detected value of the temperature sensor T of the pre-stage catalyst device 12a (S10). When the exhaust gas temperature Te is acquired, the ECU 40 determines whether the exhaust gas temperature Te supplied to the high temperature heat exchanger 26 (substantially, the temperature of the high temperature heat exchanger 26) is equal to or higher than a predetermined threshold. It is determined whether or not (S12).

  When it is determined in S12 that the temperature Te of the exhaust gas supplied to the high-temperature heat exchanger 26 is equal to or higher than the threshold value, the ECU 40 opens the refrigerant supply control valve 17 (S14). Thereby, when the temperature Te of the exhaust gas from the internal combustion engine 1 is sufficiently high, the cooling medium is supplied to all the heat transfer tubes 271 and 272 of the low-temperature heat exchanger 27 via the refrigerant supply tube L4 and the branch tube L6. As a result, engine cooling water is supplied.

  On the other hand, when it is determined in S12 that the temperature Te of the exhaust gas supplied to the high temperature heat exchanger 26 is below the threshold value, the ECU 40 closes the refrigerant supply control valve 17 (S16). Thereby, for example, when the temperature Te of the exhaust gas is lower than a predetermined temperature, such as when the internal combustion engine 1 is started or idling, (all) of the heat transfer tubes 271 and 272 of the low-temperature heat exchanger 27. Only 271 is supplied with engine cooling water as a cooling medium via the refrigerant supply pipe L4.

  Thus, in the thermoacoustic engine 20, when a negative determination is made in S12, the heat transfer area of the low-temperature heat exchanger 27 is decreased (in this embodiment, 50%). As a result, even when the temperature Te of the exhaust gas is lower than a predetermined temperature, for example, when the internal combustion engine 1 is started or idling, a sufficient temperature gradient is formed between both ends of the heat accumulator 25 to operate. It becomes possible to reliably generate the thermoacoustic self-excited vibration of the fluid.

  Instead of installing the temperature sensor T in the upstream catalyst device 12a, a temperature sensor may be installed at a predetermined location of the high temperature heat exchanger 26. In this case, in S10 of FIG. 5, the temperature at a predetermined location of the high temperature heat exchanger 26 is acquired based on the detection value of the temperature sensor, and in S12, the temperature of the high temperature heat exchanger 26 is equal to or higher than a predetermined threshold. It is good to determine whether or not.

It is a schematic block diagram which shows the thermoacoustic engine by this invention. When the amount of heat stored in the heat accumulator by the high-temperature heat exchanger is small, the amount of cooling medium supplied to the low-temperature heat exchanger is kept constant, while the heat transfer tube heat medium is changed when the heat-transfer area of the low-temperature heat exchanger is changed It is a graph for demonstrating the temperature change of a high temperature heat exchanger and a low-temperature heat exchanger between an inlet_port | entrance and a heat-medium exit. When the amount of heat stored in the regenerator by the high-temperature heat exchanger is small, the supply amount of the cooling medium to the low-temperature heat exchanger is kept constant while the supply amount of the cooling medium to the low-temperature heat exchanger is changed. It is a graph for demonstrating the temperature change of a high temperature heat exchanger and a low temperature heat exchanger between a heat-medium entrance and a heat-medium exit. It is a schematic diagram for demonstrating the low-temperature heat exchanger contained in the thermoacoustic engine of FIG. 2 is a flowchart for explaining a routine for controlling a heat transfer area of a low-temperature heat exchanger in the thermoacoustic engine of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 14 Cooling water pump 15 Radiator 16 On-off valve 17 Refrigerant supply control valve 20 Thermoacoustic engine 21 Air column tube 22 Loop part 23 Resonance part 24 Transducer 25 Heat accumulator 26 High temperature heat exchanger 27 Low temperature heat exchanger 271, 272 Heat pipe L3 Cooling system L4 Refrigerant supply pipe L5 Refrigerant return pipe L6 Branch pipe T Temperature sensor

Claims (4)

An air column tube in which the working fluid is sealed, and heat storage means disposed inside the air column tube, and a temperature gradient is formed between both end portions of the heat storage unit so that the thermoacoustic self-excitation of the working fluid is performed. In a thermoacoustic engine that generates vibration,
In order to form the temperature gradient, heat exchange means provided close to one end of the heat storage means is provided, and the heat exchange means is configured to change the heat transfer area. A thermoacoustic engine. The heat exchange means is a low-temperature heat exchanger for cooling one end of the heat storage means,
A high-temperature heat exchanger for heating the other end of the heat storage means;
The thermoacoustic engine according to claim 1, further comprising a control unit that changes a heat transfer area of the low-temperature heat exchanger according to a temperature of the high-temperature heat exchanger.   The low-temperature heat exchanger includes a plurality of heat transfer tubes and a refrigerant supply setting unit that stops or allows supply of a cooling medium to a part of the plurality of heat transfer tubes, and the control unit includes the high-temperature heat exchanger. The thermoacoustic engine according to claim 2, wherein the refrigerant supply setting unit is controlled according to temperature. The thermoacoustic engine according to claim 2, wherein the high-temperature heat exchanger uses exhaust gas from an internal combustion engine as a heat source.

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