JP2019183793A - Exhaust heat recovery device of engine - Google Patents

Abstract

To improve heat efficiency of an engine by heat recovery of an exhaust gas even when a temperature of the exhaust gas is low.SOLUTION: An exhaust heat recovery device 3 of an engine 1 includes a water recovery portion (condenser 32) disposed in an exhaust passage 40 for recovering water in an exhaust gas, a heating portion (heat exchanger 31) heating the water recovered by the water recovery portion, and a water injection portion (water injection valve 5) having a passage portion 52 in which the water heated by the heating portion flows, and a nozzle 53 communicated to the passage portion and opened to a combustion chamber, and injecting the water into the combustion chamber through the nozzle. The water injection portion is mounted on the engine, heat of the exhaust gas is supplied to the water flowing in the nozzle, a temperature of the water in the passage portion is 280°C or more and less than 374°C, a pressure of the water in the passage portion is 10 MPa or more and 30 MPa or less, a diameter D of the nozzle is 0.1 mm or more and 1 mm or less, and a length L of the nozzle is determined to satisfy that L/D is 5 or more and 50 or less.SELECTED DRAWING: Figure 3

Description

  The technology disclosed herein relates to an exhaust heat recovery device for an engine.

  Patent Document 1 describes a diesel engine that improves efficiency by injecting subcritical water or supercritical water into a combustion chamber. More specifically, the diesel engine generates subcritical water or supercritical water by performing heat exchange between water and exhaust gas. The generated subcritical water or supercritical water is injected into the combustion chamber by the water injection valve before the air-fuel mixture is ignited in the compression stroke.

  Patent Document 2 describes an injection control device that injects water into a combustion chamber of a diesel engine. The water injection valve injects water during the combustion period. Water receives heat from the combustion flame and is vaporized, thereby increasing the vaporization expansion force and improving the fuel efficiency of the diesel engine.

Japanese Patent No. 4648466 JP 2012-112326 A

  For example, when the engine is operating at a high load, the temperature of the exhaust gas is high. When the engine is operating at a high load, as described in Patent Document 1, heat exchange between water and exhaust gas causes the water temperature to rise above the critical temperature, generating supercritical water. Is possible. When supercritical water is injected into the combustion chamber, superheated steam is generated without using the heat in the combustion chamber. By injecting supercritical water into the combustion chamber, for example, at a timing near the compression top dead center from the compression stroke, the amount of working gas in the expansion stroke can be increased, and the thermal efficiency of the engine is improved. In other words, the exhaust heat recovery apparatus having this configuration can improve the thermal efficiency of the engine by recovering the heat of the exhaust gas through water.

  However, when the engine is operating at a low load and / or when the combustion air-fuel ratio of the engine is leaner than the stoichiometric air-fuel ratio, the temperature of the exhaust gas becomes low. Therefore, even if heat exchange between water and exhaust gas is performed, supercritical water cannot be generated. If supercritical water cannot be generated, the water injected into the combustion chamber is vaporized using the heat in the combustion chamber, as described in Patent Document 2. In this case, the thermal efficiency is lower than when supercritical water generated using the heat of the exhaust gas is injected into the combustion chamber.

  The technique disclosed here improves the thermal efficiency of the engine by recovering heat of the exhaust gas even when the temperature of the exhaust gas is low.

  The inventors of the present application focus on supplying saturated steam into the combustion chamber using the reduced-pressure boiling phenomenon when the temperature of the exhaust gas is low and supercritical water cannot be generated by heat recovery of the exhaust gas. Did.

  However, due to the relationship between the low heat energy of the exhaust gas and the pressure state in the combustion chamber at the timing when water is injected into the combustion chamber, the required amount of saturated steam cannot be generated only by the reduced-pressure boiling phenomenon. In addition, the present inventors have noticed.

  Therefore, the inventors of the present invention supply the heat through the wall surface of the nozzle while water (liquid) flows through the nozzle of the water injection unit, whereby the boiling heat caused by the vacuum boiling and the vacuum boiling is generated in the nozzle. Saturated steam was generated using both transmission and transmission. And the shape of the nozzle which became possible to produce | generate saturated vapor | steam in a nozzle was discovered, and it came to complete the technique disclosed here.

  Specifically, the technology disclosed herein relates to an engine exhaust heat recovery device. The engine exhaust heat recovery device includes an engine having a combustion chamber, a water recovery unit that is provided in an exhaust passage of the engine and recovers water in exhaust gas flowing in the exhaust passage, and the water recovery unit recovers A heating section that heats the heated water, a passage section through which water heated in the heating section flows, and a nozzle that communicates with the passage section and opens into the combustion chamber, and through the nozzle into the combustion chamber. A water injection unit for injecting water.

  The water injection unit is attached to the engine, and the heat of the exhaust gas is supplied to the water flowing through the nozzle. The temperature of the water in the passage unit is 280 ° C. or more and less than 374 ° C. The pressure of water is 10 MPa or more and 30 MPa or less, the nozzle diameter D is 0.1 mm or more and 1 mm or less, and the nozzle length L is such that L / D is 5 or more and 50 or less. Is set.

  According to this configuration, the water recovered from the exhaust gas is heated in the heating unit and then injected into the combustion chamber by the water injection unit. Here, the water injection part is attached to the engine, and the heat of the exhaust gas is transmitted from the inner peripheral surface of the nozzle to the water flowing in the nozzle.

  In the passage part of the water injection part, the temperature of the water is 280 ° C. or more and less than 374 ° C. In other words, in the exhaust heat recovery apparatus having this configuration in which the water temperature is equal to or lower than the critical temperature, the water injection unit does not inject supercritical water into the combustion chamber.

  In the passage part of the water injection part, the pressure of water is 10 MPa or more and 30 MPa or less. You may raise the pressure of water by arrange | positioning in a channel | path which supplies water to a water injection part in a high pressure pump. The high pressure pump may be configured to be driven by an engine, for example. The high pressure pump may be configured to be driven by electric energy.

  The nozzle of the water injection part is opened in the combustion chamber. The pressure in the nozzle matches or substantially matches the pressure in the combustion chamber. At the timing when the water injection unit injects water, the pressure in the combustion chamber (and the nozzle) is, for example, about 5 MPa. When the water injection unit injects water, a part of the water (liquid) in the nozzle becomes saturated vapor due to the reduced pressure boiling phenomenon. In the nozzle, the heat of the exhaust gas is supplied to the water by the wall surface heat transfer. Furthermore, with boiling under reduced pressure, heat is supplied to the water by boiling heat transfer in the nozzle. By both the reduced-pressure boiling phenomenon and the boiling heat transfer, water becomes saturated steam in the nozzle and is injected (that is, supplied) into the combustion chamber.

  Thus, the exhaust heat recovery apparatus having the above-described configuration can supply saturated steam into the combustion chamber without using the heat in the combustion chamber. As in the case of injecting supercritical water generated using the heat of the exhaust gas into the combustion chamber, the thermal efficiency of the engine can be improved.

  The water recovery unit condenses water in the exhaust gas by cooling the exhaust gas, the heating unit is provided upstream of the water recovery unit in the exhaust passage, and the heat of the exhaust gas The water may be heated.

  By doing so, the heat of the exhaust gas can be recovered using water as a medium, and the thermal efficiency of the engine is further improved. In particular, this configuration does not require heating the water above the critical temperature in the heating section, so heat recovery can be performed when the temperature of the exhaust gas is low.

The water ejection unit may include a plurality of the nozzles, and an area of an inner peripheral surface of each nozzle may be 0.16 mm ² or more and 160 mm ² or less.

  By doing so, saturated steam generated using both the reduced-pressure boiling phenomenon and the boiling heat transfer in each of the plurality of nozzles can be supplied into the combustion chamber.

  The water injection unit may be provided with a heat pipe heat dissipation unit that transports heat of the exhaust gas.

  By using the heat pipe, the heat of the exhaust gas can be efficiently transported to the nozzle of the water injection unit. Since sufficient heat can be supplied to the water flowing in the nozzle, it is advantageous in producing saturated steam.

  The combustion air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio at least in a low-load region where the load is lower than a predetermined load in the entire operation region of the engine, and the water injection unit is at least in the low-load region. Water may be injected into the combustion chamber.

  If the combustion air-fuel ratio of the air-fuel mixture is made leaner than the stoichiometric air-fuel ratio when the engine load is low, the temperature of the exhaust gas decreases. As described above, the technology disclosed herein is advantageous in improving the fuel efficiency of the engine because the exhaust gas can recover heat even when the temperature of the exhaust gas is low.

  As described above, according to the engine exhaust heat recovery apparatus, even when the temperature of the exhaust gas is low, the thermal efficiency of the engine can be improved by the heat recovery of the exhaust gas.

FIG. 1 is a diagram illustrating the configuration of an exhaust heat recovery device for an engine. FIG. 2 is a cross-sectional view illustrating the configuration of the tip of the water injection valve. FIG. 3 is an explanatory diagram schematically showing the process of changing from liquid water to saturated vapor in the nozzle. FIG. 4 is a cross-sectional view illustrating the configuration of the tip of the water injection valve having a configuration different from that in FIG.

  Hereinafter, the configuration of the exhaust heat recovery device for an engine disclosed herein will be described with reference to the drawings. The following description is an example of the configuration of the exhaust heat recovery apparatus.

  FIG. 1 shows a configuration example of an exhaust heat recovery device 3 for an engine. The engine 1 is mounted on an automobile. The engine 1 is a multi-cylinder engine having a plurality of cylinders 20. The engine 1 may be, for example, an in-line four cylinder engine.

  The engine 1 includes a cylinder block 21 and a cylinder head 22 placed on the cylinder block 21. The cylinder 20 is formed in the cylinder block 21.

  The engine 1 has a piston 24 disposed in each cylinder 20. A cavity is formed on the upper surface of the piston 24. A combustion chamber 29 is formed by the cylinder 20 and the piston 24. The engine 1 is configured to cause compression air to ignite in the combustion chamber 29 an air-fuel mixture containing at least gasoline. The geometric compression ratio of the engine 1 is set to 15 or more and 30 or less, for example. A heat shield layer may be provided on the surfaces of the piston 24 and the cylinder head 22 that form the combustion chamber 29.

  In the configuration example shown in FIG. 1, the engine 1 is not provided with a spark plug, but the engine 1 may be configured to assist the compression ignition of the air-fuel mixture using the spark plug.

  A fuel injection valve 220 is attached to the cylinder head 22. The fuel injection valve 220 is provided for each cylinder 20. The fuel injection valve 220 directly injects fuel into the combustion chamber 29.

  An intake port 27 is formed in the cylinder head 22. The intake port 27 communicates with the combustion chamber 29. Although not shown, an intake valve that opens and closes the intake port 27 is disposed in the opening 26 of the intake port 27. Although not shown, an intake pipe is connected to the intake port 27.

  An exhaust port 47 is also formed in the cylinder head 22. The exhaust port 47 communicates with the combustion chamber 29. Although not shown, an exhaust valve that opens and closes the exhaust port 47 is disposed in the opening 46 of the exhaust port 47. Although schematically shown in FIG. 1, an exhaust pipe 45 is connected to the exhaust port 47. The exhaust port 47 and the exhaust pipe 45 constitute an exhaust passage 40 through which exhaust gas discharged from the combustion chamber 29 flows.

  In the exhaust pipe 45, a catalyst device 41, a heat exchanger 31, and a condenser 32 are arranged in order from upstream to downstream. The catalyst device 41 purifies the exhaust gas. For example, the catalyst device 41 may include a three-way catalyst.

  The exhaust heat recovery device 3 of the engine 1 includes a heat exchanger 31, a condenser 32, a water tank 33, a high pressure pump 34, and a water injection valve 5.

  The condenser 32 is configured to condense the water in the exhaust gas by cooling the exhaust gas flowing in the exhaust pipe 45. That is, the condenser 32 is a heat exchanger that cools the exhaust gas by heat exchange with the refrigerant. The condenser 32 is an example of a water recovery unit. A water tank 33 is connected to the condenser 32 via a first pipe 35.

  The water tank 33 is disposed vertically below the condenser 32. The water condensed in the condenser 32 flows through the first pipe 35 to the water tank 33 by natural flow.

  As described above, the heat exchanger 31 is disposed upstream of the condenser 32 in the exhaust pipe 45. The heat exchanger 31 is configured to heat the water condensed in the condenser 32 using the heat of the exhaust gas. The heat exchanger 31 is an example of a heating unit. The heat exchanger 31 and the water tank 33 are connected via a second pipe 36. The high pressure pump 34 is disposed in the second pipe 36. The high-pressure pump 34 pumps water from the water tank 33 toward the heat exchanger 31. The high pressure pump 34 may be configured to be driven by the engine 1. The high pressure pump 34 may be configured to be driven by an electric motor.

  The water injection valve 5 is attached to the cylinder head 22. The water injection valve 5 is provided for each cylinder 20. The water injection valve 5 is attached near the exhaust port 47. In the configuration example of FIG. 1, the water injection valve 5 is inclined with respect to the central axis of the cylinder 20. The mounting configuration of the water injection valve 5 is not limited to the configuration example of FIG.

  The heat exchanger 31 and the water injection valve 5 are connected via a third pipe 37. The water heated in the heat exchanger 31 is sent to the water injection valve 5 through the third pipe 37.

  The water injection valve 5 injects water into the combustion chamber 29. The water injection valve 5 is an example of a water injection unit. FIG. 2 illustrates the configuration of the tip of the water injection valve 5. The water injection valve 5 includes a cylindrical main body 51. A passage portion 52 through which water heated in the heat exchanger 31 flows is formed in the main body portion 51.

  The tip of the main body 51 is closed. A plurality of nozzles 53 are formed at the tip of the main body 51. The base end of each nozzle 53 communicates with the passage portion 52. The tip of each nozzle 53 opens into the combustion chamber 29. The arrangement of the nozzles 53 can be set as appropriate.

  A needle valve 54 is disposed in the passage portion 52 of the water injection valve 5. The needle valve 54 is configured to reciprocate along the axis of the water injection valve 5 by a drive mechanism (not shown). The drive mechanism has a solenoid or a piezo element.

  The distal end of the needle valve 54 is in contact with a seat portion 55 provided at the distal end portion of the passage portion 52. When the needle valve 54 moves toward the proximal end side of the water injection valve 5, the tip of the needle valve 54 moves away from the seat portion 55, and water in the passage portion 52 is injected into the combustion chamber 29 through each nozzle 53. Is done.

  The exhaust heat recovery device 3 improves the thermal efficiency of the engine 1 by recovering the heat of the exhaust gas of the engine 1 using water as a medium. Specifically, the exhaust heat recovery device 3 generates supercritical water by heating the water condensed in the condenser 32 to the critical temperature in the heat exchanger 31 using the heat of the exhaust gas. The water injection valve 5 injects supercritical water into the combustion chamber 29 at a timing near the compression top dead center or during the compression stroke, so that the supercritical water heats the combustion chamber 29. Without being used, it becomes superheated steam in the combustion chamber 29. Since the amount of working gas in the expansion stroke increases, the thermal efficiency of the engine 1 is improved. Further, by injecting water into the combustion chamber 29, the gas temperature in the combustion chamber 29 is lowered. This is advantageous in improving the controllability of combustion by compression ignition, and may be advantageous in reducing cooling loss and improving emission performance.

  Here, the engine 1 makes the combustion air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio at least in a low load region lower than the predetermined load. The engine 1 may be A / F lean or G / F lean in the entire operation region. Especially when the engine 1 is operated in a low load region, the fuel injection amount is relatively small and the working gas amount is large, so that the temperature of the exhaust gas becomes low. Therefore, in the heat exchanger 31, it becomes impossible to heat water to the critical temperature using the heat of the exhaust gas.

  Therefore, the exhaust heat recovery device 3 of the engine 1 uses both the reduced-pressure boiling phenomenon and the boiling heat transfer accompanying the reduced-pressure boiling phenomenon at the nozzle 53 of the water injection valve 5 when the temperature of the exhaust gas is low. Thus, saturated steam is generated.

  That is, when the high-pressure pump 34 pumps water, the water pressure in the passage 52 of the water injection valve 5 is set to 10 MPa or more and 30 MPa or less. On the other hand, the pressure in the combustion chamber 29 when water is injected into the combustion chamber 29 is about 5 MPa. Since the nozzle 53 of the water injection valve 5 is opened in the combustion chamber 29, the pressure in the nozzle 53 matches or substantially matches the pressure in the combustion chamber 29. Therefore, when the needle valve 54 moves and water flows from the passage portion 52 into the nozzle 53, a part of the water in the nozzle 53 becomes saturated steam due to the reduced-pressure boiling phenomenon.

  However, from the difference between the energy of the water sent from the heat exchanger 31 to the water injection valve 5 and the enthalpy of the saturated liquid in the pressure state in the combustion chamber 29, all the necessary amount of water is saturated only by the reduced-pressure boiling phenomenon. It cannot be made into steam. Therefore, the exhaust heat recovery device 3 supplies heat to the water flowing through the nozzle 53 through the inner peripheral surface of the nozzle 53. In this way, water is changed to saturated steam in the nozzle 53 by supplying the heat to the water through the reduced-pressure boiling phenomenon and the inner peripheral surface of the nozzle 53.

  Hereinafter, the configuration of the exhaust heat recovery apparatus 3 will be described with reference to the drawings. In the configuration example of the exhaust heat recovery apparatus 3 shown in FIG. 1, the exhaust gas thermal energy Qex includes sensible heat energy Qinj given to water in the heat exchanger 31 and latent heat energy Qlat given to water in the nozzle 53 of the water injection valve 5. And distributed to. That means

  Further, the sensible heat energy Qinj and the latent heat energy Qlat are expressed by the following equations (2) and (3), respectively.

Here, m ₁ is the amount of water injected by the water injection valve 5, h ₁ ′ is the specific enthalpy given to water (liquid) in the heat exchanger 31, X is the dryness, and r ₂ is water Is the latent heat of water at the pressure in the combustion chamber 29 at the timing of injecting. That is, by appropriately distributing the heat energy Qex of the exhaust gas to the sensible heat energy Qinj and the latent heat energy Qlat, saturated steam can be generated in the nozzle 53 when the heat energy Qex of the exhaust gas is small. it can. It can be said that the latent heat energy Qlat is a target latent heat energy for generating saturated steam in the nozzle 53.

  The temperature of water in the passage 52 of the water injection valve 5 is set to be 280 ° C. or higher and lower than 374 ° C. by the heat exchanger 31 of the exhaust heat recovery device 3. That is, since the temperature of the exhaust gas is low, water cannot reach the critical temperature (374 ° C.) by heat exchange in the heat exchanger 31.

  FIG. 3 schematically shows the phase change of water in the nozzle 53 of the water injection valve 5. As described above, the pressure of water in the passage portion 52 of the water injection valve 5 is 10 MPa or more and 30 MPa or less. Further, since the pressure in the nozzle 53 opened in the combustion chamber 29 is about 5 MPa, when the needle valve 54 of the water injection valve 5 moves and water flows from the passage portion 52 to the nozzle 53, the reduced pressure boiling effect As a result, a part of the water starts boiling (that is, nucleate boiling).

In the nozzle 53 of the water injection valve 5 that is attached to the cylinder head 22 of the engine 1, a portion of the heat of the exhaust gas, the wall heat transfer, is supplied to the water flowing through the nozzle 53 (see q _w 3 )). Further, in the nozzle 53, heat is supplied to the water by boiling heat transfer with the reduced-pressure boiling (that is, forced convection evaporation).

  Here, the thermal energy Qw supplied to the water flowing in the nozzle 53 by the wall surface heat transfer is expressed by the following equation (4).

Here, As is the total area of the inner peripheral surface of the plurality of nozzles 53, Tw is the temperature of the inner peripheral surface of the nozzle 53, Tsat is the saturation temperature at the pressure in the combustion chamber 29 at the timing of injecting water, α _TP is a heat transfer coefficient by boiling heat transfer.

  Therefore, the thermal energy Qw supplied to the water flowing in the nozzle 53 by the wall surface heat transfer becomes larger than the target latent heat energy Qlat so that all the water injected into the combustion chamber 29 becomes saturated steam in the nozzle 53. If (Qw> Qlat), the water injected from the water injection valve 5 can be supplied into the combustion chamber 29 as saturated steam having a dryness of 1. That means

So that the nozzle 53 of the water injection valve 5 may be configured.

_αTP can be calculated using various known correlation equations. For example, when Tw is 370 ° C., the pressure in the combustion chamber 29 is 5 MPa, and α _TP is, for example, 364 MW / m ² K, the number of nozzles 53 is 10, and the diameter D of the nozzles 53 is 0.1 mm or more and 1 mm or less. If the length L of the nozzle 53 is set so that L / D is 5 or more and 50 or less, the formula (6) can be satisfied. The area of the inner peripheral surface of each nozzle 53 is 0.16 mm ² or more and 160 mm ² or less.

  In such a water injection valve 5, as illustrated in FIG. 2, the length of the nozzle 53 tends to be longer than the length of the nozzle of the fuel injection valve 220. That is, the length of the nozzle of the fuel injection valve 220 is about 1 mm or less, while the nozzle 53 of the water injection valve 5 can be about 15 mm.

  Here, the mass of the tip portion where the nozzle 53 of the water injection valve 5 is formed may be set to about 0.7 to 5 g in order to have a function of storing the heat of the exhaust gas. The tip portion of the water injection valve 5 here may be a portion surrounded by a one-dot chain line in FIG. By doing so, heat can be sufficiently supplied to the water flowing in the nozzle 53.

  Thus, the exhaust heat recovery apparatus 3 having the above-described configuration can supply saturated steam into the combustion chamber 29 without using the heat in the combustion chamber 29. Therefore, by supplying water (that is, saturated steam) into the combustion chamber 29 at a timing near the compression top dead center or during the compression stroke, the amount of working gas in the expansion stroke increases. Thermal efficiency is improved. Heat recovery can be performed when the temperature of the exhaust gas is low.

  In the above configuration, the heat of the exhaust gas is supplied through the engine 1 to the tip of the water injection valve 5 attached to the cylinder head 22. Unlike this, for example, as schematically shown in FIG. 4, a heat pipe 6 may be attached to the tip of the water injection valve 5. In the heat pipe 6, a heat receiving portion (not shown) is disposed in the exhaust port 47 or the exhaust pipe 45, and a heat radiating portion 61 is attached to the distal end portion of the water injection valve 5. By doing so, the heat of the exhaust gas can be efficiently transported to the tip of the water injection valve 5 by the heat pipe 6. Since necessary heat can be supplied to the water flowing in the nozzle 53, it is advantageous in generating saturated steam in the nozzle 53.

  In addition, although illustration is abbreviate | omitted, instead of attaching the thermal radiation part 61 of the heat pipe 6 to the front-end | tip part of the water injection valve 5, you may attach an electric heater to the front-end | tip part of the water injection valve 5. FIG.

1 Engine 29 Combustion chamber 3 Waste heat recovery device 31 Heat exchanger (heating unit)
32 condenser (water recovery unit)
40 Exhaust passage 45 Exhaust pipe (exhaust passage)
47 Exhaust port (exhaust passage)
5 Water injection valve (water injection part)
52 Passage 53 Nozzle 6 Heat Pipe 61 Heat Dissipation

Claims (5)

An engine having a combustion chamber;
A water recovery part that is provided in the exhaust passage of the engine and recovers water in the exhaust gas flowing in the exhaust passage;
A heating unit for heating the water recovered by the water recovery unit;
A water injection portion that has a passage portion through which water heated in the heating portion flows, a nozzle that communicates with the passage portion and opens into the combustion chamber, and injects water into the combustion chamber through the nozzle; With
The water injection unit is attached to the engine, and the heat of the exhaust gas is supplied to the water flowing through the nozzle,
The temperature of water in the passage portion is 280 ° C. or more and less than 374 ° C., and the pressure of water in the passage portion is 10 MPa or more and 30 MPa or less,
The diameter D of the nozzle is 0.1 mm or more and 1 mm or less,
The length L of the nozzle is an exhaust heat recovery device for an engine that is set so that L / D is 5 or more and 50 or less. The engine exhaust heat recovery device according to claim 1,
The water recovery unit condenses water in the exhaust gas by cooling the exhaust gas,
The heating unit is an exhaust heat recovery device for an engine that is provided upstream of the water recovery unit in the exhaust passage and heats the water by the heat of the exhaust gas. The exhaust heat recovery device for an engine according to claim 1 or 2,
The water injection unit has a plurality of the nozzles,
The exhaust heat recovery device for an engine has an inner peripheral surface area of each nozzle of 0.16 mm ² or more and 160 mm ² or less. The exhaust heat recovery device for an engine according to any one of claims 1 to 3,
An exhaust heat recovery device for an engine in which a heat radiating portion of a heat pipe for transporting heat of exhaust gas is attached to the water injection portion. The engine exhaust heat recovery apparatus according to any one of claims 1 to 4,
The combustion air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio in at least a low load region where the load is lower than a predetermined load in the entire operation region of the engine.
The water injection unit is an exhaust heat recovery device for an engine that injects water into the combustion chamber at least in the low load region.

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