JP2018003682A - Engine with exhaust heat recovery function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an illustrative efficiency of an engine by recovering heat of exhaust.SOLUTION: An engine with exhaust heat recovery function includes: a cylinder 2; a suction passage 20 and an exhaust passage 30; a condenser 52 which condenses water vapor contained in exhaust circulating in the exhaust passage 20 and prepares condensed water; water temperature elevating devices (51, 56) which elevate temperature of the condensed water according to heat exchange with the exhaust before flowing into the condenser 52; a water injection device 57 which injects supercritical water or subcritical water generated through temperature elevation processing of the condensed water on the water temperature elevation to the cylinder 2; and a suction temperature elevating device 26 which elevates temperature of suction according to heat exchange with the exhaust circulating through the exhaust passage of the downstream side from the water temperature elevating device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an engine with an exhaust heat recovery function capable of recovering heat of exhaust and converting it into work.

  As an engine with an exhaust heat recovery function as described above, one disclosed in Patent Document 1 below is known. The engine disclosed in Patent Document 1 includes an exhaust passage through which exhaust discharged from a cylinder flows, a condenser (condenser) that condenses water vapor contained in the exhaust flowing through the exhaust passage, and condensed water generated by the condenser. A heat exchanger that raises the temperature by exchanging heat with the exhaust, and a high-temperature water injection valve that injects high-temperature water (water that is above the critical temperature and above the critical pressure) generated through a temperature raising process by the heat exchanger into the cylinder It has.

  According to the engine of Patent Document 1 configured as described above, high-temperature water generated using exhaust heat is injected into the cylinder, so that the high-temperature water expands in the cylinder and reduces the pressure in the cylinder. Raise. And it is supposed that the thermal efficiency of an engine improves by converting the energy of high temperature water into pressure (work) in this way.

Japanese Patent No. 5045569

  Here, the inventor of the present application is conducting research to significantly increase the fuel efficiency of the engine compared to the conventional one. It came to the conclusion that it is important to make an assessment based on a certain exergy. And when the evaluation based on such an exergy standard was advanced, even if the high-temperature water generated using the exhaust heat recovered as in Patent Document 1 is injected into the cylinder, the expected fuel efficiency improvement effect is obtained. It was found that there is a possibility that it cannot be obtained.

  That is, when high temperature water is injected into a cylinder, there is a loss of exergy that occurs in the process of generating high temperature water, and an exergy loss that occurs due to heat exchange between the injected high temperature water and the gas in the cylinder. It turned out that the total loss reached a non-negligible level. And, the occurrence of such a loss diminishes the positive effect of injecting high-temperature water, and as a result, the efficiency of illustration, which is the ratio of the input energy (fuel energy) taken out as external work, may not be improved. I found out.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an engine with an exhaust heat recovery function that can effectively improve the efficiency of illustration of the engine.

  An engine with an exhaust heat recovery function according to the present invention for solving the above-described problems includes a cylinder in which a mixture of fuel and air burns, an intake passage through which intake air introduced into the cylinder flows, and the cylinder The condensed water is exchanged by heat exchange between an exhaust passage through which the discharged exhaust gas flows, a condenser for condensing water vapor contained in the exhaust gas flowing through the exhaust passage to generate condensed water, and the exhaust gas before flowing into the condenser. A water temperature raising device for raising the temperature of the water, a water injection device for injecting supercritical water or subcritical water generated through the temperature raising treatment of the condensed water in the water temperature raising device into the cylinder, and the water rising temperature And an intake air temperature raising device for raising the temperature of the intake air by exchanging heat with the exhaust gas flowing through the exhaust passage on the downstream side of the temperature device (Claim 1).

  According to the present invention, the temperature of the intake air introduced into the cylinder is increased by the intake air temperature raising device, so that the temperature of the combustion is increased and the combustion exergy loss can be reduced. Here, exergy is the maximum amount of work that can be theoretically extracted from the system, and combustion exergy loss is a loss of exergy caused by an increase in entropy due to combustion of the air-fuel mixture. The combustion exergy loss is a loss accompanying combustion of the air-fuel mixture, which is an irreversible phenomenon, and is a net loss that cannot be avoided when operating the engine. Therefore, if the combustion exergy loss having such a property can be reduced, the efficiency of the engine (the ratio of the input energy taken out as external work) may be improved.

  However, simply increasing the intake air temperature reduces the combustion exergy loss, but the temperature of the exhaust exhausted from the cylinder rises. Therefore, the exhaust exergy loss, that is, the exergy of the exhaust itself (exhaust exergy) Of these, the amount discarded without being used as work increases, and on the contrary, the efficiency of illustration decreases. On the other hand, in the present invention, the condensed water taken out from the exhaust gas by the condenser is heated by a water temperature raising device provided on the upstream side of the condenser, and the supercritical water generated through such treatment or Since the subcritical water is injected from the water injection device into the cylinder, the heat recovered from the exhaust can be efficiently converted into work by expanding the injected supercritical water / subcritical water in the cylinder. As a result, the exhaust exergy loss is reduced, and in combination with the reduction in the combustion exergy loss described above, the illustrated efficiency of the engine can be effectively improved.

  Preferably, the intake air temperature raising device raises the temperature of the intake air by heat exchange with the exhaust gas flowing downstream from the water temperature raising device and upstream from the condenser.

  According to this configuration, the condenser can be made compact while sufficiently raising the temperature of the condensed water by the water temperature raising device. That is, in the water temperature raising device, the temperature of the condensed water is raised by heat exchange with the high-temperature exhaust before the heat is taken away by the intake air (before flowing into the intake air temperature raising device). Can be made sufficiently high. In addition, since the low-temperature exhaust after the heat is taken away by the intake air flows into the condenser, the cooling capacity necessary for condensing (liquefying) the water vapor contained in the exhaust is small, and securing the cooling capacity Therefore, it is possible to effectively prevent the capacitor from becoming large.

  In the above-described configuration, more preferably, the water temperature raising device includes a first heat exchanger that raises the temperature of the condensed water by heat exchange with exhaust gas flowing through an exhaust passage upstream of the condenser, and a first heat. A second heat exchanger that further raises the temperature of the condensed water by exchanging heat with the exhaust before flowing into the exchanger, and the intake air temperature raising device is provided with a temperature after the temperature rise in the first heat exchanger. The intake air is heated to a temperature lower than the temperature of the condensed water and higher than the outside air temperature.

  Thus, not only the first heat exchanger that raises the temperature of the condensed water by heat exchange with the exhaust before flowing into the condenser, but also the condensed water by heat exchange with the exhaust before flowing into the first heat exchanger. If a second heat exchanger is provided that further raises the temperature, the heat of the exhaust can be sufficiently recovered by these two heat exchangers, and the condensed water is sufficiently heated by the recovered heat to be supercritical. Water / subcritical water can be generated efficiently.

  In addition, since the temperature of the intake air after the temperature rise in the intake air temperature riser is set lower than the temperature of the condensed water after the temperature rise in the first heat exchanger, the intake air is excessively heated. Therefore, it is possible to avoid the adverse effects such as the need for heat-treating various components provided in the intake passage.

  Preferably, the water injection device injects the supercritical water or subcritical water into the cylinder at least in a high load region of the engine, and air in the air-fuel mixture in the cylinder at least during operation in the high load region. The excess ratio is set to 1 or the vicinity thereof (Claim 4).

  As described above, when the excess air ratio in the high load region where supercritical water / subcritical water is injected is set to 1 or in the vicinity thereof, the lean environment where the excess air ratio is considerably larger than 1 is set. In comparison, the combustion temperature of the air-fuel mixture in the high load region can be increased. As a result, the temperature of the exhaust gas discharged from the cylinder becomes high, so that the condensed water can be sufficiently heated using the heat of the exhaust gas, and the supercritical water / subcritical water necessary for high-load operation can be obtained. It can be generated efficiently.

  In the above-described configuration, more preferably, the engine is provided with an EGR device that performs EGR for returning a part of the exhaust gas flowing through the exhaust passage to the intake passage, and the EGR device is configured to perform the EGR in a low load region of the engine. And the EGR is stopped in the high load range of the engine or the EGR amount is decreased more than in the low load range.

  According to this configuration, the pumping loss in the low load region can be reduced, and the temperature of the exhaust can be increased in the high load region to promote the generation of supercritical water / subcritical water.

  As described above, according to the engine with the exhaust heat recovery function of the present invention, the illustrated efficiency of the engine can be effectively improved.

1 is a diagram illustrating an overall configuration of an engine with an exhaust heat recovery function according to an embodiment of the present invention. It is a top view of an engine body. It is sectional drawing of an engine main body. It is a schematic sectional drawing for demonstrating operation | movement of a heat pipe. It is a figure which shows the state change of the water accompanying the increase / decrease in enthalpy and pressure, and is a figure for demonstrating the property of supercritical water. It is a block diagram which shows the control system of an engine. It is a map figure which shows the difference in control according to the driving | running state of an engine. It is the graph which represented the combustion cycle of the engine on the TS diagram. It is a graph which shows the change of the exergy ratio according to the difference in intake air temperature. It is a graph which shows the change of the exergy ratio according to the presence or absence of water injection, and the difference in intake air temperature. FIG. 6 is a diagram corresponding to FIG. 5 for explaining subcritical water.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine with an exhaust heat recovery function according to an embodiment of the present invention. The engine shown in the figure is a four-cycle gasoline engine mounted on a vehicle as a driving power source, and includes an in-line multi-cylinder engine main body 1 including four cylinders 2 arranged in a row, and an engine main body 1. An intake passage 20 through which intake air introduced into the engine flows, an exhaust passage 30 through which exhaust gas discharged from the engine body 1 flows, and an EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust passage 30 to the intake passage 20. And a water supply system 50 for supplying water extracted from the exhaust gas flowing through the exhaust passage 30 to each cylinder 2 of the engine body 1.

  2 and 3 are a plan view and a cross-sectional view schematically showing the structure of the engine body 1. As shown in these drawings, an engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and each cylinder. 2 and a piston 5 inserted in a reciprocating manner.

  A combustion chamber C is defined above the piston 5, and fuel mainly composed of gasoline injected from a fuel injection device 11 described later is supplied to the combustion chamber C. The supplied fuel burns in the combustion chamber C, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction.

  Below the piston 5, a crankshaft 15 that is an output shaft of the engine body 1 is disposed. The crankshaft 15 is connected to the piston 5 via the connecting rod 14 and rotates around the central axis according to the reciprocating motion of the piston 5. The cylinder block 3 is provided with an engine rotation sensor SN1 that detects the rotation speed of the crankshaft 15, that is, the output rotation speed of the engine body 1.

  A cavity 10 is formed in the crown surface (upper surface) of the piston 5, with its central portion recessed on the opposite side (downward) from the cylinder head 4. The cavity 10 is formed to have a volume that occupies most of the combustion chamber C when the piston 5 rises to the top dead center.

  The cylinder head 4 is provided with a fuel injection device 11 for injecting fuel (gasoline) supplied from a fuel pump (not shown) into the combustion chamber C, one for each cylinder 2 (four in total). Each fuel injection device 11 has a tip portion exposed to the combustion chamber C in the vicinity of the central axis of the cylinder 2, and is provided so as to inject fuel from the tip portion toward the cavity 10 of the piston 5.

  The fuel injection device 11 injects fuel into the combustion chamber C before the compression top dead center (during the intake stroke or the compression stroke). The injected fuel is self-ignited near the compression top dead center after being mixed with the air (intake air) introduced into the combustion chamber C. That is, in the engine of the present embodiment, instead of the spark ignition combustion (combustion in which the air-fuel mixture is forcibly burned by spark ignition) generally employed when gasoline is used as the fuel, the air-fuel mixture is mixed with the piston. HCCI combustion (premixed compression self-ignition combustion) that is self-ignited in accordance with the compression of No. 5 is performed in all operating regions of the engine. For this reason, the engine of this embodiment is not provided with a spark plug for igniting the air-fuel mixture. However, as an alternative mode, it is conceivable to perform spark ignition combustion instead of HCCI combustion in a situation where self-ignition is difficult, such as immediately after the engine is cold started, and after the engine is warmed up. It is conceivable to perform so-called spark assist to assist HCCI combustion. Therefore, a spark plug may be provided to perform such control.

  In the cylinder head 4, for each cylinder 2, the intake port 6 for introducing the air supplied from the intake passage 20 into the combustion chamber C and the exhaust generated in the combustion chamber C are led to the exhaust passage 30. An exhaust port 7, an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber C side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber C side are provided. In this embodiment, two intake ports 6 and two exhaust ports 7 are opened to the combustion chamber C of one cylinder 2. Correspondingly, two intake valves 8 and two exhaust valves 9 are provided for each cylinder 2.

  As shown in FIGS. 1 and 2, the intake passage 20 includes an intake manifold 21 branched so as to communicate with each cylinder 2 via an intake port 6, and a single tubular common connected to the intake manifold 21 from the upstream side. And an intake pipe 22. In the present specification, the upstream (or downstream) in the intake passage 20 refers to the upstream (or downstream) in the flow direction of the intake air flowing through the intake passage 20.

  The common intake pipe 22 circulates through the common intake pipe 22, and an air temperature riser 26 that raises the intake air by heat exchange with an air cleaner 25 that removes foreign matters contained in the intake air, and exhaust gas that flows through the exhaust passage 30. An openable and closable throttle valve 27 for adjusting the flow rate of the intake air is provided in this order from the upstream side.

  Further, an air flow sensor SN <b> 2 that detects the flow rate of the intake air flowing through the common intake pipe 22 is provided on the downstream side of the throttle valve 27 in the common intake pipe 22.

  The exhaust passage 30 has an exhaust manifold 31 branched so as to communicate with each cylinder 2 via the exhaust port 7, and a single tubular common exhaust pipe 32 connected to the exhaust manifold 31 from the upstream side. In the present specification, upstream (or downstream) in the exhaust passage 30 means upstream (or downstream) in the flow direction of the exhaust gas flowing through the exhaust passage 30.

  The common exhaust pipe 32 is provided with a catalyst device 35, a first heat exchanger 51, a condenser 52, and an exhaust shutter valve 36 in this order from the upstream side.

  The catalyst device 35 is for purifying harmful components contained in the exhaust gas. For example, the catalyst device 35 has a built-in catalyst composed of any one or combination of a three-way catalyst, an oxidation catalyst, and an NOx catalyst. In addition to such a catalyst, a filter for collecting PM contained in the exhaust gas may be included.

  The exhaust shutter valve 36 is provided to be openable and closable at a position downstream of the capacitor 52 in the common exhaust pipe 32. The exhaust shutter valve 36 is normally fully opened or held at an opening close thereto. For example, the exhaust gas recirculation operation by the EGR device 40 (that is, a part of the exhaust gas flowing through the exhaust passage 30 is transferred to the intake passage 20). When it is necessary to perform an operation of refluxing (hereinafter referred to as EGR), the valve is driven to the valve closing side as necessary in order to promote the EGR. That is, when the exhaust shutter valve 36 is driven to the valve closing side and the opening thereof is reduced, the pressure of the exhaust gas in the exhaust passage 30 increases, and the difference from the pressure of the intake air in the intake passage 20 increases. Thereby, the flow of the exhaust from the exhaust passage 30 to the intake passage 20 is promoted, and a sufficient EGR amount is secured.

  The condenser 52 condenses the water vapor contained in the exhaust, and the first heat exchanger 51 raises the temperature of the condensed water generated by the condenser 52. The first heat exchanger 51 and the condenser 52 are elements that constitute a part of the water supply system 50 (details will be described later).

  In the portion 32b between the first heat exchanger 51 and the condenser 52 in the common exhaust pipe 32, an extended portion 26a extended from the portion 32b to the common intake pipe 22 side is integrally formed. The exhaust gas that has passed through the first heat exchanger 51 is introduced into the condenser 52 after at least a part of the exhaust gas has passed through the expansion portion 26a. In addition, the intake air temperature raising device 26 includes a number of branched narrow tubes whose cross-sectional areas are sufficiently smaller than the common intake pipe 22 upstream and downstream of the intake air temperature raising device 26 in the expansion portion 26a. Have. The intake air introduced into these narrow tubes is heated by heat exchange with the exhaust gas flowing through the expansion portion 26a. In this way, the intake air temperature raising device 26 is configured to raise the temperature of the intake air by heat exchange with the exhaust gas flowing between the first heat exchanger 51 and the condenser 52 (expansion portion 26a).

  Although the temperature of the intake air after passing through the intake air temperature raising device 26 as described above varies depending on the operating state of the engine, the outside air temperature, and the like, it is generally raised to 100 to 150 ° C. This temperature is set lower than the temperature of condensed water after passing through the first heat exchanger 51 (about 150 to 250 ° C. as will be described later).

  The EGR device 40 includes an EGR passage 41 that allows the common exhaust pipe 32 and the common intake pipe 22 to communicate with each other, and an EGR valve 42 and an EGR cooler 43 that are provided in the EGR passage 41.

  The EGR passage 41 connects a part of the common exhaust pipe 32 upstream of the catalyst device 35 and a part of the common intake pipe 22 downstream of the throttle valve 27. The EGR valve 42 is an open / close valve for adjusting the flow rate of exhaust gas (EGR gas) recirculated from the common exhaust pipe 32 to the common intake pipe 22 through the EGR passage 41. The EGR cooler 43 is a heat exchanger that cools the EGR gas flowing through the EGR passage 41 by heat exchange with a predetermined refrigerant (for example, engine coolant).

(2) Specific Configuration of Water Supply System As shown in FIG. 1, the water supply system 50 includes a first heat exchanger 51 and a condenser 52 described above, and a water tank 53 that stores the condensed water generated by the condenser 52. A low pressure pump 54 that pumps the condensed water stored in the water tank 53, a high pressure pump 55 that pressurizes the condensed water that is pumped from the low pressure pump 54 and passes through the first heat exchanger 51, and a high pressure pump 55. The second heat exchanger 56 that generates supercritical water by further raising the temperature of the condensed water pumped from the cylinder, and a plurality (4) of injecting supercritical water generated by the second heat exchanger 56 into each cylinder 2. Water injection device 57, first water pipe 61 connecting condenser 52 and water tank 53, second water pipe 62 connecting water tank 53 and first heat exchanger 51, and first heat exchange. The heat exchanger 51 and the second heat exchanger 56 And a third water pipe 63 for connecting the two. In addition, the combination of the 1st heat exchanger 51 and the 2nd heat exchanger 56 is equivalent to the "water temperature rising apparatus" said to a claim. Although details will be described later, supercritical water has a temperature of 647 K (374 ° C.) or higher and a pressure of 22 MPa or higher, so that it has both liquid and gaseous properties (three phases of liquid, gas, and solid). Water that is in a special state.

  The condenser 52 is a heat exchanger for condensing the water vapor contained in the exhaust gas flowing through the common exhaust pipe 32, and the water vapor contained in the exhaust gas is cooled by cooling the exhaust gas by heat exchange with a predetermined refrigerant. Condense. Specifically, the condenser 52 incorporates a long narrow tube through which engine coolant as a coolant flows, and the water vapor contained in the exhaust gas passing outside the thin tube is exchanged with the cooling water. It is configured to cool and condense (liquefy). The condensed water generated by the condenser 52 naturally flows down to the water tank 53 through the first water pipe 61 and is stored in the water tank 53.

  The low pressure pump 54 is provided in the middle of the second water pipe 62, pressurizes the condensed water stored in the water tank 53, and sends it to the first heat exchanger 51 (a thin tube 65 described later).

  The first heat exchanger 51 is a heat exchanger that raises the temperature of the condensed water generated by the condenser 52 by heat exchange with the exhaust before flowing into the condenser 52. Specifically, the first heat exchanger 51 includes a long narrow tube 65 inserted into the catalyst downstream piping portion 32a, which is a portion located immediately downstream of the catalyst device 35 in the common exhaust pipe 32, It has a heat insulation case 66 having a double-pipe structure that covers the catalyst downstream piping portion 32a, and a heat storage material 67 filled in a space portion of the heat insulation case 66 (between the outer tube and the inner tube). The narrow tube 65 is provided so that the condensed water from the condenser 52 circulates therein, and the condensed water in the narrow tube 65 is heated by heat exchange with high-temperature exhaust gas that passes outside the thin tube 65. The temperature of the condensed water after the temperature rise generally reaches 150 to 250 ° C., although it varies depending on the operating state of the engine.

  The heat retaining case 66 is formed so as to cover not only the catalyst downstream piping portion 32 a of the common exhaust pipe 32 but also the outer periphery of the catalyst device 35. In the heat storage material 67 filled in the heat retaining case 66, the heat of the exhaust gas flowing through the catalyst device 35 and the catalyst downstream pipe portion 32a and the reaction heat in the catalyst device 35 are transmitted, and the transferred heat is transmitted. Is stored in the heat storage material 67. The heat storage material 67 that stores heat and the heat retaining case 66 that accommodates the heat retain the catalyst device 35 and the thin tube 65, so that the active state of the catalyst device 35 can be easily maintained, and the condensed water flowing through the thin tube 65 can be maintained. The temperature rise effect of can be enhanced. Specific examples of the heat storage material 67 include a latent heat storage material such as erythritol that accumulates thermal energy due to melting accompanying heating, and a chemical heat storage material such as calcium chloride that accumulates thermal energy due to a chemical reaction associated with heating. Can do.

  The high-pressure pump 55 is provided in the middle of the third water pipe 63, and further pressurizes the condensed water pressurized by the low-pressure pump 54 and heated by the first heat exchanger 51, and thereby the second heat exchanger. 56. Specifically, the high-pressure pump 55 pressurizes the condensed water in the third water pipe 63 so that the pressure in the pressure accumulation rail 75 described later becomes 22 MPa or more.

  As shown in FIGS. 2 and 3, the second heat exchanger 56 includes a plurality of heat pipes 70 attached to a plurality of locations in the cylinder head 4 corresponding to the exhaust ports 7 of the cylinders 2, and the exhaust ports 7. It has a single pressure accumulation rail 75 attached so as to extend in the cylinder row direction on the side surface of the cylinder head 4 located in the vicinity of the upper side. A downstream end portion of the third water pipe 63 is connected to the pressure accumulation rail 75, and condensed water pumped from the high pressure pump 55 through the third water pipe 63 is stored in the pressure accumulation rail 75 in a pressure accumulation state. ing. A plurality of (four) branch pipes 76 extend from the pressure accumulation rail 75, and each branch pipe 76 is connected to the water injection device 57.

  The pressure accumulation rail 75 is provided with a water pressure sensor SN3 that detects the pressure of water stored therein.

  FIG. 4 is a schematic cross-sectional view for explaining the operation of the heat pipe 70. As shown in FIG. 4 and FIG. 3 above, the heat pipe 70 has a substantially cylindrical outer shape extending substantially in the vertical direction, and its lower end portion 70a is inserted into the exhaust port 7 so that the exhaust pipe 70 While being in contact with the exhaust in the port 7, the upper end portion 70 b is inserted into the pressure accumulation rail 75 so as to be in contact with water in the pressure accumulation rail 75. Hereinafter, the lower end portion 70a of the heat pipe 70 inserted into the exhaust port 7 is referred to as a heat receiving side end portion, and the upper end portion 70b of the heat pipe 70 inserted into the pressure accumulation rail 75 is referred to as a heat receiving side end portion. It is called the heat radiation side end.

  In this embodiment, two exhaust ports 7 are provided for each cylinder 2, and one (a total of eight) heat pipes 70 are attached to the total eight exhaust ports 7. These eight heat pipes 70 extend upward from the exhaust port 7 and are connected to a common pressure accumulation rail 75.

  The heat pipe 70 is made of a metal material having excellent heat conductivity and heat resistance, and a liquid working medium S is sealed in a vacuum state therein. A wick 71 for moving the working medium S by a so-called capillary phenomenon is provided on the inner wall of the heat pipe 70. The wick 71 is made of, for example, a fine metal mesh. Stack fins 72 made of a large number of metal plates arranged close to each other in the vertical direction are attached to the heat receiving side end portion 70a of the heat pipe 70. The stack fins 72 serve to increase the amount of heat transferred from the exhaust in the exhaust port 7 to the heat receiving side end 70a.

  The heat pipe 70 having the above structure functions so as to transmit the heat energy of the exhaust to the water in the pressure accumulation rail 75 only when the temperature of the exhaust is high. That is, when the temperature of the exhaust gas flowing into the exhaust port 7 from the cylinder 2 is sufficiently high, the heat receiving side end portion 70a of the heat pipe 70 is sufficiently heated by the exhaust in the exhaust port 7, and the heat receiving side end portion 70a The working medium S evaporates. The vapor | steam of the working medium S produced | generated by the said evaporation moves upward toward the thermal radiation side edge part 70b of the heat pipe 70, as shown by the arrow Y1 of FIG. The vapor | steam of the working medium S which reached | attained the thermal radiation side edge part 70b is condensed by thermally radiating to the water in the pressure accumulation rail 75, and is returned to a liquid again. Accordingly, the water in the pressure accumulation rail 75 is heated by receiving heat energy from the working medium S. The working medium S returned to the liquid moves downward toward the heat receiving side end 70a as shown by an arrow Y2 in FIG. 4 due to capillary action by the wick 71. The liquid working medium that has reached the heat receiving side end portion 70a evaporates again by receiving heat from the exhaust gas, and moves to the heat radiation side end portion 70b to raise the temperature of the water in the pressure accumulation rail 75.

  In the present embodiment, the temperature of the exhaust gas in which the above heat transfer occurs (hereinafter referred to as a reference temperature) is set to about 650 K, and the working medium S having a boiling point suitable for this is a heat pipe. 70 is enclosed. As the working medium S having such properties, for example, sodium can be used.

  As described above, the heat pipe 70 of the present embodiment transfers the heat energy of the exhaust in the pressure accumulation rail 75 when the temperature of the exhaust flowing into the exhaust port 7 from the cylinder 2 is equal to or higher than a predetermined reference temperature (about 650 K). The temperature of the water is increased by being transmitted to the water. And the heating performed intermittently (only when the exhaust temperature is high) in the second heat exchanger 56 including the heat pipe 70, the heating always performed in the first heat exchanger 51 as the previous stage, By the pressurization by the low pressure pump 54 and the high pressure pump 55, the water in the pressure accumulation rail 75 is sufficiently heated to a high pressure and maintained in a supercritical state (temperature: 647K or more and pressure: 22 MPa or more). ing.

  The supercritical water stored in the pressure accumulation rail 75 is supplied to the water injection device 57 of each cylinder 2 through the branch pipe 76. The water injection device 57 is attached to a position below the exhaust port 7 in the cylinder head 4 and injects supercritical water into the combustion chamber C of each cylinder 2 from the side on the exhaust side.

  Here, the supercritical water is injected from the water injection device 57 into the cylinder 2 by injecting the supercritical water generated using the heat of the exhaust into the cylinder 2 to perform expansion work, thereby improving the fuel consumption of the engine. This is to improve performance. This will be described in detail below.

FIG. 5 is a diagram showing changes in the state of water accompanying increases and decreases in enthalpy and pressure, with the horizontal axis representing enthalpy (kJ / kg) and the vertical axis representing pressure (MPa). In FIG. 5, a region Z2 is a liquid region, a region Z3 is a gas region, and a region Z4 is a region where liquid and gas coexist. Lines LT350, LT400,..., LT1000 indicated by solid lines are isothermal lines having the same temperature, and the number following LT represents the temperature (K). For example, LT350 is a 350K isotherm, and LT1000 is a 1000K isotherm. Lines LD0.01, LD0.1,..., LD1000 indicated by broken lines are isodensity lines having the same density, and the number following the LD represents the density (kg / m ³ ). For example, LD0.01 the density of isopycnic line of 0.01kg / ^{m 3,} LD1000 density is isopycnic line of 1000 kg / ^{m 3.}

  5 is a critical point of water, the temperature of the critical point X is 647K (more precisely 647.3K), and the pressure is 22 MPa (more precisely 22.12 MPa). Supercritical water is water contained in the region Z1 having a temperature and pressure higher than the critical point X, that is, water having a temperature of 647 K or higher and a pressure of 22 MPa or higher.

In particular, in this embodiment, as supercritical water, a region having a relatively high density in the region Z1, more specifically, a region excluding a region having a density of less than 250 kg / m ³ (a region on the right side of the line LD250) from the region Z1. Water contained in Z1a is jetted. That is, the supercritical water jetted from the water jet device 57 in this embodiment is water having a temperature of 647 K or higher, a pressure of 22 MPa or higher, and a density of 250 kg / m ³ or higher.

  By injecting such supercritical water (water contained in the region Z1a) into the cylinder 2 from the water injection device 57, a relatively large amount of water is supplied to the cylinder 2 while suppressing a temperature drop in the cylinder 2 due to the injection. The expansion work can be efficiently performed by supplying the inside.

  That is, the density of supercritical water (water included in the region Z1a) used in the present embodiment is higher than that of gaseous water (water vapor) included in the region Z3. For this reason, when supercritical water is injected as in this embodiment, a large amount of water can be supplied into the cylinder 2 more efficiently than when gaseous water is injected. A large amount of water supplied into the cylinder 2 expands rapidly in the cylinder 2 and works to push down the piston 5. Thereby, the amount of fuel to be injected from the fuel injection device 11 can be reduced while ensuring an equivalent engine output.

  Further, as indicated by an arrow W1 in FIG. 5, supercritical water requires little enthalpy (latent heat) to change into gaseous water. On the other hand, the liquid water contained in the region Z2 requires a large enthalpy (latent heat) in order to change into a gas as indicated by an arrow W2. For this reason, when supercritical water is injected as in this embodiment, it is possible to avoid a significant decrease in the temperature in the cylinder 2 due to the absorption latent heat of water, compared to the case of injecting liquid water. Heat recovered from the exhaust can be efficiently converted into work.

(3) Engine Control System FIG. 6 is a block diagram showing the engine control system. The PCM 100 shown in this figure is a microprocessor for overall control of the engine, and includes a known CPU, ROM, RAM, and the like.

  Detection signals from various sensors are input to the PCM 100. For example, the PCM 100 is electrically connected to the above-described engine rotation sensor SN1, airflow sensor SN2, and water pressure sensor SN3, and information detected by these sensors (that is, engine rotation speed, intake air flow rate, water pressure, etc.). The signals are sequentially input to the PCM 100 as electrical signals.

  Further, the vehicle is provided with an accelerator sensor SN4 that detects an opening degree of an accelerator pedal (not shown) operated by a driver driving the vehicle, and a detection signal from the accelerator sensor SN4 is also input to the PCM 100. .

  The PCM 100 controls each part of the engine while executing various determinations and calculations based on input signals from the various sensors. That is, the PCM 100 is electrically connected to the fuel injection device 11, the throttle valve 27, the exhaust shutter valve 36, the EGR valve 42, the low pressure pump 54, the high pressure pump 55, the water injection device 57, and the like, and as a result of the above calculation. Based on the above, a control signal is output to each of these devices.

  For example, the PCM 100 is based on the pressure in the pressure accumulation rail 75 (the pressure of water stored in the pressure accumulation rail 75) detected by the water pressure sensor SN3, and the pressure is equal to or higher than the necessary pressure (22 MPa) as supercritical water. The low-pressure pump 54 and the high-pressure pump 55 are driven so as to be held at

  Further, the PCM 100 performs fuel injection based on the engine load specified from the detected values (intake flow rate and accelerator opening) of the air flow sensor SN2 and the accelerator sensor SN4 and the engine rotation speed detected by the engine rotation sensor SN1. The fuel amount of the injection from the device 11 and the target value of the injection timing are set, and the injection amount of the supercritical water and the target value of the injection timing from the water injection device 57 are set, and the injection amounts that match the respective target values And the fuel injection device 11 and the water injection device 57 are controlled so that the injection timing is obtained. Further, a target value of the EGR rate that is the ratio of EGR gas to the total gas amount introduced into the cylinder 2 is set based on the engine load or the like, and the EGR valve 42 is obtained so that an EGR rate that matches the target value is obtained. And the exhaust shutter valve 36 is controlled. More specifically, the PCM 100 controls the fuel injection device 11, the water injection device 57, the EGR valve 42, and the exhaust shutter valve 36 as follows.

(4) Control According to Operating State FIG. 7 is a map for explaining the difference in control according to the operating state (load / rotational speed) of the engine. As described above, in the present embodiment, HCCI combustion is performed in all operating regions of the engine, in which an air-fuel mixture of fuel and air is self-ignited with compression by the piston. However, the types of HCCI combustion in the present embodiment are roughly classified into HCCI combustion accompanied by supercritical water injection from the water injector 57 and HCCI combustion not accompanied by supercritical water injection from the water injector 57. The That is, as shown in FIG. 7, when the engine operating region is divided into a first operating region A1 and a second operating region A2 having a lower load, water injection is performed in the first operating region A1 on the high load side. HCCI combustion is executed while supercritical water is injected from the device 57, and HCCI combustion is executed in a state where injection of supercritical water is stopped in the second operating region A2 on the low load side. Hereinafter, the control in each operation area | region A1, A2 is demonstrated.

(A) Control in the first operation region In the first operation region A1, which is the execution region of HCCI combustion with water injection, the water injection device 57 is controlled so that the injection amount of supercritical water increases toward the higher load side. The In addition, the supercritical water injection timing is such that the ratio of the center of gravity of water injection (the amount of water injection is half of the required injection amount) so that the ratio of the injected supercritical water to expand and convert to work is as much as possible. Is set to a timing such that the crank angle is within a predetermined crank angle range near the compression top dead center.

  The amount of fuel injected from the fuel injection device 11 is controlled to increase as the load increases. In addition, the fuel injection timing is an appropriate timing considering the expected ignition delay time so that the fuel self-ignites at an appropriate timing (in the vicinity of compression top dead center) in the environment where supercritical water is injected. Set to

  The throttle valve 27 is not particularly controlled to be opened and closed, and as a rule is maintained at an opening corresponding to full opening.

  The opening degrees of the EGR valve 42 and the exhaust shutter valve 36 are controlled so that the excess air ratio λ is 1 or in the vicinity thereof with the throttle valve 27 being fully opened. That is, when the throttle valve 27 is fully opened, the gas introduced into the cylinder 2 is occupied by air (fresh air) and EGR gas equivalent to λ≈1, in other words, the total gas amount when the throttle is fully opened. The opening degrees of the EGR valve 42 and the exhaust shutter valve 36 are controlled so that an EGR gas amount obtained by subtracting an air amount corresponding to λ≈1 is secured. The excess air ratio λ is a value obtained by dividing the actual air amount introduced into the cylinder 2 by the air amount necessary to realize the theoretical air-fuel ratio (air amount / fuel amount = 14.7). It is.

  Here, since the fuel injection amount increases as the engine load increases, the air amount corresponding to λ≈1 also increases as the load increases. For this reason, the EGR rate, which is the ratio of the EGR gas to the total gas amount in the cylinder 2, needs to be reduced as the load becomes higher. In particular, the EGR rate (EGR amount) is set to zero in the portion with the highest load in the first operating region A1 (the entire load line of the engine and its vicinity) in order to secure a large amount of air commensurate with the load. (That is, EGR itself is stopped). The opening degrees of the EGR valve 42 and the exhaust shutter valve 36 are controlled so that an EGR rate (EGR amount) that changes with such a tendency is realized.

(B) Control in the second operation region In the second operation region A2, which is an execution region of HCCI combustion not accompanied by water injection, the water injection device 57 is maintained in a closed state, and supercritical water injection is stopped. The The fuel injection amount from the fuel injection device 11 is controlled so as to increase toward the higher load side, but the injection amount is generally smaller than that in the first operation region A1. The throttle valve 27 is maintained at an opening corresponding to full opening, and the EGR valve 42 and the exhaust shutter valve 36 are controlled so that an air amount corresponding to λ≈1 is secured in this state. Since the fuel injection amount is smaller in the second operation region A2 than in the first operation region A1, an air amount corresponding to λ≈1 (that is, an air amount smaller than that in the second operation region A2) is applied to the cylinder 2. In order to introduce, the EGR rate (EGR amount) in the second operation region A2 is set to a value higher than that in the first operation region A1.

(5) Operational Effects As described above, the engine of the present embodiment condenses water vapor contained in the exhaust gas flowing through the exhaust passage 30 to generate condensed water, and the exhaust before flowing into the capacitor 52. The first and second heat exchangers 51 and 56 (water temperature raising devices) for raising the temperature of the condensed water by heat exchange with each other, and the supercriticality generated through the temperature raising process in each of the heat exchangers 51 and 56 An intake air temperature raising device 26 for raising the temperature of the intake air by heat exchange between the water injection device 57 for injecting water into the cylinder 2 and the exhaust gas flowing downstream from the first heat exchanger 51 and upstream from the condenser 52. And. According to such a configuration, both combustion exergy loss and exhaust exergy loss can be reduced, and there is an advantage that the efficiency of engine illustration can be effectively improved.

  That is, in the above-described embodiment, the temperature of the intake air introduced into the cylinder 2 is increased by the intake air temperature raising device 26, so that the combustion becomes high temperature and the combustion exergy loss can be reduced. Here, exergy is the maximum amount of work that can be theoretically extracted from the system, and combustion exergy loss is a loss of exergy caused by an increase in entropy due to combustion of the air-fuel mixture. The combustion exergy loss is a loss accompanying combustion of the air-fuel mixture, which is an irreversible phenomenon, and is a net loss that cannot be avoided when operating the engine. Therefore, if the combustion exergy loss having such a property can be reduced, there is a possibility that the illustrated efficiency of the engine, that is, the ratio of the input energy (fuel energy) extracted as external work may be improved.

  However, simply increasing the intake air temperature reduces the combustion exergy loss, but the temperature of the exhaust discharged from the cylinder 2 rises. Therefore, the exhaust exergy loss, that is, the exergy of the exhaust itself (exhaust exergy) ) Increases the amount discarded without being used as work, and on the contrary, the efficiency of illustration decreases. On the other hand, in the above embodiment, the condensed water taken out from the exhaust by the condenser 52 is heated by the first and second heat exchangers 51 and 56 provided on the upstream side of the condenser 52, Since the supercritical water generated through the treatment is injected into the cylinder 2 from the water injection device 57, the recovered supercritical water is expanded in the cylinder 2 to efficiently convert the heat recovered from the exhaust into work. can do. Thereby, since the exhaust exergy loss is reduced, the illustrated efficiency of the engine can be effectively improved in combination with the reduction of the combustion exergy loss described above.

  The above effect will be described in more detail with reference to FIGS.

  FIG. 8 is a TS diagram in which the horizontal axis is entropy (J / K) and the vertical axis is temperature (K), and represents the combustion cycle of an engine operated at ambient temperature T0 (298 K). Yes. In this case, point P1 at the start of the compression stroke, point P2 at the end of the compression stroke (at the start of combustion), point P3 at the end of combustion (at the start of the expansion stroke), and at the end of the expansion stroke The area surrounded by the point P4 corresponds to the work amount taken out to the outside, that is, the cycle work. Further, the area of the region between the line Q connecting the points P1 and P4 and the line R, which is an isotherm with a constant environmental temperature T0, corresponds to exhaust exergy, and the area of the region below the line R burns. Equivalent to exergy loss.

  When the amount of increase in entropy accompanying the combustion of the air-fuel mixture is the generated entropy ΔS, the combustion exergy loss is calculated by T0 × ΔS, which is the product of the generated entropy ΔS and the environmental temperature T0. Since heat below the ambient temperature T0 cannot be taken out as work, this combustion exergy loss is a net loss that cannot be converted into work.

  Here, it is known that increasing the intake air temperature, that is, the pre-combustion temperature, reduces the generation entropy as a result of suppressing thermal diffusion associated with combustion. Therefore, if the ambient temperature T0 is the same, the generation entropy ΔS is reduced by increasing the intake air temperature, and accordingly, the combustion exergy loss (T0 × ΔS) is also reduced. From this, it can be said that increasing the intake air temperature (temperature before combustion) is effective in reducing the combustion exergy loss, which is a net loss.

  However, when the intake air temperature rises, each point P1 to P4 of the combustion cycle moves to the high temperature side as a whole. As a result, the exhaust exergy, which is the region between the line Q and the line R, increases on the contrary regardless of the decrease in the generation entropy ΔS. That is, even if the generation entropy ΔS decreases as the intake air temperature increases, the increase in exhaust exergy due to the movement of each point of the cycle to the high temperature side exceeds the decrease in exhaust exergy due to that. As a result, exhaust exergy increases.

  FIG. 9 is a graph showing how the ratio of combustion exergy loss, exhaust exergy, and cycle work changes in relation to the intake air temperature. As shown in this graph, the higher the intake air temperature, the lower the combustion exergy loss rate, but the exhaust exergy rate increases. As a result, the cycle work rate (shown efficiency) decreases. However, as described above, the exhaust exergy is not a net loss but an exergy that can be converted into work. Therefore, the limit efficiency is defined as the sum of the ratio of exhaust exergy and the ratio of cycle work. This marginal efficiency increases as the intake air temperature increases. A large marginal efficiency means that if the exhaust exergy is successfully converted into work and extracted as cycle work, the ratio of cycle work, that is, the efficiency of illustration can be improved.

  Therefore, supercritical water was injected into the cylinder to convert the exhaust exergy into work, and the exergy ratio in that case was calculated to obtain the result shown in FIG. In FIG. 10, the graph G3 on the right side shows the exergy ratio when supercritical water is injected and the intake air temperature is increased, and the center graph G2 increases the intake air temperature without injecting supercritical water. The graph G1 on the left side shows the exergy ratio when the supercritical water is not injected and the intake air temperature is not increased. More specifically, the parameter W / F shown on the horizontal axis of each graph is a value (water injection ratio) obtained by dividing the injection amount of supercritical water by the injection amount of fuel. This means that the injection amount of critical water is large. The parameter Tin is the intake air temperature (K). The graph G3 on the right (with water injection and intake air temperature rise) sets the water injection ratio W / F to 3 (that is, sets the injection amount of supercritical water to 3 times the fuel injection amount) and sets the intake air temperature Tin. The exergy ratio in the case of 410K (137 ° C.) that is 112K higher than the environmental temperature is shown. The central graph G2 (without water injection and with intake air temperature rise) shows the exergy ratio when the water injection ratio W / F is 0 and the intake air temperature Tin is 410K. The graph G1 on the left (no water injection, no intake air temperature rise) shows the exergy ratio when the water injection ratio W / F is 0 and the intake air temperature Tin is 298K (25 ° C.) which is the same as the environmental temperature.

  As understood from the comparison between the graphs G1 and G2, when only the intake air temperature rise is performed and water injection is not performed (G2), the normal case where neither the intake air temperature rise nor water injection is performed (G1). In comparison, although the combustion exergy loss is reduced, the exhaust exergy loss (the amount of exhaust sexual energy that is discarded without being used for work) is slightly increased. Furthermore, as a new loss, a loss due to a rise in intake air temperature, that is, a loss due to a decrease in exergy due to heat exchange between the intake air and the exhaust occurs. As a result, the cycle work (shown efficiency) of the engine is slightly reduced as compared with the case where the intake air is not heated.

  On the other hand, as understood from the comparison between the graphs G1 and G3, when the temperature of the intake air is raised and supercritical water is injected (G3), neither the intake air temperature rise nor the water injection is performed. Compared to the normal case (G1), the combustion exergy loss is reduced (as much as G2), and the exhaust exergy loss is greatly reduced. On the other hand, as new losses, there are losses associated with water injection, losses associated with water temperature rise, and losses associated with intake air temperature rise, but the amount of reduction in exhaust exergy loss is sufficiently large. Even if a large loss is subtracted, the cycle work (illustration efficiency) of the engine increases. The loss due to water injection is the loss due to the decrease in exergy due to heat exchange between the water after injection and the in-cylinder gas, and the loss due to water temperature rise is due to the heat exchange between water and exhaust. This is a loss due to a decrease in exergy.

  As understood from the above, according to the above embodiment, combustion Excel is combined by combining the temperature rise of the intake air by heat exchange with the exhaust and the injection of supercritical water generated using the exhaust heat. Ghee loss and exhaust exergy loss can be reduced, and the efficiency of illustration can be improved.

  Further, in the above embodiment, in the intake air temperature raising device 26, the intake air is heated by heat exchange with the exhaust gas flowing downstream from the first heat exchanger 51 and upstream from the condenser 52. The condenser 52 can be made compact while the temperature of the condensed water is sufficiently raised by the one heat exchanger 51. That is, in the first heat exchanger 51, the temperature of the condensed water is raised by heat exchange with the high-temperature exhaust before being deprived of heat by the intake air (before flowing into the intake air temperature raising device 26). The temperature of the condensed water can be made sufficiently high. Further, since the low-temperature exhaust gas after the heat is taken away by the intake air flows into the condenser 52, the cooling capacity necessary for condensing (liquefying) the water vapor contained in the exhaust gas is reduced, and the cooling capacity is ensured. Therefore, it is possible to effectively prevent the capacitor 52 from becoming large.

  Moreover, in the said embodiment, not only the 1st heat exchanger 51 which heats up condensed water by heat exchange with the exhaust_gas | exhaustion before flowing in into the capacitor | condenser 52, but also the exhaust (exhaust gas) before flowing into the 1st heat exchanger 51. Since the second heat exchanger 56 that further raises the temperature of the condensed water by heat exchange with the exhaust in the port 7 is provided, the heat of the exhaust can be sufficiently recovered by these two heat exchangers 51 and 56. The condensed water can be sufficiently heated by the recovered heat, and supercritical water can be efficiently generated.

  In particular, in the above embodiment, since the heat pipe 70 inserted into the exhaust port 7 is used for the second heat exchanger 56, the heat of the high-temperature exhaust immediately after being discharged from the cylinder 2 is made efficient by the heat pipe 70. It absorbs well and can raise the temperature of condensed water sufficiently. Further, when the temperature of the exhaust gas discharged from the cylinder 2 is not so high (for example, less than 650 K in the above embodiment), for example, when the engine is under low load operation, the heat pipe 70 absorbs heat from the exhaust gas. Therefore, the temperature of the exhaust gas flowing into the catalyst device 35 provided on the downstream side of the heat pipe 70 and on the upstream side of the first heat exchanger 51 can be prevented from extremely decreasing, and the catalyst The temperature of the device 35 can be maintained within an appropriate range (temperature range necessary for maintaining the active state).

  Moreover, in the said embodiment, the temperature (about 150-250 degreeC) of the condensed water after the temperature rise in the 1st heat exchanger 51 and the temperature (100-150) of the intake air after the temperature rise in the intake air temperature raising device 26 are obtained. The former is set higher than the latter, the adverse effects of excessively high temperatures of the intake air, for example, measures to increase the heat resistance of various components provided in the intake passage 20 It is possible to avoid adverse effects such as necessity.

  Further, in the above embodiment, supercritical water is injected into the cylinder 2 in the first operating region A1 on the high load side, and the excess air ratio λ in the first operating region A1 is set to 1 or in the vicinity thereof. Therefore, the combustion temperature of the air-fuel mixture can be made higher than in a lean environment where λ is considerably larger than 1. As a result, the temperature of the exhaust gas discharged from the cylinder 2 becomes high, so that the condensed water can be sufficiently heated using the heat of the exhaust gas, and the supercriticality required during operation in the first operation region A1. Water can be generated efficiently.

  In the above embodiment, the EGR device 40 performs EGR (an operation for returning a part of the exhaust gas to the intake passage 20) in the second operation region A2 on the low load side, while the first operation region A1 on the high load side. Then, the EGR is stopped or the EGR amount is reduced as compared with the second operation region A2, so that the pumping loss in the low load region (second operation region A2) can be reduced and the high load region (first operation region). In A1), the temperature of the exhaust can be increased to promote the production of supercritical water.

(6) Modification In the above embodiment, the water injected from the water injection device 57 into the cylinder 2 has a relatively high density having a temperature of 647 K or higher, a pressure of 22 MPa or higher, and a density of 250 kg / m ³ or higher. Although supercritical water (water contained in the region Z1a in FIG. 5) is used, instead of this, subcritical water having properties close to supercritical water may be used. For example, water contained in the region Z10 shown in FIG. 11, that is, water having a temperature of 600 K or more and less than 647 K and a density of 250 kg / m ³ or more can be used as the subcritical water. This subcritical water property is also similar to supercritical water in the sense that it has a higher density than water vapor and very little latent heat. Even when such subcritical water is injected into a cylinder, exhaust exergy loss can be sufficiently reduced to improve the efficiency of engine illustration.

  Moreover, in the said embodiment, although the capacitor | condenser 52 and the intake air temperature raising apparatus 26 were provided separately, you may incorporate these capacitors and an intake air temperature raising apparatus in the substantially same heat exchanger. According to this, the exhaust can be cooled by the intake air having substantially the same temperature as the outside air temperature, and the intake air can be heated using the heat released when the water vapor in the exhaust is condensed.

  Further, in the above embodiment, the excess air ratio λ is set to 1 or in the vicinity thereof in the entire operation region of the engine by increasing or decreasing the EGR amount according to the load while maintaining the opening degree of the throttle valve 27 to be fully open. However, for example, in the second operation region A2 having a relatively low load, the ratio of air (fresh air) to the total gas amount introduced into the cylinder 2 is sufficiently increased (in other words, the EGR amount is reduced). The engine may be operated under a lean air-fuel ratio where the excess air ratio λ is greater than 1.

  Moreover, although the said embodiment demonstrated the example which applied this invention to the gasoline engine by which the HCCI combustion which compresses and self-ignites the mixture of gasoline and air is performed in all the operation areas, this invention is applied. Possible engines are not limited to such engines. For example, the present invention is also applied to a gasoline engine in which HCCI combustion is executed in a part of the operation region and spark ignition combustion is executed in the remaining operation region, or a gasoline engine in which spark ignition combustion is executed in the whole operation region. Further, the present invention can also be applied to a diesel engine that self-ignites by injecting light oil into a cylinder heated to high temperature by compression.

2 cylinder 20 intake passage 26 intake temperature raising device 30 exhaust passage 40 EGR device 51 first heat exchanger (water temperature raising device)
52 condenser 56 2nd heat exchanger (water temperature rising device)
57 Water injection device

Claims (5)

A cylinder in which a mixture of fuel and air burns,
An intake passage through which intake air introduced into the cylinder flows;
An exhaust passage through which the exhaust discharged from the cylinder flows;
A condenser for condensing water vapor contained in the exhaust gas flowing through the exhaust passage to generate condensed water;
A water temperature raising device for raising the temperature of the condensed water by heat exchange with the exhaust before flowing into the condenser;
A water injection device for injecting supercritical water or subcritical water generated through the temperature raising process of the condensed water in the water temperature raising device into the cylinder;
An engine with an exhaust heat recovery function, comprising: an intake air temperature raising device that raises the temperature of the intake air by exchanging heat with exhaust gas flowing through an exhaust passage downstream of the water temperature raising device. The engine with exhaust heat recovery function according to claim 1,
The intake air temperature raising device raises the temperature of the intake air by exchanging heat with exhaust flowing downstream from the water temperature raising device and upstream from the condenser. engine. The engine with exhaust heat recovery function according to claim 2,
The water temperature raising device includes a first heat exchanger that raises the temperature of the condensed water by heat exchange with the exhaust gas that flows through an exhaust passage upstream of the condenser, and an exhaust gas before flowing into the first heat exchanger. A second heat exchanger that further raises the temperature of the condensed water by heat exchange with
The exhaust air temperature raising device raises the temperature of the intake air to a temperature lower than the temperature of the condensed water after the temperature rise in the first heat exchanger and higher than the outside air temperature. With engine. The engine with an exhaust heat recovery function according to any one of claims 1 to 3,
The water injection device injects the supercritical water or subcritical water into the cylinder at least in a high load region of the engine,
An engine with an exhaust heat recovery function, wherein the excess air ratio of the air-fuel mixture in the cylinder is set to 1 or in the vicinity thereof at least during operation in the high load region. The engine with exhaust heat recovery function according to claim 4,
An EGR device for performing EGR for returning a part of the exhaust gas flowing through the exhaust passage to the intake passage;
The EGR device performs the EGR in a low load region of the engine, and stops the EGR in the high load region of the engine or reduces the EGR amount more than the low load region. Engine with recovery function.

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