JP2017089554A - Control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an engine capable of surely suppressing cooling loss while realizing proper combustion.SOLUTION: A water injection device 22 for injecting supercritical water or subcritical water, is disposed in a combustion chamber 6. The water injection device 22 implements latter-stage water injection W2 for injecting the supercritical water or the subcritical water into the combustion chamber 6 before starting combustion of a mixture gas of fuel and air in a combustion chamber 6, in a latter stage of a compression stroke, and a front-stage water injection W1 for injecting the supercritical water or the subcritical water into the combustion chamber 6 before the latter stage of the compression stroke, in a water injection region A2 determined on at least a part of an operation region of an engine.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a control device for an engine in which a piston is fitted in a cylinder so as to be able to reciprocate, and a combustion chamber whose bottom surface is a crown surface of the piston is partitioned into the cylinder.

  2. Description of the Related Art Conventionally, in an engine, in order to improve fuel efficiency, it is required to suppress a loss, that is, a cooling loss caused by the release of thermal energy of combustion gas from the wall surface of the combustion chamber to the outside of the engine.

  On the other hand, for example, in Patent Document 1, fuel is accumulated in the central portion of the combustion chamber to form an air layer in the outer peripheral portion of the combustion chamber, and the heat energy of the combustion gas is released to the outside by this air layer. An engine that suppresses this is disclosed.

Japanese Patent Laying-Open No. 2015-102004

  According to the engine of Patent Document 1, it is possible to improve the fuel consumption performance while suppressing the cooling loss to be small. However, in this engine, since the fuel is concentrated in the central portion of the combustion chamber, a locally rich mixture (a mixture having a high fuel ratio) is likely to be generated in the combustion chamber. Therefore, proper combustion is not performed in the combustion chamber, and smoke or the like may be deteriorated.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an engine control device that can more reliably suppress a cooling loss while realizing proper combustion.

  In order to solve the above problems, the present invention provides an engine control apparatus in which a piston is fitted in a cylinder so as to be capable of reciprocating, and a combustion chamber whose bottom surface is a crown surface of the piston is partitioned into the cylinder. A fuel supply device that supplies fuel into the combustion chamber, a water injection device that injects supercritical water or subcritical water into the combustion chamber, and controls each part of the engine including the fuel supply device and the water injection device. Control means, and in the water injection region set in at least a part of the engine operation region, the control unit is configured to start the combustion of the fuel-air mixture in the combustion chamber before starting combustion. A latter-stage water injection that injects the supercritical water or the subcritical water into the combustion chamber at a later stage, and a front-stage water jet that injects the supercritical water or the subcritical water into the combustion chamber before the later stage of the compression stroke. Preparative, to provide a control apparatus for an engine, characterized in that to carried to the water injection system (claim 1).

  According to the present invention, since water is injected into the combustion chamber separately in the latter half of the compression stroke and before this, a heat shield layer can be reliably formed by the entire wall surface of the combustion chamber. Therefore, it is possible to more reliably suppress the cooling loss by this heat shield layer while realizing proper combustion by burning the air-fuel mixture in a homogeneous state.

  Specifically, at a timing before the latter stage of the compression stroke, the pressure in the combustion chamber is relatively low, and thus the penetration (penetration force) of the water injected into the combustion chamber is relatively high. Therefore, in the front stage water injection, water can reach a portion relatively far from the water injection device on the wall surface of the combustion chamber. On the other hand, in the latter half of the compression stroke, the pressure in the combustion chamber is relatively high, so the penetration of water injected into the combustion chamber is relatively low. Therefore, in the latter-stage water injection, water can be retained in the portion of the wall surface of the combustion chamber close to the water injection device. Accordingly, it is possible to form a heat shield layer of water on the entire wall surface of the combustion chamber.

  In particular, in the present invention, supercritical water or subcritical water having a density higher than that of normal gaseous water is used as the water. Therefore, it is possible to increase the density of water in the heat shielding layer to obtain a high heat insulating effect, to more reliably reduce the cooling loss, and to improve the fuel efficiency.

  In the present invention, the latter stage of the compression stroke is the latter stage when the compression stroke is divided into three (initial stage, middle stage, and late stage), and the compression top dead center from 60 ° CA (crank angle) before the compression top dead center. The period until.

  In the present invention, the water injection device includes an intake valve that opens and closes an intake port for introducing intake air into the cylinder, and the control unit is configured to perform the water injection device before the latter stage of the compression stroke and after the intake valve is closed. It is preferable to perform the pre-stage water injection.

  In this way, the airflow generated in the combustion chamber as the intake air flows from the intake port can be suppressed to have a small effect on the water related to the upstream water injection, and is injected into the cylinder by the upstream water injection. Water can reach a relatively far part of the wall surface of the combustion chamber more reliably.

  In the present invention, examples of the water injection device include those attached to the center of the ceiling surface of the combustion chamber so as to face the center of the crown surface of the piston (Claim 3).

  In this case, supercritical water or subcritical water is made to reach the crown surface of the piston, that is, the entire bottom surface of the combustion chamber by the front water injection, and supercritical water or subcritical water is made to stay on the ceiling surface of the combustion chamber by the rear water injection. In this way, a thermal barrier layer of supercritical water or subcritical water can be formed on the entire wall surface of the combustion chamber.

  Further, as a configuration different from the above, as the water injection device, the inner peripheral surface on the other side in the radial direction of the cylinder is disposed at a position shifted from the center of the ceiling surface of the combustion chamber to one side in the radial direction of the cylinder. What is attached with the posture which faces is mentioned (Claim 4).

  In this case, supercritical water or subcritical water is made to reach the portion of the wall surface of the combustion chamber that is located on the opposite side of the water injection device in the radial direction of the cylinder by the front water injection, and the wall surface of the combustion chamber is injected by the rear water injection. Among them, supercritical water or subcritical water can be retained in the water injection device side in the radial direction, thereby forming a thermal barrier layer of supercritical water or subcritical water on the entire wall of the combustion chamber. it can.

  In the present invention, it is preferable that the water injection region is a region where the engine load is equal to or higher than a preset reference load.

  In this way, it is possible to effectively reduce the cooling loss that tends to increase with a high engine load and a high combustion temperature.

  In the present invention, the geometric compression ratio of the engine body is set to 18 or more and 35 or less, and the effective compression ratio of the engine body in the water injection region is set to 15 or more. Preferred (claim 6).

  If it does in this way, an effective compression ratio can be made high and an engine torque can be raised, suppressing the cooling loss which tends to increase with a high effective compression ratio small.

  As described above, according to the engine control apparatus of the present invention, it is possible to more reliably suppress the cooling loss while realizing proper combustion.

It is a figure showing composition of an engine system concerning one embodiment of the present invention. It is a schematic sectional drawing of an engine main body. It is the figure which showed the piston crown surface. It is a state diagram of water for explaining supercritical water. It is a phase diagram of water for explaining subcritical water. It is a schematic sectional drawing for demonstrating operation | movement of a heat pipe. It is a block diagram which shows the control system of an engine. It is the figure which showed the control area | region of the engine. It is the figure which showed the cylinder pressure in the high load area | region, the lift curve of the intake valve, and the water injection rate. It is a schematic sectional drawing of the engine main part which showed the mode of the front | former stage water injection which concerns on 1st Embodiment. It is a schematic sectional drawing of the engine main part which showed the mode of the back | latter stage water injection which concerns on 1st Embodiment. It is a schematic longitudinal cross-sectional view of the engine main body which showed the mode of the front | former stage water injection which concerns on 2nd Embodiment. It is a schematic longitudinal cross-sectional view of the engine main body which showed the mode of the back | latter stage water injection which concerns on 2nd Embodiment. It is a schematic cross-sectional view of the engine body showing the state of the pre-stage water injection according to the second embodiment. It is a schematic cross-sectional view of an engine body showing a state of rear-stage water injection according to the second embodiment. It is the schematic which showed the piston crown surface which concerns on other embodiment.

  FIG. 1 is a diagram showing a configuration of an engine system according to an embodiment of the present invention. The engine system of the present embodiment includes a four-stroke engine main body 1, an intake passage 30 for introducing combustion air into the engine main body 1, and an exhaust passage 40 for discharging exhaust generated by the engine main body 1. And a water circulation device 60.

  The engine body 1 is a four-cylinder engine having four cylinders 2, for example. In the present embodiment, the engine main body 1 is driven by receiving supply of fuel including gasoline. The engine system of this embodiment is mounted on a vehicle, and the engine body 1 is used as a drive source for the vehicle.

(1) Engine Body FIG. 2 is a schematic sectional view of the engine body 1.

  The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston 5 fitted to the cylinder 2 so as to be able to reciprocate (up and down). have.

  A combustion chamber 6 is formed above the piston 5. The combustion chamber 6 is a so-called pent roof type, and the ceiling surface 4a of the combustion chamber 6 constituted by the lower surface of the cylinder head 4 has a triangular roof shape composed of two inclined surfaces on the intake side and the exhaust side.

  FIG. 3 is a cross-sectional view showing the inside of the cylinder 2 and showing the crown surface 5 a of the piston 5. A cavity 10 is formed in the crown surface 5a of the piston 5 by denting a region including the center thereof 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 6 when the piston 5 rises to the top dead center.

  In this embodiment, the geometric compression ratio of the engine body 1, that is, the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center and the volume of the combustion chamber 6 when the piston 5 is at the top dead center. The ratio is set to 18 or more and 35 or less (for example, about 20).

  The cylinder head 4 has an intake port 16 for introducing air supplied from the intake passage 30 into the cylinder 2 (combustion chamber 6), and exhaust for generating exhaust gas generated in the cylinder 2 to the exhaust passage 40. An exhaust port 17 is formed. Two intake ports 16 and two exhaust ports 17 are formed for each cylinder 2. The cylinder head 4 is provided with an intake valve 18 that opens and closes an opening on the cylinder 2 side of each intake port 16 and an exhaust valve 19 that opens and closes an opening on the cylinder 2 side of each exhaust port 17. .

  A heat pipe 70 is attached to each exhaust port 17. In the present embodiment, one heat pipe 70 is attached to each exhaust port 17, and two heat pipes 70 are arranged in one cylinder 2. The heat pipe 70 is a component that constitutes a part of the water circulation device 60. Details of the heat pipe 70 will be described later.

  The cylinder head 4 is provided with a fuel injection device (fuel supply device) 21 for injecting fuel into the combustion chamber 6. In this embodiment, the fuel injection device 21 is attached to the cylinder head 4 so as to inject fuel into the combustion chamber 6 by a side injection method, and the tip of the fuel injection device 21 extends from the inner peripheral surface of the combustion chamber 6 to the inside of the combustion chamber 6. It is arranged to face.

  The fuel injection device 21 injects fuel pumped by a fuel pump (not shown) into the cylinder 2. In the present embodiment, premixed compression autoignition combustion is performed in which an air-fuel mixture of fuel and air is mixed in advance in the entire operation region, and the air-fuel mixture is self-ignited near the compression top dead center (TDC). Has been. Accordingly, in the example shown in FIG. 2, the engine main body 1 is not provided with a spark plug for igniting the gas in the cylinder 2, but for the proper combustion of the air-fuel mixture at the cold start or the like. When ignition is necessary, an ignition plug may be provided in the engine body 1 as appropriate.

  The cylinder head 4 is further provided with a water injection device 22 that injects supercritical water or subcritical water into the cylinder 2.

  As shown in FIG. 2, in the present embodiment, the water injection device 22 is attached in such a posture that the tip thereof is located at the center of the ceiling surface of the combustion chamber 6 and faces almost the center of the crown surface 5 a of the piston 5. Yes. As the water injection device 22, for example, a device for injecting fuel into the cylinder 2 used in a conventional engine can be applied, and a detailed description of the structure is omitted. The water injection device 22 injects supercritical water into the cylinder 2 at, for example, about 20 MPa.

  Supercritical water is water having a temperature and pressure higher than the critical point of water, and has a high density close to that of a liquid while molecules move vigorously like a gas. That is, supercritical water is water that does not require latent heat to change phase into gaseous or liquid water. Although details will be described later, in this embodiment, water having such properties is injected into the cylinder 2 to form a heat shield layer on the wall surface of the combustion chamber 6 formed in the cylinder 2.

  This will be specifically described with reference to FIG. FIG. 4 shows a state diagram of water when the horizontal axis is enthalpy and the vertical axis is pressure. In FIG. 4, 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 connecting points having the same temperature, and the numbers indicate the temperature (K). For example, LT 350 is an isothermal line of 350K, and LT1000 is an isothermal line of 1000K. The point C1 is a critical point, the region Z1 is a region having a higher temperature and pressure than the critical point C1, and the supercritical water is water contained in the region Z1. Specifically, while the critical point of water is a point of temperature: 647.3K and pressure: 22.12 MPa, supercritical water has a temperature and pressure higher than these, that is, a temperature of 647.3K and higher. The water is 22.12 MPa or more.

In FIG. 4, lines LR0.01, LR0.1..., LR500 indicated by broken lines are equal density lines connecting points having the same density, and the numbers indicate the density (kg / m ³ ). Show. For example, LR0.01 the density of isopycnic line of 0.01kg / ^{m 3,} LR1000 density is isopycnic line of 500 kg / ^{m 3.}

As is clear from a comparison between the isodensity line LR and the regions Z1 and Z3, the density of the water contained in the region Z1, that is, supercritical water, is about 50 kg / m ³ to 500 kg / m ^3, which is a value close to liquid water. Therefore, the value is much higher than the density of the gas.

As supercritical water generated by the engine system and injected into the cylinder 2, it is preferable to use supercritical water having a density of 250 kg / m ³ or more.

  Further, as indicated by an arrow Y1 in FIG. 4, a normal liquid water requires a large enthalpy to change into a gas. That is, normal liquid water requires a relatively large latent heat to change into a gas. On the other hand, as indicated by arrow Y2, supercritical water requires little enthalpy, that is, latent heat, to change to normal gaseous water.

Here, as is apparent from FIG. 4, the water contained in the region close to the region Z1 has a high density and a small latent heat for changing to gas, and has properties close to supercritical water. Therefore, in the present embodiment, supercritical water is injected into the cylinder 2 as described above, but subcritical water, which is water contained in a region close to the region Z1, is generated in the cylinder 2 instead of the supercritical water. You may spray. For example, subcritical water contained in the region Z10 shown in FIG. 5 and having a temperature of 600 K or higher and a density of 250 kg / m ³ or higher may be generated and injected.

(2) Intake passage The intake passage 30 is provided with an air cleaner 31 and a throttle valve 32 in order from the upstream side, and the air after passing through the air cleaner 31 and the throttle valve 32 is introduced into the engine body 1. .

  The throttle valve 32 opens and closes the intake passage 30. However, in the present embodiment, during engine operation, the throttle valve 32 is basically fully opened or close to the opening, and is closed only under limited operating conditions such as when the engine is stopped. Then, the intake passage 30 is shut off.

(3) Exhaust passage The exhaust passage 40 is provided with a purification device 41 for purifying exhaust, a heat exchanger 42, a condenser 43, and an exhaust shutter valve 44 in order from the upstream side. The heat exchanger 42 and the condenser 43 constitute a part of the water circulation device 60. The purification device 41 includes, for example, a three-way catalyst 41.

  In the present embodiment, as shown in FIG. 1 and the like, the purification device 41 and the heat exchanger 42 are accommodated inside a heat storage case 49 for keeping them warm. The heat storage case 49 has a double tube structure, and a space 49a is formed inside the outer peripheral wall. The space 49a is filled with a heat storage material, and the heat purification material 41 and the heat exchanger 42 are kept warm by the heat storage material. That is, when high-temperature exhaust flows into the purification device 41 or the like located inside the heat storage case 49, the heat storage material in the space 49c is warmed by the exhaust, and the purification device 41 and the heat exchanger 42 are kept warm by this heat storage material. Is done. As the heat storage material, for example, a latent heat storage material that melts by being heated like Elsultol and stores heat energy thereby, or a chemical reaction by being heated like calcium chloride, etc. Examples include chemical heat storage materials that store energy.

  The exhaust shutter valve 44 is for accelerating the recirculation of EGR gas to the intake passage 30.

  That is, in the engine system of the present embodiment, an EGR passage 51 that communicates a portion of the intake passage 30 downstream of the throttle valve 32 and a portion of the exhaust passage 40 upstream of the purification device 41 is provided. A part of the exhaust gas is recirculated to the intake passage 30 as EGR gas. The exhaust shutter valve 44 is a valve capable of opening and closing the exhaust passage 40, and is operated to the valve closing side when EGR is performed and the pressure of the exhaust passage 40 is low, so that the upstream side of the EGR passage 51 is operated. Increase the pressure of the part to promote the reflux of EGR gas.

  The EGR passage 51 is provided with an EGR valve 52 that opens and closes the EGR passage 51, and the amount of EGR gas recirculated to the intake passage 30 is adjusted by the amount of opening of the EGR valve 52. In the present embodiment, the EGR passage 51 is provided with an EGR cooler 53 for cooling the EGR gas passing through the EGR passage 51, and the EGR gas is cooled by the EGR cooler 53 and then returned to the intake passage 30. The

(4) Water Circulation Device The water circulation device 60 is for generating supercritical water using the thermal energy of the exhaust.

  In addition to the heat pipe 70, the heat exchanger 42, and the condenser 43, the water circulation device 60 includes a water supply passage 61 that connects the water injection device 22 and the condenser 43, a water tank 62, a low pressure pump 63, and a high pressure pump 64. And.

  The condenser 43 is for condensing water (water vapor) in the exhaust gas passing through the exhaust passage 40, and the water condensed in the condenser 43 is supplied to the water injection device 22. Thus, in the present embodiment, water in the exhaust is used as water that is injected into the cylinder 2. The water tank 62 stores condensed water inside. The condensed water generated by the condenser 43 is introduced into the water tank 62 via the water supply passage 61 and stored in the water tank 62.

  The low-pressure pump 63 is a pump for feeding the condensed water in the water tank 62 to the heat exchanger 42, and is disposed between the water tank 62 and the heat exchanger 42 in the water supply passage 61. The condensed water in the water tank 62 is sent to the heat exchanger 42 by the low pressure pump 63.

  The heat exchanger 42 is for causing heat exchange between the condensed water pumped from the low pressure pump 63 and the exhaust gas passing through the exhaust passage 40. The heat exchanger 42 is disposed adjacent to the purification device 41 in a portion of the exhaust passage 40 on the downstream side of the purification device 41.

  In the present embodiment, the heat exchanger 42 is formed by inserting a part 61 a of the water supply passage 61 into the exhaust passage 40, and the part 61 a of the water supply passage 61 is connected to the exhaust passage 40. Of these, the inside of the part immediately downstream of the purification device 41 is inserted. Hereinafter, the portion of the water supply passage 61 that is inserted into the exhaust passage 40 will be referred to as a heat exchange passage 61a.

  The heat exchange passage 61a is inserted into the exhaust passage 40 located inside the heat storage case 49. As described above, in the present embodiment, the heat storage case 49 adds the heat exchanger 42 and the heat exchanger 42 in addition to the purification device 41. The heat exchange passage 61a is also kept warm.

  The condensed water in the heat exchange passage 61a is heated by the exhaust passing through the portion of the exhaust passage 40 where the heat exchange passage 61a is inserted. Specifically, if the temperature of the exhaust gas passing through the portion of the exhaust passage 40 through which the heat exchange passage 61a is inserted is higher than the temperature of the condensed water in the heat exchange passage 61a, thermal energy is transferred from the exhaust to the condensed water. It is given and the condensed water is heated up. However, the temperature of the exhaust discharged from the engine body 1 is always at least 100 degrees or more, and the temperature of the exhaust is always higher than the temperature of the condensed water that is liquid water. Therefore, the temperature of the condensed water in the heat exchange passage 61a is always raised by exhaust.

  In the present embodiment, the heat exchange passage 61a is arranged immediately downstream of the purification device 41 as described above, so that the heat of reaction in the purification device 41 is also given to the condensed water in the heat exchange passage 61a. Therefore, the temperature of the condensed water is effectively increased. Further, the temperature of the condensed water is also effectively increased by the heat exchange passage 61 a and the heat exchange passage 61 a being kept warm by the heat storage case 49.

  The high-pressure pump 64 is a pump for pumping condensed water from the heat exchanger 42 toward the water injection device 22. The high pressure pump 64 is disposed between the heat exchanger 42, that is, the heat exchange passage 61 a and the heat pipe 70 in the water supply passage 61. This high-pressure pump 64 pressurizes the condensed water heated by the heat exchanger 42 and feeds it into the water injection device 22 while making it supercritical water.

  Here, high-pressure supercritical water after being pressurized by the high-pressure pump 64 flows through a portion of the water supply passage 61 on the downstream side of the high-pressure pump 64. Therefore, high-pressure piping is used for this part.

  Thus, in the present embodiment, basically, the condensed water is heated and raised by the heat exchanger 42 and the high-pressure pump 64 to generate supercritical water, which is supplied to the water injection device 22.

  However, when the temperature of the exhaust discharged from the engine body 1, specifically the cylinder 2, is relatively high, the water in the water supply passage 61 is heated by the high-temperature exhaust through the heat pipe 70. It is like that.

  That is, the heat pipe 70 is for causing heat exchange between the water pumped from the high-pressure pump 64 and the exhaust gas passing through the exhaust passage 40. The temperature of the condensed water is raised only when the temperature is higher.

  In the present embodiment, the heat pipe 70 has a substantially cylindrical outer shape extending in a predetermined direction. FIG. 6 is a schematic cross-sectional view for explaining the operation of the heat pipe 70. As shown in FIGS. 6 and 2, the heat pipe 70 is disposed such that one end 71 in the longitudinal direction is inserted inside the exhaust port 17 and comes into contact with the exhaust, and the other end 72. Is inserted inside the water supply passage 61 so as to be in contact with the water in the water supply passage 61.

  As shown in FIG. 1 and FIG. 2 and as described above, in the present embodiment, the heat pipe 70 is inserted into each exhaust port 17. Specifically, the water supply passage 61 is provided with a pressure accumulating portion 65 extending in the arrangement direction of the cylinders 2 in the vicinity of the downstream end thereof, and from the pressure accumulating portion 65 toward each water injection device 22. An independent passage 61b extends. One heat pipe 70 is provided for each exhaust port 17, and each end 71, 72 of the heat pipe 70 is inserted into each exhaust port 17 and the pressure accumulating portion 65.

  In the present embodiment, as shown in FIG. 2, the pressure accumulating portion 65 is disposed close to the cylinder head 4, and the heat pipe 70 is built in the cylinder head 4. Specifically, the pressure accumulating portion 65 is located above the exhaust port 17, and the heat pipe 70 extends upward from the inner space of the exhaust port 17 and is inserted into the pressure accumulating portion 65. In the present embodiment, a stack fin 73 configured by stacking metal plate-like members in the vertical direction is provided at an end 71 of the heat pipe 70 on the exhaust port 17 side. Thus, more heat of the exhaust in the exhaust port 17 is transmitted.

  As shown in FIG. 6, the heat pipe 70 is a pipe member formed of a material having high thermal conductivity (for example, metal), and inside the working medium S is sealed in a liquid state in a vacuum state. Has been. A porous member 70a (for example, a metal net) is provided on the inner wall of the heat pipe 70, and a capillary structure called a wick is formed.

  In this heat pipe 70, one end portion (hereinafter referred to as “heat receiving side end portion” where appropriate) 71 inserted into the exhaust port 17 is warmed by the exhaust, and when the temperature exceeds a predetermined temperature, the working medium S evaporates. Then, as indicated by an arrow Y10 in FIG. 6, it diffuses toward the other end portion (hereinafter referred to as a heat dissipation side end portion) 72 inserted into the water supply passage 61. At this time, the temperature of the exhaust gas in the exhaust port 17 is lowered by applying the heat energy to the heat pipe 70, that is, the working medium S. Then, the vapor of the working medium S dissipates heat in the water supply passage 61 at the heat dissipating side end 72, condenses, and returns to the liquid again. At this time, the water in the water supply passage 61 is heated by receiving heat energy from the working medium S. The working medium S that has returned to the liquid again returns to the heat receiving side end 71 as shown by the arrow Y20 in FIG. 6 due to the capillary phenomenon in the porous member 70a, and again becomes steam by taking the thermal energy from the exhaust again. This thermal energy is applied to the water in the water supply passage 61.

  In the present embodiment, the exhaust gas temperature (reference temperature) at which this heat transfer occurs is set to about 650 K, and the working medium S corresponding thereto is enclosed in the heat pipe 70. For example, cesium is used as the working medium S.

  Thus, in the present embodiment, when the temperature of the exhaust gas becomes higher than the predetermined temperature by the heat pipe 70 and the temperature of the working medium S becomes higher than the boiling point, the heat energy of the exhaust gas in the exhaust port 17 is changed to the water supply passage. The water in the water supply passage 61 is heated by being given to 61. Therefore, the water in the water supply passage 61 is almost always heated by the exhaust gas by the heat exchanger 42, and when the temperature of the exhaust gas is higher than the reference temperature, the heat pipe 70 further supplies the water in the water supply passage 61. Water is heated by exhaust gas, and supercritical water can be generated by effectively using the energy of the exhaust gas. In particular, since the heat pipe 70 is disposed at a position close to the cylinder 2, the heat pipe 70 can effectively raise the temperature of the water in the water supply passage 61 using the high heat energy of the exhaust. Further, when the temperature of the exhaust gas is excessively high, the temperature of the exhaust gas flowing into the purification device 41 can be kept low by the heat pipe 70, and when the temperature of the exhaust gas is low, the exhaust gas is directly passed to the purification device 41. The temperature can be maintained high in the purification device 41 by flowing in, and the temperature of the purification device 41 can be maintained in an appropriate range.

(5) Control System (5-1) System Configuration FIG. 7 is a block diagram showing an engine control system. As shown in the figure, the engine system of the present embodiment is comprehensively controlled by a PCM (powertrain control module, control means) 100. As is well known, the PCM 100 is a microprocessor including a CPU, a ROM, a RAM, and the like.

  The PCM 100 is electrically connected to various sensors for detecting the operating state of the engine.

  For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects a rotation angle and a rotation speed of the crankshaft, that is, an engine speed. An air flow sensor SN2 that detects the amount of air (fresh air amount) that passes through the air cleaner 31 and is sucked into each cylinder 2 is provided in a portion of the intake passage 30 between the air cleaner 31 and the throttle valve 32. ing. Further, the vehicle is provided with an accelerator opening sensor SN3 for detecting the opening degree of an accelerator pedal (accelerator opening degree) operated by the driver, which is not shown.

  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 21, the water injection device 22, the throttle valve 32, the exhaust shutter valve 44, the EGR valve 52, the low pressure pump 63, the high pressure pump 64, and the like. Based on the above, a drive control signal is output to each of these devices.

  FIG. 8 shows a control map of the engine speed on the horizontal axis and the engine load on the vertical axis. In the present embodiment, a low load region A1 where the engine load is less than a preset reference load Tq1 and a high load region (water injection region) A2 where the engine load is greater than or equal to the reference load Tq1 are set as the control region. . Below, the control content of each area | region A1, A2 is demonstrated.

(5-2) Low load region In the low load region A1, the required engine torque is small, so the effective compression ratio can be reduced. Therefore, in the low load region A1, the effective compression ratio is set to a small value in order to suppress the pumping loss and increase the energy efficiency. For example, the effective compression ratio is suppressed to a value smaller than 15. Specifically, the intake valve 18 is closed at a later timing than the intake bottom dead center and relatively late, thereby reducing the effective compression ratio.

  In the low load region A1, since the calorific value of the air-fuel mixture is small and the combustion temperature is relatively low, NOx (so-called Raw NOx) generated by combustion is suppressed to a small amount. Therefore, in this region A1, it is not necessary to purify NOx by the three-way catalyst 41, and the air-fuel ratio does not have to be a stoichiometric air-fuel ratio that can be purified by the three-way catalyst. Therefore, in the low load region A1, the air-fuel ratio of the air-fuel mixture is made lean, that is, the excess air ratio λ> 1 in order to improve fuel efficiency.

  In the low load region A1, the EGR gas is recirculated into the cylinder 2. That is, in the low load region A1, the EGR valve 52 is opened, and a part of the exhaust gas in the exhaust passage 40 is recirculated to the intake passage 30 as EGR gas. Further, in an operation region where the engine load is very low and the pressure in the exhaust passage 40, that is, the pressure on the upstream side of the EGR passage 51 is low, the exhaust shutter valve 44 is controlled to the closed side to promote the recirculation of EGR gas.

  In the present embodiment, in the low load region A1, the EGR gas is recirculated so that G / F, which is the ratio of the total gas weight in the combustion chamber 6 to the fuel amount, is 35 or more. Further, as the engine load is higher, the EGR rate (the ratio of the EGR gas capacity to the total gas capacity in the cylinder 2) is increased.

  In the low load region A1, the supercritical water injection into the combustion chamber 6 by the water injection device 22 is stopped. Accordingly, the driving of the low pressure pump 63 and the high pressure pump 64 is stopped.

  In the low load region A1, all fuel is injected into the combustion chamber 6 by the fuel injection device 21 in the latter half of the compression stroke (from 90 ° CA before compression top dead center to compression top dead center). For example, all the fuel is injected into the combustion chamber 6 near 30 ° CA before compression top dead center.

(5-3) High load region In the high load region A2, the effective compression ratio is made larger than the effective compression ratio in the low load region A1 in order to ensure engine torque. In the present embodiment, the effective compression ratio is 15 or more in the high load region A2. Specifically, the valve closing timing of the intake valve 18 is set to an advance side with respect to the valve closing timing in the low load region A1, and thereby the effective compression ratio is made higher than that in the low load region A1.

  In the high load region A2, the air-fuel ratio is set to the stoichiometric air-fuel ratio so that NOx purification by the three-way catalyst is possible. That is, the excess air ratio λ is set to 1. In the high load region A2, the EGR valve 52 is closed to stop the recirculation of the EGR gas, and the G / F is set to a value smaller than 35.

  Here, in the high load region A2, the temperature in the combustion chamber 6 increases because the engine load is high and the amount of fuel and heat generated in the combustion chamber 6 is large. In particular, in this embodiment, the temperature in the combustion chamber 6 becomes higher as the effective compression ratio is higher. Therefore, the cooling loss may increase in the high load region A2. Further, as the temperature in the combustion chamber 6 increases, particularly in the high load region A2, the fuel and air are not sufficiently mixed, that is, the air-fuel mixture is not homogeneous in the combustion chamber 6 (air-fuel mixture). If the combustion is started in a state where the air-fuel ratio of the fuel is not uniform, smoke may be deteriorated.

  Therefore, in the high load region A2, the fuel is injected into the cylinder 2 in a plurality of times so that combustion starts in a state where the air-fuel mixture in the combustion chamber 6 is more homogenized. Specifically, a relatively large amount of fuel is injected in the first half of the compression stroke (from intake bottom dead center to 90 ° CA before compression top dead center), and a part of the remaining fuel is injected in the second half of the compression stroke. The remaining fuel is injected at a timing slightly ahead of the compression top dead center. Thus, the air-fuel mixture is made to self-ignite after compression top dead center while the air-fuel mixture is homogenized.

  Further, in the high load region A2, supercritical water is injected into the combustion chamber 6 by the water injection device 22 so that the supercritical water layer X (see FIG. 10) is formed on the wall surface of the combustion chamber 6. That is, the pressure pump 63 and the high pressure pump 64 are driven to inject supercritical water into the combustion chamber 6 from the water injection device 22.

  FIG. 9 shows the timing of water injection in the high load region A2, the lift curve of the intake valve 18, the pressure in the combustion chamber 6, that is, the in-cylinder pressure that is the pressure in the cylinder 2. FIG. 9 shows a plurality of in-cylinder pressure changes when the effective compression ratio is varied.

  As shown in FIG. 9, in the high load region A2, before the combustion of the fuel and air mixture starts combustion, the latter half of the compression stroke (on the compression side) when the compression stroke is divided into the initial stage, the middle stage, and the latter stage. Subsequent water injection W2 is performed at a predetermined time t2 (60 ° CA before dead center to compression top dead center). Further, the pre-stage water injection W1 is performed before the later stage of the compression stroke and at a timing t1 that is retarded from the closing timing IVC of the intake valve 18.

  In the present embodiment, the pre-stage water injection W1 is started at the initial stage of the compression stroke (intake bottom dead center BDC to 120 ° CA before compression top dead center). Further, the latter-stage water injection W2 is performed during a later phase of the later stage of the compression stroke (for example, 30 ° CA before compression top dead center to compression top dead center).

  As described above, the water injection is performed at different times, so that the heat shielding layer X is formed on the entire wall surface of the combustion chamber 6 in the high load region A2.

  Specifically, the pre-stage water injection W1 is performed before the later stage of the compression stroke and at a time when the in-cylinder pressure P1 is relatively low. Therefore, the penetration (penetration force) of the supercritical water spray related to the pre-stage water jet W <b> 1 is relatively high, and the supercritical water spray is scattered to a position farther from the water jet device 22.

  As shown in FIG. 9, the in-cylinder pressure changes according to the effective compression ratio. However, in any effective compression ratio, the in-cylinder pressure before the latter half of the compression stroke is small, and the in-cylinder pressure at the latter half of the compression stroke becomes high. .

  In the present embodiment, the water injection device 22 is located at the center of the ceiling surface 4a of the combustion chamber 6 as described above. Therefore, as shown in FIG. 10, in the pre-stage water injection W <b> 1, the supercritical water spray X <b> 1 scatters toward the crown surface 5 a of the piston 5 while spreading outward in the radial direction of the cylinder 2, and the crown surface 5 a of the piston 5. The heat shield layer X is formed on the entire crown surface 5a by reaching the entire surface.

  On the other hand, the latter-stage water injection W2 is performed at a later stage of the compression stroke and at a relatively high in-cylinder pressure P2. Therefore, the penetration (penetration force) of the supercritical water spray related to the latter-stage water injection W2 is relatively low, and the scattering distance of the supercritical water spray is shorter than that of the previous-stage water injection W1. Therefore, the supercritical water spray X <b> 2 related to the latter-stage water jet W <b> 2 stays around the water jet device 22. In the present embodiment, since the water injection device 22 is attached to the center of the ceiling surface 4a of the combustion chamber 6 as described above, the spray X2 of the rear-stage water injection W2 is generated in the combustion chamber 6 as shown in FIG. It stays in the center of the ceiling surface 4a and its periphery, and the heat shield layer X2 is formed on the ceiling surface 4a. Therefore, the heat shielding layer X is formed over the entire wall surface of the combustion chamber 6 by the front water injection W1 and the rear water injection W2.

  Here, it is conceivable to use normal liquid water instead of supercritical water (or subcritical water) as a material for forming the heat shield layer X. However, as described above, ordinary liquid water requires latent heat when changing to water vapor. Therefore, when normal liquid water is ejected, the temperature of the air-fuel mixture decreases as the water evaporates, and thermal efficiency deteriorates.

  Therefore, in the present embodiment, as described above, supercritical water that has a high density and does not require latent heat is injected into the combustion chamber 6 to form the heat shield layer X with the supercritical water.

(6) Action, etc. As described above, in this embodiment, in the high load region A2, supercritical water is injected into the combustion chamber 6 to form the thermal barrier layer X by the supercritical water on the wall surface of the combustion chamber 6. By doing so, the cooling loss can be kept small and the fuel efficiency can be improved. In particular, this control is performed in the high load region and the region A2 in which the effective compression ratio is 15 or more and the combustion temperature is high and the cooling loss is likely to be large, so that the cooling loss is effectively reduced. Can do.

  Further, as described above, smoke may be deteriorated in the high load region A2, but in this embodiment, the heat shield layer X can be formed by supercritical water while homogeneously mixing fuel and air. The fuel efficiency can be improved while suppressing the deterioration of smoke. Specifically, if the heat shield layer is formed of air, air and fuel cannot be mixed homogeneously. On the other hand, in this embodiment, since the heat shield layer X is formed with supercritical water, the air-fuel mixture can be made homogeneous while forming the heat shield layer X, and it is appropriate while suppressing cooling loss. Can be achieved to suppress the deterioration of smoke.

  In particular, in the present embodiment, supercritical water is injected into the combustion chamber 6 separately at the later stage of the compression stroke and before this, so that it is reliably exceeded by the entire wall surface of the combustion chamber 6 as described above. Critical water can be present. Therefore, the cooling loss can be more reliably suppressed by the heat shield layer X formed of supercritical water while realizing proper combustion.

  In the above embodiment, the pre-stage water injection W1 is performed after the intake valve 18 is closed. Therefore, the influence of the airflow generated in the combustion chamber 6 as the intake air flows from the intake port 16 on the water spray related to the pre-stage water injection W1 can be reduced. Therefore, it is possible to more reliably cause the water spray related to the front-stage water injection W <b> 1 to reach a relatively far part of the wall surface of the combustion chamber 6.

(7) 2nd Embodiment In the said embodiment, the water injection apparatus 22 is attached so that the front-end | tip may be located in the center of the ceiling surface 4a of the combustion chamber 6, and may face the substantially center of the crown surface 5a of the piston 5. FIG. However, the water injection device 22 may be attached as shown in FIG. That is, the water injection device 22 may be arranged as a side injection method so that the tip of the water injection device 22 faces the inside of the combustion chamber 6 from the inner peripheral surface of the combustion chamber 6. Specifically, the water injection device 22 is positioned at a position shifted from the center of the ceiling surface 4a of the combustion chamber 6 to one side in the radial direction of the cylinder 2 (left side in FIG. 11). You may attach with the attitude | position which faces the part of the other side (right side in FIG. 11) of radial direction of this.

  The second embodiment is the same as the first embodiment except for the arrangement of the water injection device 22 and the fuel injection device 21. Also in the second embodiment, the front-stage water injection W1 and the rear-stage in the high load region A2. Water injection W2 is performed.

  However, in the second embodiment, as the water injection device 22 is arranged as described above, the supercritical water spray X10 related to the pre-stage water injection W1 is generated in the combustion chamber 6 as shown in FIG. In the radial direction of the cylinder 2 is scattered toward the portion opposite to the side where the water injection device 22 is disposed. Accordingly, as shown in FIGS. 12 and 14 (FIG. 14 is a view corresponding to FIG. 12 and the combustion chamber 6 is viewed from above), approximately half of the piston crown surface 5a and the combustion chamber. The heat shielding layer X10_a is formed in a portion on the opposite side to the side where the water injection device 22 is arranged in the radial direction of the cylinder 2 in about the half of the wall surface.

  And, as shown in FIG. 13 and FIG. 15 (FIG. 15 is a view corresponding to FIG. 13 and viewing the inside of the combustion chamber 6 from above), the supercritical water spray X20 related to the latter-stage water injection W2 is as follows. A heat shield layer X20_a is formed around the water injection device 22 and is formed on the portion near the water injection device 22 that is approximately half of the piston crown surface 5a and on the ceiling surface 4a of the combustion chamber 6. As a result, the heat shield layer X is formed on almost the entire wall surface of the combustion chamber 6.

  Therefore, also in the second embodiment, the cooling loss is reduced by the heat shield layer X formed of supercritical water, and the fuel efficiency is improved.

(8) Other Modifications Here, in the above-described embodiment, the case where the thermal barrier layer X made of supercritical water is formed on the wall surface of the combustion chamber 6 only in the high load region A2, but in the low load region A1. Water injection similar to that in the high load region A <b> 2 may be performed to form a heat shield layer with supercritical water on the wall surface of the combustion chamber 6. Moreover, the effective compression ratio of the operation area | region (high load area | region A2 in the said embodiment) which forms the thermal-insulation layer X by supercritical water may be less than 15.

  However, when the engine load is high or the effective compression ratio is high, the combustion temperature becomes high, so that the cooling loss tends to increase. Also, smoke is likely to deteriorate. Therefore, a high effect can be obtained even if the thermal barrier layer made of supercritical water is formed only in a region where the engine load is high or a region where the effective compression ratio is 15 or more.

  Further, as in the above embodiment, in the case where the water circulation device 60 is provided and supercritical water is generated using the thermal energy of the exhaust gas, the combustion temperature is low in the low load region where the engine load is low or in the region where the effective compression ratio is low. The required amount of supercritical water may not be generated due to the low temperature of the exhaust gas. In addition, when the insufficient energy is supplemented by a heater or the like provided separately, the energy efficiency is deteriorated. Therefore, in this case, it is preferable to inject supercritical water only in an operation region where the engine load is high or the effective compression ratio is high and the temperature of the exhaust gas is high.

  Further, the water circulation device 60 may be omitted, and supercritical water may be generated using a heater or the like separately provided as described above. However, if the water circulation device 60 is used as described above, an appropriate amount of ignition delay can be secured while increasing energy efficiency.

  In the above embodiment, the case where supercritical water is injected as water into the combustion chamber 6 has been described. However, as described above, water that is subcritical water and has properties close to supercritical water is supercritical. You may inject in the cylinder 2 instead of water. Even in this case, since the density is higher than that of normal water and the latent heat is very small, the ignition delay time can be extended.

  The combustion mode is not limited to self-ignition combustion, but may be a mode in which combustion starts when the air-fuel mixture is ignited by an ignition plug. Moreover, the fuel which does not contain gasoline may be used as a fuel.

  In the above embodiment, the case where the cavity 510 is provided at the center of the crown surface 5a of the piston 5 has been described. For example, as shown in FIG. It may be provided in a state of being biased radially outward. In this case, since the cavity 510 and the wall surface of the combustion chamber 6 are close to each other, there is a cooling loss due to contact between the flame (combustion gas) F generated in the cavity 510 and the wall surface of the combustion chamber 6. May be very large. Therefore, in such a case, the cooling loss can be effectively reduced by injecting the supercritical water according to the above-described embodiment and forming a thermal barrier layer of supercritical water on the wall surface of the combustion chamber 6.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinders 4a Combustion chamber ceiling 5 Piston 5a Piston crown 10 Combustion chamber 18 Intake valve 21 Fuel injection device 22 Water injection device 40 Exhaust passage 41 Purification device X Heat insulation layer

Claims (6)

In a control device for an engine in which a piston is fitted in a cylinder so as to be capable of reciprocating, and a combustion chamber whose bottom surface is a crown surface of the piston is partitioned into the cylinder,
A fuel supply device for supplying fuel into the combustion chamber;
A water injection device for injecting supercritical water or subcritical water into the combustion chamber;
Control means for controlling each part of the engine including the fuel supply device and the water injection device,
In the water injection region set in at least a part of the engine operation region, the control means includes the supercritical water before the start of combustion of the fuel / air mixture in the combustion chamber and in the latter half of the compression stroke. Alternatively, the water injection device includes: a post-stage water injection for injecting subcritical water into the combustion chamber; and a pre-stage water injection for injecting the supercritical water or subcritical water into the combustion chamber before the latter stage of the compression stroke. An engine control device characterized in that the engine control device is implemented. The engine control device according to claim 1,
An intake valve for opening and closing an intake port for introducing intake air into the cylinder;
The engine control device according to claim 1, wherein the control means causes the water injection device to perform the pre-stage water injection before a later stage of the compression stroke and after the intake valve is closed. The engine control apparatus according to claim 1 or 2,
The engine control device according to claim 1, wherein the water injection device is attached to the center of the ceiling surface of the combustion chamber in a posture facing the center of the crown surface of the piston. The engine control apparatus according to claim 1 or 2,
The water injection device is mounted in a posture facing the inner peripheral surface on the other side in the radial direction of the cylinder at a position shifted from the center of the ceiling surface of the combustion chamber to one side in the radial direction of the cylinder. An engine control device. The engine control apparatus according to any one of claims 1 to 4,
The engine control apparatus according to claim 1, wherein the water injection region is a region where an engine load is equal to or greater than a preset reference load. The engine control apparatus according to any one of claims 1 to 5,
The geometric compression ratio of the engine body is set to 18 or more and 35 or less,
The engine control apparatus according to claim 1, wherein an effective compression ratio of the engine body in the water injection region is set to 15 or more.

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