JP2018035763A - Controller of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure output torque of an engine and also suppress increase of in-cylinder pressure.SOLUTION: A controller is applied to a premixed compression ignition type engine including: a fuel injection valve configured to inject fuel into a cylinder; and a water injection valve configured to inject supercritical water or subcritical water into the cylinder. The controller includes: a fuel injection control unit configured to inject fuel from the fuel injection valve into the cylinder at such timing that fuel self-ignites in a latter period of a compression stroke or an initial period of an expansion stroke; and a water injection control unit configured to continuously inject supercritical water or subcritical water from the water injection valve over a series of periods containing a period from a combustion start point when fuel self-ignites until internal pressure in the cylinder reaches a maximum value during combustion.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an engine capable of premixed compression ignition combustion in which fuel is self-ignited while being mixed with air.

  As the engine as described above, one disclosed in Patent Document 1 is known. In the engine disclosed in Patent Document 1, a part of the exhaust discharged into the exhaust passage is introduced into the cylinder as EGR gas during operation in a predetermined premixed combustion region, and the timing is earlier than the compression top dead center. Thus, control for injecting fuel into the cylinder is executed. In this way, by injecting fuel into the cylinder in which EGR gas, which is an inert gas, is present, the injected fuel can be self-ignited after a predetermined ignition delay, thereby reducing the amount of NOx and soot generated. Less proper combustion is expected to be realized.

JP 2009-209809 A

  Here, when the engine load increases, it is necessary to introduce a large amount of air (fresh air) into the cylinder in order to ensure a high output corresponding to the load. For this reason, in the high load region of the engine, a sufficient amount of EGR gas cannot be introduced into the cylinder, and there is a concern that self-ignition may be accelerated or combustion may be abrupt. On the other hand, for example, if a large turbocharger is applied to the engine, it is considered that both air and EGR gas can be sufficiently introduced into the cylinder. (Internal pressure) may increase excessively, resulting in loud noise and adverse effects on engine reliability.

  Therefore, as a method for solving the above problems, it is proposed to inject water directly into the cylinder. With this method, the required amount of water can be supplied into the cylinder without causing a shortage of air, so combustion can be controlled to the extent that the in-cylinder pressure does not rise excessively while ensuring sufficient output torque. There is. However, if the injection period is not set so that water is present at an appropriate time during combustion, for example, a large increase in in-cylinder pressure immediately after the start of combustion may cause a large combustion noise, or in-cylinder pressure during the progress of combustion. The maximum value of can be adversely affected by engine reliability.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine control device capable of suppressing an increase in in-cylinder pressure while ensuring engine output torque. .

  In order to solve the above-described problems, the present invention provides a cylinder in which a piston is reciprocably accommodated, a fuel injection valve that injects fuel into the cylinder, and supercritical water or subcritical water is injected into the cylinder. And a water injection valve for controlling an engine capable of premixed compression ignition combustion in which fuel injected from the fuel injection valve is self-ignited while being mixed with air, the latter stage of the compression stroke or the initial stage of the expansion stroke A fuel injection control unit that injects fuel into the cylinder from the fuel injection valve at a timing such that the fuel self-ignites, and the internal pressure of the cylinder reaches a maximum value during the combustion from the start of combustion when the fuel self-ignites. And a water injection control unit that continuously injects supercritical water or subcritical water from the water injection valve over a series of periods including a period up to a point of time (Claim 1). ).

  In the present invention, the latter stage of the compression stroke refers to a range from 60 ° CA before compression top dead center (BTDC) to the compression top dead center, and the initial stage of the expansion stroke refers to compression top dead center from the compression top dead center. It means the range up to 60 ° CA after ATDC.

  According to the present invention, supercritical water or subcritical water injection (hereinafter also simply referred to as water injection) from the water injection valve is started almost simultaneously with or before the self-ignition of the fuel. The progress of combustion (HCCI combustion) immediately after that is suppressed by the presence of water, which is an inert substance that does not react with fuel components. Thereby, it is possible to avoid a sudden increase in the in-cylinder pressure immediately after the self-ignition, and it is possible to suppress an increase in combustion noise due to a rapid increase in the in-cylinder pressure (an increase in the pressure increase rate).

  Further, since the water injection is continued at least until the in-cylinder pressure reaches the maximum value during combustion, the maximum value of the in-cylinder pressure becomes excessively large due to the action of the continuously injected water (for example, design It is possible to avoid such a situation that the above allowable value is exceeded. As a result, a situation in which excessive pressure is applied to the components such as the piston and the cylinder head and the components are damaged can be avoided, and the reliability of the engine can be ensured satisfactorily.

  Furthermore, since the water injected from the water injection valve to the cylinder is supercritical water or subcritical water, more water can be supplied to the cylinder in a shorter time than when low density gas water (water vapor) is injected. A sufficient amount of water that can appropriately suppress the in-cylinder pressure can be efficiently supplied to the cylinder. Further, compared to the case of injecting liquid water, the temperature drop of the cylinder due to the absorption of latent heat of water can be greatly reduced, and the reduction in engine output torque due to the temperature drop is effectively suppressed. be able to. In addition, the supercritical water / subcritical water injected into the cylinder works to push down the piston by rapidly expanding in the cylinder. Therefore, according to the present invention that continuously injects supercritical water / subcritical water having such properties into the cylinder, it is possible to sufficiently secure the output torque of the engine while efficiently suppressing an increase in the in-cylinder pressure. it can.

  Preferably, the control device includes an ignition determination unit that determines that the fuel has self-ignited, and the water injection control unit is configured to detect the supercritical water or the sub-water when the ignition determination unit determines that the fuel has self-ignited. The injection of critical water is started (Claim 2).

  According to this configuration, water injection can be started without delay in accordance with the self-ignition of fuel, and a rapid increase in in-cylinder pressure immediately after self-ignition and an accompanying increase in combustion noise can be effectively suppressed. Moreover, since water injection is not performed before self-ignition, the consumption of water by water injection can be suppressed.

  Preferably, the control device includes an in-cylinder pressure sensor that detects an internal pressure (in-cylinder pressure) of the cylinder, and the water injection control unit is configured to input the internal pressure of the cylinder based on input information from the in-cylinder pressure sensor. Is reached, and after the maximum value is reached, the injection of the supercritical water or subcritical water is stopped (Claim 3).

  According to this configuration, the water injection can be reliably continued until the in-cylinder pressure starts to decrease, and the increase in the in-cylinder pressure can be effectively suppressed as it affects the reliability of the engine. .

  Preferably, the effective compression ratio of the cylinder is set to 13 or more and 27 or less, and the water injection control unit is configured to perform after the time point when 40 to 95% of the mass of fuel injected from the fuel injection valve in one cycle burns. And the injection of the supercritical water or subcritical water is stopped.

  A high effective compression ratio of 13 or more and 27 or less is advantageous for creating a high-temperature and high-pressure environment in which fuel is easily ignited, and is also advantageous for improving thermal efficiency. However, when the effective compression ratio is so high, there is a concern that the maximum value of the in-cylinder pressure becomes excessively large and adversely affects the reliability of the engine. Therefore, it is necessary to continue water injection until the in-cylinder pressure reaches the maximum value, but according to the study of the present inventor, the in-cylinder pressure reaches the maximum value when the effective compression ratio is 13 or more and 27 or less. Timing corresponds to a point in time when 40 to 95% of the mass of fuel injected during one cycle burns. Therefore, according to the configuration in which the water injection is continued until 40 to 95% of the fuel is combusted, the maximum value of the in-cylinder pressure can be effectively avoided due to the water injection, and the reliability of the engine can be improved. It can be ensured satisfactorily.

  Preferably, the engine raises the temperature of the condensed water by heat exchange between a condenser that condenses water vapor contained in the exhaust discharged from the cylinder to generate condensed water and an exhaust before flowing into the condenser. A heat exchanger, and the water injection valve injects supercritical water generated through a temperature raising process by the heat exchanger into the cylinder.

  According to this configuration, it is possible to efficiently generate supercritical water using the heat recovered from the exhaust (without adding a special heat source) and inject the supercritical water thus generated into the cylinder. Thus, the heat recovered from the exhaust can be efficiently converted into work. Thereby, the fuel efficiency performance of the engine can be effectively improved while sufficiently securing the output torque of the engine.

  The fuel injection valve preferably injects fuel mainly composed of gasoline (Claim 6).

  That is, the present invention can be suitably applied to an HCCI-type gasoline engine in which fuel containing gasoline as a main component is premixed compression ignition combustion.

  As described above, according to the engine control apparatus of the present invention, there is an advantage that an increase in in-cylinder pressure can be effectively suppressed while securing an output torque of the engine.

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 sectional drawing of an engine main body. It is a figure which shows the state change of the water accompanying the change of 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 a flowchart which shows the specific procedure of the control at the time of performing fuel injection and water injection at the time of high load operation of an engine. It is a time chart which shows the state change of the cylinder accompanying fuel injection and water injection. FIG. 4 is a view corresponding to FIG. 3 for explaining subcritical water.

(1) Overall Configuration of Engine FIGS. 1 and 2 are views showing a preferred embodiment of an engine to which the control device of the present invention is applied. 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.

  As shown in FIG. 2, the engine body 1 includes a cylinder block 3 in which the 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 accommodated 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 valve 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 a crank angle sensor SN1 that detects a rotation angle (crank angle) of the crankshaft 15. The crank angle sensor SN1 also serves as a sensor for detecting the rotational speed of the crankshaft 15, that is, the output rotational speed of the engine body 1 (engine rotational speed).

  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 fuel injection valves 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 valve 11 is provided adjacent to a water injection valve 57, which will be described later, with the central axis of the cylinder 2 interposed therebetween. As shown in FIG. 1, a fuel rail 16 is provided above the fuel injection valve 11 to store the fuel supplied from the fuel pump in a pressure accumulation state. The fuel stored in the fuel rail 16 is supplied to each fuel injection valve 11 through the same number (four) of distribution pipes 17 as the fuel injection valves 11.

  The fuel injection valve 11 has a front end 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 front end toward the cavity 10 of the piston 5. Specifically, the fuel injection valve 11 injects at least a part of the amount of fuel to be injected during one cycle into the combustion chamber C before the compression top dead center. The injected fuel is mixed with air (intake air) introduced into the combustion chamber C, and then self-ignited, for example, near the compression top dead center.

  That is, in the engine of the present embodiment, instead of spark ignition combustion (combustion in which an air-fuel mixture is forcibly ignited by spark ignition) generally employed when gasoline is used as a fuel, an air-fuel mixture of fuel and air is used as a piston. HCCI combustion (premixed compression ignition combustion) that is self-ignited in accordance with compression by 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 order to enable the HCCI combustion as described above, the compression ratio of each cylinder 2 is set higher in the engine of the present embodiment than in a general gasoline engine that employs spark ignition combustion. Specifically, in this embodiment, the geometric compression ratio of each cylinder 2, that is, the volume of the combustion chamber C when the piston 5 is at the top dead center and the combustion chamber C when the piston 5 is at the bottom dead center. The volume ratio is set to 18 to 35, more preferably 18 to 30.

  As shown in FIG. 2, the cylinder head 4 exhausts the exhaust gas generated in the combustion chamber C and the intake port 6 for introducing the air supplied from the intake passage 20 into the combustion chamber C for each cylinder 2. An exhaust port 7 for leading to the passage 30, an intake valve 8 for opening and closing the opening on the combustion chamber C side of the intake port 6, and an exhaust valve 9 for opening and closing the opening on the combustion chamber C side of the exhaust port 7 are provided. It has been.

  The intake valve 8 and the exhaust valve 9 are driven to open and close in conjunction with the rotation of the crankshaft 15 by a valve drive mechanism (not shown). The valve drive mechanism for the intake valve 8 incorporates an intake valve variable mechanism 18 (FIG. 4) that can change at least the closing timing of the intake valve 8. The intake valve variable mechanism 18 changes the closing timing of the intake valve 8 according to the operating conditions of the engine, and accompanying this change, the effective compression ratio of each cylinder 2, that is, the combustion when the piston 5 is at the top dead center. The ratio between the volume of the chamber C and the volume of the combustion chamber C when the intake valve 8 is closed is changed. The intake valve variable mechanism 18 may be a variable mechanism of a type that changes only the closing timing (the lift amount is changed accordingly) while the opening timing of the intake valve 8 is fixed. A phase-type variable mechanism that simultaneously changes the opening timing and the closing timing may be used.

  In each part constituting the inner wall of the combustion chamber C, that is, the inner wall surface of the cylinder block 3, the crown surface of the piston 5, the lower surface of the cylinder head 4, and the lower surfaces of the valve heads of the intake valve 8 and the exhaust valve 9, A heat insulating layer 13 is provided for each. The heat insulating layer 13 provided on the inner wall surface of the cylinder block 3 is limited to a portion located above the piston ring 5a (on the cylinder head 4 side) in a state where the piston 5 is at the top dead center. The ring 5 a does not slide on the heat insulating layer 13.

  The heat insulating layer 13 is made of a material having lower thermal conductivity and specific heat capacity than the cylinder block 3, the cylinder head 4, the piston 5, and the intake / exhaust valves 8 and 9. This is because the heat of the combustion gas generated in the combustion chamber C is suppressed from being released to the outside of the combustion chamber C, and the cooling loss of the engine is reduced. That is, since the heat conductivity of the heat insulating layer 13 is low, the heat of the combustion gas is suppressed from being transmitted to the cylinder block 3, the cylinder head 4, and the like through the heat insulating layer 13. Moreover, since the volume specific heat of the heat insulation layer 13 is low, the temperature difference between the heat insulation layer 13 and the combustion gas is suppressed to be small, and the movement of heat due to this temperature difference is suppressed. For example, the main components of the engine body 1 such as the cylinder block 3 and the cylinder head 4 have a large volumetric specific heat and are cooled by cooling water. Therefore, even if the inside of the cylinder 2 is temporarily heated due to combustion, The temperature of the main parts is maintained at a relatively low temperature. For this reason, if the heat insulating layer 13 is not present, the high-temperature combustion gas directly contacts the inner wall surface of the low-temperature main component, resulting in a large heat transfer due to the temperature difference between the two. On the other hand, when the heat insulating layer 13 having a low volumetric specific heat is provided, the temperature of the heat insulating layer 13 changes with good responsiveness in conjunction with the temperature of the combustion gas. Loss can be reduced.

The heat insulating layer 13 can be formed by coating a ceramic material such as ZrO ₂ by plasma spraying. In this case, a large number of pores can be included in the heat insulating layer 13. Such a porous heat insulating layer is advantageous in reducing the thermal conductivity and the specific volume heat.

  As shown in FIG. 2, the cylinder head 4 is provided with in-cylinder pressure sensors SN2 for detecting the internal pressure of the cylinder 2 (hereinafter also referred to as in-cylinder pressure), one for each cylinder 2 (four in total). ing. Each in-cylinder pressure sensor SN2 has a detection element whose electromotive force changes according to the magnitude of pressure at the tip, and is attached to the cylinder head 4 in a state where the detection element is exposed to the combustion chamber C. Yes.

  As shown in FIG. 1, the intake passage 20 includes a single tubular common intake pipe 22 and an intake manifold 21 formed to branch from the downstream end of the common intake pipe 22. Each branch pipe of the intake manifold 21 is connected to the engine body 1 (cylinder head 4) so as to communicate with each cylinder 2 via the intake port 6. The downstream end of the common intake pipe 22 is connected to the intake manifold 21. Of the branch pipes (the part where the upstream ends of the branch pipes gather together). 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 is provided with an air cleaner 25 for removing foreign substances contained in the intake air and an openable / closable throttle valve 27 for adjusting the flow rate of the intake air flowing through the common intake pipe 22 in this order from the upstream side. Yes. Further, an air flow sensor SN3 for detecting the flow rate of the intake air flowing through the common intake pipe 22 is provided on the downstream side of the common intake pipe 22 from the throttle valve 27.

  The exhaust passage 30 includes a single tubular common exhaust pipe 32 and an exhaust manifold 31 formed so as to branch from the upstream end of the common exhaust pipe 32. Each branch pipe of the exhaust manifold 31 is connected to the engine body 1 (cylinder head 4) so as to communicate with each cylinder 2 via the exhaust port 7, and the upstream end portion of the common exhaust pipe 32 is connected to the exhaust manifold 31. Of the branch pipes (the part where the downstream ends of the branch pipes gather together). 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.

  In the common exhaust pipe 32, a catalyst device 35, a heat exchanger 54, a condenser 51, and an exhaust shutter valve 36 are provided 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 51 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 51 condenses the water vapor contained in the exhaust gas, and the heat exchanger 54 raises the temperature of the condensed water generated by the condenser 51. The heat exchanger 54 and the condenser 51 are elements that constitute a part of the water supply system 50 (details 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 condenser 51 and a heat exchanger 54 described above, a water tank 52 that stores the condensed water generated by the condenser 51, and A water supply pump 53 that pumps the condensed water stored in the water tank 52 toward the heat exchanger 54, and a high pressure and high pressure water that is pressurized by the water pump 53 and heated by the heat exchanger 54 while accumulating pressure. Accumulator rail 56 stored in a state, water injection valves 57 provided for each cylinder 2 (four in total) for injecting water stored in the accumulator rail 56 into the cylinder 2, a condenser 51 and water A first water pipe 61 that connects the tank 52, a second water pipe 62 that connects the water tank 52 and the heat exchanger 54, and a third water pipe 63 that connects the heat exchanger 54 and the pressure accumulation rail 56. , Pressure accumulation rail 56 and A plurality of (four) distribution pipes 64 for connecting the water injection valves 57 are provided.

  The condenser 51 is a heat exchanger for condensing water vapor contained in the exhaust gas flowing through the common exhaust pipe 32, and by cooling the exhaust gas by heat exchange with a predetermined refrigerant (for example, engine cooling water), Water vapor contained in the exhaust is condensed. The condensed water generated by the condenser 51 flows out downstream through the first water pipe 61 and is stored in the water tank 52.

  The water feed pump 53 is provided in the middle of the second water pipe 62 and feeds the condensed water stored in the water tank 52 toward the heat exchanger 54 while pressurizing the condensed water. The water pumped from the water pump 53 has a pressure of about 24 MPa and a temperature of about 80 ° C., for example.

  The heat exchanger 54 heats the water supplied from the water pump 53 by heat exchange with the exhaust before flowing into the condenser 51. Although not shown in detail, the heat exchanger 54 includes a small-diameter and long-shaped thin tube 54a inserted into a portion of the common exhaust pipe 32 positioned between the catalyst device 35 and the condenser 51, and the thin tube 54a. A heat insulation case having a double-pipe structure provided so as to cover the common exhaust pipe 32 of the portion into which the heat exchanger is inserted, and a heat storage material filled in a space portion (between the outer tube and the inner tube) of the heat insulation case Have. Thus, the heat retaining case with the heat storage material is used for the heat exchanger 54 because the heating effect of the water by the heat exchanger 54 exceeds a certain level regardless of the temperature change of the exhaust gas according to the operating conditions of the engine. This is to ensure.

  The water heated by the heat exchanger 54 is sent to the downstream side through the third water pipe 63 and stored in the pressure accumulation rail 56. The pressure accumulation rail 56 is provided with a water pressure sensor SN4 that detects the pressure of the internal water.

  The heat exchanger 54 has a sufficient heating capacity so that water can be heated to a supercritical state. That is, the water having a pressure of about 24 MPa and a temperature of about 80 ° C. immediately before flowing into the heat exchanger 54 is greatly heated as it passes through the heat exchanger 54 and is in a supercritical state. It becomes water (supercritical water). Supercritical water has a temperature of 647 K (374 ° C.) or higher and a pressure of 22 MPa or higher, so it has both liquid and gas properties (it does not apply to any of the three phases of liquid, gas, and solid). No) Water in a special state. The supercritical water generated by the heat exchanger 54 is stored and stored in the pressure storage rail 56 while being stored and is injected into the cylinder 2 through the water injection valve 57 when necessary. That is, in this embodiment, supercritical water is used as the water injected from the water injection valve 57 to the cylinder 2.

Furthermore, the supercritical water used in the present embodiment is generated through the above-described process (via the water supply pump 53 and the heat exchanger 54), thereby having a relatively high density of 250 kg / m ³ or more. Have. That is, the supercritical water injected from the water injection valve 57 in this embodiment is a high-temperature, high-pressure, high-density 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. It is.

The nature of supercritical water will be described with reference to FIG. FIG. 3 is a diagram showing changes in the state of water accompanying changes in enthalpy and pressure, with the horizontal axis representing enthalpy (kJ / kg) and the vertical axis representing pressure (MPa). In FIG. 3, 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.}

  3 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.

Further, in FIG. 3, and the Z1a a region excluding the (right area than the line LD250) density 250 kg / ^{m 3} below from one area Z1 of the supercritical water. The water contained in this region Z1a represents supercritical water (water having a temperature of 647 K or more, a pressure of 22 MPa or more, and a density of 250 kg / m ³ or more) used in this embodiment.

  As understood from FIG. 3, the supercritical water (water included in the region Z1a) used in this embodiment has a higher density than the gaseous water (water vapor) included in the region Z3. Injecting such supercritical water into the cylinder 2 means that more water can be supplied to the cylinder 2 in a shorter time than in the case of injecting gaseous water. Also, as indicated by arrow W1 in FIG. 3, supercritical water requires little enthalpy (latent heat) to change to 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. This means that injecting supercritical water into the cylinder 2 can significantly reduce the temperature drop of the cylinder 2 due to absorption of latent heat of water, compared to injecting liquid water.

(3) Engine Control System FIG. 4 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 crank angle sensor SN1, in-cylinder pressure sensor SN2, airflow sensor SN3, and water pressure sensor SN4, and information detected by these sensors (that is, crank angle, in-cylinder pressure). , Intake flow rate, water pressure, etc.) are sequentially input to the PCM 100 as electrical signals.

  Further, the vehicle is provided with an accelerator sensor SN5 for detecting the opening of an accelerator pedal (not shown) operated by a driver who drives the vehicle, and a detection signal from the accelerator sensor SN5 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 valve 11, the intake valve variable mechanism 18, the throttle valve 27, the exhaust shutter valve 36, the EGR valve 42, the water supply pump 53, the water injection valve 57, etc. The control signals are output to these devices based on the results of the above.

  As functional elements related to the above control, the PCM 100 includes a fuel injection control unit 101, a water injection control unit 102, an EGR control unit 103, and a valve control unit 104.

  The fuel injection control unit 101 uses the engine load specified by the detected value (accelerator opening) of the accelerator sensor SN5, the engine rotational speed detected by the crank angle sensor SN1, and the intake air flow detected by the airflow sensor SN3. Based on this, the fuel injection amount from the fuel injection valve 11 and the injection timing are determined, and the fuel injection valve 11 is controlled according to the determination.

  Based on the internal pressure of the pressure accumulation rail 56 detected by the water pressure sensor SN4 (the pressure of the water stored in the pressure accumulation rail 56), the water injection control unit 102 determines the required pressure (22 MPa) as supercritical water. ) The water supply pump 53 is driven so as to be held as described above. Further, the water injection control unit 102 determines a period during which supercritical water is to be injected based on the internal pressure (in-cylinder pressure) of the cylinder 2 detected by the in-cylinder pressure sensor SN2, and from the water injection valve 57 over the period. Inject supercritical water.

  The EGR control unit 103 determines a target value of the EGR rate that is a ratio of the EGR gas in the total gas amount introduced into the cylinder 2 based on the engine load and the like, and an EGR rate that matches the target value is obtained. In this manner, the EGR valve 42 and the exhaust shutter valve 36 are controlled.

  The valve control unit 104 is effective in accordance with engine operating conditions (engine load and rotational speed) by driving the intake valve variable mechanism 18 to variably set the opening / closing characteristics (at least the closing timing) of the intake valve 8. Increase or decrease the compression ratio. That is, the valve control unit 104 stores a predetermined target opening / closing characteristic of the intake valve 8 so as to obtain an appropriate effective compression ratio according to the operating condition, and the intake valve 8 is driven according to the target opening / closing characteristic. Thus, the intake valve variable mechanism 18 is controlled. In the engine of this embodiment in which the geometric compression ratio of each cylinder 2 is set to 18 or more and 35 or less (preferably 18 or more and 30 or less), the valve control unit 104 has an effective compression ratio of 13 or more and 27 or less. Set variably in the range. In particular, when the geometric compression ratio is set to 18 or more and 30 or less, the valve control unit 104 variably sets the effective compression ratio in the range of 13 to 23.

(4) Control according to operation conditions Next, the control of the fuel injection valve 11, the water injection valve 57, the EGR valve 42, and the exhaust shutter valve 36 by the PCM 100 will be described in detail.

  FIG. 5 is a map for explaining the difference in control according to the engine operating conditions (load / rotational speed). 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 injection valve 57 and HCCI combustion not accompanied by supercritical water injection from the water injection valve 57. The That is, as shown in FIG. 5, 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. Control for performing HCCI combustion while injecting supercritical water from the valve 57 is selected, and control for executing HCCI combustion with the supercritical water injection stopped is selected in the second operating region A2 on the low load side. The The outline of the control in each of the operation areas A1 and A2 is as follows.

(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 fuel injection valve 11 is controlled so that the fuel injection amount increases toward the higher load side. Also, the fuel injection timing is higher than the target ignition timing so that the fuel self-ignites at an appropriate timing (for example, near the compression top dead center) according to the engine operating conditions (load / rotation speed). It is set at an appropriate timing a little earlier.

  The water injection valve 57 is controlled so that supercritical water is continuously injected over a period from the time when the fuel self-ignites (that is, the start of combustion) to the time when the in-cylinder pressure reaches the maximum value during the combustion. The That is, the injection of supercritical water from the water injection valve 57 is started at a timing almost coincident with the self-ignition of fuel (start of combustion), and the in-cylinder pressure reaches the maximum value during the combustion. It is finished almost at the same time.

  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 the execution region of HCCI combustion without water injection, the water injection valve 57 is maintained in the closed state, and the injection of supercritical water is stopped. The The fuel injection amount from the fuel injection valve 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) Specific control example in the first operation region Next, a specific control example (mainly the fuel injection valve 11 and the water injection valve) in the first operation region A1 in which HCCI combustion with water injection is performed. 57) will be described with reference to FIGS. FIG. 6 is a flowchart showing a specific procedure of control of the fuel injection valve 11 and the water injection valve 57 executed in the first operation region A1, and FIG. 7 shows fuel injection and water injection in the first operation region A1. 6 is a time chart showing a change in the state of a cylinder 2 associated with. Specifically, the chart (a) in FIG. 7 shows the change in the in-cylinder pressure (Pa) with respect to the crank angle, and the chart (b) shows the change in the in-cylinder pressure increase rate (Pa / deg) with respect to the crank angle. The chart (c) shows the change in the heat generation rate (J / deg) with respect to the crank angle, and the chart (d) shows the fuel injection pulse and the water injection pulse. In FIG. 7, the crank angle on the horizontal axis represents the crank angle (deg. ATDC) when the compression top dead center is 0 °.

  When the control shown in the flowchart of FIG. 6 starts, the fuel injection control unit 101 determines the fuel injection amount and injection timing from the fuel injection valve 11 (step S1). Specifically, the fuel injection control unit 101 acquires the engine load, the engine rotation speed, and the intake air flow rate from the detected values of the accelerator sensor SN5, the crank angle sensor SN1, and the airflow sensor SN3, and based on the acquired values, The fuel injection amount and injection timing from the fuel injection valve 11 are determined (step S1).

  As already described, the fuel injection amount from the fuel injection valve 11 is determined so as to increase as the engine load increases. The fuel injection timing is determined at an appropriate timing in consideration of the predicted ignition delay time so that the injected fuel self-ignites at a predetermined target ignition timing. Here, the target ignition timing of the fuel is typically set near the compression top dead center. With respect to this target ignition timing, an ignition delay time (time from injection to ignition) is predicted and calculated based on the fuel injection amount, the intake air flow rate, the engine speed, etc., and the target ignition is calculated by the calculated ignition delay time. A timing earlier than the timing is determined as the fuel injection timing. The target ignition timing is not limited to the vicinity of the compression top dead center, and may be advanced or retarded to some extent with respect to the compression top dead center depending on the operating conditions of the engine. However, in any case, the target ignition timing is set so as to be included in either the later stage of the compression stroke or the early stage of the expansion stroke. The late compression stroke here refers to the range from 60 ° CA before compression top dead center (BTDC) to compression top dead center, and the early expansion stroke refers to after compression top dead center from compression top dead center ( ATDC) The range up to 60 ° CA. That is, in the present embodiment, the fuel injection timing from the fuel injection valve 11 is determined to be a timing at which the fuel self-ignites in the late compression stroke or early expansion stroke (BTDC 60 ° CA to ATDC 60 ° CA).

  Next, the fuel injection control unit 101 injects fuel from the fuel injection valve 11 (step S2). That is, the fuel injection control unit 101 injects an amount of fuel that matches the injection amount determined in step S1 from the fuel injection valve 11, and the injection timing matches the injection timing determined in step S1. Thus, the valve opening operation of the fuel injection valve 11 is controlled. FIG. 7 (chart (d)) shows an example in which fuel is injected from the fuel injection valve 11 before and after BTDC 20 ° CA.

  Next, the water injection control unit 102 determines whether or not there is heat generation due to combustion (step S3). That is, the fuel injected in step S2 is self-ignited after a predetermined ignition delay time while being mixed with air inside the cylinder 2, thereby starting combustion (HCCI combustion). Then, the in-cylinder pressure starts to rise rapidly due to the heat generation accompanying the combustion. The water injection control unit 102 detects this rapid increase in the in-cylinder pressure based on the detection value of the in-cylinder pressure sensor SN2, and determines that heat has been generated (that is, the fuel has self-ignited) at the time of detection. The fuel self-ignition (start of HCCI combustion) specified in this way is the timing at which 5 to 15% of the mass of fuel injected from the fuel injection valve 11 in one cycle has completed combustion. Equivalent to. Further, the combination of the in-cylinder pressure sensor SN2 that detects the in-cylinder pressure and the water injection control unit 102 (PCM 100) that determines self-ignition of fuel based on the detected value corresponds to the “ignition determination means” in the claims. To do.

  If it is determined as YES in step S3 and it is confirmed that heat has been generated (the fuel has self-ignited), the water injection control unit 102 opens the water injection valve 57 to open the water injection valve 57. The control for injecting supercritical water from the start is started (step S4). In the example of FIG. 7, the fuel self-ignites in the vicinity of the compression top dead center (0 ° CA), and accordingly, the in-cylinder pressure, the pressure increase rate, and the heat generation rate start to increase rapidly. Yes. In this case, the injection of supercritical water is started in the vicinity of the compression top dead center which is substantially the same timing as the self-ignition.

  Next, the water injection control unit 102 determines whether or not the in-cylinder pressure has reached the maximum value (step S5). That is, the water injection control unit 102 examines a change in the in-cylinder pressure detected by the in-cylinder pressure sensor SN2 after the start of water injection, and identifies that the in-cylinder pressure has changed from an increasing tendency to a decreasing tendency. Then, it is determined that the in-cylinder pressure has reached the maximum value (Pmax shown in the chart (a) of FIG. 7) at the time when it is specified that the tendency has been reduced. Note that the timing at which the in-cylinder pressure reaches the maximum value Pmax differs depending on the effective compression ratio of the engine, but in the case where the effective compression ratio is set to any one of 13 to 27 as in the present embodiment, the timing is reached during one cycle. 40 to 95% of the injected fuel mass corresponds to the time when combustion is completed. When the effective compression ratio is set to any one of 13 to 23, the above timing (the timing at which the in-cylinder pressure reaches the maximum value Pmax) corresponds to the time when 50 to 95% of the fuel mass has completed combustion. To do.

  When it is determined YES in step S5 and it is confirmed that the in-cylinder pressure has reached the maximum value, the water injection control unit 102 closes the water injection valve 57 and stops the injection of supercritical water ( Step S6). In the example of FIG. 7, the in-cylinder pressure reaches the maximum value Pmax slightly before ATDC 20 ° CA (see chart (a)), and supercritical water injection is stopped at this point.

(6) Effects As described above, the engine of the present embodiment includes the fuel injection valve 11 that injects fuel into the cylinder 2 and the water injection valve 57 that injects supercritical water into the cylinder 2. When the engine is operated in the first operating region A1 on the high load side, the water injection valve 57 is in the combustion from the time when the fuel injected from the fuel injection valve 11 self-ignites (that is, the start time of combustion). Then, supercritical water is continuously injected over a series of periods until the cylinder pressure reaches the maximum value Pmax. According to such a structure, there exists an advantage that the raise of a cylinder pressure can be suppressed effectively, ensuring the output torque of an engine.

  That is, in the above embodiment, supercritical water injection from the water injection valve 57 (hereinafter also simply referred to as water injection) is started almost simultaneously with the self-ignition of the fuel, so that combustion immediately after self-ignition (HCCI combustion) Is suppressed by the presence of water, which is an inert substance that does not react with the fuel component. Thereby, it is possible to avoid a sudden increase in the in-cylinder pressure immediately after the self-ignition, and it is possible to suppress an increase in combustion noise due to a rapid increase in the in-cylinder pressure (an increase in the pressure increase rate). For example, as shown by broken line waveforms in charts (b) and (c) of FIG. 7, if water injection is not performed, combustion proceeds rapidly immediately after self-ignition, and a large amount of heat is generated in a short time. It is considered that the in-cylinder pressure suddenly increases. This leads to an increase in the rate of pressure increase that correlates with the combustion noise, that is, an increase in the combustion noise, leading to a decrease in the commercial quality of the engine. On the other hand, according to the above-described embodiment in which water injection is started almost simultaneously with self-ignition, an increase in in-cylinder pressure (pressure increase rate) is suppressed by the injected water, so that an increase in combustion noise is suppressed. Can improve the merchantability of the engine.

  Further, since the water injection is continued until the in-cylinder pressure reaches the maximum value Pmax during combustion, the maximum value Pmax of the in-cylinder pressure becomes excessively large due to the action of the continuously injected water (for example, It is possible to avoid such a situation that the design tolerance is exceeded. For example, if the water injection is terminated before the in-cylinder pressure reaches the maximum value Pmax, as shown by the one-dot chain line block in the chart (d) of FIG. 7, the chart (a) ( As indicated by the dashed line waveform in c), the progress of combustion becomes steep immediately after the stop of water injection, and as a result, the in-cylinder pressure may increase until it exceeds the allowable value. On the other hand, according to the embodiment in which the water injection is continued until the in-cylinder pressure reaches the maximum value Pmax, the maximum value Pmax of the in-cylinder pressure can be suppressed to an appropriate level that does not exceed the allowable value. As a result, a situation in which excessive pressure is applied to components such as the piston 5 and the cylinder head 4 and the components are damaged can be avoided, and the reliability of the engine (engine body 1) can be ensured satisfactorily.

  Furthermore, since the water injected from the water injection valve 57 to the cylinder 2 is supercritical water, a larger amount of water is supplied to the cylinder 2 in a shorter time than when low-density gaseous water (water vapor) is injected. It is possible to supply the cylinder 2 with a sufficient amount of water capable of appropriately suppressing the in-cylinder pressure. In addition, compared with the case of injecting liquid water, the temperature drop of the cylinder 2 due to the absorption of latent heat of water can be greatly reduced, and the reduction in engine output torque due to the temperature drop is effectively suppressed. can do. Moreover, the supercritical water injected into the cylinder 2 works to push down the piston 5 by rapidly expanding in the cylinder 2. Therefore, according to the above-described embodiment in which supercritical water having such a property is continuously injected into the cylinder 2, it is possible to sufficiently secure the output torque of the engine while efficiently suppressing the increase in the in-cylinder pressure.

  Further, in the above embodiment, when the self-ignition of the fuel injected from the fuel injection valve 11 is specified based on the detection value of the in-cylinder pressure sensor SN2, that is, the in-cylinder pressure detected by the in-cylinder pressure sensor SN2 is the fuel injection. The water injection is started when it is confirmed that it has suddenly started to rise later, so that the water injection can be started without delay in accordance with the self-ignition of the fuel. The sudden increase and the accompanying increase in combustion noise can be effectively suppressed. Moreover, since water injection is not performed before self-ignition, the consumption of water by water injection can be suppressed.

  Further, in the above embodiment, since the water injection is stopped when it is determined that the in-cylinder pressure during combustion has reached the maximum value Pmax based on the detection value of the in-cylinder pressure sensor SN2, the in-cylinder pressure decreases. The water injection can be surely continued until it starts, and the increase in the in-cylinder pressure can be effectively suppressed as the reliability of the engine is affected.

  In the above embodiment, the temperature of the condensed water is raised by heat exchange between the condenser 51 that condenses the water vapor contained in the exhaust discharged from the cylinder 2 to generate condensed water and the exhaust before flowing into the condenser 51. Since the engine is equipped with a heat exchanger 54 and the supercritical water generated through the temperature raising process by the heat exchanger 54 is injected from the water injection valve 57, the heat recovered from the exhaust gas can be used efficiently. Supercritical water can be generated (without adding a special heat source), and the supercritical water thus generated is injected into the cylinder 2 to expand it, so that the heat recovered from the exhaust can be efficiently used for work. Can be converted. Thereby, the fuel efficiency performance of the engine can be effectively improved while sufficiently securing the output torque of the engine.

(7) Modification In the above embodiment, each cylinder 2 of the engine body 1 is provided with the in-cylinder pressure sensor SN2 for detecting the internal pressure, and based on the detected value of the in-cylinder pressure sensor SN2, that is, the actually measured value of the in-cylinder pressure. Although the timing of water injection from the water injection valve 57 has been determined, the in-cylinder pressure sensor is not essential in the present invention and can be omitted.

  When the in-cylinder pressure sensor is omitted, for example, the timing for starting water injection can be determined in accordance with a target ignition timing that is predetermined for each operation condition. Further, the timing for stopping water injection is determined based on, for example, a predicted value of in-cylinder pressure calculated from an effective compression ratio, intake air flow rate, intake air temperature, intake air pressure, fuel injection amount, etc. at each time point during operation. can do. In the above embodiment, the presence of a sensor for detecting the intake pressure and the intake air temperature is not particularly mentioned, but such a sensor is widely used in a vehicle engine. Therefore, the in-cylinder pressure prediction calculation as described above can be performed without adding a special sensor.

  In the above embodiment, water injection is started when the fuel self-ignites in the cylinder 2 (that is, when combustion starts), and water injection is performed when the in-cylinder pressure reaches the maximum value Pmax during the combustion. Although stopped, the period during which the water injection is continued may be a series of periods including the period from the time when the fuel self-ignites until the time when the in-cylinder pressure reaches the maximum value Pmax. For this reason, the water injection may be started before the self-ignition of the fuel, or may be stopped when the in-cylinder pressure reaches a maximum value Pmax somewhat later.

  For example, when water injection is continued even after the in-cylinder pressure reaches the maximum value Pmax, the timing at which the water injection is stopped can be the timing at which a predetermined amount of supercritical water has been injected. . Here, according to the research of the inventors of the present application, when supercritical water generated by heat recovery of exhaust is injected into the cylinder 2 as in the above embodiment, both improvement in fuel efficiency and securing of output torque are achieved. It has been found that a suitable supercritical water injection amount is 3 to 6 times the fuel injection amount (mass of fuel injected during one cycle). Therefore, the water injection may be stopped when the supercritical water injection of 3 to 6 times the fuel injection amount is completed.

  Further, when water injection is started before the self-ignition of fuel, the injection start timing can be advanced to about 5 to 15 ° CA ahead of the self-ignition timing.

Moreover, in the said embodiment, as water injected in the cylinder 2 from the water injection valve 57, the comparatively high-density supercritical water which has the temperature of 647K or more, the pressure of 22 MPa or more, and the density of 250 kg / m < ³ > or more. (Water contained in the region Z1a in FIG. 5) is used, but subcritical water having properties close to supercritical water may be used instead. For example, water contained in the region Z10 shown in FIG. 8, 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 the cylinder, an increase in the in-cylinder pressure can be suppressed while securing the output torque of the engine.

  In addition, when supercritical water or subcritical water is injected from a water injection valve, the injection pressure can be variously changed. However, in consideration of injection efficiency and practical use, the injection pressure may be set to 20 MPa or more and 30 MPa or less. preferable.

  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 can also be applied to a gasoline engine in which HCCI combustion is performed in a part of the operation region and spark ignition combustion is performed in the remaining operation region, or an engine in which fuel other than gasoline is HCCI-combusted.

2 cylinder 5 piston 11 fuel injection valve 51 condenser 54 heat exchanger 57 water injection valve 101 fuel injection control unit 102 water injection control unit SN2 in-cylinder pressure sensor

Claims (6)

A cylinder in which a piston is reciprocally movable; a fuel injection valve that injects fuel into the cylinder; and a water injection valve that injects supercritical water or subcritical water into the cylinder, and is injected from the fuel injection valve. A device for controlling an engine capable of premixed compression ignition combustion in which the mixed fuel is self-ignited while being mixed with air,
A fuel injection control unit that injects fuel into the cylinder from the fuel injection valve at a timing such that the fuel self-ignites at the later stage of the compression stroke or the early stage of the expansion stroke;
Supercritical water or subcritical water is continuously injected from the water injection valve over a series of periods including the time from the start of combustion when the fuel self-ignites until the time when the internal pressure of the cylinder reaches the maximum value during the combustion. An engine control device comprising: a water injection control unit for controlling the engine. The engine control device according to claim 1,
An ignition determination means for determining that the fuel self-ignited,
The engine control apparatus according to claim 1, wherein the water injection control unit starts the injection of the supercritical water or the subcritical water when the ignition determination unit determines that the fuel is self-ignited. The engine control apparatus according to claim 1 or 2,
An in-cylinder pressure sensor for detecting the internal pressure of the cylinder;
The water injection control unit specifies that the internal pressure of the cylinder has reached a maximum value based on input information from the in-cylinder pressure sensor, and the supercritical water or subcritical water after the time when the maximum value is reached. The engine control apparatus is characterized in that the injection of the engine is stopped. The engine control apparatus according to any one of claims 1 to 3,
The effective compression ratio of the cylinder is set to 13 or more and 27 or less,
The water injection control unit stops the injection of the supercritical water or the subcritical water after 40 to 95% of the mass of fuel injected from the fuel injection valve in one cycle is combusted. Engine control device. In the engine control device according to any one of claims 1 to 4,
The engine is a heat exchanger that raises the temperature of the condensed water by heat exchange between a condenser that condenses water vapor contained in the exhaust discharged from the cylinder to generate condensed water and an exhaust before flowing into the condenser. And
The engine control device according to claim 1, wherein the water injection valve injects supercritical water generated through a temperature raising process by the heat exchanger into the cylinder. The engine control apparatus according to any one of claims 1 to 5,
The engine control device according to claim 1, wherein the fuel injection valve is for injecting fuel mainly composed of gasoline.

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