JP6436220B1 - Premixed compression ignition engine - Google Patents

Abstract

A premixed compression ignition engine capable of reducing combustion noise while ensuring high thermal efficiency is provided.
A premixed compression ignition type engine capable of self-igniting a fuel-air mixture containing gasoline in a combustion chamber 6 and having a radial direction of the piston 5 on a crown surface 5a of the piston 5. A cavity 19 recessed in the central region is provided, and a water injection means 15 for supplying water into the combustion chamber 6 and a fuel supply means 14 for supplying fuel into the combustion chamber 6 are provided. The fuel supply means 14 supplies fuel into the combustion chamber 6 so that an air-fuel mixture is formed in the cavity 19 and self-ignition of the air-fuel mixture starts in the cavity 19, and the water injection means 15 A region located between the radial center portion R1 and the outer peripheral portion R2 of the cavity 19 in the combustion chamber 6 before the high-temperature oxidation reaction in the cavity 19 in the late compression stroke or early expansion stroke. Water is sprayed on R3.
[Selection] Figure 9

Description

  The present invention includes a premixed compression ignition type engine having an engine body including a cylinder having a combustion chamber and having a piston fitted therein, and capable of self-igniting a fuel-air mixture containing gasoline in the combustion chamber. About.

  Conventionally, it has been studied to perform so-called premixed compression ignition combustion in which fuel containing gasoline and air are mixed in advance and the mixture is ignited in a combustion chamber.

  In the premixed compression ignition combustion, compared with flame propagation combustion, it is possible to increase the compression ratio of the engine body and increase the thermal efficiency as the combustion time is shortened. There is a problem that the in-cylinder pressure is rapidly increased and combustion noise is easily deteriorated.

  On the other hand, for example, in Patent Document 1, fuel is divided into first-stage injection and second-stage injection and injected into the combustion chamber, and the air-fuel mixture is ignited between these first-stage injection and second-stage injection. The disclosed engine is disclosed. According to the engine disclosed in Patent Document 1, combustion of the air-fuel mixture formed by the pre-stage injection can be started by ignition. Therefore, the ignition timing can be appropriately controlled by adjusting the ignition timing, and the pre-stage injection can be controlled. Combustion of the air-fuel mixture formed by the above and the air-fuel mixture formed by the post-injection can be started at different timings, and the rapid increase of the in-cylinder pressure can be suppressed to suppress the deterioration of combustion noise.

JP 2012-241590 A

  However, even in the configuration of Patent Document 1, when the compression ratio of the engine body is further increased or when the engine load is high, the air-fuel mixture starts self-ignition earlier than a desired timing (for example, ignition timing). There is a possibility that the combustion noise cannot be reduced sufficiently.

  On the other hand, for example, a part of the exhaust gas, that is, EGR gas may be recirculated to the cylinder in a large amount. However, in this method, the combustion in the entire combustion chamber becomes slow, the end time of the combustion is delayed, and the thermal efficiency is lowered.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a premixed compression ignition engine capable of reducing combustion noise while ensuring high thermal efficiency.

  In order to solve the above problems, the present invention comprises an engine body including a cylinder having a combustion chamber and a piston fitted therein, and self-igniting a fuel / air mixture containing gasoline in the combustion chamber. A possible premixed compression ignition type engine, wherein a crown surface of the piston includes a cavity recessed in a central region in a radial direction of the piston, and water injection means for injecting water into the combustion chamber; A fuel supply means for supplying fuel into the combustion chamber; and a control means for controlling the water injection means and the fuel supply means. The control means forms the air-fuel mixture in the cavity in the fuel supply means. The fuel is supplied into the combustion chamber so that the self-ignition of the air-fuel mixture is started in the cavity, and the water injection means is in the latter half of the compression stroke or the first half of the expansion stroke and the cavity. Before the air-fuel mixture undergoes a high-temperature oxidation reaction, injecting water into a region located between the radially central portion and the outer peripheral portion of the cavity in the combustion chamber, A premixed compression ignition type engine is provided.

  According to this configuration, when air-fuel mixture is formed in the cavity and combustion mainly occurs in the cavity, the combustion period is shortened while suppressing a sudden increase in the in-cylinder pressure and suppressing combustion noise by water injection. It can suppress and can improve thermal efficiency.

  Specifically, in the self-ignition combustion, when the air-fuel mixture is warmed, first, a low-temperature oxidation reaction with a slight exotherm that exceeds the cooling loss occurs, and the heat of the air-fuel mixture is further warmed by this heat of reaction. A high temperature oxidation reaction that generates energy occurs. In addition, when an air-fuel mixture is formed in the cavity and combustion is mainly performed in the cavity, the air-fuel mixture starts to combust first in the central portion of the cavity that is far from the outer periphery of the cavity and has a relatively high temperature, and the generated thermal energy. The surrounding air-fuel mixture is ignited by being heated by the self-ignition, and the self-ignition of the air-fuel mixture proceeds from the center of the cavity toward the outer peripheral side.

  Therefore, in order to auto-ignite the entire air-fuel mixture in the cavity, it is necessary to reliably cause a low-temperature oxidation reaction of the air-fuel mixture in the central portion of the cavity. On the other hand, in order to prevent the entire air-fuel mixture from burning suddenly, the time when the air-fuel mixture around the air-fuel mixture that initially undergoes the low-temperature oxidation reaction starts the high-temperature oxidation reaction or the oxidation reaction of the air-fuel mixture around this air-fuel mixture. Need to slow down.

  On the other hand, in this configuration, the central portion and the outer peripheral portion in the radial direction of the cavity are formed by the water injection means before the high-temperature oxidation reaction of the air-fuel mixture is started in the later stage of the compression stroke or the early stage of the expansion stroke. Water is sprayed on the intermediate part located between the two. That is, water is not injected into the central portion of the cavity, and water is injected into the intermediate portion located around the central portion immediately before the high-temperature oxidation reaction of the air-fuel mixture starts.

  Therefore, the temperature of the air-fuel mixture in the middle part is kept low by the latent heat action of water and the action of increasing the specific heat while keeping the air-fuel mixture in the middle part of the cavity appropriately at low temperature. Or the rate of the oxidation reaction of the surrounding air-fuel mixture can be slowed. Accordingly, it is possible to suppress a sudden rise in the in-cylinder pressure while enabling the air-fuel mixture to self-ignite.

  In addition, in this configuration, water is not sprayed on the outer peripheral portion of the cavity of the cavity, which is the region where the air-fuel mixture finally burns. For this reason, it is possible to prevent the combustion at the outer peripheral portion from slowing down, and it is possible to shorten the combustion period by terminating the combustion at an early stage.

  In the above-described configuration, the operation range in which the injection control is performed is an intermediate load range in which the engine load is higher than the first reference load indicating a preset low load and lower than the second reference load indicating a high load. (Claim 2).

  In the above-described configuration, the control means causes the air-fuel mixture to undergo a high-temperature oxidation reaction with the water injection means in the latter half of the compression stroke or the first half of the expansion stroke and in the combustion chamber in a high load region where the engine load is greater than or equal to the second reference load. Before the water is injected into a region including the outer peripheral portion of the cavity and located between the radial central portion of the cavity and the radial outer peripheral portion of the combustion chamber. (Claim 3).

  In this way, even in the high load region where the air-fuel mixture is formed almost entirely in the combustion chamber, the air-fuel mixture is appropriately subjected to a low-temperature oxidation reaction in the central portion of the cavity, and the region around the central portion. This makes it possible to slow the combustion of the air-fuel mixture and suppress an increase in combustion noise. Furthermore, it is possible to increase the thermal efficiency by preventing the combustion at the outer periphery of the combustion chamber from becoming excessively slow.

  As described above, according to the premixed compression ignition type engine of the present invention, combustion noise can be reduced while ensuring high thermal efficiency.

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 a schematic sectional drawing of a combustion chamber. It is a schematic sectional drawing of an outward opening type water injector. It is a block diagram which shows the control system of an engine. It is the figure which showed the control map. It is the schematic which showed the heat release rate. It is a figure for demonstrating a low temperature oxidation reaction and a high temperature oxidation reaction. It is a schematic sectional drawing of the combustion chamber which showed the middle field in a middle load field. It is a schematic sectional drawing of the engine main part which showed the mode of the water injection in a medium load area | region. It is a schematic sectional drawing of the combustion chamber which showed the middle field in a high load field. It is a schematic sectional drawing of the engine main part which showed the mode of the water injection in a high load area | region.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which a premixed compression ignition engine of the present invention is applied. The engine system of the present embodiment includes a four-stroke engine main body 1, an intake passage 20 for introducing combustion air into the engine main body 1, and an exhaust passage 30 for discharging exhaust gas generated by the engine main body 1. With.

  The engine body 1 is, for example, an in-line four-cylinder engine in which four cylinders 2 are arranged in series in a direction orthogonal to the paper surface of FIG. This engine system is mounted on a vehicle, and the engine body 1 is used as a drive source for the vehicle. In the present embodiment, the engine main body 1 is driven by receiving supply of fuel including gasoline. The fuel may be gasoline containing bioethanol or the like.

  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 6a 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.

  On the crown surface 5a of the piston 5 (hereinafter simply referred to as the piston crown surface 5a), a cavity 19 is provided that is recessed in a central region including the center of the piston 5 in the radial direction. The cavity 19 has a substantially circular shape when viewed from above, and is formed so as to be recessed downward (in the direction opposite to the cylinder head 4) in the central region of the piston crown surface 5a in the radial direction of the combustion chamber 6. Yes. In the present embodiment, the surface of the piston crown surface 5a is coated with the heat insulating layer 5b.

  Here, the space between the piston crown surface 5a and the ceiling surface 6a of the combustion chamber in the inner space of the cylinder 2 regardless of the position of the piston 5 and the combustion state of the air-fuel mixture is referred to as the combustion chamber 6.

  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 13 or more and 25 or less (for example, about 20).

  The cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6), and an exhaust for generating exhaust gas generated in the cylinder 2 to the exhaust passage 30. An exhaust port 10 is formed. Two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2.

  The cylinder head 4 is provided with an intake valve 11 that opens and closes an opening on the cylinder 2 side of each intake port 9 and an exhaust valve 12 that opens and closes an opening on the cylinder 2 side of each exhaust port 10.

  The cylinder head 4 is provided with a fuel injector (fuel supply means) 14 for injecting fuel. The fuel injector 14 is attached so that the tip portion where the injection port is formed is located near the center of the ceiling surface 6 a of the combustion chamber and faces the center of the combustion chamber 6. The fuel injector 14 is configured to inject fuel in a cone shape (specifically, a hollow cone shape) around the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface 6a of the combustion chamber toward the piston crown surface 5a. Yes. The taper angle (spray angle) of the cone is, for example, 90 ° to 100 °.

  In the present embodiment, an outward-opening type injector is used as the fuel injector 14. The fuel injector 14 is not limited to an open-open type, but is a VCO (Valve Covered Orifice) nozzle type injector or a multi-hole type in which a plurality of injection holes are provided at the tip and fuel is injected at a predetermined spray angle. It may also be an injector or a swirl injector that injects fuel in a holo-cone shape.

  The cylinder head 4 is provided with a spark plug (ignition device) 13 for igniting the air-fuel mixture in the combustion chamber 6. The spark plug 13 has an electrode portion 13a in which an electrode for discharging sparks to ignite the air-fuel mixture and impart ignition energy to the air-fuel mixture is formed. The spark plug 13 is disposed so that the electrode portion 13a is positioned near the center of the ceiling surface 6a of the combustion chamber and faces the center of the combustion chamber 6.

  FIG. 3 is a schematic sectional view of the combustion chamber 6. As shown in FIG. 3, the cylinder head 4 is further provided with a water injector (water injection means) 15 for injecting water into the combustion chamber 6. The water injector 15 is attached such that the tip portion where the injection port is formed is located near the center of the ceiling surface 6a of the combustion chamber and faces the center of the combustion chamber 6. The fuel injector 14 and the water injector 15 are arranged close to each other in a direction orthogonal to the paper surface of FIG.

  The water injector 15 is configured to inject water in a cone shape (specifically, a hollow cone shape) centering on the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface 6a of the combustion chamber toward the piston crown surface 5a. ing. For example, the taper angle of this cone is 90 ° to 100 ° (the taper angle of the hollow portion inside the hollow cone is about 70 °).

  In the present embodiment, as the water injector 15, an outward-opening type injector is used similarly to the fuel injector 14.

  FIG. 4 is a schematic cross-sectional view of the outward-opening water injector 15. As shown in FIG. 4, the open-type water injector 15 includes a fuel pipe 15 c having a nozzle port 15 b formed at the tip, and an open valve 15 a that is disposed inside the fuel tube 15 c and opens and closes the nozzle port 15 b. And have. The outer opening valve 15a is connected to a piezo element 15d that deforms according to the applied voltage. The outer opening valve 15a is in contact with the nozzle port 15b in a state where no voltage is applied to the piezo element 15d and closes the nozzle port 15b. The nozzle port 15b is opened by protruding from 15b to the tip side.

  The portion of the nozzle port 15b and the outer opening valve 15a that contacts the nozzle port 21b has a tapered shape whose diameter increases toward the tip side. Thereby, fuel is injected from the nozzle port 15b in a cone shape around the central axis of the nozzle port 15b, that is, the substantially central axis of the cylinder 2.

  The lift amount of the outer opening valve 15a (the lift amount is the amount of protrusion from the valve closing position of the outer opening valve 15a and the opening amount of the nozzle port 15b) is the period of voltage application to the piezoelectric element 15d and the magnitude of the voltage. It changes according to the height. And according to the lift amount of the outer opening valve 15a, the particle size of the water injected from the nozzle port 15b changes, and further, the spread of the spray in the radial direction orthogonal to the axial direction of the water injector 15 changes.

  Specifically, when the lift amount is increased, the particle size of the spray is increased and the penetration is increased. Along with this, the negative pressure formed inside the hollow cone is increased by the Coanda effect, and the spray is attracted to this negative pressure, so that the spread of the spray is suppressed to be small. On the other hand, when the lift amount is reduced, the particle size of the spray is reduced and the penetration is weakened, the negative pressure formed inside the hollow cone is lowered, and the spread of the spray is increased.

  Returning to FIG. 1, an air cleaner 21 and a throttle valve 22 for opening and closing the intake passage 20 are provided in the intake passage 20 in order from the upstream side. In the present embodiment, during operation of the engine, the throttle valve 22 is basically fully opened or close to the opening, and is closed only when the engine is in a limited operating condition such as when the engine is stopped. The passage 20 is blocked.

  The exhaust passage 30 is provided with a purification device 41 and a condenser 32 for purifying exhaust gas in order from the upstream side. The purification device 41 includes, for example, a three-way catalyst.

  The condenser 32 is for condensing water (water vapor) in the exhaust gas that passes through the exhaust passage 30. The condenser 32 and the water injector 15 are connected by a water supply passage 35, and the condensed water generated in the condenser 32 is supplied to the water injector 15 through the water supply passage 35. Thus, in this embodiment, the water injector 15 receives the supply of water generated from the exhaust and injects it into the combustion chamber 6. More specifically, the water supply passage 35 is provided with a water tank 33 for storing the condensed water generated by the condenser 32 and a water pump 34 for pumping water in the water tank 33. Condensed water is supplied from the water tank 33 to the water injector 15 by the water pump 34. For example, water is pumped to the water injector 15 so that the injection pressure becomes 20 MPa. In the present embodiment, the water pump 34 is a relatively low-pressure pump, and the water injected from the water injector 15 is 90 ° C., which is about the same as the temperature of the engine cooling water. Instead of this, the temperature and pressure of water may be further increased using a high-pressure pump. For example, water may be pressurized so that supercritical water is jetted from the water injector 15.

  The exhaust passage 30 is provided with an EGR device 46 for returning a part of the exhaust gas passing through the exhaust passage 30 as EGR gas to the intake passage 20. The EGR device 46 opens and closes an EGR passage 47 that connects a portion of the intake passage 20 downstream of the throttle valve 22 and a portion of the exhaust passage 30 upstream of the purification device 41, and the EGR passage 47. An EGR valve 48 is provided. In the present embodiment, the EGR passage 47 is provided with an EGR cooler 49 for cooling the EGR gas passing therethrough, and the EGR gas is cooled by the EGR cooler 49 and then returned to the intake passage 20. The

(2) Control System (2-1) System Configuration FIG. 5 is a block diagram showing an engine control system. As shown in FIG. 5, 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.

  Various sensors are provided in the vehicle, and the PCM 100 is electrically connected to these sensors. For example, the cylinder block 3 is provided with a crank angle sensor SN1 that detects the engine speed. Further, an air flow sensor SN2 that detects the amount of air taken into each cylinder 2 through the intake passage 20 is provided. 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 executes various calculations based on input signals from these sensors SN1 to SN3 and controls each part of the engine such as the spark plug 13, the fuel injector 14, and the water injector 15.

(2-2) Combustion control In this embodiment, premixed compression ignition combustion (CI combustion, self-ignition combustion) is performed in the entire operation region.

  Specifically, fuel is injected into the combustion chamber 6 from the fuel injector 14 before the compression top dead center, and the mixture of the fuel and air is compressed to a high temperature and self-ignited near the compression top dead center. To do.

  Here, the thermal efficiency (engine torque) can be increased in the CI combustion as compared with the flame propagation combustion. Specifically, in CI combustion, combustion can be started in a plurality of regions in the combustion chamber 6. Accordingly, the combustion period can be shortened and the thermal efficiency can be improved as compared with flame propagation combustion in which combustion proceeds by flame propagation.

  However, if it is attempted to auto-ignite the air-fuel mixture when the engine load is high, the air-fuel mixture starts to burn (at substantially the same time) in each part of the combustion chamber 6 as the temperature in the combustion chamber 6 increases. The pressure in the combustion chamber 6, that is, the in-cylinder pressure, rises rapidly and combustion noise tends to increase. Further, the temperature in the combustion chamber 6, that is, the in-cylinder temperature, becomes very high and NOx is likely to be generated.

  Further, even when the engine load is relatively low and the engine speed is high, the reaction time is short, so that the air-fuel mixture is also burned all at once in each portion of the combustion chamber 6 and the amount of combustion noise and NOx generated increases.

  Therefore, in the present embodiment, water is injected into the combustion chamber 6 in order to prevent the air-fuel mixture from starting at once in a region where the engine load is relatively high.

  FIG. 6 is a control map of the engine speed on the horizontal axis and the engine load on the vertical axis. As shown in FIG. 6, the medium load region A1 is set in a region where the engine load is equal to or higher than the first reference load Tq1 and lower than the second reference load Tq2. The first reference load Tq1 is set to a lower value as the engine speed is higher. Further, the high load area A2 is set in an area where the engine load is equal to or higher than a preset second reference load Tq2. Then, water is injected into the combustion chamber 6 in the medium load region A1 and the high load region A2.

  By injecting water into the combustion chamber 6, the temperature rise in the combustion chamber 6 can be suppressed by increasing the latent heat action of water and the specific heat, and the combustion of the air-fuel mixture can be slowed (the air-fuel mixture starts to burn at once). Can be prevented). However, if water is simply and uniformly supplied to the entire combustion chamber 6, the thermal efficiency deteriorates. This will be specifically described with reference to FIG. FIG. 7 is a schematic view showing a change in the heat generation rate with respect to the crank angle.

  When water is not supplied to the combustion chamber 6 (hereinafter referred to as Comparative Example 1), the air-fuel mixture starts to burn at once in the combustion chamber 6, so that the heat generation rate dQ1 as shown by the broken line in FIG. Stands up suddenly.

  On the other hand, when water is uniformly supplied to the entire combustion chamber 6 (hereinafter referred to as Comparative Example 2), the temperature rise in the combustion chamber 6 is suppressed and the combustion becomes slow, as shown by the chain line in FIG. In addition, the rise of the heat generation rate dQ2 becomes gradual. As a result, in Comparative Example 2, rapid increases in the in-cylinder pressure and the in-cylinder temperature are suppressed.

  However, in Comparative Example 2, the slope of the heat release rate in the later stage of combustion also becomes gentle, and the combustion period becomes longer. Therefore, in Comparative Example 2, the thermal efficiency is deteriorated.

  Moreover, in the comparative example 2, there exists a possibility that self-ignition of air-fuel | gaseous mixture itself may not arise but it may misfire. That is, in Comparative Example 2, there is a possibility that self-ignition of the air-fuel mixture cannot be realized stably and appropriately.

  The above phenomenon occurs in Comparative Example 2 for the following reason.

  In auto-ignition combustion (premixed compression ignition combustion), when the air-fuel mixture is warmed, first, a low-temperature oxidation reaction with slight exotherm that exceeds the cooling loss occurs, and this heat of reaction further warms the air-fuel mixture. A high temperature oxidation reaction that generates thermal energy begins. The low temperature oxidation reaction is an oxidation reaction of the air-fuel mixture with a slight exotherm that exceeds the cooling loss. FIG. 8 is a graph showing an increase amount with respect to the in-cylinder temperature during motoring of the in-cylinder temperature when the air-fuel mixture self-ignites (when combustion is not generated in the combustion chamber 6). As shown in this graph, in the self-ignition combustion, first, the temperature starts to slightly increase from the crank angle CA1, and then the temperature rapidly increases at the crank angle CA2. The low temperature oxidation reaction is a reaction that occurs from the crank angle CA1 to the crank angle CA2, and the reaction that causes a rapid temperature increase after the crank angle CA2 is the high temperature oxidation reaction.

  In the combustion chamber 6, the oxidation reaction of the air-fuel mixture starts first at a relatively high temperature portion far from the wall surface of the combustion chamber 6, and the surrounding air-fuel mixture self-ignites by being heated by this reaction heat. . That is, the self-ignition of the air-fuel mixture proceeds from the portion far from the wall surface of the combustion chamber 6 toward the outer peripheral side. In this embodiment, the temperature at the central portion C of the cavity 19 is highest, and the oxidation reaction of the air-fuel mixture is first started at the central portion C of the cavity 19. Therefore, in order to self-ignite the air-fuel mixture in the combustion chamber 6, a combustion nucleus that reliably causes a low-temperature oxidation reaction of the air-fuel mixture in the central portion C of the cavity 19 and induces subsequent combustion is reliably generated. There is a need.

  On the other hand, in Comparative Example 2, water is also injected into the central portion C of the cavity 19 to keep the temperature of the central portion C low. Therefore, in Comparative Example 2, the oxidation reaction cannot be sufficiently caused at the central portion C of the cavity 19 and there is a risk of misfire.

  Further, as described above, the self-ignition of the air-fuel mixture proceeds from the central portion C of the cavity 19 toward the outer peripheral side, and the air-fuel mixture in the region on the outer peripheral side of the combustion chamber 6 burns last. Therefore, when this combustion becomes slow, the combustion period becomes long.

  On the other hand, in Comparative Example 2, water is also injected into the region on the outer peripheral side of the combustion chamber 6, and the air-fuel mixture that exists in the region on the outer peripheral side of the combustion chamber 6 and is cooled by the wall surface of the combustion chamber 6. It is further cooled by water. Therefore, the combustion of the air-fuel mixture in the region on the outer peripheral side of the combustion chamber 6 becomes excessively slow, and the combustion period becomes long.

  From this, in this embodiment, before the air-fuel mixture starts a high-temperature oxidation reaction in the combustion chamber 6, the first region R1 including the central portion C of the cavity 19 and the second region on the outer peripheral side of the combustion chamber 6 are used. Water is injected into the combustion chamber 6 so that water is unevenly distributed in the intermediate region R3 located between R2.

  If it does in this way, the temperature rise of the center part C can be suppressed, without reducing the temperature of the center part C of the cavity 19 too much. Specifically, water is injected into the intermediate region R3 and the intermediate region R3 is cooled, so that the first region R1 adjacent thereto is also cooled, but the cooling effect is that water is directly injected into the first region R1. The temperature rise of the air-fuel mixture in the first region R1 can be suppressed to such an extent that the temperature does not decrease excessively. Accordingly, it is possible to reliably realize the low temperature oxidation reaction at the central portion C and prevent misfire while slowing the start time of the high temperature oxidation reaction at the central portion C of the cavity 19 or the speed of the high temperature oxidation reaction.

  Further, the temperature rise of the air-fuel mixture in the intermediate region R3 that has received the heat of reaction generated in the central portion C of the cavity 19 is suppressed, and the combustion of the air-fuel mixture in the intermediate region R3 is made slow (high-temperature oxidation reaction). The starting time or the rate of the high-temperature oxidation reaction can be slowed). Therefore, it is possible to prevent the air-fuel mixture from being burned at once in the central portion C of the cavity 19 and its periphery.

  Moreover, it can prevent that the temperature of the area | region of the outer peripheral side of the combustion chamber 6 falls further with water, and can avoid that combustion in this outer peripheral side area | region becomes slow. Therefore, the combustion period can be shortened.

  The first region R1 only needs to be set in a range in which the combustion energy generated by the air-fuel mixture existing in the first region R1 can induce self-ignition of the air-fuel mixture in the entire combustion chamber 6, and its specific Although the range is not limited, for example, the first region R1 is set to have a diameter of about 2 mm or more and about half or less of the diameter of the cavity 19.

  In the present embodiment, in order to make water unevenly distributed in the intermediate region R3 and to increase the chance of contact between the water and the air-fuel mixture in the intermediate region R3, in the present embodiment, the air-fuel mixture is in the later stage of the compression stroke or the earlier stage of the expansion stroke. Prior to the start of the high-temperature oxidation reaction, water is injected into the intermediate region R3. That is, when water is jetted excessively early, water easily diffuses to the region other than the intermediate region R3, and water adheres to the wall surface of the combustion chamber 6 to reduce the chance of contact between the air-fuel mixture and water. The cooling effect of the air-fuel mixture by water and the effect of suppressing the temperature rise of the air-fuel mixture by water are reduced. Therefore, in this embodiment, as described above, water is injected after the latter stage of the compression stroke and immediately before the high-temperature oxidation reaction of the air-fuel mixture starts. In the present specification, the first, middle, and second half of the XX stroke such as the compression stroke refers to the first, middle, and second half when the stroke is divided into three equal parts.

  Furthermore, in order to slow down the low temperature oxidation reaction of the air-fuel mixture in the intermediate region R3 more effectively, in this embodiment, the timing at which the low temperature oxidation reaction starts in the combustion chamber 6 (crank angle CA1 in the example of FIG. 8) and Water is injected before and after the start of the low temperature oxidation reaction of the air-fuel mixture in the intermediate region R3 at a timing between the start of the high temperature oxidation reaction (crank angle CA2 in the example of FIG. 8).

  Specifically, the timing (crank angle CA1 in the example of FIG. 8) and the high-temperature oxidation reaction start at each operating condition (each engine speed, each engine load, etc.) and the high-temperature oxidation reaction through experiments and the like in advance. A timing (crank angle CA2 in the example of FIG. 8) is obtained, and an intermediate timing between these timings is set as a water injection start timing and stored in the PCM 100 as a map or the like. Then, the PCM 100 extracts the start time of water injection from this map or the like corresponding to the operating conditions, and causes the water injector 15 to inject water into the combustion chamber 6 at this time. Instead of this, an in-cylinder pressure sensor for detecting the pressure in the combustion chamber 6 is provided, the heat generation rate is calculated using the in-cylinder pressure detected by the in-cylinder pressure sensor, and the timing at which the heat generation rate rises is calculated. The time after the predetermined crank angle may be set as the water injection start time.

  In addition, it has been found that when high-octane gasoline is used as the fuel, the low-temperature oxidation reaction hardly appears clearly. Therefore, when high-octane gasoline is likely to be used, the timing at which the high-temperature oxidation reaction starts under each operating condition is determined, and an angle approximately 10 ° CA before this timing is set as the start timing of water injection. And stored in the PCM 100 as a map or the like. When it is detected by a sensor or the like that high-octane gasoline is used, the start timing of water injection is set using the map for high-octane gasoline.

  However, the area where the air-fuel mixture is formed and the detailed area where water is injected are different between the middle load area A1 and the high load area A2. This will be described next.

(2-3) Medium load region A1
In the middle load region A1, the following injection control is performed.

  First, in the middle load region A1, in order to improve fuel efficiency, fuel is injected into the cavity 19 so that the air-fuel mixture is mainly formed in the cavity 19, and the air-fuel mixture is mainly burned in the cavity 19. In other words, in the middle load region A1, the air-fuel ratio of the air-fuel mixture in the cavity 19 is appropriately increased to realize self-ignition, while the air-fuel ratio in the entire combustion chamber 6 is lean to improve fuel efficiency. Specifically, in the medium load region A1, fuel is injected into the cavity 19 at approximately the middle stage of the compression stroke.

  Thus, in the medium load region A1, combustion of the air-fuel mixture occurs mainly in the cavity 19, and the air-fuel mixture near the outermost peripheral portion of the cavity 19, that is, in the vicinity of the opening edge 19a, burns last. Therefore, in order to shorten the combustion period, it is necessary to suppress a temperature drop near the opening edge 19a of the cavity 19.

  Therefore, in the middle load region A1, the intermediate region R3 shown in FIG. 9 in the cavity 19 immediately before the start of the high-temperature oxidation reaction in the combustion chamber 6 in the late stage of the compression stroke or the early stage of the expansion stroke, Water is jetted.

  Specifically, in the middle load region A1, the first region R1 including the central portion C of the cavity 19 and the second region R2 constituted by the outer peripheral portion of the cavity 19 and the outer peripheral portion of the cavity 19, Then, the area between the line L1 radially inward from the opening edge 19a of the cavity 19 and the second area R2 radially outside is an intermediate area R3, and water is injected into the intermediate area R3. . Specifically, as shown in FIG. 10, water W is injected from the water injector 15 toward a portion slightly inside in the radial direction from the boundary line L1 between the intermediate region R3 and the second region R2. In the example of FIG. 9, the first region R <b> 1 is set to a region centered on the center of the cavity 19 and having a diameter of about ¼ of the diameter of the cavity 19.

(2-4) High load area A2
In the high load region A2, the amount of fuel that must be supplied into the combustion chamber 6 increases as the engine load increases. Therefore, in the high load region A2, fuel is injected into the cavity 19, but the fuel diffuses to the outside in the radial direction with respect to the cavity 19, and an air-fuel mixture is formed almost entirely in the combustion chamber 6.

  Thus, in the high load region A2, the air-fuel mixture is burned almost entirely in the combustion chamber 6, so the air-fuel mixture near the outer peripheral edge of the combustion chamber 6 is burned last. Therefore, in order to shorten the combustion period, it is necessary to suppress a temperature drop near the outer peripheral edge of the cavity 19. Further, in the high load region A2, combustion tends to become steeper due to the high temperature in the combustion chamber 6 and the large amount of fuel.

  Therefore, in the high load region A2, the intermediate region R13 shown in FIG. 11 in the cavity 19 has water in the late stage of the compression stroke or the early stage of the expansion stroke and immediately before the air-fuel mixture starts the high temperature oxidation reaction in the combustion chamber 6. Is injected.

  Specifically, even in the high load region A2, the first region is in a region including the central portion C of the cavity 19 and capable of generating combustion nuclei and in a region substantially the same as the first region R1 of the medium load region A1. R11 is set. On the other hand, in the high load region A2, the region from the outer peripheral edge of the combustion chamber 6 to the line L11 radially outside the opening edge 19a of the cavity 19 and including the outer peripheral portion of the cavity 19 is the second region R12. Is done. And the area | region between these 1st area | region R1 and 2nd area | region R2 is made into intermediate | middle area | region R13, and water is injected into this intermediate | middle area | region R13. That is, in the high load region A2, the region where water is jetted is a region from the line L12 radially inward of the opening edge 19a of the cavity 19 to the line L11 radially outward of the opening edge 19a of the cavity 19. Thus, the region is wider than the medium load region A1.

  Specifically, in the high load region A2, the lift amount of the water injector 15 is made smaller than that in the middle load region A1 to increase the water spray angle, and as shown in FIG. 12, toward the opening edge 19a of the cavity 19 Water W is jetted from the water injector 15. And since the lift amount of the water injector 15 is made small, the particle size of water becomes small and the penetration of water becomes small. Accordingly, in the high load region A2, water is diffused in a wider range than in the medium load region A1, and water is supplied to a region wider than the medium load region A1.

(3) Operation, etc. As described above, in the present embodiment, in the middle load region A1 where the air-fuel mixture is formed in the cavity 19 and the air-fuel mixture mainly burns in the cavity 19, the central portion C in the radial direction of the cavity 19 Water is injected into the intermediate region R3 between the outer peripheral portion and the outer peripheral portion (second region R2) before the high-temperature oxidation reaction of the air-fuel mixture starts in the late compression stroke or early expansion stroke and in the combustion chamber 6. As a result, in the combustion that occurs in the cavity 19, it is possible to suppress the combustion noise by slowing the initial combustion, and to suppress the slow combustion of the latter period and to increase the thermal efficiency.

  Furthermore, in the present embodiment, in the high load region A2 where the air-fuel mixture burns in almost the entire combustion chamber 6, the radially outer peripheral portion (medium of the cavity 19 extends from the radially inner side to the outer region of the opening edge 19a of the cavity 19. A wide area including the second area R2 in the load area A1 is set as the intermediate area R13. Then, water is injected into the intermediate region R13. For this reason, even in the high load region A2, the initial combustion can be made even slower, and the combustion noise can be reliably reduced.

(4) Modification In the above embodiment, air-fuel mixture is formed in the cavity 19 and water is supplied to the intermediate region R3 between the central portion C in the radial direction of the cavity 19 and the outer peripheral portion (second region R2). Although the case where the injection control is performed only in the middle load region A1 has been described, the region in which this control is performed is not limited thereto.

  Moreover, although the said embodiment demonstrated the case where a fuel contains gasoline, the specific kind of fuel is not restricted to this, A naphtha (naphtha) may be sufficient.

  The geometric compression ratio of the engine body is not limited to the above. However, the geometric compression ratio is preferably set as in the above-described embodiment in order to achieve appropriate self-ignition combustion of the air-fuel mixture and obtain high thermal efficiency.

  Moreover, in the said embodiment, the case where water was injected to the area | region different in medium load area | region A1 and high load area | region A2 by changing the lift amount of the water injector 15 by making it the outside opening type was demonstrated. However, the specific configuration for making the water injection region different is not limited thereto. For example, the water injection region may be changed by changing the injection angle using a water injector 15 that can inject water at different injection angles.

  In the above-described embodiment, the case where the fuel is injected into the combustion chamber 6 by the fuel injector 14 has been described. Alternatively, the fuel may be supplied to the intake port 9.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder 5 Piston 5a Piston crown 6 Combustion chamber 14 Fuel injector (fuel supply means)
15 Water injector (water injection means)
100 PCM (control means)
R1 First region R2 Second region R3 Intermediate region R11 First region R12 Second region R13 Intermediate region

Claims (3)

A premixed compression ignition type engine comprising an engine body including a cylinder having a combustion chamber and a piston fitted therein, and capable of self-igniting a fuel-air mixture containing gasoline in the combustion chamber,
The crown surface of the piston includes a cavity recessed in the central region in the radial direction of the piston,
Water injection means for injecting water into the combustion chamber;
Fuel supply means for supplying fuel into the combustion chamber;
Control means for controlling the water injection means and the fuel supply means,
The control means includes
Causing the fuel supply means to supply fuel into the combustion chamber such that the mixture is formed in the cavity and self-ignition of the mixture starts in the cavity; and
Before the air-fuel mixture is subjected to a high-temperature oxidation reaction in the cavity in the latter half of the compression stroke or in the early stage of the expansion stroke, the water injection means is provided between the radially central portion and the outer peripheral portion of the cavity. A premixed compression ignition type engine characterized in that injection control is performed to inject water into a region located in the area. The premixed compression ignition type engine according to claim 1,
The control means performs the injection control in a medium load region in which an engine load is higher than a first reference load indicating a preset low load and lower than a second reference load indicating a high load. A premixed compression ignition engine. The premixed compression ignition engine according to claim 2,
In a high load region where the engine load is equal to or higher than the second reference load, the control means causes the water injection means to be in the late stage of the compression stroke or the early stage of the expansion stroke and before the air-fuel mixture undergoes a high temperature oxidation reaction in the combustion chamber. And water is injected into a region that includes the outer periphery of the cavity and that is located between the radial center of the cavity and the outer periphery of the combustion chamber in the radial direction of the combustion chamber. Premixed compression ignition engine.

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