JP6477847B1 - Premixed compression ignition engine - Google Patents

Abstract

A premixed compression ignition engine capable of reducing combustion noise while realizing high thermal efficiency is provided.
In a premixed compression ignition engine in which self-ignition combustion in which a mixture of fuel and air is combusted by self-ignition in a combustion chamber 6 is performed under predetermined conditions, the mixture is contained in the combustion chamber 6. There is provided an inert substance supply means 15 for supplying an inert substance made of a substance that does not burn during the combustion. When the combustion chamber 6 is divided into the first region R1 including the central portion in the radial direction and the second region R2 outside in the radial direction with respect to the first region R1, the self-ignition combustion is performed during the operation by the self-ignition combustion. The inert substance supply means 15 is controlled so that the concentration of the inert substance in the first region R1 is higher than the concentration of the inert substance in the second region R2 at the time of starting.
[Selection] Figure 3

Description

  The present invention relates to a premixed compression ignition type engine including an engine body having a cylinder in which a combustion chamber is formed, and capable of self-igniting a mixture of fuel and air in the combustion chamber.

  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. On the other hand, in the premixed compression ignition combustion, there is a problem that the pressure in the combustion chamber, that is, the in-cylinder pressure rises rapidly and combustion noise is likely to deteriorate.

  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 of 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 mixture is formed by the pre-stage injection. Thus, the combustion of the air-fuel mixture and the air-fuel mixture formed by the latter-stage injection can be started at different timings, and the rapid increase in the in-cylinder pressure can be suppressed.

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.

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

In order to solve the above problems, the present invention includes an engine body having a cylinder in which a combustion chamber is formed, and self-ignition combustion in which a mixture of fuel and air is burned by self-ignition in the combustion chamber is performed under a predetermined condition. A premixed compression ignition engine executed below, wherein water , which is an inert substance made of a substance that does not burn during combustion of the air-fuel mixture , can be injected into the combustion chamber in a plurality of times. An inert substance supply means; and a control means for controlling the inert substance supply means. The combustion chamber includes a first region including a central portion in the radial direction, and a radially outer side than the first region. When dividing into the second region, the self-ignition combustion starts from the first region, and the control means is configured to start the self-ignition combustion at the start of the self-ignition combustion during the operation by the self-ignition combustion. Inactive in one region Performed inert material supply control for controlling the inert substance feed as towards the concentration of quality is higher than the concentration of the inert material of the second region, the implementation of the inert material supply control Pre-mixing, characterized in that the inert substance supply means performs at least a first injection for injecting water into the second region and a second injection for injecting water into the first region. A compression ignition engine is provided.

  According to this configuration, the combustion period can be shortened while suppressing a rapid increase in the in-cylinder pressure, and high thermal efficiency can be obtained while suppressing combustion noise.

  Specifically, in the combustion chamber, the self-ignition combustion of the air-fuel mixture starts at the central portion in the radial direction that is far from the wall surface of the combustion chamber and has a high temperature, and then spreads to the outer peripheral side. On the other hand, in this structure, many inert substances are present in the first region including the central portion of the combustion chamber at the start of the self-ignition combustion. Therefore, at the time of the initial combustion that occurs in the first region including the central portion of the combustion chamber, it is possible to suppress the rapid increase in the combustion temperature and to slow down the combustion. On the other hand, the concentration of the inert substance in the second region located on the outer peripheral side of the first region is suppressed to a low level. Therefore, it is possible to prevent the combustion from becoming suddenly or excessively slow at the time of combustion in the second region, that is, at the later stage of combustion. Therefore, it is possible to prevent the combustion end time from being delayed while suppressing a rapid increase in the in-cylinder pressure at the initial stage of combustion, thereby shortening the combustion period.

Moreover, since the inert substance is water, the temperature in the combustion chamber can be lowered by the latent heat action of water, and combustion can be made slower.

In addition, by performing the first injection and the second injection, the concentration of water (inert substance) in the first region and the second region can be varied with a relatively simple configuration.

Further, in the above configuration, the control means is configured so that, when the inert substance supply control is performed, a radial direction from a radial center of the combustion chamber toward a vicinity of a boundary between the first region and the second region. It is preferable to control the inert substance supply means so that the concentration of the inert substance increases toward the outer side (Claim 2 ).

  In this case, the temperature gradient in the radial direction in the first region is further reduced by lowering the temperature of the region outside the first region in the radial direction and having a relatively low temperature in the first region. Can be increased. Therefore, the timing at which the air-fuel mixture starts self-ignition in the first region can be varied greatly in the radial direction. That is, the air-fuel mixture can be prevented from self-igniting at once in the first region, and the rapid increase in the in-cylinder pressure can be further suppressed.

  As described above, according to the premixed compression ignition type engine of the present invention, combustion noise can be reduced while realizing 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 block diagram which shows the control system of an engine. It is the figure which showed the control map. It is a schematic sectional drawing of the engine body which showed the range of the 1st field and the 2nd field. It is the figure which showed the density | concentration distribution of the water in a high load area | region. It is the schematic which showed the injection pattern and heat generation rate of the fuel and water in a high load area | region. It is the figure which showed the mode in the combustion chamber in a high load area | region, (1)-(4) has shown the mode in the combustion chamber in a mutually different time. It is the schematic which showed the change of the heat release rate with respect to a crank angle. It is the figure which showed the other example of the density | concentration distribution of the water in a high load area | region. It is a schematic sectional drawing of the engine main body which showed the other example of the water-injection structure. It is the schematic which showed the other example of the injection pattern of a fuel and water in a high load area | region, and a heat release rate.

  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.

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

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

  A combustion chamber 6 is formed above the piston 5. The combustion chamber 6 is a so-called pent roof type, and the ceiling surface 6a of the combustion chamber 6 formed by the lower surface of the cylinder head 4 (hereinafter simply referred to as the combustion chamber ceiling surface 6a) is formed from two inclined surfaces on the intake side and the exhaust side. It has a triangular roof shape. A cavity 19 is formed in the crown surface 5a of the piston 5 (hereinafter, simply referred to as the piston crown surface 5a) in which a region including the center portion is recessed on the side opposite to the cylinder head 4 (downward). Here, the space between the piston crown surface 5 a and the combustion chamber ceiling surface 6 a 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 15 or more and 30 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 an injector (fuel injection means) 14 for injecting fuel. The injector 14 is attached so that the tip portion where the injection port is formed is located near the center of the combustion chamber ceiling surface 6a and faces the center of the combustion chamber 6. The 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 combustion chamber ceiling surface 6a toward the piston crown surface 5a. 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 injector 14. The injector 14 may have any configuration as long as it can inject fuel in a cone shape around the central axis of the cylinder 2 as described above. VCO (Valve Covered Orifice) nozzle type injectors, multi-hole type injectors having a plurality of injection holes at the tip and injecting fuel at a predetermined spray angle, and swirl injectors injecting fuel in a holo-cone shape It may be.

  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.

  As shown in FIG. 3, which is a schematic sectional view of the combustion chamber 6, the cylinder head 4 is further provided with a water injector (non-injection) that injects water, which is an inert substance that does not burn during combustion of the air-fuel mixture, into the combustion chamber 6. Active substance supply means) 15 is provided. The water injector 15 is attached so that the tip portion where the injection port is formed is located near the center of the combustion chamber ceiling surface 6a and faces the center of the combustion chamber 6. The water injector 15 is configured to inject water 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 combustion chamber ceiling surface 6a toward the piston crown surface 5a. Yes. The taper angle (spray angle) of this cone is, for example, 90 ° to 100 °. As the water injector 15, for example, an apparatus having the same structure as the injector 14 can be applied. The injector 14 and the water injector 15 are arranged close to each other in a direction orthogonal to the paper surface of FIG.

  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 31 and a condenser 32 for purifying exhaust gas in order from the upstream side. The purification device 31 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 40 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 40 opens and closes an EGR passage 41 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 31, and the EGR passage 41. An EGR valve 42 is provided. In the present embodiment, the EGR passage 41 is provided with an EGR cooler 43 for cooling the EGR gas passing through the EGR passage 41, and the EGR gas is cooled by the EGR cooler 43 and then returned to the intake passage 20. The

(2) Control System (2-1) System Configuration FIG. 4 is a block diagram showing an engine control system. As shown in FIG. 4, 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 injector 14, and the water injector 15.

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

  Specifically, fuel is injected from the injector 14 into the combustion chamber 6 before the compression top dead center. Then, the temperature of the fuel / air mixture is increased by compressing the fuel and air, and self-ignition is performed near the compression top dead center.

  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, in the CI combustion, when the engine load increases, the temperature in the combustion chamber 6 increases and the air-fuel mixture in the combustion chamber 6 burns at once (very in a short time). The pressure in the cylinder, 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.

  Therefore, in the present embodiment, in the high load region A1 where the engine load is equal to or higher than a preset reference load Tq1 in the control map of FIG. 5 in which the horizontal axis is the engine speed and the vertical axis is the engine load, combustion noise and NOx. In order to suppress the generation of the above, the high load control described below is performed.

  In the high load region A1, water is injected into the combustion chamber 6. At this time, immediately before the air-fuel mixture starts self-ignition (hereinafter, appropriately referred to as self-ignition start time), the concentration of water in the first region R1 including the central portion C in the radial direction of the combustion chamber 6 is the first. Control is performed so as to be higher than the concentration of water in the second region radially outside the first region R1 (inert substance supply control is performed). Specifically, the local water concentration at each location in the first region R1 is controlled to be higher than the local water concentration at each location in the second region R2.

  As shown in FIGS. 3 and 6, in the present embodiment, a region where the cavity 19 is formed is set as the first region R <b> 1 when viewed from the direction along the central axis of the cylinder 2. Specifically, when the line X1 is drawn slightly radially outward from the opening edge 19a of the cavity 19 in a top view, a region radially inward from the line L10 is set as the first region R1. The second region R2 is set in the entire region in the radial direction of the combustion chamber 6 rather than the first region R1.

  Further, in the present embodiment, at the time of starting self-ignition, the water concentration is controlled so as to be different in the radial direction even in each of the regions R1 and R2.

  FIG. 7 is a diagram showing the concentration distribution of water in the high load region A1. The horizontal axis in FIG. 7 is the distance in the radial direction from the center of the combustion chamber 6 (a point on the central axis of the cylinder 2), and the vertical axis in FIG. 7 is the water concentration (local water at each location). Density).

  As shown in FIG. 7, in the present embodiment, radially outward from the center C of the combustion chamber 6 toward the opening edge 19a of the cavity 19 located near the boundary line X1 between the first region R1 and the second region R2. The higher the water concentration, the higher the water concentration. Further, the concentration of water decreases as it goes radially outward from the opening edge 19 a of the cavity 19 toward the outer peripheral edge of the combustion chamber 6.

  Thus, in the present embodiment, in the high load region A1, the concentration of water in the first region R1 is made higher than the concentration of water in the second region R2 at the start of self-ignition. Further, in the first region R1, the concentration of water is increased toward the outside in the radial direction except for the vicinity of the boundary line X1 with the second region R2. Further, in the second region R2, the concentration of water is lowered toward the outer side in the radial direction.

  In order to realize the water concentration distribution as described above, in the high load region A1, water and fuel are injected as shown in FIG.

  FIG. 8 is a diagram schematically showing the fuel injection pattern, the water injection pattern, and the heat generation rate dQ in the high load region A1. FIG. 9 is a diagram schematically showing the inside of the combustion chamber 6 in the high load region A1. 9 (1) to (4), the time has passed in this order, and (1) to (4) in FIG. 9 show the inside of the combustion chamber 6 during the compression stroke.

  As shown in (1) of FIG. 8 and FIG. 9, the water injector 15 first performs the first water injection W11 mainly for unevenly distributing water in the second region R2. In the first water injection W11, as shown in (1) of FIG. 9, the water injector 15 injects water at the timing when the water scatters toward the portion slightly outside the opening edge 19a of the cavity 19 in the radial direction. To do. In the present embodiment, the first water injection W11 is performed in the middle of the compression stroke. In this specification, the first, middle, and second half of the XX process, such as the compression process, refer to the first, middle, and second half when this process is divided into three equal parts. This refers to the first half and the second half when the process is divided into two equal parts.

  After a while after the first water injection W11 is performed, as shown in FIG. 9 (2), the water injected by the first water injection W11 is divided into the second region R2 and the region radially inward from this. It spreads to the containing area. At this time, as the volume is larger on the outer side in the radial direction, the concentration of water decreases from the vicinity of the opening edge 19a of the cavity 19 toward the outer side in the radial direction.

  Next, the water injector 15 performs the second water injection W12 for causing water to be unevenly distributed in the first region R1. In the second water injection W12, as shown in (3) of FIG. 9, the water injector 15 injects water at a timing when the water scatters toward a portion slightly inward in the radial direction from the opening edge 19a of the cavity 19. To do. In the present embodiment, the second water injection W12 is performed at the latter stage of the compression stroke.

  By the second water jet W12, water is also introduced into the cavity 19 as shown in FIG. Here, the space inside the cavity 19 has a small volume. Therefore, the concentration of water in the inner space of the cavity 19 is increased. Further, the water is scattered toward the inner portion in the radial direction slightly from the opening edge 19 a of the cavity 19, so that the concentration of water increases from the central portion C of the combustion chamber 6 toward the vicinity of the opening edge 19 a of the cavity 19. Become. Further, a relatively large amount of water already exists in the vicinity of the opening edge 19a of the cavity 19 due to the first water jet W11. For this reason, the water and the water from the second water jet W12 are combined to increase the concentration of water near the opening edge 19a of the cavity 19. Thus, after the second water injection W12, the concentration distribution of water in the combustion chamber 6 becomes as shown in FIG.

  Next, fuel is supplied into the combustion chamber 6 by the injector 14. For example, the fuel injection F11 is performed immediately after the second water injection W12 and before the compression top dead center. In the high load region A1, only one fuel injection F11 is performed in one combustion cycle, and at this time, an amount of fuel corresponding to the required engine torque is injected. Specifically, in the present embodiment, the air-fuel ratio in the combustion chamber 6 is set to the stoichiometric air-fuel ratio in the high load region A1. First, an amount of air corresponding to the required engine torque is introduced into the combustion chamber 6, and an amount of fuel such that the air-fuel ratio becomes the stoichiometric air-fuel ratio according to the amount of air introduced into the combustion chamber 6. Is injected.

  The fuel supplied into the combustion chamber 6 by the fuel injection F11 is mixed with air, and the formed air-fuel mixture self-ignites near the compression top dead center.

  Thus, in the present embodiment, the air-fuel mixture self-ignites with the water concentration distribution as shown in FIG.

(3) Operation, etc. The reason why the generation of combustion noise and NOx can be suppressed by implementing the high load control, that is, the operation of high load control will be described.

  FIG. 10 is a graph in which the horizontal axis represents the crank angle and the vertical axis represents the heat generation rate. FIG. 10 shows a heat generation rate dQ2 (solid line) when high load control is performed and a heat generation rate dQ1 (broken line) when high load control is not performed as a comparative example. In the comparative example, the fuel injection F11 is performed similarly to the case where the high load control is performed (same timing and the same injection amount). On the other hand, unlike the case where the high load control is performed, the first water injection W11 and the second water injection W12. And do not implement.

  In the comparative example, the heat generation rate rises rapidly after compression top dead center. That is, after the air-fuel mixture starts self-ignition at the crank angle CA1, many air-fuel mixtures burn at once (in a very short time). As a result, in the comparative example, the in-cylinder pressure rises rapidly and high combustion noise is generated. In addition, the in-cylinder temperature rapidly rises and a large amount of NOx is generated.

  Here, the outer peripheral portion of the combustion chamber 6 is cooled by the wall surface of the combustion chamber 6, so that the temperature is relatively low, and the temperature of the central portion is the highest in the combustion chamber 6. Therefore, the self-ignition of the air-fuel mixture first occurs in the center portion in the combustion chamber 6, and then sequentially occurs radially outward. Therefore, in the comparative example, in the vicinity of the crank angle CA1, the central portion of the combustion chamber and the air-fuel mixture around it are combusting all at once.

  On the other hand, in the present embodiment, a large amount of water is unevenly distributed (at a high concentration) in the first region R1 including the central portion of the combustion chamber immediately before the start of self-ignition by performing the high load control. Therefore, before combustion, the temperature of the first region R1 can be lowered by the latent heat action of water. Furthermore, the temperature rise of 1st area | region R1 can be suppressed because the specific heat is raised with a lot of water at the time of combustion. Therefore, the air-fuel mixture in the first region R1 can be prevented from burning rapidly.

  In particular, in the present embodiment, the concentration of water is increased toward the radially outer side in the first region R1. Therefore, the combustion in the first region R1 can be further slowed down.

  Specifically, as described above, the temperature in the combustion chamber 6 decreases as it goes radially outward, but in addition, the concentration of water in the first region R1 increases as it goes radially outward. Thus, the temperature in the first region R1 becomes lower as it goes outward in the radial direction. That is, the temperature gradient in the first region R1 is increased by setting the water concentration as described above. Therefore, in the first region R1, the timing at which the air-fuel mixture starts self-ignition can be more reliably varied in the radial direction (can be made slower toward the outer side in the radial direction), and the mixing in the first region R1 It is possible to suppress the burning of qi at a stretch.

  In this way, in the present embodiment, as shown by the solid line in FIG. 10, the combustion after the start of self-ignition of the air-fuel mixture at the crank angle CA1 and the initial combustion becomes slow (the rate of heat generation is reduced). The slope becomes gentle.) Therefore, in this embodiment, the rapid increase of the in-cylinder pressure and the in-cylinder temperature can be suppressed, and the generation amount of combustion noise and NOx can be reduced.

  Here, if the combustion is only slowed, for example, there is a method in which a large amount of water is simply present in the entire combustion chamber 6 at a uniform concentration. However, in this method, as shown by the chain line in FIG. 10, combustion is performed at the outer peripheral side portion of the combustion chamber 6, and combustion in the later stage of combustion is also slow. Therefore, the end time of combustion is delayed (the combustion period is lengthened), and the thermal efficiency is deteriorated.

  In contrast, in the present embodiment, the concentration of water in the second region R2 located on the outer peripheral side of the combustion chamber 6 is made smaller than that in the first region R1. Therefore, it is possible to prevent the combustion in the second region R2, that is, the combustion in the later stage of combustion, from becoming excessively slow, and to shorten the combustion period.

  In particular, in the present embodiment, in the second region R2, the concentration of water is reduced toward the outer side in the radial direction, and the temperature drop near the outer peripheral edge of the combustion chamber 6 due to water is suppressed to be small. Therefore, it is possible to more reliably avoid excessively slow combustion in the vicinity of the outer peripheral edge of the combustion chamber 6 and to more reliably suppress the combustion period.

  As described above, in the present embodiment, it is possible to prevent the combustion in the second region R2 from being excessively slow and the combustion in the second region R2 while slowing the combustion in the first region R1. It is possible to ensure high thermal efficiency while suppressing the generation amount of noise and NOx.

(4) Modification In the above embodiment, the case where the concentration of water is controlled so as to increase radially outward from the central portion C in the first region R1 has been described. The concentration of may be uniform. Similarly, the concentration of water in the second region R2 may be uniform. Further, the water concentration distribution may be in a form as shown by a solid line or a chain line in FIG.

  In the embodiment, the first water injection W11 is performed in the middle of the compression stroke, the second water injection W12 is performed in the latter half of the compression stroke, and the fuel injection F11 is performed immediately before the compression top dead center. Although explained, the specific time of these injections is not restricted to this.

  Further, the number of water injections may be two or more. For example, the water jetted by the first water jet W11 may be jetted in two more steps.

  Moreover, although the said embodiment demonstrated the case where the density | concentration of water was made to differ in 1st area | region R1 and 2nd area | region R2 by changing the injection timing of the water injector 15, the density | concentration of water was changed to area | region. The concrete means for making it differ for every R1 and R2 is not restricted to this. For example, a water injector 15 that can inject fuel into different regions, such as one that can inject water at different injection angles, is used to change the first region R1 and the first region by changing the injection region. You may change the density | concentration of water in 2 area | region R2.

  Moreover, although the said embodiment demonstrated the case where water was supplied in the combustion chamber 6 only using the water injector 15 which injects water in the combustion chamber 6, in addition to this water injector 15 (2nd means), As shown in FIG. 12, a water injection device (first means) 115 for injecting (supplying) water to the intake port 9 is provided, and water is supplied into the combustion chamber 6 using these. May be.

  In this case, as shown in FIG. 13, the first water injection W101 for injecting water into the intake port 9 is performed by the water injection device 115 before the timing at which the intake valve 11 is closed (intake valve closing timing). Similarly to the above-described embodiment, the second water injection W102 for injecting water into the combustion chamber 6 by the water injector 15 is performed in the latter half or the latter half of the compression stroke. Even in this case, when the water supplied by the first water injection W101 is diffused almost throughout the combustion chamber 6, the water is supplied to the second region R2 by the second water injection device 115. The concentration of water in the second region R2 can be made higher than the concentration of water in the first region R1.

  Moreover, although the said embodiment demonstrated the case where water was used as an inert substance for making combustion slow, exhaust gas, nitrogen, etc. which are distribute | circulating the exhaust passage 30 instead of water were used as an inert substance. It may be used.

  However, if water is used, the temperature in the combustion chamber 6 can be further lowered by the latent heat action.

  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, although the said embodiment demonstrated the case where the supercharger was not provided in the engine system, the said embodiment may be applied to the engine system provided with the supercharger. In an engine system equipped with a supercharger, the temperature in the combustion chamber 6 becomes higher due to supercharging. Therefore, if the embodiment is applied to this system, combustion noise can be effectively increased while increasing thermal efficiency or increasing engine torque. And the amount of NOx produced can be reduced.

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder 6 Combustion chamber 14 Injector 15 Water injector (Inert substance supply means, 2nd means)
19 cavity 100 PCM (control means)
115 Water injection device (first means)
R1 first region R2 second region

Claims (2)

A premixed compression ignition type engine having an engine body having a cylinder in which a combustion chamber is formed, wherein self-ignition combustion in which a mixture of fuel and air is burned by self-ignition in the combustion chamber is performed under predetermined conditions. There,
An inert substance supply means capable of injecting water , which is an inert substance made of a substance that does not burn during combustion of the air-fuel mixture , into the combustion chamber in a plurality of times ;
Control means for controlling the inert substance supply means,
When the combustion chamber is divided into a first region including a central portion in the radial direction and a second region outside the first region in the radial direction, the self-ignition combustion starts from the first region. Because
In the operation by the self-ignition combustion, the control means is configured such that the concentration of the inert substance in the first region is higher than the concentration of the inert material in the second region at the start of the self-ignition combustion. Inert substance supply control for controlling the inert substance supply means so as to be higher , and at the time of performing the inert substance supply control, water is supplied to at least the second region in the inert substance supply means. A premixed compression ignition engine characterized in that a first injection to be injected and a second injection to inject water into the first region are performed . The premixed compression ignition type engine according to claim 1 ,
When the inert substance supply control is performed, the control means is configured such that the inert substance is located toward the outer side in the radial direction from the radial center of the combustion chamber toward the vicinity of the boundary between the first area and the second area. The premixed compression ignition type engine is characterized in that the inert substance supply means is controlled so that the concentration of the mixture increases.

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