JP6477848B1 - Premixed compression ignition engine - Google Patents

Abstract

The present invention provides a premixed compression ignition engine capable of suppressing discharge of unburned fuel while realizing high thermal efficiency.
In a premixed compression ignition engine capable of self-igniting a fuel / air mixture in a combustion chamber, water injection means for injecting water into the combustion chamber, And a fuel supply means 15 for injecting fuel. The fuel supply means 14 supplies fuel into the combustion chamber 6 before the compression top dead center so that the air-fuel mixture starts self-ignition in the combustion chamber 6 in the medium load region A1. Further, fuel is supplied to the water injection means 15 so that water is unevenly distributed in the radially outer peripheral portion R2 in the combustion chamber 6 when the air-fuel mixture starts self-ignition in the combustion chamber 6 in the medium load region A1. Water is injected into the combustion chamber 6 after the fuel is supplied to the combustion chamber 6 by the means 14 until the self-ignition of the air-fuel mixture starts.
[Selection] Figure 7

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, in an engine in which fuel including gasoline is used, a combustion mode in which the air-fuel mixture is forcibly ignited by spark ignition of a spark plug and then the air-fuel mixture in the combustion chamber is combusted by flame propagation has been common. In place of such a combustion mode, research is being carried out to so-called premixed compression ignition combustion of a mixture of fuel containing gasoline and air.

  Premixed compression ignition combustion is a combustion mode in which fuel containing gasoline and air are mixed in advance, and this mixture is self-ignited in a high-temperature and high-pressure environment. It is said that the thermal efficiency can be increased along with the fact that a higher compression ratio is possible.

  For example, Patent Document 1 discloses an engine in which self-ignition of an air-fuel mixture is induced by spark ignition by a spark plug.

JP 2012-241590 A

  In premixed compression ignition combustion, it is necessary to raise the mixture to a temperature at which self-ignition is possible. However, in the vicinity of the wall surface of the combustion chamber, the temperature of the air-fuel mixture can be kept low by releasing heat energy to the outside of the combustion chamber. For this reason, when the temperature in the combustion chamber is relatively low, the air-fuel mixture in the vicinity of the wall surface of the combustion chamber does not properly self-ignite, and there is a possibility that unburned substances such as CO discharged outside the combustion chamber increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a premixed compression ignition engine capable of suppressing discharge of unburned fuel while realizing high thermal efficiency.

In order to solve the above-mentioned problems, the present invention includes a premixed compression ignition engine that includes an engine body having a cylinder in which a combustion chamber is formed, and is capable of self-igniting a mixture of fuel and air in the combustion chamber. The water injection means for injecting water into the combustion chamber; fuel supply means for supplying fuel into the combustion chamber; and control means for controlling the water injection means and the fuel supply means. In the fuel supply means, the air-fuel mixture starts self-ignition in the combustion chamber in an intermediate load region set in an operation region excluding an operation region where the engine load is minimum and an operation region where the engine load is maximum. The fuel is supplied into the combustion chamber before the compression top dead center, and the water injection means causes the water injection means to start self-ignition in the combustion chamber in the intermediate load region. So that the direction to the outer peripheral portion of water is unevenly distributed, during the compression stroke after the intake valve is closed for opening and closing the intake port for introducing intake air into the combustion chamber, and, to the combustion chamber by the fuel supply means Provided is a premixed compression ignition engine characterized in that water is injected into the combustion chamber between the time when fuel is injected and the time when self-ignition of the air-fuel mixture starts.

  According to this configuration, it is possible to suppress the discharge of unburned substances such as CO in the medium load region and to increase the thermal efficiency.

  Specifically, unburned fuel tends to remain in the radially outer peripheral portion of the combustion chamber in the medium load region. This is because the temperature of the outer peripheral portion of the combustion chamber is kept low by being cooled by the wall surface of the combustion chamber in addition to the relatively low engine load. On the other hand, if water is unevenly distributed on the outer periphery of the combustion chamber in a high temperature and high pressure state where the air-fuel mixture starts self-ignition, the water chemically reacts to promote combustion. More specifically, when water is supplied to the combustion chamber in a high-temperature and high-pressure state, it is vaporized to become water vapor and OH radicals increase. This OH radical has a strong oxidizing action. Therefore, if water is unevenly distributed in the outer peripheral portion of the combustion chamber when the air-fuel mixture starts self-ignition, combustion of the outer peripheral portion can be promoted and discharge of unburned substances such as CO can be suppressed. Further, if the combustion at the outer peripheral portion of the combustion chamber is promoted, the combustion period can be shortened. Therefore, thermal efficiency can be increased.

  In addition, in this configuration, since water is injected after the fuel is supplied into the combustion chamber, the flow formed in the combustion chamber by the fuel injection suppresses the movement of water from the outer peripheral portion to the central portion side. Thus, water can be more unevenly distributed on the outer periphery of the combustion chamber.

  And according to this structure, since the discharge | emission of an unburned substance is suppressed and thermal efficiency is maintained highly as mentioned above, in order to implement | achieve these, it is not necessary to make the start time of combustion early. That is, according to this configuration, it is possible to delay the start time of combustion. Therefore, it is possible to suppress the discharge of unburned substances and increase the thermal efficiency while suppressing the sudden rise in the in-cylinder pressure generated in the early stage of combustion and the combustion noise.

  In the above configuration, it is preferable that the control means ignites the air-fuel mixture by the ignition means in the medium load region (claim 2).

  According to this configuration, even when the temperature of the air-fuel mixture becomes excessively low due to the latent heat action of water, the air-fuel mixture can be self-ignited more reliably in the middle load region.

  In the above configuration, it is preferable that the control means injects water so that the volume concentration of water in the outer peripheral portion of the combustion chamber is 5% or more in the medium load region.

  In this way, more OH radicals can be unevenly distributed in the outer peripheral portion of the combustion chamber in the medium load region.

  In the above configuration, it is preferable that the geometric compression ratio of the engine body is set to 13 or more and 25 or less, and the effective compression ratio of the engine body is set to 11 or more and 23 or less in the medium load region. (Claim 4).

  According to this configuration, the thermal efficiency can be more reliably increased by the high compression ratio.

  As described above, according to the premixed compression ignition type engine of the present invention, it is possible to suppress discharge of unburned fuel 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 the graph which showed the relationship between the reaction rate and temperature of reaction with which OH radical is produced | generated from water. It is the schematic which showed the injection pattern and heat release rate of the fuel and water in a medium 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.

(1) Overall Engine Configuration 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 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 geometric compression ratio is set to 13 or more and 25 or less (for example, about 20). However, the effective compression ratio of the engine body is changed by changing the closing timing of the intake valve. In the present embodiment, the effective compression ratio of the engine body is set to 11 or more and 23 or less (for example, about 18) in a middle load region A1 described later. That is, the closing timing of the intake valve 18 is set so that this is realized.

  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 supply 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 (water) that injects water, which is an inert substance that does not burn during combustion of the air-fuel mixture, into the combustion chamber 6. (Injection 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, when the engine load is relatively low and the temperature in the combustion chamber 6 is relatively low, the air-fuel mixture at the outer peripheral portion in the radial direction of the combustion chamber 6 and in the vicinity of the wall surface of the combustion chamber 6 is not completely combusted. Many unburned substances such as HC are easily generated. That is, the wall surface of the combustion chamber 6 is cooled by engine cooling water or the like. Therefore, the temperature of the outer peripheral part of the combustion chamber 6 close to the wall surface of the combustion chamber 6 can be kept low. Thus, when the temperature in the combustion chamber 6 is relatively low, the combustion of the air-fuel mixture tends to be incomplete combustion in the outer peripheral portion of the combustion chamber 6.

  On the other hand, the inventors of the present application focused on OH radicals generated from water, and suppressed emission of CO and the like by OH radicals.

Specifically, when water is injected into the high-temperature combustion chamber 6, OH radicals are generated. The OH radical has a strong oxidizing action. Therefore, even when the air-fuel mixture is incompletely combusted, if water is supplied into the air-fuel mixture, OH radicals generated from water react with CO and HC (to oxidize CO and HC), and CO ₂ or H ₂ O.

  However, the central portion of the combustion chamber 6 in the radial direction is far from the wall surface of the combustion chamber 6 and has a high temperature. For this reason, when water is supplied to the central portion of the combustion chamber 6, the combustion in the central portion of the combustion chamber 6 becomes excessively fast due to the action of the generated OH radicals, and the in-cylinder pressure may rise rapidly to cause combustion noise.

  Therefore, in the present embodiment, water is supplied into the combustion chamber 6 so that water is unevenly distributed on the outer peripheral portion R2 of the combustion chamber 6.

  In the present embodiment, as shown in FIG. 3, a region R <b> 2 radially outside the opening edge 19 a of the cavity 19 when viewed from the direction along the central axis of the cylinder 2 is set as the outer peripheral portion of the combustion chamber 6. . That is, the internal space of the combustion chamber 6 is defined as a second region R2 in a region radially outward from the opening edge 19a of the cavity 19 and a first region R1 in a region radially inward of the second region R2. Water is unevenly distributed in the two regions R2.

  Further, the temperature inside the combustion chamber 6 is low in a region where the engine load is particularly low. Therefore, if water is supplied to the combustion chamber 6 in this region, the temperature in the combustion chamber 6 is further lowered by the latent heat action of water, and as a result, the self-ignition of the air-fuel mixture itself may be hindered.

  Therefore, in the present embodiment, water is supplied into the combustion chamber 6 in the medium load region set in the operation region excluding the operation region where the engine load is minimum and the maximum operation region. As shown in the control map of FIG. 5, in the middle load region A1, the engine load is set to a value equal to or lower than a preset second reference load Tq1 and lower than the first reference load Tq2 (first reference load Tq1). ) The above region A1 is set to a region A1 in which the temperature in the combustion chamber 6 is not excessively lowered by the latent heat action of water, but unburned CO is easily generated.

  In the middle load region A1, the self-ignition of the air-fuel mixture may be hindered by the latent heat action of water. Therefore, in the present embodiment, in order to surely cause the self-ignition of the air-fuel mixture, the air-fuel mixture is ignited by the spark plug in the middle load region A1 to induce self-ignition of the air-fuel mixture.

  Further, as shown in FIG. 6, it is known that OH radicals can be generated more reliably if the volume concentration of water is 5% or more. Therefore, in the present embodiment, water is supplied to the combustion chamber 6 so that the concentration of water in the second region R2 is 5% or more (for example, about 10%).

  FIG. 6 is a graph showing the relationship between the temperature of the reaction shown in the following (1) in the combustion chamber 6, that is, the reaction of generating OH radicals from water and the temperature.

  Three lines L <b> 1 to L <b> 3 in FIG. 6 are lines when water is supplied into the combustion chamber 6. In each of the lines L1 to L3, the amount of supplied water is different. Line L1 is a line when supplying an amount of water having a volume concentration of 5% in the combustion chamber 6, and Line L2 is a line when supplying an amount of water having a volume concentration of 10% in the combustion chamber 6. The line L3 is a line when supplying an amount of water whose volume concentration is 20%. On the other hand, the line L0 is a line when water is not supplied.

In FIG. 6, the area above the line where the reaction rate is 0 is an area where a reaction in the right direction occurs in the reaction equation (1). On the other hand, the area below the 0 line is an area where a reaction in the left direction occurs in the reaction formula (1). For example, when the volume concentration of water is 5% and the temperature is T1, the point is X1 on the line L1, and at this time, the reaction (H ₂ + OH → H ₂ O + H) in the right direction of the reaction formula (1) occurs. On the other hand, when the volume concentration of water is 5% and the temperature is T2, the point X2 on the line L1 is obtained, and at this time, the leftward reaction (H ₂ O + H → H ₂ + OH) of the reaction formula (1) occurs. When the temperature exceeds about 1000 K, the rate of the reaction (H ₂ + OH → H ₂ O + H) in the right direction of the reaction formula (1) increases as the temperature increases. However, when the temperature rises to some extent, the reaction rate decreases, and when the temperature rises further, the leftward reaction (H ₂ O + H → H ₂ + OH) of reaction formula (1) begins to occur, and OH radicals are generated from water. .

  And as FIG. 6 shows, if the volume concentration of water shall be 5% or more, OH radical will be produced | generated reliably. Therefore, in the present embodiment, as described above, water is supplied to the outer peripheral portion of the combustion chamber 6 so that the concentration of water in the outer peripheral portion of the combustion chamber 6 is 5% or more. As the volume concentration of water increases, OH radicals can be generated in a wider temperature range, and the OH radical generation rate increases.

  Next, the water and fuel injection pattern in the medium load region A1 will be described.

  FIG. 7 is a diagram schematically showing the fuel injection pattern, the water injection pattern, and the heat generation rate dQ in the medium load region A1. FIG. 8 is a diagram for explaining the procedure for forming the air-fuel mixture in the medium load region A1. 8 (1) to (4) have elapsed in this order, and (1) to (4) in FIG. 8 show the state in the combustion chamber 6 during the compression stroke.

  As shown in (1) of FIG. 7 and FIG. 8, first, fuel injection F <b> 11 is performed, and fuel is injected into the combustion chamber 6 by the injector 14.

  For example, the fuel injection F11 is performed in the first half of the compression stroke. In the medium load region A1, only one fuel injection F11 is performed in one combustion cycle, and an amount of fuel corresponding to the required engine torque is in the combustion chamber 6 in the first half of the compression stroke. Is injected into. Specifically, in the present embodiment, the air-fuel ratio in the combustion chamber 6 is leaner (larger) than the stoichiometric air-fuel ratio in the medium load region A1, and first, the air corresponding to the required engine torque. Is introduced into the combustion chamber 6 and an amount of fuel is injected such that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio with respect to the amount of air.

  In the present specification, the first half and the second half of the XX stroke such as the compression stroke indicate the first half and the second half when the stroke is divided into two equal parts.

  After a while after the fuel injection F11, the fuel diffuses throughout the combustion chamber 6 as shown in FIG.

  Next, as shown in (3) of FIG. 7 and FIG. 8, water injection W11 is performed.

  As shown in FIG. 8 (3), the water injection W11 is such that the water injected from the water injector 15 is slightly radially inward of the outer peripheral edge of the combustion chamber 6, that is, the outer peripheral edge of the piston crown surface 5a. It is carried out at the timing of flying toward. In the present embodiment, the water injection W11 is performed in the latter half of the compression stroke and at a time slightly advanced from the compression top dead center.

  In the present embodiment, as described above, in the water injection W11, an amount of water is injected such that the volume concentration of water in the second region R2 is 5% or more. That is, an amount of water corresponding to 5% of the volume of the second region R2 is injected.

  The water jetted by the water jet W11 diffuses into the second region R2, and the water is unevenly distributed in the second region R2 as shown in (4) of FIG.

  Here, the fuel injection F11 is performed before the water injection W11. Therefore, it is prevented that the injected water is diffused throughout the combustion chamber 6 by the fuel spray. That is, even if water is injected near the second region R2 as described above, if fuel is subsequently injected, a large flow occurs in the combustion chamber 6 due to this fuel injection, and the water in the second region R2 burns. There is a risk of spreading throughout the chamber 6. On the other hand, since the fuel injection F11 is performed before the water injection W11, this water diffusion can be prevented and water can be more unevenly distributed in the second region R2.

  Thereafter, as shown in FIG. 7, the air-fuel mixture is ignited by the spark plug 13 near the compression top dead center, and self-ignition of the air-fuel mixture starts near the compression top dead center.

  Thus, in the present embodiment, in the medium load region A1, water is unevenly distributed in the second region R2 during combustion of the air-fuel mixture, and the air-fuel mixture burns in a state where a large amount of OH radicals exist in the second region R2. .

  Note that, in the region where the engine load is less than the first reference load Tq1, as described above, the water injection is stopped so that the self-ignition of the air-fuel mixture occurs reliably.

(3) Action, etc. As described above, in the present embodiment, in the middle load region A1, the water is unevenly distributed in the outer peripheral portion (second region R2) of the combustion chamber 6 before the air-fuel mixture self-ignites. A large amount of OH radicals can be present at the outer peripheral portion during combustion of the air-fuel mixture at the outer peripheral portion of the chamber 6. Therefore, the combustion of the air-fuel mixture can be promoted by the oxidizing action of OH radicals at the outer peripheral portion of the combustion chamber 6, and the production of unburned substances such as CO and HC can be suppressed. Even if the combustion chamber becomes incomplete due to cooling to the wall surface of the combustion chamber 6 at the outer peripheral portion of the combustion chamber 6 and unburned substances such as CO and HC are generated, these are oxidized by OH radicals to produce CO. ₂ or H ₂ O.

  In addition, as described above, combustion is promoted at the outer peripheral portion of the combustion chamber 6, so that the combustion period in the combustion chamber 6 can be shortened and the thermal efficiency can be increased.

  Specifically, the self-ignition combustion of the air-fuel mixture starts from the central portion in the radial direction that is far from the wall surface of the combustion chamber 6 and has a high temperature, and then spreads to the outer peripheral side. Therefore, the air-fuel mixture in the outer peripheral portion of the combustion chamber 6 is generated at the later stage of combustion, that is, at the retard side from the compression top dead center and at a timing when the retard amount is large. Therefore, if the combustion at the outer peripheral portion of the combustion chamber 6 becomes slow, the combustion period becomes longer and the thermal efficiency is deteriorated. On the other hand, in this embodiment, since the combustion of the outer peripheral part 6 of the combustion chamber 6 is promoted as described above, the combustion period can be shortened.

  In particular, in this embodiment, since water is injected after fuel is supplied into the combustion chamber 6, it is possible to suppress the flow formed in the combustion chamber 6 by fuel injection from diffusing water. Therefore, water can be unevenly distributed on the outer peripheral portion of the combustion chamber 6 more reliably.

  Further, in the present embodiment, it is not necessary to advance the start timing of combustion in order to suppress the discharge of unburned substances and / or to increase the thermal efficiency, thereby reducing the combustion noise and reducing the amount of NOx generated. It becomes possible.

  This will be specifically described with reference to FIG. FIG. 9 is a graph schematically showing the relationship between the crank angle and the heat generation rate dQ in the medium load region A1. The solid line in FIG. 9 represents the heat generation rate dQ2 when the control of the present embodiment is performed (when water is injected to the outer peripheral portion of the combustion chamber 6). The heat generation rate dQ1 indicated by a broken line and the heat generation rate dQ3 indicated by a chain line in FIG. 9 are heat generation rates when water is not injected into the combustion chamber 6, respectively.

  As indicated by the chain line, when water is not injected into the combustion chamber 6 and when the combustion start timing is relatively late, the combustion at the outer peripheral portion of the combustion chamber 6 becomes slow and the combustion period. Becomes longer and thermal efficiency decreases. In addition, the timing at which the air-fuel mixture burns at the outer peripheral portion of the combustion chamber 6 is delayed and the temperature at the outer peripheral portion of the combustion chamber 6 is lowered, so that the amount of emission of CO and the like increases.

  On the other hand, if the combustion start timing is advanced as shown by the broken line, the combustion period can be shortened to increase the thermal efficiency, and the combustion at the outer peripheral portion of the combustion chamber 6 is close to the compression top dead center and the temperature is high. CO 2 emission can be suppressed. However, in this case, the heat generation rate rises rapidly in the early stage of combustion. That is, the combustion in the combustion chamber 6 becomes abrupt. Therefore, the pressure in the combustion chamber 6, that is, the in-cylinder pressure rises rapidly, and the combustion noise increases. Further, the temperature in the combustion chamber 6, that is, the in-cylinder temperature becomes very high, and the amount of NOx generated increases.

  On the other hand, in the present embodiment, the combustion at the outer peripheral portion of the combustion chamber 6 as described above and the combustion in the later stage of combustion are promoted, so that the combustion start time is shown as shown by the solid line in FIG. The combustion end time can be advanced even if the combustion is relatively delayed. Therefore, it is possible to suppress an increase in combustion noise and NOx generation amount while suppressing emission of CO and the like and increasing thermal efficiency.

(4) Modification In the embodiment, the case where the volume concentration of water in the second region R2 is set to 5% or more has been described, but the specific value of the volume concentration is not limited to this.

  Further, the specific implementation timing of the water injection W11 and the fuel injection F11 is not limited to the above.

  Moreover, although the said embodiment demonstrated the case where the water injection W11 was implemented only once in one combustion cycle, in addition to the water injection W11 implemented before the self-ignition of air-fuel mixture starts, the air-fuel mixture auto-ignites. In this state, water may be injected to the outer peripheral portion (second region R2) of the combustion chamber 6.

  Moreover, although the said embodiment demonstrated the case where the ignition with a spark plug was performed in medium load area | region A1, this ignition may be abbreviate | omitted. However, as described above, since the temperature in the combustion chamber 6 may be excessively lowered due to the latent heat action of water and the self-ignition of the air-fuel mixture may be hindered, ignition is performed to ensure the self-ignition of the air-fuel mixture. Is preferably performed.

  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.

  Further, the geometric compression ratio of the engine body and the effective compression ratio in the middle load region A1 are not limited to the above. However, it is preferable that the geometric compression ratio and the effective compression ratio in the middle load region A1 are set as described above in order to achieve appropriate self-ignition combustion of the air-fuel mixture and obtain high thermal efficiency.

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

1 Engine body 2 Cylinder 6 Combustion chamber 13 Spark plug (ignition means)
14 Injector (fuel supply means)
15 Water injector (water injection means)
100 PCM (control means)
R2 second region (outer periphery of combustion chamber)

Claims (4)

A premixed compression ignition engine comprising 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,
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
In the fuel supply means, in an intermediate load region set in an operation region excluding an operation region where the engine load is minimum and an operation region where the engine load is maximum, the air-fuel mixture starts to self-ignite in the combustion chamber. While supplying fuel into the combustion chamber before the dead center,
The water injection means introduces intake air into the combustion chamber so that water is unevenly distributed in the radially outer periphery of the combustion chamber when the air- fuel mixture starts self-ignition in the combustion chamber in the medium load region. During the compression stroke after the intake valve for opening and closing the intake port for closing is closed, and after the fuel is injected into the combustion chamber by the fuel supply means until the self-ignition of the air-fuel mixture starts A premixed compression ignition engine characterized by injecting water into the combustion chamber. The premixed compression ignition type engine according to claim 1,
Further comprising ignition means for igniting the air-fuel mixture;
The premixed compression ignition type engine characterized in that the control means ignites the air-fuel mixture by the ignition means in the medium load region. The premixed compression ignition type engine according to claim 1 or 2,
The premixed compression ignition engine characterized in that the control means injects water so that the volume concentration of water in the outer peripheral portion of the combustion chamber is 5% or more in the medium load region. The premixed compression ignition type engine according to any one of claims 1 to 3,
The geometric compression ratio of the engine body is set to 13 or more and 25 or less,
The premixed compression ignition type engine, wherein an effective compression ratio of the engine body is set to 11 or more and 23 or less in the medium load region.

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