JPH08254137A - Lean-burn engine for automobile - Google Patents

Abstract

PURPOSE: To reduce the generated quantity of NOx as flammability on the condition of lean burning is improved in a lean-burn engine. CONSTITUTION: An injector 40 for jetting fuel is severally provided in each cylinder, and set up to be an air mixture type injector, and an air supply passage 52 which supply air for atomizing the fuel and an air control valve 51 are provided in each injector 40, and at least, the air control valve 51 is opened in a lean operation zone for suppling the air to each injector 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean burn engine for an automobile, which reduces fuel consumption by performing lean combustion in a specific operation region.

[0002]

2. Description of the Related Art In recent years, various lean burn engines have been developed which perform lean burn (lean burn) by setting the air-fuel ratio to lean in an operating region such as low speed and low load of the engine. When the air-fuel ratio is made lean, the amount of air to the fuel increases, so that pumping loss (especially loss due to negative pressure resistance in the intake stroke) is reduced, and the combustion gas temperature decreases to reduce heat loss (around the combustion chamber). The heat energy taken from the cooling system to the cooling system) and the exhaust gas loss are reduced, and the thermal efficiency is improved by the reduction of these pumping loss and heat loss, and the fuel consumption is saved.

To make the air-fuel ratio lean,
The improvement of air-fuel ratio control accuracy, the promotion of leanness by improving combustibility, and the improvement of emissions have been conventionally considered.

For example, Japanese Laid-Open Patent Publication No. 59-208141 uses a lean sensor that produces an output signal approximately proportional to the oxygen concentration in the exhaust gas, and uses the lean sensor with an air-fuel ratio leaner than the theoretical air-fuel ratio. The lean control method is designed to improve the control accuracy by performing feedback control of the air-fuel ratio according to the output and setting and correcting the control target value of the lean sensor output according to the target air-fuel ratio. It is shown.

[0005] In addition, in the "Development of a new generation lean burn engine" 92048 of "Academic Lecture Preprint 924 Volume 2" issued by the Society of Automotive Engineers of Japan, the lean limit of the air-fuel ratio is raised by increasing the swirl while the lean limit is being reached. It describes a lean burn engine in which the air-fuel ratio is set to a lean level such that the NOx emission amount from the combustion chamber becomes sufficiently low within the range that does not reach.

[0006]

In this type of lean burn engine, there are still points to be improved in order to reduce NOx.

More specifically, as described in the above-mentioned preprints for academic lectures, the NOx ratio in the exhaust gas from the engine is highest near the air-fuel ratio of 16, and on the lean side. Although NOx tends to gradually decrease as it becomes leaner, conventionally, in order to sufficiently reduce NOx, the air-fuel ratio must be made extremely large and lean,
Therefore, it is necessary to increase the lean limit, and there is a limit to the torque obtained in such a high lean state, and there is a problem that the operating range in which lean burn is possible is limited. Therefore, not only by increasing the lean air-fuel ratio as described above, but also by other methods, it is required to further reduce the NOx generation amount in the lean burn operation region.

Conventionally, for example, Japanese Patent Laid-Open No. 4-208814 is used.
As shown in Japanese Patent Laid-Open No. 1-58, an injector for injecting fuel is provided for each cylinder, and an air assist mechanism for supplying mixing air to the injector is provided, so that the air assist can be performed when the engine is cold. A technique is known in which a mechanism is operated to promote atomization of fuel to improve combustibility. However, the means for promoting combustion by means of this air assist mechanism is to promote the combustion and the H
It is used for reducing C and CO, etc., and it was generally thought that NOx will increase when combustion is promoted. Therefore, it is completely considered in the past to use an air assist mechanism for reducing NOx. It wasn't done.

In view of the above circumstances, it is an object of the present invention to reduce the amount of NOx produced while improving the burnability in a lean burn state in a lean burn engine for automobiles. In particular, as will be described later in detail, when the air-fuel ratio is set to a lean state and the air assist mechanism is used to promote atomization of the fuel, it is found that NOx is reduced although the combustibility is improved. Based on the above, a lean burn engine capable of effectively reducing NOx in a lean operation region is provided.

[0010]

According to a first aspect of the present invention, in a lean burn engine for an automobile having a lean operation region in which combustion is performed at an air-fuel ratio leaner than a stoichiometric air-fuel ratio, each injector for injecting fuel is provided. An air assist mechanism is provided for each cylinder, and an air assist mechanism for supplying air to atomize the injected fuel is provided to each injector, and an air assist mechanism is provided to supply air to each injector at least in the lean operation region. This is the structure of the mechanism.

According to a second aspect of the present invention, in the first aspect of the present invention, a control means for controlling the fuel injection from each of the injectors to be performed in the intake stroke of each cylinder is provided.

According to a third aspect of the present invention, in the second aspect of the invention, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to an air-fuel ratio near the lean combustion limit in the lean operation region, and ignition is performed. The fuel injection timing from each injector is set such that a stratified state in which the local air-fuel ratio near the plug is rich by about 10% with respect to the air-fuel ratio of the entire air-fuel mixture is obtained.

[0013]

According to the engine of the first aspect, when in the lean operation range, the air assist mechanism supplies air to each injector to atomize the fuel. When the fuel is atomized in this manner in the lean burn state, the combustibility is enhanced, and moreover, the lean burn is uniformly performed, so that the portion having a high combustion temperature is reduced and the NOx generation amount is reduced.

In the present invention, when the fuel injection from each injector is performed in the intake stroke of each cylinder as described in claim 2, the lean combustion limit is increased by stratification, and the lean lean and the air assist are provided. With the atomization promoting action, the NOx reducing action is enhanced. In particular, when the stratified state in which the local air-fuel ratio near the spark plug is richer by about 10% with respect to the air-fuel ratio of the entire air-fuel mixture as described in claim 3, proper stratification is achieved. By improving the lean burn limit and promoting the atomization by air assist,
The NOx reduction action is sufficiently enhanced.

[0015]

An embodiment of the present invention will be described with reference to the drawings.
First, an outline of a lean burn engine according to an embodiment of the present invention will be described with reference to FIG. In the figure, reference numeral 1 denotes an engine main body, and a combustion chamber 2 is formed in each cylinder thereof. The combustion chamber 2 has first and second combustion chambers, which will be described in detail later.
Intake ports 3 and 4 and first and second exhaust ports 5 and 6
The intake valves 7 and 8 and the exhaust valves 9 and 10 are installed in these ports 3 to 6.

The intake system 20 of the engine is provided with an intake manifold 21 and a common intake passage 30 on the upstream side thereof. The common intake passage 30 includes an air cleaner 31, a thermal air flow sensor 32, and a throttle valve in order from the upstream side. 33
Is provided. Further, an intake bypass passage 34 that bypasses the throttle valve 33 is formed. The intake bypass passage 34 includes an ISC passage 35 for adjusting the intake air amount during idling and the like, and an air passage 36 for increasing the intake air amount during cold conditions. Above ISC
The passage 35 is provided with an ISC valve 37 that is duty-controlled to control the air flow rate of the ISC passage 35, and the air passage 36 is provided with a temperature-sensitive valve 38 that opens when cold.

Further, in the vicinity of the intake port on the downstream side of the intake system 20, the injector 4 for injecting and supplying the fuel for each cylinder.
0 is provided, and an on-off valve 41 that opens and closes the second intake port 4 is provided. The on-off valve 41 is operated by a negative pressure responsive actuator 42, and a drive system for the same is provided with a vacuum tank 43 for storing the negative pressure introduced from the surge tank of the intake manifold 21, and between the tank 43 and the actuator 42. Solenoid valve 4 that is arranged in the
4 etc. are provided.

The injector 40 is a so-called AMI (air mixture type injector) which atomizes the fuel by supplying mixing air near the injection port. The injector 40 is provided with a fuel supply system including a fuel supply passage 48 for supplying fuel from a fuel tank 45 via a fuel pump 46 and a filter 47, a return passage 50 in which a pressure regulator 49 is provided, and the like. A mixing air supply system (air assist means) and an evaporated fuel supply system, which will be described later in detail, are provided.

On the other hand, the exhaust system has an oxygen concentration sensor 6 for detecting the oxygen concentration in the exhaust gas corresponding to the air-fuel ratio of the air-fuel mixture.
0 and a catalyst device 61 are provided. The oxygen concentration sensor 60 is adapted to obtain an output substantially proportional to the oxygen concentration in the exhaust gas so that the lean air-fuel ratio can be detected. Further, the catalyst device 61 has a function of reducing NOx even at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and specifically, the Japanese Patent Application No. 5-126552 previously filed by the applicant of the present invention has been described. The catalyst device described is used. That is, the catalyst in the catalyst device 61 is one in which a noble metal is supported as the active species on the active species-supporting base material. Preferably, zeolite is used as an active species-supporting base material, and Ir and Pt are supported as active species, or Ir, Pt, and Rt are supported as active species.

In addition to the air flow sensor 32 and the oxygen concentration sensor 60, a throttle opening sensor 62 for detecting the opening of the throttle valve and a fully closed throttle are detected as various detecting elements for controlling the air-fuel ratio. Is provided with an idle switch 63, an intake air temperature sensor 64 for detecting the intake air temperature, a water temperature sensor 65 for detecting the engine water temperature, a knock sensor 66 for detecting the engine knocking, and an ignition system distributor 67 with a crank angle signal. Is provided, and a cylinder discrimination sensor 69 that outputs a cylinder discrimination signal is provided.

Signals from these detection elements are input to a control unit (ECU) 70 for controlling the engine. The control unit 70 controls the fuel injection amount and injection timing from the injector 40, and further controls the ISC valve 37, the solenoid valve 44 in the drive system of the on-off valve 41, and the mixing air supply system for the injector 40. The air control valve 51, which will be described later, and the purge solenoid valve 58, which will be described later, which is provided in the evaporated fuel supply system will also be controlled by the control unit 70.

Next, the specific structure of each part of the lean burn engine will be described.

2 to 4 show a specific structure of the engine body. As shown in these figures, the engine body 1
In each of the cylinders, basically, when the first and second intake valves 7 and 8 are opened, the air-fuel mixture is sucked into the combustion chamber 2 from the first and second intake ports 3 and 4, and After the air-fuel mixture is compressed by the piston 11, it is ignited by the spark plug 12,
Combustion gas is discharged from the first and second exhaust ports 5 and 6 when the first and second exhaust valves 9 and 10 are combusted and opened. An injector 40 is provided on the first intake port (hereinafter referred to as P port) 3 and an opening / closing control is performed on the second intake port (hereinafter referred to as S port) 4 or a passage upstream thereof according to an operating state. An on-off valve 41 is provided.

In this embodiment, when the on-off valve (hereinafter referred to as TSC valve) 41 as a tumble / swirl control valve is closed, a strong tumble (vertical vortex) and swirl (horizontal vortex) are combined. The port arrangement, the port shape, etc. are set so that such a spiral oblique swirl is generated in the combustion chamber 2.

More specifically, the P port 3 and the S port 4 are straight portions 3a, 4a extending substantially linearly in the upstream portion in the intake air flow direction, and the straight portion 3
a, 4a, and curved portions 3b, 4b that curve downward to reach the respective valve seats 13, 14 (see FIGS. 3 and 4). Then, the straight portions 3 of the P port 3 and the S port 4 respectively.
The extension lines of the port center lines Lp1 and Ls1 of a and 4a are valve ends 7a located on the center side of the combustion chamber 2 at the time of maximum lift of the valve seats 13 and 14 and the first and second intake valves 7 and 8. ，
8a. This allows
The flow resistance of intake air supplied from the P and S ports 3 and 4 to the combustion chamber 2 is reduced. The above-mentioned port center lines Lp1, L
The extension line of s1 is the valve seats 13 and 14 and the valve end portions 7a and 8a.
The best setting is to pass through the center of.

The combustion chamber 2 is a pent roof lens type combustion chamber, and the valve grip angle θ between the intake valves 7 and 8 and the exhaust valves 9 and 10 is narrowed to about 30 °, which is a DOHC direct drive type. It is adapted to be driven by a valve mechanism (not shown). Further, the angle formed between the valve center line L1 of the first intake valve 7 and the throat center line Lp1 of the P port 3 (throat offset angle α1) is relatively large, and
Angle formed by the valve center line L2 of the intake valve 8 and the throat center line Ls1 of the S port 4 (throat offset angle α2)
Is set relatively small, for example, α1 = 30 °,
α2 = 12 °. In this way, when the intake is performed only from the P port 3, the vortex S having an inclination angle (angle with the cylinder center line) γ of 35 ° to 55 ° is generated. Further, the S port 4 is adapted to generate a tumble T in the combustion chamber 2.

Further, the intake valves 7 and 8 are respectively
The valve shaft portion 7b, 8b and the umbrella portion 7c, 8c, and the umbrella portion 7
The lower surfaces of c and 8c are arranged so as to be parallel to the ceiling surface of the combustion chamber 2. The valve umbrella angle β1 of the first intake valve 7 (the angle between the lower surface and the upper surface of the umbrella portion) β1 is the valve umbrella angle β of the second intake valve 8.
It is set larger than 2. As a result, the flow path between the first intake valve 7 and the throat portion of the P port 3 at the time of valve lift becomes narrower than the flow path between the second intake valve 8 and the throat portion of the S port 4, and thus , The intake flow velocity is increased on the P port 3 side, and the flow rate is secured on the S port 4 side.

Further, a port edge 15 is formed in the lower portion of the outlet of the P port 3, and a squish area 16 is formed around the first intake valve 7 in the combustion chamber 2, whereby the exhaust gas from the P port 3 is formed. The flow velocity of air blown to the valve side is increased.

According to such a structure of the combustion chamber and the intake port, the intake of the P port 3 produces a strong vortex which is a combination of tumble and swirl.
Even in lean burn conditions where the burning speed tends to be slow,
The formation of a uniform air-fuel mixture and the improvement of the combustion speed are compatible with each other to obtain a good combustion state.

That is, as shown in FIG. 6, the swirl is
The turbulence intensity from the intake to the first half of the compression stroke is great,
Although the effect of homogenizing the air-fuel mixture is large, the turbulence strength in the latter half of the compression stroke is small, and conversely, the tumble has a small turbulence strength in the first half of the compression stroke but a large turbulence strength in the latter half of the compression stroke.
Further, in the case of the above intake port structure, the advantages of both swirl and tumble are obtained, and the average turbulence intensity from the intake stroke to the compression stroke is increased. FIG. 5 shows the case where the swirl ratio Sr is 3.3 and 4.2,
The relationship between the swirl inclination angle (angle formed by the swirl center line and the cylinder center line) γ and the average turbulence intensity R is shown.
As shown in this figure, by setting the swirl ratio Sr to about 3 or more and the swirl inclination angle γ in the range of 35 ° to 55 °, particularly preferably 45 °, the average turbulence intensity is significantly increased. , The homogenization of the air-fuel mixture and the burning rate are improved.

Here, the definition and method of obtaining the swirl ratio will be described. The swirl ratio is generally defined as a value obtained by dividing the number of revolutions of the lateral vortex of the air-fuel mixture (intake air) in the cylinder by the engine speed.

The swirl number of the lateral vortex of the air-fuel mixture is set to a position F ₂ below the cylinder head lower surface F ₁ by a distance of 1.75 D in an engine having a bore diameter D as shown in FIG. 7, for example. The impulse swirl meter 80 is arranged, the torque acting on the impulse swirl meter 80 (impulse swirl meter torque) is detected, and it is calculated by a well-known method based on this impulse swirl meter torque. In FIG. 7, F ₃ represents the top surface of the piston 11 at the bottom dead center position.

The impulse swirl meter torque is measured by the following procedure. That is, by arranging the impulse swirl meter 80 at the position of F ₂ and reproducing the energy of the swirl acting on the piston top surface by the impulse swirl meter 80, how much revolving energy is generated in the vicinity of the piston top surface under normal conditions. Determine if it is present. The impulse swirl meter 80 is equipped with a large number of honeycombs.
When a swirl acts on the honeycomb, a force in the swirl flow direction acts on each honeycomb, and the impulse swirl meter torque G acting on the whole is calculated by integrating the forces applied to each honeycomb.

More specifically, assuming that the air-fuel mixture is being sucked into the combustion chamber 2 during the period from the opening of the intake valve to the bottom dead center, the air-fuel mixture is kept in the inner peripheral surface of the combustion chamber 2 during this period. It makes a turn along and the turning speed becomes maximum at the bottom dead center position.
Therefore, the swirl ratio can be obtained by integrating the angular momentum of each crank from the start of opening of the intake valve to the bottom dead center. Based on such knowledge, in this example, the swirl ratio Sr is calculated by the following equations (1) and (2).

[0035]

[Equation 1] Sr = ηv · {D · S · ∫ (cf · Nr · dα)} / {n · d ² · (∫cf · dα) ² } ... (1) Nr = 8 · G / (M・ D ・ V ₀ ) (2) where Sr is the swirl ratio and ηv is the volumetric efficiency (ηv =
1), D is the bore diameter, S is the stroke, n is the number of intake valves, d
Is the throat diameter, cf is the flow coefficient for each valve lift,
Nr is a dimensionless rig swirl value for each valve lift,
α is the crank angle, G is the impulse swirl meter torque, M is the mass of air filled in the cylinder during the intake stroke, and V ₀ is the speed head.

The above equation (2) is derived by the following procedure.

[0037]

[Number 2] G = I · ωr ...... (3 ) I = M · D 2/8 ...... (4) (4) and (3) an assignment ^{G = M · D 2 · ωr} / 8 ...... (5 ) From (5) D ・ ωr = 8 ・ G / (M ・ D) …… (6) By the way, Nr = D ・ ωr / V ₀ …… (7) (6) is substituted into (7) Nr = 8 ・G / (M · D · V ₀ ), where I is the moment of inertia of the air in the cylinder at the end of the intake stroke (piston bottom dead center), and ωr is the rig swirl value.

FIG. 8 shows a mixing air supply system and an evaporated fuel supply system for the injector 40. In this figure, an injector 40 is installed for each P port 3 of a plurality of cylinders (for example, four cylinders), and an air control valve 51 is provided in a mixing air supply system for these injectors 40.
2 are provided. This AMI air supply passage 52
The upstream side is connected to the intake bypass passage 34 (see FIG. 1), and the downstream side is branched and connected to each injector 40.

Further, the AMI air supply passage 52 has a bypass passage 5 bypassing the air control valve 51.
The bypass passage 53 is provided with an orifice 54 through which a small amount of air is made to flow when idle.

Further, the evaporated fuel supply system is a canister 56.
A purge passage 57 extending from (see FIG. 1) is provided, and a purge solenoid valve 58 is provided in the purge passage 57. The purge passage 57 is the AMI air supply passage 5
Mixing chamber 55 formed upstream of the branch point of 2
It is connected to the. The vaporized fuel generated in the fuel tank or the like and trapped in the canister 56 is supplied to the vicinity of the injection port of each injector 40 via the purge passage 57 when the purge solenoid valve 58 is opened, and together with the fuel spray during the intake stroke. It is supplied to the combustion chamber 2 of each cylinder. The purge solenoid valve 58 is driven when a predetermined purge execution condition is satisfied (for example, during feedback control of the air-fuel ratio and when the engine water temperature is equal to or higher than a predetermined temperature) to obtain a predetermined purge amount. It is controlled according to the operating state of.

9 and 10 show the injector 40.
The concrete structure of is shown. In these drawings, an injector mounting hole 400 communicating with the P port 3 is formed in the cylinder head 1a of the engine, and the injector 40 is fitted into the injector mounting hole 400. The tip end side portion 401 of the injector 40 is formed in a tubular shape so as to surround the injection port, and the tip end side portion 401
A ring-shaped air introduction space 402 is formed between the air introduction space 402 and the peripheral wall of the injector mounting hole 400, and an air introduction port 403 is formed in the cylinder head 1a for communicating the air introduction space 402 with an external air supply passage. ing. Further, the tip side portion 401 of the injector 40
In the space in front of the nozzle and inside the air introduction space 4
Communication holes 404 that communicate with No. 02 are radially arranged, and orifices 405 are formed in the communication holes 404.

Then, fuel is injected from the injection port of the injector 40 toward the P port 3 at a predetermined timing, and is introduced into the air introduction space 402 when an intake negative pressure acts on the space in front of the injection port. The air is ejected through the orifice 405 into the space in front of the nozzle, and the injected fuel is mixed by the air.

The control of the air-fuel ratio by the control unit 70 shown in FIG. 1, the control of the fuel injection timing from the injector 40, and the control of the mixing air supply system are carried out as follows.

As the control of the air-fuel ratio, the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio in a predetermined operating range. For example, as shown in FIG. 11, in the low and medium speed range of the engine, the air-fuel ratio is theoretical It is set to lean (λ> 1) rather than the fuel ratio. In the illustrated example, a predetermined lean air-fuel ratio in the vicinity of the lean combustion limit is set in most of the lean operation region, and in this embodiment, swirl generation, stratification, and AM are performed.
Since the lean combustion limit is increased to about 25 by the action of promoting combustion by atomizing the fuel in I, the air-fuel ratio in this region is set to about 22. In lean operating regions other than this region, the air-fuel ratio is within a certain range (for example, 19
22 to 22) are changed according to the driving state. Further, the air-fuel ratio is set to the stoichiometric air-fuel ratio (λ = 1) or richer than this (λ <1) in the high load side and the high speed side of the idle region and lean operation region, and fuel cut is performed in the fully closed deceleration region. To be done.

However, the control of the air-fuel ratio is not limited to this example, and may be set to a constant lean air-fuel ratio in the entire lean operation region.

As the control of the fuel injection timing from the injector 40, so-called sequential timed injection in which fuel is injected at a predetermined timing for each cylinder is performed, and the air-fuel mixture in the combustion chamber is made substantially uniform while the ignition plug is rotated. The fuel is injected at a predetermined timing of the intake stroke so that the air-fuel mixture is slightly richer than the other portions.
Desirably, the degree of stratification is adjusted so that the air-fuel mixture around the spark plug does not become too rich and causes an increase in NOx, and specifically, injection is performed within a period up to ATDC 60 °. Has become.

In order to control the mixing air supply system, the air control valve 51 is opened to supply air to the injector 40 in an operating region including the lean operating region. For example, when the air control valve 51 is idle. It is closed and opened at other times.

The TSC valve 41 is also controlled in accordance with the operating state, and for example, as shown in FIG.
The open / close switching line of the C valve 41 is set so as to substantially coincide with the limit line on the high speed side of the lean operation region. The TSC valve 41 is closed on the low speed side and the TSC valve 41 is opened on the high speed side of the open / close switching line. .

According to the lean burn engine of the present embodiment as described above, the air-fuel ratio is set to lean in the predetermined operating region of the engine, and lean burn is performed, so that
Fuel economy is improved in this operating range. AMI is used for the injector 40, and the injector 40
The fuel is atomized by supplying the mixing air to the mixture, thereby homogenizing the air-fuel mixture and improving the combustibility.

Particularly, even in the lean operating region where the lean burn is performed, the mixing air is supplied to the injector 40, whereby the action of reducing the NOx generation amount in the lean burn state can be obtained.
2 to 14 will be described.

FIG. 12 shows the relationship between the air-fuel ratio and the NOx emission amount examined by the present inventor. Line A shows NOx on the upstream side of the catalyst when mixing air is not supplied to the injector. Emissions (NOx of engine
Similarly, the line B indicates the NOx emission amount in the downstream of the catalyst when the mixing air is not supplied and the conventional general three-way catalyst is used as the catalyst device. The NOx emission amount downstream of the catalyst when the mixing air is supplied and the conventional general three-way catalyst is used as the catalyst device, the line C2 indicates that the mixing device supplies the mixing air as in the present embodiment. Shows the NOx emission amount in the downstream of the catalyst when the catalyst having the NOx purification performance even with the lean air-fuel ratio is used. Note that FIG. 12 also shows the relationship between the air-fuel ratio, the fuel consumption rate, and the torque fluctuation when the engine of the embodiment is used.

As shown in this figure, when the mixing air is supplied even when the air-fuel ratio is lean, the N in the lean region is increased as compared with the case where the mixing air is not supplied.
Ox emissions are greatly reduced. The reason is that the average combustion temperature in the combustion chamber is relatively low in the lean burn state, and if the fuel is atomized by the mixing air in such a situation, the local variation in the combustion temperature becomes small, and NOx is reduced. It is considered that this is because the portion where the temperature is higher than the generation temperature is reduced.

This will be specifically described with reference to FIG. 13. In this figure, the first example shows a fuel distribution state in the combustion chamber when a normal injector is provided in the intake port to inject fuel, and a second example. Is the fuel distribution state in the combustion chamber when the fuel is injected while supplying the mixing air by using the injector 40, that is, the AMI of the present embodiment, and the third example is the fuel when the fuel is supplied in the gasified state. The distribution states are shown schematically, and as shown in this figure, the AMI
With the use of, due to the action of the mixing air, the fuel is significantly atomized as compared with a normal injector. And
When the air-fuel ratio is lean, if the fuel particle size is large, NOx is likely to occur in the high combustion temperature portion due to the local variation in the combustion temperature, as in the case where the air-fuel mixture distribution is uneven. On the other hand, the smaller the fuel particle size, the more uniformly the lean burn is performed, so that the portion where the combustion temperature is high decreases and the NOx generation amount decreases. For this reason,
As shown in No. 4, when AMI is used, the NOx emission amount becomes smaller in the lean region than in the normal injector 40.

If the fuel can be gasified and supplied, the NOx emission amount will be further reduced, but an injector is provided in the intake port for accurate air-fuel ratio control and stratification by sequential timed injection. In this case, it is practically difficult to gasify and supply the fuel. Therefore, atomizing the fuel injected from the injector 40 with mixing air is an effective method for reducing NOx in the lean region while performing good air-fuel ratio control and the like.

Further, in this embodiment, the fuel injection from the injector 40 is performed in the intake stroke so that the air-fuel ratio near the spark plug becomes slightly richer than the air-fuel ratio of the entire air-fuel mixture in the combustion chamber. Stratification is performed, and the ignitability in a lean state is secured by this, so that a sufficient lean air-fuel ratio can be achieved.

In particular, in the lean operation region, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to a value near the lean combustion limit, and the local air-fuel ratio in the vicinity of the spark plug is compared with the air-fuel ratio of the entire air-fuel mixture. If the fuel injection timing from each of the injectors is set so that a stratified state that is about 10% rich is obtained, thermal efficiency and NO
The x reduction effect is enhanced.

That is, FIG. 15 shows that the injector has an AM.
While using I to supply the mixing air,
By changing the fuel injection timing from the injector, the local air-fuel mixture distribution is changed in various ways, and the rate of change in thermal efficiency, NOx
The data when investigating the rate of change and the lean burn limit are shown. Note that [(local air-fuel mixture distribution) = (overall air-fuel ratio)-
(Air-fuel ratio near the spark plug)]. Regarding the rate of change in thermal efficiency and the rate of change in NOx, there are data when the overall air-fuel ratio is a constant value (approximately 22) and when the overall air-fuel ratio is a value smaller than the lean burn limit by a certain margin α. And data.

As shown in this figure, the local mixture distribution is 2
In the case of a stratified state of a certain degree, the lean burn limit is significantly increased as compared with the case where no stratification is performed (when the local air-fuel mixture distribution is 0). If stratification is excessively higher than this, the lean combustion limit is lowered due to the nonuniform distribution of the air-fuel mixture, which in turn impairs combustion stability. Increase, and the thermal efficiency also deteriorates.

Then, the local air-fuel mixture distribution is set to a stratified state in which the air-fuel ratio is about 2 (that is, the air-fuel ratio near the spark plug is about 10% rich with respect to the entire air-fuel ratio), and the air-fuel ratio is a value near the lean combustion limit ( When set to a value that is smaller by a certain margin α), the air-fuel ratio is made lean by appropriate stratification, and the atomization of fuel is promoted by the AMI, and NOx is greatly reduced. Moreover, the thermal efficiency is improved.

In the stratified state in which the local air-fuel mixture distribution is about 2, the end of fuel injection from the injector is set to A in the intake stroke.
It can be obtained by setting TDC to about 60 °.

[0061]

As described above, the present invention provides the lean burn engine with the air assist mechanism for supplying the air for atomizing the fuel to the injector provided for each cylinder, and at least in the lean operation region. Since the air is supplied to each of the injectors, the high combustion temperature portion is reduced by promoting atomization of the fuel in the lean burn state,
The amount of NOx generated can be greatly reduced.

In the present invention, fuel injection from each injector is performed in the intake stroke of each cylinder to stratify the air-fuel mixture in the combustion chamber to some extent. By setting the fuel injection timing so that it is richer by about 10% with respect to the fuel ratio, an appropriate stratified state in which the air-fuel mixture distribution in the combustion chamber does not become significantly uneven is obtained, which results in lean air-fuel ratio and air assist. The NOx reduction action can be further enhanced by the atomization promotion action by the.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a lean burn engine of the present invention.

FIG. 2 is a schematic plan view showing a combustion chamber structure.

FIG. 3 is a schematic sectional view of a first intake port side.

FIG. 4 is a schematic sectional view of a second intake port side.

FIG. 5 is a characteristic diagram of average turbulence intensity.

FIG. 6 is a diagram showing a comparison between swirl and tumble.

FIG. 7 is an explanatory diagram showing a measuring means and a measuring method for swirl.

FIG. 8 is a diagram showing an air supply system and an evaporated fuel supply system for an injector.

FIG. 9 is a cross-sectional view showing a specific structure of an air mixture type injector.

FIG. 10 is a partially cutaway perspective view of the injector.

FIG. 11 is a diagram showing an air-fuel ratio control region in association with engine speed and throttle opening.

FIG. 12 is a diagram showing a relationship between an air-fuel ratio, fuel efficiency, torque fluctuation, and NOx emission amount.

FIG. 13 is a diagram showing various examples of a fuel distribution state in a combustion chamber.

FIG. 14 is a diagram showing the relationship between the various examples shown in FIG. 12 and the NOx emission amount.

FIG. 15: Local mixture distribution and lean burn limit in the combustion chamber,
It is a figure which shows the relationship with a NOx change rate and a thermal efficiency change rate.

[Explanation of reference numerals] 1 engine body 2 combustion chamber 40 injector 41 opening / closing valve 51 air control valve 52 air supply passage 70 control unit

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location F02D 45/00 301 F02D 45/00 301G F02M 69/00 310 F02M 69/00 310E 360 360C 69/04 69/04 G (72) Inventor Yasuyoshi Hori 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Futoshi Nishioka 3-3, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture (72) Inventor Tetsuji Hosogai 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Kenji Oka 3-3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture (72) Inventor Hideshi Terao Aki-gun, Hiroshima Prefecture Fuchu-cho Shinchi No. 3 Mazda Co., Ltd. (72) Inventor Misao Fujimoto No. 3 Fuchu-cho Shinchi, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Masaki Harada No. 3 Fuchu-cho, Aki-gun, Hiroshima Prefecture No. Mazda Co., Ltd.

Claims (3)

[Claims] 1. In a lean-burn engine for an automobile having a lean operation region in which combustion is performed at an air-fuel ratio leaner than a stoichiometric air-fuel ratio, injectors for injecting fuel are provided for each cylinder, and injection is performed for each injector. A lean burn for an automobile, characterized in that an air assist mechanism for supplying air for atomizing fuel is provided, and the air assist mechanism is configured to supply air to each injector in at least the lean operation region. engine. 2. The lean burn engine for an automobile according to claim 1, further comprising control means for controlling the fuel injection from each injector so as to be performed in an intake stroke of each cylinder. 3. In the lean operation region, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to an air-fuel ratio near the lean combustion limit, and the local air-fuel ratio near the spark plug becomes the air-fuel ratio of the entire air-fuel mixture. The lean burn engine for an automobile according to claim 2, wherein the fuel injection timing from each of the injectors is set so that a stratified state of about 10% rich is obtained.