JPH06221163A - Combustion chamber structure of direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To provide a means to uniformize air utilizing characteristics of fuel directly injected through each fuel injection nozzle and improve emission performance and an engine output, in a direct injection type diesel engine wherein a fuel injection nozzle is arranged in a state to be inclined based on the axis of a cylinder. CONSTITUTION:A piston recessed part 3 approximately in a columnar shape is arranged in an inclined state in the top part of the piston 2 of a direct injection type diesel engine in a position relation wherein a given recessed part inclination angle theta is nipped between an axis M2 and a piston axis M1. The air utilizing characteristics of air injected through each of fuel injection nozzles 6 are uniformized by the inclination, which causes improvement of emission performance and an engine output. Further, the recessed part inclination angle 9 is set such that a distance between the tips of fuel spraying bodies 12a, 12d and the recessed part wall surface of a piston, resulting in further improvement of emission performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure of a direct injection diesel engine.

[0002]

2. Description of the Related Art The top of a piston fitted in a cylinder
A piston recess that forms a part of the combustion chamber is formed in the (crown part), and when the piston is almost at the top dead center, fuel is injected from the fuel injection nozzle into the high temperature and high pressure intake air in the piston recess. A direct injection diesel engine in which this fuel is burned by spontaneous ignition (self-ignition) has been conventionally known.

In the direct injection diesel engine,
A single intake / exhaust valve type in which one intake valve and one exhaust valve are provided in each cylinder has been widely used, but in such a direct injection diesel engine with one intake / exhaust valve, the valve system is Due to various restrictions in layout, it is extremely difficult to arrange the fuel injection nozzle near the center of the cylinder in an upright posture (with the cylinder axis direction). Therefore, in a direct-injection diesel engine with a single intake / exhaust valve, if the fuel injection nozzle is to be arranged in an upright posture, the fuel injection nozzle has to be arranged eccentrically from the center of the cylinder in plan view. In this case, the piston concave portion must also be eccentric from the piston central portion so as to correspond to the eccentricity of the fuel injection nozzle. However, in order to make the explosive load on the piston uniform, it is preferable to form the piston recess in the center of the piston (without eccentricity) in plan view as much as possible.

Therefore, in a conventional direct-injection diesel engine of the intake / exhaust one-valve type, in general, the piston recess is arranged in the center of the piston as much as possible in a plan view, and the fuel injection nozzle is attached so that the tip end is substantially in the center of the cylinder. Is positioned so that it is located in the section and is inclined with respect to the cylinder axis.
(See, for example, JP-A-2-245418).

[0005]

Generally, in a direct injection diesel engine, a plurality of fuel injection ports facing the recessed portion of the piston are formed near the tip of the fuel injection nozzle. The angle formed by the axis (fuel injection direction) and the cylinder axis (hereinafter referred to as the injection inclination angle) is formed to be substantially uniform for all injection ports. Therefore, the angle formed by the axis of each fuel injection port (fuel injection direction) and the axis of the fuel injection nozzle (hereinafter referred to as the fuel refraction angle) is different for each fuel injection port. Here, when the fuel refraction angle is 0, that is, when the fuel injection direction matches the axial direction (fuel flow direction) of the fuel injection nozzle, the flow of fuel from the nozzle body to the fuel injection port is smoothed. The amount of fuel injected from the fuel injection port is the largest. On the other hand, when the fuel refraction angle is not 0, the larger the fuel refraction angle is, the more the fuel is prevented from flowing into the fuel injection port, and the fuel injection amount from the fuel injection port is reduced.

For example, as shown in FIGS. 5 (a) and 5 (b), a piston recess 103 is formed at the top of a piston 102 fitted in a cylinder 101, while a fuel injection having four fuel injection ports is provided. In a conventional direct injection diesel engine with a single intake / exhaust valve, in which the nozzle 105 is arranged to be inclined with respect to the cylinder axis, the fuel injection characteristics from each fuel injection port are 106a to 106d due to the difference in fuel refraction angle. It becomes uneven like.

For this reason, in the conventional direct injection diesel engine of the intake / exhaust one-valve type in which the fuel injection nozzle is arranged to be inclined with respect to the cylinder axis, the fuel refraction angle is small and therefore the fuel injection amount is large. In the combustion of the fuel injected from the mouth (for example, 106a in FIG. 5), the amount of smoke or HC generated increases due to lack of air, while the fuel refraction angle is large, and therefore the fuel injection amount decreases. The injected fuel (see, for example, FIG.
In the combustion of 106d), the air becomes excessive and the effective use of intake air in the entire combustion chamber is hindered. Therefore, since the fuel distribution in the combustion chamber or the air utilization characteristic is non-uniform, there are problems that the emission performance is reduced and the engine output is reduced.

The present invention has been made in order to solve the above-mentioned problems of the prior art. Each fuel injection is performed on a direct injection diesel engine in which a fuel injection nozzle is arranged to be inclined with respect to a cylinder axis. It is an object of the present invention to provide a means capable of making the air use characteristics of fuel injected from the mouth uniform and enhancing emission performance and engine output.

[0009]

In order to achieve the above object, the first aspect of the present invention is such that a piston recess that forms a part of a combustion chamber is formed at the top of a piston that is fitted into a cylinder, and is inclined with respect to the cylinder axis. Is provided with a plurality of fuel injection nozzles facing the recessed portion of the piston when the piston is at the top dead center position. In a combustion chamber structure of a direct injection type diesel engine in which the angle formed by the fuel injection direction and the cylinder axis is substantially uniform, the piston recess has a fuel injection amount injected from a certain fuel injection port. A direct injection diesel characterized in that the ratio of the fuel spray to the volume that can be occupied in the piston recess is substantially uniform for all fuel injection ports. To provide a combustion chamber structure of the engine.

According to a second aspect of the present invention, in the combustion chamber structure for a direct injection type diesel engine according to the first aspect, the piston recess has a substantially cylindrical shape, and the axis of the piston recess is predetermined with respect to the piston axis. Is formed so as to be inclined with respect to the piston axis, and the amount of fuel injected from a certain fuel injection port and the atomized body of the fuel are Provided is a combustion chamber structure for a direct injection diesel engine, which is characterized in that the ratio to the volume that it can occupy is substantially uniform for all fuel injection ports.

A third aspect of the present invention is the direct injection type diesel engine combustion chamber structure according to the second aspect, wherein the inclination angle of the concave portion is the tip of the atomized body of the fuel injected from one fuel injection port, and Provided is a combustion chamber structure of a direct injection diesel engine, wherein a distance between a tip end portion and a wall surface of a piston recess closest to the tip end portion is set to be substantially uniform for all fuel injection ports.

A fourth aspect of the present invention is a direct injection type diesel engine combustion chamber structure according to the second or third aspect,
Provided is a combustion chamber structure of a direct injection diesel engine, wherein a recess inclination angle is set such that a center of a lip portion of a piston recess substantially coincides with a center of the piston in a plan view.

[0013]

EXAMPLES Examples of the present invention will be specifically described below.
As shown in FIGS. 2 (a) and 2 (b), a piston 2 adapted to reciprocate in the cylinder axis direction is fitted in the cylinder 1 of the direct injection diesel engine DE. Then, a substantially columnar piston recess 3 is provided at the top (crown) of the piston 2. The space inside the piston recess 3 forms part of the combustion chamber 4.

This diesel engine DE is a so-called intake / exhaust system in which each cylinder is provided with one intake valve and one exhaust valve.
A diesel engine with one exhaust valve, in which air is sucked into the combustion chamber 4 when the intake valve 5 is opened, and the intake air in the combustion chamber 4 is compressed by the piston 2 so that the piston 2 is substantially above. At the dead center position, the fuel is injected from the fuel injection nozzle 6 into the intake air of high temperature and high pressure in the combustion chamber 4 (piston recess 3).
(For example, light oil) is injected to burn the fuel by spontaneous ignition, and the combustion gas is discharged to an exhaust passage (not shown) when an exhaust valve (not shown) is opened.

As shown in FIG. 3, the fuel injection nozzle 6 is provided with a substantially cylindrical nozzle housing 7, and in this nozzle housing 7, a substantially cylindrical large diameter hollow portion 8 and the large diameter hollow portion are provided. A small-diameter hollow portion 9 communicating with 8 is formed.
The projection 7a formed at the tip of the nozzle housing 7 is formed with first to fourth fuel injection ports 10a to 10d for communicating the small diameter hollow portion 9 with the outside. Further, inside the nozzle housing 7, there is provided a needle valve 11 that opens and closes a communication portion between the hollow portions 8 and 9. Here, the needle valve 11 is adapted to open the communicating portion of both hollow portions 8 and 9 at a predetermined timing. When the communicating portion is opened, the inside of the small diameter hollow portion 9 or the large diameter hollow portion 8 is opened.
The fuel inside is injected into the combustion chamber 4 (piston recess 3) from the first to fourth fuel injection ports 10a to 10d.

The fuel injection nozzle 6 has its axis L in an elevation view due to restrictions in layout of a valve train (not shown).
₄ is inclined with respect to the cylinder axis L ₁ so as to sandwich a predetermined angle, and the first to fourth fuel injection ports 10a to 10d have their axes in the elevation view, that is, fuel injection. The direction is inclined with respect to the cylinder axis L ₁ so as to sandwich a predetermined angle α. Note that FIG.
Among them, the axes L ₂ , L of the first and fourth fuel injection ports 10a, 10d
Only ₃ is shown, and the axes of the second and third fuel injection ports 10b and 10c are not shown.

By the way, the substantially cylindrical piston recess 3 formed at the top of the piston 2 has fuel injection ports 10a-1a.
In order to make the air use characteristics (air use rate, etc.) of the fuel injected from 0d into the piston recess 3 (combustion chamber 4) uniform, its axis is a predetermined distance from the piston axis (cylinder axis) in elevation. The angle (hereinafter, this angle is referred to as the recessed portion inclination angle) is arranged so as to be inclined, and the specific shape of the piston recessed portion 3 will be described below.

As shown in FIGS. 1 (a) and 1 (b), the substantially cylindrical piston recess 3 has a predetermined axis M ₂ between the piston axis M ₁ (that is, the cylinder axis) in elevation. It is formed by drilling in such a positional relationship as to sandwich the recess inclination angle θ. It should be noted that such drilling is extremely easy and can be easily performed by using a conventional piston machining apparatus.
Here, the concave portion inclination angle θ is set so as to satisfy the following three conditions.

(1) Condition 1 The inclination angle θ of the recess is one fuel injection port 10a (10b, 1).
Injection quantity Q ₁ (Q ₂ , Q ₃ , Q of fuel injected from 0c, 10d)
₄ ) to the volume V ₁ (V ₂ , V ₃ , V ₄ ) that can be occupied by the fuel sprayer 12a (12b, 12c, 12d) in the piston recess 3 is substantially uniform for all fuel injection ports. Is set. Here, the atomizer is a mixture of fuel particles and intake air. Specifically, the injection amounts Q _{1 to} Q ₄ and the volume V ₁
The inclination angle θ of the concave portion is set so that the following expression 1 is satisfied between V ₄ and V ₄ . It should be noted that the volumes V _{1 to} V ₄ are volumes of partial regions divided by the straight lines M ₃ and M _{4 in} a plan view.

[Formula 1] Q ₁ / V ₁ = Q ₂ / V ₂ = Q ₃ / V ₃ = Q ₄ / V ₄ ………………………… Formula 1

Here, the magnitude relation between V _{1 to} V ₄ is V
₁ > V ₂ = V ₃ > V ₄ , but the larger θ becomes, the larger the difference between them becomes. On the other hand, the magnitude relationship between the fuel injection amount Q ₁ to Q ₄ from the first to fourth fuel injection port 10a~10d, for example, as shown in FIG. _{4, Q 1> Q 2 =} Q 3>
Although the Q _4, these values Q ₁ to Q ₄ does not change the value of theta. Therefore, θ that almost satisfies Expression 1 is always obtained. When this condition 1 is satisfied, the ratio of the fuel injected from each of the fuel injection ports 10a to 10d to the amount of air involved in the combustion of the fuel, that is, the air utilization rate is substantially uniform in all fuel injection ports. To be done. Therefore, local air shortage or excess air does not occur at the time of fuel combustion in the piston recess 3 (combustion chamber 4). Therefore, the amount of smoke or HC generated is reduced to improve emission performance and fuel efficiency performance, and the intake air is effectively used for combustion of fuel to increase engine output.

(2) Condition 2 The inclination angle θ of the concave portion is set to a certain one fuel injection port 10a (10b, 1b).
0c, 10d) fuel spray body 12a (12b, 1)
2c, 12d) and the distance between the tip and the wall surface of the piston recess 3 closest to the tip are set to be substantially uniform for all fuel injection ports. In this case, the spray body 1
The lengths in the fuel injection direction of 2a to 12d, that is, the distances between the tip of the spray body and the wall surface are made uniform only with respect to the fuel injection port where the fuel reaches the maximum and the fuel injection port where the fuel reaches the minimum. Good. That is, in the example shown in FIG.
At the fourth fuel injection ports 10a, 10d, the distances A ₁ , A ₄ between the tip portions of the fuel injection ports 10a, 10d and the wall surface of the piston recess 3 as viewed in the fuel injection direction, and the fuel spray body 12a,
The recess inclination angle θ is set so that the following expression 2 is established between the reaching distances a ₁ and a _{4 of} 12d. The fuel reaching distances at the first to fourth fuel injection ports 10a to 10d have characteristics as shown in FIG. 4, for example.

[Formula 2] A ₁ −a ₁ = A ₄ −a ₄ ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… Light Injection port 10a-1
Since the adhering rate of the fuel injected from 0d to the wall surface of the piston concave portion 3 is made substantially uniform, the generation amount of HC is further reduced.

(3) Condition 3 The inclination angle θ of the recess is such that the lip 3 of the piston recess 3 is seen in a plan view.
The center of a is set so as to almost coincide with the center of the piston. That is, the recess inclination angle θ is set so that the widths (radial lengths) of the substantially annular portion of the top of the piston 2 where the piston recess 3 is not formed are substantially equal. For example,
Regarding the first and fourth fuel injection ports 10a and 10d, the recess inclination angle θ is set so that the following expression 3 is established between the lip lengths D ₁ and D ₄ .

[Formula 3] D ₁ = D ₄ …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… Since it is made uniform in the circumferential direction of 2, the mixing intensity of fuel and air at each of the fuel injection ports 10a to 10d is made uniform, the amount of smoke or HC generated is further reduced, and the emission performance is significantly improved.

Thus, the recess inclination angle θ is set so as to satisfy the above conditions 1 to 3, but if the recess inclination angle θ that completely satisfies the three conditions cannot be obtained, the condition 1 is satisfied.
Within the range that satisfies the above condition, first, the condition 2 should be made as close as possible, and then the condition 3 should be made as close as possible.

In this embodiment, the fuel injection nozzle 6 has four
Although the single fuel injection ports 10a to 10d are provided, the number of the fuel injection ports is not limited to this, and the present invention can be applied to a device provided with an arbitrary number of fuel injection ports. is there.

[0025]

According to the first aspect of the present invention, the ratio of the fuel injected from each fuel injection port to the amount of air involved in the combustion of the fuel, that is, the air utilization rate of the fuel is the same for all fuel injection ports. Almost uniformized. Therefore, local air shortage or excess air does not occur during fuel combustion in the piston recess. Therefore, the amount of smoke or HC generated is reduced to improve emission performance and fuel efficiency performance, and the intake air is effectively used for combustion of fuel to increase engine output.

According to the second invention, basically, the same operation and effect as those of the first invention can be obtained. Further, since the piston concave portion is formed into a substantially columnar shape, the air utilization rate of fuel can be made uniform by simple processing such as inclining the piston concave portion by a predetermined concave portion inclination angle, for example, drilling, so that the manufacturing cost is reduced. It

According to the third invention, basically the same action and effect as the second invention can be obtained. Further, the rate of adherence of the fuel injected from each fuel injection port to the wall surface of the piston recess is made substantially uniform, so that the amount of HC generated is further reduced.

According to the fourth invention, basically, the same operation and effect as those of the second or third invention can be obtained. further,
Since the squish area is made uniform in the circumferential direction of the piston, the mixing strength of the fuel and air at each fuel injection port is made uniform, the amount of smoke or HC generated is further reduced, and the emission performance is significantly improved.

[Brief description of drawings]

FIG. 1A is an elevation cross-sectional explanatory view of a piston of a direct injection diesel engine according to the present invention, and FIG. 1B is a plan explanatory view of the piston shown in FIG.

FIG. 2 (a) is an elevation cross-sectional explanatory view around a cylinder of a direct injection diesel engine according to the present invention, and FIG. 2 (b) is
It is a plane explanatory view of the piston of the engine shown in (a).

FIG. 3 is an elevational cross-sectional explanatory view of a fuel injection nozzle.

FIG. 4 is a diagram showing a fuel injection amount or a fuel reaching distance of each fuel injection port.

5 (a) is an elevation sectional view around a cylinder of a conventional direct injection diesel engine, and FIG. 5 (b) is a plane explanatory view of a piston of the engine shown in FIG. 5 (a).

[Explanation of symbols]

 DE ... Diesel engine 1 ... Cylinder 2 ... Piston 3 ... Piston recess 4 ... Combustion chamber 6 ... Fuel injection nozzle 10a-10d ... 1st-4th fuel injection port 12a-12d ... Fuel spray body

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masaaki Kashimoto 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Mazda Motor Corporation

Claims (4)

[Claims] 1. A piston recess that forms a part of a combustion chamber is formed at the top of a piston that is fitted in a cylinder, and a fuel injection nozzle that is arranged obliquely with respect to the cylinder axis is provided. The nozzle is provided with a plurality of fuel injection ports that face the piston recess when the piston is at the top dead center position, so that the angles formed by the fuel injection direction and the cylinder axis are substantially uniform. In the formed combustion chamber structure of a direct injection diesel engine, a piston recess is a ratio of an injection amount of fuel injected from a certain fuel injection port to a volume that a spray body of the fuel can occupy in the piston recess. However, the combustion chamber structure of the direct injection diesel engine is characterized in that it is formed so as to be substantially uniform over all fuel injection ports. 2. The combustion chamber structure for a direct injection diesel engine according to claim 1, wherein the piston recess has a substantially cylindrical shape, and the piston recess has a predetermined inclination relative to the piston axis. It is formed so as to have an angle with respect to the piston axis, and due to the inclination, the injection amount of fuel injected from a certain fuel injection port and the volume that can be occupied by the fuel spray body in the piston recess The structure of the combustion chamber of a direct injection diesel engine is characterized in that the ratio with the is almost uniform for all fuel injection ports. 3. The direct-injection diesel engine combustion chamber structure according to claim 2, wherein the inclination angle of the concave portion is the tip of a fuel spray body injected from a certain fuel injection port, and the tip. A combustion chamber structure for a direct injection diesel engine, characterized in that the distance to the wall surface of the closest piston recess is set to be substantially uniform for all fuel injection ports. 4. The combustion chamber structure for a direct injection diesel engine according to claim 2 or 3, wherein the recess inclination angle is such that the center of the lip of the piston recess is substantially coincident with the center of the piston in plan view. The combustion chamber structure of a direct injection diesel engine characterized by being set.