JPH07238836A - Combustion chamber of direct injection diesel engine - Google Patents

Abstract

PURPOSE:To provide the same speed profile of rotating flow in a cavity as that in the combustion chamber of a diesel engine in the entire cavity. CONSTITUTION:A cavity 2 is recessed and provided on the top surface 5 of a piston 4 by off-setting from the cylinder center O1. Projections 12 protruded toward the opening 6 of the cavity 2 are provided on the bottom 11 of the cavity 2. A multi-nozzle hole nozzle 3 for supplying fuel spray toward the multidirections is provided in the cavity by off-setting from the cylinder center O1. The projections 12 are off-set to the cylinder center O1 side from the cavity center O2 by satisfying the relation of d1+I1=d2+I2=d3+I3. Where, the distance connecting the contact point of each nozzle hole 13 of the multi-nozzle hole nozzle 3 to the contact point of the first inner wall 9 of each fuel spray F sprayed from each nozzle hole with a straight line are d1, d2...,dn; the distance connecting each contact point to the center O3 of the projections 12 are I1, 12...,In.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in a direct injection diesel engine, an intake port is provided with combustion air (intake air) in order to generate a swirling flow that promotes mixing of fuel spray and air in a cavity. The swirl port for generating the swirling flow is provided, and a protrusion is provided in the central part of the cavity, that is, a part where the swirling flow is weak, to fill this part and improve the air utilization rate in the cavity. In order to improve the layout, there is one in which multiple nozzle nozzles are offset and the cavity that is the combustion chamber is offset from the center of the cylinder accordingly, and is formed on the top surface of the piston (JP-A-2-245418, etc.).

[0003]

However, the above-mentioned JP-A-2-
If a protrusion is provided at the center of the offset cavity as in Japanese Patent No. 245418, the sum of the distance from each nozzle of the multiple nozzle to the inner wall of the cavity and the distance from the inner wall to the center of the protrusion becomes shorter on the offset side. In the fuel spray injected as shown in FIG. 5, the spray F ₁ on the offset side reaches the projection 12 earlier and is wound up along the outer peripheral surface of the projection 12 into the cavity opening 6.
Further, the wind-up energy at this time also becomes larger in the spray F ₁ on the offset side, the mixing with air becomes non-uniform among the sprays, and unevenness occurs in the concentration of the air-fuel mixture generated in the cavity 2, In addition, since an excessively lean air-fuel mixture is locally formed, or an excessively rich air-fuel mixture is locally formed, NOx and smoke are deteriorated.

Further, the center of the cavity is the center of the cylinder O ₁
When offsetting from, the velocity of the swirling flow swirling in the cavity 2 becomes non-uniform, and there is a problem that the mixing of the combustion air and the fuel spray fails.

That is, as shown in FIG. 3, when the cylinder center O ₁ is aligned with the cavity center O ₂ , the velocity of the swirling flow v in the cavity 1 becomes uniform,
As shown in FIG. 4, when the cavity center O ₂ is offset from the cylinder center O ₁ , the flow velocity of the swirling flow in the cavity is high on the offset direction side and slow on the opposite side to the offset direction. The above problem is further exacerbated.

An object of the present invention is to provide a combustion chamber of a direct injection type diesel engine configured so as to generate an even combustible mixture in the entire cavity.

[0007]

A first means according to the present invention is a cavity formed in the top surface of a piston, and a projection provided at the bottom of the cavity so as to project toward the opening of the cavity. And a multi-injection nozzle for supplying fuel spray in multiple directions into the cavity, and the multi-injection nozzle in a combustion chamber of a direct injection diesel engine in which the center of the multi-injection nozzle and the cavity center are offset from the cylinder center. The distances connecting the contact points between the respective nozzles and the first inner wall of the respective fuel sprays injected from this with straight lines are d ₁ , d ₂ , ..., D _n , respectively, and each contact point and the center of the projection are straight lines. I _1, I ₂ connecting distance traveled, respectively, ..., is obtained as a I _n, may satisfy the relation _{d 1 + I 1 = d 2} + I 2 = d n + I n.

Further, the second means is that a cavity is provided in the top surface of the piston, a projection is provided at the bottom of the cavity so as to project toward the opening of the cavity, and the fuel spray is supplied in multiple directions in the cavity. In a combustion chamber of a direct injection diesel engine in which the multi-injection nozzles and the cavity center are offset from the cylinder center. d _1, d ₂ the distance connecting the contact points with a straight line between the first inner wall of the fuel spray, respectively, ..., and d _n,
Let I ₁ , I ₂ , ..., I _{n be the} distances that connect each contact point and the center of the protrusion with a straight line, respectively, and d ₁ + I ₁ = d ₂ + I
The projections are offset from the center of the cavity toward the center of the cylinder so as to satisfy the relationship of ₂ = d _n + I _n .

[0009]

According to the first means, the fuel spray injected from the multi-injection nozzle swirls in a U-shape in the order of the inner wall, the bottom and the outer peripheral surface of the protrusion, and winds up near the cavity opening. At this time, since the distance from each injection port to the center of the protrusion is the same, the flight distance and flight time of each fuel spray become approximately the same value, and the time at which each fuel spray winds up near the cavity opening and its winding energy are the same. And the mixing of each fuel spray with the air is equalized.

According to the second means, as compared with the combustion chamber of the conventional direct injection diesel engine in which the projection is provided in the center of the cavity and the cavity is offset from the center of the cylinder, the cross-sectional area of the cavity with respect to the swirling flow is The center side of the protrusion is smaller than the conventional one, and the opposite side is larger than the conventional one. Therefore, the speed of the swirling flow is higher on the cylinder center side than the conventional centering on the protrusion and lower on the opposite side than the conventional one. Therefore, the non-uniformity of the velocity of the swirling flow in the cavity is eliminated, and when the multiple nozzles supply fuel spray to the cavity in multiple directions, the mixture of uniform concentration is mixed in the cavity. Is generated evenly.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a sectional view of a cylinder head, a cylinder and a piston along the axial direction of the cylinder, and FIG. 2 shows a plan view of the piston as seen from the cylinder head side.

The cavity 2 which defines the combustion chamber 1 extends from the cylinder center O ₁ of the cylinder 14 to the cavity center O _1.
2 is provided with an offset, and the multi-injection nozzle 3 allows the piston 4 to move when the piston 4 rises near the top dead center.
Between the relief portion (recessed portion) of the valve face of the intake valve (not shown) on the top surface 5 and the relief portion (recessed portion) of the valve face of the exhaust valve (not shown) and of the opening 6 of the cavity 2. The nozzle head 7 is attached to the cylinder head 8 so that the nozzle portion 7 is located near the center (near the center O _{2 of the} cavity).

In the present embodiment, the cavity 2 has a round cross section (a cross section along a direction orthogonal to the axial direction of the piston 4), and an inner wall 9 thereof has an upper portion in a circumferential direction. A lip 10 is provided along the edge of the cavity 11, and a protrusion is formed on the bottom 11 so as to extend substantially vertically from a position where the round opening 6 of the cavity 2 defined by the lip 10 can be seen toward the opening 6. 12 are provided.

In this case, as shown in FIG. 1, the bottom portion 11 of the cavity 2 is constituted by a curved surface outward in the radial direction that smoothly connects the projection 12 and the inner wall 9, and the inner wall 9 of the cavity 2 is formed. Is configured by a downward curved surface that smoothly connects the radially outer end side of the bottom portion 11 and the lower end of the lip 10.

In this embodiment, the directions of the nozzles 13 of the multiple nozzles 3 with respect to the cavity 2 and the positions of the projections 12 were determined as follows.

First, as a premise, the inner wall 9 of the cavity 2 is
Is divided by the number of nozzles 13 to equally divide the cavity 2 in the circumferential direction, and a large number of nozzles 13 are provided at each position obtained by the division.
To assign each one of. In this case, the direction of each nozzle 13 is set so that the upper portion of the inner wall 9 can be seen from above through the opening 6 of the cavity 2. further,
The direction of the fuel spray F injected from each nozzle 13 is set as follows.

That is, the direction of each injection port 13 is set so that the fuel spray F injected from the injection port 13 first contacts the upper portion of the inner wall 9. Secondly, almost all of the fuel spray F after coming into contact with the inner wall 9 goes to the bottom 11 of the cavity 2 along the inner wall 9 of the cavity 2, and further along the bottom 11 of the cavity 2 the outer peripheral surface of the projection 12 on the base side. Set to go to. In this case, the nozzles 13 of the multiple nozzles 3 have the same diameter, and the fuel injection pumps (not shown) acting on the nozzles 13 have the same oil feed pressure. Then, the flight distance and flight time of each fuel spray F are made equal to each other so that the air-fuel mixture of the same concentration is evenly dispersed throughout the cavity 2, and the air-fuel mixture made by the fuel spray F simultaneously projects. In order to make it roll up from the nozzle to the cavity opening, as shown in FIG.
The distances of straight lines connecting the first contact points X ₁ , X ₂ , ..., X _n with the inner wall 9 of the cavity 2 of each fuel spray F injected from these nozzles 13 are d ₁ , d ₂ ,. _{, n,} and a distance connecting each contact point X ₁ , X ₂ , ..., X _n with the center O ₃ of the protrusion 12 of each spray F by a straight line is I ₁ , respectively.
When I ₂ , ..., I _n , d ₁ + I ₁ = d ₂ + I ₂
= D _n + I _n The position of the projection 12 or the direction of each nozzle 13 or the curvature and depth of the inner wall 9 and the bottom 11 are modified so as to satisfy the relationship of = d _n + I _n .

That is, each fuel spray F is applied to the inner wall 9 and the bottom portion 1.
1 and the outer peripheral surface of the protrusion 12 are swung up and down in a U-shape in this order, and are wound up near the opening 6 of the cavity 2. At this time, since the distance from each nozzle 13 to the center O ₃ of the protrusion is the same, the flight distance and flight time of each fuel spray F become substantially the same value, and each fuel spray F rolls up near the opening 6 of the cavity 2. The time and the winding energy thereof are substantially the same between the fuel sprays F, and the mixing of the fuel sprays F with the air is equalized.

Further, in this embodiment, the protrusion 12 is
It is formed in the shape of a cylinder or a cone, and the position thereof is such that the center O _{1 of} the cylinder and the center O _{2 of the} cavity are satisfied while satisfying the above-mentioned configuration.
It is provided at a position between the cavity center O ₂ and the cylinder center O ₁ and on the cylinder center O ₁ side in a straight line passing through and.

When the projection 12 is set in such a position, the projection 12 is provided in the center of the cavity 2 and the cavity 2 is offset from the cylinder center O ₁ as compared with the combustion chamber of the conventional direct injection diesel engine. The cross-sectional area of the cavity 2 with respect to the swirling flow v becomes smaller on the cylinder center O ₁ side than the conventional centering on the protrusion 12 and larger on the opposite side than the conventional one. Therefore, as for the flow velocity of the swirling flow v of the cavity 2, the flow velocity on the cylinder center O ₁ side with respect to the protrusion 12 becomes higher than that in the conventional case, and the flow rate on the opposite side becomes smaller than that in the conventional case. Therefore, the nonuniformity of the velocity of the swirling flow v in the cavity 2 due to the offset of the cavity 2 is eliminated.

[0022] Here, provided with the projections 12 cylinder center O ₁ side, while satisfying the above-described configuration, the turning of the flow velocity and the opposite side of the swirling flow v of the cylinder center O ₁ side around the projection 12 It is nothing but the provision of the projection 12 at a position where the flow velocity of the flow v can be made substantially the same.

In such a cavity 2, if fuel spray is supplied from each of the nozzles 13 of the multi-nozzle nozzle 3 in multiple directions of the cavity 2, a mixture of a certain concentration (preliminary It is possible to evenly disperse the mixture.

Further, the lip 10 has a protruding length inward in the radial direction, which prevents intake air (combustion air) supplied into the cavity 2 after being swirled by the intake port from spilling out of the cavity 2. It is determined so that the fuel spray F ejected from each of the nozzles 13 of the multi-nozzle nozzle 3 can be prevented from spilling out of the cavity 2, and the mixture can be prevented from diffusing out of the cavity 2 and the combustion flame flowing out. ing.

Combustion starts with spontaneous ignition of the air-fuel mixture vaporized in the periphery of each fuel spray F as it contacts the inner wall 9. This flame is propagated to the air-fuel mixture that grows toward the projection 12, and completes combustion when the flame is propagated to the tip of the air-fuel mixture. Therefore, ignition timing, ignition position,
The flame propagation speed is also the same for each fuel spray F, and the end timing and end position of combustion are the same for each fuel spray F, so that even combustion is performed.

Therefore, a uniform air-fuel mixture is formed, combustion with a high air utilization rate is realized, and NOx and smoke can be greatly reduced.

Incidentally, it is of course possible to form a thin fuel film which is diffused downward on the inner wall 9 when the fuel spray F injected from each of the injection ports 13 contacts the inner wall 9.

[0028]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) Since the distance from each nozzle to the center of the protrusion is made equal, the flight distance and flight time of each fuel spray become approximately the same value, and the time when each fuel spray rolls up near the cavity opening. And the winding energy thereof is substantially the same between the fuel sprays. Therefore, the mixing of each fuel spray with the air can be made uniform.

(2) A swirling flow having uniform velocity can be generated in the cavity, and a mixture having uniform concentration can be generated in the cavity.

(3) The ignition timing, the ignition position, and the flame propagation speed are the same for each fuel spray, and the end timing and the end position of combustion can be the same for each fuel spray, so that even combustion can be achieved. Can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a preferred embodiment of the present invention.

FIG. 2 shows a plan view of the piston as seen from the cylinder head side.

FIG. 3 is a diagram for explaining a velocity distribution of a swirling flow in a cavity when the center of the cylinder and the center of the cavity are aligned with each other.

FIG. 4 is a view for explaining a velocity distribution of a swirling flow in a cavity when the center of the cavity is offset from the center of the cylinder.

FIG. 5 is a view showing a combustion chamber of a conventional direct injection diesel engine.

[Explanation of symbols]

2 Cavity 3 Multiple injection nozzle 4 Piston 5 Top surface 6 Opening 9 Inner wall 10 Lip 11 Bottom 12 Protrusion 13 Injection port O ₁ Cylinder center O ₂ Cavity center O ₃ Protrusion center F Fuel spray

Claims (4)

[Claims] 1. A cavity formed as a recess on the top surface of a piston, a projection provided at the bottom of the cavity so as to project toward the opening of the cavity, and fuel spray is supplied into the cavity in multiple directions. In a combustion chamber of a direct injection type diesel engine having a multi-injection nozzle and offsetting the center of the cavity and the center of the cavity from the center of the cylinder, each injection port of the multi-injection nozzle and the first of the fuel sprays injected therefrom d ₁ of the distance connecting the contact points with a straight line of the inner wall, respectively, d _2, ..., and d _n, each contact and the projection center and the the distance that connecting with straight lines I _1, I _2, ...,
As I _n, the combustion chamber of _{d 1 + I 1 = d 2} + I 2 = d n + I n direct injection diesel engine, characterized in that it has adapted to satisfy the relation. 2. A cavity formed as a recess in the top surface of the piston, a protrusion provided at the bottom of the cavity so as to project toward the opening of the cavity, and fuel spray is supplied into the cavity in multiple directions. In a combustion chamber of a direct injection type diesel engine having a multi-injection nozzle and offsetting the center of the cavity and the center of the cavity from the center of the cylinder, each injection port of the multi-injection nozzle and the first of the fuel sprays injected therefrom d ₁ of the distance connecting the contact points with a straight line of the inner wall, respectively, d _2, ..., and d _n, each contact and the projection center and the the distance that connecting with straight lines I _1, I _2, ...,
As I _n, the combustion of _{d 1 + I 1 = d 2} + I 2 = d n + I n direct injection diesel engine of the projections so as to be able to satisfy, characterized in that is offset from the cavity center cylinder center side relationship Room. 3. The inner wall and the bottom wall of the cavity are curved surfaces and are connected to each other so as to smoothly guide each fuel spray to the outer peripheral surface of the protrusion.
Combustion chamber of the direct injection diesel engine described. 4. The combustion chamber of a direct injection diesel engine according to claim 1, wherein the cavity has a lip at an upper end portion of an inner wall thereof so as to circumferentially border the inner wall.