JPS63109221A - Combustion chamber for direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To improve utilization factor of the air in a combustion chamber for restraining discharge of unburnt exhaust substance, by forming a combustion chamber on piston top for arranging a fuel injection nozzle that injects fuel into the combustion chamber and also forming the combustion chamber in a specified form. CONSTITUTION:On a piston top 2, is formed, a combustion chamber 4 whose opening diameter is enlarged gradually along a center axis direction. The peripheral side wall 4a and the bottom wall 4b of the combustion chamber 4 are connected to each other with a curved surface. A fuel injection nozzle 10, which injects fuel into the combustion chamber 4, is arranged and set. The combustion chamber 4 is formed in such wise that the inlet opening diameter (d) of the combustion chamber 4, the depth (H) of the combustion chamber 4 and the maximum opening diameter (D) of the combustion chamber 4 are set in a range of 0.6<=d/D<=0.8, 2.5<=D/H<=3.5. According to this, it is vanished that squish flow rushes out from the combustion chamber 4 to a cylinder. In such wise, utilization factor of the air in the combustion chamber can be improved and discharge of unburnt exhaust substance can be restrained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to the combustion chamber of a direct injection diesel engine that supplies atomized fuel directly into the combustion chamber, and particularly improves the air utilization rate by giving flow to the air in the combustion chamber. The present invention relates to a combustion chamber of a direct injection diesel engine that aims to reduce unburned exhaust gas and smoke concentration while increasing the fuel efficiency and obtaining the desired output.

[Prior Art] A toroidal combustion chamber in which the bottom center of the combustion chamber is raised is generally known as the combustion chamber of a diesel engine.
In this toroidal combustion chamber, the air flow for mixing air and atomized fuel was weak, and good combustion was not obtained in terms of output and smoke.

Therefore, in recent years, as shown in Fig. 4, a combustion chamber with a circular horizontal cross section and a lip part a protruding radially inward at the circumferential portion of the upper part of the opening has been developed. As shown in the figure, a combustion chamber d whose horizontal cross section perpendicular to the axial direction of a piston C is square is formed, and a combustion chamber d is designed to generate turbulent flow T at a corner of the combustion chamber d.

However, in the square combustion chamber d, the squish flow (2) is not actively used, and in the combustion chamber with the lip part (a), the turbulent flow T of the combustion chamber (6) cannot be utilized.
As shown in the figure, because the swirling direction of the squish flow (■) and the radius of rotation (R) are not appropriate, a fuel reservoir q is created on the bottom wall e side, and an air zone h that cannot be used for mixing is created in the upper part of the combustion chamber f. HC is easily discharged in large quantities due to the formation of HC. On the other hand, if the turning radius R is set large as shown in FIG. 7, a part of the squish flow V will fly out of the combustion chamber, causing atomized fuel and air to flow out.

Part of the air-fuel mixture was also carried out of the combustion chamber, resulting in a reduction in power and causing misfires.

A combustion chamber structure described in West German Patent Application No. M 202631 a/46a2 is known as an attempt to solve this type of problem.

As shown in FIG. 8, this combustion chamber is located at the top of the piston.
is recessed along the axial direction to form a combustion chamber i whose horizontal cross section perpendicular to the axial direction of the piston is approximately square, and the peripheral side wall j of the combustion chamber i is gently recessed radially outward. Further, a lip portion n protruding radially inward is formed at the upper part of the opening excluding the corner m of the combustion chamber i,
The entrance opening formed by this lip part n is formed into a square shape.

[Problems to be Solved by the Invention] The above-mentioned combustion chamber is intended to create a swirl flow and a squish flow within the combustion chamber to increase the mixing of fuel spray and air to improve combustion performance. It is conceivable that, depending on the swirling direction and radius of the squish flow, a fuel pool may be created as described above, or a portion of the injected fuel, air, and mixture may be combusted along with a portion of the squish flow. This is not desirable as it will have to be carried outside.

[Means for Solving the Problems] The present invention aims to solve the various problems described above, and the present invention forms a combustion chamber at the top of the piston, the opening diameter of which is sequentially enlarged along the axial direction. The circumferential side wall and bottom wall of this combustion chamber are connected by a curved surface, and a fuel injection nozzle for injecting fuel into the combustion chamber is arranged, and the inlet opening diameter of the combustion chamber is d, and the depth of the combustion chamber is The maximum opening diameter of the H1 combustion chamber is D
Then, the shape of this combustion chamber is formed based on the following equation to configure the combustion chamber of a direct injection diesel engine.

0.6≦d/D≦0.8 2.5≦D/H≦3.5 [Function] Opening diameter d of the combustion chamber inlet opening, depth H of the combustion chamber, and maximum opening diameter of the combustion chamber The shape of the combustion chamber is determined by setting the angle in the range of 0.6≦d/D≦0.8 and 2.5≦D/H≦3.5, and connecting the bottom wall and peripheral side wall of the combustion chamber with a curved surface. This means that the turning radius of the squish flow that is pushed into the combustion chamber from the upper part of the opening of the combustion chamber is set to a radius that prevents the squish flow from jumping out from the combustion chamber into the cylinder. Also, the flow velocity of the squish flow is is set at a flow rate that does not cause partial fuel accumulation in the combustion chamber, so the air utilization rate in the combustion chamber is improved and the desired output is obtained, while unburned substances (HC, NOx, etc.) are removed from the exhaust gas.
etc.) and significantly reduce the smoke emission concentration.

[Embodiment] A preferred embodiment of a combustion chamber of a direct injection diesel engine according to the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a combustion chamber 4 is recessed in the piston top 2 of the piston 1 along the axial direction with the top surface 3 as a reference plane. The opening diameter of this combustion chamber 4 increases gradually along the axial direction, and the vertical cross section of the piston 1 passing through the axis line roughly forms a trapezoid, and the horizontal cross section of the piston 1 with respect to the vertical cross section is shown in FIG. It is formed into a rectangular shape as shown in .

Now, the feature of the direct injection diesel engine of the present invention is that the intensity and direction of the swirl flow and squish flow generated in the combustion chamber 4 are adjusted to generate an appropriate air flow, thereby improving combustion performance. It is in.

Therefore, each part of the combustion chamber 4 is constructed as follows.

Forming the combustion chamber 4 by sequentially expanding its diameter along the axial direction means forming a lip portion 5 projecting radially inward at the upper part of the combustion chamber 4. The opening diameter d of the inlet opening 6 to be formed affects the strength of the squish flow (2) and the engine output.

That is, if the opening diameter d is reduced to narrow the inlet opening 6, the strength of the culm squish flow (2) will increase, but the pumping loss of the piston 1 due to the narrowing will also increase. Keeping the bombing loss to a minimum and achieving the desired squish flow V
In order to obtain this strength, it is first necessary to set the opening diameter of the inlet opening 6 to an opening diameter d that minimizes the pumping loss, and then to form the squish flow V so that it can be easily swirled within the combustion chamber 4.

Therefore, the opening diameter d of the inlet opening 6 and the bottom wall 4b of the combustion chamber 4 are
The maximum opening diameter on the side is set based on equation (1).

0.6≦d/D≦0,8...Equation (1) (
1), the squish flow ■ with the desired strength flows into the combustion chamber 4.
However, the pushed squish flow ■ is dispersed by the bottom wall 4b, and a part of the dispersed squish flow ■ rides on the swirl flow S flowing toward the center of the combustion chamber 4 and becomes a swirl. The flow S is strengthened, and the remaining part is on the peripheral side wall 4.
It is reversed along the curved surface 4C where a and the bottom wall 4b are in contact. Here, the size of the radius of curvature R8 of the curved surface 4C gives a large effect on the air utilization rate of the combustion chamber 4 and the adhesion of the atomized fuel supplied to the combustion chamber 4 to the wall surface. That is, as shown in FIG. 6, if the radius of curvature R8 is too small, an air zone that is not used for mixing will be formed in the upper part of the combustion chamber 4, and the flow velocity of the squish flow V in the reversed portion will be increased. Become,
A fuel reservoir (referring to the state in which the atomized fuel becomes a liquid state and gathers in a part) is formed on the curved surface 4C side, and conversely, the radius of curvature R
If 8 is too large, the squish flow (2) of the reversed portion will jump out to the cylinder side as shown in Fig. 7, and as a result, part of the atomized fuel and part of the mixture in the combustion chamber This is undesirable as the parts are carried towards the cylinder side.

Since the formation of a fuel reservoir makes it difficult to vaporize the fuel, IC,
The amount of smoke emitted increases, and a portion of the air, air-fuel mixture, and fuel vapor is carried toward the cylinder, making misfires more likely to occur.

Therefore, when the depth of the combustion chamber is set to H, the curved surface R8 is determined based on the formula (W).

0.18≦R8ZH≦ 0, 32-(21 As a result, the radius of curvature of the curved surface 4C changes the radius of gyration of the squish flow ① in the reversed portion to also stir the air zone on the side of the inlet opening 6 of the combustion chamber 4, and It is possible to set the radius to such a value that no fuel pool is formed on the curved surface 4C.In other words, the air utilization rate is greatly improved.

Incidentally, the bottom wall 4b needs to be formed so that a part of the pushed squish flow (2) can easily move toward the peripheral wall 4a, and the remaining part can easily move toward the center of the combustion chamber 4. Therefore, the radius of curvature R of the bottom wall 4b is determined based on equation (3).

1.6≦R,≦2.2 (3) Here, it is assumed that the curved surface 4C and the bottom wall 4b are smoothly connected.

Next, in order to separate the squish flow V that is reversed from the curved surface 4C along the peripheral wall 4a and reverse it again to the bottom wall 4b, the peripheral wall 4a of the part that becomes the oblique side of the trapezoid has a straight smooth part 4d. is formed.

Therefore, even if the atomized fuel is injected near the smooth portion 4d, it is possible to prevent the atomized fuel from excessively adhering to the circumferential wall 4a.

Furthermore, as shown in FIG. 2, the combustion chamber 4 in this embodiment
is formed with a rectangular horizontal cross section so that the turbulent flow T that promotes the mixing of the atomized fuel and air is generated at the four circumferential corners of the combustion chamber 4. If each corner 7 is formed with
This may cause smoke to occur. Therefore, the four corners are clearly connected by the curved surface 8, and the radius of curvature R6 of this curved surface 8 is set based on the formula (4).

0.35 D≦Rc≦ 0, 5 [) ・(41
In addition, in order to completely separate a part of the squish flow (2) reversed along the circumferential wall 4a and to make it easier to push the squish flow V into the combustion chamber 4, the top surface 3 and the circumferential wall 4 are
The portion that connects the lip portion a, that is, the tip of the lip portion 5 is formed in an arc shape with a predetermined radius r. This radius r is formed based on equation (5).

0.2≦r/R8≦0.6 (51 By determining the shape of each part of the combustion chamber 4 as described above, the combustion chamber 4
The depth H and maximum opening diameter of the combustion chamber 4 are determined by the formula: [F]
) is formed based on.

2.5≦D/l-1≦3.5 ... [F]
) Next, the injection direction of the fuel injection nozzle 10 disposed on the bottom wall 4b side of the combustion chamber 4 and facing the peripheral side wall 4a is determined by the equation (7).
) is set based on

0.78 ≦h/H≦ 0.83 ... (
7) Here, h indicates the height based on the deepest part of the bottom wall 4b of the combustion chamber.

The operation of the combustion chamber of the direct injection diesel engine of the present invention will be explained below based on the accompanying drawings.

At the end of the compression stroke of the piston 1, inside the combustion chamber 4,
A swirl flow is generated that moves downward from the center of the combustion chamber 4 while swirling in the circumferential direction due to fluid inertia. At this time, a squish flow is pushed into the combustion chamber 4 from the outer peripheral side of the top surface 3a due to compression. ■ is generated.

This squish flow V has a radius of curvature 8 of the bottom wall 4b of the combustion chamber 4.
According to this, a part strengthens the swirl flow S along the swirl flow S, and the remaining part is reversed according to the radius of curvature R8 of the curved surface 4C. The squish flow (2) in the inverted portion is gradually separated by the smooth portion 4d that is a part of the circumferential wall 4a, and is completely separated at the portion connected to the tip of the lip portion 5.

Since the separated squish flow (2) is again reversed toward the bottom wall 4b, all of the air in the combustion chamber 4 is fluidized. Further, since turbulent flow T is generated at the corners of the combustion chamber 4, air flow in these parts is also ensured.

At the end of the compression stroke of the piston 1, that is, near the top dead center, fuel corresponding to the load is atomized and injected from the fuel injection nozzle. This atomized fuel is distributed on the bottom wall 4b side of the combustion chamber 4 and on the peripheral side wall 4.
a, that is, it is injected toward the vicinity of the smooth portion 4d. A part of the injected atomized fuel is vaporized by crossing the squish flow ■, and depending on the dispersion of the squish flow V, a part of the injected atomized fuel rides on the swirl flow S and is combusted. It is carried to the center side of the chamber 4, and the remaining part is carried on the squish flow V of the part to be inverted.

On the other hand, the remaining part of the atomized fuel that is about to penetrate the squish flow (2) and reach the peripheral wall 4a side is completely vaporized here because it flows counter-currently to the reversed part of the squish flow (2) and reaches the combustion chamber 4a again. is carried to the bottom wall 4b.

Therefore, the vaporized n-fuel is introduced into the squish flow v, producing a partially rich mixture, while the entire combustion chamber 4 has a uniform swirl flow S. A dispersed distribution of the air-fuel mixture is achieved, and the ignition of the rich air-fuel mixture is quickly propagated to the air-fuel mixture in the combustion chamber 4.

Therefore, in terms of combustion, the ignition delay is greatly shortened, and while maintaining the desired output performance, the combustion unburnt materials (HC, N
Combustion can be achieved with reduced smoke emissions and low smoke levels.

FIG. 3 shows the HC emission concentration and the smoke emission concentration when the radius of curvature R6 of the curved surface 8 is formed based on equation (4). According to the figure, the HC emission concentration is 420 [p,
p, m col 305' [p, p, m], the smoke emission concentration can be suppressed to within 2 [Bosch] at maximum.

Incidentally, a fuel injection nozzle 10 is disposed facing into the combustion chamber 4, and the fuel injection nozzle may be one that injects atomized fuel at intervals in the circumferential direction of the combustion chamber 4, or one that injects atomized fuel at intervals in the circumferential direction of the combustion chamber 4. It is configured to inject the main spray after injecting the atomized fuel spray, and the atomized fuel spray is injected at light loads, and the main spray is also injected when the load exceeds the light load. There are things that have been done. When these various fuel injection nozzles are provided, the spray direction is directed in a direction that intersects the above-mentioned squish flow V or in a direction that opposes it. At this time, the spray direction is determined so that the amount of air-fuel mixture in the combustion chamber can be generated in accordance with the load, with sufficient consideration given to the penetration force of the spray.

[Effects of the Invention] As is clear from the above explanation, the combustion chamber of the direct injection diesel engine of the present invention can exhibit the following excellent effects.

(1) A fuel that forms a combustion chamber whose opening diameter is gradually enlarged along the axial direction at the top of the piston, connects the peripheral side wall and bottom wall of this combustion chamber with a curved surface, and injects fuel into the combustion chamber. The injection nozzle is arranged, and the opening diameter d of the entrance part of the combustion chamber is
The combustion chamber was formed by setting the depth H of the combustion chamber and the maximum opening diameter of the combustion chamber within the range of 0.6≦d/D≦0.8 and 2.5≦D/H≦3.5. , the squish flow does not jump out from the combustion chamber to the cylinder, and as a result, the fuel spray and air can be confined in the combustion chamber and agitated effectively.

(2) Since no zone is formed in the combustion chamber where no air is used, combustion is improved and unburned substances (HC, NOx,
, smoke, etc.) emissions can be kept low.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a piston showing a preferred embodiment of the present invention, FIG. 2 is a top view of FIG. 1, and FIG. 3 is a performance showing the HC emission concentration and smoke emission concentration of the embodiment of the invention. figure,
FIGS. 4 to 8 are diagrams showing conventional combustion chambers. In the figure, 1 is the piston, 2 is the top of the piston, 3 is the top surface, 4
is a combustion chamber, 4a is a peripheral wall, 4b is a bottom wall, 4C is a curved surface, 4
d is a smooth portion, 5 is a lip portion, 6 is an inlet opening, and 10 is a fuel injection nozzle.

Claims (2)

[Claims] (1) A combustion chamber whose opening diameter is gradually enlarged along the axial direction is formed at the top of the piston, and the circumferential side wall and bottom wall of the combustion chamber are connected by a curved surface, and fuel is injected into the combustion chamber. A combustion chamber for a direct injection diesel engine, characterized in that an injection nozzle is provided and the combustion chamber has a shape based on the following formula. 0.6≦d/D≦0.8 2.5≦D/H≦3.5 In the formula, d is the opening diameter of the combustion chamber inlet opening H is the depth of the combustion chamber D is the maximum opening diameter (2) The combustion chamber is located in the axial direction of the piston. Claim 1, wherein the perpendicular cross section perpendicular to is formed into a substantially quadrangular shape, the circumferential side walls are connected to each other by a curved surface, and the bottom wall is formed by being recessed in an arc shape in the axial direction. Combustion chamber of a direct injection diesel engine.