JPH03182617A - Combustion chamber for direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To enable the heating of combustion chamber walls to high temperature by forming the whole of a combustion chamber or only fuel spray collision wall surface parts of ceramic. CONSTITUTION:Spray collision walls 4a-4d, against which fuel spray injected from a fuel injection nozzle 3 to the inner wall of a cavity 2 in a piston 1 collides, are formed in such a way that the axial center of each nozzle hole is inclined being deviated to the swirl downstream side in their sectional forms vertical to a cylinder axis and expanded downward in their sectional forms in the axial direction of the cylinder. Protruding parts 7a-7d protruding inward the cavity 2 are formed more on the swirl downstream side than intersections between the inner wall of the cavity 2 and the respective axes of nozzle holes. In this case, the whole cavity 2 or only the parts around the spray collision walls 4a-4d are made of ceramic. The combustion chamber wall is thereby heated to high temperature so as to accelerate fuel evaporation as well as reduce initial combustion and combustion noise. In addition, unburnt fuel and soot discharge can be reduced by the high temperature combustion chamber wall.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a combustion chamber of a direct injection diesel engine, and in particular, significantly improves combustibility by suppressing the dispersion of fuel spray and subsequently improving the mixing of fuel and air. The present invention relates to a combustion chamber of a direct injection diesel engine that can be used for direct injection.

[Prior Art] Conventionally, a direct-injection diesel engine injects fuel from a plurality of injection holes of a fuel injection nozzle into a canty formed on the top surface of the piston when the piston is near the top dead center. For example, Makoto Matsuoka's research perspective ``Elucidation of the black box in diesel combustion'' in the Transactions of the Japan Society of Mechanical Engineers (B edition), Vol. 51, No. 461, published in January 1985, is known as an explanation of combustion in engines. . According to this, the momentum of the fuel spray is strongly concentrated on the central axis of the spray, so in small direct-injection diesel engines, the distance between the injection nozzle and the inner wall of the cavity may be short, or the spray may reach the inner wall of the cavity. When a collision occurs at right angles, the fuel/air mixture is concentrated on the wall surface, and the outside is covered with combustion/burnt gas, resulting in poor air supply (air introduction-trapping phenomenon). However, when the spray collides obliquely with the wall at a predetermined angle from the upstream side of the swirl, a mixture of the spray and air is first formed, and then the generated burnt gas is drawn in, creating a rolled carpet that is more powerful than the three-layer structure. By forming a shaped mixed mass, the above-mentioned trap phenomenon caused by the burnt gas can effectively disperse the reduced fuel, and when a vortex with a large acceleration acts on this, the formed mixed mass is destroyed and the air is It has been clarified that the usage rate will improve.

On the other hand, in the case of small direct injection diesel engines, reduction of combustion noise is required. Therefore, in order to improve quietness while maintaining output, fuel efficiency, etc., it is necessary to take into account Makoto Matsuoka's outlook and develop a realistic deep-dish type of compact direct-injection diesel engine installed in vehicles. It is thought that by introducing and developing the above theory into the cavity (combustion chamber at the top of the piston), it will be possible to develop a quieter combustion chamber with better combustibility.

Therefore, in Japanese Patent Application No. 62-28979 (see Japanese Patent Application Laid-Open No. 63-95315), the present inventors proposed that when the piston is near the top dead center, the fuel injection nozzle is injected from one or more nozzle holes. In the combustion chamber of a direct-injection diesel engine in which fuel is injected into the cavity formed on the top surface of the piston, the spray collision wall where the fuel spray collides with the cavity inner wall is cut into a cross section perpendicular to the cylinder axis. The shape is such that the axis of each nozzle hole is tilted toward the downstream side of the swirl, and gradually expands downward in the longitudinal cross-sectional shape along the cylinder axis direction, and the axis of each nozzle hole on the inner wall of the cavity is We proposed a combustion chamber for a direct-injection diesel engine that has a structure in which protrusions protrude inward from the swirl downstream of the intersection with the swirl.

By configuring the combustion chamber as described above, while reducing the initial combustion and silencing the noise caused by the rapid combustion, the air-fuel mixture By forming a sufficiently stratified mixture of fuel spray, air, and burnt gas due to the wrapped carpet effect, the dispersion of fuel spray is suppressed and air introduction is increased, and each protrusion on the downstream side of the swirl This destroys the rolling stratified mixture as described above, mixes the fuel spray with suppressed dispersion and air well, and also generates turbulent flow to take in the remaining air from the entire cavity. Enhancing the mixing of the entire gas is achieved.

[Problems to be Solved by the Invention] However, the above-mentioned conventional techniques do not mention the material of the combustion chamber. For example, when a normal metal material is used as the material for the combustion chamber, the combustion chamber cannot be heated above a predetermined temperature, so the fuel OII flows along the low-temperature combustion chamber wall, which prevents fuel evaporation and temperature rise. As a result, the ignition delay increases, resulting in the opposite effect of rapid initial combustion. Furthermore, during low-load or startup operation, fuel adheres to the wall surface of the combustion chamber, resulting in an increase in the amount of unburned fuel discharged.

The present invention has been made in view of the above-mentioned problems, and makes use of the advantages of the above-mentioned Japanese Patent Application No. 62-28979, namely, it sprays fuel both in a plane perpendicular to the cylinder axis and in a plane in the direction of the cylinder axis. By colliding with the inner wall of the cavity at a predetermined angle and forcefully rolling the fuel spray throughout the cavity, a sufficient stratified mixture of the fuel spray, air, and burnt gas is formed while avoiding rapid combustion that impairs quietness. By making the combustion chamber with ceramic to suppress the dispersion of fuel spray, it is possible to raise the temperature of the combustion chamber wall, further improving the advantages of the above patent application No. 62-28979, reducing initial combustion and reducing combustion noise. The present invention was based on the discovery that it is possible to reduce the

[Means for Solving the Problems] According to the present invention, when the piston is near the top dead center, fuel is injected into the cavity formed in the top surface of the piston from one or more injection holes of the fuel injection nozzle. A combustion chamber of a direct injection diesel engine configured to inject fuel, the combustion chamber is made of ceramic, and a spray collision wall on which the fuel spray injected from the injection hole collides with the inner wall of the cavity is connected to the cylinder. In a cross-sectional shape perpendicular to the axis, the axes of each of the nozzle holes are inclined toward the downstream side of the swirl, and in a cross-sectional shape in the cylinder axis direction, the axes of the nozzle holes are formed so as to expand downward, and the inner wall of the cavity and the axis of each of the nozzle holes There is provided a combustion chamber for a direct injection diesel engine, characterized in that protrusions projecting inward of the cavity are formed on the downstream side of the swirl from the intersection with the center.

[Operation] By employing the above-described configuration, the present invention allows the fuel spray from the fuel injection nozzle to obliquely collide with the spray collision wall (inner wall of the cavity), in a plane perpendicular to the cylinder axis, and in a plane perpendicular to the cylinder axis. While rolling in the plane of the direction, burnt gas is drawn in through the air to form a three-layer mixture, thereby suppressing the dispersion of the fuel spray and slowing down the evaporation and mixing state of the spray. Aim for good initial combustion by avoiding rapid combustion that may cause noise problems.

Furthermore, on the downstream side, this rolled mixture encounters separation-like turbulent flow generated at a protrusion (or layered cross-section) installed approximately at right angles or obliquely to the flow. The roll-shaped three-layer mixture (mixture separation) is strongly destroyed and peeled off from the wall, and the contact area with the remaining air in the cavity increases, resulting in good mixing of the fuel spray and air. This improves combustibility after initial combustion.

Furthermore, in the present invention, the entire combustion chamber or only the vicinity of the fuel spray collision wall is made of ceramic.

Therefore, the temperature of the combustion chamber wall is increased, and the evaporation of the fuel is promoted, so that the initial combustion is further reduced and the combustion noise is further reduced compared to a combustion chamber made of a metal material. Also,
Even during low-load operation or during start-up, the combustion chamber walls become hotter, reducing the amount of unburned fuel discharged. Furthermore, due to the high temperature of the combustion chamber wall due to ceramicization, the reaction rate of harmful emissions such as soot is increased compared to a metal combustion chamber, and the combustion reaction is sufficient to support the above-mentioned good mixing of the fuel spray and air. The resulting soot emissions are reduced and the combustion period is shortened, further improving thermal efficiency. Moreover, as a result, even if injection timing is delayed or EGR is performed in order to reduce nitrogen oxides, the thermal efficiency will be reduced or reduced.

The type of ceramic used as the material for the combustion chamber in the present invention is not particularly limited, and any type of ceramic such as alumina, zirconia, silicon nitride, silicon carbide, etc. can be used. From this point of view, silicon nitride and zirconia are preferably used.

In addition, in the combustion chamber of the present invention, the protrusion amount or layered cross-section of the protrusion protruding inward of the cavity so as to be approximately perpendicular or oblique to the spray flow direction is 0.03D to 0.10 (D is It is preferable to set the diameter within the range of the reference diameter of the cavity), since the mixing of fuel and air will be even better.

If the protrusion amount of the protrusion or the layered cross section is smaller than 0.03D, the strength of the turbulent flow will be weak, and the rolled layered mixture will not be sufficiently destroyed, resulting in poor mixing of fuel and air.

In addition, if the protrusion amount or layered cross section is made larger than O or 1D, the attenuation of the swirl becomes too large, which reduces the turbulence that has been generated. can't receive it,
Mixing of fuel and air becomes worse.

On the other hand, when the combustion chamber is made of metal, if the protrusion amount or the layered cross-section of the protrusion exceeds 0.1D, melting or cracking will occur, resulting in damage.

[Examples] Hereinafter, the present invention will be described in more detail based on illustrated embodiments, but the present invention is not limited to these embodiments.

FIGS. 1 to 3 show an embodiment of the combustion chamber of the direct injection diesel engine according to the present invention, in which the combustion chamber is made of ceramic only near the spray impingement side or entirely.
1 is a piston, and a cavity 2 is formed in the top surface of the piston 1 in a concave shape. Further, a fuel injection nozzle 3 having a plurality of injection holes is arranged above the cavity 2, and the six injection holes are provided downward at 0 degrees from the horizontal plane (Fig. 4), and the piston 1 is located at the top dead center. When the fuel injection nozzle 3 is nearby, fuel is injected into the cavity 2 from each injection hole of the fuel injection nozzle 3.

Further, as shown in FIG. 3, among the inner walls of the cavity 2, the spray collision walls 4a to 4d with which the fuel spray collides have an axial center 6a to 6d of each nozzle hole in a cross-sectional shape perpendicular to the cylinder axis. are respectively 0 on the swirl downstream side (thick arrow side)
．． It is formed to be inclined by ~θ4. These inclination angles 01 to θ4 are, for example, θ1 and 04 are approximately 15 degrees, θ
, and θ3 are approximately 5 degrees. Each of these angles of inclination is 0,
The difference in ~θ4 is due to the fact that the center of the tip nozzle hole of the fuel injection nozzle 3 is offset from the center of the cavity 2, and the reason why the inclination angle is set to this degree is to prevent the collision of the spray. If the angle is too small (01 to θ4 is small), the spray cannot roll sufficiently in the plane perpendicular to the cylinder axis, and if the fuel, air, and burnt gas are stratified, the new and old gases will be separated by swirl. On the other hand, if the spray impact angle is too large (0
1 to θ4), the R (R2) of the cavity wall on the downstream side of the swirl becomes too small due to the spray collision site, and the roll of the spray becomes too small, making it impossible to form a large stratified mixture, and the swirl is attenuated more than necessary. This is because giving sufficient turbulence to the spray will result in poor mixing of fuel and air.

Further, as shown in FIG. 4, the spray collision walls 4a to 4
d is formed so that its cross-sectional shape in the cylinder axis direction gradually expands downward, and as a result of various experiments, it is preferable that the angle between it and the horizontal plane is about 75°±10@.

Furthermore, as shown in FIG. 5, the positional relationship between the spray axis and the protrusion in a plane perpendicular to the cylinder axis, that is, the protrusion 7a, 7d on the swirl downstream side of each axis 6a to 6d and the fuel injection nozzle. The rim connecting the tip nozzle nozzle 3 and each axis 6
Let φ be the angle formed by the axes 6 a to 6 d, and φ is the angle between the edge 2 and the edge connecting the protrusions 7 a to 7 d on the upstream side of the swirl of each axis 6 a to 6 d and the nozzle hole. When φ, /φ.

is preferably in the range of 0.4D to 0.85 from the viewpoint of improving noise and engine output.

This is because if the collision site of the spray is too close to the protrusion on the downstream side of the swirl (φ, /φ is smaller than 0.40), the length of the cavity wall along which the spray runs is short, resulting in insufficient roll formation. This is because the roll is destroyed before it is formed due to the closeness of the turbulent flow generation part, and a sufficient layered mixture cannot be produced in the roll.

On the other hand, if the collision site of the spray reaches the protrusion on the downstream side of the swirl too much (if φ1/φ0 is larger than 0.85), the swirl will not be as strong at low or medium speeds of the engine because it is far from the turbulence generation area. This is because the stratified mixture of rolls and the turbulent flow do not match well in the castle, and this stratified mixture is not sufficiently destroyed.

Further, the circumferential edge of the cavity 2 extends inward to form a lip portion 5, which confines the jet flow within the cavity 2 and draws the squish flow from the top surface of the piston into the cavity so that it can move in the axial direction of the cylinder. Small swirls (micro-swirls) are formed within the plane to promote mixing of fuel and air.

Further, each nozzle hole axis 6 on the inner wall of the cavity
Protrusions 7a to 7d projecting inward of the cavity are formed downstream of the swirl from the intersections a to 6d, respectively. Here, the protrusion includes a cliff-like section,
Examples of this are shown in the partial cross-sectional views of FIG. 6(a) (example of a protrusion) and FIG.
The figure shows the positional relationship in the combustion chamber in the case of four nozzle holes in the protrusion or layered cross section. Figure 7 (a) is a plan view of the interior of the combustion chamber, and Figure 7 (b) is an expanded view of the interior of the combustion chamber. Figure, Figure 7 (
C) shows a cross-sectional view of the inside of the combustion chamber. Moreover, FIG. 7(d) is a sectional view showing a modification of FIG. 7(c). It can be seen from FIGS. 7(a), 7(b), 7(c), and 7(d) that the spray streams 8a to 8d collide with the protrusions or layered cross sections 7a to 7d, respectively, obliquely rather than at right angles. Here, the protrusion amounts t1 to t4 of each protrusion or layered cross-section portion 7a to 7d are as follows:
As mentioned above, it is within the range of 103D to 0.1D (D is the standard diameter of the cavity).

Incidentally, the ratio D/)l between the reference diameter of the cavity 2 and the depth H of the cavity 2 is preferably about 2.2 to 3.2, and the ratio h/H between the injection height h and the cavity depth H is 0.2-0.5
Also, as shown in Figure 3, R1 of the cavity periphery between the protrusions is swirl upstream R1 is the width of the entire band-shaped spray (spray with a width of about 20") or the swirl relative to the cavity wall surface. Large R that can be directed downstream
R2 on the downstream side of the swirl should be set to about (0.4 to 0.6>・D), and R2 should be set so that it does not become a sharp protrusion that could be destroyed before the roll-wound stratified mixture is generated.
It is preferable to set R00 to be smaller than R1 (0.5 to 0.7) so that a sufficient roll can be generated.

Next, the operation of the embodiment will be explained.

When the piston l is near the top dead center, the fuel injection nozzle 3
The spray injected from the plurality of nozzle holes hits each of the spray collision walls 4a to 4d at an inclination angle of θ, -θ4 in a plane perpendicular to the cylinder axis, and at an inclination angle of (9) in a plane in the cylinder axis direction.
The liquid fuel collides with the high-temperature ceramic wall at a temperature of 0 - ma + α), evaporates rapidly, and rolls in the plane perpendicular to the cylinder axis and in the cylinder axis direction, as shown in Figures 1 and 2. By drawing in burnt gas through air to form a three-layer mixture, fuel dispersion is suppressed, and compared to conventional engines, air promotes combustion and burnt gas inhibits combustion. By involving the fuel in a good proportion, good initial combustion is achieved with rapid combustion suppressed, and noise is reduced.

Furthermore, the air-fuel mixture that moves to the downstream side of the swirl while rolling is separated from the wall surface because each of the protrusions or layered cross sections 7a to 7d are installed so as to be approximately perpendicular or oblique to the spray flow. However, it also works well with the turbulent flow generated there (fifth
According to the angle of φ shown in the figure), the introduction of fresh air is promoted, the three-layer mixture is strongly destroyed, and the fuel and air are mixed well, suppressing dispersion in the cavity. In addition, this mixing is further promoted by the microswirl, and the combustibility is significantly improved.

As a result, compared to engines using conventional metal combustion chambers, initial combustion is suppressed and noise is reduced, mid-term combustion is activated, engine output increases, and combustion (described below) ends earlier. This reduces fuel consumption and smoke.

In the present invention, it is preferable that the fuel injection nozzle has about 1 to 6 nozzle holes.

Further, FIG. 8 is a longitudinal cross-sectional side view of the combustion chamber in the case where only the fuel spray collision wall portion is formed of ceramic. shows an example formed of metal.

Hereinafter, in order to provide a detailed explanation of the present invention, specific implementation results will be described.

(Example 1) A piston having almost the same combustion chamber shape as in FIGS. 1 to 3, two types of conventional metal pistons (2 types of impact angle θ (FIG. 3) = 90" B: Impact Angle θ (Figure 3)
=90''-140°), and using the piston (C) of the present invention, which is made of ceramic (made of silicon nitride) of the piston B,
The relationship between the noise level and the net average effective pressure was compared under the following operating conditions: the number of injection holes was 4, the swirl ratio was 2.5, the injection timing was fixed, the smoke was constant, and the rotation speed was 2200 rpm. The results are shown in the graph of FIG.

Among the metal pistons A and B, the reason why B is quieter than A is because the angle of impact with the wall surface was oblique, creating a carpet roll effect. In addition, piston C, which is made of ceramic and has the same shape as piston B, has a lower noise level at almost the same net average effective pressure, indicating that the piston of the present invention is effective in reducing noise.

Further, regarding the piston C of the present invention, N in the exhaust gas when the injection timing is changed.

The change in the amount of X is shown in Figure io. As is clear from Figure io, NOx is the lowest in the case of X, where the injection timing is delayed the most, and as shown in Figure 11, the net average effective pressure is larger in Z+Y, and is the same in Y-+X. In both cases, noise is reduced while maintaining the same level of noise.

This is because the injection timing is delayed as shown in (Z-4Y-4X), which lowers the gas temperature and reduces NOx, and also changes the piston position to optimize the wall collision angle of the spray.
It is estimated that an increase in the net average effective pressure or a reduction in noise and interference was achieved.

[Effects of the Invention] As explained above, according to the combustion chamber of the direct injection diesel engine of the present invention, the dispersion of fuel spray is suppressed, and the fuel, air, and burnt gas in the cavity are well mixed, and moreover, By partially or entirely ceramicizing, it is possible to raise the temperature of the fuel chamber wall during fuel collision, which promotes fuel evaporation within the cavity and mixes well with air, significantly improving combustibility and improving engine output. In addition, initial combustion can be reduced and combustion noise can be reduced.

[Brief explanation of drawings]

Figure 1 is a plan view of the piston, Figure 2 is its vertical side view,
Fig. 3 is an enlarged plan view of the cavity, Fig. 4 is a vertical side view thereof, Fig. 5 is an explanatory diagram showing the positional relationship between the spray axis and the protrusion, and Fig. 6 is a partially enlarged view of the protrusion. (A) shows an example of a protrusion, and (0) shows an example of a cliff-like cross section. Figure 7 shows the positional relationship of the protrusion or cliff-like cross-section in the combustion chamber. Figure 7 (a) is a plan view of the inside of the combustion chamber, Figure 7 (b) is a developed view of the interior of the combustion chamber, and Figure 7 (c) is a cross-sectional view inside the combustion chamber.
FIG. 7(d) shows a sectional view of a modification of FIG. 7(c). Figure 8 is a longitudinal cross-sectional side view of a combustion chamber in which only the fuel spray collision wall is made of ceramic, and Figure 9 is a graph comparing the relationship between noise level and net average effective pressure for three types of combustion chambers. Figure 10 shows the piston C of the present invention.
(FIG. 9) is a graph comparing the relationship between injection timing, NO, and amount. FIG. 11 is a graph comparing the relationship between noise level and net average effective pressure when the injection timing is changed in the piston of the present invention. l...Biss I/N, 2...Cavity, 3...Fuel injection nozzle, 4a-4d...Spray collision wall, 63-6
d...Axle center, 7a-7d...Protrusion or cliff-like cross section, 8a-8d...N jet flow.

Claims (2)

[Claims] (1) Combustion of a direct injection diesel engine in which fuel is injected from one or more injection holes of a fuel injection nozzle into a cavity formed on the top surface of the piston when the piston is near top dead center. The combustion chamber is made of ceramic, and has a spray collision wall on which the fuel spray injected from the nozzle hole collides with the inner wall of the cavity, and has a cross-sectional shape perpendicular to the cylinder axis. The axis of each nozzle hole is inclined toward the downstream side of the swirl, and is formed so as to expand downward in the longitudinal cross-sectional shape along the cylinder axis direction, and from the intersection of the inner wall of the cavity and the axis of each nozzle hole. A combustion chamber for a direct injection diesel engine, characterized in that protrusions projecting inward from the cavity are formed on the downstream side of the swirl. (2) The combustion chamber of a direct injection diesel engine according to claim 1, wherein the protrusion amount of the protrusion is 0.03D to 0.1D. (However, D indicates the standard diameter of the cavity.) (3) The combustion chamber of a direct injection diesel engine according to claim 1 or 2, wherein the fuel injection nozzle has four or more injection holes.