JPH04272447A - Direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To reduce NOx in exhaust gas and improve the rate of fuel consumption. CONSTITUTION:The fuel injection is controlled so that the injection rate is suppressed in the initial period of injection and thereafter the injection pressure maximizes. The surface of combustion chamber 2 shall consist of a smooth curvature obtained through rounding of the top opening 23 having a smaller dia, than thee max. chamber dia. d3. In the initial period of infection, the fuel 5 is injected toward that side wall 22 part of combustion chamber 2 which is situated below the top opening 23 and formed inclined, while is injected toward the top opening 23 in the period when the injection pressure maximizes.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to control of fuel injection and improvement of the shape of a combustion chamber in a direct injection diesel engine.

0002

BACKGROUND OF THE INVENTION Combustion chambers for direct injection diesel engines in which the upper end opening is formed to have a smaller diameter than the maximum internal diameter are known. Examples of improved combustion chamber shapes include, for example, Japanese Patent Application Laid-Open No. 55-51.
There is Japanese Patent No. 917, which aims to improve combustion conditions, increase output, and at the same time reduce the amount of NOx generated. The upper end opening of a conventional combustion chamber generally has a relatively sharp edge with a natural radius created during machining, and the injected fuel is divided into upper and lower halves at this edge, and is distributed between the upper surface of the piston and the inside of the combustion chamber. I will be heading to . The same applies to the above publication. Further, in the above-mentioned publication, fuel is injected toward this upper end opening from the initial stage of injection start.

0003

[Problem to be solved by the invention] However, society's demands for improving fuel consumption rate and purifying exhaust gas are becoming stricter year by year, and it has become difficult to meet these demands simply by improving the shape of the combustion chamber. It's coming. This invention focused on this point, and was made with the aim of further improving the combustion state and reducing NOx.The invention focused on the shape of the combustion chamber, the fuel injection direction, and the injection rate, which had not received much attention in the past. This is a study of the relationship between

0004

[Means for Solving the Problems] In order to achieve the above object, in the present invention, the injection pressure is maximized after the injection rate is suppressed for at least 1/3 of the total injection period at the beginning of the injection period. The combustion chamber is formed to have a smaller diameter than its maximum diameter and has a smooth curved surface with an R-shaped upper opening.During the period when the injection rate is suppressed, the combustion chamber The fuel is injected from the upper end opening toward the lower inclined side wall, and at the time when the injection pressure is at its maximum, the fuel is injected toward the upper end opening as the piston descends. There is. Further, by providing a shallow recess around the upper end opening of the upper surface of the piston, a thin combustion space that smoothly continues from the upper end opening of the combustion chamber to the upper surface of the piston is formed. Further, the portion of the upper end opening where the center of the injected fuel hits is made to protrude toward the nozzle.

[0005]

[Effect] At the beginning of injection, the fuel does not hit the top opening, so turbulence does not occur, and the injection rate is suppressed, so combustion is relatively quiet and gradual, resulting in less NOx generation. Become. In addition, after the middle stage of combustion, the center of the high-pressure fuel spray hits the rounded upper end opening, and the low-concentration fuel at the outer periphery of the spray quickly diffuses to the top surface of the piston, resulting in lean combustion, which reduces the generation of NOx. A highly efficient combustion state with low fuel consumption can be obtained. Furthermore, by providing a thin combustion space on the upper surface of the piston, the air within this combustion space can be effectively utilized, resulting in better combustion conditions. In addition, by making the part of the upper end opening where the center of the injected fuel hits protrude toward the nozzle,
The air-fuel mixture and flame quickly diffuse into the combustion space at the top of the piston created when the piston descends, resulting in better combustion conditions.

[0006]

[Embodiment 1] The illustrated embodiment will be described below. First, fuel injection control in the present invention will be described with reference to FIG. The horizontal axis of the figure is the crank angle, and the vertical axis is the valve lift amount and injection pressure.As shown in the figure, the injection rate is suppressed at the beginning of the injection period, and then fuel injection is controlled so that the injection pressure is maximized. Therefore, the injection rate suppression period θ1 is selected to be 1/3 or more of the total injection period θ. For example, injection is 10 degrees before top dead center.
From near to near top dead center, preferably 5 degrees before top dead center
The injection period θ is controlled to start at around 25° to around 35° after top dead center, preferably to end at around 30°, and the entire injection period θ is about 25 to 35°. Further, the injection pressure is controlled so as to reach its maximum at around 20 degrees after top dead center. Such fuel injection control is common to each embodiment described below.

Embodiment 1 shown in FIGS. 3 and 4 is the first embodiment of the invention according to claim 1. Figure 3 shows the state at the start of injection near top dead center, and Figure 4 shows the state at high pressure injection at around 20 degrees after top dead center.
b) is a sectional view. In the figure, 1 is a piston, 2 is a combustion chamber, 3 is a cylinder, and 4 is an injection nozzle. In addition,
Only the position of the injection nozzle is shown. The combustion chamber 2 is formed by hollowing out the upper surface 11 of the piston 1 in a concave manner, as in the conventional case, and is provided with a raised part 21 at the center of the bottom.
The side wall 22 that continues smoothly from the top is inclined inward so that the upper part has a small diameter. An upper end opening 23 is formed at the upper end of this side wall 22 and is rounded to have a smooth curved surface, and is continuous with the upper surface 11 of the piston 1.

As shown in the figure, the cylinder diameter is D, the diameter of the upper end opening 23 is d1, the diameter of the boundary with the upper surface 11 is d2,
If the maximum diameter of the combustion chamber 2 is d3, and the radius of the rounded part of the upper end opening 23 is R, then there is a relationship of d1<d3, d2=d1+2R, and d1/D=50 to 80%, R=3. ~
It is selected to be 10mm. In addition, 5 indicates the injected fuel, and 5
1 indicates the center, and the nozzle hole angle α of the nozzle 4 is such that fuel is injected against the side wall 22 at the beginning of injection when the injection rate is suppressed, and when the injection pressure is at its maximum, the piston 1 Depending on the shape and dimensions of the combustion chamber 2, for example, 120~
The angle is selected to be approximately 160°.

The embodiment has the above-described configuration, and the injected fuel 5 is injected against the side wall 22 at the start of injection when the piston 1 is near the top dead center as shown in FIG. Therefore, turbulence does not occur, and since the injection rate is suppressed at this time and the fuel supply is small, combustion is relatively quiet and gradual, resulting in less NOx generation. After the middle stage of combustion, the injection pressure increases, and the piston 1 gradually descends so that the center 51 of the high-pressure fuel spray hits the upper end opening 23.
The flow is divided vertically along the surface of the rounded upper end opening 23. Therefore, the fuel is well mixed with the air in the combustion chamber 2, and is also quickly diffused into the upper surface 11 of the piston 1 to be burned. In particular, the low-concentration fuel from the outer periphery of the spray flows into the upper surface 11 along with the back squish flow, and combustion is performed in a lean state, which suppresses the generation of NOx and provides a highly efficient combustion state with low fuel consumption. become.

0010

Embodiment 2 Embodiment 2 shown in FIGS. 5 and 6 is a second embodiment of the invention according to claim 1, in which a tapered portion 24 is provided at the upper peripheral edge of the upper end opening 23. FIG. FIG. 5 shows the state at the start of injection near top dead center, and FIG. 6 shows the state during high pressure injection at around 20 degrees after top dead center. (a) is a plan view,
(b) is a sectional view. The dimensions of each part are d1<d3, d
2>d3, d1/D=50-65%, d2/D≧70%
In addition, R=3 to 15 mm is selected, and the nozzle hole angle α of the nozzle 4 is selected to be slightly smaller than that of the first embodiment described above, for example, about 110 to 150°. In this embodiment, the action of the tapered portion 24 promotes the mixing of air and fuel on the upper surface 11 of the piston 1, so that the emission of black smoke is particularly reduced as explained in FIG. 2.

[0011]

[Embodiment 3] Embodiment 3 shown in FIGS. 7 and 8 is an embodiment of the invention according to claim 2. FIG. 7 shows the state at the start of injection near top dead center, and FIG. 8 shows the state after top dead center. Each figure shows the state during high-pressure injection at around 20°. (a) is a plan view, and (b) is a sectional view taken along the line A-A in (a). Conventionally, depending on the type of engine or the shape of the valve, a valve recess may be provided on the top surface 11 to prevent the piston 1 from coming into contact with the valve, but in this embodiment, a valve recess is provided at the top of the top opening 23 instead of these valve recesses. By providing a shallow recess 25 around the entire periphery, a thin combustion space 26 that smoothly continues from the upper end opening 23 of the combustion chamber 2 to the upper surface 11 of the piston 1 is formed. This embodiment shows a case of an engine having a valve recess, and the recess 25 and the valve recess 27 are formed continuously. Note that although the recess 25 is shallower than the valve recess 27 in the figure, it may be formed to the same depth depending on the case. This embodiment has the above-mentioned configuration, and since the air in the thin combustion space 26 formed over the entire upper surface of the piston is effectively used for combustion, the combustion condition is better than that in which only the valve recess is formed. Improved.

0012

[Embodiment 4] Embodiment 4 shown in FIGS. 9 and 10 is claim 3.
FIG. 9 shows the state at the time of starting injection near top dead center, and FIG. 10 shows the state during high pressure injection at around 20 degrees after top dead center. (a) is a plan view, (b)
) is a sectional view taken along line A-A in (a). This example is shown in Figure 3.
The shape of the upper end opening 23 in Example 1 and 4 is improved. That is, the radius R1 of the rounded part of the portion 23a of the upper end opening 23 that is hit by the center 51 of the fuel spray and the portion 23b that exists between the radius R1 and the center 51 of the fuel spray that is not hit.
The radius R2 of the R-processed part is made different, and the portion 23a is made to protrude relatively in the direction of the nozzle 4 with R1<R2, and the dimension d1 between the portion 23a and the portion 2 corresponding to the diameter,
The dimension d4 between 3b has a relationship of d1<d4. Also, the protrusion radius of the portion 23a seen from above is R3, and the portion 23
The radius of the recess b is R4, but the portion 23a is in a spherical protruding state, and both are continuous with a smooth curved surface as a whole. Note that the protruding portion 23a
The number is the same as the number of sprays from the nozzle 4.

With the above-described configuration, at the start of injection when the piston 1 is near the top dead center as shown in FIG. This is unrelated, and as in Example 1, combustion is relatively quiet and gradual, and little NOx is generated. On the other hand, when the injection pressure increases after the middle stage of combustion, the center 51 of the high-pressure fuel spray hits the protruding portion 23a of the upper end opening 23, and the fuel spray is divided into the surrounding areas along the spherical surface of the portion 23a. Therefore, the mixing of fuel and air within the combustion chamber 2 is promoted, and the diffusion to the upper surface 11 of the piston 1 is also actively performed, and the diffusion is more widespread than in the case of Example 1, resulting in a good combustion state. You can get it.

FIG. 2 compares the above embodiment and the conventional example with respect to NOx amount and black smoke or exhaust color Sd, where the horizontal axis is a dimensionless display of fuel consumption rate and the vertical axis is the conventional example with 1 It is a dimensionless display. In the figure, black circles indicate the conventional example, white circles indicate the first embodiment, triangles indicate the second embodiment, and X indicate the fourth embodiment.Since the third embodiment was almost the same as the first embodiment, it has been omitted. Focusing on Example 1 and comparing it with the conventional example, for example, at the same fuel consumption rate f=0.9, NOx
is reduced from 1 to 0.8, which is about a 20% reduction, and black smoke (exhaust color) Sd is reduced from 1 to 0.75, which is about a 25% reduction. Also, for the same NOx (=0.8), the fuel consumption rate f
is reduced from 1 to 0.9, which is a reduction of about 10%. In addition, as a whole, Example 1 and Example 2 are superior to the conventional example, although their superiority is reversed in terms of NOx and Sd. Furthermore, Example 4 had the best results in all respects, demonstrating the effects of the present invention. It should be noted that it is also possible to use the structure of claim 3 together with the structure of claim 2 in which the combustion space is provided, and the synergistic effect can provide a better effect than when implemented alone. Moreover, the structure of claim 3 can also be adopted for a valve recessed valve.

[0015]

[Effects of the Invention] As is clear from the above description, the direct injection diesel engine of the present invention controls fuel injection so that the injection rate is suppressed at the beginning of the injection period and then the injection pressure is maximized. In addition, the upper end opening of the combustion chamber has a radius smaller than its maximum diameter to have a smooth curved surface, and during the injection rate suppression period, fuel is injected to the sloped side wall below the upper end opening of the combustion chamber. At the same time, fuel is injected into the upper end opening when the injection pressure is at its maximum. Therefore, turbulence does not occur in the initial stage of injection, and combustion occurs slowly under a suppressed injection rate, resulting in less NOx generation. In addition, after the middle stage of combustion, the injected fuel hits the rounded upper end opening, and the fuel quickly diffuses over the top surface of the piston, resulting in lean combustion, which suppresses the generation of NOx and reduces fuel consumption. This makes it possible to achieve a more efficient combustion state, making it possible to meet strict demands for improved fuel consumption and exhaust gas purification.

Furthermore, in the case where a thin combustion space is formed that smoothly continues from the upper end opening of the combustion chamber to the upper surface of the piston, the air within this combustion space is effectively utilized, and better combustion conditions can be obtained. Furthermore, in the case where the part of the upper end opening where the center of the injected fuel hits protrudes toward the nozzle, the fuel injected after the middle stage of combustion hits the protruding part and the air-fuel mixture and flame quickly diffuse into the combustion space generated at the top of the piston. This results in a better combustion state, making it possible to further improve the fuel consumption rate and purify the exhaust gas.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of fuel injection control in the present invention.

FIG. 2 is a graph comparing a conventional example and an embodiment of the present invention regarding the relationship between NOx amount, black smoke or exhaust color, and fuel consumption rate.

FIG. 3 is a plan view and a sectional view of the top of the piston at the start of injection in Example 1.

FIG. 4 is a plan view and a sectional view of the top of the piston during high-pressure injection in the same embodiment.

FIG. 5 is a plan view and a cross-sectional view of the top of the piston at the start of injection in Example 2.

FIG. 6 is a plan view and a sectional view of the top of the piston during high-pressure injection in the same embodiment.

FIG. 7 is a plan view and a cross-sectional view taken along line A-A of the top of the piston at the start of injection in Example 3;

FIG. 8 is a plan view and a sectional view taken along line A-A of the top of the piston during high-pressure injection in the same embodiment.

FIG. 9 is a plan view and a cross-sectional view taken along line A-A of the top of the piston at the start of injection in Example 4;

FIG. 10 is a plan view and a cross-sectional view taken along the line A-A of the top of the piston during high-pressure injection in the same embodiment.

[Explanation of symbols]

1 Piston 2 Combustion chamber 3 Cylinder 4 Injection nozzle 11 Top surface 22 Side wall 23 Upper end opening 24 Taper part 25 Recess 26 Thin combustion space 23a Protruding part θ　Full injection period θ1 Injection rate suppression period α　Nozzle nozzle hole angle

Claims (3)

[Claims] Claim 1: A direct injection diesel engine that injects fuel toward a combustion chamber formed at the top of a piston, wherein the injection rate is suppressed for at least 1/3 of the entire injection period at the beginning of the injection period. After that, the fuel injection is controlled so that the injection pressure is maximized, and the upper end opening of the combustion chamber is formed to have a diameter smaller than its maximum diameter and has a smooth curved surface with R processing to suppress the injection rate. During this period, fuel is injected from the upper end opening of the combustion chamber to the lower inclined side wall of the combustion chamber, and when the injection pressure is at its maximum, fuel is injected toward the upper end opening as the piston descends. A direct injection diesel engine, characterized in that it is configured to be injected. 2. The direct injection diesel according to claim 1, wherein a shallow recess is provided around the upper opening of the upper surface of the piston to form a thin combustion space that smoothly continues from the upper opening of the combustion chamber to the upper surface of the piston. institution. 3. The direct injection diesel engine according to claim 1, wherein a portion of the upper end opening where the center of the injected fuel hits projects toward the nozzle.