JP2571792Y2 - Combustion chamber shape of direct injection diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a combustion chamber shape of a direct-injection diesel engine which suppresses generation of black smoke.

In particular (Prior Art and Problems to be solved) exhaust gas, it is effective to delay the fuel injection timing as a NO _x measure, which by the air and fuel before ignition in order to prevent the flue gas of degradation There is a need to promote mixing. The mixing of the injected fuel and air is performed by the evaporation of the fuel droplets due to heat and the relative movement of the air.

Therefore, in general, a direct-injection diesel engine for an automobile employs a medium vortex, and the vortex is used for both distribution and mixing of fuel into the air. As the injected fuel travels across the swirling airflow, the spray is sequentially distributed into fresh air. At this time, if the strength of the vortex is rotated by the angle between two adjacent sprays during the injection period, the fuel will be distributed in a circumferentially nearly uniform state.

The diameter of this type of combustion chamber, i.e., the recess at the top of the piston, is often about 50% of the cylinder diameter, and this diameter is slightly smaller than the penetration force of the fuel spray. Will reach. Ignition occurs in the fuel spray initially injected into the swirling airflow. The flame spreads over the entire fuel spray dispersed in the circumferential direction by the vortex, and the flame concentrates on the center of the combustion chamber due to centrifugal action, and the outflow from the combustion chamber to the outer peripheral part due to the piston lowering balances the air. Best performance is obtained at the highest utilization.

By the way, as shown in FIG. 4, the diameter of the piston 1 is D ₁ , the diameter of the open end of the combustion chamber 2 is D ₂ , and the maximum inner diameter of the combustion chamber 2 is a parameter for determining the shape of the combustion chamber of the direct injection diesel engine. the D _3, when the depth of the deepest portion of the combustion chamber 2 is set to _{h, a = D 1 / D} 2, B = D 2 / D 3, C = h / D 2 or the like. Although the values of A to C vary depending on the matching point, generally, A = 0.4 to 0.6, B = 0.8 to 1.0,
C is set to 0.2 to 0.4.

Among these parameters, it is particularly effective to set B <0.9 in order to reduce the generation of black smoke. However, when this value B is set to an appropriate value (B <0.9), the other values of A and C may not aim at the appropriate values.

The present invention has been made in view of the above points, and a direct-injection diesel engine in which air near the center of the combustion chamber, which is not significantly involved in combustion, is effectively used to increase the air utilization rate and reduce black smoke. It is an object of the present invention to provide a combustion chamber shape.

(Means for Solving the Problems) According to the present invention, in order to achieve the above object, the center of the bottom of a circular recess formed at the top of the piston forms a protrusion that rises in a conical shape, and the peripheral portion that follows the protrusion. Is formed in a combustion chamber shape of a direct injection type diesel engine connected to a side wall surface in an arc shape, the projection is formed large so that an upper end thereof is close to a fuel injection nozzle, a lower portion is steeply raised, and an upper portion is formed as a gentle cone. Formed in a trapezoidal shape, and the apex angle of the truncated cone is 10 to more than the cone angle of the fuel injection nozzle.
It was set to be smaller by 30 °, and the side wall surface of the combustion chamber was set to spread toward the open end of the combustion chamber at an angle of 0 to 30 ° with respect to the lower slope of the projection facing the side wall surface. Things.

(Operation) The fuel injected from the injection nozzle travels across the swirling airflow generated in the combustion chamber toward the lower portion of the side wall surface of the combustion chamber, and the spray is sequentially distributed into fresh air. At this time, since the center projection is formed large, the center of the air flow in the combustion chamber is shifted toward the side wall surface, and air near the center of the combustion chamber, which does not significantly contribute to combustion, can be effectively used. As a result, ignitability is improved, black smoke is reduced, and engine performance is improved.

(Embodiment) An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a sectional shape of a combustion chamber of a direct injection type diesel engine to which the present invention is applied. A combustion chamber 2 formed at the center of the top of a piston 1 is a circular recess, and has an inner diameter D _{2 of an} open end 2a. Is smaller than the maximum inner diameter D ₃ inside the combustion chamber (D ₂ <
D ₃ ), and a projection 3 is formed at the center of the bottom surface.

The projection 3 is formed in a shape larger than that of the conventional projection, and has a substantially lower half (hereinafter, referred to as “lower”) 3a in a conical shape in which it rises sharply, and an upper half (hereinafter, referred to as “lower”) 3a. The upper part 3b has a substantially frustoconical shape having a gentler slope than the lower part 3a, and the top plane, that is, the depth at the center of the combustion chamber 2 is slightly shallower than before.

The apex angle β of the upper part of the projection 3, that is, the truncated cone 3b is slightly smaller than the cone angle θ of the injection nozzle 4 arranged above the projection 3 and on the center line of the combustion chamber 2, specifically, 10 to 30 ° smaller angle [β = θ- (10 to 30 °)]
Is set to The upper part 3b of the projection 3 is formed in a truncated cone shape and the top is made flat to prevent interference with the injection nozzle 4. Further, the lower portion 3a of the projection 3 is raised with a steep slope, and the slope of the upper portion 3b is made gentle to prevent the fuel injected from the injection nozzle 4 from hitting the slope 3c of the lower portion 3a of the projection 3.

The bottom edge and the lower part of the side wall surface following the lower part 3a of the projection 3 of the combustion chamber 2, that is, the bottom radius part 2b,
Of the combustion chamber 2, and the cross-sectional shape of the outer portion of the bottom surface of the combustion chamber 2 has a shape including a part of a circle, that is, an arc shape. The radius R of this arc is set in the range of R = 0.12D _{2 to} 0.18D ₂ . Here, the value D ₂ is the inner diameter of the open end 2a of the combustion chamber 2 described above.

The side wall surface 2c following the bottom radius portion 2b of the combustion chamber 2 has an inclined surface tapering upward in a tapered shape. The side wall surface 2c and the inclined surface 3c of the lower portion 3a of the projection 3 are opposed to each other at a parallel angle or a small angle α. This angle α is set in the range of 0 to 30 °. Connecting portion near the side wall surface 2c of the bottom rounded portion 2b of the combustion chamber 2 is formed into a maximum inner diameter D ₃ of the combustion chamber 2.

Combustion chamber 2 in this way, reduce the internal diameter D ₂ of the opening end 2a, increasing the maximum internal diameter D _3, increase the depth h of the deepest and are largely formed projections 3.

 The operation will be described below.

The fuel injected from the injection nozzle 4 proceeds across the swirling air flow, that is, the vortex generated in the combustion chamber 2 toward the lower portion of the side wall surface 2c of the combustion chamber 2, and the spray is sequentially distributed into new air. . Further, since the central projection 3 is formed large, the center of the air flow in the combustion chamber 2 is closer to the side wall surface 2c of the combustion chamber 2, and the air near the center of the combustion chamber, which is not significantly involved in combustion, is effectively used. can do. Furthermore, the combustion chamber 2 is smaller inner diameter D ₂ of the opening end 2a, increasing the maximum internal diameter D _3, the vortex even when the piston 1 descends to being formed deeper the depth h of the deepest i.e., the air flow It becomes possible to store well.

As a result, atomization of the fuel is promoted, the ignitability is improved, and the fuel is satisfactorily burned in the combustion chamber 2 to suppress the generation of black smoke. As a result, the engine performance is improved.

FIG. 2 shows another embodiment of the combustion chamber shape of the present invention. The combustion chamber 2 'has a side wall surface 2'c of a bottom radius portion 2'b in addition to the shape of the combustion chamber 2 shown in FIG. to continuously arranged on the outer curved surface 2'd a radius R _1, the inner curved surface 2'e that continuously arranged in the lower portion 3'a of the projection 3 'and the radius _{R 2 (R 1 ≠ R 2} ), and a combustion chamber area of diameter d _i position of 2 '(combustion area) S ₁ = π × d _i
× l _i is used as an evaluation item, and the curved surface 2 ′ is set so that the area S _i expands at substantially the center of the combustion chamber 2 ′ as shown in FIG.
The center O ₁ , O ₂ of the radii R ₁ , R ₂ of d, 2′e is the distance a (= 2
A flat portion 2'f is provided on the bottom surface of the combustion chamber 2 ', i.e., on the bottom radius portion 2'b.

By forming the combustion chamber 2 'in such a shape, the flame spreads toward the center of the combustion chamber 2', so that the combustion after ignition is further improved and the fuel efficiency is improved.

(Effects of the Invention) As described above, according to the present invention, the center of the bottom of the circular recess formed at the top of the piston forms a projection that rises in a conical shape, and the peripheral edge following the projection forms an arc. In the combustion chamber shape of the direct-injection diesel engine connected to the side wall surface, the protrusion is formed so as to be large so that the upper end thereof is close to the fuel injection nozzle, the lower portion is steeply raised, and the upper portion is formed in a gentle truncated cone shape, And, the apex angle of the truncated cone is set to be 10 to 30 ° smaller than the cone angle of the fuel injection nozzle, and the side wall surface of the combustion chamber is 0 to 30 ° with respect to the lower slope of the projection facing the side wall surface. With the shape set so as to spread toward the open end of the combustion chamber at an angle of, the center of the air flow of the combustion chamber can be brought as close as possible to the outer wall of the combustion chamber. Involvement It is possible to effectively utilize the air without combustion chamber center near, ignitability of fuel in the combustion chamber, the combustion is improved, reduces the generation of black smoke, the improvement of engine performance can be achieved. Further, by making the side wall surface of the combustion chamber face the slope of the lower portion of the projection at an angle of 0 to 30 °, there is an effect that processing of the combustion chamber becomes easy.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a combustion chamber shape of the direct injection diesel engine according to the present invention, FIG. 2 is a cross-sectional view showing another embodiment of the combustion chamber of the direct injection diesel engine according to the present invention, FIG. 3 is a graph showing the relationship between the diameter and the area of the combustion chamber in the combustion chamber of FIG. 2, and FIG. 4 is a sectional view of the combustion chamber of a conventional direct injection diesel engine. DESCRIPTION OF SYMBOLS 1 ... Piston, 2 and 2 '... Combustion chamber, 2'b ... Bottom radius part, 3 ... Projection, 3a ... Projection lower part, 3b ... Projection upper part, 4 ... Injection nozzle.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshihisa Yamaki 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (56) References JP-A-56-50214 (JP, A) JP-A 1963-162925 (JP, A)

Claims (1)

(57) [Scope of request for utility model registration] A combustion chamber of a direct-injection diesel engine in which the center of the bottom of a circular recess formed at the top of a piston forms a projection that rises in a conical shape, and the peripheral edge following the projection forms an arc and continues to the side wall surface. In the shape, the protrusion is formed large so that the upper end thereof is close to the fuel injection nozzle, the lower portion is steeply raised, and the upper portion is formed in a gentle frustoconical shape. The opening angle of the combustion chamber is set to be smaller than the cone angle of the nozzle by 10 to 30 °, and the side wall surface of the combustion chamber is formed at an angle of 0 to 30 ° with respect to the lower slope of the projection facing the side wall surface. The combustion chamber shape of a direct-injection diesel engine, which is set so as to expand toward.