JPH0151658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion chamber for a direct injection internal combustion engine having a main combustion chamber having a concave portion at the top of a piston.

Conventionally, the combustion chamber of a general direct injection internal combustion engine has a first
As shown in the side sectional view in the figure and the plan view in Figure 2,
A toroidal type piston 1 is used which has a concave main combustion chamber at the top.If the diameter d of the concave part 2 is increased for the same cylinder inner diameter D, the amount of fuel flowing from the nozzle of the fuel injection valve 3 will be increased. The spray reach l increases indirectly, and for the spray reach l ₁ < l ₂ ,
The exhaust odor level at low speeds and low loads becomes good when the effective compression ratio ε is the same, as shown in FIG. 3, and improves when the effective compression ratio ε is further increased.

In FIG. 2, θ indicates the spread angle of the fuel spray from each nozzle, and arrow S indicates the swirl direction.

Increasing the above effective compression ratio ε means that the piston 1
In addition, increasing the diameter d of the recess 2 reduces the squishing speed in inverse proportion to d/D.

As a result, the main combustion chamber volume ratio and squishing speed decrease, and as shown in Figure 4, the maximum output Ps decreases significantly, and the diameter d is enlarged and effective to reduce the irritating odor of the exhaust at low speeds and low loads. Improving the compression ratio ε reduces the maximum output at high speeds and high loads.

That is, in order to completely burn the small amount of fuel injected at low speed and low load in the direct injection internal combustion engine in the recess 2 of the piston 1 and improve the irritating odor of the exhaust, it is necessary to increase the effective compression ratio ε;
It is necessary to expand the spray reach distance l.

If this is done in a conventional toroidal combustion chamber, it is possible to reduce the irritating odor of the exhaust, but at high speeds and high outputs, the high compression ratio and the extended spray reach cause premature ignition of the fuel, and the squeezing force is reduced. As a result, the combustion period becomes longer and maximum power, exhaust color, and fuel consumption worsen.

As a countermeasure for the above, the following measures were taken: Special Publication No. 51-29242 concerning the combustion chamber of direct injection diesel engines;
In the inventions of No. 29243 and Japanese Patent Publication No. 51-29244, the fuel spray is not applied to the corners of the main combustion chamber of the recessed part, but is applied to the straight part and reflected. Since the ratio r/R to the collision radius from 0 to 0.075, r is always smaller than R.

If the curvature r is small, the fuel spray will accumulate after collision, slowing down the evaporation rate, prolonging combustion, and deteriorating the performance. In addition, residues in the fuel will accumulate, further deteriorating the above-mentioned performance.

In addition, as in the invention of Utility Model Application Publication No. 168729/1983 regarding the combustion chamber structure and the invention of Japanese Patent Publication No. 16881/1983 regarding the combustion chamber of a diesel engine, attempts have been made to curve the impact surface of the fuel spray to a small extent or to scatter it by reflection. When a small amount of fuel is injected at low force, the injection speed is very low compared to when there is a high load, and there is almost no reflection.As a result, unburned fuel accumulates on the wall that was set up to reflect it, and unburned or unburned gas occurs,
It has the disadvantage of emitting a pungent exhaust odor.

Furthermore, Utility Model Application Publication No. 57-107821 regarding the combustion chamber of a diesel engine, and Utility Model Application Publication No. 55-4515 and Utility Model Application Publication No. 1983 concerning the combustion chamber of a direct injection diesel engine.
- In each of the inventions in No. 139631, a small amount of spray is completely combusted in compressed air at low force.
Considering the shape of the concave part, there is a drawback that the brake is applied to the swirl during compression, and in reality, the spray does not flow due to the swirl.
In the invention of No. 139631, since the curvature of the inner wall of the fuel collision part is small, unburned fuel does not spread during a small amount of spraying, emitting unburned gas, and the opening area is large relative to the piston area, reducing the squishing force. Another disadvantage is that the airflow in the recess due to swirl decreases during compression.

SUMMARY OF THE INVENTION Therefore, the present invention solves the above-mentioned conventional drawbacks, improves the irritating odor of the exhaust when a direct injection internal combustion engine is running at low speeds and low power, and improves maximum output, exhaust color, fuel efficiency, etc. when running at high speeds and high outputs. This was done for the purpose of

That is, the present invention provides a direct injection internal combustion engine having a main combustion chamber with a concave portion at the top of the piston, in which the concave portion is provided with an air flow from the center of the nozzle to the wall surface on which the fuel spray of fuel injected from each nozzle of the fuel injection valve collides. distance
L ₁ is set to 0.25 to 0.35 times the inner diameter of the cylinder, and fuel collision walls of 18° to 25° are formed in accordance with the number of nozzles depending on each fuel spray angle, and between these fuel collision walls, The distance from the nozzle center is set to 0.8 to 0.9 times the distance L ₁ above, and the curvature r ₁
Continuously with an intermediate wall surface with a larger curvature r ₂ ,
The concave portion is formed in the shape of a windmill, and furthermore, an inclined surface is formed at an angle of 5° to 15° from the intermediate portion of the intermediate wall surface.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 is a side sectional view showing a combustion chamber of a direct injection internal combustion engine in Embodiment 1 of the present invention, and FIG. 6 is a plan view of FIG. 5. In this direct injection internal combustion engine, which has a main combustion chamber consisting of a recess 2 at the top of the piston 1,
The shape of the wall surface 2A with which the fuel spray injected from each nozzle of the fuel spray valve 3 collides with the concave portion 2 at the spread angle θ = 18° to 25° is as shown in the plan sectional view of the main part in FIG. , the distance L ₁ from the nozzle center No. to the colliding wall surface 2A to the cylinder inner diameter D,
Set L ₁ = (0.25 to 0.35) × D, and set the width of the collision wall to be 18° to 25°, corresponding to each spray, and set the width of the collision wall to be 18° to 25 _° . The wall surface 2C is formed to correspond to the number of nozzles of the fuel injection valve 3.

Next, the distance between the four fuel collision walls 2A is set to a distance _L2 from the nozzle center No. corresponding to _0.8 to 0.9 times the distance L1 from the nozzle center No.
It is formed of an intermediate wall surface 2B on the swirl outflow side having a curvature _r2 larger than the curvature _r1 , and the wall surface 2A with which the fuel spray collides and the intermediate wall surfaces 2C and 2B are continuously formed into a windmill shape.

In the recess 2 formed in the shape of a windmill in this way, the swirl shown in the S direction in FIG.
The fuel film after the collision flows smoothly and is formed on the inner wall of the piston, which reduces the opening area relative to the piston surface area and prevents the squishing force from decreasing.

Furthermore, in this embodiment, the bottom of the main combustion chamber of the recess 2 is formed with a deep bottom so that the injected fuel sprays do not touch each other, and the bottom is deep so as to fill the wasteful parts between the fuel sprays. No. 8 with a shallower height
A polyhedral pyramidal convex portion 2D having the same number of nozzles as shown in the figure is formed.

As mentioned above, the nozzle center No. on the inner wall surface of the recess 2
By setting the distances L ₁ and L ₂ from L ₂ /L ₁ = 0.7 to 0.9, a vortex flow as shown by the arrow E in FIG. 9 is generated in the recess 2, and the fuel spray and air are The mixing of the air is promoted and the air is discharged to the upper surface of the piston 1, thereby improving the utilization of air.

Note that the position of the center point of the curvature _r1 is not limited to the first embodiment shown in FIG. 7, and may coincide with the center of the injected fuel spray as shown in the second embodiment shown in FIG. good.

Next, in the combustion chamber of the present invention, A
As shown in FIG. 11 showing the -A cross section, the intermediate part of the intermediate wall surface 2B, that is, the upper part from the depth _h2 from the top surface of the piston 1 has an inclination angle of 5° to 15° with respect to the vertical direction. An inclined surface 4 of dθ ₂ is formed.

The wall portion of the intermediate wall surface 2B having a curvature r ₂ from the bottom of the depth h ₁ to the intermediate portion is also formed into an inclined surface having a small inclination angle dθ ₁ of 1° to 3°.

To explain the effect of the above-mentioned inclined surface 4, when the internal combustion engine is at low speed and low power, the amount of fuel injected from the fuel injection valve 3 is small, and the amount of fuel injected from the fuel injection valve 3 is completely reduced during flight within a distance L ₁ from the fuel injection valve 3. Since it burns and the fuel spray does not touch the wall surface 2A, no blue-white smoke or irritating exhaust odor is generated.

However, at high speeds and high loads, the fuel injection amount increases by 5 to 8 times that at low speeds and low forces, and as shown in Figure 12, the fuel spray F collides with the wall surface 2A, and further increases by 50 to 100 m due to high speed rotation. The fuel spray F is also flown by the speed of the swirl S of /s, and the fuel spray F adhering to the wall surface 2A is also evaporated while being flowed by the swirl S on the intermediate wall surface 2B, and is followed downward from the top dead center of the piston 1. Then, the flame H flows out from the intermediate wall surface 2B as shown by the broken line.

However, as in the present invention, the intermediate wall surface 2B
By forming the inclined surface 4 above the middle part of the piston 1, when a part of the fuel spray is flowed by the swirl S, it flows above the piston 1 on the inclined surface 4 as shown in FIG. Since the air flows out smoothly to the upper surface and the utilization of the air on the upper surface of the piston 1 is improved, the output of the internal combustion engine can be increased.

That is, in the present invention, the fuel spray F that collides with the wall surface 2A is rotated within the recess 2 of the piston 1, and is directed upwardly by the inclined surface 4 provided to utilize the air on the upper surface of the piston 1. I try to divide it into two parts: the one that will flow out.

Therefore, in a direct injection internal combustion engine to which the combustion chamber of the present invention is applied, in order to completely burn a small amount of fuel in compressed air at low speed and low power, it is necessary to reduce the spray reach under an appropriate effective compression ratio. The bottom part is also shaped so that the fuel spray does not hit the bottom part, and at high speeds and high forces, a large amount of fuel hits the collision part, but the shape is such that it flows smoothly in a film form on the inner wall surface downstream of the swirl caused by the suction swirl. The inner wall shape is such that the shape of the inlet side is such that the swirl flowing into the injected fuel does not generate unnecessary swirl.

In addition, a portion of unburned fuel spray flows out from the intermediate wall surface downstream of the swirl after the fuel collision to the upper surface of the piston, improving the utilization of air on the upper surface of the piston, thereby increasing the output of the internal combustion engine.

As a result, the maximum output at high speeds and high loads increases, and the exhaust color and fuel efficiency are improved.

Note that the present invention is mainly effectively applied to direct injection diesel engines.

[Brief explanation of drawings]

Figure 1 is a side sectional view of the combustion chamber of a conventional direct injection internal combustion engine, Figure 2 is a plan view of Figure 1, and Figure 3 is the exhaust odor level, effective compression ratio, and spray in the combustion chamber of Figure 1. Figure 4 is a diagram showing the relationship between the maximum output, effective compression ratio, and spray travel distance in the combustion chamber of Figure 1, and Figure 5 is a diagram showing the relationship between the maximum output and effective compression ratio in the combustion chamber of Figure 1, and the spray travel distance. A side sectional view showing the combustion chamber of a direct injection internal combustion engine, FIG. 6 is a plan view of FIG. 5, and FIG.
The figure is a plan sectional view of the recess shown in Fig. 5, Fig. 8 is a plan sectional view showing the bottom of the recess shown in Fig. 5, Fig. 9 is a plan view showing the vortex generated in the recess shown in Fig. 5, and Fig. 10. is a plan sectional view of a recessed part of a combustion chamber in Example 2 of the present invention,
FIG. 11 is a longitudinal sectional view of the main part in the direction A-A of FIG. 6,
FIG. 12 is a plan view of a main part explaining the flow of fuel spray on the intermediate wall surface of FIG. 5, and FIG. 13 is a longitudinal cross-sectional view of a main part of FIG. 12. 1...Piston, 2...Recess, 2A...Wall surface, 2B...
Intermediate wall surface, 4... Inclined surface, D... Cylinder inner diameter, L ₁ ,
L ₂ ...distance, No...center of nozzle, r ₁ , r ₂ ...curvature, dθ ₂ ...
Tilt angle.

Claims (1)

[Claims] 1 In a direct-injection internal combustion engine that has a main combustion chamber with a recess at the top of the piston, the distance L ₁ from the center of the nozzle to the wall surface on which the fuel spray of fuel injected from each nozzle of the fuel injection valve collides with the recess is defined as It is set to 0.25 to 0.35 times the inner diameter of the cylinder, and a fuel collision wall surface of 18° to 25° is formed in accordance with the number of nozzles depending on each fuel spray angle, and a swirl of this wall surface is created between each fuel collision wall surface. A wall of curvature r ₁ on the inflow side of,
The concave portion is formed in a windmill shape by being continuous with an intermediate wall surface set on the outflow side at a distance from the center of the nozzle that is 0.8 to 0.9 times the distance L ₁ and having a curvature r ₂ larger than the curvature r ₁ , A combustion chamber for a direct injection internal combustion engine, further comprising an inclined surface having an angle of 5° to 15° from the intermediate portion of the intermediate wall surface.