JP2841122B2 - Combustion device for direct injection diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion apparatus for a direct injection diesel engine.

[0002]

2. Description of the Related Art FIG. 6 shows a combustion chamber of a conventional direct injection type engine and an injection pattern of its spray.

The combustion chamber 1 is a concave dish with a raised portion 2 at the center of the bottom, and is formed so as to go under the piston top surface 3. The spray 4 injected from the nozzle starts to be injected from a position at which the center L reaches a position slightly higher than the middle in the vertical direction of the side wall 5 of the combustion chamber, and then gradually decreases with the lowering of the lower piston in the figure. Then, the injection is terminated near the top surface 3 of the combustion chamber.
In this conventional example, the reaching distance of the spray 4 to the side wall 5 is substantially the same throughout the entire injection period, and the side wall 5 rises straight from the boundary with the bottom. The injection angle 4 from the nozzle is set to a large angle of 140 to 150 °. Further, the injection rate is all injections from the start to the end.

Particularly problematic in this type of direct injection diesel engine are nitrogen oxides (hereinafter referred to as NOx) and exhaust colors (black smoke). Recently, it has recently been difficult to reduce NOx due to pollution problems. Strongly required. In general, the amount of NOx generated increases when rapid combustion is performed in a short time,
On the other hand, black smoke is generated by the unburned spray. In the above-described conventional combustion structure, since the injection is completed in a short period from the position higher than the middle of the side wall to the upper end at a large injection angle, the entire required amount of fuel is injected in this short period. It is necessary to perform rapid combustion in a very short time, and the exhaust color is good, but NOx deteriorates. When the end of the injection reaches the combustion chamber top surface 3, the exhaust color also deteriorates. SUMMARY OF THE INVENTION An object of the present invention is to provide a direct injection type diesel engine combustion apparatus which solves such conventional disadvantages.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, in a direct injection type diesel engine in which fuel is injected toward a concave combustion chamber at the top of a piston, an injection angle from a nozzle is set to 90 to 130. In the range of ゜, the injection at the position with the largest reach near the bottom of the combustion chamber is defined as the injection start position, and the injection is performed when the spray center is at least in the combustion chamber after the upward movement of the arrival position due to the lowering of the piston. In addition, the injection rate is suppressed during at least one-third or more of the entire injection period from the start of the injection, and thereafter the injection is completed and the injection is completed.

Further, in the second invention of the present application, the throttle device according to the first invention is characterized in that a throttle portion for generating reverse squish is formed at an upper end opening of the combustion chamber.

Similarly, in a third invention of this application, in the first or second invention, the shape of the side wall of the combustion chamber is
It is characterized in that it has an outward opening shape that spreads outward toward the upper end opening.

According to the present invention, the injection angle from the nozzle is 90
Since the injection is started at a point that is relatively small to about 130 ° and the start of injection is the largest in the vicinity of the bottom of the side wall, the injection period is long, and the injection rate is suppressed during this long-term injection. This makes it possible to reduce NOx and noise, and also to increase the reach, so that the atomization of the spray during the suppression period is sufficiently promoted, and the generation of black smoke due to the generation of unburned gas is greatly increased. Can be reduced. In addition, in the latter half of the combustion, rapid combustion by full injection is performed, thereby improving the fuel consumption rate.

In the present invention, the injection angle, the injection period, and the injection rate suppression period are as described above. Further, the injection start timing is set at a crank angle of -10 ° to 0 °, preferably at a position near -5 °. By setting the injection end to 40 ° to 55 °, preferably around 45 °, these can be reduced more effectively. Further, it is desirable that such an injection pattern be implemented in a full load region from idling to full load.

[0010]

FIG. 1 shows a first embodiment of the present invention. (A) of the figure shows the start of the injection, the stage at which the injection has progressed toward the lower stage, and (e) of the figure shows the end of the injection. The numbers on the left side of each figure show the corresponding crank angles. In this embodiment, the combustion chamber 11 has a dish-like shape in which a piston top surface 12 is concavely formed as in the prior art, and has a raised portion 13 at the bottom center. Side wall 15 continuous with R shape 14 around bottom
Has an inwardly-opening shape that gradually contracts inward toward the upper end opening, and a narrowed portion 16 is formed in the upper end opening. At the start of the injection shown in FIG. 9A, the spray center L of the spray injected from the nozzle 17 is directed to the point where the reaching distance to the side wall 15 is greatest near the boundary with the R-shaped portion 14. . When the injection is started and the piston descends, the arrival point to the side wall gradually moves upward as shown in FIG. (B) below, and at the end of FIG. Combustion chamber 11
It is set so as to end at the narrowed portion 16 at the upper end portion inside. In such an injection process, the injection suppression period of the present invention is between (a) and (c) in the figure, and then, at the stage immediately before the shift to (C) in FIG. At this stage of the full injection, a strong reverse squish is generated by the throttle portion 16 near the opening of the combustion chamber 11. The fuel is burned rapidly. FIG. 2 shows a graph of the injection pattern control.

FIG. 3 shows that each of the N is varied by changing the injection angle ψ.
The values of Ox and black smoke (Sd) are measured, and are shown in a dimensionless display with the case where ψ = 150 ° as 1 and as shown in this figure, the angle range of the present invention is 90 to 130 °. At N
It can be seen that both Ox and black smoke give good results. On the other hand, in the case of the related art in which the injection angle is set in the range of 140 to 160 °, very bad results are obtained.

FIG. 4 is a graph showing a dimensionless display in which the values of NOx and black smoke at that time are measured while changing the injection period θ, and the case where θ = 20 ° is set to 1 as a dimensionless display. 40
Good results have been obtained with this invention set at ~ 65 °. On the other hand, in the case of the related art having a short injection period of 15 to 30 °, the generation of NOx is particularly large.

FIG. 5 shows another embodiment manufactured in accordance with the second and third aspects of the present invention, in which the side wall 15 of the combustion chamber 11 is extended from near the boundary with the R-shaped portion 14 around the bottom to the upper end. It has an outward opening shape that expands toward the opening, and further has a large throttle 16 provided at the upper end of the side wall 15. With such a configuration, the reach of the spray during the injection suppression period is reduced by the crank angle. It can be made longer as the process proceeds, to further reduce the generation of NOx, and to promote the finer spraying to effectively reduce the generation of black smoke. In addition, since the throttle is enlarged, the flow rate of the reverse squish near the throttle is increased, and the fuel injected by the reverse squish is made to impinge on the reverse squish to rapidly burn, thereby further reducing the fuel consumption rate.

[0014]

As described above, according to the present invention, the injection angle from the nozzle is made relatively small, the injection period is lengthened, and the injection is suppressed during at least one third of the injection period. By doing, N compared to the conventional one
The generation of Ox and black smoke was greatly reduced, and a combustion device with low noise and high fuel consumption was obtained. Further, in the second invention of this application, by providing a throttle at the upper end opening of the combustion chamber, the reverse squish flow velocity in this portion is increased, and rapid combustion in the latter half of combustion is increased.
This can improve fuel consumption more,
There is an effect that the injection suppression period during the injection period is lengthened correspondingly, and the lowest position of NOx and black smoke can be selected.
Further, in the third invention of this application, by making the side wall of the combustion chamber open outward, the reach of the spray during the injection suppression period can be made longer, and the generation of NOx and black smoke can be further reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a piston top showing a change in a spray reaching position according to a lowering of a combustion chamber and a piston according to the present invention.

FIG. 2 is a graph showing an injection rate control pattern according to a change in crank angle.

FIG. 3 is a graph showing a relationship between an injection angle from a nozzle and generation of NOx and black smoke.

FIG. 4 is a graph showing the relationship between the injection period and the generation of NOx and black smoke.

FIG. 5 is a cross-sectional view of a combustion chamber and a top portion of a piston showing a change in a spray reaching position as the piston descends according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of a conventional example showing a combustion chamber and a piston top showing a change in a spray reaching position caused by a lowering of a piston.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Combustion chamber 12 Piston top surface 15 Side wall 16 Throttle part 17 Nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-87609 (JP, A) JP-A-4-31653 (JP, A) JP-A-4-49657 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) F02B 1/00-23/10 F02D 41/00-41/40

Claims (3)

(57) [Claims] In a direct injection type diesel engine in which fuel is injected toward a concave combustion chamber at the top of a piston, an injection angle from a nozzle is set in a range of 90 to 130 °, and a position where the reaching distance is the longest in the vicinity of the bottom of the combustion chamber. Is defined as an injection start position, and the injection is terminated when at least the center of the spray is within the combustion chamber after the upward shift of the arrival position accompanying the lowering of the piston. A direct-injection diesel engine combustion device, characterized in that the injection rate is suppressed during the above period, and thereafter all injections are completed to terminate the injection. 2. The direct injection type diesel engine combustion device according to claim 1, wherein a throttle portion for generating reverse squish is formed at an upper end opening of the combustion chamber. 3. The combustion apparatus for a direct injection diesel engine according to claim 1, wherein the side wall of the combustion chamber has an outwardly open shape that extends outward toward an upper end opening.