JPH01147116A - Combustion method for direct-injection type diesel engine and combustion chamber thereof - Google Patents

Abstract

PURPOSE:To make an air utilization factor improvable by shifting an injection fuel onward movement toward an inner wall surface in a cavity at the time of fuel injection in regular succession from a cavity central part to its peripheral part. CONSTITUTION:In a piston 2, a cavity 6 is formed in a flat piston top face 2a, and a ring lip 7 being projected inward is formed in an upper end of the peripheral wall surface 6a. Injection fuel F is sprayed toward a convex fuel reflecting surface 7a of the lip 7 from a fuel injection valve 5. Here, a form of the convex fuel reflecting surface 7a is set so as to cause the forward direction of reflecting fuel G to be continuously moved toward the peripheral part from the central part of the cavity 6 till the piston 2 is reached to a top dead point since the fuel injection has started. With this constitution, since the reflecting fuel G is burned by utilizing excessive air, an air utilization factor is thus improvable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion method and a combustion chamber for a direct injection diesel engine.

[Conventional technology]

An annular lip protruding inward is formed at the upper end of the inner circumferential surface of the cavity formed on the top surface of the piston, and the inner circumferential surface of the annular lip is formed into a conical shape that expands downward;
Fuel is injected from the fuel injection valve toward the conical inner circumferential surface of the annular lip, and a portion of the injected fuel reflected from the conical inner circumferential surface is collected in the center of the cavity, resulting in liquid fuel adhering to the conical inner circumferential surface. A diesel engine is known in which the fuel is fed into the periphery of the cavity (see Japanese Utility Model Application Publication No. 59-56324). In this diesel engine, the injected fuel is dispersed in the center of the cavity and the periphery of the cavity, so the air utilization rate can be increased.

However, in this diesel engine, it is not known where combustion will start within the cavity, and when combustion starts, a sudden pressure rise occurs and a problem arises in that severe combustion noise is generated. Another problem is that when the combustion temperature increases due to a sudden pressure increase, the amount of NOx generated increases.

Furthermore, even though the air utilization rate increases, the injected fuel is not supplied between the center of the cavity and the periphery of the cavity, so the air between the center of the cavity and the periphery of the cavity is not fully utilized, resulting in a large amount of air being used. There is a problem in that unburned HC and Co are generated.

In order to solve this problem, a concave fuel reflecting surface with an arcuate cross section is formed on the inner peripheral wall surface of the cavity formed on the top surface of the piston, and fuel is injected from the fuel injection valve toward the concave fuel reflecting surface. The present applicant has provided a direct injection diesel engine in which the formation position and cross-sectional shape of the concave fuel reflecting surface are determined so that the injected fuel reflected by the concave fuel reflecting surface sequentially moves from the periphery of the cavity to the center of the cavity as the piston rises. has already been proposed by (Patent Application 1986-1
41450). In this diesel engine, combustion starts at the periphery of the cavity and progresses slowly toward the center of the cavity, which suppresses combustion noise and reduces the number of combustion noises.Furthermore, because the air utilization rate is high, unburned HC
, Co can also be suppressed.

[Problem that the invention seeks to solve]

However, especially when the engine is started, the temperature of the surrounding wall of the cavity is low. Therefore, if combustion starts from the periphery of the cavity, the flame will be cooled and the flame will not grow sufficiently, resulting in not only poor combustion, but also unburned fuel There is a problem in that the gas is discharged as is, producing white smoke and pungent odors.

[Means for solving problems]

In order to solve the above problems, according to the present invention, during fuel injection, the direction in which the injected fuel travels toward the inner wall surface of the cavity formed on the top surface of the piston is sequentially moved from the center of the cavity to the periphery of the cavity, thereby directing the ignition flame to the cavity. It is made to propagate from the center toward the periphery of the cavity.

Furthermore, in order to solve the above-mentioned problems, according to the present invention, a convex fuel reflecting surface having an arcuate cross section is formed on the inner circumferential wall surface of the cavity formed on the top surface of the piston, and the convex fuel reflecting surface is directed from the fuel injection valve to the convex fuel reflecting surface. The formation position and cross-sectional shape of the convex fuel reflecting surface are determined so that the injected fuel reflected by the convex fuel reflecting surface sequentially moves from the center of the cavity to the periphery of the cavity as the piston rises. ing.

[Example] Fig. 1 shows a side sectional view of a direct injection diesel engine. Referring to FIG. 1, ■ is a cylinder block, 2 is a piston that can reciprocate within cylinder block l, 3 is a cylinder head fixed to cylinder block 1, and 4 is a flat inner wall surface of cylinder block 1 and a piston. A combustion chamber 2 is formed between the combustion chambers 2 and 5, and a fuel injection valve 5 is located at the center of the top of the combustion chamber 4. Although not shown in the drawing, cylinder block 1
An intake port and an exhaust port are formed therein, and an intake valve and an exhaust valve are arranged at the openings of these intake ports and exhaust ports into the combustion chamber 4, respectively. In order to give swirling flow to the intake air flowing into the combustion chamber 4, a helical intake port is used as the intake port, or a shrouded intake valve is used as the intake valve. A swirling flow can be given to the intake air flowing into the combustion chamber 4 by other means such as connecting an intake boat in the combustion chamber 4 toward the periphery of the combustion chamber 4 . In the embodiment shown in FIG. 1, the fuel injection valve 5 is arranged diagonally to avoid interference with these intake and exhaust valves and intake and exhaust ports.

As shown in FIGS. 1 and 2, the piston 2 has a flat top surface 2a, and a cavity 6 is formed in the flat piston top surface 2a. An annular lip 7 that protrudes inward is formed at the upper end of the peripheral wall surface 6a of the cavity 6, and the inner peripheral surface 7a of this annular lip 7 is connected to the piston top surface 2a.
It extends smoothly from the bottom wall surface 7b of the annular lip 7 while being curved. Therefore, the inner peripheral surface of the annular lip forms a convex curved surface having an arcuate cross section. On the other hand, the annular lip lower wall surface 7b is substantially parallel to the piston top surface 2a, and the annular lip lower wall surface 7b intersects the cavity lower peripheral wall surface 6b at an approximately right angle. The bottom portion 6c of the cavity 6 is formed into a substantially conical shape with a raised central portion, but it may also be formed from an unfilled flat surface.

The fuel injection valve 5 has one or more nozzle holes, and fuel is injected from the one or more nozzle holes toward the annular lip inner circumferential surface 7a as shown by arrow F in FIG. Ru. A portion of this injected fuel is reflected at the inner circumferential surface 7a, and therefore, this inner circumferential surface 7a is hereinafter referred to as a convex fuel reflecting surface.

In the present invention, the function of the convex fuel reflecting surface 7a is important, so first, the function of the convex fuel reflecting surface 7a will be explained with reference to FIG.

FIGS. 3(a) to 3(e) show the time course from the start of fuel injection to the fuel injection path. FIG. 3(a) shows a state when the piston 2 is located a little before the top dead center and fuel injection is started. FIG. 3(b) shows the piston 2 rising slightly toward the top dead center, and FIG. 3(C) shows the piston 2 reaching the top dead center. FIG. 3(d) shows the piston 2 slightly lowered beyond the top dead center, and FIG. 3(e) shows the piston 2 further lowered at the completion of injection. As shown in FIG. 3(a), at the start of fuel injection, the injected fuel F collides with the upper part of the convex fuel reflecting surface 7a, and as shown in FIG. 3(C), the piston 2 reaches the top dead center. When it reaches the point, the injected fuel F collides with the lower part of the convex fuel reflecting surface 7a. That is, in other words, the position of the convex fuel reflecting surface 7a and the direction of fuel injection from the fuel injection valve 5 are such that the injected fuel F collides with the upper part of the convex fuel reflecting surface 7a at the start of fuel injection, and the piston 2 is at the top dead center. It is determined that the injected fuel F collides with the lower part of the convex fuel reflecting surface 7a when it reaches this point.

On the other hand, the convex fuel reflecting surface 7a has an arcuate cross section as described above. Therefore, as shown in FIGS. 3(a) to 3(C), as the piston 2 rises, the angle between the convex fuel reflection surface 7a and the injected fuel F at the fuel collision point gradually decreases, and therefore the convex fuel reflection The angle formed between the axis of the injected fuel F toward the surface 7a and the axis of the reflected fuel G reflected at the convex fuel reflecting surface 7a gradually increases as the piston 2 moves upward. As shown in FIG. 3(a), at the start of fuel injection, the reflected fuel G heads toward the center of the cavity 6, and as shown in FIG. 3(b), when the piston 2 rises a little, the reflected fuel G moves in the direction of travel. moves from the center of the cavity 6 toward the periphery, and when the piston 2 reaches the top dead center as shown in FIG. 3(C), the reflected fuel G moves toward the periphery of the cavity 6. That is, from the start of fuel injection until the piston 2 reaches the top dead center, the traveling direction of the reflected fuel G continuously moves from the center of the cavity 6 toward the periphery. In other words, the shape of the convex fuel reflecting surface 7a is such that the traveling direction of the reflected fuel G continuously moves from the center of the cavity 6 toward the periphery from the start of fuel injection until the piston 2 reaches the top dead center. It is prescribed to do so. As shown in FIG. 3 (C) to (e), from the time the piston 2 reaches the top dead center until the fuel injection is completed, the reflected fuel G continuously flows from the periphery to the center of the cavity 6. Move to.

As shown in FIG. 3(a), when fuel injection is started, the injected fuel F collides with the upper part of the convex fuel reflecting surface 7a.

At this time, fuel particles with a relatively large particle size adhere to the convex fuel reflecting surface 7a, and other fuel particles adhere to the convex fuel reflecting surface 7a.
It is reflected at point a and heads toward the space above the center of the cavity 6 as shown by arrow G. Moreover, as shown in FIG. 3(a), when the piston 2 approaches the top dead center, the piston top surface 2
A squish flow flows out toward the center of the combustion chamber 4 from the squish area 8 formed between the peripheral part of the cylinder head 3 and the cylinder head 3 . This squish flow flows downward along the convex fuel reflecting surface 7a as shown by arrow S. Therefore, this squish flow S not only prevents the fuel from flowing out from inside the cavity 6, but also promotes vaporization of the fuel adhering to the convex fuel reflecting surface 7a. Also, a part of the fuel adhering to the convex fuel reflecting surface 7a flows onto the annular lip lower wall surface 7b, but since this annular lip lower wall surface 7b is horizontal and almost parallel to the piston top surface 2a, the fuel It stays on the annular lip lower wall surface 7b without reaching the cavity lower peripheral wall surface 6b.

Next, as shown in FIG. 3), when the piston 2 rises, the traveling direction of the reflected fuel G moves toward the periphery of the cavity 6. On the other hand, when the temperature of the fuel particles increases sufficiently, the air-fuel mixture in the space above the center of the cavity 6 is ignited and burned. This ignition flame is transmitted to the surrounding cavity peripheral wall surface 6.
Since it is far away from a, it is not cooled by the cavity peripheral wall surface 6a, and therefore the ignition flame grows well.

This combustion flame propagates toward the periphery of the cavity 6,
Therefore, as shown in FIG. 3(b), the flame propagates so as to chase the reflected fuel Q.

In other words, when an air-fuel mixture is formed by the reflected fuel G, a flame is immediately propagated to the air-fuel mixture in a timely manner, and the air-fuel mixture is combusted.

Therefore, as shown in FIG. 3(C), when the reflected fuel G moves towards the periphery of the cavity 6, the air-fuel mixture formed in the periphery of the cavity 6 is ignited and combusted by the flame moving towards the periphery. It will be done. On the other hand, when the ignition flame starts to propagate from the center of the cavity 6 toward the periphery, the fuel adhering to the convex fuel reflecting surface 7a of the annular lip 7 and the annular lip lower wall surface 7b starts to evaporate on the wall surface, and therefore the annular lip 7 The fuel adhering to the fuel is slowly combusted little by little. On the other hand, since no liquid fuel exists on the lower peripheral wall surface 6b of the cavity 6, these liquid fuels are cooled by the cavity peripheral wall surface and are prevented from being discharged unburned. In this way, the injected fuel is sequentially burned by the ignition flame, and the fuel adhering to the annular lip 7 is sequentially evaporated on the wall surface and burnt slowly, so that unburned H
It is possible to reduce the amount of C and CO emissions and to suppress the generation of NOx.

Next, as shown in FIGS. 3(d) to (e), when the piston 2 starts descending and the traveling direction of the reflected fuel G moves from the periphery to the center of the cavity 6, the reflected fuel G removes the excess air. It can be used and burned.

(Effects of the Invention) Since the traveling direction of the injected fuel sequentially moves from the center of the cavity to the periphery, the air utilization rate can be increased. Furthermore, since the flame propagates in a timely manner to the injected fuel, which moves sequentially from the center of the cavity toward the periphery, controlled combustion without sudden pressure increases can be ensured. In addition, since combustion starts at the center of the cavity, the ignition flame is not cooled by the cavity peripheral wall, and therefore the ignition flame grows reliably even when the engine is started, ensuring good combustion. .

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a diesel engine according to the present invention, FIG. 2 is an enlarged side sectional view of FIG. 1, and FIG. 3 is a diagram for explaining a combustion method. 2...Piston, 3...Cylinder head, 5...Fuel injection valve, 6...
...Cavity, 7...Annular lip,
7a...Convex fuel reflecting surface. 81 Fig. 5...Fuel injection valve 7a... Convex fuel reflecting surface ζ Fig. 2 Fig. 3 Fig. 3

Claims (2)

[Claims] 1. At the time of fuel injection, the injected fuel traveling direction toward the inner wall surface of the cavity formed on the top surface of the piston is sequentially moved from the center of the cavity to the periphery of the cavity, so that the ignition flame is propagated from the center of the cavity toward the periphery of the cavity. Direct injection diesel engine combustion method. 2. A convex fuel reflecting surface with an arcuate cross section is formed on the inner peripheral wall surface of the cavity formed on the top surface of the piston, and fuel is injected from the fuel injection valve toward the convex fuel reflecting surface, thereby forming the convex fuel reflecting surface. A combustion chamber of a direct injection diesel engine whose position and cross-sectional shape are determined so that the injected fuel reflected by a convex fuel reflecting surface sequentially moves from the center of the cavity to the periphery of the cavity as the piston rises.