JPH10141063A - Combustion chamber structure of direct injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the combustion chamber structure of a direct injection type diesel engine to prevent fuel from being exhausted in exhaust gas with fuel left unburnt due to adhesion of a liquid phase part of fuel injected through a fuel injection nozzle to the wall surface of a combustion chamber. SOLUTION: A recessed part 13 corresponding to the collision region of a liquid phase part is formed in a collision portion wherein a liquid phase part 12 of fuel injected through the nozzle hole 9 of a fuel injection nozzle arranged fronting on approximately the central part of a combustion chamber 6 is collided with the wall surface 10 of the combustion chamber 6. Fuel reflected by the recessed part 13 is not adhered in a film-form state on the wall surface 10 but flied in the combustion chamber 6 for combustion. Since a slope 15 is formed in the direction of a swirl B from the bottom 14 of the recessed part 13, flying of reflection fuel to the combustion chamber 6 is promoted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure in a direct injection diesel engine in which fuel is directly injected into a combustion chamber by a fuel injection nozzle.

[0002]

2. Description of the Related Art Conventionally, especially in a small direct injection type diesel engine, a so-called reentrant type engine in which a combustion chamber is constituted by a cavity formed at the top of a piston in order to maintain the strength of swirl at the top dead center. Pistons are used. This type of engine generally includes a combustion chamber formed in a piston that reciprocates in a cylinder, and a fuel injection nozzle provided in a cylinder head facing a substantially center of the combustion chamber and having a plurality of injection holes. The fuel is injected from the injection hole directly into a combustion chamber formed at the top of the piston.

[0003]

However, in a small direct-injection diesel engine, the ratio of the diameter of the opening of the cavity to the diameter of the piston is concentrated around about 0.5. As shown in the conventional combustion chamber structure shown in the drawing, the non-evaporated portion of the fuel injected from the injection hole 29 of the fuel injection nozzle, that is, the liquid phase portion 32 collides with the wall surface 30 of the combustion chamber 26 formed in the piston 23. I do.
The colliding fuel spreads in the form of a film in the circumferential direction of the wall surface 30 and in a direction orthogonal thereto, over a wide range of the wall surface 30 of the combustion chamber from the collision site (an arrow F indicates the spread of the fuel in the circumferential direction of the wall surface).

[0004] At the time of start-up or low load operation, the temperature of the wall 30 of the combustion chamber is relatively low, so that the fuel after collision spreads in a film along the wall 30 and adheres to the wall 30 without evaporating. Become. In FIG. 7, the combustion chamber 26
The region indicated by G is a region where the flame does not reach, and the liquid phase fuel that has reached the region G ends the combustion cycle without completely burning. As a result, there is a problem that unburned hydrocarbons which evaporate thereafter are discharged into the combustion gas.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a liquid phase portion of an injected fuel from adhering to a wall surface even when fuel injected from a fuel injection nozzle collides with a wall surface of a combustion chamber. An object of the present invention is to provide a combustion chamber structure in a direct injection diesel engine that does not emit hydrocarbons into gas.

[0006] The present invention has been made in order to solve the above-mentioned object.
It is configured as follows. That is, the present invention includes a combustion chamber formed in a piston that reciprocates in a cylinder, and a fuel injection nozzle provided in a cylinder head facing a substantially center of the combustion chamber and having a plurality of injection holes. In a direct injection diesel engine, a concave portion having a shape corresponding to the collision region of the liquid phase portion is formed on the collision surface of the combustion chamber where the liquid phase portion of the fuel injected from the injection hole of the fuel injection nozzle collides. The invention relates to a combustion chamber structure in a direct injection diesel engine.

According to the present invention, the fuel injected from the plurality of injection holes of the fuel injection nozzle provided substantially at the center of the combustion chamber does not immediately vaporize all the fuel, and a considerable amount of fuel is supplied. In the state of the phase, it collides with the wall of the combustion chamber formed on the piston reciprocating in the cylinder. The liquid phase portion of the injected fuel collides with a concave portion formed on the collision surface of the combustion chamber and corresponding to the collision region of the liquid phase portion, and the reflection flow is in the opposite direction to the injection direction. become. Therefore, the injected fuel is provided for combustion in the combustion chamber after the collision with the collision surface. When the temperature of the combustion chamber is relatively low at the time of starting or operating at a low load, the ratio of the liquid phase portion to the injected fuel tends to increase. However, not only when the temperature is relatively high as in a normal operation state, but also when the temperature is relatively low, the liquid phase portion is less likely to adhere to the wall surface of the combustion chamber. As a result, unburned hydrocarbons contained in the exhaust gas are reduced.

[0008] The recess has a smooth inclined surface extending from the bottom surface in the flow direction of the swirl generated in the combustion chamber. According to this combustion chamber structure, the liquid-phase fuel that collides with the concave portion and reflects does not spread while remaining attached to the wall surface of the combustion chamber from the inclined surface with the aid of the flow of the swirl generated in the combustion chamber. It scatters into the combustion chamber and is used for combustion.

Furthermore, a sharp edge is formed at the boundary between the inclined surface on the downstream side of the swirl flow direction and the wall surface of the combustion chamber. According to this combustion chamber structure, when the liquid fuel flows out of the inclined surface with the assistance of the swirl flow, the liquid fuel is easily separated from the wall surface of the combustion chamber by the sharp edge, and the liquid fuel is separated from the combustion chamber. The phenomenon of spreading while remaining attached to the wall surface of the substrate is further suppressed.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view showing one embodiment of a combustion chamber structure in a direct injection diesel engine according to the present invention, and is a sectional view on a plane including a line Y-Y shown in FIG. FIG. 2 is a cross-sectional view of the combustion chamber shown in FIG. 1, and is a cross-sectional view of a plane including line XX of FIG. 1. Referring to FIG. 1, a direct-injection diesel engine 1 includes a piston 3 that reciprocates while being sealed by an O-ring 4 in a cylinder 2, and a combustion chamber 6 is formed by a cavity formed in a top 5 of the piston 3. Have been. A fuel injection nozzle 8 is provided in the cylinder head 7 so as to face substantially the center of the combustion chamber 6, and fuel is injected at the tip of the fuel injection nozzle 8 in a direction toward the wall surface 10 of the combustion chamber 6. A plurality of (five in the example in the figure) injection holes 9 are arranged at intervals in the circumferential direction.

The liquid phase portion 12 of the injected fuel 11 is
A concave portion 13 corresponding to the shape of the collision region of the liquid phase portion 12 is formed at a portion where the collision occurs on the wall surface 10. Often, the shape of the collision area is substantially circular,
The shape of the concave portion 13 also has a circular portion so as to include the collision region (see the region S in the example shown in FIG. 4 described later).
As shown in FIG. 2, a swirl is generated in the combustion chamber 6 as shown by an arrow B, and the recess 13 has a bottom surface 14.
And a smooth inclined surface 15 that extends continuously in the flow direction of the swirl B. The liquid phase portion 12 of the injected fuel 11 has a substantially circular cross section and a diameter of about 4 mm, so that the diameter of the bottom surface 14 excluding the inclined surface of the recess 13 is also about 4 mm.
From the efficiency of the rebound of the liquid phase portion 12, the depth of the concave portion 13 is also set to about 4 mm similarly to the diameter. Note that, in FIG. 1, the concave portion 13 that should be seen at the front center and the opening of the combustion chamber 6 that should be seen in FIG. 2 are omitted to avoid complication of the drawing.

The liquid phase portion 12 of the injected fuel 11 rebounds after colliding in the recess 13 of the wall surface 10, and the rebounded fuel is directed in the opposite direction to the injection direction as shown by the arrow A in the figure. Although some of the fuel flows, most of the rebound fuel spreads into the combustion chamber 6 along the inclined surface 15, that is, the flow direction of the swirl B, and the unevaporated fuel diffuses in the combustion chamber 6 and is subjected to combustion. You. Therefore, unlike the conventional engine, the film does not spread along the wall surface 10 in a vertical or horizontal direction. In addition, the swirl B sweeps out carbon that easily accumulates in the recess 13 due to combustion, and functions to maintain the function of the recess 13.

FIG. 3 is an enlarged sectional view showing another example of the recess formed in the combustion chamber in another embodiment of the combustion chamber structure in the direct injection type diesel engine according to the present invention, in the same direction as FIG. FIG. FIG. 4 is a front view of the recess shown in FIG. As shown in FIGS. 3 and 4, a collision region S of the injected fuel 11 with the wall surface 10 of the liquid phase portion 12 has a substantially circular shape, and a concave portion 16 is formed on the wall surface 10 corresponding to the collision region S. Is formed. The concave portion 16 has an inclined surface 18 so as to gradually approach the wall surface 10 along a downstream direction of the swirl B generated in the combustion chamber 6 from the bottom surface 17. Therefore, the flow of the liquid phase portion 12 of the injected fuel 11 reflected on the bottom surface 17 of the concave portion 16 is guided by the inclined surface 18 so as to flow in the direction of the swirl B as shown by C.

The fuel guided to the inclined surface 18 is supplied to the combustion chamber 6.
It scatters inside, but in order to make its action more certain,
A sharp edge 19 is formed at the boundary between the inclined surface 18 on the downstream side in the flow direction of the swirl B and the wall surface 10 of the combustion chamber 6. Injected fuel 1 guided and guided by the inclined surface 18
The first liquid phase portion 12 is easily scattered directly into the combustion chamber 6 at the sharp edge 19, so that it flows and spreads like a film along the wall surface 10 as seen in a conventional engine. Never. Further, the swirl B sweeps out carbon generated by combustion from the concave portion 16 in the same manner as described in the example shown in FIG. 2, and thus functions to maintain the original function of the concave portion 16.

FIG. 5 is a longitudinal sectional view showing a part of still another embodiment of the combustion chamber structure in the direct injection diesel engine according to the present invention. FIG. 6 is a cross-sectional view of the concave portion shown in FIG.
It is sectional drawing in the plane which passes through Z. In the embodiment shown in FIGS. 5 and 6, substantially the same components as those in the embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals. Omitted. As shown in FIGS. 5 and 6, a concave portion 20 is formed on the collision surface where the liquid phase portion 12 of the injected fuel 11 collides with the wall surface 10, corresponding to the collision region. The concave surface forming the concave portion 20 is a conical surface with the central line D of the liquid phase portion 12 of the injected fuel 11 as a central axis, and the deepest point of the concave portion 20 corresponds to the apex of this cone. The apex angle of the cone is preferably 20 ° to 40 ° in view of the fuel rebound characteristics. The opening width of the recess 20 in the wall surface 10 is about 4 mm. The flow of the fuel bounced off by the concave portion 20 is in a direction opposite to the injection direction as shown by an arrow E, and scatters into the combustion chamber 6 without spreading and adhering to the wall surface 10 of the combustion chamber 6 in a film shape.

[0016]

Since the present invention is configured as described above, it has the following effects. That is, according to the combustion chamber structure of the direct injection diesel engine according to the present invention, the liquid phase portion of the injected fuel is formed in the recess formed on the collision surface of the combustion chamber and having a shape corresponding to the collision region of the liquid phase portion. The collision will cause the reflected flow to be in the opposite direction of the injection, and the injected fuel will, after impact with the impact surface,
Provided for combustion in the combustion chamber. Therefore, even when the temperature of the combustion chamber is relatively low, the liquid phase is less likely to adhere to the wall surface of the combustion chamber in the form of a film, and the liquid phase portion flows and adheres to the film along the collision surface. As a result, the fuel is not discharged into the combustion gas in a hydrocarbon state without being burned. Moreover, the flow direction of the liquid phase portion of the reflected fuel guided by the inclined portion formed in the concave portion is in the forward direction with respect to the flow of the swirl B, so that the liquid phase portion enters the combustion chamber with the assistance of the swirl flow. It becomes easy to fly and is used for combustion. Further, even if carbon is generated in the concave portion due to combustion, it is swept out by the swirl B and the concave portion 1
3 is prevented from sticking inside, and the function of the concave portion is maintained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a combustion chamber structure in a direct injection diesel engine according to the present invention, and FIG.
It is sectional drawing in the plane which passes along the line YY.

FIG. 2 is a cross-sectional view of the combustion chamber structure shown in FIG. 1 taken along a line XX.

FIG. 3 is an enlarged sectional view showing a recess formed in the combustion chamber in another embodiment of the combustion chamber structure in the direct injection diesel engine according to the present invention.

FIG. 4 is a front view of a recess shown in FIG. 3;

FIG. 5 is a sectional view showing a part of still another embodiment of the combustion chamber structure in the direct injection diesel engine according to the present invention.

FIG. 6 is a cross-sectional view taken along a plane passing through line ZZ of the concave portion shown in FIG.

FIG. 7 is a cross-sectional view of a combustion chamber structure of a conventional direct injection engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Direct injection diesel engine 2 Cylinder 3 Piston 5 Piston top 6 Combustion chamber 7 Cylinder head 8 Fuel injection nozzle 9 Injection hole 10 Wall surface 11 Injected fuel 12 Liquid phase part 13, 16, 20 Concave part 14, 17 Bottom surface 15, 18 Inclined surface 19 Sharp Edge B Swirl

Claims (3)

[Claims] 1. A direct combustion engine comprising: a combustion chamber formed in a piston reciprocating in a cylinder; and a fuel injection nozzle provided in a cylinder head facing a substantially center of the combustion chamber and having a plurality of injection holes. In the injection diesel engine, a concave portion having a shape corresponding to the collision region of the liquid phase portion is formed on a collision surface of the combustion chamber where the liquid phase portion of the fuel injected from the injection hole of the fuel injection nozzle collides. The combustion chamber structure of a direct injection diesel engine characterized by the following. 2. The combustion chamber structure in a direct-injection diesel engine according to claim 1, wherein said recess has a smooth inclined surface extending from a bottom surface thereof in a flow direction of swirl generated in said combustion chamber. 3. A combustion chamber structure in a direct-injection diesel engine according to claim 2, wherein a sharp edge is formed at a boundary between the inclined surface on the downstream side in the flow direction of the swirl and a wall surface of the combustion chamber. .