JP4580309B2 - Combustion chamber structure of direct injection diesel engine - Google Patents

Description

  The present invention relates to a combustion chamber structure of a direct injection diesel engine.

  Some vehicle engines employ exhaust gas recirculation (EGR) that reduces the generation of NOx by returning exhaust gas that has been diverted from the exhaust path to the intake path.

  FIG. 8 shows an example of a vehicle engine that employs exhaust gas recirculation. In the diesel engine 1 shown here, an exhaust passage 3 through which exhaust gas 2 circulates and an intake passage 4 are connected by an EGR pipe 5. An EGR valve 6 is incorporated in the pipe 5.

  When the EGR valve 6 is opened, a part of the exhaust 2 sent from the diesel engine 1 to the exhaust passage 3 is guided to the intake passage 4 through the EGR pipe 5 and sent into the cylinder of the diesel engine 1 together with the intake air 7.

  Thereby, the combustion temperature in the cylinder is lowered, and the generation of NOx is reduced.

  The ceiling of each cylinder of the diesel engine 1 is equipped with a porous injector 8 that injects fuel (light oil) into the cylinder, and the top of the piston 9 is recessed to form most of the combustion chamber. A cavity 10 is formed.

  As shown in FIG. 9, the cavity 10 at the top of the piston 9 is lowered into an inlet lip portion 11 that forms the outer edge of the opening, and descends from the inlet lip portion 11 so as to draw a gentle S-shaped curve. A reentrant portion 12 that protrudes further outward in the radial direction, an outer curved surface portion 13 that forms a gentle concave curved surface that extends radially inward from the reentrant portion 12, and a piston center O from the entire lower end of the outer curved surface portion 13. And a center cone 14 having a flat conical shape.

  The fuel injection from the injector 8 is executed at the end of the compression stroke (in the vicinity of the compression top dead center) where the in-cylinder temperature increases based on the fuel injection command 8a from the control device 15.

  The control device 15 receives an accelerator opening signal 16a from the accelerator sensor 16 that detects the accelerator opening as an engine load, a rotation speed signal 17a from the rotation sensor 17 that detects the engine rotation speed, and the like. The operation state of the diesel engine 1 is constantly monitored according to various controls.

  Further, in FIG. 8, 18 is a crankshaft, 19 is an exhaust port, 20 is an exhaust valve, 21 is an intake port, 22 is an intake valve, and the intake valve 22 and the exhaust valve 20 are attached to an engine-driven camshaft. The open cam is operated at an appropriate time according to the stroke of each cylinder through the push rod and the rocker arm.

As prior art document information related to the combustion chamber structure of this type of direct injection diesel engine, for example, the following Patent Document 1 and Patent Document 2 have already been proposed.
Japanese Patent Laid-Open No. 6-212973 JP 7-150944 A

  However, in the conventional vehicle engine as shown in FIG. 8, reducing the NOx by sending the exhaust 2 diverted from the exhaust passage 3 into the cylinder generates black smoke due to combustion failure in the cylinder. There is a trade-off relationship between

  That is, if the recirculation amount of the exhaust 2 is increased in order to realize a substantial reduction in NOx, problems such as generation of black smoke and deterioration of fuel consumption are caused.

  Therefore, the present inventor has conducted intensive research on the existing combustion chamber structure shown in FIG. 9 while paying attention to the diffusion state of the fuel. As shown in FIG. 10 (compression top dead center), the inventor is directed toward the reentrant portion 12. As shown in FIG. 11 (crank angle 6 °) and FIG. 12 (crank angle 12 °), the fuel injected in this way collides with the reentrant portion 12, and the air flow generated by the injection of the fuel enters the outer curved surface portion 13. As shown in FIG. 13 (crank angle 18 °), the air flow toward the outer side in the latter half of the fuel injection remains above, as shown in FIG. 13 (crank angle 18 °). A large vortex circulating in the cavity 10 as shown in FIG. 14 (crank angle 30 °) is formed, and most of the fuel stays in the cavity 10 as shown in FIG. Region is locally I found the fact that black smoke is easily formed.

  10 to 15 schematically show the diffusion state of the distribution by concentration of the injected fuel, and indicates that the concentration of the fuel is higher in the inner distribution region.

  The fuel is directed from the cavity 10 to the squish area S (region between the top surface of the piston 9 around the cavity 10 and the cylinder ceiling 23), thereby improving the diffusibility of the fuel and the cylinder. The inventors have come up with a technique for suppressing the generation of black smoke by successfully burning on the outer peripheral side where there is more oxygen than the inner peripheral side (the larger the volume, the greater the amount of oxygen). Document 2 and the like pay attention only to the mixing property of fuel and air, and it has not been possible to realize effective diffusion of fuel from the cavity 10 to the squish area S.

  The present invention has been made in view of the above circumstances, and provides a combustion chamber structure of a direct injection type diesel engine that can avoid generation of black smoke and deterioration of fuel consumption as much as possible even if the amount of exhaust gas recirculation is increased. The purpose is to do.

The present invention
Shape the cavity recessed so as to form the majority of the combustion chamber in the piston crown, a combustion chamber structure for a direct injection diesel engine to self-ignition by injecting fuel into the cavity inwardly when said piston reaches the top dead center And
An inlet lip that forms the outer edge of the cavity opening;
A reentrant portion that descends from the inlet lip portion so as to draw a gentle S-curve and protrudes radially outward from the inlet lip portion;
An outer curved surface portion forming a concave curved surface radially inward from the reentrant portion;
An inner curved surface portion that forms a concave curved surface that descends radially inward from the entire circumference of the lower end portion of the outer curved surface portion and subsequently rises;
A center cone having a flat conical shape from the entire upper end of the inner curved surface to the center of the piston,
As the concave curved surface of the inner curved surface part is gentler than the concave curved surface of the outer curved surface part,
As the piston approaches the compression top dead center, the air flowing from the squish area into the cavity descends toward the outer curved surface portion and the inner curved surface portion, and along the inner curved surface portion. Causing a vertically long vortex to flow from the outside in the radial direction to the inside and further upward,
The air pushed out by fuel injection when the piston reaches the vicinity of the compression top dead center eliminates the vortex descending toward the outer curved surface portion and has a vertically long shape above the inner curved surface portion. Energize the vortex,
A configuration is adopted in which the vortex above the inner curved surface portion can be guided to the upper portion of the combustion chamber along with the fuel mixture .

  In other words, as the piston in the compression stroke approaches the compression top dead center, air flows from the squish area into the cavity, and a vortex corresponding to the outer curved surface portion and a vertically long vortex corresponding to the inner curved surface portion are formed. Arise.

  When the piston reaches the compression top dead center and fuel injection is executed, the vortex corresponding to the outer curved surface portion disappears, and the air pushed out by the fuel injection corresponds to the inner curved surface portion. The vortex is strengthened, and the vortex is stretched upward by its own centrifugal force.

  This vortex leads the fuel mixture to the upper part of the combustion chamber where there is a lot of oxygen, and the fuel mixture diffuses into the squish area, thereby promoting soot reoxidation.

  According to the combustion chamber structure of the direct injection type diesel engine of the present invention, fuel mixing is not performed in the squish area where a lot of oxygen exists without locally generating a fuel-rich region near the inner bottom portion or the center portion of the cavity. As the air diffuses effectively, it is possible to increase the amount of exhaust gas recirculation to an area where it has not been possible so far, while avoiding the generation of black smoke and the deterioration of fuel consumption as much as possible, and significantly reducing NOx. It is possible to achieve an excellent effect that can be achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIGS. 1-7 is an example of the combustion chamber structure of the direct-injection diesel engine of this invention, In the figure, the part which attached | subjected the code | symbol same as FIG. 8, FIG. 9 represents the same thing.

  The cavity 10 at the top of the piston 9 has an inlet lip portion 11 that forms the outer edge of the opening, and descends from the inlet lip portion 11 so as to draw a gentle S-curve, and extends outward in the radial direction from the inlet lip portion 11. A reentrant portion 12 to be ejected, an outer curved surface portion 24 that forms a concave curved surface radially inward from the reentrant portion 12, and a concave portion that descends radially inward from the entire lower end of the outer curved surface portion 24 and rises continuously. An inner curved surface portion 25 that forms a curved surface, and a center cone 26 that forms a flat conical shape from the entire circumference of the upper end portion of the inner curved surface portion 25 toward the piston center O are provided.

  The radius R2 of the longitudinal section of the inner curved surface portion 25 is set to be larger than the radius R1 of the longitudinal section of the outer curved surface portion 24 (Since these concave curved surfaces are not necessarily single radii, The expression that the curvature of the surface is set smaller than the curvature of the longitudinal section of the outer curved surface portion 24 is suitable).

  Further, the outer curved surface portion 24 and the inner curved surface portion 25 are separated by a boundary portion 27 where both concave curved surfaces face each other.

  Further, the inner curved surface portion 25 and the center cone 26 are separated by an edge portion 28 where the concave curved surface and the flat surface abut each other.

  In addition, the structure of the vehicle engine which incorporates the piston 9 mentioned above is not different from the diesel engine 1 shown in FIG.

  In the combustion chamber structure of this direct injection type diesel engine, as the piston 9 in the compression stroke approaches the compression top dead center, air flows from the squish area S into the cavity 10, and as shown in FIG. The vortex I descends from the upper side toward the outer curved surface portion 24.

  In addition, a vertically long vortex II descending from the upper side of the boundary portion 27 toward the inner curved surface portion 25 and moving along the inner curved surface portion 25 toward the edge portion 28 is reversed from the vortex I due to the viscous effect. It arises as follows.

  In order to make the vortex II vertically long, it is necessary to set the curvature of the longitudinal section of the inner curved surface portion 25 to be smaller than the curvature of the longitudinal section of the outer curved surface portion 24.

  When the piston 9 reaches near the compression top dead center and fuel injection is executed toward the reentrant portion 12, the vortex I disappears and is pushed out by the previous fuel injection as shown in FIG. 3 (crank angle 6 °). The generated air III urges the vortex II to strengthen the vortex II as shown in FIG. 4 (crank angle 12 °), and the vortex II is stretched upward by its own centrifugal force.

  Further, as shown in FIG. 5 (crank angle 18 °), the fuel distribution region indicated by the symbol F, in other words, the fuel mixture is accompanied by the vortex II to the upper part of the combustion chamber where a large amount of oxygen exists. As the piston 9 in the expansion stroke moves away from the compression top dead center, the fuel mixture becomes squish area S as shown in FIG. 6 (crank angle 30 °) and FIG. 7 (crank angle 40 °). This promotes soot reoxidation.

  As described above, according to the combustion chamber structure of the direct injection type diesel engine described above, a squish area where there is a large amount of oxygen without locally producing a fuel-rich region near the inner bottom portion or the central portion of the cavity 10. Since the fuel mixture is effectively diffused into S, the recirculation amount of the exhaust 2 (see FIG. 8) could not be realized with the existing diesel engine 1 while avoiding the generation of black smoke and the deterioration of fuel consumption as much as possible. And a significant reduction in NOx can be achieved.

  It should be noted that the combustion chamber structure of the direct injection diesel engine of the present invention is not limited to the above-described embodiment, and it is needless to say that changes can be made without departing from the gist of the present invention.

It is sectional drawing which shows the detail of the cavity of the piston in an example of the combustion chamber structure of the direct injection type diesel engine of this invention. It is sectional drawing which shows the combustion injection condition in the compression top dead center of the piston of FIG. FIG. 2 is a cross-sectional view showing a state of combustion injection at a crank angle of 6 ° of the piston of FIG. 1. FIG. 2 is a cross-sectional view showing a state of combustion injection at a crank angle of 12 ° of the piston of FIG. 1. FIG. 2 is a cross-sectional view showing a state of combustion injection at a crank angle of 18 ° of the piston of FIG. 1. FIG. 2 is a cross-sectional view showing a state of combustion injection at a crank angle of 30 ° of the piston of FIG. 1. FIG. 2 is a cross-sectional view showing a state of combustion injection at a crank angle of 40 ° of the piston of FIG. 1. It is a conceptual diagram which shows an example of the diesel engine for vehicles which employ | adopted exhaust gas recirculation. It is sectional drawing which shows the detail of the cavity of the piston relevant to FIG. It is sectional drawing which shows the combustion injection condition in the compression top dead center of the piston of FIG. FIG. 10 is a cross-sectional view showing a state of combustion injection at a crank angle of 6 ° of the piston of FIG. 9. FIG. 10 is a cross-sectional view showing a state of combustion injection at a crank angle of 12 ° of the piston of FIG. 9. FIG. 10 is a cross-sectional view showing a state of combustion injection at a crank angle of 18 ° of the piston of FIG. 9. FIG. 10 is a cross-sectional view showing a state of combustion injection at a crank angle of 30 ° of the piston of FIG. 9. FIG. 10 is a cross-sectional view showing a state of combustion injection when the crank angle of the piston of FIG. 9 is 40 °.

Explanation of symbols

9 Piston 10 Cavity 11 Inlet lip portion 12 Reentrant portion 24 Outer curved surface portion 25 Inner curved surface portion 26 Center cone

Claims (1)

Shape the cavity recessed so as to form the majority of the combustion chamber in the piston crown, a combustion chamber structure for a direct injection diesel engine to self-ignition by injecting fuel into the cavity inwardly when said piston reaches the top dead center And
An inlet lip that forms the outer edge of the cavity opening;
A reentrant portion that descends from the inlet lip portion so as to draw a gentle S-curve and protrudes radially outward from the inlet lip portion;
An outer curved surface portion forming a concave curved surface radially inward from the reentrant portion;
An inner curved surface portion that forms a concave curved surface that descends radially inward from the entire circumference of the lower end portion of the outer curved surface portion and subsequently rises;
A center cone having a flat conical shape from the entire upper end of the inner curved surface to the center of the piston,
As the concave curved surface of the inner curved surface part is gentler than the concave curved surface of the outer curved surface part,
As the piston approaches the compression top dead center, the air flowing from the squish area into the cavity descends toward the outer curved surface portion and the inner curved surface portion, and along the inner curved surface portion. Causing a vertically long vortex to flow from the outside in the radial direction to the inside and further upward,
The air pushed out by fuel injection when the piston reaches the vicinity of the compression top dead center eliminates the vortex descending toward the outer curved surface portion and has a vertically long shape above the inner curved surface portion. Energize the vortex,
A combustion chamber structure of a direct injection diesel engine, characterized in that the vortex above the inner curved surface portion can be guided to the upper portion of the combustion chamber with the fuel mixture .

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