JP2023131833A - Combustion chamber structure - Google Patents

Abstract

To improve thermal efficiency by activating combustion.SOLUTION: A combustion chamber structure 100, having a cavity 10 circular in a planar view, recessed downward with respect to a piston top surface 9a, and provided for a direct injection diesel engine 1 where fuel is radially injected from a nozzle 8 at the center of a cylinder ceiling part 11 into the cavity 10 to cause self-ignition, includes a first rising part 102 rising upward from the radial outer end of a bottom face 101 so as to encircle the bottom face 101 of the cavity 10, and a protrusion part 30 provided between the nozzle 8 and the first rising part 102 in the radial direction of the bottom face 101 while extending upward from the bottom face 101 so as to hit fuel spray Fu injected from the nozzle 8 and vertically divide the fuel spray Fu.SELECTED DRAWING: Figure 2

Description

One aspect of the present invention relates to a combustion chamber structure of a diesel engine.

BACKGROUND ART As a combustion chamber structure of a direct injection diesel engine, a structure is known in which, in contrast to a reentrant combustion chamber shape, stages are provided from a squish area to a combustion space and a lip structure is provided at the entrance of the combustion chamber (for example, see Patent Document 1).

Patent No. 4906055

In the combustion chamber structure as described above, fuel is injected into the combustion space from a nozzle provided at the center of the cylinder ceiling. In diesel combustion, it is ideal to burn the entire bore, so it is necessary to spray the fuel far from the nozzle. According to such fuel spraying, while the air utilization rate outside the combustion chamber increases, the air utilization rate inside the combustion chamber decreases. In addition, since air is difficult to enter inside the mist fuel, the inside of the fuel becomes rich, making it impossible to sufficiently promote the mixing of fuel and air. As mentioned above, in the conventional combustion chamber structure, it is not possible to improve the air utilization efficiency inside the combustion chamber space (center side), and the mixing of fuel and air is not promoted sufficiently. It has not been possible to activate combustion.

One aspect of the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a combustion chamber structure for a diesel engine that can improve thermal efficiency by activating combustion.

The combustion chamber structure according to one aspect of the present invention includes a cavity that is circular in plan view and is depressed downward from the top surface of the piston, and fuel is injected radially into the cavity from a nozzle provided at the center of the cylinder ceiling. This is a combustion chamber structure of a direct injection diesel engine that self-ignites through a combustion chamber, and includes a wall portion that rises upward from a radially outer end of the bottom surface so as to surround the bottom surface of the cavity, and a nozzle and a wall portion in the radial direction of the bottom surface. and a protrusion extending upward from the bottom surface so as to catch the fuel injected from the nozzle and divide the fuel into upper and lower parts.

In the combustion chamber structure according to one aspect of the present invention, a projection extending upward from the bottom surface is provided between the wall portion surrounding the bottom surface of the cavity and the nozzle that injects fuel radially (in the radial direction of the bottom surface of the cavity). A section has been established. The protrusion extends so as to hit the fuel injected from the nozzle and divide the fuel into upper and lower parts. In this way, the protrusion provided at the radial midpoint (area between the center and the outer edge) on the bottom divides the fuel into upper and lower parts, thereby changing the locus of the fuel in the lower half of the division. Specifically, the trajectory changes to return to the inside (center side) of the combustion chamber space, and the air utilization rate inside the combustion chamber space (center side) can be improved. Furthermore, since the fuel is divided into upper and lower parts, the inside of the fuel can be exposed, the rich condition inside the fuel can be eliminated, and the mixing of fuel and air can be promoted. As described above, according to the combustion chamber structure according to one aspect of the present invention, the air utilization rate is improved inside (the center side) of the combustion chamber space, and the mixing of fuel air is promoted to activate combustion. thermal efficiency can be improved.

The upper end of the protrusion may be located below the fuel injection port in the nozzle. According to such a configuration, the fuel injected downward from the nozzle can be appropriately divided into upper and lower parts by the protrusion.

The upper end of the protrusion may be located below the center of the spray axis of the fuel injected from the nozzle. According to such a configuration, the fuel above the center of the spray axis does not hit the protrusion, so it is possible to appropriately avoid an excessive amount of fuel that hits the protrusion and changes its locus. That is, the fuel can be appropriately divided into upper and lower portions.

According to the combustion chamber structure according to one aspect of the present invention, thermal efficiency can be improved by activating combustion.

1 is a schematic diagram of a diesel engine with a mechanism for recirculating exhaust gas; FIG. 1 is a diagram schematically showing a combustion chamber structure of a diesel engine. It is a figure explaining division of sprayed fuel. It is a figure which shows the situation of the sprayed fuel compared with a comparative example. FIG. 6 is a diagram showing an increase in ROHR compared to a comparative example. It is a figure which shows the improvement of thermal efficiency compared with a comparative example.

Hereinafter, a combustion chamber structure of a diesel engine according to an embodiment will be described with reference to the drawings. In addition, in the following description, the same or equivalent elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 is a schematic diagram of a diesel engine 1 equipped with a mechanism for recirculating exhaust gas. The diesel engine 1 is a direct injection diesel engine, and for example, part of the exhaust gas from the exhaust side is extracted and returned to the exhalation side, and the exhaust gas returned to the exhalation side suppresses combustion of fuel in the engine. It is also possible to employ so-called exhaust gas recirculation (EGR), which reduces the generation of NOx by lowering the combustion temperature.

In the diesel engine 1, an exhaust passage 3 through which exhaust gas 2 flows and an exhalation passage 4 are connected by an EGR pipe 5. A portion of the air is recirculated together with the intake air 7 and fed into the cylinders of the diesel engine 1, thereby lowering the combustion temperature within the cylinders and reducing NOx.

A multi-hole nozzle 8 (injector) for injecting fuel (light oil) into the cylinder is provided at the center of a cylinder ceiling 11 that is the ceiling of each cylinder of the diesel engine 1. Further, a cavity 10 which is circular in plan view and is depressed downward is formed in the top surface of the piston 9, and fuel is radially injected from the tip of the nozzle 8 onto the inner peripheral surface of the cavity 10 to perform a compression stroke. Self-ignition occurs due to the high temperature inside the cylinder at the end of the cylinder.

The injection operation of the nozzle 8 in the diesel engine 1 is controlled by a fuel injection command 8a from a control device 12 constituting an engine control computer, and the fuel injection command 8a is sent to the nozzle 8 near compression top dead center. It is designed to output power and inject fuel.

The control device 12 also receives an accelerator opening signal 13a from an accelerator sensor 13 that detects the accelerator opening as a load on the diesel engine 1, and a rotational speed signal from a rotation sensor 14 that detects the engine speed of the diesel engine 1. 14a etc. are input. In this way, the operating state of the diesel engine 1 is constantly monitored in order to execute various engine controls.

As shown in FIG. 1, the diesel engine 1 includes a crankshaft 15, an exhaust port 16, an exhaust valve 17, an exhalation port 18, and an exhalation valve 19. The exhalation valve 19 and the exhaust valve 17 are opened by a cam provided on an engine-driven camshaft (not shown) via push rods and rocker arms at appropriate timings according to the stroke of each cylinder. There is.

Next, the combustion chamber structure 100 of the diesel engine 1 including the cavity 10 described above will be described with reference to FIGS. 2 to 6.

As shown in FIG. 2, the combustion chamber structure 100 includes a cavity 10 that is recessed downward with respect to the piston top surface 9a, which is the top surface of the piston 9, and is located in the center of the cylinder ceiling 11 (see FIG. 1). This is a combustion chamber structure of a direct injection diesel engine in which fuel is radially injected into a cavity 10 from a provided nozzle 8 and self-ignited.

The combustion chamber structure 100 includes a first rising portion 102 (wall-like portion), a first horizontal portion 103, and a second rising portion 104.

The first rising portion 102 is a wall-shaped portion rising upward from the radially outer end of the bottom surface 101 so as to surround the bottom surface 101 of the cavity 10 which is circular in plan view. The first horizontal portion 103 is a portion that is continuous with the upper end of the first rising portion 102 and extends substantially horizontally in the outer circumferential direction (radially outward) of the cavity 10 . The second rising portion 104 is a wall-shaped portion that is continuous with the radially outer end of the first horizontal portion 103 and rises upward. The upper end of the second rising portion 104 reaches the piston top surface 9a. The first rising portion 102 and the first horizontal portion 103 form a lip portion.

The diameter (bore diameter) of the piston top surface 9a is, for example, about Φ112 mm. Further, the diameter of the bottom surface 101 of the cavity 10 is, for example, approximately 55 to 80 mm, and is approximately 61.5 mm, for example. The distance between the first rising portion 102 and the second rising portion 104 in the radial direction (that is, the length of the first horizontal portion 103) is, for example, about 8 mm.

Further, the combustion chamber structure 100 includes a protrusion 30 extending upward from the bottom surface 101. The protruding portion 30 is provided on the circumference between the nozzle 8 and the first rising portion 102 in the radial direction of the bottom surface 101 so as to surround the center of the bottom surface 101 . The protrusion 30 is provided, for example, at a position approximately 7.5 to 15 mm (for example, approximately 12.5 mm) radially outward from the center of the bottom surface 101 (that is, directly below the nozzle 8). The protrusion 30 extends upward to a height where it can hit the sprayed fuel Fu injected from the nozzle 8 and divide the sprayed fuel Fu into upper and lower parts. The height of the protrusion 30 is, for example, about 3 to 7 mm (for example, about 3.8 mm).

The upper end 30a of the protrusion 30 is located below the injection port of the sprayed fuel Fu in the nozzle 8. More specifically, the upper end 30a of the protrusion 30 is located below the spray axis center Ac of the sprayed fuel injected from the nozzle 8. The upper end 30a of the protrusion 30 is located approximately 1 to 3 mm (for example, approximately 1.2 mm) below the spray axis center Ac. Note that the spray axis center Ac is derived from the mounting position of the nozzle 8 and the cone angle.

As described above, the protrusion 30 hits the sprayed fuel Fu and divides the sprayed fuel Fu into upper and lower parts. The trajectory of the lower sprayed fuel (lower sprayed fuel Fun) that hits the protrusion 30 and is peeled off changes to a trajectory that returns to the inside (center side) of the combustion chamber space, which is the direction of the nozzle 8. In this way, the lower sprayed fuel Fun flows back to the inside (center side) of the combustion chamber space, thereby improving the air utilization rate inside the combustion chamber space (center side).

FIG. 3 is a diagram illustrating division of the sprayed fuel Fu. FIG. 3(a) shows the sprayed fuel Fu that is not divided (before division), and FIG. 3(b) shows the sprayed fuel Fu that is divided (after division). As shown in FIG. 3(a), air Ai is difficult to enter into the sprayed fuel F injected from the nozzle 8, and the interior of the sprayed fuel Fu becomes rich, promoting fuel-air mixing. is difficult. In this regard, as shown in FIG. 3(b), when the sprayed fuel Fu is divided into upper and lower parts by hitting the protrusion 30 and the inside of the sprayed fuel Fu is exposed, the upper sprayed fuel (upper sprayed fuel Fup) Air Ar enters from between the lower spray fuel Fun and the rich state inside the spray fuel Fu, thereby promoting fuel-air mixing.

Furthermore, due to the above-mentioned changes in the locus of the lower sprayed fuel Fun and exposure of the inside of the sprayed fuel Fu, there is a concern that cooling loss will increase due to an increase in the portion of the sprayed fuel Fu that collides with the wall and an increase in the surface area. However, since the protrusion 30 is provided relatively near the nozzle 8, the spray flame that is in a low temperature state collides with the spray fuel Fu while it is still developing, so cooling loss increases compared to the conventional method. There's nothing to do.

Next, the effects of the combustion chamber structure 100 according to this embodiment will be explained.

The combustion chamber structure 100 according to the present embodiment includes a cavity 10 that is circular in plan view and is depressed downward with respect to the piston top surface 9a, and fuel is supplied into the cavity 10 from a nozzle 8 provided at the center of the cylinder ceiling 11. A combustion chamber structure of a direct-injection diesel engine 1 that performs self-ignition through radial injection, and a first rising portion 102 that rises upward from the radial outer end of the bottom surface 101 so as to surround the bottom surface 101 of the cavity 10; It is provided between the nozzle 8 and the first rising part 102 in the radial direction of the bottom surface 101, and extends upward from the bottom surface 101 so as to hit the sprayed fuel Fu injected from the nozzle 8 and divide the sprayed fuel Fu into upper and lower parts. and a protrusion 30.

In the combustion chamber structure 100 according to the present embodiment, between the first rising portion 102 surrounding the bottom surface 101 of the cavity 10 and the nozzle 8 that injects the atomized fuel Fu radially (between the bottom surface 101 of the cavity 10 in the radial direction) A protrusion 30 extending upward from the bottom surface 101 is provided. The protrusion 30 hits the sprayed fuel Fu injected from the nozzle 8 and extends so as to divide the sprayed fuel Fu into upper and lower parts. In this way, the protrusion 30 provided at the radial intermediate point (region between the center and the outer end) on the bottom surface 101 divides the sprayed fuel Fu into the upper and lower parts, thereby dividing the lower sprayed fuel Fun. The trajectory changes, specifically, changes to a trajectory that returns to the inside (center side) of the combustion chamber space, and the air utilization rate inside the combustion chamber space (center side) can be improved. Moreover, since the sprayed fuel Fu is divided into upper and lower parts, the inside of the sprayed fuel Fu can be exposed, the rich state inside the sprayed fuel Fu can be eliminated, and the mixing of fuel and air can be promoted. As described above, according to the combustion chamber structure 100 according to the present embodiment, the air utilization rate is improved inside (the center side) of the combustion chamber space, and the mixing of fuel air is promoted to activate combustion. Thermal efficiency can be improved.

4 to 6 are diagrams for explaining the effects of the combustion chamber structure 100 compared to a comparative example. The comparative example here refers to a conventional combustion chamber structure that does not have the protrusion 30.

FIG. 4(a) shows the state of the sprayed fuel according to the comparative example. FIG. 4(b) shows the state of the sprayed fuel according to this embodiment. In FIGS. 4(a) and 4(b), the equivalence ratio of the sprayed fuel is shown by the shade of color. As shown in FIG. 4(a), in the combustion chamber according to the comparative example, the equivalence ratio of the sprayed fuel is small in the inner side A1 (center side) of the combustion chamber space. Furthermore, the equivalence ratio of the sprayed fuel is large on the outside A2 (near the wall surface) of the combustion chamber space. On the other hand, as shown in FIG. 4(b), in the fuel quality according to the present embodiment, even on the inside A101 (center side) of the combustion chamber space, the equivalence ratio of the sprayed fuel is large compared to the comparative example. It has become. Furthermore, in the region A102 outside the center of the combustion chamber space, the excessive equivalence ratio in the region up to the wall surface as shown in the comparative example is eliminated.

FIG. 5 is a diagram showing the increase in heat release rate (ROHR) compared to the comparative example. In FIG. 5, the horizontal axis represents the crank angle, and the vertical axis represents the heat release rate (ROHR) due to combustion. In FIG. 5, "without protrusions" means the combustion chamber structure of the comparative example, and "with protrusions" means the combustion chamber structure of the present embodiment. As shown in FIG. 5, the combustion chamber structure of this embodiment is able to activate combustion compared to the combustion chamber structure of the comparative example, especially when the crank angle is between 5° and 10°.

FIG. 6 is a diagram showing an improvement in thermal efficiency compared to a comparative example. In FIG. 6, the vertical axis indicates the heat balance (balance of ITE, cooling loss, and exhaust loss). In FIG. 6, "without protrusions" means the combustion chamber structure of the comparative example, and "with protrusions" means the combustion chamber structure of the present embodiment. As shown in FIG. 6, in the combustion chamber structure of this embodiment, the ITE increases by about 0.6% compared to the combustion chamber structure of the comparative example, and the thermal efficiency can be improved. Note that, as shown in FIG. 6, the cooling loss is approximately the same as that of the comparative example (specifically, a decrease of 0.1%).

The upper end 30a of the protrusion 30 may be located below the injection port of the sprayed fuel Fu in the nozzle 8. According to such a configuration, the atomized fuel Fu injected downward from the nozzle 8 can be appropriately divided into upper and lower parts by the protrusion 30.

The upper end 30a of the protrusion may be located below the spray axis center Ac of the spray fuel Fu injected from the nozzle 8. According to such a configuration, it is possible to appropriately avoid an excessive amount of fuel (lower spray fuel Fun) whose trajectory changes upon hitting the protrusion 30.

DESCRIPTION OF SYMBOLS 1...Diesel engine, 8...Nozzle, 9a...Piston top surface, 10...Cavity, 11...Cylinder ceiling, 30...Protrusion, 30a...Top end, 100...Combustion chamber structure, 101...Bottom surface, 102...First rising part (wall-shaped part), Ac... center of spray axis, Fu... spray fuel (fuel).

Claims (3)

Combustion in a direct-injection diesel engine, which has a circular cavity in plan view that is recessed downward from the top surface of the piston, and injects fuel radially into the cavity from a nozzle installed at the center of the cylinder ceiling to cause self-ignition. A chamber structure,
a wall portion rising upward from a radially outer end of the bottom surface so as to surround the bottom surface of the cavity;
a protrusion provided between the nozzle and the wall portion in the radial direction of the bottom surface and extending upward from the bottom surface so as to hit the fuel injected from the nozzle and divide the fuel into upper and lower parts; Combustion chamber structure with. The combustion chamber structure according to claim 1, wherein an upper end of the protrusion is located below a fuel injection port in the nozzle. 3. The combustion chamber structure according to claim 2, wherein the upper end of the protrusion is located below the center of the spray axis of the fuel injected from the nozzle.

Images