JP2024090954A - Diesel engine with separate chamber - Google Patents

Abstract

[Problem] To provide an improved pre-combustion chamber (IDI) type diesel engine that improves the combustion state by increasing the combustion speed, etc., thereby enabling improvements in fuel efficiency and smoke, through further intensive research focusing on the relationship between the injection hole and the recess.
[Solution] A main combustion chamber 5 and an auxiliary chamber 6 located eccentrically from the main combustion chamber 5 are connected by a nozzle hole H, and a receiving recess R is formed at the point on the ceiling wall 8A of the piston 8 where the combustion flow ejected from the nozzle hole H is blown. The nozzle hole H has a main nozzle hole 9 and a pair of auxiliary nozzle holes 15, 15 arranged on the left and right upstream of the main nozzle hole 9 in the flow direction of the combustion flow. The receiving recess R is formed so that the base end 20 of the recess on the most upstream side in the flow direction Q of the combustion flow is located in a position corresponding to the auxiliary nozzle hole 15. A pre-chamber type diesel engine in which the shape of the receiving recess R in a plan view is set to a flared shape whose width increases toward the downstream side in the flow direction Q of the combustion flow.
[Selected figure] Figure 2

Description

The present invention relates to a diesel engine with a structure in which a pre-chamber is provided that is connected to the main combustion chamber via a nozzle hole, i.e., a pre-chamber type diesel engine.

Indirect injection (IDI) diesel engines have a pre-combustion chamber in addition to the main combustion chamber. Fuel is injected into the pre-combustion chamber, where it is ignited, and the combustion gas in the pre-combustion chamber is ejected into the main chamber through a nozzle (throttle) to complete the combustion. Direct injection (DI) diesel engines have the advantage of being able to cover the weakness of IDI engines, which have a large combustion chamber surface area, resulting in large throttling losses and heat losses, and have come to be used more frequently in recent years.

The pre-chamber (IDI) system has the advantage that the flame flow rate can be increased and ignition can be ensured even with a low-pressure injection valve because the fuel is injected within a limited pre-chamber. In addition, because the amount of air in the pre-chamber is small and the combustion pressure and temperature are low, there is also the advantage that diesel knock is less likely to occur and less NOx is produced than with the direct injection (DI) system. Therefore, the pre-chamber system is a system suitable for relatively low-speed engines, and it remains an important power source for agricultural and construction machinery, generators, and various industrial equipment for developing countries.

In a pre-chamber diesel engine, it is considered important to strengthen the vortex in the pre-chamber, which is essentially the combustion chamber, and to increase the flame propagation speed from the pre-chamber to the main combustion chamber. Patent Document 1 discloses a technology that makes it possible to improve starting performance without weakening the vortex, and Patent Document 2 discloses a technology that improves combustion efficiency by improving the structure of a recess provided in the ceiling wall of the piston.

However, due to technological advances and environmental factors, there is a demand for further improvements in fuel efficiency and smoke reduction even in pre-chamber engines.

JP 2010-180744 A Japanese Patent Application Laid-Open No. 7-279671

The object of the present invention is to provide an improved pre-combustion chamber (IDI) diesel engine that improves the combustion state by increasing the combustion speed, thereby improving fuel economy and smoke, through further intensive research focusing on the relationship between the nozzle hole and the recess.

The present invention relates to a pre-combustion chamber type diesel engine,
A main combustion chamber and an auxiliary chamber provided at a position eccentric to the main combustion chamber are communicated through a nozzle hole, and a receiving recess is formed at a position on the ceiling wall of the piston where the combustion flow ejected from the nozzle hole into the main combustion chamber is blown,
the nozzle hole includes a main nozzle hole and a pair of auxiliary nozzle holes disposed on the left and right sides of the main nozzle hole and spaced apart from each other on the upstream side of the main nozzle hole in the flow direction of the combustion flow,
The receiving recess is formed so that its base end on the most upstream side in the flow direction of the combustion flow is located at a position corresponding to the auxiliary hole, and the shape of the receiving recess in a plan view is set to a flared shape whose width increases toward the downstream side in the flow direction of the combustion flow.

In this case, it is advantageous if the shape of the receiving recess in plan view is set to a sector shape that starts at a position corresponding to the auxiliary nozzle hole and increases in width downstream in the flow direction of the combustion flow.

For features and means of the present invention other than those described above, please refer to claims 3 and onwards.

According to the present invention, the base end of the receiving recess, which is formed to have a flared shape in a plan view, is formed in a position corresponding to the auxiliary nozzle hole, making it easier for the combustion gas (combustion flow) in the auxiliary chamber to flow into the main combustion chamber.

In other words, the unburned gas ejected from the auxiliary nozzle hole mixes with the air in the receiving recess to promote combustion, so the high-temperature combustion gas can be urged quickly into the main combustion chamber, reducing smoke and improving combustion (improving fuel efficiency). As a result, a pre-chamber diesel engine has been realized that can achieve the various effects of reducing smoke and improving fuel efficiency.

As a result, through further intensive research focusing on the relationship between the nozzle hole and the recess, it will be possible to provide an improved pre-combustion chamber (IDI) diesel engine that improves the combustion state by increasing the combustion speed, thereby enabling improvements in fuel efficiency and smoke.

A longitudinal cross-sectional view of the main part of a pre-chamber diesel engine showing the combustion chamber. (A) is an enlarged cross-sectional view showing the vicinity of the nozzle hole in FIG. 1; (B) is a development showing the relationship between the piston (ceiling wall) and the nozzle (nozzle hole);

Below, an embodiment of a pre-chamber diesel engine according to the present invention will be described with reference to the drawings, in the case of an industrial diesel engine used in agricultural tractors and the like. Figure 1 corresponds to a cross-sectional view of a cylinder head cut along a line (plane) inclined at about 25 degrees to its longitudinal direction (direction in which the cylinders are aligned in series) so as to include an injector and a glow plug.

Figure 1 shows a cross-sectional view of the area surrounding the pre-chamber of a swirl-flow type industrial diesel engine, which is an example of a pre-chamber type diesel engine. 1 is the cylinder block, 2 is the cylinder head, 3 is the injector, 4 is the glow plug, 5 is the main combustion chamber (main chamber), 6 is the pre-chamber (pre-combustion chamber), 7 is a nozzle for forming the pre-chamber, 8 is the piston, 8P is the center of the piston, H is a nozzle formed in the nozzle 7, and 10 is a water jacket (a cooling water passage in the cylinder head 2).

The cylinder block 1 has a cylinder barrel (cylinder wall) 1A that forms a cylinder (cylinder bore) 1B, and a piston 8 is fitted into the cylinder 1B. A gasket 11 is sandwiched (interposed) between the top surface (notation omitted) of the cylinder block 1 and the bottom surface 2a of the cylinder head 2. At the top dead center of compression of the piston 8 (approximately the state shown in Figure 1), the volume of the main combustion chamber 5 approaches 0 (zero), and the auxiliary chamber 6 essentially becomes the combustion chamber.

The cylinder head 2 is equipped with an injector 3, and the tip injection part 3a of the injector 3 is positioned so that it faces the upper part of the auxiliary chamber 6. The auxiliary chamber 6 is connected to the main combustion chamber 5 formed in the cylinder 1B via a nozzle hole H provided at an eccentric part of the main combustion chamber 5. The nozzle hole H is composed of a main nozzle hole 9 and a pair of auxiliary nozzle holes 15, 15 that are located on the left and right of the main nozzle hole 9 upstream in the flow direction Q of the combustion flow (the direction of the hole center 9P).

The nozzle hole 9 is formed in a tilted hole (see also FIG. 2(A)) with a hole center 9P that is approximately tangential to the wall surface (inner peripheral surface) w of the auxiliary combustion chamber 6 and faces the center of the main combustion chamber 5 (piston axis 8P) at an inclination angle θ with respect to the cylinder head bottom surface 2a (horizontal in this embodiment). The injector 3 is tilted so that the fuel injected from the tip injection part 3a faces the nozzle hole 9. Note that the gasket 11 (see FIG. 1) is omitted in FIG. 2(A).

As shown in Figures 1 and 2(A), an auxiliary chamber forming hole 2A that opens into the cylinder 1B is formed in a position eccentric to the cylinder peripheral wall side from the axis 8P of the piston 8 in the cylinder head 2, and a nozzle (chamber) 7 for forming the auxiliary chamber is housed in the auxiliary chamber forming hole 2A. The auxiliary chamber forming hole 2A is configured to have, in order from the cylinder head bottom surface 2a facing the main combustion chamber 5 of the cylinder head 2 upwards, a large diameter opening 12, a small diameter body accommodating portion 13, and a hollow portion 14 located behind the body accommodating portion 13.

The opening 12 accommodates the bottom 7A of the nozzle 7, which is formed in a cup shape. The body accommodating section 13 accommodates the body 7B of the nozzle 7 and has a smaller diameter than the opening 12. The hollow section 14 is formed in a recessed area that is roughly hemispherical and slightly larger than a hemisphere, and is connected to the body accommodating section 13 by a stepped surface (not shown). The auxiliary chamber 6 is positioned with respect to the cylinder 1B so that its center line (not shown) extending in the vertical direction is slightly closer to the piston axis 8P than the outer circumferential end of the piston 8.

As shown in Figures 1 and 2 (A), the nozzle 7 is formed of a stepped cylindrical metal fitting including a cylindrical body 7B and a bottom 7A. The bottom 7A is a flange-like portion that protrudes circumferentially from one end side of the body 7B with a diameter larger than the outer diameter of the body 7B and has a flat bottom surface 7a. At the other end side of the body 7B, a sub-chamber forming recess 7C that is approximately hemispherical and slightly smaller than a hemisphere is formed from the upper end surface of the body 7B.

The spherical (egg-spherical, cocoon-shaped) auxiliary chamber 6 is composed of a hollow portion 14 and an auxiliary chamber forming recess 7C, and the injection hole 9 is formed from the bottom 7A to the body 7B as a section that connects the auxiliary chamber forming recess 7C with the main combustion chamber 5. In other words, the nozzle 7, which is fitted into the auxiliary chamber forming hole 2A adjacent to the main combustion chamber 5 in the cylinder head 2, is formed with the body 7B where the auxiliary chamber forming recess 7C for forming the auxiliary chamber 6 is formed, and the injection hole 9.

As shown in Figures 1 to 2 (A) and (B), the main nozzle hole 9 is formed as a trefoil-shaped hole (one example of a compound-leaf shape) in which a main nozzle hole 9A and a pair of auxiliary nozzle holes 9B, 9B arranged on either side of the main nozzle hole 9A are connected. In other words, the main nozzle hole 9 has a tip that is smoothly divided into three parts, and a rounded base end, forming a fan shape (the trefoil shape of the main nozzle hole 9 has a heart-shaped bulge with another bulge toward the outside in the center of the tip side, giving a total of three bulges), but is not limited to this. A pair of auxiliary nozzle holes 15, 15 are arranged slightly apart on the upstream side of the main nozzle hole 9 in the flow direction of the combustion flow, on the left and right sides.

Figure 2(B) shows the piston 8 in plan view and the nozzle 7 in bottom view next to each other in the flow direction Q (the direction of the hole center 9P), with the piston 8 and nozzle 7 in corresponding positions on the left and right of the hole center 9P, which is the nozzle hole axis. Each auxiliary nozzle hole 15 is formed as a small circular vertical hole along the piston axis 8P, and a pair of auxiliary nozzle holes 15, 15 are positioned symmetrically with respect to the hole center 9P. Note that the flow direction Q of the combustion flow that is changed direction from the main nozzle hole 9 and flows into the main combustion chamber 5 [see Figure 2(A)] is the same as the hole center 9P direction in plan view [see Figure 2(B)].

As shown in FIG. 2(B), the main nozzle hole 9 opening on the bottom surface 7a of the nozzle 7 is formed in a horizontally elongated shape in which the left-right length (width) a, which is the length in the left-right direction relative to the combustion flow direction Q, is greater than the front-to-back length (total length) b, which is the length in the combustion flow direction Q, which is the direction along the hole center 9P (a>b). In other words, the length in the line-up direction of the main nozzle hole 9A and the pair of auxiliary nozzle holes 9B, 9B (left-to-right length a) is set to be longer than the total length of the main nozzle hole 9 (main nozzle hole 9A) (length in the direction of the hole center 9P: front-to-back length b).

As shown in Figures 1 and 2(A) and (B), a receiving recess R is formed at the location on the ceiling wall 8A of the piston 8 where the combustion flow ejected from the main nozzle hole 9 into the main combustion chamber 5 hits, and an intake valve recess 16 and an exhaust valve recess 17 are also formed. In Figure 1, 18 is an axial hole through which the shaft of the intake valve (not shown) passes, 18A is a valve seat, and 19 is a seal material. Also, the inclination angle θ of the main nozzle hole 9 is depicted as 45 degrees in Figures 1 and 2, but it may be any other angle or may be in a range such as 40 to 50 degrees.

As shown in FIG. 2(B), the receiving recess R is formed so that its recess base end 20 on the most upstream side in the flow direction Q of the combustion flow corresponds to a pair of auxiliary nozzle holes 15, 15, and the shape of the receiving recess R in a plan view is set to a fan-shaped shape whose width increases toward the downstream side in the flow direction Q of the combustion flow. Specifically, the shape of the receiving recess R in a plan view is set to a sector whose width increases toward the downstream side in the flow direction Q of the combustion flow, starting from a position corresponding to each auxiliary nozzle hole 15, 15.

The receiving recess R, which is fan-shaped in plan view, has a narrow base edge 20A, an arc-shaped outer peripheral edge 22, one side (left side) edge 24, and the other side (right side) edge 25. Most of the tip side of the one side edge 24 is absorbed into the exhaust valve recess 17 due to the depth relationship, and the tip side of the other side edge 25 and the other side edge 25 side portion of the outer peripheral edge 22 are absorbed into the intake valve recess 16 due to the depth relationship (see FIG. 2B).

As shown in FIG. 2(A), the receiving recess R is formed as a recess of non-uniform depth with a bottom surface that is smoothly curved (or has a small curvature) and convex downward in side view, or a straight bottom surface (notation omitted), so that the depth is greatest at the recess base end 20 and becomes shallower toward the downstream side in the flow direction Q of the combustion flow. The depth of the recess base end 20 becomes deeper smoothly and suddenly from its base end edge 20A, and soon reaches its maximum depth, for example, directly below the auxiliary nozzle hole 15. The base end edge 20A has a relatively wide mesh width (left-right length) so that the lower end openings (notation omitted) of the pair of auxiliary nozzle holes 15, 15 are positioned within the receiving recess R.

As shown in FIG. 2(B), the outer periphery of the exhaust valve recess 17 overlaps with the middle portion of the receiving recess R in the flow direction Q of the combustion flow, and the outer periphery of the intake valve recess 16 overlaps with the downstream portion of the receiving recess R in the flow direction Q of the combustion flow. The depth of the intake valve recess 16 and the exhaust valve recess 17 is slightly deeper than the depth of the receiving recess R at the overlapping portion with the receiving recess R, but is not limited to this. In FIG. 2(B), for ease of understanding, the positions of the auxiliary nozzle holes 15, 15 in a plan view are shown in solid lines on the ceiling wall 8A.

As shown by the imaginary line (imaginary line, two-dot dashed line) in Figure 2 (B), the conventional sector-shaped receiving recess 23 is a pointed sector with a narrow starting end, and the width of the starting end 23a (the edge line of the starting end 23a is also shown in Figure 1 with a solid line to make it easier to understand on the drawing) is extremely narrow, and the starting end position in the flow direction Q of the combustion flow corresponds to the nozzle hole 9. In other words, the receiving recess R of the present invention greatly expands the width of the starting end 23a of the conventional sector-shaped receiving recess 23, and the starting end position is clearly shifted upstream in the flow direction Q of the combustion flow.

Here, regarding the aspect ratio of the injection hole 9, the range of the length ratio of the left-right length a to the front-rear length b of the injection hole 9 is set to 1.3b≦a≦1.6b, and preferably 1.4b≦a≦1.5b. In FIG. 2(B), a is depicted as about 1.46b. The dimensional ratio of the width (notation omitted) of the recess base end 20 to the left-right length a of the injection hole 9 is arbitrary. In addition, a very shallow auxiliary recess 21 may be provided in the shape of a circular arc centered near the position of the recess base end 20 in the ceiling wall 8A (the position of the upstream end in the flow direction Q of the combustion flow) so as to correspond to the pair of auxiliary injection holes 15, 15.

The recess base end 20 of the receiving recess R, which is formed in a fan-shaped shape in plan view, is formed in a position corresponding to the auxiliary nozzle holes 15, 15, so that the combustion gas (combustion flow) in the auxiliary chamber 6 can easily flow into the main combustion chamber 5. In other words, the unburned gas ejected from the auxiliary nozzle holes 15, 15 mixes with the air in the receiving recess R to promote combustion, so that the high-temperature combustion gas can be urged quickly into the main combustion chamber 5, reducing smoke and improving combustion (improving fuel efficiency). Thus, a pre-chamber type diesel engine that can achieve various effects such as reducing smoke and improving fuel efficiency has been realized.

Conventionally, there have been nozzles that have auxiliary nozzle holes, but in those cases, the combustion flow from the auxiliary nozzle holes hits the ceiling wall 8A of the piston 8. However, in the present invention, the recess base end 20 is expanded upstream in the combustion flow direction Q, which has the advantage that the combustion flow from the auxiliary nozzle holes 15, 15 flows smoothly through the main combustion chamber 5 along the recess base end 20.

[Another embodiment]
The shape of the nozzle hole 9 can be changed in various ways, such as a single hole having an elliptical shape, a double-leaf shape such as a heart shape, etc. The arrangement positions and the number of the auxiliary nozzle holes 15 can be other than those shown in FIG.

5 Main combustion chamber 6 Auxiliary chamber 8 Piston 8A Ceiling wall 9 Main nozzle hole 9A Main nozzle hole 9B Auxiliary nozzle hole 15 Auxiliary nozzle hole 16 Intake valve recess 17 Exhaust valve recess 20 Recess base end (upstream most side in the flow direction of the combustion flow of the receiving recess)
H: nozzle hole Q: flow direction of combustion flow R: receiving recess

Claims (6)

A main combustion chamber and an auxiliary chamber provided at a position eccentric to the main combustion chamber are communicated through a nozzle hole, and a receiving recess is formed at a position on the ceiling wall of the piston where the combustion flow ejected from the nozzle hole into the main combustion chamber is blown,
the nozzle hole includes a main nozzle hole and a pair of auxiliary nozzle holes disposed on the left and right sides of the main nozzle hole and spaced apart from each other on the upstream side of the main nozzle hole in the flow direction of the combustion flow,
The receiving recess is formed so that its base end on the most upstream side in the flow direction of the combustion flow is located at a position corresponding to the auxiliary nozzle hole, and the shape of the receiving recess in a plan view is set to a flared shape whose width increases toward the downstream side in the flow direction of the combustion flow. The diesel engine with a pre-chamber according to claim 1, wherein the shape of the receiving recess in a plan view is set to a sector shape that starts at a position corresponding to the auxiliary nozzle hole and increases in width downstream in the flow direction of the combustion flow. The diesel engine with a pre-chamber according to claim 2, wherein an intake valve recess and/or an exhaust valve recess are formed in the ceiling wall of the piston, and the receiving recess and the intake valve recess and/or the exhaust valve recess overlap. The diesel engine with a pre-chamber according to any one of claims 1 to 3, wherein the auxiliary nozzle hole is formed as a vertical hole along the piston movement direction. The pre-chamber diesel engine according to claim 4, wherein the main nozzle hole is formed as an inclined hole extending from the pre-chamber toward the center of the main combustion chamber. The diesel engine with a pre-chamber according to claim 5, wherein the main nozzle hole is formed as a multi-plane hole in which a main nozzle hole and a pair of auxiliary nozzle holes arranged on both sides of the main nozzle hole are connected.

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