JP2024090956A - 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 via a nozzle hole 9, and a receiving recess R is formed at a point on the ceiling wall 8A of a piston 8 where the combustion flow ejected from the nozzle hole 9 into the main combustion chamber 5 is blown onto it, and the position of the recess starting end 20A, which is the most upstream side in the flow direction Q of the combustion flow of the receiving recess R, is positioned upstream in the flow direction Q of the combustion flow compared to the position of the nozzle hole exit starting end 9a, which is the most upstream side in the flow direction Q of the combustion flow at the main combustion chamber side opening of the nozzle hole 9, and a front portion d, which is upstream in the flow direction Q of the combustion flow in the auxiliary chamber 6, is recessed towards the side where the volume of the auxiliary chamber 6 becomes larger.
[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 diesel engine with a pre-combustion chamber, in which a main combustion chamber and a pre-combustion 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 where a combustion flow ejected from the nozzle hole into the main combustion chamber is blown on a ceiling wall of a piston,
a position of a recess start end of the receiving recess which is the most upstream side in the flow direction of the combustion flow is shifted toward the upstream side in the flow direction of the combustion flow with respect to a position of a nozzle hole outlet start end of a main combustion chamber side opening of the nozzle hole which is the most upstream side in the flow direction of the combustion flow,
The present invention is characterized in that a front portion of the pre-chamber, which is on the upstream side in the flow direction of the combustion flow, is recessed on the side where the volume of the pre-chamber becomes larger.

The second aspect of the present invention is a pre-chamber 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 position of the recess start end of the receiving recess, which is the most upstream side in the flow direction of the combustion flow, is shifted upstream in the flow direction of the combustion flow with respect to the position of the nozzle hole outlet start end, which is the most upstream side in the flow direction of the combustion flow at the main combustion chamber side opening of the nozzle hole,
The depth of a nozzle hole corresponding portion of the receiving recess which corresponds to the nozzle hole is deeper than a portion of the receiving recess other than the nozzle hole corresponding portion.

For features and means other than those described above, please refer to claims 2 and claims 4 to 7 in the claims section.

According to the present invention, the position of the recess start is offset upstream from the position of the nozzle outlet start in the flow direction of the combustion flow, so that the combustion flow (combustion gas) ejected from the nozzle into the main combustion chamber flows smoothly to the recess start without the risk of hitting the piston (the ceiling wall).

The front portion, which is upstream in the flow direction of the combustion flow in the auxiliary chamber, is recessed toward the side where the volume of the auxiliary chamber is larger, which provides the following effect. That is, when compressed air enters the auxiliary chamber from the main combustion chamber through the nozzle hole as 8 moves upward during the compression stroke, the edge (corner) of the lower end (end on the main combustion chamber side) of the front portion bulges outward, causing a new vortex, i.e. a reverse vortex, to be formed in the front portion in a direction different from the normal vortex caused by the normal compressed air flow.

As a result, the synergistic effect of the normal vortex and the reverse vortex further promotes combustion in the pre-chamber, and combined with the offset structure at the beginning of the recess, it is possible to provide a pre-chamber diesel engine that can quickly urge high-temperature combustion gas into the main combustion chamber, achieving various benefits such as reduced smoke and improved fuel efficiency.

According to the second aspect of the present invention, the position of the recess start is offset upstream from the position of the nozzle outlet start in the flow direction of the combustion flow, so that the combustion flow (combustion gas) ejected from the nozzle into the main combustion chamber flows smoothly to the recess start without the risk of hitting the piston (the ceiling wall).

In addition, because the depth of the area corresponding to the nozzle hole is made deeper than the depth of other areas in the receiving recess, the flow of compressed air from the main combustion chamber through the nozzle hole to the auxiliary combustion chamber as the piston moves upward during the compression stroke is promoted smoothly and efficiently.

As a result, the combination of a deeper nozzle hole location and an offset structure at the beginning of the recess allows high-temperature combustion gas to be swiftly directed into the main combustion chamber, providing a pre-chamber diesel engine that achieves a variety of benefits, including reduced smoke and improved fuel economy.

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) Enlarged cross-sectional view of the nozzle hole area including the receiving recess with a different structure

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 a cylinder block, 2 is a cylinder head, 3 is an injector, 4 is a glow plug, 5 is a main combustion chamber (main chamber), 6 is a pre-chamber (pre-combustion chamber), 7 is a nozzle for forming the pre-chamber, 8 is a piston, 8P is the center of the piston, 9 is a nozzle hole 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 arranged so as to face 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 through a nozzle hole 9 provided at an eccentric part of the main combustion chamber 5. Note that in Figure 2 (A), the gasket 11 (see Figure 1) is omitted from the illustration.

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

The auxiliary chamber forming hole 2A, which opens into the cylinder 1B, is formed in the cylinder head 2 at a position eccentric to the cylinder peripheral wall side from the axis 8P of the piston 8, and the auxiliary chamber forming hole 2A accommodates a nozzle (chamber) 7 for forming the auxiliary chamber. The auxiliary chamber forming hole 2A is configured with, in order from the cylinder head bottom surface 2a facing the main combustion chamber 5 of the cylinder head 2 upward, a large diameter opening 12, a small diameter body accommodating portion 13, and a cavity 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 nozzle 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 that 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 nozzle hole 9.

As shown in Figures 1 to 2 (A) and (B), the nozzle hole 9 is formed in a trefoil shape (one example of a compound leaf shape) with a main nozzle hole 9A and a pair of auxiliary nozzle holes 9B, 9B arranged on either side of the main nozzle hole 9A. In other words, the nozzle hole 9 has a tip that is smoothly divided into three parts and a rounded base end, forming a sector shape (the trefoil shape of the 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). In addition, a pair of auxiliary nozzle holes 15, 15 may be provided on the left and right sides of the nozzle hole 9, slightly spaced apart from each other upstream in the flow direction of the combustion flow.

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

As shown in FIG. 2(B), the 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 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), 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 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 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 Figures 2(A) and (B), the receiving recess R is formed in a planar shape (as viewed in the direction of the piston axis 8P) that flares out toward the downstream side in the combustion flow direction Q. More specifically, it is set to a sector shape that starts at a position corresponding to the nozzle hole 9 and increases in width toward the downstream side in the combustion flow direction Q. The shape of the receiving recess R may be trapezoidal, rectangular, or any other shape other than a sector.

The receiving recess R, which is fan-shaped in plan view, has a narrow starting edge (starting end) 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. 2(B)], but this is not limited to this.

2B, the aspect ratio of the nozzle hole 9 is in the range of 1.3b≦a≦1.6b, and preferably 1.4b≦a≦1.5b (shown as a = approx. 1.46b). Also, a very shallow auxiliary recess 21 may be provided in the ceiling wall 8A in a circular arc shape centered near the recess start end 20 (the most upstream end in the flow direction Q of the combustion flow) to correspond to the pair of auxiliary nozzle holes 15, 15.

As shown in Figures 1 and 2(A), the receiving recess R is formed as a recess of non-uniform depth with a smoothly curved or straight bottom surface (notation omitted) so that the depth is greatest at the recess start end 20, which is the upstream portion in the flow direction Q of the combustion flow, and the depth becomes shallower toward the downstream side in the flow direction Q of the combustion flow. The position of the recess start end 20A, which is the most upstream side in the flow direction Q of the combustion flow of the receiving recess R, is closer to the upstream side in the flow direction Q of the combustion flow than the position of the nozzle outlet start end 9a, which is the most upstream side in the flow direction Q of the combustion flow at the main combustion chamber side opening (notation omitted) of the nozzle 9.

In other words, as shown in FIG. 2(A), the position of the recess start end 20A in the flow direction Q of the combustion flow is offset by a length (distance) e from the position of the nozzle hole exit start end 9a (see also FIG. 3). It is convenient if the offset amount e is 10-20% of the length b of the nozzle hole 9 in the flow direction of the combustion flow (0.1b≦e≦0.2b), but it is not limited to this.

As shown in FIG. 2(A), the front portion d, which is upstream of the nozzle hole 9 in the flow direction Q of the combustion flow in the auxiliary chamber 6, is recessed toward the side where the volume of the auxiliary chamber 6 becomes larger. Specifically, the front portion d is provided by recessing the lower half of the chamber 6, which is closer to the main combustion chamber, i.e., the auxiliary chamber forming recess 7C of the nozzle 7 so that the auxiliary chamber 6 bulges outward. The shape of the front portion d can be any shape, such as a relatively pointed curved recess as shown in the figure, or a spherical recess (not shown).

The start position of the receiving recess R is offset slightly (length e) from the start position of the nozzle hole 9 on the bottom surface 7a of the nozzle 7 (the position of the recess start end 20A is shifted upstream from the position of the nozzle hole outlet start end 9a in the flow direction Q of the combustion flow), so that the combustion flow (combustion gas) ejected from the nozzle hole 9 into the main combustion chamber 5 flows smoothly to the recess start end 20 without the risk of hitting the piston ceiling wall 8A.

The upstream auxiliary chamber forming recess 7C is bulged outward in the flow direction Q of the combustion flow from the nozzle hole 9 to provide the front portion d, which provides the following effect. That is, when compressed air enters the auxiliary chamber 6 from the main combustion chamber 5 via the nozzle hole 9 as the piston 8 moves upward during the compression stroke, a new vortex, i.e., a reverse vortex u, separate from the normal vortex U caused by the normal compressed air flow, is formed in the auxiliary chamber 6 at the edge (corner) formed by the lower end of the front portion d and the nozzle hole 9, that is, in the front portion d, as shown in FIG. 2(A). The rotation direction of the reverse vortex u is opposite to that of the normal vortex U.

As a result, the normal vortex U and reverse vortex u [see Figure 2 (A)] caused by the compressed air flow that flows from the main combustion chamber 5 to the auxiliary combustion chamber 6 during the compression process work together to further promote combustion in the auxiliary combustion chamber 6. Combined with the offset structure of the recess start end 20A described above, this quickly guides the high-temperature combustion gas into the main combustion chamber 5, resulting in a pre-chamber diesel engine that can achieve various effects such as reduced smoke and improved fuel efficiency.

[Another embodiment]
As shown in Fig. 3, the diesel engine may have a configuration in which the depth h of the nozzle hole corresponding portion f of the receiving recess R corresponding to the nozzle hole 9 is deeper than the depth s of the portion t of the receiving recess R other than the nozzle hole corresponding portion f (h>s). The nozzle hole corresponding portion f is smoothly recessed in a spherical or arcuate shape, or in a cone shape, in a cross section cut vertically along the flow direction Q of the combustion flow. The "other portion t" refers to a portion of the receiving recess R other than the nozzle hole corresponding portion f. In addition, the recess start end 20 and the nozzle hole corresponding portion f may be equal to or different from each other.

As shown in FIG. 3, the receiving recess R is formed so that the depth h of the nozzle hole corresponding portion f is deeper than the depth s of the other portions t. For example, it is advantageous to set the depth h of the nozzle hole corresponding portion f to at least twice the depth s of the other portions t (h≧2s). In addition, the receiving recess R (its bottom surface) smoothly connects the other portions t and the nozzle hole corresponding portion f in the flow direction Q of the combustion flow.

In Figure 3, the depth of the receiving recess is depicted as being uniform, but in the case of a non-uniform depth (see receiving recess R in Figure 1), it is convenient to apply a depth of at least twice the maximum depth as h of the nozzle corresponding point f. Note that in the configuration shown in Figure 3, as in the case shown in Figure 2(A), the starting position of the receiving recess R is offset by a small amount (length e) from the starting position of the nozzle 9 on the bottom surface 7a of the nozzle 7.

In the diesel engine with an auxiliary combustion chamber according to another embodiment, the depth h of the nozzle hole corresponding point f is formed deeper than the depth s of the other points t, so that the flow of compressed air from the main combustion chamber 5 through the nozzle hole 9 into the auxiliary combustion chamber 6 caused by the upward movement of the piston 8 during the compression stroke is promoted smoothly and efficiently. Therefore, in combination with the aforementioned "offset structure of the recess start end 20A", the high-temperature combustion gas can be urged quickly into the main combustion chamber 5, achieving various effects such as reducing smoke and improving fuel efficiency.

[Another embodiment]
The offset amount e by which the position of the recess start end 20A is moved upstream from the position of the nozzle hole exit start end 9a in the flow direction Q of the combustion flow can be less than 10% (0<e<0.1b) or more than 20% (0.2b<e<g: g = distance between the outer peripheral edge of the ceiling wall 8A and 9a) of the length b of the nozzle hole 9 in the flow direction of the combustion flow. In addition, the recess start end 20A may be in the range of the distance x (not shown) from the nozzle hole exit start end 9a to the auxiliary nozzle hole 15 (0.1b≦e≦x). The distance x can be up to the center of the auxiliary nozzle hole 15 or the outer peripheral edge of the nozzle hole on the near or far side.

The amount (length) of recession from the sub-chamber forming recess 7C at the front location d and the recess area can be changed in various ways. The shape of the nozzle hole 9 can be other than a three-lobe or horizontally elongated shape, such as a vertically elongated shape or a two-lobe shape.

5 Main combustion chamber 6 Auxiliary chamber 8 Piston 8A Ceiling wall 9 Injection hole 9A Main injection hole 9B Auxiliary injection hole 9a Injection hole outlet start end 20A Recess start end Q Flow direction of combustion flow R Receiving recess d Front position f Injection hole corresponding position h Depth (injection hole corresponding position)
s Depth (other parts)
t Other parts

Claims (7)

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,
a position of a recess start end of the receiving recess which is the most upstream side in the flow direction of the combustion flow is shifted toward the upstream side in the flow direction of the combustion flow with respect to a position of a nozzle hole outlet start end of a main combustion chamber side opening of the nozzle hole which is the most upstream side in the flow direction of the combustion flow,
A pre-chamber type diesel engine, wherein a front portion of the pre-chamber, which is upstream in the flow direction of the combustion flow, is recessed toward the side where the volume of the pre-chamber becomes larger. The pre-chamber diesel engine according to claim 1, wherein the forward location is located in the pre-chamber closer to the main combustion chamber. 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 position of the recess start end of the receiving recess, which is the most upstream side in the flow direction of the combustion flow, is shifted upstream in the flow direction of the combustion flow with respect to the position of the nozzle hole outlet start end, which is the most upstream side in the flow direction of the combustion flow at the main combustion chamber side opening of the nozzle hole,
A diesel engine with a separate chamber, wherein a depth of a nozzle hole corresponding portion of the receiving recess corresponding to the nozzle hole is deeper than a depth of a portion of the receiving recess other than the nozzle hole corresponding portion. The diesel engine with a pre-chamber according to claim 3, wherein the nozzle hole corresponding portion is recessed into a spherical or arc shape in a cross section cut vertically along the flow direction of the combustion flow. The pre-chamber diesel engine according to any one of claims 1 to 4, wherein the position of the recess start end is shifted from the position of the nozzle hole exit start end by 10 to 20% of the length of the nozzle hole in the flow direction of the combustion flow. The pre-chamber diesel engine according to any one of claims 1 to 4, wherein the injection 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 as described in claim 6, wherein the 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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