Pre-chamber diesel engine

Abstract

To provide a further improved indirect injection (IDI) diesel engine so as to improve fuel consumption and smoke, by improving a combustion state by increasing a combustion speed and the like as a result of earnest studies focused on a relationship between an injection hole and a recess.SOLUTION: In an indirect injection diesel engine, a main combustion chamber 5 and an auxiliary chamber 6 disposed at a place eccentric from the main combustion chamber 5 are communicated via an injection hole H. A receiving recess R is formed at a place of a ceiling wall 8A of a piston 8 to which combustion flow injected from the injection hole H is blown. The injection hole H has a main injection hole 9 and a pair of auxiliary injection holes 15, 15 disposed on the right and left at an upstream side of the main injection hole 9 in a flowing direction of the combustion flow. A receiving recess R is formed in a state that a recess basic end portion 20 at a most upstream side in a flowing direction Q of the combustion flow is located at a position corresponding to the auxiliary injection holes 15, and the shape of the receiving recess R in a plane view is set to be widened toward a leading end so that the lateral width is gradually increased toward a downstream side in the flowing direction Q of the combustion flow.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a diesel engine having a structure in which a sub-chamber is provided in series with a main combustion chamber via a nozzle hole, that is, an indirect injection diesel engine (IDI).

Background Art

[0002] An indirect injection (IDI) diesel engine provided with a sub-combustion chamber (sub-chamber) in addition to a main combustion chamber (main chamber) injects fuel into the sub-chamber to ignite it, and the combustion gas in the sub-chamber is ejected into the main chamber through a nozzle hole (throttle) to complete combustion. A direct injection (DI) diesel engine has the advantage of being able to cover the weakness of IDI, namely, "the combustion chamber surface area is large and the throttle loss and heat loss are large", and has been widely used in recent years.

[0003] In the indirect injection (IDI) type, since fuel is injected in a limited sub-chamber, there is an advantage that the flow velocity of the flame can be increased and reliable ignition can be achieved even with a low-pressure injection valve. In addition, since the amount of air in the sub-chamber is small and the combustion pressure and combustion temperature are low, compared with the direct injection (DI) type, there is also an advantage that diesel knock is less likely to occur and the amount of NOx generated is small. Therefore, since the indirect injection type is a system suitable for relatively low-speed engines, it is still an important power source in agricultural machinery, construction machinery, generators, or various industrial equipment for developing countries.

[0004] In an indirect injection diesel engine, it is considered important to strengthen the swirl in the sub-chamber that substantially serves as a combustion chamber and to increase the flame propagation speed from the sub-chamber to the main combustion chamber. Patent Document 1 discloses a technique that enables improvement of starting performance without weakening the swirl, and Patent Document 2 discloses a technique for improving combustion efficiency by devising the structure of a recess provided in the ceiling wall of the piston.

[0005] However, due to technological progress and environmental factors, further improvement in fuel consumption and reduction of smoke are also required in the indirect injection type.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-180744 [Patent Document 2] Japanese Patent Application Publication No. 7-279671 [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of this invention is to provide an improved pre-injection (IDI) type diesel engine that improves the combustion state by increasing the combustion speed, etc., through further intensive research focusing on the relationship between the injection holes and recesses, thereby enabling improvements in fuel efficiency and smoke. [Means for solving the problem]

[0008] The present invention relates to a pre-chamber diesel engine in which a main combustion chamber and a pre-chamber provided at an eccentric location from the main combustion chamber are connected via injection holes, and a receiving recess is formed in the ceiling wall of the piston at a location where the combustion flow ejected from the injection holes into the main combustion chamber is blown. The nozzle comprises a main nozzle and a pair of auxiliary nozzles, each positioned on the left and right sides, separated from the main nozzle in the flow direction of the combustion flow. The receiving recess is formed such that the uppermost recess base end in the flow direction of the combustion flow is located at a position corresponding to the auxiliary injection hole, Viewed in a direction along the axis of the piston. The shape of the receiving recess in plan view is such that the downstream side in the direction of the combustion flow is Left and right It is designed with a widening shape that increases in width. 、 The shape of the receiving recess in plan view is set to be a fan shape, starting from the position of the auxiliary injection hole facing the jet outlet on the main combustion chamber side, with the width increasing towards the downstream side in the direction of the combustion flow. It is characterized by having this feature.

[0010] Regarding the present invention, any feature configurations or means other than those described above are as described in the claims. Claim 2 See below for further information. [Effects of the Invention]

[0011] According to the present invention, the base end of the receiving recess, which is formed in a flared shape when viewed from above, is formed at a position corresponding to the auxiliary injection hole, so that the combustion gas (combustion flow) in the sub-chamber can easily flow into the main combustion chamber.

[0012] In other words, the unburned gas ejected from the auxiliary nozzles is mixed with the air in the receiving recess, promoting combustion. This allows the high-temperature combustion gases to be quickly directed to the main combustion chamber, resulting in reduced smoke and improved combustion (fuel efficiency). Consequently, a pre-chamber diesel engine capable of achieving various effects such as smoke reduction and improved fuel efficiency has been realized.

[0013] As a result, through further intensive research focusing on the relationship between the nozzle and recess, it is possible to provide an improved pre-injection (IDI) type diesel engine that improves the combustion state by increasing the combustion speed, thereby enabling improvements in fuel efficiency and smoke. [Brief explanation of the drawing]

[0014] [Figure 1] A longitudinal cross-sectional view of the main part showing the combustion chamber of a pre-chamber diesel engine. [Figure 2] (A) Enlarged cross-sectional view showing the area around the nozzle in Figure 1, (B) Developed view showing the relationship between the piston (ceiling wall) and the nozzle (nozzle), [Modes for carrying out the invention]

[0015] Below, an embodiment of the pre-chamber diesel engine according to the present invention will be described with reference to the drawings, focusing on the case of an industrial diesel engine applicable to agricultural tractors and the like. Figure 1 corresponds to a cross-sectional view of the cylinder head, including the injector and glow plug, cut by a line (plane) inclined at approximately 25 degrees with respect to its longitudinal direction (cylinder in-line direction).

[0016] Figure 1 shows a cross-sectional view of the periphery of a sub-chamber of a flow-through industrial diesel engine, which is an example of a sub-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 sub-chamber (sub-combustion chamber), 7 is a base for forming the sub-chamber, 8 is a piston, 8P is the center of the piston, H is a nozzle hole formed in the base 7, and 10 is a water jacket (cooling water passage of the cylinder head 2).

[0017] The cylinder block 1 has a cylinder barrel (cylinder wall) 1A that forms a cylinder (cylinder bore) 1B, and a piston 8 is fitted inside the cylinder 1B. A gasket 11 is sandwiched (interposed) between the upper surface (symbol omitted) of the cylinder block 1 and the bottom surface 2a of the cylinder head 2. At the compression top dead center of the piston 8 (substantially the state shown in Figure 1), the volume of the main combustion chamber 5 approaches 0 (zero), and substantially the sub-chamber 6 becomes the combustion chamber.

[0018] 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 sub-chamber 6. The sub-chamber 6 is communicated with the main combustion chamber 5 formed in the cylinder 1B through a nozzle hole H provided at an eccentric position of the main combustion chamber 5. The nozzle hole H is composed of this main nozzle hole 9 and a pair of auxiliary nozzle holes 15, 15 arranged on the left and right respectively at a distance upstream of the main nozzle hole 9 in the flow direction Q (hole center 9P direction) of the combustion flow.

[0019] The main nozzle hole 9 is formed as an inclined hole [see also Figure 2(A)] having a hole center 9P inclined at an inclination angle θ with respect to the bottom surface 2a of the cylinder head (horizontal line in this embodiment) in a substantially tangential direction of the wall surface (inner peripheral surface) w of the sub-chamber 6 and facing the central part (piston axis 8P) of the main combustion chamber 5. The injector 3 is inclined so that the injected fuel from the tip injection part 3a faces the nozzle hole 9. In Figure 2(A), the gasket 11 (see Figure 1) is omitted from the illustration.

[0020] As shown in FIGS. 1 and 2(A), an auxiliary chamber forming hole 2A that opens into the cylinder 1B is formed at a position eccentric from the axis 8P of the piston 8 toward the cylinder peripheral wall side in the cylinder head 2, and a base (chamber) 7 for forming the auxiliary chamber is accommodated in the auxiliary chamber forming hole 2A. The auxiliary chamber forming hole 2A is composed of, in order from the bottom surface 2a of the cylinder head 2 facing the main combustion chamber 5 of the cylinder head, a large-diameter opening 12, a small-diameter body accommodating portion 13, and a cavity portion 14 located deeper than the body accommodating portion 13.

[0021] The bottom 7A of the base 7 formed in a cup shape is accommodated in the opening 12. The body accommodating portion 13 is a location where the body 7B of the base 7 is accommodated and has a smaller diameter than the opening 12. The cavity portion 14 is formed in a substantially hemispherical concave portion slightly larger than a hemisphere and is configured to be connected to the body accommodating portion 13 by a stepped surface (symbol omitted). The auxiliary chamber 6 is arranged with respect to the cylinder 1B such that its center line (not shown) extending in the vertical direction is slightly closer to the piston axis 8P than the outer peripheral end of the piston 8.

[0022] As shown in FIGS. 1 and 2(A), the base 7 is formed of a stepped cylindrical fitting including a cylindrical body 7B and a bottom 7A. The bottom 7A is a flange-shaped portion that projects in the circumferential direction with a larger diameter than the outer diameter of the body 7B at one end side of the body 7B and has a flat bottom surface 7a. At the other end side of the body 7B, a substantially hemispherical auxiliary chamber forming concave portion 7C slightly smaller than a hemisphere is formed from the upper end surface of the body 7B.

[0023] The spherical (oval, egg-shaped) auxiliary chamber 6 is composed of the cavity portion 14 and the auxiliary chamber forming concave portion 7C, and the main injection hole 9 is formed from the bottom 7A to the body 7B as a portion that connects the auxiliary chamber forming concave portion 7C and the main combustion chamber 5. That is, in the base 7 fitted in the auxiliary chamber forming hole 2A in a state adjacent to the main combustion chamber 5 in the cylinder head 2, a body 7B in which an auxiliary chamber forming concave portion 7C for forming the auxiliary chamber 6 is formed and an injection hole 9 are formed.

[0024] As shown in Figures 1 and 2(A) and (B), the main nozzle 9 is formed as a three-lobed shape (an example of a compound leaf shape) consisting of a main nozzle 9A and a pair of secondary nozzles 9B, 9B located on either side of the main nozzle 9A. In other words, the main nozzle 9 is formed as a fan shape with a smoothly divided tip and a rounded base (the three-lobed shape of the main nozzle 9 has a heart-shaped bulge, and another bulge is provided in the center of the tip, with a total of three bulges), but it is not limited to this. A pair of auxiliary nozzles 15, 15 are provided on the left and right sides, slightly separated from the main nozzle 9 in the direction of the combustion flow.

[0025] Figure 2(B) shows the piston 8 in plan view and the nozzle 7 in bottom view, placed side by side in the combustion flow direction Q (direction of the nozzle center 9P). With respect to the nozzle center 9P, which is the nozzle axis, the piston 8 and the nozzle 7 are in a corresponding positional relationship. Each auxiliary nozzle 15 is formed in a small-diameter vertical hole along the piston axis 8P, and a pair of auxiliary nozzles 15, 15 are in a symmetrical positional relationship with respect to the nozzle center 9P. The combustion flow direction Q [see Figure 2(A)], which changes direction from the main nozzle 9 and flows into the main combustion chamber 5, is in the same direction as the direction of the nozzle center 9P [see Figure 2(B)] in plan view.

[0026] As shown in Figure 2(B), the main nozzle 9 opening at the bottom surface 7a of the nozzle 7 is formed in a horizontally elongated shape where the width a (the length in the left-right direction relative to the combustion flow direction Q) is greater than the length b (the length in the front-to-back direction of the combustion flow Q, which is the length along the nozzle center 9P) (a > b). In other words, the length (left-to-right length a) in the direction of alignment between the main nozzle 9A and the pair of sub-nozzles 9B, 9B is set to be longer than the total length of the main nozzle 9 (length in the direction of the nozzle center 9P: front-to-back length b).

[0027] As shown in Figures 1 and 2(A) and (B), a receiving recess R is formed in the ceiling wall 8A of the piston 8 where the combustion flow ejected from the main injection hole 9 into the main combustion chamber 5 is blown, and an intake valve recess 16 and an exhaust valve recess 17 are also formed. In Figure 1, 18 is a shaft hole through which the shaft of the intake valve (not shown) passes, 18A is the valve seat, and 19 is a sealing material. In addition, the inclination angle θ of the main injection hole 9 is depicted as 45 degrees in Figures 1 and 2, but it may be any other angle, or in a range such as 40 to 50 degrees.

[0028] As shown in Figure 2(B), the receiving recess R is formed such that the upstream recess base end 20 in the combustion flow direction Q is located in a position corresponding to the pair of auxiliary injection holes 15, 15, Viewed in a direction along the axis 8P of the piston 8. The shape of the receiving recess R in plan view is such that the downstream side in the combustion flow direction Q is Left and right The shape is set to widen towards the end, increasing in width. Specifically, the shape of the receiving recess R in plan view corresponds to each of the auxiliary injection holes 15, 15. The position, that is, the position of the auxiliary injection holes 15, 15 facing the jet outlets 15a, 15a on the main combustion chamber 5 side. The shape is set to a sector with the starting point as the combustion flow direction Q, and the width increases towards the downstream side.

[0029] The receiving recess R, which exhibits a fan shape in plan view, has a narrow base edge 20A, an arc-shaped outer edge 22, one side (left side) edge 24, and the other side (right side) edge 25. The majority of the tip end of the one side edge 24 is absorbed into the exhaust valve recess 17 due to the depth relationship, and the tip end of the other side edge 25 and the portion of the outer edge 22 on the other side edge 25 are absorbed into the intake valve recess 16 due to the depth relationship [see Figure 2(B)].

[0030] As shown in Figure 2(A), the receiving recess R is formed as a recess of non-uniform depth, having a bottom surface that is concave downwards with a smooth curve (or small curvature) in a side view, or a straight bottom surface (notation omitted), such that the depth is deepest at the base end 20 of the recess and decreases as it moves downstream in the combustion flow direction Q. The depth of the base end 20 of the recess increases smoothly and abruptly from its base edge 20A, and quickly reaches its maximum depth, for example, directly below the auxiliary nozzle 15. Furthermore, the base edge 20A is defined to have a relatively wide width (left-right length) so that the lower end openings (notation omitted) of the pair of auxiliary nozzles 15, 15 are located within the receiving recess R.

[0031] As shown in Figure 2(B), the outer circumference of the exhaust valve recess 17 overlaps the intermediate portion of the receiving recess R in the combustion flow direction Q, and the outer circumference of the intake valve recess 16 overlaps the downstream portion of the receiving recess R in the combustion flow direction Q. The depths of the intake valve recess 16 and exhaust valve recess 17 are slightly deeper than the depth of the receiving recess R at the overlapping portion, but this is not limited to this. Note that in Figure 2(B), the positions of the auxiliary injection holes 15, 15 in a plan view are intentionally shown with solid lines on the ceiling wall 8A for the purpose of understanding the drawing.

[0032] Conventional fan-shaped receiving recesses 23, as shown by the dashed lines (imaginary lines, dotted lines) in Figure 2(B), are fan-shaped with a narrow starting width and a pointed base, and the width of the starting end 23a (for easier understanding in the drawing, the edge line of the starting end 23a is also shown as a solid line in Figure 1) is extremely narrow, and the starting end position in the combustion flow direction Q corresponds to the main injection hole 9. In other words, the receiving recess R according to the present invention greatly enlarges the width of the starting end 23a of the conventional fan-shaped receiving recess 23, and clearly shifts the starting end position to the upstream side in the combustion flow direction Q.

[0033] Here, regarding the aspect ratio of the main nozzle 9, the range of the length ratio between the left-right length a and the front-to-back length b of the main nozzle 9 is 1.3b ≤ a ≤ 1.6b, and preferably set to 1.4b ≤ a ≤ 1.5b. In Figure 2(B), a is depicted as approximately 1.46b. Furthermore, the aspect ratio between the width of the recess base end 20 (notation omitted) and the left-right length a of the main nozzle 9 is arbitrary. In addition, a very shallow auxiliary recess 21 may be provided in the shape of an arc centered near the position of the recess base end 20 on the ceiling wall 8A (the position of the upstream end in the combustion flow direction Q) to correspond to the pair of auxiliary nozzles 15, 15. Figure 2(B) shows a rear-expanding auxiliary recess 21 on the ceiling wall 8A of the piston 8, which gradually widens in the left-right direction from the base end 20 of the receiving recess R to the peripheral edge of the piston 8.

[0034] The base end 20 of the receiving recess R, which is formed in a fan shape that widens towards the end when viewed from above, is located at a position corresponding to the auxiliary injection holes 15, 15. This makes it easier for the combustion gas (combustion flow) in the sub-chamber 6 to flow into the main combustion chamber 5. In other words, the unburned gas ejected from the auxiliary injection holes 15, 15 is mixed with the air in the receiving recess R, promoting combustion. This quickly directs the high-temperature combustion gas to the main combustion chamber 5, resulting in reduced smoke and improved combustion (improved fuel efficiency). Therefore, a sub-chamber diesel engine that can achieve various effects such as reduced smoke and improved fuel efficiency has been realized.

[0035] Conventionally, there have been designs that have auxiliary nozzles as injection holes, but in those cases, the combustion flow coming out of the auxiliary nozzles hit the ceiling wall 8A of the piston 8. However, in the present invention, the recess base end 20 is enlarged upstream in the combustion flow direction Q, which has the advantage that the combustion flow coming out of the auxiliary nozzles 15, 15 flows smoothly along the recess base end 20 inside the main combustion chamber 5.

[0036] [Another embodiment] The shape of the main nozzle 9 can be changed in various ways, such as a single nozzle exhibiting an elliptical shape or a bilobed shape (compound leaf shape) such as a heart shape. Furthermore, the placement and number of auxiliary nozzles 15 can be other than those shown in Figure 2, etc. [Explanation of Symbols]

[0037] 5. Main combustion chamber 6 Antechamber 8 pistons 8A Ceiling and Wall 9 nozzle holes 9A Main nozzle hole 9B Sub-nozzle hole 15 Auxiliary nozzles 16 Intake valve recess 17 Exhaust valve recess 20 Recess base end (upstream side in the combustion flow direction of the receiving recess) H Nozzle hole Q: Direction of combustion flow R receiving recess

Claims

1. A main combustion chamber and a sub-chamber located eccentrically from the main combustion chamber are connected via injection holes, and a receiving recess is formed in the ceiling wall of the piston where the combustion flow ejected from the injection holes into the main combustion chamber is blown. The nozzle comprises a main nozzle and a pair of auxiliary nozzles, each positioned on the left and right sides, separated from the main nozzle in the flow direction of the combustion flow. The receiving recess is formed such that the base end of the recess on the upstream side in the direction of the combustion flow is at a position corresponding to the auxiliary injection hole, and the shape of the receiving recess in a plan view along the axis of the piston is set to a flared shape in which the width in the left-right direction increases towards the downstream side in the direction of the combustion flow. The shape of the receiving recess in plan view is set to be a fan shape, starting from a position opposite the jet outlet on the main combustion chamber side of the auxiliary injection hole, with the width increasing towards the downstream side in the direction of the combustion flow in a sub-chamber type diesel engine.

2. The pre-chamber type diesel engine according to claim 1, wherein the ceiling wall of the piston is provided with a rear-expanding auxiliary recess that gradually widens in the left-right direction from the base end of the receiving recess to the peripheral edge of the piston.

3. The pre-chamber type diesel engine according to claim 1, wherein an intake valve recess and / or exhaust valve recess are formed in the ceiling wall of the piston, and the receiving recess and the intake valve recess and / or exhaust valve recess overlap.

4. The auxiliary injection hole is formed as a vertical hole along the piston movement direction, as described in any one of claims 1 to 3, for the pre-chamber type diesel engine.

5. The aforementioned injection hole is formed as an inclined hole extending from the sub-chamber toward the central part of the main combustion chamber, as described in claim 4 of the sub-chamber type diesel engine.

6. The pre-chamber diesel engine according to claim 5, wherein the main nozzle is formed in a bifurcated shape, comprising a main nozzle and a pair of sub-nozzles arranged on either side of the main nozzle.

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