Pre-chamber diesel engine

Abstract

To provide a further improved indirect injection (IDI) diesel engine by improving a combustion state by increasing a combustion speed and the like so as to improve fuel consumption and smoke, as a result of earnest studies focused on a relationship between an injection hole and a recess.SOLUTION: 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 9, and a receiving recess R is formed at a place of a ceiling wall 8A of a piston 8 to which a combustion flow injected from the injection hole 9 to the main combustion chamber 5 is blown. A position of a recess starting end 20A as a most upstream side in a flowing direction Q of the combustion flow, of the receiving recess R is closer to an upstream side in the flowing direction Q of the combustion flow, than a position of an injection hole outlet starting end 9a as a most upstream side in the flowing direction Q of the combustion flow at a main combustion chamber-side opening of the injection hole 9, and a front part d as an upstream side in the flowing direction Q of the combustion flow, of the auxiliary chamber 6 is recessed to a side where a volume of the auxiliary chamber 6 increases.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a diesel engine having a structure in which an auxiliary combustion chamber is provided which is connected to a main combustion chamber via a nozzle hole, i.e., a diesel engine with an auxiliary combustion chamber. [Background technology]

[0002] Indirect injection (IDI) diesel engines have a pre-combustion chamber in addition to the main combustion chamber, and fuel is injected into the pre-combustion chamber to ignite it, and the combustion gas in the pre-combustion chamber is ejected into the main chamber through a nozzle hole (throttle), completing the combustion. Direct injection (DI) diesel engines have the advantage of being able to overcome the weakness of IDI, which is that the combustion chamber surface area is large, resulting in large throttling losses and heat losses, and have been widely used in recent years.

[0003] The IDI (Indirect Injection) system injects fuel into a limited area within the pre-chamber, which allows for a high flame velocity and ensures reliable ignition even with a low-pressure injector. Furthermore, because the amount of air in the pre-chamber is small and the combustion pressure and temperature are low, it has the advantage of being less susceptible to diesel knock and producing less NOx than the direct injection (DI) system. Therefore, the IDI system is suitable for relatively low-speed engines, and remains an important power source for agricultural and construction machinery, generators, and various industrial equipment for developing countries.

[0004] In a pre-chamber diesel engine, it is considered important to strengthen the swirl in the pre-chamber, which essentially serves as 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 swirl, and Patent Document 2 discloses a technology that improves combustion efficiency by devising the structure of a recess provided in the ceiling wall of the piston.

[0005] However, due to technological advances and environmental factors, there is a demand for further improvements in fuel economy and smoke reduction even in pre-chamber engines. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-180744 [Patent Document 2] Japanese Patent Application Publication No. 7-279671 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide an improved indirect combustion chamber (IDI) diesel engine that improves the combustion state by increasing the combustion speed, thereby enabling improvements in fuel economy and smoke, through further intensive research focusing on the relationship between the injection hole and the recess. [Means for solving the problem]

[0009] The present invention provides In a pre-chamber diesel engine, The main combustion chamber and an auxiliary chamber provided at a location eccentric to the main combustion chamber are communicated through a nozzle hole, and a receiving recess is formed in the top wall of the piston at a location 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 located on the most upstream side in the flow direction of the combustion flow, is shifted upstream in the flow direction of the combustion flow relative to a position of an injection hole outlet start end of the main combustion chamber side opening of the injection hole, which is located on the most upstream side in the flow direction of the combustion flow; The depth of the nozzle hole corresponding portion of the receiving recess corresponding to the nozzle hole is deeper than the depth of the other portion of the receiving recess other than the nozzle hole corresponding portion.

[0010] Regarding the present invention, the characteristic configurations and means other than the above-mentioned configurations (means) are as defined in the claims. Claims 2 to 6 Please refer to. [Effects of the Invention]

[0014] According to the present invention, The position of the recess start is offset upstream from the position of the nozzle outlet start in the 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 (ceiling wall).

[0015] Furthermore, since the depth of the portion corresponding to the injection hole is formed deeper than the depth of other portions of the receiving recess, the flow of compressed air from the main combustion chamber through the injection hole to the auxiliary combustion chamber as the piston moves upward during the compression stroke is promoted smoothly and efficiently.

[0016] As a result, the combination of a configuration that deepens the depth of the nozzle corresponding area and the offset structure at the start of the recess allows for the provision of a pre-chamber diesel engine that can quickly urge high-temperature combustion gas into the main combustion chamber, thereby achieving various effects such as reduced smoke and improved fuel efficiency. [Brief explanation of the drawings]

[0017] [Figure 1] A longitudinal cross-sectional view of the main part of a pre-chamber diesel engine showing the combustion chamber. [Figure 2] (A) is an enlarged cross-sectional view showing the vicinity of the nozzle hole in FIG. 1 in a reference embodiment of the present invention, and (B) is a development view showing the relationship between the piston (ceiling wall) and the nozzle (nozzle hole). [Figure 3] FIG. 10 is an enlarged cross-sectional view of the vicinity of the nozzle hole including the receiving recess in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following is a description of the pre-chamber diesel engine according to the present invention. Embodiments and Reference Embodiments This will be explained with reference to the drawings for an industrial diesel engine used in agricultural tractors, etc. Figure 1 corresponds to a cross-sectional view of a cylinder head including an injector and a glow plug, cut along a line (plane) inclined at about 25 degrees to its longitudinal direction (direction of the cylinders in line).

[0019] Figure 1 shows a cross-sectional view of the area surrounding the pre-chamber of a vortex-type industrial diesel engine, which is an example of a pre-chamber diesel engine. Reference numeral 1 denotes the cylinder block, 2 denotes the cylinder head, 3 denotes the injector, 4 denotes the glow plug, 5 denotes the main combustion chamber (main chamber), 6 denotes the pre-chamber (pre-combustion chamber), 7 denotes the nozzle that forms the pre-chamber, 8 denotes the piston, 8P denotes the center of the piston, 9 denotes the nozzle formed in the nozzle 7, and 10 denotes the water jacket (the cooling water passage of the cylinder head 2).

[0020] 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 FIG. 1), the volume of the main combustion chamber 5 approaches 0 (zero), and the auxiliary combustion chamber 6 essentially becomes the combustion chamber.

[0021] The cylinder head 2 is equipped with an injector 3, and the tip injection portion 3a of the injector 3 is positioned so as to face the upper part of the auxiliary combustion chamber 6. The auxiliary combustion chamber 6 is connected to the main combustion chamber 5 formed in the cylinder 1B via a nozzle hole 9 provided at an eccentric position of the main combustion chamber 5. Note that in Figure 2(A) the gasket 11 (see Figure 1) is not shown.

[0022] 1 and 2(A), the injection hole 9 is formed as an inclined hole having a hole center 9P that is inclined at an inclination angle θ with respect to the cylinder head bottom surface 2a (horizontal in this embodiment) in a direction approximately tangential to the wall surface (inner peripheral surface) w of the auxiliary combustion chamber 6 and toward the center (piston axis 8P) of the main combustion chamber 5. The injector 3 is disposed at an angle so that the injected fuel from the tip injection portion 3a is directed toward the injection hole 9.

[0023] An auxiliary chamber forming hole 2A that opens into the cylinder 1B is formed in the cylinder head 2 at a position eccentric to the cylinder peripheral wall from the axis 8P of the piston 8, 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 upward, a large-diameter opening 12, a small-diameter body portion accommodating portion 13, and a hollow portion 14 located deeper than the body portion accommodating portion 13.

[0024] The opening 12 accommodates the cup-shaped bottom 7A of the nozzle 7. 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, approximately hemispherical shape that is slightly larger than a hemisphere, and is connected to the body accommodating section 13 by a stepped surface (not shown). The sub-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 edge of the piston 8.

[0025] 1 and 2(A), the nozzle 7 is formed of a stepped cylindrical metal fitting including a cylindrical body portion 7B and a bottom portion 7A. The bottom portion 7A is formed at one end of the body portion 7B as a flange-like portion that protrudes circumferentially with a diameter larger than the outer diameter of the body portion 7B and has a flat bottom surface 7a. At the other end of the body portion 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 portion 7B.

[0026] The spherical (oval or cocoon-shaped) auxiliary chamber 6 is made up of a hollow portion 14 and an auxiliary chamber-forming recess 7C, and the injection hole 9 is formed from the bottom portion 7A to the body portion 7B as a portion 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 portion 7B, in which the auxiliary chamber-forming recess 7C for forming the auxiliary chamber 6 is formed, and the injection hole 9.

[0027] 1 to 2(A) and 2(B), the nozzle hole 9 is formed in a trefoil shape (an example of a bilobe shape) consisting of a main nozzle hole 9A and a pair of auxiliary nozzle holes 9B, 9B located on either side of the main nozzle hole 9A. That is, the nozzle hole 9 has a tip that is smoothly divided into three parts and a rounded base end, forming a fan-shaped nozzle hole 9 (the trefoil shape of the nozzle hole 9 has a heart-shaped bulge with another outward bulge in the center of the tip, resulting in 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 upstream of the nozzle hole 9 in the flow direction of the combustion flow.

[0028] 2(B) shows the piston 8 in a plan view and the nozzle 7 in a bottom view, side by side in the combustion flow direction Q (toward the hole center 9P), with the piston 8 and nozzle 7 positioned to correspond to each other on the left and right of the hole center 9P, which is the injection hole axis. For example, the auxiliary injection hole 15 is formed as a small, vertical hole aligned with the piston axis 8P, and the pair of auxiliary injection holes 15, 15 are positioned symmetrically with respect to the hole center 9P. Note that the flow direction Q of the combustion flow that changes direction from the injection hole 9 and flows into the main combustion chamber 5 [see FIG. 2(A)] is the same as the direction of the hole center 9P [see FIG. 2(B)] in a plan view.

[0029] 2(B), the nozzle hole 9 opening to 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 overall length of the nozzle hole 9 (main nozzle hole 9A) (length in the direction of the hole center 9P: front-to-back length b).

[0030] 1 and 2(A), a receiving recess R is formed in the top wall 8A of the piston 8 at a location 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 FIG. 1, reference numeral 18 denotes a shaft hole through which the shaft of the intake valve (not shown) passes, 18A denotes a valve seat, and 19 denotes a seal material. Furthermore, although the inclination angle θ of the nozzle hole 9 is depicted as 45 degrees in FIGS. 1 and 2, it may be any other angle or may be in the range of 40 to 50 degrees.

[0031] 2(A) and 2(B), the receiving recess R has a planar shape (as viewed in the direction of the piston axis 8P) that widens toward the downstream side in the combustion flow direction Q. Specifically, the receiving recess R is set to have a sector shape that starts at a position corresponding to the injection hole 9 and widens toward the downstream side in the combustion flow direction Q. Note that the shape of the receiving recess R may be trapezoidal, rectangular, or any other shape other than a sector.

[0032] 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 part of the outer peripheral edge 22 closer to the other side edge 25 are absorbed into the intake valve recess 16 due to the depth relationship (see FIG. 2(B)), but this is not limited to this.

[0033] 2(B), the range of the aspect ratio of the injection hole 9, that is, the 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 (shown as a = approximately 1.46b). Also, a very shallow auxiliary recess 21 may be provided in the ceiling wall 8A in the shape of a circular arc centered near the position of the recess start end 20 (the most upstream end position in the flow direction Q of the combustion flow) so as to correspond to the pair of auxiliary injection holes 15, 15.

[0034] 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 combustion flow direction Q, and the depth becomes shallower toward the downstream side in the combustion flow direction Q. The position of the recess start end 20A, which is the most upstream side in the combustion flow direction Q of the receiving recess R, is positioned more upstream in the combustion flow direction Q than the position of the nozzle hole outlet start end 9a, which is the most upstream side in the combustion flow direction Q of the main combustion chamber side opening (notation omitted) of the nozzle hole 9.

[0035] That is, as shown in Figure 2(A), the position of the recess start point 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 point 9a (see also Figure 3). The offset amount e is preferably 10 to 20% of the length b of the nozzle hole 9 in the flow direction of the combustion flow (0.1b ≦ e ≦ 0.2b), but is not limited to this.

[0036] As shown in Figure 2(A), In a reference embodiment of the present invention, The front portion d, which is upstream of the injection hole 9 in the flow direction Q of the combustion flow in the pre-chamber 6, is recessed on the side where the volume of the pre-chamber 6 increases. 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 pre-chamber forming recess 7C of the nozzle 7, so that the pre-chamber 6 bulges outward. The shape of the front portion d can be any shape, such as a curved recess with a relatively pointed tip as shown in the figure, or a spherical recess (not shown).

[0037] The starting position of the receiving recess R is offset by a small amount (length e) from the starting position of the nozzle hole 9 on the bottom surface 7a of the nozzle 7 (the position of the recess starting end 20A is shifted upstream from the position of the nozzle hole outlet starting 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 starting end 20 without the risk of hitting the piston ceiling wall 8A.

[0038] Furthermore, the provision of the front area d, which is formed by outwardly bulging the pre-chamber-forming recess 7C upstream in the flow direction Q of the combustion flow from the injection hole 9, provides the following advantageous effects: When compressed air flows from the main combustion chamber 5 through the injection hole 9 into the pre-chamber 6 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 flow of compressed air, is formed in the pre-chamber 6 at the edge (corner) formed by the lower end of the front area d and the injection hole 9, as shown in Figure 2(A). The rotation direction of the reverse vortex u is opposite to that of the normal vortex U.

[0039] As a result, the combustion in the pre-combustion chamber 6 is further promoted by the synergistic action of the normal vortex U and reverse vortex u (see Figure 2(A)) caused by the compressed air flowing from the main combustion chamber 5 to the pre-combustion chamber 6 during the compression stroke, and combined with the aforementioned ``offset structure of the recess start end 20A'', the high-temperature combustion gas can be quickly urged into the main combustion chamber 5, resulting in a pre-combustion chamber diesel engine that can achieve various effects such as reduced smoke and improved fuel efficiency.

[0040] As shown in Figure 3, In an embodiment of the present invention, A pre-chamber diesel engine having a configuration in which the depth h of the nozzle hole corresponding portion f corresponding to the nozzle hole 9 of the receiving recess R is deeper than the depth s of the portion t other than the nozzle hole corresponding portion f in the receiving recess R (h>s). is used. The nozzle hole corresponding portion f is smoothly recessed in a spherical, arc-shaped, or cone-shaped cross section taken vertically along the flow direction Q of the combustion flow. "Other portions t" refer to portions other than the nozzle hole corresponding portion f in the receiving recess R. In addition, the recess start end 20 and the nozzle hole corresponding portion f may be equal or different.

[0041] As shown in Fig. 3, the receiving recess R is formed so that the depth h of the injection 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 injection hole corresponding portion f to at least twice the depth s of the other portions t (h ≥ 2s). Furthermore, the receiving recess R (its bottom surface) smoothly connects the other portions t and the injection hole corresponding portion f in the flow direction Q of the combustion flow.

[0042] Figure 3 depicts the depth of the receiving recess as uniform. In the case of a non-uniform depth (refer to the receiving recess R in Figure 1), it is convenient to apply a depth that is more than twice the maximum depth as h at the hole corresponding portion f. In addition, even in the configuration shown in Figure 3, similar to the case shown in Figure 2(A), the starting position of the receiving recess R is offset by a certain amount (length e) from the starting position of the injection hole 9 on the bottom surface 7a of the base 7.

[0043] Embodiments of the present invention In the pre-chamber type diesel engine according to, since the depth h of the hole corresponding portion f is formed deeper than the depth s of other portions t, the flow of compressed air from the main combustion chamber 5 into the pre-chamber 6 through the injection hole 9 along with the upward movement of the piston 8 during the compression stroke is smoothly and efficiently promoted. Therefore, combined with the above-mentioned "offset structure of the recess start end 20A", high-temperature combustion gas can be quickly promoted into the main combustion chamber 5, and various effects such as smoke reduction and fuel consumption improvement can be achieved.

[0044] [Variations] The offset amount e that moves the position of the recess start end 20A upstream from the position of the injection hole outlet 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 = the distance between the outer peripheral end of the ceiling wall 8A and 9a) of the length b of the injection hole 9 in the flow direction of the combustion flow. Also, the recess start end 20A may be within the range (0.1b ≤ e ≤ x) of the distance x (not shown in the figure) from the injection hole outlet start end 9a to the auxiliary injection hole 15. The distance x can be considered up to the center of the auxiliary injection hole 15 or the outer peripheral edge of the hole on the near and far sides.

[0045] In the reference form shown in FIG. 2(A) The amount of depression (length) and the depression area from the recess 7C for forming the pre-chamber at the front portion d can be set with various changes. The shape of the injection hole 9 may be a vertically long shape, a two-lobed shape, etc., other than a three-lobed or horizontally long shape.

Explanation of Reference Numerals

[0046] 5 Main combustion chamber 6 Pre-chamber 8 pistons 8A Ceiling wall 9 nozzle holes 9A Main nozzle hole 9B Sub-nozzle hole 9a Starting point of nozzle hole outlet 20A Recess start Q Flow direction of combustion flow R Receiving recess d Preamble f Injection hole corresponding part h Depth (corresponding to nozzle hole) s Depth (other areas) t Other parts

Claims

1. The main combustion chamber and an auxiliary chamber provided at a location eccentric to the main combustion chamber are communicated through a nozzle hole, and a receiving recess is formed in the top wall of the piston at a location 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 located on the most upstream side in the flow direction of the combustion flow, is positioned more upstream in the flow direction of the combustion flow than a position of an injection hole outlet start end of the main combustion chamber side opening of the injection hole, which is located on the most upstream side in the flow direction of the combustion flow; A diesel engine with a pre-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.

2. 2. The diesel engine of claim 1, wherein the nozzle hole corresponding portion is recessed in a spherical or arc shape in a cross section taken vertically along the flow direction of the combustion flow.

3. 2. The diesel engine of claim 1, wherein the position of the recess start end is shifted from the position of the nozzle hole outlet start end by 10 to 20% of the length of the nozzle hole in the flow direction of the combustion flow.

4. 3. The diesel engine of claim 2, wherein the position of the recess start end is shifted from the position of the nozzle hole outlet start end by 10 to 20% of the length of the nozzle hole in the flow direction of the combustion flow.

5. 5. The diesel engine of claim 1, wherein the injection hole is formed as an inclined hole extending from the auxiliary combustion chamber toward a center of the main combustion chamber.

6. 6. The diesel engine of claim 5, 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.

Images