Pre-chamber diesel engine

Abstract

To provide a further improve indirect injection 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 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 9, and 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 9 to the main combustion chamber 5 is blown. A shape of the receiving recess R in a plane view is set to be a shape widened toward a leading end so that a lateral width is gradually increased toward a downstream side in a flowing direction Q of the combustion flow. The receiving recess R is formed in a manner that a depth h of an injection hole correspondent part f corresponding to the injection hole 9 is deeper than another part t, and the injection hole correspondent part f is recessed into a curved shape.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 continuously with a main combustion chamber through a nozzle hole, that is, an indirect injection (IDI) diesel engine with a sub-chamber.

Background Art

[0002] An indirect injection (IDI) diesel engine provided with a sub-combustion chamber (sub-chamber) in addition to the 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, there is also an advantage that diesel knock is less likely to occur and the amount of NOx generated is small compared to the direct injection (DI) type. 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 vortex in the sub-chamber that substantially serves as the combustion chamber and to increase the flame propagation speed from the sub-chamber to the main combustion chamber. In Patent Document 1, a technique that enables improvement of starting performance without weakening the vortex is disclosed, 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 the present 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] In a pre-chamber type diesel engine, 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 shape of the receiving recess in plan view is set to be a flared shape, with the width increasing towards the downstream side in the direction of the combustion flow. The receiving recess is formed such that the depth of the area corresponding to the injection hole is deeper than the other areas, and the area corresponding to the injection hole is recessed in a curved shape. The ceiling wall of the piston gradually widens from the base end of the receiving recess to the peripheral edge of the piston. Rear-flaring shape It is characterized by having auxiliary recesses.

[0009] In this case, the above Nozzle-compatible locations It is preferable that the surface is concave in a spherical or arc shape when viewed in a cross-sectional view taken vertically along the direction of the combustion flow.

[0010] For features and means other than those described above in relation to the present invention, please refer to claims 3 and onward in the claims. [Effects of the Invention]

[0011] According to the present invention, the depth of the injection hole-corresponding portion of the receiving recess is made deeper than the depth of other portions and is formed in a curved recess, thereby promoting a smooth and efficient flow of compressed air from the main combustion chamber into the sub-chamber through the injection hole as the piston moves upward during the compression stroke.

[0012] In addition, because the shape of the receiving recess is a fan shape in which the width on the downstream side widens with the flow of the combustion flow, just before top dead center, the receiving recess acts as a guide, accelerating the flow velocity of the compressed air, and also promoting the flow of compressed air from the main combustion chamber to the sub-chamber through the nozzles during the compression stroke.

[0013] In other words, by making the receiving recess a fan shape and increasing the depth of the injection hole in a curved manner, the flow rate of compressed air from the main combustion chamber to the sub-chamber is increased, promoting and improving the mixing of fuel and air, and making it possible to obtain various benefits such as reduced smoke, improved fuel efficiency, and reduced NOx.

[0014] 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]

[0015] [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) Development view showing the relationship between the piston (ceiling wall) and the nozzle (nozzle). [Figure 3]A further enlarged view showing the shape of the starting end portion of the receiving recess, where (A) is the present embodiment and (B) is another embodiment

Embodiments for Carrying out the Invention

[0016] Hereinafter, embodiments of a prechamber type diesel engine according to the present invention will be described with reference to the drawings in the case of an industrial diesel engine applied to an agricultural tractor or the like. FIG. 1 corresponds to a cross-sectional view obtained by cutting a cylinder head so as to be inclined by about 25 degrees with respect to its longitudinal direction (cylinder in-line direction) so as to include an injector and a glow plug.

[0017] FIG. 1 shows a cross-sectional view of the periphery of a prechamber of an over-flow type industrial diesel engine, which is an example of a prechamber 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 prechamber (auxiliary combustion chamber), 7 is a base for forming the prechamber, 8 is a piston, 8P is the center of the piston, 9 is an injection hole formed in the base 7, and 10 is a water jacket (cooling water passage of the cylinder head 2).

[0018] The cylinder block 1 has a cylinder barrel (cylinder wall) 1A forming 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 (reference numeral omitted) of the cylinder block 1 and the bottom surface 2a of the cylinder head 2. In addition, at the compression top dead center of the piston 8 (substantially the state shown in FIG. 1), the volume of the main combustion chamber 5 approaches 0 (zero), and substantially the prechamber 6 becomes the combustion chamber.

[0019] The cylinder head 2 is equipped with an injector 3, and the tip injection portion 3a of the injector 3 is arranged so as to face the upper part of the prechamber 6. The prechamber 6 is communicated with the main combustion chamber 5 formed in the cylinder 1B through an injection hole 9 provided at an eccentric portion of the main combustion chamber 5. In addition, in FIG. 2(A), the illustration of the gasket 11 (see FIG. 1) is omitted.

[0020] As shown in FIGS. 1 and 2(A), the injection hole 9 is formed as an inclined hole having a hole center 9P inclined at an inclination angle θ with respect to the bottom surface 2a of the cylinder head (in this embodiment, a horizontal line) in a substantially tangential direction of the wall surface (inner peripheral surface) w of the auxiliary chamber 6 and toward the central portion (piston axis 8P) of the main combustion chamber 5. The injector 3 is inclined so that the injected fuel from the tip injection portion 3a faces the injection hole 9.

[0021] 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 in the cylinder head 2 toward the cylinder peripheral wall side. 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 configured to have, in order from the bottom surface 2a of the cylinder head 2 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 deeper than the body accommodating portion 13.

[0022] The bottom portion 7A of the base 7 formed in a cup shape is accommodated in the opening 12. The body accommodating portion 13 is a portion where the body portion 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 that is slightly larger than a hemisphere and is configured to be connected to the body accommodating portion 13 by a stepped surface (reference numeral 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.

[0023] As shown in FIGS. 1 and 2(A), the base 7 is formed as a stepped cylindrical fitting including a cylindrical body portion 7B and a bottom portion 7A. The bottom portion 7A is a flange-shaped portion that projects in the circumferential direction with a diameter larger than the outer diameter of the body portion 7B at one end side of the body portion 7B and has a flat bottom surface 7a. A substantially hemispherical auxiliary chamber forming concave portion 7C that is slightly smaller than a hemisphere is formed at the other end side of the body portion 7B from the upper end surface of the body portion 7B.

[0024] The spherical (egg-shaped, cocoon-shaped) sub-chamber 6 is composed of a cavity 14 and a recess 7C for forming the sub-chamber, and the injection hole 9 is formed from the bottom 7A to the body 7B as a part that connects the recess 7C for forming the sub-chamber and the main combustion chamber 5. In other words, the nozzle 7 that is fitted into the sub-chamber forming hole 2A adjacent to the main combustion chamber 5 in the cylinder head 2 has a body 7B in which the recess 7C for forming the sub-chamber 6 is formed, and an injection hole 9 is formed therein.

[0025] As shown in Figures 1 and 2(A) and (B), the nozzle 9 is formed in a three-lobe 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 nozzle 9 is formed in a fan shape with a smoothly divided tip and a rounded base (the three-lobe shape of the nozzle 9 has a total of three bulges, with another bulge pointing outwards in the center of the tip of the heart-shaped bulge). Alternatively, a pair of auxiliary nozzles 15, 15 may be provided, positioned slightly apart on the left and right sides upstream of the nozzle 9 in the direction of combustion flow.

[0026] Figure 2(B) shows the piston 8 in a plan view and the nozzle 7 in a bottom view, placed side by side in the combustion flow direction Q (direction of the nozzle center 9P). With respect to the left and right of the nozzle center 9P, which is the nozzle axis, the piston 8 and the nozzle 7 are in a corresponding positional relationship. For example, the auxiliary nozzle 15 is formed in a small-diameter vertical hole along the piston axis 8P, and the 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 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 a plan view.

[0027] As shown in Figure 2(B), the 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 nozzle 9 (the length in the direction of the nozzle center 9P: front-to-back length b) (of the main nozzle 9A).

[0028] As shown in Figures 1 and 2(A), a receiving recess R is formed in the ceiling wall 8A of the piston 8 where the combustion flow ejected from the 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 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.

[0029] As shown in Figures 2(A) and 2(B), the receiving recess R is formed such that the recess initiation end 20, which is the upstream portion in the combustion flow direction Q, is located at a position corresponding to the nozzle 9. Furthermore, as shown in Figure 2(B), the shape of the receiving recess R in plan view (viewed in the direction of the piston axis 8P) is set to a flared shape where the width increases towards the downstream side in the combustion flow direction Q. More specifically, it is set to a fan shape with the starting point at the position corresponding to the nozzle 9 and the width increasing towards the downstream side in the combustion flow direction Q.

[0030] The receiving recess R, which exhibits a fan shape in plan view, has a narrow starting edge (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 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 peripheral 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)], but is not limited to this.

[0031] As shown in Figure 2(B), the aspect ratio of the nozzle 9, where the ratio of the left-right length a to the front-back length b of the nozzle 9 is within the range of 1.3b ≤ a ≤ 1.6b, preferably set to 1.4b ≤ a ≤ 1.5b (shown as a = approximately 1.46b). In addition, a very shallow auxiliary recess 21 may be provided in the shape of an arc centered near the position of the recess start end 20 in the ceiling wall 8A (the upstream end in the combustion flow direction Q) to correspond to a pair of auxiliary nozzles 15, 15.

[0032] The receiving recess R is basically formed as a recess of non-uniform depth with a smooth curved bottom or a straight bottom (notation omitted), as shown in Figure 2(A), where the depth is deepest at the recess initiation point 20 and decreases as it moves downstream in the combustion flow direction Q. Alternatively, although not shown, sub-chamber engines with receiving recesses of uniform depth are also common. The general recess initiation point is denoted by reference numeral 23, and the recess initiation point according to the present invention is denoted by reference numeral 20.

[0033] As shown in Figures 2(A) and 3(A), the receiving recess R according to the present invention is characterized in that the depth h of the nozzle-corresponding location f at the recess initiation end 20, which corresponds to the nozzle 9, is formed to be deeper than the depth s of the other locations t, and the nozzle-corresponding location f is curved and recessed downwards. The nozzle-corresponding location f is smoothly recessed in a spherical, arc-shaped, or mortar-shaped form when viewed in a cross-sectional view cut vertically along the combustion flow direction Q. The "other locations t" refer to locations other than the nozzle-corresponding location f in the fan-shaped receiving recess R, and the relationship between the recess initiation end 20 and the nozzle-corresponding location f can be in various cases, such as "the same," "mostly the same," or "different."

[0034] It is advantageous if the maximum depth hm of the nozzle-corresponding location f (= recess start end 20), shown by the arc of the imaginary line (dotted line) in Figure 3(A), is set to be at least twice the depth s of the other locations t (hm ≥ 2s). Furthermore, the receiving recess R (its bottom surface) is smoothly continuous with the nozzle-corresponding location f in the flow direction Q of the combustion flow at the nozzle-corresponding location f at the other locations t [see Figure 3(A)].

[0035] Since the recess initiation point 20 has a depth h greater than the depth s of the other locations t, and is formed in a curved recessed location f corresponding to the injection hole, the flow of compressed air from the main combustion chamber 5 to the sub-chamber 6 via the injection hole 9 as the piston 8 moves upward during the compression stroke is facilitated smoothly and efficiently. In addition, because the receiving recess R has a fan shape, a nozzle action (the action of accelerating the fluid by a convergent nozzle) is exerted, which also facilitates the flow of compressed air from the main combustion chamber 5 to the sub-chamber 6 via the injection hole 9 during the compression stroke.

[0036] In other words, the nozzle-corresponding portion f in the receiving recess R is made relatively deep to facilitate the flow (introduction) of compressed air from the main combustion chamber 5 to the nozzle 9. This allows the nozzle-corresponding portion f (recess start end 20) to function as a guide for the compressed air flow, resulting in a reduction in the flow coefficient and an increase in flow velocity. As a result, the inflow rate of compressed air from the main combustion chamber 5 to the sub-chamber 6 is increased, promoting and improving the mixing of fuel and air, resulting in a sub-chamber diesel engine that can achieve various effects such as reduced smoke and improved fuel efficiency.

[0037] Furthermore, even when ignition occurs in the sub-chamber 6 and the combustion flow is ejected from the nozzle 9 to the main combustion chamber 5, the receiving recess R with a deep nozzle-compatible location f ensures that the combustion flow spreads smoothly and quickly into the main combustion chamber 5. Therefore, not only is the compressed air flow improved, but the combustion flow is also improved, which in turn contributes to smoke reduction and improved fuel efficiency. [Summary of the Embodiments] In this embodiment, as shown in Figure 2(B), the width of the piston 8 gradually widens from the base end Ra of the receiving recess R to the peripheral edge 8a of the piston 8 on the ceiling wall 8A of the piston 8. Rear-flaring shape An auxiliary recess 21 is provided. Furthermore, as shown in Figures 2(A) and 2(B), this engine is equipped with a pair of auxiliary injection holes 15·15 between the main combustion chamber 5 and the sub-chamber 6. As shown in Figure 2(B), the pair of auxiliary injection holes 15·15 are located on the left and right sides, separated from the injection hole 9, and as is clear from Figures 2(A) and 2(B), the jet outlets 15a of the pair of auxiliary injection holes 15·15 on the main combustion chamber side 5 face the auxiliary recess 21.

[0038] [Another embodiment] As shown in Figure 3(B), the receiving recess R has a basically uniform depth, and the pre-chamber diesel engine may also have a recess starting end 20 of a deeply recessed nozzle-corresponding location f. For example, the nozzle-corresponding location f is formed in a concave spherical shape, and its depth h is deeper than the depth of the nozzle-corresponding location f with a uniform depth shown by the dashed line, i.e., the depth s of the other locations t, and it is even better if it is twice or more in depth. In the case of the receiving recess R with the structure shown in Figure 3(B), the depth h of the nozzle-corresponding location f and the maximum depth hm are the same [see Figure 3(A)].

[0039] [Another example] The shape and depth of the deep recess at the nozzle-compatible area f can be modified in various ways. Furthermore, the width (horizontal length) of the starting edge 20A of the recess starting end 20 may be longer than that shown in Figure 2(B), and the receiving recess R may also be longer. The shape of the nozzle 9 may be a vertically elongated shape, a two-leaf shape, or other shapes besides the horizontally elongated three-leaf shape. [Explanation of Symbols]

[0040] 5. Main combustion chamber 6 Antechamber 8 pistons 8A Ceiling and Wall 9 nozzles 9A Main nozzle hole 9B Sub-nozzle hole Q: Direction of combustion flow R receiving recess f. Nozzle-compatible locations hm Maximum depth h Depth (location of nozzle) s Depth (other locations) t Other parts

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 shape of the receiving recess in plan view is set to be a flared shape, with the width increasing towards the downstream side in the direction of the combustion flow. The receiving recess is formed such that the depth of the area corresponding to the injection hole is deeper than the other areas, and the area corresponding to the injection hole is recessed in a curved shape. A pre-chamber type diesel engine is provided with an auxiliary recess in the ceiling wall of the piston, which has a rearward-expanding shape and gradually widens from the base end of the receiving recess to the peripheral edge of the piston.

2. The pre-chamber type diesel engine according to claim 1, wherein the nozzle-corresponding area is recessed in a spherical or arc shape when viewed in a cross-sectional view taken vertically along the direction of the combustion flow.

3. The pre-chamber type diesel engine according to claim 1 or 2, wherein the maximum depth of the injection port corresponding location is set to twice or more the depth of the other locations.

4. The pre-chamber type diesel engine according to claim 3, wherein the portion of the nozzle-corresponding location in the other location described above that is downstream in the direction of the combustion flow is smoothly continuous with the nozzle-corresponding location.

5. The pre-chamber type diesel engine according to claim 1 or 2, wherein the injection holes are formed as inclined holes extending from the pre-chamber toward the central part of the main combustion chamber.

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

7. A sub-chamber diesel engine according to claim 1 or 2, wherein a pair of auxiliary nozzles are provided between the main combustion chamber and the sub-chamber, the pair of auxiliary nozzles are arranged on the left and right sides, respectively, separated upstream of the nozzles in the direction of combustion flow, and the nozzle outlets of the pair of auxiliary nozzles on the main combustion chamber side face the auxiliary recess.

8. The pre-chamber diesel engine according to claim 7, wherein a pair of auxiliary nozzles are formed as small-diameter vertical holes along the piston axis.

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