JP-7857213-B2 - Pre-chamber diesel engine

Inventors

• 末廣 貴一
• 小林 泰
• 天呑 将成
• 高▲崎▼ 慧斗

Assignees

• 株式会社クボタ

Dates

Publication Date

20260512

Application Date

20221223

Claims (8)

1. A main combustion chamber and a sub-chamber located eccentrically from the main combustion chamber are connected via injection holes, and receiving recesses are 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 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 location is set to at least twice the depth of the other locations.
4. The sub-chamber diesel engine according to claim 3, wherein the portion of the nozzle-corresponding location in the other location 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 bifurcated shape, comprising a main nozzle and a pair of secondary nozzles positioned on either side of the main nozzle.
7. A sub-chamber diesel engine according to claim 1 or 2, comprising a pair of auxiliary injection holes between the main combustion chamber and the sub-chamber, wherein the pair of auxiliary injection holes are arranged on the left and right lateral sides, separated upstream of the injection holes in the direction of combustion flow, and the injection outlets of the pair of auxiliary injection holes on the main combustion chamber side face the auxiliary recess.
8. The pair of auxiliary nozzles are formed as small-diameter vertical holes along the piston axis of the pre-chamber diesel engine according to claim 7.

Description

This invention relates to a diesel engine having a structure in which a sub-chamber is provided in the main combustion chamber via injection holes, that is, a sub-chamber type diesel engine. In a direct injection (IDI) diesel engine, which has a secondary combustion chamber in addition to the main combustion chamber, fuel is injected into the secondary chamber for ignition, and the combustion gases from the secondary chamber are ejected into the main chamber through nozzles (throttles) to complete combustion. Direct injection (DI) diesel engines have the advantage of overcoming the weaknesses of IDI, such as a large combustion chamber surface area resulting in high throttling and heat losses, and have become widely used in recent years. The pre-chamber (IDI) system injects fuel within a limited pre-chamber, allowing for higher flame velocity and reliable ignition even with low-pressure injectors. Furthermore, because the pre-chamber has less air and lower combustion pressure and temperature, it is less prone to diesel knock and produces less NOx compared to direct injection (DI) systems. Therefore, the pre-chamber system is well-suited to relatively low-speed engines and remains an important power source in agricultural machinery, construction equipment, generators, and various industrial equipment for developing countries. In pre-chamber diesel engines, it is considered crucial to strengthen the vortex in the pre-chamber, which effectively becomes 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 enables improved starting performance without weakening the vortex, while Patent Document 2 discloses a technology that improves combustion efficiency through structural improvements to recesses provided in the piston ceiling wall. However, due to technological advancements and environmental factors, there is a growing demand for further improvements in fuel efficiency and smoke reduction, even in sub-chamber type systems. Japanese Patent Publication No. 2010-180744Japanese Patent Application Publication No. 7-279671 A longitudinal cross-sectional view of the main part showing the combustion chamber of a pre-chamber diesel engine.(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).A further enlarged view showing the shape of the starting end of the receiving recess, where (A) is this embodiment and (B) is another embodiment. Below, an embodiment of the pre-chamber diesel engine according to the present invention will be described with reference to the drawings, focusing on an industrial diesel engine applicable to agricultural tractors and the like. Figure 1 is a cross-sectional view of the cylinder head, including the injector and glow plug, cut by a line (plane) inclined approximately 25 degrees with respect to its longitudinal direction (cylinder in-line direction). Figure 1 shows a cross-sectional view of the area around the sub-chamber of a swirl-type industrial diesel engine, an example of a sub-chamber diesel engine. 1 is the cylinder block, 2 is the cylinder head, 3 is the injector, 4 is the glow plug, 5 is the main combustion chamber, 6 is the sub-chamber, 7 is the nozzle for forming the sub-chamber, 8 is the piston, 8P is the piston center, 9 is the injection hole formed in nozzle 7, and 10 is the water jacket (cooling water passage in cylinder head 2). The cylinder block 1 has a cylinder barrel (cylinder wall) 1A that forms the cylinder (cylinder bore) 1B, and a piston 8 is fitted inside the cylinder 1B. A gasket 11 is sandwiched (interposed) between the upper surface (notation omitted) of the cylinder block 1 and the bottom surface 2a of the cylinder head 2. At the top dead center of the compression stroke of the piston 8 (approximately the state shown in Figure 1), the volume of the main combustion chamber 5 approaches 0 (zero), and the sub-chamber 6 effectively becomes the combustion chamber. The cylinder head 2 is equipped with an injector 3, and the tip of the injector 3, the injection portion 3a, is positioned to face the upper part of the sub-chamber 6. The sub-chamber 6 is connected to the main combustion chamber 5 formed within the cylinder 1B via an injection hole 9 located at an eccentric position within the main combustion chamber 5. Note that the gasket 11 (see Figure 1) is omitted from the illustration in Figure 2(A). As shown in Figures 1 and 2(A), the injection hole 9 is formed as an inclined hole with a hole center 9P that is inclined at an angle θ with respect to the cylinder head bottom surface 2a (horizontal line in this embodiment), and is approximately tangential to the wall surface (inner circumferential surface) w of the sub-chamber 6 and toward the center of the main combustion chamber 5 (piston axis 8P). The injector 3 is inclined so