Piston combustion chamber suitable for opposed piston two-stroke diesel engine

Abstract

The invention provides a piston combustion chamber suitable for an opposed-piston two-stroke diesel engine, which is characterized in that the combustion chamber structure is a half-rugby-type structure, two opposed notches are formed in the edges of the two sides of a piston, the middle of the half-rugby-type structure is in a concave bowl shape, and the inner wall surface of the half-rugby-type structure is a smooth surface; the two oppositely-arranged notches are correspondingly formed in the central axis of the combustion chamber, the two oil sprayers are oppositely arranged and located at the two oppositely-arranged notches, each oil sprayer is provided with three oil spraying holes, and the oil beam included angle formed by the three oil spraying holes is smaller than the taper angle formed by connecting lines from the top faces of the oil sprayers to the center of the bottom of the boss. According to the two-stroke diesel engine, the good scavenging performance of an original combustion chamber structure can be guaranteed, oil and gas can be rapidly and fully mixed on the basis that materials of the combustion chamber are not changed, the combustion process is improved, and the combustion efficiency is improved.

Description

Technical Field

[0001] This application belongs to the field of engine combustion technology, and in particular relates to a piston combustion chamber suitable for opposed piston two-stroke diesel engines. Background Technology

[0002] Opposed-piston two-stroke (OP2S) diesel engines are characterized by high power density and high indicated thermal efficiency, and are widely used in unmanned aerial vehicles (UAVs), military vehicles, auxiliary power units, and light-duty vehicles. Unlike conventional diesel engines, OP2S engines lack a cylinder head; the combustion space is formed by the tops of the two pistons and the cylinder walls, resulting in a significantly different mixture formation area and shape. Furthermore, due to the absence of a cylinder head, the fuel injectors in OP2S engines must be mounted on the cylinder liners on the cylinder side, with fuel injected from one side into the center of the cylinder. In summary, the differences in combustion space and injector direction mean that OP2S engines cannot directly utilize the piston combustion chamber of conventional four-stroke diesel engines.

[0003] Furthermore, the air exchange time of opposed piston two-stroke diesel engines is only about 1 / 3 of the entire cycle, and the valve overlap angle is relatively large. This makes the airflow movement in the cylinder more complex and more prone to problems such as uneven distribution of the air-fuel mixture in the cylinder. In addition, the combustion and power frequency of the engine doubles in the two-stroke working mode, and the heat released in the cylinder per unit time also increases significantly. If the piston combustion chamber used in traditional four-stroke diesel engines is directly used in opposed piston two-stroke diesel engines, it is easy to cause piston burning and cylinder scoring failure due to excessive heat load.

[0004] To improve the combustion performance of opposed-piston two-stroke diesel engines, common techniques include balancing the swirl ratio and flow efficiency to increase intake and scavenging efficiency, or studying the injector parameters and arrangement, including injection curves, injection pressure, nozzle diameter, and injection advance angle. However, techniques for improving the combustion performance of opposed-piston two-stroke diesel engines by changing the combustion chamber shape are fewer and have limited application. Summary of the Invention

[0005] In view of this, the present application aims to provide a piston combustion chamber suitable for opposed piston two-stroke diesel engines to solve at least one of the above-mentioned problems.

[0006] To achieve the above objectives, the technical solution of this application is implemented as follows: This application provides a piston combustion chamber suitable for an opposed-piston two-stroke diesel engine, comprising: The combustion chamber structure consists of two opposing recesses on both sides of the piston edge, and a concave bowl-shaped semi-rugby structure in the middle, with a smooth inner wall surface. Two opposing recesses are respectively set on the central axis of the combustion chamber, and two fuel injectors are set opposite each other and located at the two opposing recesses. Each fuel injector is provided with three fuel injection holes, wherein the included angle of the fuel jet formed by the three fuel injection holes is smaller than the cone angle formed by the line connecting the top surface of the fuel injector to the center of the bottom of the boss.

[0007] Furthermore, the diameter of the combustion chamber is 80~140mm.

[0008] Furthermore, the depth of the combustion chamber is 14-18 mm.

[0009] Furthermore, the combustion chamber has a bowl width of 45-55mm and a bowl rim width of 15-20mm.

[0010] Furthermore, the vertical angle of the bowl in the combustion chamber is 20°.

[0011] Furthermore, the horizontal angle of the combustion chamber bowl is 5°~10°.

[0012] Furthermore, in response to the piston being at top dead center, the first injection orifice of the injector has a range of 18° to 22°, the second injection orifice of the injector has a range of 5° to 10°, and the first injection orifice of the injector has a range of 28° to 32°.

[0013] Furthermore, the compression ratio of the combustion chamber is equal to that of the original combustion chamber.

[0014] Compared with the prior art, the piston combustion chamber of the opposed piston two-stroke diesel engine described in this application has the following beneficial effects: (1) The combustion chamber structure described in this application is based on the original opposed piston two-stroke diesel engine's combustion chamber compression ratio and material unchanged, ensuring the universality of tooling and process, and also ensuring good scavenging performance under the original combustion chamber structure.

[0015] (2) The combustion chamber structure described in this application can effectively improve the oil jet breaking and mixing rate, improve air utilization and combustion rate, thereby improving engine thermal efficiency and load.

[0016] (3) The combustion chamber structure design described in this application takes into account the number of injector holes and the fuel jet angle used in conjunction with it, and the combustion system formed therewith has a wider range of adaptability. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the piston combustion chamber structure of a conventional opposed-piston two-stroke diesel engine as described in an embodiment of this application; Figure 2 This is a cross-sectional view of the combustion system of a conventional opposed piston two-piston diesel engine as described in the embodiments of this application; Figure 3 This is a schematic diagram of the semi-rugby-shaped combustion chamber structure described in the embodiments of this application; Figure 4 This is a cross-sectional view of the semi-rugby-shaped combustion chamber system described in the embodiments of this application; Figure 5 This is a top view of the injector jet angle described in the embodiment of this application; Figure 6 This is a side view of the injector jet angle as described in the embodiment of this application; Figure 7 The diagram shows the in-cylinder pressure curves of the semi-oval combustion chamber described in the embodiments of this application and the piston combustion chamber of a conventional opposed-piston two-stroke diesel engine. Figure 8 The heat release rate curves of the semi-oval combustion chamber described in the embodiments of this application and the original opposed piston two-stroke diesel engine piston combustion chamber are shown. Figure 9 This is a graph showing the air utilization rate of the semi-oval combustion chamber described in the embodiments of this application and the original opposed piston two-stroke diesel engine piston combustion chamber. Figure 10 This is a comparison diagram of the in-cylinder air-fuel equivalence ratio distribution between the semi-rugby-shaped combustion chamber described in the embodiments of this application and the original opposed piston two-stroke diesel engine piston combustion chamber. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0019] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] Figure 1 The piston is from an existing opposed-piston two-stroke diesel engine. Figure 2 This is a schematic diagram of its combustion system. Fuel is injected when the piston reaches near top dead center. To avoid impacting the piston combustion chamber wall, the injector orifice angle is relatively small. This combustion system is currently the most commonly used in opposed piston two-stroke diesel engines; however, it suffers from poor spray mixing and combustion efficiency. In the matching process of the air-fuel chamber in an opposed piston two-stroke diesel engine, a single injector with multiple nozzles forms a complex spatial fuel jet, which is more conducive to achieving rapid and complete fuel-air mixing, improving the combustion process, and increasing combustion efficiency. However, the prerequisite for a single injector with multiple nozzles to form a complex spatial fuel jet is to expand the range of nozzle arrangement angles.

[0021] To achieve the above objectives, this embodiment proposes a piston combustion chamber suitable for an opposed-piston two-stroke diesel engine. The combustion chamber is semi-oval shaped (see details below). Figure 3 As shown in the figure, to avoid impacting the parallel wall of the piston combustion chamber, the spray mixing effect is improved by increasing the range of possible arrangement angles of the injector nozzles in the vertical plane. At the same time, it can ensure good scavenging performance under the original combustion chamber structure in a two-stroke diesel engine, and achieve rapid and sufficient mixing of oil and air without changing the combustion chamber material, thereby improving the combustion process and increasing combustion efficiency.

[0022] This combustion chamber is based on the original opposed piston two-stroke diesel engine's combustion chamber compression ratio and materials, ensuring the commonality of tooling and processes, including: The diameter and length D1 of the combustion chamber and the position of the fuel injector are the same as the original combustion chamber, with a length of 80~140mm. The purpose is to ensure that the cylinder edge and cylinder center have the same distance in both types of combustion chambers.

[0023] Because the opening of the semi-rugby-shaped combustion chamber is significantly smaller than that of the original opposed piston two-stroke diesel engine piston, in order to ensure that the compression ratio of the semi-rugby-shaped combustion chamber is equal to that of the original combustion chamber, the bowl depth d is increased by about 1 / 4 compared with the original combustion chamber. The specific increment can be calculated based on the volume removed from the "semi-rugby" and the volume removed from the original combustion shape. In this embodiment, the bowl depth d is 14~18mm.

[0024] The vertical angle α of the nozzle is slightly smaller than that of the original combustion chamber, but the angle change is small (<1°). The nozzle edge a is about twice as large as that of the original combustion chamber, specifically 15~20mm. This is because the parallel wall c and lip circle r of the original combustion chamber have been removed. The purpose is to increase the range of angles that the injector nozzles can be arranged on the vertical plane, in order to avoid impacting the parallel wall of the piston combustion chamber and improve the spray mixing effect.

[0025] The bowl width h is reduced by about 1 / 3 compared with the original combustion chamber, specifically 45~55mm. The purpose is to remove the redundant part of the original combustion chamber on the horizontal plane, where the spray mixing and combustion effect is poor. The horizontal angle β of the bowl is between 5° and 10°, in order to ensure that the oil jets can be arranged well and that the oil jets do not interfere with each other.

[0026] To accommodate the combustion chamber structure described in the above embodiments, this embodiment also provides an injector solution for use with the semi-rugby piston combustion chamber, such as... Figure 5 and Figure 6 As shown. Among them, When the piston is at top dead center, the oil jet angle (θ1) is between 18° and 22°, the oil jet angle (θ2) is between 5° and 10°, and the oil jet angle (θ3) is between 28° and 32°. Otherwise, the oil jets will interfere with each other or collide directly with the combustion chamber wall, resulting in poor spray mixing in the combustion chamber. When the piston is at top dead center, the included angle (θ4) of the fuel jet formed by the three injection holes cannot be greater than the cone angle (θ5) formed by the line connecting the top surface of the injector and the center of the bottom of the boss. That is, θ5≥θ4. Otherwise, the fuel jet will collide directly with the combustion chamber wall, resulting in low air utilization at the bottom of the piston and deterioration of combustion. Figure 7 The comparison of the in-cylinder pressure of the semi-rugby-shaped combustion chamber and the original opposed piston two-stroke diesel engine combustion chamber shows that the maximum cylinder pressure of the semi-rugby-shaped combustion chamber is increased by 7.3% compared to the original combustion chamber. This indicates that the semi-rugby-shaped combustion chamber can improve combustion performance and increase combustion rate.

[0027] Figure 8The comparison of the heat release rate of the semi-rugby-shaped combustion chamber and the original opposed piston two-stroke diesel engine combustion chamber shows that during the rapid combustion period (crankshaft angle between 360° and 390°), the heat release rate of the semi-rugby-shaped combustion chamber is significantly higher than that of the original combustion chamber. This indicates that the semi-rugby-shaped combustion chamber can improve combustion performance and increase combustion rate.

[0028] Figure 9 The comparison of air utilization rates between the semi-rugby-shaped combustion chamber and the original opposed-piston two-stroke diesel engine piston combustion chamber shows that during the rapid combustion period (crankshaft angle between 360° and 390°), the air utilization rate of the semi-rugby-shaped combustion chamber is similar in the early stage, but significantly higher than that of the original combustion chamber in the later stage as the crankshaft angle increases. This indicates that the semi-rugby-shaped combustion chamber can improve the fuel jet breaking and mixing rate, improve air utilization and combustion rate, and thus improve engine thermal efficiency and load.

[0029] Figure 10 The comparison shows the distribution of in-cylinder air-fuel equivalence ratio between the semi-rugby-shaped combustion chamber and the original opposed-piston two-stroke diesel engine piston combustion chamber. It can be seen that the semi-rugby-shaped combustion chamber reduces the area with a low equivalence ratio on both sides of the cylinder during the combustion process compared to the original combustion chamber. At the same time, it forms a mixed air-fuel equivalence area with a high equivalence ratio in the rugby-shaped recess area in the center of the cylinder, making the equivalence ratio distribution more uniform and reasonable. This indicates that the semi-rugby-shaped combustion chamber can improve spray mixing performance and increase the combustion rate.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0031] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A piston combustion chamber suitable for use in an opposed-piston two-stroke diesel engine, characterized in that, The application relates to a piston combustion chamber structure. The combustion chamber structure is a semi-olive ball structure with two opposite notches arranged at the edge positions of the two sides of the piston and a concave bowl in the middle, and the inner wall surface is a smooth surface. The two opposite notches are arranged on the central axis of the combustion chamber, two oil injectors are oppositely arranged and located at the two opposite notches, three oil injection holes are arranged on each oil injector, and the included angle of the oil beams formed by the three oil injection holes is smaller than the cone angle formed by the center line from the top surface of the oil injector to the bottom of the boss.

2. The piston combustion chamber according to claim 1, wherein: The diameter of the combustion chamber is 80-140 mm.

3. The piston combustion chamber according to claim 1, wherein: The bowl depth of the combustion chamber is 14-18 mm.

4. The piston combustion chamber according to claim 1, wherein: The bowl width of the combustion chamber is 45-55 mm, and the bowl edge is 15-20 mm.

5. The piston combustion chamber according to claim 1, wherein: The bowl vertical angle of the combustion chamber is 20 degrees.

6. The piston combustion chamber according to claim 1, wherein: The bowl horizontal angle of the combustion chamber is 5-10 degrees.

7. The piston combustion chamber according to claim 1, wherein: In response to the piston being located at the top dead center, the range of the first oil injection hole of the oil injector is 18-22 degrees, the range of the second oil injection hole of the oil injector is 5-10 degrees, and the range of the first oil injection hole of the oil injector is 28-32 degrees.

8. The piston combustion chamber according to claim 1, wherein: The compression ratio of the combustion chamber is equal to that of the original combustion chamber.

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