Two-stroke engine and control method thereof

Abstract

The present invention discloses a two-stroke engine system and a control method thereof, comprising a cylinder and an ECU electronic control unit, wherein two exhaust ports are respectively located on opposite side walls of the cylinder wall and are positioned horizontally, a plurality of scavenging ports are arranged on the cylinder wall in a horizontal arrangement relative to the cylinder wall, and the intake direction of the scavenging ports is at an angle of 10°-20° with the tangent direction of the cylinder wall, thereby causing the incoming fresh air to form a swirl flow within the cylinder; two methanol injectors and a high-pressure injector are disposed within the cylinder head, and the nozzles of the methanol injector and the high-pressure injector both extend into the combustion chamber; two diesel injectors are also disposed within the cylinder wall, located between the exhaust ports and the scavenging ports, and their nozzles extend into the combustion chamber; the ECU electronic control unit is configured to control the injection of the methanol injector, the diesel injector, and the high-pressure injector according to the engine load. The present invention controls the injection ratio of the diesel injector and the methanol injector according to the engine operating condition, and controls whether the high-pressure injector participates in enhancing the mixing of the mixture.

Description

Technical Field

[0001] The invention belongs to a fuel engine system, and in particular relates to a marine two-stroke engine capable of rapidly atomizing and mixing diesel and methanol, and a control method thereof. Background Art

[0002] Given the dual pressures of energy conservation and emission reduction and the energy crisis, green shipping has become a key development direction for future ships. Methanol, with its many advantages such as cleanliness, environmental friendliness, renewability, and high availability, has become a top choice for future marine fuels. However, direct application of methanol fuel in engines presents certain difficulties. Existing methanol engines require two independent fuel injection pumps and injector systems: one for injecting diesel fuel and the other for injecting methanol fuel. Diesel fuel is used to ignite the methanol fuel, addressing issues such as starting difficulties with pure methanol fuel engines. However, this technology suffers from the significant and costly modifications required to the original engine. Therefore, a marine methanol fuel engine system that rapidly atomizes diesel and methanol is needed for large-bore, high-volume marine two-stroke engines. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and propose a marine two-stroke engine with rapid atomization and mixing of diesel and methanol and a control method thereof. The engine can quickly form a highly active atmosphere of a methanol-diesel mixture in the cylinder, and at the same time, coupled with a high-pressure air auxiliary system, spray high-pressure air into the cylinder to enhance the mixing of the mixture, thereby enabling the methanol engine to operate efficiently; at the same time, the designed scavenging port can cause the incoming fresh air to form a swirl in the cylinder, thereby further strengthening the flow in the cylinder to accelerate the formation of the mixture.

[0004] The first aspect of the present invention is to provide a two-stroke engine system, including a cylinder and an ECU electronic control unit, wherein the cylinder is defined by a combustion chamber defined by a reciprocating piston, the piston being driven by a connecting rod, and the engine scavenging exhaust being controlled by controlling the lift of the piston; the cylinder wall including, from the bottom of the cylinder head downward, an exhaust port and a scavenging port, the exhaust port being used to discharge exhaust gas from the combustion chamber, and the scavenging port being used to introduce fresh air into the combustion chamber; the two exhaust ports being respectively located on opposite side walls of the cylinder wall and being arranged horizontally relative to each other, allowing exhaust gas to enter an exhaust duct through the exhaust ports and then be discharged; the multiple scavenging ports being arranged on the cylinder wall horizontally relative to the cylinder wall, and the angle between the intake direction of the scavenging ports and the tangent direction of the cylinder wall being 10°-20°, thereby causing the incoming fresh air to form a swirl in the cylinder;

[0005] Two methanol injectors and a high-pressure injector are provided in the cylinder head, and the nozzles of the methanol injectors and the high-pressure injectors both extend into the combustion chamber; two diesel injectors are also provided on the opposite side walls of the cylinder wall, and the diesel injectors are located between the exhaust port and the scavenging port, and their nozzles extend into the combustion chamber;

[0006] The ECU electronic control unit is used to control the diesel injector, methanol injector and high-pressure injector to spray in sequence when the engine is under high load and low load, thereby forming a fully mixed methanol and diesel mixed spray; and when the engine is under medium load, it controls the diesel injector and methanol injector to spray in sequence, and the high-pressure injector does not work.

[0007] Furthermore, the high-pressure injector is centrally located with its nozzle facing the center of the combustion chamber. The methanol injectors are located on either side of the high-pressure injector, with the central axis of the methanol injector forming an angle of 30°-60° with the central axis of the high-pressure injector. This arrangement facilitates better collision of the high-pressure air with the methanol spray. Furthermore, when the methanol injector and the high-pressure injector are sprayed simultaneously, the methanol spray ejected from the methanol injector can be quickly and effectively fragmented under the impact of the high-pressure air. Furthermore, in the high-pressure air atmosphere, the methanol spray can collide with the diesel spray more quickly, further improving its fragmentation and mixing with the diesel spray, allowing a highly active atmosphere to be formed more quickly and effectively within the cylinder.

[0008] Furthermore, the methanol spray injected by the methanol injector has a pressure of 50-150 MPa and a temperature of room temperature 25°C; the high-pressure injector injects high-pressure air at a pressure of 60-150 MPa; and the diesel injector has an injection pressure of 50-150 MPa.

[0009] A second aspect of the present invention provides a control method for the two-stroke engine system, comprising:

[0010] When the engine is under low load, before the piston reaches the top dead center, the diesel injector is controlled to inject diesel with an energy ratio of 20%-30%, and then the methanol injector is controlled to inject methanol fuel with an energy ratio of 70%-80%. While the methanol and diesel injectors are spraying spray to form a mixed spray, the nozzle of the high-pressure injector is controlled to inject high-pressure air into the combustion chamber to enhance the flow in the cylinder and improve the mixing of the mixed gas.

[0011] When the engine is under heavy load, before the piston reaches the top dead center, the diesel injector is controlled to inject diesel fuel with an energy ratio of 10%-15%, and then the methanol injector is controlled to inject methanol fuel with an energy ratio of 85%-90%. While the methanol and diesel injectors are spraying spray to form a mixed spray, the nozzle of the high-pressure injector is controlled to inject high-pressure air into the combustion chamber to enhance the flow in the cylinder and improve the mixing of the mixed gas.

[0012] When the engine is under medium load, before the piston reaches the top dead center, the diesel injector is controlled to inject diesel with an energy ratio of 15%-20%, and then the methanol injector is controlled to inject methanol fuel with an energy ratio of 80%-85%; at this time, the high-pressure injector does not work.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0014] The present invention proposes a strategy of diesel-assisted methanol mixed spray. Through the arrangement of methanol and diesel injectors, the spray discharge is reasonably controlled according to the working conditions at low load and high load. The collision of methanol and diesel sprays accelerates the spray breakup, quickly forming a highly active atmosphere of methanol and diesel spray mixture. At the same time, the high-pressure jet port on the cylinder head is coupled to further accelerate the formation of the mixture, so as to optimize combustion and reduce incomplete combustion emissions, thereby improving engine power. In addition, the air intake direction of the scavenging port designed by the present invention can make the incoming fresh air form a swirl in the cylinder, so as to further strengthen the flow in the cylinder to accelerate the formation of the mixture, so that the mixed fuel can burn quickly and more completely in the combustion chamber, thereby improving combustion efficiency and improving the power of the methanol engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional schematic diagram of the fuel engine system of the present invention.

[0016] Figure 2 This is a schematic diagram of the air intake direction of the scavenging port of the present invention.

[0017] In the picture:

[0018] 1: Cylinder head 2: Exhaust port 3: Exhaust port

[0019] 4: Methanol injector 5: Methanol injector 6: High pressure injector

[0020] 7: Diesel fuel injector 8: Diesel fuel injector 9: Scavenging port

[0021] 10: Scavenging port 11: Cylinder wall 12: Piston

[0022] 13: Connecting rod 14: Combustion chamber DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described are only used to explain the present invention and are not intended to limit the present invention.

[0024] like Figure 1The illustrated system, which uses methanol fuel for marine fuel and features a rapidly atomized mixture of diesel and methanol, includes a cylinder and an ECU. The cylinder consists of a cylinder head 1 and a cylinder wall 11. Within the cylinder, a combustion chamber 14 is defined by a reciprocating piston 12. The piston 12 drives a crankshaft mounted within the crankcase via a connecting rod 13. Controlling the lift of the piston 12 controls the engine's scavenging and exhaust, regulating the amount of air entering the combustion chamber through the scavenging port. Under different operating conditions, the engine requires varying power and torque output. The reciprocating motion of the piston 12 generates sufficient power output. The cylinder wall 11, extending downward from the bottom of the cylinder head 1, includes exhaust ports 2 and 3 and scavenging ports 9 and 10. Exhaust ports 2 and 3 are used to exhaust exhaust from the combustion chamber, while scavenging ports 9 and 10 are used to introduce fresh air into the combustion chamber. The exhaust ports are located higher than the scavenging ports. The two exhaust ports 2 and 3 are located on opposite sides of the cylinder wall 11 and are positioned horizontally opposite each other, allowing exhaust gas to enter the exhaust duct and be discharged. Figure 2 A cross-sectional view of the cylinder wall is shown (the arrow in the figure indicates the air intake direction). Eighteen scavenging ports 9, 10 are evenly spaced on the cylinder wall 11 of the annular cylinder. The scavenging ports are arranged horizontally relative to the cylinder wall 11, and the angle between the air intake direction of the scavenging ports and the tangent direction of the cylinder wall 11 is 10°-20° (depending on the engine model), thereby causing the incoming fresh air to form a swirl in the cylinder.

[0025] The cylinder head 1 is equipped with two methanol injectors 4 and 5 and a high-pressure injector 6. The nozzles of the two injectors extend into the combustion chamber. The high-pressure injector 6 is centrally positioned, with its nozzle facing the center of the combustion chamber. The two injectors 4 and 5 are located on either side of the high-pressure injector 6, with the central axes of the two injectors 4 and 5 forming an angle of 30°-60° with the central axis of the high-pressure injector 6 (depending on the engine model). Depending on the operating conditions, the methanol injectors 4 and 5 spray a corresponding amount of methanol spray at a pressure of 50-150 MPa (depending on the load) at room temperature (25°C). The high-pressure injector 6 sprays high-pressure air at a pressure of 60-150 MPa (depending on the load).

[0026] Existing marine two-stroke methanol engines suffer from problems such as methanol fuel's difficulty in burning, and the large cylinder diameter and spatial dimensions of two-stroke engines, which result in a long mixing time between methanol fuel and fresh air entering from the scavenging ports. These issues lead to difficulties in cold starting, low combustion efficiency, and low power output. The present invention, however, proposes a diesel-assisted methanol mixed spray system. By arranging the injector's position and angle, the spray discharge is rationally controlled according to operating conditions. The collision of methanol and diesel sprays accelerates spray breakup, quickly forming a highly active atmosphere for the methanol and diesel spray mixture. This system also couples with the high-pressure jet ports on the cylinder head to further accelerate mixture formation. Furthermore, the scavenging port intake direction shown in the present invention allows the incoming fresh air to form a swirl flow within the cylinder, further strengthening the flow within the cylinder to accelerate mixture formation. This allows the mixed fuel to burn quickly and more fully within the combustion chamber, improving combustion efficiency and boosting the power of the methanol engine.

[0027] Two diesel injectors 7 and 8 are also located on opposite sides of the cylinder. These are positioned between the exhaust ports 2 and 3 and the scavenging ports 9 and 10, with their nozzles extending into the combustion chamber. These injectors 7 and 8 are used to inject diesel into the combustion chamber at a pressure of 50-150 MPa (depending on the load).

[0028] The ECU electronic control unit is used to control the methanol injectors 4, 5, the diesel injectors 7, 8 and the high-pressure injector 6. The specific control method is as follows:

[0029] When the engine is under low load (30% rated power), before the piston moves up to the top dead center, the ECU controls the diesel injectors 7 and 8 to inject diesel with an energy ratio of 20%-30% (depending on the engine model, this ratio is only a guide), and then controls the methanol injectors 4 and 5 to inject methanol fuel with an energy ratio of 70%-80% (depending on the engine model, this ratio is only a guide). The injected methanol fuel collides with the diesel spray, quickly forming a highly active atmosphere of methanol and diesel mixture, reducing the mixing time. While the methanol and diesel injectors are spraying spray to form a mixed spray, the nozzle of the high-pressure injector 6 injects high-pressure air into the combustion chamber to strengthen the flow in the cylinder and enhance the mixing of the mixed gas.

[0030] When the engine is under a heavy load (75% of rated power or above), the ECU electronic control unit controls the diesel injectors 7 and 8 to inject diesel with an energy ratio of 10%-15% (depending on the engine model, it is only a guiding ratio) before the piston moves up to the top dead center. Then, the methanol injectors 4 and 5 are controlled to inject methanol fuel with an energy ratio of 85%-90% (depending on the engine model, it is only a guiding ratio). At this time, the proportion of diesel injected is slightly less and the methanol injected is more. The injected methanol fuel collides with the diesel spray, and a highly active atmosphere of methanol and diesel mixture is formed more quickly to reduce the mixing time. While the methanol and diesel injectors spray spray to form a mixed spray, the nozzle of the high-pressure injector 6 injects high-pressure air into the combustion chamber. The injection of high-pressure air under this load can replenish fresh air in the cylinder to increase the total power output to adapt to high-load working conditions.

[0031] When the engine is under medium load, the ECU electronic control unit only needs to control the diesel injectors 7 and 8 to inject diesel with an energy ratio of 15%-20% (depending on the engine model, it is only a guiding ratio) and the methanol injectors 4 and 5 to inject methanol fuel with an energy ratio of 80%-85% (depending on the engine model, it is only a guiding ratio) to accelerate the mixing of the fuel in the cylinder. At this time, the high-pressure injector is not needed.

[0032] The present invention couples a high-pressure injector with a methanol injector and a diesel injector, so that when methanol fuel is injected into a cylinder already sprayed with diesel, a combustible mixture is quickly formed, thereby optimizing combustion and reducing incomplete combustion emissions, thereby improving engine power.

[0033] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, which all fall within the scope of protection of the present invention.

[0034] References:

[0035] [1] Diesel / methanol combined combustion technology[J]. Internal Combustion Engine and Power Plant, 2020, 37(06):2.

[0036] [2] Pei Zili, Yang Xiaoli, Wang Qingli, Liang Xiaobo, Bao Tao, Chen Tingbo. Design of fuel injection system for marine pure methanol engine[J].

[0037] Journal of Naval Architecture and Marine Engineering, 2020, 42(S1): 202-204+263. DOI: 10.13788 / j.cnki.cbgc.2020.S1.047.

[0038] [3] Wang Hui. Research and application of diesel-methanol combined combustion in marine diesel engines[D]. Tianjin University

[0039] Science, 2019.DOI:10.27356 / d.cnki.gtjdu.2019.004588.

[0040] [4] Zhen Xudong. Research on combustion process and knock mechanism of spark ignition methanol engine[D]. Tianjin University, 2014.

[0041] [5] Jiang Liyong, Li Yufeng, Liu Zhongchang, Liu Jinshan, Liu Xunjun. Combustion characteristics of spark-ignition methanol fuel engine[J]. Journal of Internal Combustion Engines, 1994(03):244-248. DOI:10.16236 / j.cnki.nrjxb.1994.03.007.

Claims

1. A two-stroke engine system comprising a cylinder and an ECU electronic control unit, wherein the cylinder is defined by a combustion chamber (14) defined by a reciprocating piston (12), the piston (12) being driven by a connecting rod (13), and the engine scavenging and exhausting is controlled by controlling the lift of the piston (12); characterized in that: The cylinder wall (11) includes, from the bottom of the cylinder head (1) downward, an exhaust port (2, 3) and a scavenging port, wherein the exhaust ports (2, 3) are used to discharge exhaust gas from the combustion chamber, and the scavenging port is used to introduce fresh air into the combustion chamber; the two exhaust ports (2, 3) are arranged on opposite side walls of the cylinder wall (11) and are arranged horizontally, so that the exhaust gas enters the exhaust duct from the exhaust ports and is then discharged; the plurality of scavenging ports are arranged on the cylinder wall (11) horizontally relative to the cylinder wall, and the angle between the intake direction of the scavenging port and the tangent direction of the cylinder wall (11) is 10°-20°, so that the fresh air entering forms a swirl in the cylinder; Two methanol injectors (4, 5) and a high-pressure injector (6) are provided in the cylinder head (1), and the nozzles of the methanol injectors (4, 5) and the high-pressure injector (6) both extend into the combustion chamber (14); two diesel injectors (7, 8) are also provided on the opposite side walls of the cylinder wall (11), and the diesel injectors are located between the exhaust ports (2, 3) and the scavenging ports, and their nozzles extend into the combustion chamber; The ECU electronic control unit is used to control the diesel injectors (7, 8), the methanol injectors (4, 5) and the high-pressure injector (6) to spray in sequence when the engine is under high load and low load, thereby forming a fully mixed methanol and diesel mixed spray; and when the engine is under medium load, the diesel injectors (7, 8) and the methanol injectors (4, 5) are controlled to spray in sequence, and the high-pressure injector (6) is not operated; The high-pressure injector (6) is centrally arranged and its nozzle is facing the center of the combustion chamber (14); the methanol injectors (4, 5) are respectively located on both sides of the high-pressure injector (6); and the central axis of the methanol injectors (4, 5) forms an angle of 30°-60° with the central axis of the high-pressure injector (6); The methanol spray injected by the methanol injector (4, 5) has a pressure of 50-150 MPa and a temperature of 25°C, which is room temperature; the high-pressure injector (6) injects high-pressure air at a pressure of 60-150 MPa; and the diesel injector (7, 8) has an injection pressure of 50-150 MPa.

2. The control method of the two-stroke engine system according to claim 1, characterized in that: include: When the engine is under low load, before the piston reaches the top dead center, the diesel injectors (7, 8) are controlled to inject diesel fuel with an energy ratio of 20%-30%, and then the methanol injectors (4, 5) are controlled to inject methanol fuel with an energy ratio of 70%-80%. While the methanol and diesel injectors are spraying sprays to form a mixed spray, the nozzle of the high-pressure injector (6) is controlled to inject high-pressure air into the combustion chamber to strengthen the flow in the cylinder and enhance the mixing of the mixed gas. When the engine is under a high load, before the piston reaches the top dead center, the diesel injectors (7, 8) are controlled to inject diesel fuel with an energy ratio of 10%-15%, and then the methanol injectors (4, 5) are controlled to inject methanol fuel with an energy ratio of 85%-90%. While the methanol and diesel injectors are spraying sprays to form a mixed spray, the nozzle of the high-pressure injector (6) is controlled to inject high-pressure air into the combustion chamber to strengthen the flow in the cylinder and enhance the mixing of the mixed gas. When the engine is at a medium load, before the piston reaches the top dead center, the diesel injectors (7, 8) are controlled to inject diesel with an energy ratio of 15%-20%, and then the methanol injectors (4, 5) are controlled to inject methanol fuel with an energy ratio of 80%-85%; at this time, the high-pressure injector (6) does not work.

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