Diesel engine open dc double loop cooling method and device

Abstract

This invention relates to an open-circuit DC dual-loop cooling method and apparatus for diesel engines, belonging to the field of internal combustion engine cooling technology. In this apparatus, the coolant is pressurized by a water pump and divided into two paths: In the first cooling loop, the coolant enters the engine block water chamber to cool the cylinder liners of each cylinder, then enters the oil cooler for preheating, and then enters the cylinder head water chamber to cool the top surface of the combustion chamber. After passing through the thermostat, it flows into the exhaust pipe's hot water jacket for discharge. In the second cooling loop, the coolant first enters the intercooler, then is heated by the exhaust pipe's hot water jacket before entering the turbocharger turbine housing cooling water jacket, and finally flows into the exhaust pipe's hot water jacket for discharge. This invention effectively prevents high-temperature seawater crystallization and blockage by controlling the intercooler outlet water temperature below 50°C; through the parallel water chamber design of the engine block water chamber and the series preheating of the oil cooler, it solves the problems of uneven cooling of each cylinder and overcooling of the diesel engine, improving the reliability of marine diesel engines and the consistency of cylinder operation.

Description

Technical Field

[0001] This invention belongs to the field of internal combustion engine cooling technology, specifically relating to an open-circuit DC dual-loop cooling method and device for diesel engines, which is particularly suitable for marine diesel engines using seawater as the cooling medium. Background Technology

[0002] Marine diesel engines operate in the marine environment for extended periods, and their cooling systems often face the following technical challenges: Seawater corrosion and crystallization blockage: When seawater is used as a cooling medium, salt crystals easily precipitate in the seawater under high temperature conditions, which can lead to blockage of the intercooler, oil cooler and engine water passages, seriously affecting cooling efficiency. Uneven cooling of cylinders: Traditional series cooling method causes the coolant temperature to gradually rise as it flows through each cylinder, resulting in inconsistent cooling intensity of each cylinder, affecting the working consistency of each cylinder of the engine, and even causing the crankcase exhaust gas pressure to rise. Low-temperature overcooling problem: When operating in cold sea areas, low-temperature seawater directly enters the engine, which can easily cause the diesel engine to overcool, affecting combustion efficiency and emission performance; Cylinder head thermal stress: When the coolant temperature is too low and it enters the cylinder head directly, the temperature difference on the top surface of the combustion chamber is too large, which can easily lead to thermal fatigue cracks.

[0003] Therefore, it is necessary to develop cooling methods and devices that meet the above-mentioned usage scenarios and solve the crystallization problem when seawater is used as a cooling medium. Summary of the Invention

[0004] To address the problems in the prior art, this invention proposes an open-circuit DC dual-loop cooling method and device for diesel engines. This device solves technical problems such as crystallization blockage during seawater cooling, uneven cooling of cylinders, and overcooling of diesel engines by optimizing the coolant flow direction and temperature control.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an open DC dual-circuit cooling device for diesel engines, comprising a water pump, an engine block water chamber, an oil cooler, a cylinder head water chamber, a thermostat, and an exhaust pipe hot water jacket arranged in series to form a first cooling circuit; The water pump, intercooler, exhaust pipe hot water jacket and flue pipe hot water jacket are connected in series to form a second cooling circuit; The water pump has a specially customized outlet, which is provided with a first flow channel and a second flow channel. After the water pump is pressurized, the first flow channel is connected to the first cooling circuit, and the second flow channel is connected to the second cooling circuit. The first cooling circuit and the second cooling circuit are designed in parallel. The cylinders in the water chamber of the machine body are designed in parallel.

[0006] Furthermore, in the first cooling circuit, the engine block water chamber, oil cooler, and cylinder head water chamber are designed in series, while in the second cooling circuit, the intercooler, exhaust pipe hot water jacket, and turbocharger turbine housing cooling water jacket are designed in series.

[0007] Furthermore, the cylinders in the water chamber of the machine body are designed in parallel, and the water flow rate of each cylinder is evenly distributed through the differential design of the cross-sectional area of ​​the water chamber. The cross-sectional area of ​​the water chamber is designed differently according to the heat load distribution of each cylinder: the cross-sectional area of ​​the water chamber of each cylinder in the middle is slightly larger than that of each cylinder at both ends, and the difference in cross-sectional area is controlled within ±8%, ensuring that the actual coolant flow rate unevenness of each cylinder does not exceed ±5%.

[0008] Furthermore, the intercooler is designed according to rated operating conditions. During the design process, the boundary condition is the rated power of the engine. The thermal balance is achieved under the rated power, and the outlet water temperature of the intercooler is controlled below 50°C.

[0009] Furthermore, the thermostat only acts on the engine, determining the opening and closing of the large circulation channel based on the engine temperature.

[0010] Furthermore, the two flow channels at the water pump outlet are integrally formed by casting. The outlet diameter of the first flow channel corresponds to the flow requirement of the first cooling circuit, and the outlet diameter of the second flow channel corresponds to the flow requirement of the second cooling circuit. The flow split ratio is determined by engineering simulation based on thermal balance analysis of the diesel engine under all operating conditions.

[0011] Furthermore, the intercooler is equipped with a temperature sensor, which is electrically connected to the ECU to provide real-time temperature feedback.

[0012] Furthermore, the device also includes a drain valve, which is located at the lowest point of the cooling water discharge channel at the bottom of the U-shaped underwater exhaust bend in the outboard motor.

[0013] Furthermore, the internal cavity of the engine is located in the outboard motor assembly, and the cooling water discharge channel at the bottom of the U-shaped underwater exhaust bend in the lower assembly is the geometric lowest point of the entire cooling system. Water from the internal cavity is collected by the hot water jacket of the exhaust pipe and flows into the cooling water discharge channel of the lower assembly through the vertical connecting pipe, and is finally discharged by the drain valve. The device also includes a flushing water inlet, which is located at the water inlet of the cooling system. After the machine stops, clean water is injected through the flushing water inlet, and the residual seawater is discharged from the drain valve.

[0014] Furthermore, the method of using the aforementioned open-circuit DC dual-loop cooling device for diesel engines, Step 1: The coolant is pressurized by the water pump and distributed to the first cooling circuit and the second cooling circuit; Step 2: In the first cooling circuit, the coolant enters the diesel engine block water chamber to cool the cylinder liners, then flows out into the oil cooler. After being heated, it enters the cylinder head water chamber to cool the top surface of the combustion chamber, and then flows out to the thermostat. When the thermostat is closed, the coolant flows into the exhaust pipe hot water jacket through the bypass branch pipe. When the thermostat is open, the coolant flows into the exhaust pipe hot water jacket through the large circulation channel and is finally discharged. Step 3: In the second cooling circuit, the coolant first enters the intercooler to cool the high-temperature boosted air after being compressed by the turbocharger, then enters the exhaust pipe hot water jacket, and after being heated, enters the turbocharger turbine housing cooling water jacket, and finally exits through the exhaust pipe hot water jacket. The first cooling circuit and the second cooling circuit converge at the hot water jacket of the exhaust pipe.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0016] 1. This invention organically combines multiple technical means, including dual-loop cooling arrangement, parallel water chamber structure of the engine block, series preheating of the oil cooler, and coordinated control of the intercooler outlet water temperature: the parallel water chamber design ensures that the initial temperature of the coolant in each cylinder is consistent, while the series preheating ensures that the temperature of the coolant entering the cylinder head is moderate. The combination of the two solves both the uneven cooling of each cylinder and the overcooling problem; the independent cooling of the intercooler by the second loop makes low-temperature control below 50°C possible, while the preheating design of the first loop avoids the overall device from becoming inefficient due to excessively low temperatures; the flow channel structure of the parallel water chamber and the pipeline layout of the series loop are optimized through engineering simulation to ensure the consistency between theoretical design and actual operation. This technology fundamentally improves the systemic technical problems faced by marine diesel engines when using seawater as a cooling medium, such as uneven cooling of cylinders, overcooling operation, and high-temperature crystallization blockage. It significantly improves the reliability of the diesel engine, the consistency of operation of each cylinder, and the service life. Through reasonable cooling circuit design, structural optimization, and temperature control strategies, it systematically solves many key technical problems in open-circuit cooling of marine diesel engines, achieving significant technical effects in improving engine reliability, reducing failure rate, and extending service life.

[0017] 2. This invention adopts a parallel design of the cooling water chambers of each cylinder in the engine block, so that the coolant is pressurized by the water pump and simultaneously distributed to the water chambers of each cylinder, ensuring that the temperature, pressure and flow rate of the coolant entering each cylinder are basically the same, thereby achieving uniform cooling of each cylinder, effectively improving the working consistency of each cylinder of the engine, and reducing the risk of abnormal increase in crankcase exhaust gas pressure caused by uneven combustion.

[0018] 3. This invention employs a series design for the engine block, oil cooler, and cylinder head water chamber. By utilizing the method where the coolant absorbs heat in the engine block and then further absorbs heat from the oil in the oil cooler, the coolant is effectively preheated before entering the cylinder head. This significantly increases the temperature of the coolant entering the cylinder head water chamber. When the thermostat is closed, the coolant flows into the exhaust pipe's hot water jacket through a bypass branch pipe. When the thermostat is open, the coolant flows into the exhaust pipe's hot water jacket through the large circulation channel. Regardless of the thermostat's state, the coolant always flows into the exhaust pipe's hot water jacket, utilizing exhaust waste heat to further increase the temperature. This avoids the diesel engine operating under excessively cold conditions, significantly reduces the risk of thermal fatigue cracks on the combustion chamber top surface caused by excessive temperature gradients, and extends the service life of the cylinder head.

[0019] 4. This invention strictly controls the outlet water temperature of the intercooler to below 50°C, ensuring that the temperature of the seawater after flowing through the intercooler remains below the temperature range for the large-scale crystallization of its main salt components. This effectively prevents high-temperature crystallization of seawater. At the same time, the preheating effect of the oil cooler in the first cooling circuit avoids local overcooling caused by the direct entry of low-temperature seawater into high-temperature components, further reducing crystal deposition caused by temperature fluctuations and significantly improving the blockage of the diesel engine's upper and lower water passages, intercooler, and oil cooler.

[0020] 5. This invention employs a dual-circuit parallel design, physically separating the cooling of the diesel engine body (engine block, cylinder head) from the cooling of the turbocharging system (intercooler, turbocharger). The first cooling circuit focuses on the thermal load management of the engine body, while the second cooling circuit optimizes the cooling of the turbocharged air and the turbocharger turbine housing. This arrangement allows the two circuits to independently adjust their flow rate and temperature according to the thermal load characteristics of their respective cooling components, avoiding the problem of mutual constraints on the cooling needs of different components in a single circuit. Furthermore, the dual-circuit design provides system redundancy protection: even if one cooling circuit is interrupted due to a fault or maintenance, the other circuit can still maintain basic cooling functions for critical components, significantly improving the operational reliability of marine diesel engines in complex marine environments.

[0021] 6. In this invention, the heat dissipation and coolant flow distribution of key structures such as the diesel engine block, cylinder head, intercooler, oil cooler, exhaust pipe, thermostat, turbocharger, and exhaust pipe are all optimized and determined through engineering simulation. By predicting and analyzing the heat load distribution and coolant flow state of each component during the design phase, parameters such as the water chamber structure, pipe diameter, and flow distribution ratio are optimized. This engineering simulation-based design method ensures a high degree of matching between the cooling device and the actual operating conditions of the diesel engine, avoids the blind spots of traditional experience-based design, significantly shortens the research and development cycle, and reduces testing costs. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram illustrating the structure and principle of the open-circuit DC dual-loop cooling method and device for diesel engines of the present invention; Figure 2 This is a schematic diagram of the parallel structure of the cylinders in the water chamber of the machine body; Figure 3 This is a schematic diagram of the casting structure of the dual-flow-channel outlet of a water pump.

[0023] Explanation of reference numerals in the attached figures: 1. Water pump; 101. First flow channel; 100. First cooling circuit; 102. Second flow channel; 200. Second cooling circuit; 2. Coolant; 3. Engine block water chamber; 4. Oil cooler; 5. Cylinder head water chamber; 6. Thermostat; 7. Exhaust pipe hot water jacket; 8. Intercooler; 9. Temperature sensor; 11. Exhaust pipe hot water jacket; 12. Turbocharger turbine housing cooling water jacket; 13. Marine seawater filter; 14. Turbocharger; 15. ECU; 16. Drain valve; 17. Flushing port; 18. Coolant drain channel. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] In the description of this invention, it should be understood that "ECU" is an abbreviation for Electronic Control Unit, which is used to receive temperature sensor signals and process, judge, and diagnose faults. Technical terms such as "top surface," "high," "lower," and "vertical" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "first," "second," "third," and similar words used in the embodiments of this invention do not indicate any order, quantity, or importance, but are only used to distinguish different components.

[0026] Words such as "include" or "contain" mean that the element preceding the word covers the elements listed after the word and their equivalents, without excluding other elements. Words such as "connect," "connect," or "fix" are not limited to a single connection or fixing method, but can include multiple connection or fixing methods, such as screw fastening, threaded connection, welding, etc.

[0027] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] A diesel engine open-circuit dual-loop cooling method and device, comprising: a water pump 1, a first flow channel 101, a first cooling circuit 100, a second flow channel 102, a second cooling circuit 200, coolant 2, engine block water chamber 3, an oil cooler 4, a cylinder head water chamber 5, a thermostat 6, an exhaust pipe hot water jacket 7, an intercooler 8, a temperature sensor 9, an exhaust pipe hot water jacket 11, a turbocharger turbine housing cooling water jacket 12, a marine seawater filter 13, a turbocharger 14, an ECU 15, a drain valve 16, a flushing port 17, and a cooling water discharge channel 18.

[0029] Coolant 2 is pressurized and distributed by water pump 1 to the first cooling circuit 100 and the second cooling circuit 200. First cooling circuit 100: Coolant 2 enters the diesel engine block water chamber 3 to cool the cylinder liners. The cooling water chambers of each cylinder in the engine block are designed in parallel, and coolant 2 is simultaneously distributed to each cylinder water chamber. Coolant 2 flowing out of the engine block water chamber 3 enters the oil cooler 4, and after being heated, it enters the cylinder head water chamber 5 to cool the top surface of the combustion chamber. Coolant 2 flowing out of the cylinder head water chamber 5 flows through the thermostat 6. When the thermostat 6 is closed, coolant 2 flows into the exhaust pipe hot water jacket 7 through the bypass branch pipe. When the thermostat 6 is open, coolant 2 flows into the exhaust pipe hot water jacket 7 through the large circulation channel and is finally discharged from the diesel engine block. The engine block water chamber 3, the oil cooler 4, and the cylinder head water chamber 5 are designed in series.

[0030] Second cooling circuit 200: Coolant 2 first enters intercooler 8 to cool the high-temperature boosted air compressed by turbocharger 14, then enters exhaust pipe hot water jacket 7, and after being heated, enters turbocharger turbine housing cooling water jacket 12, and finally enters exhaust pipe hot water jacket 7 to be discharged from the diesel engine body.

[0031] The first cooling circuit 100 and the second cooling circuit 200 merge at the hot water jacket 7 of the exhaust pipe and then discharge together.

[0032] The drain valve 16 is located at the lowest point of the cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the outboard motor assembly. It is used to discharge cooling water in the outboard motor assembly to ensure that no seawater remains.

[0033] The flushing inlet 17 is located at the water inlet of the cooling system, that is, at the connection of the marine seawater filter 13 before the water pump 1 inlet. It is used to flush the engine cooling system with clean water after the engine is stopped to prevent seawater corrosion and crystal blockage.

[0034] Preferably, the engine block water chamber 3, oil cooler 4 and cylinder head water chamber 5 in the first cooling circuit 100 are designed in series. The coolant 2 absorbs heat through the engine block water chamber 3 and is then preheated by the oil cooler 4 before finally entering the cylinder head water chamber 5, thus avoiding thermal shock to the top surface of the combustion chamber from the low temperature coolant 2. In the second cooling circuit 200, the intercooler 8, the exhaust pipe hot water jacket 11, and the turbocharger turbine housing cooling water jacket 12 are designed in series. The coolant 2 absorbs heat through the intercooler 8 and is then preheated by the exhaust pipe hot water jacket 11 before finally entering the turbocharger turbine housing cooling water jacket 12, thus avoiding the thermal shock of the low-temperature coolant 2 to the high-temperature turbine housing. The series design of the two circuits follows the temperature control logic of "heat absorption in the front stage, preheating in the back stage, and matching in the final stage", which realizes the step-by-step optimization of coolant temperature, improves the thermal reliability of key components, and simplifies the system structure.

[0035] Preferably, the cylinders in the water chamber 3 of the engine body are designed in parallel. The water flow rate of each cylinder is evenly distributed through the differential design of the cross-sectional area of ​​the water chamber. The cross-sectional area of ​​the water chamber is designed differently according to the heat load distribution of each cylinder: the cross-sectional area of ​​the water chamber of each cylinder in the middle is slightly larger than that of each cylinder at both ends, and the difference in cross-sectional area is controlled within ±8%, so as to ensure that the unevenness of the actual coolant flow 2 of each cylinder does not exceed ±5%.

[0036] The machine body adopts a three-parallel water chamber design. After the coolant 2 is pressurized by the water pump 1, it is simultaneously distributed to the water chambers of each cylinder to ensure that the water temperature and pressure of each cylinder are basically the same. The cross-sectional area of ​​the coolant cavity is differentiated based on the heat load distribution of each cylinder: the middle cylinders have higher heat loads, so the cross-sectional area of ​​the coolant cavity is slightly larger; the cylinders at both ends have lower heat loads, so the cross-sectional area of ​​the coolant cavity is slightly smaller; the difference in cross-sectional area is controlled within ±8%, ensuring that the actual coolant flow uniformity of each cylinder does not exceed ±5%. This design precisely matches the heat load requirements of each cylinder, achieving true uniform cooling of each cylinder, effectively improving the working consistency of each cylinder of the engine, reducing crankcase exhaust gas pressure, simplifying the coolant cavity structure, and improving casting processability and maintenance convenience.

[0037] Preferably, the intercooler 8 is designed according to rated operating conditions. The boundary condition during the design is the rated power of the engine. The thermal balance is achieved under the rated power, and the outlet water temperature of the intercooler 8 is controlled below 50°C. Using rated power as the design boundary condition, the heat exchange capacity, heat exchange area, and coolant flow rate of intercooler 8 are determined through thermal balance to ensure that the coolant outlet temperature of coolant 2 is controlled below 50°C under rated operating conditions. This design eliminates the need for flow control valves and complex closed-loop temperature control systems, avoiding the risk of temperature runaway due to valve jamming, sensor drift, or control failure, and fundamentally preventing high-temperature seawater crystallization blockage. Simultaneously, the precise rated operating condition design avoids redundancy and increased costs resulting from reserving structural margins for a wide operating range, enabling intercooler 8 to achieve optimal cooling efficiency and minimum flow resistance under rated operating conditions, aligning with the compact layout, high reliability, and low maintenance requirements of outboard motors.

[0038] Preferably, the thermostat 6 acts only on the engine, determining the opening and closing of the main circulation channel based on the engine temperature. The thermostat 6 is located on the cylinder head coolant outlet manifold, controlling only the opening and closing of the main circulation channel in the engine block circuit: during cold starts, the thermostat 6 closes the main circulation, and the coolant 2 flows through the bypass branch into the exhaust pipe's hot water jacket 7. The first cooling circuit 100 circulates rapidly between the engine block, oil cooler, and cylinder head, concentrating heat at the engine core for rapid warm-up. Simultaneously, the second cooling circuit 200 is unaffected by the thermostat 6, always operating at its designed flow rate, continuously cooling the intercooler 8 and the turbocharger turbine housing. This design decouples the two circuits, resulting in a single and clear control logic. It solves the engine overcooling problem while ensuring independent cooling of the turbocharger system, improving overall reliability and cold-start performance.

[0039] Preferably, the two flow channels at the outlet of water pump 1 are integrally formed by casting structure. The outlet diameter of the first flow channel 101 corresponds to the flow requirement of the first cooling circuit 100, and the outlet diameter of the second flow channel 102 corresponds to the flow requirement of the second cooling circuit 200. The flow split ratio is determined by engineering simulation based on the thermal balance analysis of the diesel engine under all operating conditions. The flow split ratio is precisely controlled by the cross-sectional area of ​​the cast flow channel and optimized through engineering simulation based on the thermal balance analysis of the diesel engine under all operating conditions. This design eliminates connection points and sealing surfaces, fundamentally eliminating the risk of leakage; the flow channel has a smooth transition, significantly reducing flow resistance; the flow split ratio is designed once and guaranteed permanently, unaffected by wear and tear during use; at the same time, the integrated structure greatly reduces space occupation and assembly processes, meeting the needs of outboard motors for compactness, high reliability, and maintenance-free operation.

[0040] Preferably, the intercooler 8 is equipped with a temperature sensor 9, which is electrically connected to the ECU 15 to provide real-time temperature feedback. The temperature sensor 9 converts the temperature signal into a digital quantity for acquisition and display, and then feeds it back to the ECU 15 for judgment. By monitoring the outlet temperature of the intercooler 8, the ECU can identify various fault modes such as insufficient water pump 1 flow, blockage of the intercooler 8, and abnormal seawater temperature, record fault codes, and prompt the operator for precise maintenance. This design not only verifies the anti-crystallization reliability of the intercooler 8 designed under rated operating conditions, but also realizes the transformation from passive maintenance to proactive prevention, improves the intelligence level and unattended operation adaptability of the outboard motor, and reduces the risk of failure and maintenance costs at sea.

[0041] Preferably, the system also includes a drain valve 16, which is located at the lowest point of the cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the outboard motor's lower assembly. By placing the single drain valve 16 at the geometrically lowest point of the entire cooling system—the bottom of the U-shaped underwater exhaust bend—water from the engine's internal cavity 3 is collected by the exhaust pipe's hot water jacket 7 and flows into the lower assembly's cooling water discharge channel 18 through a vertical connecting pipe, ultimately being discharged through the drain valve 16 at this lowest point. This design utilizes gravity to achieve complete gravity-fed drainage of residual seawater throughout the system, eliminating any dead zones. Combined with the flushing inlet 17 located at the cooling system's inlet, it forms a counter-current cleaning channel with "top in, bottom out," thoroughly removing salt and impurities from the system. Simultaneously, the single drain valve 16 simplifies operation and maintenance, reduces the risk of seal failure, fundamentally eliminates corrosion, crystallization, and freezing damage caused by residual seawater, and significantly extends the service life of the cooling system.

[0042] Preferably, the internal cavity 3 of the engine is located in the middle of the outboard motor. The cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the lower assembly is the geometric lowest point of the entire cooling system. Water from the internal cavity 3 is collected by the hot water jacket 7 of the exhaust pipe and flows into the cooling water discharge channel 18 of the lower assembly through the vertical connecting pipe, and is finally discharged by the drain valve 16. This design utilizes the height difference between the middle and lower assemblies to form a continuous liquid column. Gravity drives the residual seawater in the entire system to flow to the single lowest point for complete emptying, without the need for pump pressure or compressed air assistance. The vertical connecting pipe has a smooth downward slope and no horizontal section, eliminating air bubble accumulation and dead zones in the liquid sac. All circuits are uniformly collected into a single discharge channel, avoiding the problem of independent residues of each component caused by traditional decentralized layouts. At the same time, this structure is integrated with the U-shaped underwater exhaust bend, using its bottom concave point as a coolant collection space, realizing the dual functions of exhaust silencing and coolant discharge, saving the compact lower assembly space of the outboard motor, simplifying the structure, and improving reliability.

[0043] Preferably, it also includes a flushing water inlet 17, which is located at the water inlet of the cooling system. After the machine is stopped, clean water is injected through the flushing water inlet 17 and the residual seawater is discharged from the drain valve 16. A flushing inlet 17 with a quick-connect fitting is installed at the water inlet of the cooling system, forming a complete "one inlet, one outlet" maintenance system with the drain valve 16 at the lowest point of the lower unit. After shutdown, fresh water is injected along the normal coolant path by connecting a clean water hose through the quick-connect fitting. The clean water flows through the first cooling circuit 100, the second cooling circuit 200, and various components before being discharged from the drain valve 16, thoroughly removing residual salt, impurities, and sediment. This design utilizes the existing flow channels of the system to achieve full-coverage cleaning without any short-circuit dead zones; the quick-connect fitting is plug-and-play, allowing ordinary operators to complete flushing within minutes without the need for specialized tools or disassembly / reassembly; and in conjunction with the drain valve 16, it forms a closed-loop maintenance process of "draining-flushing-sealing," fundamentally eliminating the risks of corrosion, crystallization, and freezing damage caused by residual seawater, significantly extending the service life of the cooling system, and reducing maintenance costs and the risk of marine malfunctions.

[0044] The open-loop DC dual-circuit cooling method and device for diesel engines are detailed below: 1. Dual-loop cooling device structure 1) Structure of water pump 1: Water pump 1 is a centrifugal seawater pump, driven by a diesel engine crankshaft through gear transmission, with a rated speed of 3850 r / min to 4000 r / min, a rated flow rate of 80 L / min, and a head of ≥11 m. The inlet of water pump 1 is connected to the marine subsea filter through a DN100 rubber hose.

[0045] The water pump 1 has a specially customized outlet with two flow channels: a first flow channel 101 and a second flow channel 102. The coolant 2 is divided by a cast structure. The first flow channel 101 is DN80 and connects to the first cooling circuit 100. The second flow channel 102 is DN50 and connects to the second cooling circuit 200.

[0046] The first cooling circuit 100 distributes 65% to 75% of the total flow, and the second cooling circuit 200 distributes 25% to 35% of the total flow. The flow distribution ratio is determined by engineering simulation based on thermal balance analysis of the diesel engine under all operating conditions.

[0047] 2) Composition of the first cooling circuit 100: a. Body water cavity 3 Coolant 2, after passing through the first flow channel 101 at the outlet of water pump 1, enters the lower main inlet pipe of the diesel engine block water chamber 3 through a DN80 seamless steel pipe. The engine block water chamber 3 is a coolant flow channel located inside the six-cylinder in-line diesel engine block, with each cylinder's cooling water chamber designed in parallel. The main inlet pipe is arranged longitudinally along the engine block, connecting to the water chambers on the outer walls of each cylinder's cylinder liner through six independent inlet branch pipes. Each inlet branch pipe has a diameter of DN32, and the cross-sectional area of ​​the water chamber is differentiated according to the heat load distribution of each cylinder: the cross-sectional area of ​​the water chambers of the middle cylinders (cylinders 2, 3, 4, and 5) is slightly larger than that of the cylinders at both ends (cylinders 1 and 6), with the difference in cross-sectional area controlled within ±8% to ensure that the actual coolant 2 flow rate unevenness of each cylinder does not exceed ±5%.

[0048] Each cylinder's water chamber covers 80% of the cylinder liner's total length. The inner wall of the water chamber is equipped with spiral guide ribs, 3 mm high and 50 mm pitch, to enhance the turbulence of the coolant 2 and improve heat exchange efficiency. After absorbing heat from the cylinder liner within the engine block's water chamber 3, the coolant 2's temperature rises from 25℃~35℃ at the inlet to 55℃~65℃. Subsequently, the coolant is collected from the outlet branch pipes at the top of each cylinder's water chamber into the main outlet pipe of the engine block's water chamber 3.

[0049] b. Oil cooler 4 The main outlet pipe of the water chamber 3 in the engine block is connected to the inlet of the oil cooler 4 via a DN65 stainless steel corrugated pipe. The oil cooler 4 is a plate heat exchanger using titanium alloy plates. The plate thickness is 0.6 mm, the corrugation depth is 3.5 mm, and the effective heat exchange area is 2.8 m². 2 The design pressure is 1.0 MPa. The coolant 2 exchanges heat with the engine oil in a countercurrent manner in the oil cooler 4. The oil inlet temperature is 110℃~120℃ and the outlet temperature is 85℃~95℃. After absorbing the heat from the engine oil, the temperature of the coolant 2 is further increased to 70℃~80℃, achieving a preheating effect.

[0050] The outlet of the oil cooler 4 is connected to the main water inlet pipe of the cylinder head water chamber 5 via a DN65 seamless steel pipe.

[0051] c. Cylinder head water chamber 5 The cylinder head is a one-piece cast structure with an integrated cylinder head water chamber 5. Coolant 2 enters through the inlet manifold on one side of the cylinder head water chamber 5, flows within it, absorbs heat from the combustion chamber roof, and then flows out through the outlet manifold on the other side. The cylinder head water chamber 5 is designed to a pressure of 0.6 MPa. After absorbing heat from the combustion chamber roof within the cylinder head water chamber 5, the coolant 2's temperature rises to 85℃~95℃, effectively controlling the combustion chamber roof temperature to not exceed 220℃ and preventing thermal fatigue cracks caused by excessively low coolant 2 temperature.

[0052] d. Thermostat 6 The cylinder head water chamber 5 outlet main pipe is connected to the thermostat 6 via a DN50 connecting pipe. The thermostat 6 is a wax-type thermostat that only acts on the engine. It determines the opening and closing of the large circulation channel based on the engine temperature. The initial opening temperature is 75℃, the fully open temperature is 85℃, and the flow diameter is 50 mm.

[0053] When the temperature of coolant 2 is below 75℃, thermostat 6 closes the large circulation channel, and coolant 2 flows directly into the exhaust pipe insulated water jacket 7 through the bypass branch pipe to form a small circulation; at this time, coolant 2 does not pass through the large circulation channel, but still flows into the exhaust pipe insulated water jacket 7 for discharge.

[0054] When the temperature of coolant 2 reaches 75℃, the thermostat 6 gradually opens the large circulation channel; when the temperature reaches 85℃, it is fully opened, and all the coolant 2 flows into the exhaust pipe and is discharged through the hot water jacket 7.

[0055] The bypass branch pipe and the main circulation channel are connected in parallel, and their outlets are all connected to the exhaust pipe insulated water jacket 7. The thermostat 6 regulates the flow distribution of coolant 2 by controlling the opening of the main circulation channel, thereby achieving engine temperature control.

[0056] e. Exhaust pipe insulated water jacket 7 The outlet of thermostat 6 is connected to the exhaust pipe insulated water jacket 7 via a DN65 high-temperature resistant stainless steel pipe. The exhaust pipe insulated water jacket 7 has a double-layer structure, with the inner layer serving as the exhaust channel and the outer layer as the coolant channel. The gap between the two layers is 15 mm, and the material is heat-resistant stainless steel with a design temperature of 650℃. After absorbing the exhaust heat within the exhaust pipe insulated water jacket 7, the coolant 2's temperature rises to 95℃~105℃, and it is finally discharged from the diesel engine body through the DN80 discharge pipe.

[0057] 3) Composition of the second cooling circuit 200: a. Intercooler 8 The outlet of water pump 1, second flow channel 102, is connected to the inlet of intercooler 8 via a DN50 seamless steel pipe. Intercooler 8 is a tube-fin heat exchanger, with cooling tubes made of duplex stainless steel seamless tubing, measuring Φ16 mm × 1.5 mm, and aluminum corrugated fins with a fin spacing of 2.5 mm, providing an effective heat exchange area of ​​4.5 m². 2 The design pressure is 0.8 MPa. The outboard motor engine basically operates under rated conditions. The intercooler 8 is specially designed for rated conditions. That is, the boundary condition of the intercooler 8 during design is the rated power of the engine. Under the rated power, the thermal balance of the intercooler 8 can control the outlet water temperature below 50℃, effectively preventing seawater from crystallizing at high temperatures.

[0058] Intercooler 8 is connected to turbocharger 14 via a boost air pipeline. It is used to cool the high-temperature boost air compressed by the turbocharger. After compression, the boost air's temperature rises to 180℃~200℃. This high-temperature boost air flows into intercooler 8 through its boost air inlet, where it exchanges heat with coolant 2. The boost air temperature drops to 45℃~55℃, increasing intake air density and reducing engine thermal load. The cooled boost air flows out from the intercooler 8's boost air outlet and is distributed to each cylinder of the diesel engine via the intake manifold. Coolant 2 absorbs heat from the boost air within intercooler 8, and its outlet temperature is controlled between 40℃ and 50℃, preferably 45℃±3℃.

[0059] A temperature sensor 9 is installed at the outlet of the intercooler 8 to provide real-time temperature feedback to the ECU 15 for fault diagnosis. The temperature sensor 9 is a thermocouple temperature sensor with a range of 0℃ to 150℃ and an accuracy of ±1℃. It is installed 100 mm from the coolant outlet of the intercooler 8. By monitoring the coolant temperature 2 in the intercooler 8, the ECU 15 can determine the operating status of the cooling system and identify potential problems such as water pump failure, pipe blockage, and abnormal seawater temperature.

[0060] b. Exhaust pipe insulated water jacket 11 The outlet of the intercooler 8 is connected to the exhaust pipe insulated water jacket 11 via a DN50 high-temperature resistant stainless steel pipe. The exhaust pipe insulated water jacket 11 has a similar structure to the flue gas pipe insulated water jacket 7, featuring a double-layered design with a 12 mm gap, and is made of heat-resistant stainless steel. The coolant 2 absorbs heat from the exhaust manifold within the exhaust pipe insulated water jacket 11, raising its temperature to 70℃~85℃. This preheating process prevents thermal shock caused by the low-temperature coolant 2 directly entering the turbocharger turbine housing cooling water jacket 12.

[0061] c. Turbocharger turbine housing cooling water jacket 12 The outlet of the exhaust pipe's insulated water jacket 11 is connected to the turbocharger turbine housing cooling water jacket 12 via a DN40 stainless steel pipe. The turbocharger is an exhaust gas turbocharger, and the turbocharger turbine housing cooling water jacket 12 is an annular water channel cast onto the outer wall of the turbine housing, with a cross-sectional area of ​​350 mm². 2 The design pressure is 0.6 MPa. After absorbing heat from the turbine housing in the turbocharger, the coolant 2 rises to a temperature of 80℃~95℃, effectively controlling the surface temperature of the turbine housing to not exceed 350℃, thus preventing turbine blade coking and bearing overheating.

[0062] d. Merging and discharging The coolant outlet of the turbocharger turbine housing cooling water jacket 12 flows into the downstream of the exhaust pipe insulated water jacket 7 through a DN50 stainless steel pipe, and then merges with the coolant 2 discharged from the first cooling circuit 100 before being discharged together into the diesel engine body.

[0063] 4) Arrangement of drain valve 16 and flushing water outlet 17 The device is equipped with a drain valve 16 and a flushing port 17 for draining cooling water during the underloading of the outboard motor and for cleaning and maintenance of the system.

[0064] The drain valve 16 is located at the lowest point of the cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the outboard motor, which is the geometric lowest point of the entire cooling system.

[0065] The internal cavity of the engine (including the engine block water cavity 3, cylinder head water cavity 5, oil cooler 4, and exhaust pipe insulated water jacket 7) is located in the outboard motor mid-mount. The cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the lower mount is the geometric lowest point of the entire cooling system. Water from the internal cavity is collected by the exhaust pipe insulated water jacket 7 and flows into the lower mount cooling water discharge channel 18 through a vertical connecting pipe. Finally, it is discharged by the drain valve 16 located at the lowest point of the U-shape, using gravity to completely drain the residual seawater from the internal cavity of the engine, ensuring that no seawater remains.

[0066] The drain valve 16 is a ball valve with a diameter of DN20 and is made of 316 stainless steel. It is operated with a handle. The handle is marked in red, and a "Operate after shutdown" warning sign is attached. After opening the drain valve 16, the residual seawater in the cooling system is completely drained by gravity.

[0067] The flushing inlet 17 is located at the water inlet of the cooling system, that is, at the connection point of the marine seawater filter 13 before the inlet of the water pump 1, and is equipped with a quick-connect interface.

[0068] After shutdown, connect a clean water hose through the quick connector of flushing inlet 17 to inject fresh water or deionized water into the cooling system. After the clean water flows through the first cooling circuit 100, the second cooling circuit 200 and various components, it is discharged from the drain valve 16, carrying away residual salt and impurities, thus cleaning the engine cooling system.

[0069] 5) Working method: Step 1: Coolant 2 intake and distribution Seawater, used as coolant 2, is filtered by marine seawater filter 13 and then drawn in and pressurized by water pump 1. Water pump 1 is driven by the crankshaft of the diesel engine, and its speed is proportional to the diesel engine speed. The pressurized coolant 2 is divided into two streams at the outlet of water pump 1: the first cooling loop 100 has a flow rate of 65% to 75% of the total flow rate, and the second cooling loop 200 has a flow rate of 25% to 35% of the total flow rate. The flow split ratio is determined through engineering simulation based on thermal balance analysis of the diesel engine under all operating conditions.

[0070] Step Two: Execution Process of the First Cooling Circuit 100 Step 2.1: Cooling of the water chamber 3 of the machine body The coolant 2 from the first cooling circuit 100 enters the lower main water inlet pipe of the diesel engine block water chamber 3 through the outlet of water pump 1, the first flow channel 101, and the DN80 steel pipe. It is then simultaneously distributed to the water chambers on the outer walls of the cylinder liners of each cylinder via six parallel DN32 water inlet branch pipes. Guided by spiral guide ribs, the coolant 2 forms turbulent flow, undergoing forced convection heat exchange with the outer wall of the cylinder liner, absorbing heat from the piston-cylinder liner friction pair and the combustion gases conducted to the cylinder liner. Within the engine block water chamber 3, the coolant 2 flows from bottom to top, adapting to the heat load distribution of each cylinder. The middle cylinders, due to their higher heat load, have slightly larger water chamber cross-sectional areas to ensure uniform cooling intensity for each cylinder. After flowing through the engine block water chamber 3, the temperature of the coolant 2 rises from 25℃~35℃ at the inlet to 55℃~65℃.

[0071] Step 2.2: Preheat oil cooler 4 The coolant 2 flowing from the engine block water chamber 3 collects in the main outlet pipe and enters the oil cooler 4 through a DN65 stainless steel corrugated pipe. Inside the oil cooler 4, the coolant 2 exchanges heat with the high-temperature engine oil in a counter-current flow, absorbing heat from the oil and further raising its temperature to 70℃~80℃. This preheating process effectively increases the temperature of the coolant 2 before it enters the cylinder head water chamber 5, avoiding thermal shock caused by the low-temperature coolant 2 directly entering the cylinder head water chamber 5.

[0072] Step 2.3: Cooling the cylinder head water chamber 5 The cylinder head is a one-piece cast structure with an integrated cylinder head water chamber 5. Coolant 2 enters the cylinder head water chamber 5 from the outlet of the oil cooler 4 via a DN65 seamless steel pipe through the main inlet pipe on one side. After flowing within the cylinder head water chamber 5 and absorbing heat from the combustion chamber top surface, it flows out from the outlet pipe on the other side. The cylinder head water chamber 5 is designed to a pressure of 0.6 MPa. The coolant 2 temperature within the cylinder head water chamber 5 rises to 85℃~95℃, effectively controlling the combustion chamber top surface temperature to not exceed 220℃, thus preventing thermal fatigue cracks caused by excessively low coolant 2 temperature.

[0073] In this embodiment, the cylinder head water chamber 5 is a single integral structure with a basically uniform flow channel cross-sectional area, which is easy to manufacture and suitable for working conditions with relatively uniform heat load distribution.

[0074] Step 2.4: Thermostat 6 Adjustment Coolant 2 flows out of the cylinder head water chamber 5 and enters the thermostat 6. When the diesel engine is in the starting stage, the temperature of coolant 2 is below 75°C. The thermostat 6 closes the large circulation channel, and coolant 2 flows directly into the exhaust pipe heat insulation jacket 7 through the bypass branch pipe to form a small circulation, which quickly raises the engine temperature.

[0075] When the temperature of coolant 2 reaches 75℃, the thermostat 6 gradually opens the large circulation channel, and part of the coolant 2 flows into the exhaust pipe and the hot water jacket 7 through the large circulation channel; when the temperature reaches 85℃, it is fully opened, and all the coolant 2 flows into the exhaust pipe and the hot water jacket 7 through the large circulation channel and is discharged.

[0076] Step 2.5: Cooling and Discharge of Flue Gas Pipe Insulation Jacket 7 Coolant 2 enters the exhaust pipe insulated water jacket 7 through a stainless steel pipe, absorbs exhaust heat in the gap between the double-layer jacket, and the temperature is further increased to 95℃~105℃, and finally discharged from the diesel engine body through the DN80 discharge pipe.

[0077] Step 3: Execution process of the second cooling circuit 200 Step 3.1: Cooling the intercooler 8 The coolant 2 in the second cooling circuit 200 enters the intercooler 8 through the second flow channel 102 at the outlet of the water pump 1 and the DN50 steel pipe. There, it exchanges heat with the high-temperature pressurized air within the tube-fin heat exchange structure. The temperature of the pressurized air drops from 180℃~200℃ to 45℃~55℃, and the coolant 2 absorbs heat and its temperature rises to 40℃~50℃, preferably controlled at 45℃±3℃.

[0078] Step 3.2: Temperature Monitoring A temperature sensor 9 installed at the outlet of the intercooler 8 monitors the temperature of the coolant 2 in real time. In this embodiment, the temperature sensor 9 is a thermocouple temperature sensor with a range of 0℃ to 150℃, an accuracy of ±1℃, and a response time ≤2 seconds. The thermocouple measuring end is inserted into the coolant flow channel, 100 mm away from the coolant 2 outlet of the intercooler 8, and the signal output end is connected to the ECU 15 via a K-type compensation wire. The temperature sensor 9 provides real-time data feedback to the ECU 15. The ECU 15, by monitoring the coolant 2 temperature of the intercooler 8, determines the operating status of the cooling system for fault diagnosis. Step 3.3: Preheat the hot water jacket 11 of the exhaust pipe. After temperature regulation, the coolant 2 enters the exhaust pipe's insulating water jacket 11, where it absorbs heat from the exhaust manifold within the gap between the two jackets, raising its temperature from 40℃~50℃ to 70℃~85℃. This preheating process avoids thermal shock caused by the low-temperature coolant 2 directly entering the turbocharger turbine housing cooling water jacket 12.

[0079] Step 3.4: Cooling of the turbocharger turbine housing cooling water jacket 12 The preheated coolant 2 enters the turbocharger turbine housing cooling water jacket 12, absorbing heat from the turbine housing and bearing housing, raising its temperature to 80℃~95℃. This cooling process effectively controls the surface temperature of the turbine housing, preventing turbine blade coking, bearing overheating, and lubricant deterioration.

[0080] Step 3.5: Merging and Draining The coolant 2 flowing out of the turbocharger turbine housing cooling water jacket 12 flows into the downstream of the exhaust pipe insulated water jacket 7, and merges with the coolant 2 discharged from the first cooling circuit 100 before being discharged from the diesel engine body, completing the entire cooling cycle.

[0081] Step 4: Operation under different working conditions Step 4.1: Startup Phase When the diesel engine starts, the coolant 2 temperature is below 75℃. The thermostat 6 closes the large circulation channel, and the coolant 2 flows directly into the exhaust pipe's hot water jacket 7 through the bypass branch pipe, forming a small circulation. During this stage, the coolant 2 does not pass through the large circulation channel, and utilizes the exhaust waste heat to quickly raise the engine temperature to the normal operating range.

[0082] Step 4.2: Rated operating condition stage When the coolant 2 temperature reaches 85℃, the thermostat 6 fully opens the large circulation channel, and all the coolant 2 flows into the exhaust pipe's hot water jacket 7 through the large circulation channel. At this time, the first cooling circuit 100 and the second cooling circuit 200 operate according to the designed flow rate ratio, and the coolant 2 temperature in the intercooler 8 is determined by the rated operating condition design. The ECU 15 monitors the outlet temperature of the intercooler 8 in real time through the temperature sensor 9. When the temperature rises or falls abnormally, it records a fault code and prompts the operator to check the cooling system status.

[0083] Step 4.3: Shutdown and Maintenance Phase After shutdown, wait for the coolant 2 temperature to drop below 40℃, then perform the following steps in sequence: a. Open the drain valve 16 to completely drain the residual seawater in the cooling system using gravity, ensuring no seawater remains. The drain valve 16 is located at the lowest point of the cooling water discharge channel 18 at the bottom of the U-shaped underwater exhaust bend in the outboard motor, which is the geometric lowest point of the entire cooling system, ensuring thorough drainage and preventing corrosion from seawater stagnation and damage to components from low-temperature freezing expansion.

[0084] b. Rinse with clean water. Connect a clean water hose to the rinse water inlet 17 and inject fresh water or deionized water into the cooling system. After the clean water flows through the first cooling circuit 100, the second cooling circuit 200 and each component, it is discharged from the drain valve 18, carrying away residual salt and impurities, thus cleaning the engine cooling system.

[0085] c. Sealing and protection: When the equipment needs to be sealed for a long time, close the drain valve 16 after rinsing, inject the rust inhibitor solution through the rinsing port 17, then seal the rinsing port 17 and record the sealing date.

[0086] The above description is merely a detailed account of one embodiment of the present invention, but it is only a preferred embodiment and should not be considered as limiting the scope of the invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A diesel engine open-type DC dual-circuit cooling device, characterized in that: The diesel engine open-type DC dual-circuit cooling device includes a water pump, engine block water chamber, engine oil cooler, cylinder head water chamber, thermostat and exhaust pipe hot water jacket connected in series to form the first cooling circuit; The water pump, intercooler, exhaust pipe hot water jacket and flue pipe hot water jacket are connected in series to form a second cooling circuit; The water pump has a specially customized outlet, which is provided with a first flow channel and a second flow channel. After the water pump is pressurized, the first flow channel is connected to the first cooling circuit, and the second flow channel is connected to the second cooling circuit. The first cooling circuit and the second cooling circuit are designed in parallel. The cylinders in the water chamber of the machine body are designed in parallel.

2. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: In the first cooling circuit, the engine block water chamber, oil cooler, and cylinder head water chamber are designed in series, while in the second cooling circuit, the intercooler, exhaust pipe insulated water jacket, and turbocharger turbine housing cooling water jacket are designed in series.

3. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The cylinders in the water chamber of the engine block are designed in parallel. The water flow rate of each cylinder is evenly distributed through the differential design of the cross-sectional area of ​​the water chamber. The cross-sectional area of ​​the water chamber is designed differently according to the heat load distribution of each cylinder: the cross-sectional area of ​​the water chamber of each cylinder in the middle is slightly larger than that of each cylinder at both ends, and the difference in cross-sectional area is controlled within ±8%, ensuring that the actual coolant flow rate unevenness of each cylinder does not exceed ±5%.

4. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The intercooler is designed according to rated operating conditions. The boundary condition during the design is the rated power of the engine. The thermal balance is achieved under the rated power, and the outlet water temperature of the intercooler is controlled below 50℃.

5. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The thermostat only acts on the engine, and determines the opening and closing of the large circulation channel based on the engine temperature.

6. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The two flow channels at the water pump outlet are integrally formed by casting. The outlet diameter of the first flow channel corresponds to the flow requirement of the first cooling circuit, and the outlet diameter of the second flow channel corresponds to the flow requirement of the second cooling circuit. The flow split ratio is determined by engineering simulation based on thermal balance analysis of the diesel engine under all operating conditions.

7. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The intercooler is equipped with a temperature sensor, which is electrically connected to the ECU to provide real-time temperature feedback.

8. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The device also includes a drain valve, which is located at the lowest point of the cooling water discharge channel at the bottom of the U-shaped underwater exhaust bend in the outboard motor.

9. The diesel engine open-circuit DC dual-loop cooling device according to claim 1, characterized in that: The internal cavity of the engine is located in the outboard motor. The cooling water discharge channel at the bottom of the U-shaped underwater exhaust bend in the lower assembly is the geometric lowest point of the entire cooling system. Water from the internal cavity is collected by the hot water jacket of the exhaust pipe and flows into the cooling water discharge channel of the lower assembly through the vertical connecting pipe, and is finally discharged by the drain valve. The device also includes a flushing water inlet, which is located at the water inlet of the cooling system. After the engine stops, clean water is injected through the flushing water inlet, and the residual seawater is discharged through the drain valve.

10. A method using the diesel engine open-circuit DC dual-loop cooling device according to claims 1-9, characterized in that: Step 1: The coolant is pressurized by the water pump and distributed to the first cooling circuit and the second cooling circuit; Step 2: In the first cooling circuit, the coolant enters the diesel engine block water chamber to cool the cylinder liners, then flows out into the oil cooler. After being heated, it enters the cylinder head water chamber to cool the top surface of the combustion chamber, and then flows out to the thermostat. When the thermostat is closed, the coolant flows into the exhaust pipe hot water jacket through the bypass branch pipe. When the thermostat is open, the coolant flows into the exhaust pipe hot water jacket through the large circulation channel and is finally discharged. Step 3: In the second cooling circuit, the coolant first enters the intercooler to cool the high-temperature boosted air after being compressed by the turbocharger, then enters the exhaust pipe hot water jacket, and after being heated, enters the turbocharger turbine housing cooling water jacket, and finally exits through the exhaust pipe hot water jacket. The first cooling circuit and the second cooling circuit converge at the hot water jacket of the exhaust pipe.

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