An optimized structure of fuel atomization injection for a methanol engine

Abstract

The application relates to a methanol engine fuel atomization injection optimization structure, which comprises a nozzle body, a needle valve, a temperature-sensitive displacement driving assembly and a shielding sliding sleeve; a low-temperature cavitation-promoting micro-texture area and a high-temperature cavitation-suppressing micro-texture area are arranged on the outer surface of the needle valve in an axial direction; the temperature-sensitive displacement driving assembly is used for outputting axial displacement in response to the change of the ambient temperature of the head of the nozzle body and driving the shielding sliding sleeve to switch between a first limit position and a second limit position; when the shielding sliding sleeve is located at the first limit position, the high-temperature cavitation-suppressing micro-texture area is shielded and the low-temperature cavitation-promoting micro-texture area is exposed to methanol fluid; when the shielding sliding sleeve is located at the second limit position, the low-temperature cavitation-promoting micro-texture area is shielded and the high-temperature cavitation-suppressing micro-texture area is exposed to methanol fluid; the flow in the nozzle body forms a cavitation-enhanced atomization state in a low-temperature working condition and a stable-flowing cavitation-suppressing state in a high-temperature working condition. The application can automatically trigger regulation and control in response to temperature without additional sensors and actuators.

Description

Technical Field

[0001] This application relates to the technical field of engines, and in particular to an optimized structure for fuel atomization injection in a methanol engine. Background Technology

[0002] Methanol, due to its wide availability, high oxygen content, and relatively clean combustion, has become one of the important development directions for alternative fuels in engines. For methanol engines, the fuel atomization quality and spray stability of the injector directly affect combustion formation, cold start performance, thermal efficiency, and emission levels. Therefore, optimizing the internal flow state of the nozzle has always been a key issue in methanol injection technology.

[0003] Compared to conventional fuels, methanol exhibits more sensitive cavitation and flashing behavior to temperature changes when the local pressure in the nozzle throttling zone drops sharply. This is especially true when the nozzle head temperature experiences different operating conditions, such as cold start at low temperatures, steady-state at room temperature, and high-load hot soaking. These changes significantly alter the internal flow state of the nozzle. For instance, at lower nozzle head temperatures, methanol atomization and fragmentation are insufficient, leading to problems like larger droplet sizes and inadequate combustion preparation. Conversely, as the nozzle head temperature rises, the increased saturated vapor pressure of methanol, combined with the localized low pressure in the throttling zone, can easily induce excessive cavitation or flashing, resulting in spray pattern fluctuations, decreased flow stability, and localized nozzle cavitation wear.

[0004] Existing injector optimization solutions often employ fixed nozzle geometry, fixed needle valve clearance, injection pressure control, or fuel preheating. These solutions are typically optimized around a specific design condition, resulting in a relatively fixed flow boundary layer state and cavitation intensity within the nozzle, making it difficult to adaptively adjust to changes in nozzle tip temperature. Therefore, cavitation-enhancing designs that improve atomization at low temperatures often amplify the risk of excessive cavitation and cavitation erosion at high temperatures; conversely, structures that stabilize flow and suppress cavitation at high temperatures may lead to insufficient atomization at low temperatures.

[0005] In addition, while relying solely on external heating or electronic control strategies can improve cryogenic injection to some extent, they usually cannot directly reconstruct the local boundary layer state near the nozzle throttling zone, nor can they achieve temperature-dependent adaptive switching of the flow interface characteristics inside the nozzle without introducing additional complex actuators.

[0006] Therefore, it is necessary to propose a fuel atomization injection optimization structure suitable for methanol engine injectors, so as to both enhance beneficial cavitation to improve atomization under low temperature conditions and suppress excessive cavitation to maintain spray stability and reduce cavitation risk under high temperature conditions. Summary of the Invention

[0007] To address the contradiction between existing methanol engine injectors' inability to simultaneously meet the requirements of low-temperature atomization and high-temperature excessive cavitation, erosion, and spray instability, this application provides an optimized fuel atomization injection structure for methanol engines.

[0008] The optimized fuel atomization injection structure for a methanol engine provided in this application adopts the following technical solution: An optimized structure for methanol engine fuel atomization injection includes a nozzle body, a needle valve coaxially and reciprocally slidably disposed within the nozzle body, a temperature-sensitive displacement drive assembly disposed within the head wall of the nozzle body, and a shielding sleeve coaxially sleeved around the outer periphery of the needle valve and slidably engaged with the inner wall of the nozzle body. The annular gap between the inner wall of the shielding sleeve and the outer wall of the needle valve constitutes the methanol main flow channel. The outer surface of the needle valve is provided with low-temperature cavitation-promoting microtexture zones and high-temperature cavitation-suppressing microtexture zones spaced apart along the axial direction; The temperature-sensitive displacement drive component is thermally coupled to the nozzle head and is used to output axial displacement in response to changes in the ambient temperature of the nozzle head, and drive the shielding sleeve to switch between the first limit position and the second limit position. When the shielding sleeve is in the first extreme position, the high-temperature cavitation-suppressing microtexture region is shielded and the low-temperature cavitation-promoting microtexture region is exposed to the methanol fluid; when the shielding sleeve is in the second extreme position, the low-temperature cavitation-promoting microtexture region is shielded and the high-temperature cavitation-suppressing microtexture region is exposed to the methanol fluid; so that the nozzle body flow forms a cavitation-promoting enhanced atomization state under low-temperature conditions and a stable flow suppressing excessive cavitation state under high-temperature conditions.

[0009] Furthermore, a return spring is connected between the shielding sleeve and the nozzle body, and the return spring is used to provide a preload force to bring the shielding sleeve toward the first extreme position; The temperature-sensitive displacement drive assembly and the reset spring together constitute a switching mechanism with temperature hysteresis characteristics. When the ambient temperature at the nozzle head rises above the second threshold, the shielding sleeve is driven to switch to the second extreme position. When the ambient temperature at the nozzle head drops below the first threshold, the shielding sleeve is returned to the first extreme position. The second threshold is greater than the first threshold.

[0010] Furthermore, the temperature-sensitive displacement drive component includes a phase change energy storage cavity, a phase change material layer filled in the phase change energy storage cavity, and a displacement transmission mechanism, wherein the phase change temperature range of the phase change material layer is between the first threshold and the second threshold.

[0011] Furthermore, the phase change energy storage cavity is an annular chamber surrounding the nozzle head, and the side wall of the phase change energy storage cavity facing the combustion chamber is provided with an array of outwardly protruding heat-conducting fins, and the side wall of the phase change energy storage cavity facing the inner cavity of the nozzle body is provided with a ceramic heat insulation layer.

[0012] Furthermore, the displacement transmission mechanism includes a force-receiving ring cavity and a force-transmitting ring cavity arranged coaxially. One end of the force-receiving ring cavity is sealed and connected to the phase change energy storage cavity, and the other end is connected to the input end of the force-transmitting ring cavity. A force-receiving ring piston is sealed and slidably disposed in the force-receiving ring cavity, and a force-transmitting ring piston is sealed and slidably disposed in the force-transmitting ring cavity. The force-receiving ring cavity and the force-transmitting ring cavity are filled with transmission fluid located between the force-receiving ring piston and the force-transmitting ring piston. The cross-sectional area of ​​the force-receiving ring piston is larger than the cross-sectional area of ​​the force-transmitting ring piston. A number of force-transmitting rods are fixedly connected to one end of the force-transmitting annular piston away from the force-receiving annular piston for contacting the shielding sleeve.

[0013] Furthermore, the inner wall of the shielding sleeve has a shielding section and two working sections located at both ends of the shielding section, and the distance between the working section and the outer wall of the needle valve is greater than the distance between the shielding section and the outer wall of the needle valve. When the masking sleeve moves to the point where the masking section is aligned with a microtexture area, the function of that microtexture area is suppressed; when the masking sleeve moves to one of the working sections and is aligned with a microtexture area, the function of that microtexture area is activated.

[0014] Furthermore, the nozzle body has a guide ring groove on its inner peripheral wall, and the shielding sleeve has a guide flange that is slidably disposed in the guide ring groove on its outer peripheral wall. The force transmission rod extends out of the force transmission ring cavity and enters the guide ring groove and abuts against the guide flange. The reset spring is disposed in the guide ring groove and abuts against the end of the guide flange away from the force transmission rod. Furthermore, when the shielding sleeve slides to the first and second limit positions, the outer peripheral wall of the shielding sleeve closes the opening of the guide ring groove.

[0015] Furthermore, the low-temperature cavitation-inducing microtexture region is a microscale array used to induce local separation of the methanol fluid boundary layer, and the high-temperature cavitation-suppressing microtexture region is a smooth microchannel array used to maintain the methanol fluid boundary layer adhering to the wall.

[0016] Furthermore, the high-temperature cavitation-suppressing microtexture region and the low-temperature cavitation-promoting microtexture region are sequentially spaced along the methanol fluid flow direction on the outer surface of the needle valve, and the effective shielding length of the shielding sleeve is not less than the sum of the axial length of the low-temperature cavitation-promoting microtexture region or the high-temperature cavitation-suppressing microtexture region and the maximum lift of the needle valve, so that when the shielding sleeve is in any extreme position, only one microtexture region is exposed to the methanol fluid and is not affected by the opening and closing of the needle valve.

[0017] Furthermore, the surfaces of both the microscale array and the smooth microchannel array are covered with a fluorine-doped diamond-like coating to improve the surface's methanol-repellent properties while maintaining the coating's hardness.

[0018] In summary, the beneficial technical effects of this application are as follows: 1. By setting the temperature-sensitive displacement drive component, the low-temperature cavitation-promoting microtexture zone and the high-temperature cavitation-suppressing microtexture zone can be exposed in an adaptive manner according to temperature. This allows the same injector to enhance beneficial cavitation to improve atomization under low-temperature conditions and suppress excessive cavitation to stabilize spray under high-temperature conditions. This effectively improves the current situation where the existing fixed throttling structure can only be biased towards single-condition optimization and is difficult to take into account the temperature requirements of multiple operating conditions. 2. A passive switching mechanism with temperature hysteresis characteristics is formed by using a phase change material layer, a force-bearing ring cavity, a force-transmitting ring cavity, and a return spring. Different thresholds are corresponding to the heating and cooling processes, avoiding frequent fluctuations in the critical temperature zone and repeated switching of working modes. Compared with active execution schemes that rely on electronic control, this switching mechanism does not require additional sensors and actuators and can still maintain stable operation in high-frequency injection and high-temperature vibration environments. 3. By setting the temperature-sensitive displacement drive component inside the nozzle head wall and establishing external thermal coupling and internal thermal isolation with the ceramic insulation layer through the heat-conducting fin array, the phase change material layer mainly responds to the real thermal state of the nozzle head, rather than the transient temperature fluctuation of the fuel, thereby improving the working condition targeting and reliability of the switching judgment. 4. By covering the surface of the microscale array and the smooth microchannel array with a fluorine-doped diamond-like coating, the surface methanol repellency is improved while maintaining high hardness and wear resistance. This helps to stabilize the boundary morphology of the microtexture and slow down the performance degradation caused by methanol erosion, local cavitation and long-term wear, thereby ensuring that the nozzle maintains a relatively stable atomization optimization effect throughout its entire life cycle. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application; Figure 2 This is a cross-sectional view of the shielding sleeve in the first extreme position according to the embodiments of this application; Figure 3 This is a cross-sectional view of the shielding sleeve in the second extreme position according to the embodiments of this application; Figure 4 yes Figure 2 A magnified view of part A in the diagram.

[0020] Explanation of reference numerals in the attached figures: 1. Nozzle body; 11. Valve seat; 12. Guide ring groove; 2. Needle valve; 3. Shielding sleeve; 31. Shielding section; 32. Working section; 33. Guide flange; 4. Low-temperature cavitation-induced microtexture region; 41. Microscale array; 5. High-temperature cavitation suppression microtexture region; 51. Smooth micro-channel array; 6. Return spring; 71. Phase change energy storage cavity; 72. Phase change material layer; 73. Thermally conductive fin array; 74. Ceramic insulation layer; 81. Force-receiving ring cavity; 82. Force-transmitting ring cavity; 83. Force-receiving ring piston; 84. Force-transmitting ring piston; 85. Force-transmitting rod. Detailed Implementation

[0021] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] This application discloses an optimized fuel atomization injection structure for a methanol engine. (Refer to...) Figures 1-4 It includes a nozzle body 1, a needle valve 2 coaxially reciprocatingly sliding within the nozzle body 1, a temperature-sensitive displacement drive assembly disposed within the head wall of the nozzle body 1, and a shielding sleeve 3 coaxially sleeved around the outer periphery of the needle valve 2 and slidingly engaged with the inner wall of the nozzle body 1. The annular gap between the inner wall of the shielding sleeve 3 and the outer wall of the needle valve 2 constitutes the methanol main channel.

[0023] The nozzle body 1 has a central inner hole that extends axially. The needle valve 2 is installed in the central inner hole with a precision clearance fit. The needle valve 2 can reciprocate axially under external force to open or close the nozzle orifice on the valve seat 11 at the end of the nozzle body 1. The head of the nozzle body 1 refers to the end area of ​​the nozzle body 1 near the engine combustion chamber. This area directly bears the heat return conduction of the high-temperature gas in the combustion chamber during engine operation.

[0024] The temperature-sensitive displacement drive assembly is embedded in the wall of the nozzle body 1 head, and its temperature-sensing end is tightly thermally coupled to the wall of the nozzle body 1 head to sense changes in the ambient temperature of the area in real time. The shielding sleeve 3 has an annular sleeve structure and is coaxially sleeved on the outer cylindrical surface of the needle valve 2. A precision sliding fit clearance is formed between its outer cylindrical surface and the inner wall of the nozzle body 1; and the shielding sleeve 3 can slide axially under the driving action of the temperature-sensitive displacement drive assembly.

[0025] The outer surface of the needle valve 2 is axially spaced with a low-temperature cavitation-promoting microtexture region 4 and a high-temperature cavitation-suppressing microtexture region 5, which are arranged upstream and downstream along the axial direction of the needle valve 2. The power output end of the aforementioned temperature-sensitive displacement drive component is connected to the shielding sleeve 3 for transmission, and is used to output axial displacement in response to changes in the ambient temperature of the nozzle body 1 head, and drive the shielding sleeve 3 to switch between a first limit position and a second limit position. Specifically, when the shielding sleeve 3 is in the first limit position, its axial position allows the high-temperature cavitation-suppressing microtexture region 5 to be effectively shielded while the low-temperature cavitation-promoting microtexture region 4 is exposed to the methanol fluid flowing through the annular flow channel between the outer surface of the needle valve 2 and the inner wall of the nozzle body 1; when the shielding sleeve 3 is in the second limit position, its axial position allows the low-temperature cavitation-promoting microtexture region 4 to be effectively shielded while the high-temperature cavitation-suppressing microtexture region 5 is exposed to the methanol fluid.

[0026] Furthermore, a return spring 6 is connected between the shielding sleeve 3 and the nozzle body 1. The return spring 6 provides a preload force to bring the shielding sleeve 3 towards the first extreme position. The temperature-sensitive displacement drive assembly and the return spring 6 together constitute a switching mechanism with temperature hysteresis characteristics. The return spring 6 can be made of high-temperature resistant spring steel or nickel-based elastic alloy to ensure long-term stable elastic modulus and fatigue life under the thermal environment of the nozzle head 1. The switching mechanism is specifically configured such that when the ambient temperature of the nozzle head 1 rises above a second threshold, the shielding sleeve 3 is driven to switch to the second extreme position, and when the ambient temperature of the nozzle head 1 drops below the first threshold, the shielding sleeve 3 returns to the first extreme position, wherein the second threshold is greater than the first threshold. Specifically, when the temperature drops, due to the hysteresis of the retraction (or phase change return) of the temperature-sensitive displacement drive component, only when the temperature drops below the first threshold is its output thrust / displacement insufficient to maintain the shielding sleeve 3 in the second extreme position, and the return spring 6 pushes the shielding sleeve 3 back to the first extreme position. The introduction of this hysteresis window can effectively prevent the shielding sleeve 3 from high-frequency oscillation switching when the engine frequently accelerates and decelerates in the critical temperature range, thereby significantly improving the working stability of the atomizing nozzle.

[0027] Specifically, refer to Figure 2 and Figure 3The temperature-sensitive displacement drive component includes a phase change energy storage cavity 71, a phase change material layer 72 filled within the phase change energy storage cavity 71, and a displacement transmission mechanism. The phase change energy storage cavity 71 is an annular chamber surrounding the head of the nozzle body 1, integrally formed from the wall material of the nozzle body 1 through precision machining or additive manufacturing processes, or formed by sealing and welding an independent cavity component to the head of the nozzle body 1. The phase change material layer 72 is formed by filling a solid-liquid phase change type functional material, with its phase change temperature range between a first threshold and a second threshold. In a specific example, the first threshold is set to 60℃~70℃, and the second threshold is set to 75℃~90℃. The phase change material layer 72 is selected from paraffin-based composite phase change materials, fatty acid eutectic phase change materials, or other encapsulated phase change materials with significant volume change characteristics within the temperature range of 70℃~85℃.

[0028] The outer wall of the phase change energy storage cavity 71 facing the combustion chamber has an outwardly protruding array of heat-conducting fins 73, which increases the heat exchange area with the high-temperature gas in the combustion chamber, enhances the heat absorption rate of the phase change material layer 72, and improves the temperature rise response sensitivity. The inner wall of the phase change energy storage cavity 71 facing the inner cavity of the nozzle body 1 has a ceramic heat insulation layer 74. This ceramic heat insulation layer 74 can be a plasma-sprayed zirconium oxide coating or a silicon nitride ceramic bushing, which is used to block the reverse conduction of heat from the phase change energy storage cavity 71 to the methanol fluid in the nozzle body 1, avoids the methanol fuel being unintendedly heated before flowing through the head of the nozzle body 1, and ensures that methanol still reaches the microtexture region of the needle valve 2 at a lower temperature under low-temperature conditions, thereby maintaining the effectiveness of the cavitation microtexture.

[0029] The displacement transmission mechanism is used to convert the volume change of the phase change material layer 72 into the axial linear displacement of the shielding sleeve 3. Specifically, refer to Figure 2 , Figure 3 and Figure 4The displacement transmission mechanism includes a coaxially arranged force-receiving ring cavity 81 and a force-transmitting ring cavity 82. Both the force-receiving ring cavity 81 and the force-transmitting ring cavity 82 are machined within the wall thickness of the nozzle body 1 head, and both are coaxially arranged with the needle valve 2. One end of the force-receiving ring cavity 81 is sealed and connected to the phase change energy storage cavity 71, and the other end is connected to the input end of the force-transmitting ring cavity 82 through an internal connecting channel. A force-receiving annular piston 83 is sealed and slidably arranged in the force-receiving ring cavity 81. One end face of the force-receiving annular piston 83 is exposed to the phase change material layer 72 and directly bears the pressure generated by the melting and expansion of the phase change material. A force-transmitting annular piston 84 is sealed and slidably arranged in the force-transmitting ring cavity 82. The force-receiving ring cavity 81 and the force-transmitting ring cavity 82 are filled with a transmission fluid, which fills the sealed space between the force-receiving annular piston 83 and the force-transmitting annular piston 84. In this embodiment, the transmission fluid can be silicone oil, fluorinated inert liquid, or heat-resistant synthetic oil. The effective pressure-bearing cross-sectional area of ​​the force-bearing annular piston 83 is designed to be larger than that of the force-transmitting annular piston 84. The area ratio of the two is preferably 2:1 to 5:1 according to the required stroke magnification factor, so that sufficient shielding sleeve 3 switching stroke can still be obtained when the volume change of the phase change material layer 72 is small.

[0030] Furthermore, a plurality of force transmission rods 85 for contacting the shielding sleeve 3 are fixedly connected to the end of the force transmission annular piston 84 away from the force-receiving annular piston 83. Specifically, multiple force transmission rods 85 are provided and evenly spaced along the circumference, and their ends abut against the end face of the shielding sleeve 3 away from the return spring 6. Spherical ends or hard contact pads can be provided at the ends of the force transmission rods 85 to reduce contact stress and compensate for minor coaxiality errors. When the shielding sleeve 3 is in the first extreme position, the return spring 6 is in a compressed state, and the ends of the force transmission rods 85 remain in contact with the shielding sleeve 3. When the shielding sleeve 3 is in the second extreme position, the return spring 6 is in a more compressed state, and most of the force transmission rods 85 extend out of the force transmission annular cavity 82.

[0031] Therefore, during the engine cold start phase, the nozzle body 1 head temperature is below the first threshold, the phase change material layer 72 remains in a solid state of contraction, the force-bearing annular piston 83 is in the retracted position, the pressure in the hydraulic system is low, and the shielding sleeve 3 is stably held in the first limit position under the preload of the return spring 6. At this time, the low-temperature cavitation-enhancing microtexture zone 4 is exposed, and the flow inside the nozzle body 1 enters a cavitation-enhancing atomization state. When the methanol fluid flows through the low-temperature cavitation-enhancing microtexture zone, it forms controllable boundary layer local separation and moderate cavitation nuclei, thereby improving the initial atomization capability under low-temperature conditions and improving the cold start combustion preparation process.

[0032] As the engine heats up during operation, the heat recirculation from the combustion chamber is efficiently transmitted to the phase change energy storage cavity 71 via the heat-conducting fin array 73. When the ambient temperature at the nozzle body 1 head enters the range between the first threshold and the second threshold, the phase change material layer 72 begins to enter the phase change stage. However, due to the combined effect of the reaction force of the reset spring 6 and the latent heat absorption process of the phase change material layer 72, the shielding sleeve 3 does not immediately switch back and forth, but maintains the current working position, forming a temperature hysteresis zone.

[0033] When the ambient temperature at the nozzle head 1 rises further above the second threshold, the phase change material layer 72 completes a solid-liquid phase change and undergoes significant volume expansion, pushing the force-bearing annular piston 83 to move axially. The transmission fluid then uniformly transmits pressure to the force-transmitting annular piston 84. Since the area of ​​the force-bearing annular piston 83 is larger than that of the force-transmitting annular piston 84, the force-transmitting annular piston 84 will generate an amplified axial output displacement. Through the circumferentially distributed force transmission rods 85 fixed to its end face, it pushes the shielding sleeve 3 to overcome the elastic force of the return spring 6 and slide to the second limit position. At this time, the high-temperature cavitation-suppressing microtexture region 5 is exposed, and the internal flow of the nozzle body 1 switches to a stable flow state that suppresses excessive cavitation. This can maintain the methanol fluid boundary layer adhering to the wall and suppress localized excessive cavitation, helping to maintain the stability of the spray pattern and the amount of fuel injected, and reducing the risk of cavitation erosion under high-temperature conditions.

[0034] During the engine load reduction or shutdown cooling phase, when the ambient temperature at the nozzle head 1 drops, the phase change material layer 72 does not immediately and completely reverse reset at the second threshold. Instead, as the temperature further decreases, the output displacement weakens to a level insufficient to maintain the shielding sleeve 3 at the second limit position after it falls below the first threshold. Under the direct action of the reset spring 6, the shielding sleeve 3 resets to the first limit position, and the internal flow of the nozzle body 1 returns to the cavitation-enhanced atomization state, preparing for the next round of low-temperature operation.

[0035] Therefore, by utilizing the physical property response of phase change materials and the principle of hydraulic amplification in series with an annular piston, reliable switching of the position of the shielding sleeve 3 as the temperature changes is achieved without any external sensors, controllers, or electric drive. Furthermore, the existence of a temperature hysteresis zone avoids frequent vibrations of the shielding sleeve 3 within the critical temperature range, thus ensuring stable switching of the injection mode of the nozzle body 1 and realizing temperature-adaptive dual-mode switching of the micro-texture of the methanol engine needle valve 2. Moreover, the coaxial arrangement of the force-bearing annular cavity 81 and the force-transmitting annular cavity 82 perfectly matches the rotating geometry of the nozzle body 1 head, achieving stroke amplification within a very small annular space. This allows the micron-level volume expansion of the phase change material to be converted into an axial displacement sufficient to drive the shielding sleeve 3 to complete a millimeter-level full-stroke switching. The circumferentially uniform arrangement of the force transmission rod 85 ensures that the driving force is evenly distributed along the end face of the shielding sleeve 3, eliminating off-center load torque and significantly improving the smoothness and reliability of the precision sliding pair under high-pressure environments.

[0036] More specifically, refer to Figure 2 , Figure 3 and Figure 4 The low-temperature cavitation-inducing microtexture region 4 is configured as a microscale array 41 for initiating local boundary layer separation of the methanol fluid. The microscale array 41 consists of multiple scale units arranged in a staggered pattern along the axial and circumferential directions of the needle valve 2. Each scale unit has a wedge-shaped streamlined profile with a lower leading edge and a higher trailing edge. Its leading edge faces the direction of methanol flow, and its trailing edge forms a steep backflow step. When the methanol fluid flows through the unshielded microscale array 41, local boundary layer separation occurs at the backflow step of the scale unit, forming a low-pressure backflow zone and inducing cavitation initiation. This compensates for the insufficient cavitation capacity of the methanol fluid itself under low-temperature conditions, significantly improving atomization quality.

[0037] The high-temperature cavitation suppression microtexture region 5 is configured as a smooth micro-guide channel array 51 to maintain the boundary layer adhesion of the methanol fluid. The smooth micro-guide channel array 51 consists of multiple micron-sized shallow channels extending axially along the needle valve 2 and uniformly distributed circumferentially. The channel depth is less than one-tenth of the boundary layer thickness, and the channel cross-section has a circular arc or parabolic transition without steep steps. When the methanol fluid flows through the unshielded smooth micro-guide channel array 51, the channels produce a gentle guiding effect on the boundary layer, suppressing boundary layer separation and pressure fluctuations. This effectively delays cavitation initiation and reduces cavitation intensity under high-temperature conditions, preventing jet instability and structural cavitation erosion caused by excessive cavitation.

[0038] It should be noted that the inner wall of the shielding sleeve 3 has a shielding section 31 and two working sections 32 located at both ends of the shielding section 31. The distance between the working section 32 and the outer wall of the needle valve 2 is greater than the distance between the shielding section 31 and the outer wall of the needle valve 2, and the shielding section 31 and the working section 32 are smoothly transitioned. When the shielding sleeve 3 moves to the point where the shielding section 31 is aligned with a microtextured region, the distance between the shielding section 31 and the outer wall of the needle valve 2 is small, which restricts the flow field between the microtextured region and the shielding section 31, reduces the shear layer thickness, and makes it difficult for the vortex structure to develop. This weakens the separation induction effect of the cavitation-inducing microscale array 41 or the flow guiding and wall-adhering effect of the smooth micro-guide channel array 51, so that the flow regulation function of the microtextured region on the methanol fluid is suppressed. When the shielding sleeve 3 moves to one of the working sections 32 and aligns with a microtextured area, the distance between the working section 32 and the outer wall of the needle valve 2 is large, and the methanol fluid can fully contact the microtextured surface, thus activating the cavitation or cavitation suppression function of the microtextured area.

[0039] Furthermore, to ensure that the shielding section 31 does not introduce new cavitation sources due to excessive throttling after its operation, the minimum distance between the shielding section 31 and the outer wall of the needle valve 2 should be designed in conjunction with the methanol flow rate, viscosity, and injection pressure. In a specific example, the characteristic height or depth of the microtextured region is 5μm to 30μm; the radial distance between the shielding section 31 and the outer wall of the needle valve 2 can be 20μm to 50μm, so that the flow field disturbance near the top of the microtextured region is suppressed but the overall annular gap still maintains continuous flow; the radial distance between the working section 32 and the outer wall of the needle valve 2 can be 50μm to 120μm, so that the mainstream can form a shear layer and vortex structure of sufficient thickness above the microtextured region, thereby amplifying the regulatory effect of the microtextured region on the boundary layer of the methanol fluid.

[0040] Furthermore, a guide ring groove 12 is provided on the inner peripheral wall of the nozzle body 1, and a guide flange 33 is slidably fixed in the guide ring groove 12 on the outer peripheral wall of the shielding sleeve 3. The force transmission rod 85 extends out from the force transmission ring cavity 82 and enters the guide ring groove 12, abutting against the guide flange 33. The return spring 6 is provided in the guide ring groove 12 and abuts against the end of the guide flange 33 away from the force transmission rod 85. When the shielding sleeve 3 slides to the first limit position and the second limit position, the outer peripheral wall of the shielding sleeve 3 closes the opening of the guide ring groove 12. Thus, on the one hand, it can ensure that the shielding sleeve 3 is subjected to uniform force during movement and will not be tilted or stuck; on the other hand, it can prevent related structures in the displacement transmission mechanism from intruding into the main methanol channel and causing additional interference to the flow of methanol fluid. Specifically, the nozzle body 1 has a valve seat 11 with a spray hole threaded to its head end. The valve seat 11 has an annular groove that communicates with the guide ring groove 12. After unscrewing the valve seat 11, the shielding sleeve 3 can be directly removed from the nozzle body 1 for easy assembly. Furthermore, the high-temperature cavitation-suppressing microtexture region 5 and the low-temperature cavitation-promoting microtexture region 4 are sequentially and spaced apart on the outer surface of the needle valve 2 along the methanol fluid flow direction. The effective shielding length of the shielding sleeve 3 is not less than the sum of the axial length of either the low-temperature cavitation-promoting microtexture region 4 or the high-temperature cavitation-suppressing microtexture region 5 and the maximum lift of the needle valve 2. This ensures that when the shielding sleeve 3 is in any extreme position, only one microtexture region is exposed to the methanol fluid and is unaffected by the opening and closing of the needle valve 2, guaranteeing that the two control orientations do not interfere with each other, and the nozzle body 1 is always in a defined working mode. In this embodiment, the axial lengths of the low-temperature cavitation-promoting microtexture region 4 and the high-temperature cavitation-suppressing microtexture region 5 are equal, and the axial gap between them is less than half the maximum lift of the needle valve 2.

[0041] Therefore, when the shielding sleeve 3 moves to the first limit position, its shielding section 31 is aligned with the upstream high-temperature cavitation-suppressing microtexture zone 5, and one working section 32 is aligned with the downstream low-temperature cavitation-promoting microtexture zone 4. When the methanol fluid flows in the nozzle body 1, it first passes through the shielding annular gap between the high-temperature cavitation-suppressing microtexture zone 5 and the shielding section 31, and the flow regulation function of the high-temperature cavitation-suppressing microtexture zone 5 on the methanol fluid is suppressed; then it passes through the working annular gap between the low-temperature cavitation-promoting microtexture zone 4 and the working section 32. The larger gap of the working annular gap allows the low-temperature cavitation-promoting microtexture zone 4 to fully interact with the mainstream, so that its cavitation-promoting function can be exerted. Similarly, when the shielding sleeve 3 moves to the second limit position, the methanol fluid first passes through the working annular gap between the high-temperature cavitation-suppressing microtextured zone 5 and the working section 32, and is cavitated by its guiding and wall-adhering effect; then it passes through the shielding annular gap between the low-temperature cavitation-promoting microtextured zone 4 and the shielding section 31. At this time, the separation-inducing effect of the low-temperature cavitation-promoting microtextured zone 4 on the methanol fluid is suppressed, ensuring the cavitation suppression effect upstream, thereby ensuring that the injection optimization structure of this application can automatically achieve low-temperature cavitation-promoting enhanced atomization and high-temperature cavitation-suppressing flow stabilization and anti-cavitation under different environments.

[0042] Furthermore, both the microscale array 41 and the smooth microchannel array 51 are coated with a fluorine-doped diamond-like carbon (DLC) coating. The DLC coating itself possesses extremely high hardness and a low coefficient of friction, significantly improving the wear resistance of the microtexture structure under high-pressure, high-speed methanol scouring. Building upon this, fluorine is further doped into the coating, with a doping amount ranging from 10% to 30% atomically. The introduction of fluorine reduces the surface energy of the coating, imparting methanol-repellent properties to the surface, effectively reducing the adsorption and accumulation of methanol coking precursors on the microtexture surface, and preventing functional degradation of the microtexture morphology due to coking and carbon deposition. In practical applications, this DLC coating is prepared using plasma-enhanced chemical vapor deposition (PECVD), where a gradient transition layer is formed on the surface of the needle valve 2 substrate before depositing the fluorine-doped DLC functional layer.

[0043] The implementation principle of the optimized fuel atomization injection structure for a methanol engine in this application is as follows: During methanol engine operation, the temperature-sensitive displacement drive component within the nozzle body 1 head wall senses temperature changes caused by heat recirculation in the combustion chamber in real time. When the engine is in a cold start or low-load, low-temperature condition, the ambient temperature at the nozzle body 1 head is below a preset first threshold. The phase change material layer 72 within the temperature-sensitive displacement drive component remains in a solid, contracted state, and the shielding sleeve 3 is stably held at the first extreme position under the action of the return spring 6. At this time, the low-temperature cavitation-enhancing microtextured region 4 is exposed to the methanol fluid flowing through the surface of the needle valve 2. When the methanol fluid flows through the microscale array 41, the boundary layer undergoes local separation and induces cavitation initiation, compensating for the insufficient cavitation capacity of low-temperature methanol itself, and achieving enhanced atomization effect through cavitation enhancement.

[0044] When the engine enters a high-load, high-temperature operating condition, the temperature at the nozzle body 1 rises above the second threshold. The phase change material layer 72 melts and expands, which is converted into an amplified axial displacement by the force-bearing annular piston 83 and the force-transmitting annular piston 84. This displacement drives the shielding sleeve 3 to slide to the second limit position, overcoming the preload of the return spring 6. At this point, the high-temperature cavitation suppression microtexture region 5 is exposed, and the smooth micro-guide channel array 51 suppresses boundary layer separation and pressure fluctuations, delays cavitation initiation, reduces cavitation intensity, and avoids injection instability and structural damage caused by excessive cavitation. The setting of the temperature hysteresis window makes the switching process have a directional threshold difference, avoiding frequent oscillations near the critical temperature.

[0045] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," "third," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including" and similar terms mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, and do not exclude other elements or objects. "Above," "below," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0046] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An optimized fuel atomization injection structure for a methanol engine, characterized in that, The system includes a nozzle body, a needle valve coaxially and reciprocally slidably disposed within the nozzle body, a temperature-sensitive displacement drive assembly disposed within the head wall of the nozzle body, and a shielding sleeve coaxially sleeved around the outer periphery of the needle valve and slidably engaged with the inner wall of the nozzle body. The annular gap between the inner wall of the shielding sleeve and the outer wall of the needle valve constitutes the methanol main channel. The outer surface of the needle valve is provided with low-temperature cavitation-promoting microtexture zones and high-temperature cavitation-suppressing microtexture zones spaced apart along the axial direction; The temperature-sensitive displacement drive component is thermally coupled to the nozzle head and is used to output axial displacement in response to changes in the ambient temperature of the nozzle head, and drive the shielding sleeve to switch between the first limit position and the second limit position. When the shielding sleeve is in the first extreme position, the high-temperature cavitation-suppressing microtexture region is shielded and the low-temperature cavitation-promoting microtexture region is exposed to the methanol fluid; when the shielding sleeve is in the second extreme position, the low-temperature cavitation-promoting microtexture region is shielded and the high-temperature cavitation-suppressing microtexture region is exposed to the methanol fluid; so that the nozzle body flow forms a cavitation-promoting enhanced atomization state under low-temperature conditions and a stable flow suppressing excessive cavitation state under high-temperature conditions.

2. The optimized fuel atomization injection structure for a methanol engine according to claim 1, characterized in that, A return spring is connected between the shielding sleeve and the nozzle body. The return spring is used to provide a preload force to bring the shielding sleeve toward the first extreme position. The temperature-sensitive displacement drive assembly and the reset spring together constitute a switching mechanism with temperature hysteresis characteristics. When the ambient temperature at the nozzle head rises above the second threshold, the shielding sleeve is driven to switch to the second extreme position. When the ambient temperature at the nozzle head drops below the first threshold, the shielding sleeve is returned to the first extreme position. The second threshold is greater than the first threshold.

3. The optimized fuel atomization injection structure for a methanol engine according to claim 2, characterized in that, The temperature-sensitive displacement drive component includes a phase change energy storage cavity, a phase change material layer filled in the phase change energy storage cavity, and a displacement transmission mechanism. The phase change temperature range of the phase change material layer is between the first threshold and the second threshold.

4. The optimized fuel atomization injection structure for a methanol engine according to claim 3, characterized in that, The phase change energy storage cavity is an annular chamber surrounding the nozzle head. The side wall of the phase change energy storage cavity facing the combustion chamber is provided with an array of outwardly protruding heat-conducting fins, and the side wall of the phase change energy storage cavity facing the nozzle body cavity is provided with a ceramic heat insulation layer.

5. The optimized fuel atomization injection structure for a methanol engine according to claim 4, characterized in that, The displacement transmission mechanism includes a force-receiving ring cavity and a force-transmitting ring cavity arranged coaxially. One end of the force-receiving ring cavity is sealed and connected to the phase change energy storage cavity, and the other end is connected to the input end of the force-transmitting ring cavity. A force-receiving ring piston is sealed and slidably disposed in the force-receiving ring cavity, and a force-transmitting ring piston is sealed and slidably disposed in the force-transmitting ring cavity. The force-receiving ring cavity and the force-transmitting ring cavity are filled with transmission fluid located between the force-receiving ring piston and the force-transmitting ring piston. The cross-sectional area of ​​the force-receiving ring piston is larger than the cross-sectional area of ​​the force-transmitting ring piston. A number of force-transmitting rods are fixedly connected to one end of the force-transmitting annular piston away from the force-receiving annular piston for contacting the shielding sleeve.

6. The optimized fuel atomization injection structure for a methanol engine according to claim 5, characterized in that, The inner wall of the shielding sleeve has a shielding section and two working sections located at both ends of the shielding section. The distance between the working section and the outer wall of the needle valve is greater than the distance between the shielding section and the outer wall of the needle valve. When the masking sleeve moves to the point where the masking section is aligned with a microtexture area, the function of that microtexture area is suppressed; when the masking sleeve moves to one of the working sections and is aligned with a microtexture area, the function of that microtexture area is activated.

7. The optimized fuel atomization injection structure for a methanol engine according to claim 6, characterized in that, The nozzle body has a guide ring groove on its inner peripheral wall. The shielding sleeve has a guide flange that is slidably disposed in the guide ring groove and is coaxially fixed to its outer peripheral wall. The force transmission rod extends out of the force transmission ring cavity and enters the guide ring groove and abuts against the guide flange. The reset spring is disposed in the guide ring groove and abuts against the end of the guide flange away from the force transmission rod. Furthermore, when the shielding sleeve slides to the first and second limit positions, the outer peripheral wall of the shielding sleeve closes the opening of the guide ring groove.

8. The optimized fuel atomization injection structure for a methanol engine according to any one of claims 1-7, characterized in that, The low-temperature cavitation-inducing microtexture region is a microscale array used to induce local separation of the boundary layer of methanol fluid, and the high-temperature cavitation-suppressing microtexture region is a smooth microchannel array used to maintain the boundary layer of methanol fluid adhering to the wall.

9. The optimized fuel atomization injection structure for a methanol engine according to claim 8, characterized in that, The high-temperature cavitation-suppressing microtexture region and the low-temperature cavitation-promoting microtexture region are sequentially spaced along the methanol fluid flow direction on the outer surface of the needle valve. The effective shielding length of the shielding sleeve is not less than the sum of the axial length of the low-temperature cavitation-promoting microtexture region or the high-temperature cavitation-suppressing microtexture region and the maximum lift of the needle valve, so that when the shielding sleeve is in any extreme position, only one microtexture region is exposed to the methanol fluid and is not affected by the opening and closing of the needle valve.

10. The optimized fuel atomization injection structure for a methanol engine according to claim 8, characterized in that, Both the microscale array and the smooth microchannel array are covered with a fluorine-doped diamond-like coating to improve the surface's methanol-repellent properties while maintaining the coating's hardness.

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