Engine piston combustion chamber with superoleophobic surface micro-texture and design method

Abstract

This invention belongs to the field of engine technology, specifically relating to an engine piston combustion chamber with a superoleophobic surface microtexture and its design method. To address the problem of traditional piston combustion chambers easily leading to fuel spread, oil film adhesion, and carbon soot deposition causing piston erosion failure, this invention first constructs a micron-scale papillary array microtexture model and prepares samples using femtosecond lasers. Then, a non-reactive impact test platform is used to detect the quality of fuel adhering to the wall, and a pre-combustion constant-volume combustion bomb test platform is used to detect the quality of carbon soot on the wall, with preliminary screening performed by comparing with blank samples. The qualified microtexture is then engraved onto the piston combustion chamber surface, and the final solution is obtained through engine bench testing and iterative optimization. This invention inherently endows the combustion chamber wall with superoleophobic properties, reducing fuel adhesion and oil film formation, inhibiting carbon soot generation and Al-C interface thermal corrosion, improving engine reliability and thermal efficiency at high altitudes, and reducing emissions.

Description

Technical Field

[0001] This invention belongs to the field of engine technology, specifically relating to an engine piston combustion chamber with a superoleophobic surface microtexture and its design method. Background Technology

[0002] The piston is the core moving part of the internal combustion engine. The shape of the combustion chamber at the top of the piston directly determines the fuel atomization, fuel-air mixing and combustion process in the cylinder, which is crucial to the engine's power, thermal efficiency and emissions.

[0003] With the diversification of operating conditions, engines often face the challenges of extreme high-altitude environments and cold starts. Under these conditions, low temperatures and low intake pressures worsen the in-cylinder thermodynamics, increasing the penetration distance of liquid fuel spray and inevitably causing it to impact the top surface of the combustion chamber. This leads to a shift in the combustion mode from spatial diffusion to wall-attached dominance, resulting in decreased combustion stability. After fuel impact, a wall-attached oil film forms, easily igniting pool fire, and carbon soot generation increases by more than 30% compared to spatial diffusion combustion. After carbon soot deposition, it penetrates the aluminum alloy matrix, causing an Al-C interface carbonization and thermal corrosion reaction, generating brittle, easily hydrolyzed aluminum carbide phases. This damages the matrix integrity, reduces mechanical properties, induces cracks, and leads to piston ablation failure, severely restricting the reliability of engine operation in high-altitude environments.

[0004] The smooth surface of a traditional piston combustion chamber easily leads to the spread, adhesion, and formation of an oil film by liquid fuel, further exacerbating the aforementioned problems of fuel adhesion to the combustion chamber walls, carbon buildup, and corrosion failure. To alleviate this problem, some existing technologies rely on optimizing the fuel injection strategy, such as a fuel injection method in Chinese invention patent publication number CN111852680B, which reduces cylinder liner wall wetting by decreasing the spray penetration distance; other existing technologies rely on optimizing combustion chamber airflow, such as a dual-fuel engine piston and engine in Chinese invention patent publication number CN224266497U that can reduce methane emissions, which sets two inclined surfaces and one arc-shaped surface between the piston top surface and the piston side surface, achieving a smooth overall transition from the piston side surface to the piston top surface, thereby reducing fuel adhesion to the combustion chamber walls. However, the above methods are all passive control measures, which can only alleviate fuel adhesion to the combustion chamber walls to a certain extent, and cannot fundamentally change the adhesion characteristics of liquid fuel to the combustion chamber walls. Summary of the Invention

[0005] The present invention aims to provide an engine piston combustion chamber with a superoleophobic surface microtexture and a design method to solve the problems of severe fuel adhesion and slow evaporation on the piston walls and the resulting piston thermal corrosion failure under low temperature and low pressure conditions.

[0006] To achieve the above objectives, one aspect of the present invention provides a technical solution: a method for designing a microtextured structure for a combustion chamber wall, comprising the following steps: Constructing a microtexture model: Constructing micron-sized papillae with specific dimensions and arrangements on the surface of a metal plate to form a specific microtexture model; Model sample preparation: The designed microtexture shape is engraved on the surface of a metal plate as a test sample; a metal plate without engraved microtexture is prepared as a blank sample. Experimental testing platforms were set up: a non-reactive liquid phase fuel spray wall impact test platform was set up to detect the quality of fuel adhering to the wall, and a pre-burning constant volume combustion bomb spray wall impact combustion test platform was set up to detect the quality of carbon soot on the wall. Two tests were conducted on both the test samples and the blank samples. Comparative test analysis: If the fuel adhesion mass and soot generation mass of the test sample are not less than those of the blank sample, then return to the step of constructing a microtexture model; otherwise, carve a microtexture shape consistent with that of the test sample on the surface of the piston combustion chamber. Bench testing: The piston containing the combustion chamber microtexture is assembled into the engine and bench tested. Determine the microtexture model: If the combustion and emission performance results in the bench test are not higher than the original engine performance without microtexture, return to the step of constructing the microtexture model; otherwise, obtain the combustion chamber wall microtexture scheme.

[0007] The working principle and beneficial effects of this solution are as follows: This invention designs a specific array of micron-level protrusions to form a microtexture. Under cold start and high-altitude low-temperature conditions, when low-temperature fuel droplets impact the wall surface, the micro-protrusion structure forces the droplets to spread out in a very short time, significantly increasing the gas-liquid contact area, while simultaneously dividing the oil film thickness to the micron or even sub-micron level. According to Fick's diffusion law, the oil film evaporation rate is inversely proportional to the thickness; an extremely thin oil film can significantly shorten the evaporation time, avoiding oil film accumulation at low temperatures. At the same time, the microtexture increases the density of actual heat exchange contact points between the wall surface and the fuel, breaking down the air gap insulation layer that may exist on smooth walls, thus improving heat transfer efficiency. This solution also fundamentally blocks the long-term adhesion and penetration of carbon soot on the wall surface by reducing the total amount and residence time of the oil film adhering to the wall, avoiding the occurrence of Al-C interface carbonization thermal corrosion reaction, preventing the formation of brittle phases and crack propagation, and significantly improving the service life of the piston in extreme high-altitude environments.

[0008] This scheme changes the wettability of the combustion chamber wall through biomimetic microtexture, actively adapts to low temperature and low pressure environment, and forcibly changes the droplet breakage and spreading morphology through physical structure, solving the problem of slow fuel spreading and strong adhesion on traditional smooth surfaces at low temperature, and adapting to harsh conditions such as plateau extreme environment and cold start. (2) Utilize microscale effect to accelerate fuel evaporation, optimize fuel-air mixing rate, compensate for the combustion deterioration caused by insufficient intake oxygen concentration and low cylinder temperature under plateau conditions, and greatly improve the engine's operating stability and service life in plateau environment. (3) Reduce fuel adhesion to the wall and optimize combustion mode, which can promote full fuel-air mixing and combustion, improve engine thermal efficiency and power output, reduce emissions of pollutants such as CO, HC, and soot, and reduce the oil film adhering to the wall from the source, effectively curbing the generation of soot and piston matrix thermal corrosion caused by it, and ensuring the engine's operating stability in harsh environment.

[0009] Optionally, the micron-sized papillae may have a structural shape that is one or more of the following: cylindrical, conical, frustum, or polygonal shapes.

[0010] This scheme enriches the geometric topology of microtextures. Different shapes have different effects on the contact angle, roll-off angle and adhesion of droplets. For example, conical and frustum shapes are more likely to induce droplet detachment, while cylindrical shapes are conducive to forming a stable contact surface. By using them in combination, multi-level roughness structures can be constructed to synergistically enhance the superoleophobic effect, while avoiding the processing or durability defects that may exist in single shapes.

[0011] Optionally, in the bench test procedure, the non-reactive liquid fuel spray wall impact test platform includes a droplet generation system, a wall heating and temperature control system, a dual high-speed camera system, and an LED cold light source. The wall heating and temperature control system heats the combustion chamber wall to the target temperature and stabilizes it. The droplet generation system controls the droplets to fall freely from a fixed height and impact the wall. A trigger signal starts the dual cameras to record synchronously. The LED cold light source provides supplementary lighting to the wall.

[0012] In this solution, the platform simulates the process of fuel droplets impacting the high-temperature combustion chamber wall under real engine operating conditions. The wall heating and temperature control system ensures the consistency between the test temperature and the engine operating temperature. The droplet generation system enables controllable impact of single droplets or sprays. The dual high-speed camera system, in conjunction with the LED cold light source, can capture dynamic spreading and rebound behavior, effectively avoiding the high cost and long cycle of direct whole-machine testing and improving design iteration efficiency.

[0013] Optionally, the dual high-speed camera system includes a side-view camera and a top-view camera. The side-view camera captures the evolution sequence of the droplet's side morphology and extracts the dynamic contact angle, spreading factor, and rebound factor through edge detection and circle fitting. The top-view camera captures the spreading area of ​​the oil film on the wall surface and obtains the change of the oil film spreading area over time through binarization and pixel calibration.

[0014] In this scheme, the side-view camera, combined with edge detection and circle fitting algorithms, can extract dynamic contact angle, spreading factor and rebound factor to quantitatively characterize the dynamic wetting and detachment behavior between droplets and the wall. The top-view camera obtains the time-varying curve of the oil film spreading area through binarization and pixel calibration, which directly reflects the coverage and residual degree of the attached fuel. The data from the two perspectives complement each other and comprehensively evaluate the actual effect of microtexture on inhibiting oil film spreading and promoting droplet rebound.

[0015] Optionally, the pre-combustion constant-volume incendiary bomb spray wall-impact combustion test platform includes a constant-volume bomb body, an intake and exhaust subsystem, a temperature control subsystem, a fuel supply subsystem, and a data acquisition subsystem. The constant-volume bomb body is equipped with a symmetrical cubic closed combustion chamber as the main body, with a quartz window on the side. The intake and exhaust control system evacuates the main body of the chamber and proportionally fills it with a mixture of gases. The temperature control subsystem heats the main body of the chamber. The fuel supply subsystem controls the injection pressure and pulse width. The data acquisition system uses a high-frequency water-cooled transient in-cylinder pressure sensor to synchronously monitor the combustion heat release state.

[0016] In this solution, the platform can reproduce the high temperature and high pressure conditions of the diesel engine combustion chamber under controlled conditions, simulate the combustion process after the fuel spray hits the wall, and monitor the heat release status in real time. Compared with the actual engine bench test, the constant volume combustion bomb test has the advantages of controllable boundary conditions, good repeatability, and convenient optical diagnosis. It can quickly evaluate the impact of different microtextures on soot generation and combustion efficiency without relying on the whole machine.

[0017] Optionally, in the bench test procedure, the pre-combustion constant volume incendiary bomb spray wall impact combustion test platform uses the Dalton pressure division principle to fill the cavity with acetylene, oxygen and nitrogen. After the premixed gas is ignited, the temperature and pressure inside the cavity rise sharply. When the temperature drops to the target temperature required to simulate the operating conditions of a diesel engine, fuel injection is triggered and a high-speed camera is started simultaneously for optical imaging.

[0018] In this scheme, the pre-combustion method can realistically simulate the thermodynamic state at the end of the engine compression stroke without the need for a complex mechanical compression system, thus reducing test costs and cycle. By controlling the premixed gas ratio and ignition timing, the thermal atmosphere under extreme conditions such as different altitudes and cold starts can be stably reproduced, providing repeatable test conditions for the anti-carbon smoke performance of microtextures under a wide range of operating conditions.

[0019] Optionally, during the bench test, the heat release rate curve and performance indicators for power, economy, and emissions are obtained, including speed, torque, power, fuel consumption rate, oil consumption, CO emissions, and NO emissions. x Emissions, HC emissions, and smoke opacity.

[0020] In this scheme, the heat release rate curve can reflect the in-cylinder combustion phase and duration, determining whether the premixed combustion ratio has improved due to reduced wall adhesion; the power and economy indicators directly verify the effect of microtexture on power output and fuel efficiency; and the emission indicators quantitatively assess soot, CO, HC, and NO. x The emission reduction effect.

[0021] Another aspect of the present invention is to provide an engine piston combustion chamber, which is obtained by the aforementioned combustion chamber wall microtexture structure design method.

[0022] Alternatively, the microtexture is prepared through the following process steps: Step S1 Mask preparation: A flexible mask is used, and the mask is tightly attached to the curved surface to be processed in the combustion chamber through vacuum lamination or hot pressing transfer process; Step S2 Pattern Transfer: Using an electrochemical etching process, selective material removal is performed in the mask window area to form a protrusion array; Post-processing in step S3: Remove the mask and clean the piston body.

[0023] In this scheme, vacuum pressure difference is used to achieve the fit between the mask and the complex surface of the combustion chamber, which is adapted to the special geometric features of the non-developable surface of the piston combustion chamber. Compared with laser ablation to carve out the micro-texture by linear engraving, electrochemical etching removes the material by electrochemical dissolution, which not only maintains the integrity of the base metal, but also adapts to the complex surface of the piston combustion chamber.

[0024] Optionally, in step S1 mask preparation, the mask is constructed into a sealed cavity surrounding the combustion chamber opening and a vacuum is drawn, and the mask is pressed onto the curved surface of the combustion chamber using external atmospheric pressure.

[0025] In this scheme, the negative pressure adsorption method can not only ensure the positioning of the mask before etching, but also maintain the mask in a taut state during the etching process, thereby ensuring the geometric consistency of the array arrangement. Attached Figure Description

[0026] Figure 1 This is an overall flowchart of the combustion chamber wall microtexture structure design method in an embodiment of the present invention; Figure 2 This is a cross-sectional view of the combustion chamber in an embodiment of the present invention; Figure 3 This is a schematic diagram of the microtexture in an embodiment of the present invention; Figure 4 This describes the development pattern of fuel droplets impacting a wall surface at 150°C in an embodiment of the present invention. Figure 5 This illustrates the development pattern of fuel droplets impacting a wall surface at 200°C in an embodiment of the present invention. Detailed Implementation

[0027] The following detailed description illustrates the specific implementation method: The markings in the accompanying drawings include: fuel injector 1, cylinder head 2, piston 3, microtexture 31, and cylinder liner 4.

[0028] Example This embodiment is basically as follows: Figure 1 , Figure 2 As shown: A method for designing a microtextured structure for a combustion chamber wall, comprising the following steps: First, observations of various organisms in nature, such as lotus leaves, insect wings, fish scales, and Qinling arrow bamboo leaves, revealed that their surface structures exhibited remarkable superhydrophobicity and self-cleaning capabilities. Based on the biomimetic principle of the micro-nano composite structure of the lotus leaf surface, this embodiment determined that a square micron-scale papilla array would be used as the basic structural form of the combustion chamber wall microtexture 31.

[0029] Microstructure models with different shapes, positions and numbers were constructed on the material surface using UG software developed by Siemens PLM Software. The side length of the papillae ranged from 50 to 200 micrometers, the height ranged from 10 to 50 micrometers, and the spacing between adjacent microtextures 31 ranged from 20 to 100 micrometers.

[0030] Aluminum alloy was selected as the experimental substrate, and microtexture samples with different parameters were prepared on the surface of the aluminum alloy plate using electrochemical etching technology. At the same time, a smooth aluminum alloy plate without microtexture 31 was prepared as a blank control sample.

[0031] A non-reactive liquid fuel spray wall impact test platform was constructed to detect the quality of fuel adhering to the wall. This platform consists of a droplet generation system, a wall heating and temperature control system, a dual high-speed camera system, and an LED cold light source. Test samples and blank samples were fixed on the wall heating and temperature control system, and the wall temperature was heated to the target temperature and maintained stable. The droplet generation system produced n-dodecane droplets, which were then allowed to fall freely from a fixed height and impact the sample surface. A trigger signal simultaneously activated two high-speed cameras for synchronous imaging. The side-view camera captured the evolution sequence of the droplet's side morphology, and the dynamic contact angle, spreading factor, and rebound factor were extracted through edge detection and circle fitting. The top-view camera directly captured the oil film spreading area on the wall surface, and the change in oil film spreading area over time was obtained through binarization and pixel calibration.

[0032] A pre-combustion constant-volume incendiary bomb spray-impact combustion test platform was further constructed to detect the quality of soot on the wall surface. This platform mainly consists of the constant-volume bomb body, intake and exhaust subsystems, temperature control subsystems, fuel supply subsystems, and data acquisition subsystems. It also includes a control system, which is connected to the intake and exhaust, temperature control, fuel supply, and data acquisition subsystems. Its core working principle is to simulate the high-temperature and high-pressure environment at the moment of diesel engine fuel injection through premixed gas combustion.

[0033] Structurally, the constant-volume cartridge body is a 1.35L symmetrical cubic closed combustion chamber, made of 40CrNiMoA high-strength alloy steel resistant to ultra-high pressure thermal shock, with a quartz window on the side for optical diagnostics. The intake and exhaust control system achieves fully automated vacuuming and precise proportional injection of the gas-fuel mixture. The temperature control system uses PID to heat the main chamber to 100℃ and regulate the aluminum alloy plate with copper heating modules to below 300℃ to prevent pre-combustion water vapor condensation. The fuel supply system also includes a high-pressure common rail system, which uses a high-pressure common rail system with a maximum pressure of 175MPa in conjunction with the control system to flexibly control the injection pressure and pulse width. The data acquisition system includes a pressure sensor, which uses a high-frequency water-cooled transient in-cylinder pressure sensor to synchronously monitor the combustion heat release state.

[0034] In terms of working principle, the pre-combustion constant-volume incendiary bomb spray wall-impact combustion test platform utilizes the Dalton pressure partial principle to fill the chamber with acetylene, oxygen, and nitrogen. Acetylene combustion provides heat and determines the pressure, oxygen controls the reaction rate and the final ambient oxygen concentration, simulating 0-21%, while nitrogen is used to adjust the final ambient density. After filling, the premixed gas is ignited by a spark plug, and intense combustion causes a rapid rise in temperature and pressure within the chamber. Subsequently, the high-temperature gas transfers heat to the wall, entering the cooling phase. The control system monitors and calculates the average temperature inside the cylinder in real time. When the temperature drops to the target temperature required to simulate specific operating conditions of a diesel engine, the system immediately triggers a fuel injection signal and simultaneously activates a high-speed camera for optical imaging, thereby simulating and recording the spray wall-impact ignition and combustion characteristics.

[0035] Comparative analysis of the fuel adhesion mass and soot generation mass of aluminum alloy plates with and without microtexture 31 reveals that if the fuel adhesion mass and soot generation mass of the aluminum alloy plate with microtexture 31 are both higher than those without microtexture 31, then the microtexture 31 design does not meet the requirements and needs to be redesigned by returning to the parametric design step of microtexture 31. If the requirements are met, then the microtexture 31 with the above-mentioned optimal parameters is engraved on the surface of the piston 3 combustion chamber with the same microtexture 31 shape as the aluminum alloy plate using the same femtosecond laser processing technology.

[0036] In this embodiment, given that the combustion chamber of piston 3 is a complex, deeply concave curved surface, traditional planar mask technology cannot be directly applied. Therefore, this embodiment first prepares the mask by using dry film photoresist as a flexible mask and employing an annular sealing cap that matches the geometry of the piston 3 top surface. The dry film is then sandwiched between the cap and the top surface of piston 3, forming a sealed cavity. This cavity is then evacuated, and external standard atmospheric pressure is used to tightly press the dry film onto the complex curved surface of the combustion chamber's inner wall.

[0037] Subsequently, pattern transfer was performed, and the assembled piston 3 was immersed in an electrochemical etching solution to selectively dissolve the aluminum alloy substrate electrochemically, thereby forming a micro-protrusion array. To further enhance the high-temperature resistance and corrosion resistance of the protrusion tops, the etched surface was subjected to micro-arc oxidation treatment, resulting in the in-situ growth of a dense alumina film on the protrusion surface. This alumina film not only has extremely high hardness, capable of resisting long-term erosion by high-pressure oil jets, but more importantly, its low thermal conductivity creates a micro-thermal barrier during cold starts, effectively slowing down the temperature drop on the wall surface and promoting the rapid evaporation of the oil film adhering to the wall.

[0038] Finally, post-processing is performed, using a special stripping solution to remove residual photoresist mask, followed by ultrasonic cleaning and drying to obtain the finished product.

[0039] The machined piston and combustion chamber were assembled onto the engine for bench testing. Test conditions included idling, rated power, and low intake pressure simulating a high-altitude environment. The tests obtained heat release rate curves and performance indicators for power, economy, and emissions. The power, economy, and emissions performance indicators tested on the bench mainly included engine speed, torque and power, fuel consumption rate, oil consumption, CO emissions, NO emissions, HC emissions, and smoke opacity.

[0040] If the combustion and emission performance results of the engine bench test are both lower than the original engine performance without microtexture 31, the design does not meet the requirements and needs to be redesigned by returning to the parameterized design step of microtexture 31. If the combustion and emission performance results are both better than the original engine performance without microtexture 31, the design meets the requirements.

[0041] The optimal design scheme for the piston 3 surface microtexture 31 was obtained through experimental data comparison. In this embodiment, the optimized microtexture 31 shape, such as... Figure 3 As shown in (a), the length of the papillae in microtexture 31 is... It is 100 micrometers wide. Square protrusions, each 100 micrometers in size and 25 micrometers in height, with the spacing between each square protrusion... It is 50 micrometers.

[0042] The adhesion and adhesion time of the oil film between the microtexture 31 and the original smooth wall surface were obtained through experimental data, such as... Figure 4 As shown, at 150℃, after fuel droplets impact the wall of the microtexture 31, capillary action causes the fuel to spread rapidly, resulting in a larger adhesion area than on a smooth wall. For the same droplet volume, this larger area leads to a smaller adhesion film thickness, causing the surface oil film containing the microtexture 31 to evaporate quickly. Complete evaporation of the oil film on a smooth wall takes 6150 ms, while complete evaporation of the surface oil film containing the microtexture 31 takes only 3047 ms.

[0043] When the temperature rises to 200℃, the development pattern of fuel droplets after impacting the wall is as follows: Figure 5 As shown, the textured surface will experience boiling, causing the droplets to bounce back into the high-temperature environment inside the cylinder, where they will evaporate rapidly, thus achieving active oil resistance. On smooth walls, however, the fuel droplets will adhere to the wall surface.

[0044] This embodiment fundamentally alters the wettability of the combustion chamber wall by engraving microtextures 31 on the combustion chamber surface. During engine cold starts, the surface with microtextures 31 causes droplets to spread rapidly upon impact with the wall due to capillary action. The smaller oil film thickness significantly reduces evaporation time. During idling, when the piston 3 temperature reaches over 200°C, the surface with microtextures 31 allows droplets to rebound into the high-temperature environment for rapid evaporation. This achieves a dual synergistic effect of accelerated evaporation at low temperatures and oil resistance at high temperatures. This method achieves a self-cleaning effect by reducing fuel adhesion to the combustion chamber wall, promoting complete fuel combustion, and reducing carbon deposit formation without relying on complex fuel injection or airflow organization optimization. This improves engine thermal efficiency and power while reducing pollutant emissions and increasing reliability during high-altitude operation.

[0045] This invention also provides an engine piston 3 combustion chamber, such as... Figure 2 As shown, the system includes a fuel injector 1, a cylinder head 2, a piston 3, a microtexture 31 on the surface of the piston 3's combustion chamber, and a cylinder liner 4. The cylinder head 2 and cylinder liner 4 are fixedly connected to form the combustion chamber. The fuel injector 1 is located at the center of the cylinder head 2 and aligned with the interior of the combustion chamber. The piston 3 is assembled in the combustion chamber, and the surface of the piston 3 facing the combustion chamber is engraved with the microtexture 31.

[0046] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness or practicality of the present invention. The specific embodiments described in the specification can be used to interpret the claims.

Claims

1. Engine piston combustion chamber with superoleophobic surface microtexturing and design method, characterized by: Includes the following steps: (1) Constructing a microtexture model: Constructing micron-sized papillae with specific size and arrangement on the surface of a metal plate to form a specific microtexture model; (2) Model sample preparation: The designed micro-texture shape is engraved on the surface of a metal plate as a test sample; Prepare a blank sample of a metal plate without engraved microtexture; (3) Set up the test platform: Set up a non-reactive liquid phase fuel spray wall impact test platform to obtain the mass of fuel adhering to the wall, and set up a pre-burning constant volume combustion bomb spray wall impact combustion test platform to obtain the mass of carbon soot on the wall. Two tests were conducted on the test samples and blank samples respectively. (4) Comparative test analysis: If the mass of fuel adhering to the wall and the mass of soot generation of the test sample are not less than those of the blank sample, then return to the step of constructing a microtexture model; Conversely, a microtexture shape consistent with the test sample is engraved on the surface of the piston combustion chamber; (5) Bench test: The piston containing the combustion chamber microtexture is assembled into the engine and bench test is performed; (6) Determine the microtexture model: If the combustion and emission performance results in the bench test are not higher than the original engine performance without microtexture, return to the step to construct the microtexture model; otherwise, the combustion chamber wall microtexture scheme is obtained.

2. The engine piston combustion bowl with superoleophobic surface micro-texture and design method according to claim 1, characterized in that: The structure of micron-sized papillae is one or more combinations of cylindrical, conical, frustum, and polygonal shapes.

3. The engine piston combustion bowl with superoleophobic surface micro-texture and design method according to claim 1, characterized in that: In the bench test procedure, the non-reactive liquid fuel spray wall impact test platform includes a droplet generation system, a wall heating and temperature control system, a dual high-speed camera system, and an LED cold light source. The wall heating and temperature control system heats the combustion chamber wall to the target temperature and stabilizes it. The droplet generation system controls the droplets to fall freely from a fixed height and impact the wall. The trigger signal starts the dual cameras to record synchronously. The LED cold light source provides supplementary lighting to the wall.

4. The engine piston combustion bowl with superoleophobic surface micro-texture and design method according to claim 3, characterized in that: The dual high-speed camera system includes a side-view camera and a top-view camera. The side-view camera captures the evolution sequence of the droplet's side morphology and extracts the dynamic contact angle, spreading factor, and rebound factor through edge detection and circle fitting. The top-view camera captures the spreading area of ​​the oil film on the wall surface and obtains the change of the oil film spreading area over time through binarization and pixel calibration.

5. The engine piston combustion bowl with superoleophobic surface micro-texture and design method according to claim 1 is characterized by that: The pre-combustion constant-volume incendiary bomb spray wall-impact combustion test platform includes a constant-volume bomb body, an intake and exhaust subsystem, a temperature control subsystem, a fuel supply subsystem, and a data acquisition subsystem. The constant-volume bomb body is equipped with a symmetrical cubic closed combustion chamber as the main body, with a quartz window on the side. The intake and exhaust control system evacuates the main body of the chamber and proportionally fills it with a mixture of gas and gas. The temperature control subsystem heats the main body of the chamber. The fuel supply subsystem controls the injection pressure and pulse width. The data acquisition system uses a high-frequency water-cooled transient in-cylinder pressure sensor to synchronously monitor the combustion heat release state.

6. The engine piston combustion bowl with ultra-oleophobic surface micro-texture and design method according to claim 5, characterized in that: In the bench test procedure, the pre-combustion constant volume incendiary bomb spray wall impact combustion test platform uses the Dalton pressure division principle to fill the cavity with acetylene, oxygen and nitrogen. After the premixed gas is ignited, the temperature and pressure inside the cavity rise sharply. When the temperature drops to the target temperature required to simulate the operating conditions of a diesel engine, fuel injection is triggered and a high-speed camera is started simultaneously for optical imaging.

7. The engine piston combustion bowl with ultra-oleophobic surface micro-texture and design method according to claim 1, characterized in that: In the bench test test step, the heat release rate curve and the dynamic, economic and emission performance indexes are obtained, the indexes including the speed, torque, power, fuel consumption rate, oil consumption, CO emission, NO x emission, HC emission and smoke degree.

8. An engine piston combustion chamber characterized by: An engine piston combustion chamber obtained by adopting the combustion chamber wall microtexture structure design method according to any one of claims 1 to 7.

9. An engine piston combustion chamber according to claim 8, characterized in that, Microtextures are prepared through the following process steps: Step S1 Mask preparation: A flexible mask is used, and the mask is tightly attached to the curved surface to be processed in the combustion chamber through vacuum lamination or hot pressing transfer process; Step S2 Pattern Transfer: Using an electrochemical etching process, selective material removal is performed in the mask window area to form a protrusion array; Post-processing in step S3: Remove the mask and clean the piston body.

10. An engine piston combustion chamber according to claim 9, characterized in that, In step S1, the mask is constructed into a sealed cavity surrounding the combustion chamber opening and a vacuum is drawn. The mask is then pressed onto the curved surface of the combustion chamber using external atmospheric pressure.

Images