Aviation two-stroke engine piston, combustion chamber structure and application

Abstract

The invention relates to the technical field of aero-engines, in particular to a two-stroke engine piston for aviation, a combustion chamber structure and application. The engine piston comprises a piston body, the upper surface of the piston body is of an outwards-protruding structure with the middle higher than the edge, and a catalysis part is arranged on the upper surface of the piston body; the combustion chamber structure comprises a combustion chamber body, the interior of the combustion chamber body is of an asymmetric structure, the combustion chamber body is defined by a cylinder body, a cylinder cover and a piston, the piston is slidably connected into the cylinder body, and the piston is arranged in the cylinder cover. The ignition position of the spark plug is located in the middle of the combustion chamber body when the piston moves to the upper dead center. By implementing the scheme, the combustion efficiency of the engine under the low-load condition is improved, and carbon deposition generated in the combustion chamber is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation engines, and in particular to a piston and combustion chamber structure of an aviation two-stroke engine and applications thereof. Background Art

[0002] With the rapid development of China's low-altitude economy and the growing drone industry, aviation vehicles, especially unmanned equipment, have stricter maneuverability requirements. As the mainstream configuration of UAV power systems, aviation piston engines, as the mainstream configuration of UAV power systems, are widely used in the aviation field due to their moderate fuel supply pressure, strong system reliability, high safety redundancy, and high power-to-weight ratio. However, due to the higher fuel viscosity and low turbulence intensity of the combustion chamber, carbon deposits in the combustion chamber of non-independent lubrication two-stroke engines are more serious than those of direct injection and independent lubrication. Especially in multi-cylinder engines, the different levels of carbon deposits in each cylinder lead to different effective volumes of each combustion chamber, resulting in engine vibration and poor dynamic balance, which directly affects the engine's performance, stability, and service life.

[0003] Currently, there is little research or effective solutions for the carbon deposit problem in the combustion chambers of two-stroke aircraft engines, both domestically and internationally. Therefore, to ensure stable operation of aircraft, regular engine maintenance is required, as frequent disassembly and assembly can reduce product reliability. Typically, maintenance is required every 200 hours of flight time, and for multi-cylinder engines, each maintenance session can take around a day.

[0004] Therefore, the above-mentioned combustion chamber carbon deposit problem leads to frequent maintenance of two-stroke aviation piston engines, and the relatively short service life seriously restricts the development prospects of non-independent lubricated intake port injection two-stroke engines. Summary of the Invention

[0005] The first purpose of the present invention is to provide a two-stroke engine piston for aviation. By designing the piston surface structure, the continuity and uniformity of the surface oil film can be effectively destroyed during normal operation of the engine, thereby reducing the probability of carbon deposit formation.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a two-stroke engine piston for aviation, comprising a piston body, the upper surface of the piston body being an outwardly convex structure with the middle portion higher than the edge, the upper surface of the piston body being provided with a catalytic portion, and the catalytic portion being provided with a plurality of catalytic units coated with a catalyst for adsorbing and releasing oxygen at intervals.

[0007] Preferably, as an improvement, the upper surface of the piston body is further provided with a non-catalytic portion, and the catalytic portion is located inside the non-catalytic portion.

[0008] Preferably, as an improvement, the non-catalytic portion includes an edge non-catalytic portion and a central non-catalytic portion, and the catalytic portion is located between the edge non-catalytic portion and the central non-catalytic portion.

[0009] Preferably, as an improvement, each catalytic unit divides the catalytic part into multiple small areas, the catalytic units are distributed in rows or radially along the radial direction of the piston, and the catalytic units between two adjacent rows / layers are staggered.

[0010] Preferably, as an improvement, the catalytic units corresponding to the odd-numbered layers are located on the same radial line, and the catalytic units corresponding to the even-numbered layers are located on the same radial line.

[0011] Preferably, as an improvement, the catalytic units of the even-numbered layers are located on the angular bisector of two adjacent catalytic units of the odd-numbered layers, or the catalytic units of the odd-numbered layers are located on the angular bisector of two adjacent catalytic units of the even-numbered layers.

[0012] Preferably, as an improvement, each of the catalytic units is in one or more of a circular, polygonal, and bar shape, and the catalyst is a Pt-Pd-Rh / Al2O3 catalyst.

[0013] The second purpose of the present invention is to provide a combustion chamber structure for a two-stroke aviation engine. Through the coordinated design of the piston and the combustion chamber, the combustion efficiency of the engine under low load conditions is greatly improved and the formation of carbon deposits in the combustion chamber is reduced.

[0014] A combustion chamber structure for a two-stroke aviation engine includes a combustion chamber body, the interior of the combustion chamber body being an asymmetric structure. The combustion chamber body is enclosed by a cylinder body, a cylinder head, and a piston according to any one of claims 1 to 7, the piston being slidably connected within the cylinder body, and a spark plug being provided on the cylinder head, wherein the ignition position of the spark plug is located in the middle of the combustion chamber body when the piston moves to top dead center.

[0015] Preferably, as an improvement, the inner surface of the cylinder head is an asymmetric structure, and the inclination angles of the inner peripheral wall of the cylinder head are different.

[0016] The third object of the present invention is to provide an aviation two-stroke engine piston and combustion chamber structure applicable to the field of aviation two-stroke engines.

[0017] The principles and advantages of this solution are:

[0018] The applicant conducted in-depth research and analysis on the problem of carbon deposits in the combustion chamber of a two-stroke aviation piston engine and found that the carbon deposit problem is mainly caused by the following three reasons:

[0019] First, aircraft engines differ from land-based engines. While the operating state of land-based engines is predictable or fixed, the state of aircraft engines can change significantly as the aircraft's flight attitude changes. In particular, the thickness of the lubricating oil on the combustion chamber's inner wall changes with flight attitude, and the oil film thickness at various locations on the combustion chamber's inner surface is highly random.

[0020] Second, the use of port injection will cause the premixed fuel to have poor fluidity on the combustion chamber wall after entering the combustion chamber. The premixed fuel will be deposited on the combustion chamber wall, forming a relatively thick oil film.

[0021] Third, in terms of combustion chamber structure, with the continuous development of modern processing technology, the surface roughness of the piston and combustion chamber is low, the wetting ability of the fuel on this surface is strong, and it is difficult to break it again under the action of airflow disturbance. Therefore, the turbulence intensity in the engine cylinder is weak under low load conditions, and the ability of the liquid film in the middle of the piston to break is weak. At the same time, when the engine cylinder is not vertical, the liquid film in the middle of the piston will not spread to the surrounding area. The thick thickness of the liquid film in the middle has poor ability to break it. After the engine is ignited, the oil film will quickly form carbon deposits under high temperature and oxygen-deficient conditions. The formation of carbon deposits reduces the effective volume of the combustion chamber, changes the engine compression ratio, and increases the possibility of detonation. At the same time, due to the poor thermal conductivity of carbon deposits, the temperature of the inner surface of the combustion chamber is high, high temperature corrosion is serious and it is easy to burn, reducing the engine life and the safety of the working process.

[0022] Therefore, based on the above findings, the applicant improved the piston and combustion chamber to achieve the following effects:

[0023] 1. By setting a catalytic part on the piston surface, during the engine scavenging process, the catalyst will adsorb oxygen in the air to the catalyst surface in advance. When the combustion chamber is in the combustion stage, the catalyst reaction is triggered. At this time, there is fuel that has not been completely evaporated on the piston surface (such as cold start or wall oil film). The catalyst releases oxygen to undergo oxidation reaction with the fuel on the piston surface, and produces bubbles such as CO2 and CO. When the bubbles break out of the oil film, they break the oil film into oil mist, thereby enhancing the combination of the oil mist and the oxygen in the combustion chamber, thereby promoting the full combustion of the oil mist, on the one hand reducing the thickness of the oil film, and on the other hand avoiding the formation of carbon deposits.

[0024] 2. By spacing the catalytic units, the connection stability between the catalytic unit and the piston is enhanced. Since the combustion chamber is in a high-temperature and low-temperature alternating working environment, and the piston substrate and the catalyst are two different materials, the catalytic units are spaced to avoid the linear expansion difference between the two, which can lead to an unstable connection between the catalyst and the piston substrate. At the same time, due to the high operating frequency of the piston, up to several thousand or even tens of thousands of revolutions per minute, the alternating load is large. If the attachment between the two is unstable, it can easily affect the service life of the entire piston. Therefore, the expansion difference between the two is taken care of by spacing to prevent the catalytic unit from falling off. On the other hand, after the oil film undergoes a point-by-point catalytic reaction, the continuity and uniformity of the oil film on its surface are effectively destroyed, providing conditions for more oxygen to enter the catalyst surface. On the other hand, the local destruction of the oil film can promote the diffusion of smoke, dilute the boundary, and help block the flame from propagating to the oil film surface, further avoiding the formation of carbon deposits under high-temperature reactions.

[0025] 3. The rational design of the spark plug synergizes with the catalytic unit. This solution achieves this by designing the spark plug to extend inward and positioning its ignition position in the middle of the combustion chamber when the piston reaches top dead center. Thus, during the ignition phase, the center of the combustion chamber is the first area to ignite, followed by diffusion to the periphery. During this diffusion process, the catalyst on the piston surface receives a portion of the temperature through thermal radiation. Upon receiving this temperature, it reacts prematurely to produce bubbles, and then burns the oil mist generated by the bursting bubbles when the flame arrives. At the same time, the premature reaction of the catalytic unit rapidly consumes oxygen near the oil film, hindering the diffusion of the high-temperature flame at the core of the premixed gas to the wall, reducing the reaction temperature of the combustion chamber wall, and effectively controlling the temperature level around the oil film, further controlling the formation of carbon deposits.

[0026] 4. This solution designs the combustion chamber into an asymmetric structure. The piston utilizes this asymmetric structure during high-speed movement, which can effectively enhance the turbulence intensity of the airflow inside the combustion chamber and improve the breakability of the oil film, thereby strengthening the mass transfer on the oil film surface and further avoiding the formation of carbon deposits.

[0027] In summary, the implementation of this solution greatly improves the combustion efficiency of the engine under low-load conditions, avoids premature carbon deposits on the piston surface, ensures the safety of the combustion equipment, and increases the engine overhaul and maintenance time by at least 300 hours. Generally, there is no need to worry about the problem of product performance degradation caused by carbon deposits throughout the life cycle of the engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of the upper surface of the piston body in Example 1 of the present invention.

[0029] Figure 2This is another structural schematic diagram of the upper surface of the piston body in Example 2 of the present invention.

[0030] Figure 3 This is a schematic diagram of the structure of the combustion chamber of the aviation two-stroke engine in Example 3.

[0031] The reference numerals in the drawings of the specification include: piston body 1, edge non-catalytic portion 2, catalytic portion 3, central non-catalytic portion 4, catalytic unit 5, combustion chamber body 6, cylinder head 7, and spark plug 8. DETAILED DESCRIPTION

[0032] The following is further described in detail through specific implementation methods:

[0033] Example 1

[0034] Basically as attached Figure 1 As shown: A two-stroke engine piston for aviation, including a piston body 1, the upper surface of the piston body 1 is a convex structure with the middle portion higher than the edge. This design can adapt to the control of the liquid film thickness of the aircraft engine under different flight postures and motion conditions, while reducing the amount of inlay in the catalytic area of the piston surface to ensure uniform arrangement of the catalyst. The convex structure can be a spherical structure, a conical structure, etc., and this embodiment takes a spherical structure as an example. The upper surface of the piston body 1 is provided with a catalytic portion 3 and a non-catalytic portion 3, and the non-catalytic portion 3 surrounds the catalytic portion 3 inside. A plurality of catalytic units 5 coated with catalysts are arranged at intervals in the catalytic portion 3. The catalyst coated on the catalytic unit 5 is a precious metal catalyst suitable for hydrocarbon fuels such as 92# and above gasoline. In this embodiment, a Pt-Pd-Rh / Al2O3 catalyst is preferably used.

[0035] The effect of providing the catalytic unit 3 is that, under certain temperature conditions during the combustion phase, the catalyst's catalytic reaction with the fuel changes the thickness of the oil film. Specifically, the Pt-Pd-Rh / Al2O3 catalyst has an oxygen storage function. During the intake stroke of the combustion chamber, the catalyst pre-absorbs oxygen from the air onto the catalyst surface. When the combustion chamber is in the combustion phase, the catalytic reaction is triggered. At this time, if there is partially evaporated fuel on the piston surface (such as during a cold start or on the wall oil film), the catalyst releases oxygen to oxidize the fuel on the piston surface, generating bubbles such as CO2 and CO. When these bubbles break through the oil film, they break the oil film into oil mist, enhancing the combination of the oil mist with the oxygen in the combustion chamber and promoting its complete combustion. This consumes fuel on the wall, reducing the oil film thickness, while also preventing the formation of carbon deposits. In this way, the wall fuel is consumed, thereby reducing the liquid film thickness.

[0036] As a further optimization, the non-catalytic portion 3 comprises two parts: an edge non-catalytic portion 2 and a central non-catalytic portion 4. The catalytic portion 3 is located between the edge non-catalytic portion 2 and the central non-catalytic portion 4, and the three portions are coaxially distributed about the piston axis. The central non-catalytic portion 4 is located in the center of the piston top surface, with a radius less than 28% of the piston top surface radius. The edge non-catalytic portion 2 is located on the outer ring of the piston top surface, with a ring width of 25% of the piston top surface radius.

[0037] By rationally arranging the positions and widths of the catalytic portion 3 and two non-catalytic portions 3 on the piston surface, the development of the liquid film thickness can be effectively controlled while reducing the investment cost of the precious metal catalyst. Specifically, the peripheral non-catalytic portion 2 is located at the piston edge. High-speed movement of the piston creates a low-pressure zone in the friction pair area. This high-speed movement against the cylinder wall also promotes the destruction of the nearby oil film, ensuring sufficient oxygen supply for fuel combustion in this area, resulting in more complete combustion. The central non-catalytic portion 4 is located at the center of the piston. Taking advantage of the piston's convex structure, the liquid film thickness in this area can be effectively controlled.

[0038] The piston is made of aluminum alloy to improve the engine's power-to-weight ratio. Anodizing is performed on the upper surface of the piston to form a highly stable Al2O3 layer. This solution combines the Al2O3 layer with a Pt-Pd-Rh / Al2O3 catalyst to create a synergistic "protection + catalysis" system on the piston surface. The Al2O3 layer protects the piston substrate: Anodizing forms a dense, firmly bonded Al2O3 layer on the piston substrate, significantly improving surface wear resistance and resistance to high-temperature fuel gas corrosion. It also isolates the piston substrate from direct contact with the catalyst, preventing alloying reactions between the substrate and the precious metal. Furthermore, it provides stable mechanical support for the Pt-Pd-Rh / Al2O3 catalyst coating. The nanoscale pores in the Al2O3 layer provide anchoring points for the Pt-Pd-Rh / Al2O3 catalyst coating, enhancing the catalyst's adhesion.

[0039] At the same time, the nano-scale Al2O3 layer generated on the piston surface by anodic oxidation has extremely strong hydrophobicity, which can accelerate the discharge of the oil film in the non-catalytic part 3 and the interval area between the catalytic units 5 in the catalytic part 3.

[0040] A single catalytic unit 5 is circular, polygonal or bar-shaped, and the entire catalytic portion 3 can be composed of catalytic units 5 of any of the circular, polygonal or bar shapes, or a combination of catalytic units 5 of two or more shapes. This solution takes a circular catalytic unit 5 as an example.

[0041] By arranging the catalytic units 5 at intervals, on the one hand, since the combustion chamber is in a working environment where high temperature and low temperature alternate, and the piston base and the catalyst are two different materials, the catalytic units 5 are arranged at intervals to avoid the problem of catalyst shedding due to the expansion difference between the two during the expansion process. At the same time, since the working frequency of the piston is high, up to several thousand or even tens of thousands of revolutions per minute, the alternating load is large. If the adhesion between the two is unstable, it is very easy to affect the service life of the entire piston.

[0042] Since the posture changes of aircraft in the air are more complex and frequent, this solution divides the entire catalytic part 3 into multiple different small areas by arranging the catalytic units 5 at intervals. The purpose is to adapt to the different posture changes of the aircraft. There are many ways to arrange the catalytic units 5 at intervals. Figure 1 Take the following arrangement as an example:

[0043] like Figure 1 As shown, the catalytic units 5 are radially distributed in multiple layers along the radial direction of the piston, and the catalytic units 5 between two adjacent layers are staggered. The catalytic units 5 corresponding to each odd-numbered layer are located on the same radial line, and the catalytic units 5 corresponding to each even-numbered layer are located on the same radial line. The catalytic units 5 of the even-numbered layer are located on the angular bisector of the two adjacent catalytic units 5 in the odd-numbered layer, or the catalytic units 5 of the odd-numbered layer are located on the angular bisector of the two adjacent catalytic units 5 in the even-numbered layer.

[0044] In this embodiment, a piston with a diameter of 70 mm is used as an example. The diameter of the piston is 0-9 mm, which is the central non-catalytic portion 4. The diameter of the catalytic portion 3 is 9 mm-27 mm. The diameter of the catalytic portion 3 is 27 mm-35 mm, which is the edge non-catalytic portion 2. The catalytic portion 3 is radially distributed in four circles along the piston. The four circles of catalyst are respectively located at 20 mm, 30 mm, 40 mm, and 50 mm from the piston axis. Each circle has multiple catalytic units 5 distributed at equal intervals. Adjacent catalytic units 5 in the same circle are distributed at a circumferential angle of 20°. In order to better coordinate the catalytic units 5 in each circle, as a preferred embodiment, the diameter of the catalytic units 5 in the outermost two circles is 4 mm, and the diameter of the catalytic units 5 in the innermost circle and the second inner circle is 2 mm and 3 mm, respectively. The catalytic units 5 in the adjacent two circles are staggered. Specifically, from the inside to the outside, any catalytic unit 5 in the latter circle is located on the angle bisector of the two adjacent catalytic units 5 in the previous circle.

[0045] Example 2

[0046] The difference from Example 1 is that this embodiment arranges the catalytic units 5 in rows, the catalytic units 5 in odd-numbered rows correspond to each other and are located on the same straight line, the catalytic units 5 in even-numbered rows correspond to each other and are located on the same straight line, and the catalytic units 5 in two adjacent rows are staggered. Figure 2The structure shown is one of the structures, in which the catalytic units 5 are distributed in a regular hexagonal manner (in the figure, the connecting lines between the catalytic units 5 are only for reference and can be ignored), dividing the entire catalytic part 3 into multiple small areas of equal size.

[0047] Example 3

[0048] like Figure 3 As shown in FIG, a combustion chamber structure of a two-stroke aviation engine includes a combustion chamber body 6, which is enclosed by a cylinder block, a cylinder head 7, and the piston of Example 1. The piston is slidably connected to the cylinder block. The interior of the combustion chamber body 6 is an asymmetric structure. One approach is to design the piston as an asymmetric structure. However, in this solution, a catalytic unit 5 is required to be provided on the upper surface of the piston, so the processing technology is relatively difficult. In this embodiment, the cylinder head 7 is preferably designed as an asymmetric structure, such as Figure 3 , the angle between the left side of the cylinder head 7 and the piston is greater than the angle between the left side of the cylinder head 7 and the piston, or the top surface of the cylinder head 7 is designed to be an inclined structure, etc. By making the inner surface of the cylinder head 7 an asymmetric structure, the piston can effectively enhance the airflow turbulence inside the combustion chamber during movement, improve the flow on the combustion chamber wall, and strengthen surface mass transfer to avoid the formation of carbon deposits. The spark plug 8 on the cylinder head 7 is set inward, and the ignition position of the spark plug 8 is: located in the middle position of the combustion chamber body 6 when the piston moves to the top dead center. As a priority, the middle position can be specifically: the ignition position is located in the middle position between the cylinder head 7 and the piston, and is the middle position of the combustion chamber in the horizontal direction. In addition, the surface roughness of the combustion chamber is designed to be 1.6-6.3. Within this range, it can ensure the smoothness of the reciprocating motion of the piston, reduce the wear between the piston and the cylinder body, and improve the ability to break the oil film.

[0049] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A two-stroke engine piston for aviation, characterized by: The piston body comprises a piston body, the upper surface of which is a convex structure with the middle portion higher than the edge. The upper surface of the piston body is provided with a catalytic portion, and the catalytic portion is provided with a plurality of catalytic units coated with a catalyst for adsorbing and releasing oxygen.

2. The two-stroke engine piston for aviation according to claim 1, characterized in that: The upper surface of the piston body is further provided with a non-catalytic portion, and the catalytic portion is located inside the non-catalytic portion.

3. The two-stroke engine piston for aviation according to claim 2, characterized in that: The non-catalytic portion includes an edge non-catalytic portion and a central non-catalytic portion, and the catalytic portion is located between the edge non-catalytic portion and the central non-catalytic portion.

4. The two-stroke engine piston for aviation according to claim 3, characterized in that: Each catalytic unit divides the catalytic part into multiple small areas. The catalytic units are distributed in rows or radially along the radial direction of the piston. The catalytic units between two adjacent rows / layers are staggered.

5. The two-stroke engine piston for aviation according to claim 4, characterized in that: The catalytic units corresponding to the odd-numbered layers are located on the same radial line, and the catalytic units corresponding to the even-numbered layers are located on the same radial line.

6. The two-stroke engine piston for aviation according to claim 5, characterized in that: The catalytic units of the even-numbered layers are located on the bisector of the angle between two adjacent catalytic units of the odd-numbered layers, or the catalytic units of the odd-numbered layers are located on the bisector of the angle between two adjacent catalytic units of the even-numbered layers.

7. The two-stroke engine piston for aviation according to claim 6, characterized in that: Each of the catalytic units is in one or more of a circular, polygonal, and bar shape, and the catalyst is a Pt-Pd-Rh / Al2O3 catalyst.

8. A combustion chamber structure for a two-stroke aviation engine, characterized by: The combustion chamber body comprises a combustion chamber body having an asymmetric structure therein. The combustion chamber body is enclosed by a cylinder body, a cylinder head and a piston as described in any one of claims 1 to 7. The piston is slidably connected in the cylinder body. A spark plug is provided on the cylinder head. The ignition position of the spark plug is located in the middle of the combustion chamber body when the piston moves to the top dead center.

9. The combustion chamber structure of a two-stroke aviation engine according to claim 8, characterized in that: The inner surface of the cylinder head has an asymmetric structure, and the inclination angles of the inner peripheral wall of the cylinder head are different.

10. An application of a piston and combustion chamber structure for a two-stroke aviation engine, characterized in that: The aviation two-stroke engine piston according to any one of claims 1 to 7 and the combustion chamber structure according to claim 8 are applied to the field of aviation two-stroke engines.

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