Variable volume wave supercharged two stroke engine exhaust system for drones

Abstract

The application provides a variable volume wave supercharged two-stroke engine exhaust system for a UAV, and belongs to the technical field of aviation power, which comprises a first expansion cavity, an inlet end of which is directly connected with an engine exhaust passage; a second variable resonance cavity, which is connected with an outlet end of the first expansion cavity through a connecting pipe; and a high-altitude compensation valve, which is installed at a final exhaust outlet position of the second variable resonance cavity; wherein the second variable resonance cavity is internally provided with a flexible diaphragm, which separates the second variable resonance cavity into an upper air chamber and a lower air chamber which are isolated from each other, the lower air chamber is connected with an inner cavity of the connecting pipe; and the flexible diaphragm is configured to be elastically deformed according to changes in exhaust pulse pressure in the lower air chamber, in the application, the variable resonance cavity changes the volume dynamically, so that the resonance frequency of the exhaust system can follow changes in engine speed, and excellent power response and fuel economy can be provided in a wider throttle range.

Description

Technical Field

[0001] This invention belongs to the field of aviation power technology, specifically a variable volume wave-charged two-stroke engine exhaust system for unmanned aerial vehicles. Background Technology

[0002] Two-stroke engines are widely used in small and medium-sized unmanned aerial vehicles (UAVs) due to their simple structure and high power output per liter. Their performance is highly dependent on the design of the exhaust system. High-performance two-stroke engines generally adopt an "expansion chamber" type exhaust system, which utilizes the reflection of exhaust pressure waves in the pipe to generate negative pressure during scavenging, helping to draw out exhaust gases from the cylinder and draw in fresh charge, which is the "wave supercharging" effect.

[0003] However, existing fixed expansion chamber exhaust systems have inherent drawbacks:

[0004] Poor high-altitude adaptability: The wave boosting effect relies on the interaction between the exhaust system outlet and the ambient back pressure. When the UAV climbs, the ambient atmospheric pressure drops sharply, causing the exhaust wave system to be over-expanded, weakening or even eliminating the negative pressure effect. This results in a sharp drop in the engine's scavenging efficiency and a severe reduction in power output, becoming a key factor limiting the UAV's altitude and high-speed performance.

[0005] Narrow effective speed range: Exhaust systems with fixed geometry have a fixed resonant frequency, and can only produce optimal boost within a narrow range of engine speeds. This results in poor power and fuel economy during variable-speed flight (such as climbs and maneuvers).

[0006] Currently, some solutions, such as manually adjustable exhaust ports or complex electronically controlled variable valve mechanisms, are either not adjustable in flight or are complex in structure, have poor reliability, and are heavy, making them unsuitable for UAV platforms that are extremely sensitive to reliability and weight.

[0007] Therefore, there is an urgent need for a two-stroke engine exhaust system that can automatically adapt to changes in altitude and speed, and has a relatively simple and reliable structure. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide a variable volume wave supercharging two-stroke engine exhaust system for unmanned aerial vehicles.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] A variable volume wave-charged two-stroke engine exhaust system for unmanned aerial vehicles (UAVs), connected to the engine cylinder head exhaust port, includes:

[0011] The first-stage expansion chamber has its inlet directly connected to the engine exhaust manifold.

[0012] The secondary variable resonant cavity is connected to the outlet end of the primary expansion cavity via a connecting pipe;

[0013] A high-altitude compensation valve is installed at the final exhaust outlet position of the secondary variable resonant cavity;

[0014] The secondary variable resonant cavity is equipped with a flexible diaphragm, which divides the secondary variable resonant cavity into an upper air chamber and a lower air chamber that are isolated from each other. The lower air chamber is connected to the inner cavity of the connecting pipe. The flexible diaphragm is configured to elastically deform according to the change in exhaust pulse pressure in the lower air chamber.

[0015] As a further improvement: the high-altitude compensation valve includes a valve body, a valve disc, and a pneumatic actuator; the pneumatic actuator is a sealed diaphragm structure, which is pre-encapsulated with an inert gas at a certain pressure, and the outside of the diaphragm is in direct contact with the ambient atmosphere; when the ambient air pressure decreases, the diaphragm expands and drives the valve disc to move in the direction of reducing the exhaust opening.

[0016] As a further improvement, the valve disc can be a butterfly valve or a lift valve.

[0017] As a further improvement: the flexible diaphragm is made of high-temperature resistant metal alloy or composite material, and its shape is corrugated or flat.

[0018] As a further improvement: the volume of the primary expansion chamber is set to 1.5 to 3 times the displacement of a single engine cylinder, and the geometry of the primary expansion chamber is a gradually expanding cone or sphere.

[0019] As a further improvement, the length and cross-sectional diameter of the connecting pipe are determined by a combination of computational fluid dynamics simulation and acoustic simulation, based on the rotational speed corresponding to the engine's target power point.

[0020] As a further improvement: the entire exhaust system is formed by welding thin-walled titanium alloy or high-temperature stainless steel, and at least a portion of the outer surface is covered with a lightweight heat insulation layer.

[0021] Compared with the prior art, the beneficial effects of the present invention are: through the automatic adjustment of the high-altitude compensation valve, the exhaust wave boosting effect can be effectively maintained, the engine power attenuation rate is significantly lower than that of a fixed exhaust system, and the service ceiling and high-speed performance of the UAV are greatly improved.

[0022] The variable resonant cavity dynamically changes its volume, allowing the resonant frequency of the exhaust system to follow the engine speed, providing excellent power response and fuel economy over a wider throttle range. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of the overall structure of an exhaust system for a variable volume wave supercharged two-stroke engine used in unmanned aerial vehicles (UAVs).

[0024] Figure 2 This is a schematic diagram of the working state of a two-stage variable resonant cavity under high speed (high voltage pulse);

[0025] Figure 3 This is a schematic diagram of the working state of a two-stage variable resonant cavity under high speed (high voltage pulse);

[0026] Figure 4 This is a schematic diagram of the working state of the high-altitude compensation valve at sea level.

[0027] Figure 5 This is a schematic diagram of the working state of the high-altitude compensation valve at high altitude.

[0028] In the diagram: 1. Primary expansion chamber; 2. Secondary variable resonant chamber; 3. Connecting pipe; 4. High-altitude compensation valve; 5. Flexible diaphragm; 6. Upper air chamber; 7. Lower air chamber; 8. Valve body; 9. Valve disc; 10. Pneumatic actuator; 11. Heat insulation layer; 12. Exhaust port. Detailed Implementation

[0029] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0030] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0031] Please see Figures 1 to 5 In one embodiment, a variable volume wave-charged two-stroke engine exhaust system for a drone, connected to the engine cylinder head exhaust port, includes:

[0032] The first-stage expansion chamber 1 has its inlet end directly connected to the engine exhaust passage;

[0033] The secondary variable resonant cavity 2 is connected to the outlet end of the primary expansion cavity 1 via a connecting pipe 3;

[0034] The high-altitude compensation valve 4 is installed at the final exhaust outlet position of the secondary variable resonant cavity 2;

[0035] The secondary variable resonant cavity 2 is provided with a flexible diaphragm 5 inside, which divides the secondary variable resonant cavity 2 into an upper air chamber 6 and a lower air chamber 7 that are isolated from each other. The lower air chamber 7 is connected to the inner cavity of the connecting pipe 3. The flexible diaphragm 5 is configured to elastically deform according to the change of exhaust pulse pressure in the lower air chamber 7.

[0036] In this embodiment, an exhaust port 12 is also provided on one side of the second-stage variable resonator 2. The first-stage expansion cavity 1 is the main wave boosting structure of the system. Its function is to generate an initial negative pressure reflection wave. Its volume and shape are carefully designed to provide a powerful basic wave boosting effect within the target speed range.

[0037] The lower chamber 7 is directly connected to the exhaust pulse from the engine. When the exhaust pulse pressure acts on the flexible diaphragm 5, the diaphragm undergoes elastic deformation and bulges upward, instantly increasing the volume of the lower chamber 7. After the pulse passes, the pressure drops, and the diaphragm returns to its original position under its own elastic restoring force. This process causes the equivalent volume of the resonant cavity to change dynamically with the engine's exhaust frequency (which is related to the engine speed). The effect is equivalent to a self-tuning Helmholtz resonator, which can broaden the effective resonant frequency range of the system and adapt to a wider range of engine speeds.

[0038] In this embodiment, the exhaust system is connected to the engine cylinder head via a flange. The high-temperature, high-pressure exhaust first enters the primary expansion chamber 1, where it undergoes initial expansion and pressure wave reflection. Subsequently, the airflow passes through the optimized-size connecting pipe 3 and enters the lower chamber 7 of the secondary variable resonant chamber 2.

[0039] When the engine is at high speed, the exhaust pulse pressure and frequency are high. Under the action of high frequency and high pressure, the flexible diaphragm 5 generates a large-amplitude reciprocating vibration, which increases the equivalent average volume of the secondary variable resonant cavity 2 and decreases the resonant frequency to meet the requirements of high speed. Conversely, at low speed, the pulse pressure is lower, the vibration amplitude of the flexible diaphragm 5 is smaller, the equivalent volume is smaller, and the resonant frequency is relatively higher to match the low-speed operating conditions. In this way, the system achieves self-adaptation to engine speed.

[0040] Please see Figures 1 to 5 In one embodiment, the high-altitude compensation valve 4 includes a valve body 8, a valve disc 9, and a pneumatic actuator 10; the pneumatic actuator 10 is a sealed diaphragm structure, which is pre-encapsulated with an inert gas at a certain pressure, and the outside of the diaphragm is in direct contact with the ambient atmosphere; when the ambient air pressure decreases, the diaphragm expands and drives the valve disc 9 to move in the direction of reducing the exhaust opening.

[0041] In this embodiment, the operation of the high-altitude compensation valve 4 is as follows: At sea level, the ambient air pressure is approximately 101 kPa, which is greater than the pre-charge pressure inside the diaphragm 10 (e.g., set to 70 kPa corresponding to an altitude of 3000 meters). The diaphragm is compressed, and the valve disc 9 is in a fully open state. When the UAV climbs to an altitude of 5000 meters, the ambient air pressure drops to approximately 54 kPa, which is lower than the pre-charge pressure inside the diaphragm. The diaphragm expands, driving the valve disc 9 to rotate, reducing the opening to a predetermined position. This increases the back pressure of the entire exhaust system, ensuring the normal operation of the wave boosting effect.

[0042] At sea level, the high ambient air pressure compresses the diaphragm, keeping the valve fully or deeply open, allowing for unimpeded exhaust. As altitude increases, the ambient air pressure decreases, increasing the pressure difference between the inside and outside of the diaphragm. This causes the diaphragm to expand, driving valve disc 9 to rotate or lift, thereby reducing the exhaust opening. This process automatically increases the back pressure of the exhaust system, simulating the exhaust environment at low altitudes. This effectively prevents the failure of the wave boosting effect and suppresses high-altitude power loss in the engine.

[0043] In one embodiment, the valve disc 9 adopts a butterfly valve structure or a lift valve structure.

[0044] In this embodiment, the opening degree of valve disc 9 is continuously controlled by the ambient air pressure, achieving stepless adjustment from fully open at sea level to nearly closed at a predetermined altitude (e.g., 5000 meters).

[0045] Please see Figures 1 to 5 In one embodiment, the flexible diaphragm 5 is made of a high-temperature resistant metal alloy or composite material, and its shape is corrugated or flat.

[0046] In this embodiment, the stiffness of the flexible diaphragm 5 is designed to allow it to undergo significant reciprocating deformation under exhaust pulse pressure within the engine's operating speed range.

[0047] Please see Figures 1 to 5 In one embodiment, the volume of the primary expansion chamber 1 is set to 1.5 to 3 times the displacement of a single engine cylinder, and the geometry of the primary expansion chamber 1 is a gradually expanding conical or spherical shape.

[0048] In one embodiment, the length and cross-sectional diameter of the connecting pipe 3 are determined by a combination of computational fluid dynamics simulation and acoustic simulation, based on the rotational speed corresponding to the engine's target power point.

[0049] In this embodiment, the length and cross-sectional diameter of the connecting pipe 3 are determined by joint optimization of computational fluid dynamics simulation and acoustic simulation in order to generate a strong scavenging negative pressure wave in a specific speed range.

[0050] In one embodiment, the entire exhaust system is formed by welding of thin-walled titanium alloy or high-temperature stainless steel and is covered with a lightweight heat insulation layer 11 on at least a portion of its outer surface.

[0051] In this embodiment, the lightweight heat insulation layer 11 is an aerospace-grade glass fiber heat insulation layer 11 to reduce the thermal impact on the aircraft.

[0052] The system requires no external sensors, ECU, or actuation energy, and works automatically entirely based on physical principles (pressure difference, pressure pulse). It has extremely high reliability and environmental adaptability, making it very suitable for drone applications.

[0053] Using advanced materials such as thin-walled titanium alloy and with an integrated structural design, the weight and volume of the system are strictly controlled while increasing functionality, resulting in a significant advantage in power-to-weight ratio.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0055] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A variable volume wave-charged two-stroke engine exhaust system for unmanned aerial vehicles (UAVs), connected to the engine cylinder head exhaust port, characterized in that, include: The first-stage expansion chamber has its inlet directly connected to the engine exhaust manifold. The secondary variable resonant cavity is connected to the outlet end of the primary expansion cavity via a connecting pipe; A high-altitude compensation valve is installed at the final exhaust outlet position of the secondary variable resonant cavity; The secondary variable resonant cavity is equipped with a flexible diaphragm, which divides the secondary variable resonant cavity into an upper air chamber and a lower air chamber that are isolated from each other. The lower air chamber is connected to the inner cavity of the connecting pipe. The flexible diaphragm is configured to elastically deform according to the change in exhaust pulse pressure in the lower air chamber.

2. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 1, characterized in that, The high-altitude compensation valve includes a valve body, a valve disc, and a pneumatic actuator. The pneumatic actuator is a sealed diaphragm structure, which is pre-encapsulated with an inert gas at a certain pressure, and the outside of the diaphragm is in direct contact with the ambient atmosphere. When the ambient air pressure decreases, the diaphragm expands and drives the valve disc to move in the direction of reducing the exhaust opening.

3. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 2, characterized in that, The valve disc adopts a butterfly valve structure or a lift valve structure.

4. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 1, characterized in that, The flexible diaphragm is made of high-temperature resistant metal alloy or composite material, and its shape is corrugated or flat.

5. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 4, characterized in that, The volume of the primary expansion chamber is set to 1.5 to 3 times the displacement of a single engine cylinder, and the geometry of the primary expansion chamber is a gradually expanding cone or sphere.

6. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 5, characterized in that, The length and cross-sectional diameter of the connecting pipe are determined by a combination of computational fluid dynamics simulation and acoustic simulation, based on the rotational speed corresponding to the engine's target power point.

7. The exhaust system for a variable volume wave-charged two-stroke engine for an unmanned aerial vehicle according to claim 6, characterized in that, The entire exhaust system is formed by welding thin-walled titanium alloy or high-temperature stainless steel and is covered with a lightweight heat insulation layer on at least part of its outer surface.

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