Ejecting mode plasma enhanced combustion method for rocket-based combined cycle engine

Abstract

The invention discloses an injection mode plasma enhanced combustion method for a rocket-based combined cycle engine, and the engine comprises a ramjet combustion chamber body which is of a cavity structure with front and rear openings; the rear end of the rocket combustion chamber is connected with the side wall of the front end of the ram combustion chamber body; a plurality of air inlet pipes are connected to the front end of the shell, and a plasma generator is arranged on each air inlet pipe; kerosene cooling channels are arranged in the shell of the stamping combustion chamber body and the shell of the rocket combustion chamber; the kerosene cooling channel is used for bearing kerosene so as to absorb heat in the stamping combustion chamber body and the rocket combustion chamber, the kerosene is cracked into cracked gas after absorbing heat, the cracked gas is input into the rocket combustion chamber, mixed with the high-temperature active groups for combustion and injected into a stamping flow channel in the stamping combustion chamber body. According to the rocket-based combined cycle engine combustion chamber, waste heat of the wall face of the combustion chamber is utilized, the combustion performance of an RBCC engine in a rocket injection mode and a rocket stamping mode is improved, and therefore thrust and specific impulse are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of rocket-based combined cycle engines, and particularly relates to a method for plasma-enhanced combustion in the ejector mode of a rocket-based combined cycle engine. Background Art

[0002] As a representative of wide-speed-range and wide-envelope flight, the rocket-based combined cycle (RBCC) engine has the characteristics of high specific impulse, large thrust variation, light structural mass, and high economy, and has great potential in future hypersonic flight and reusable aircraft. In the pure rocket mode, rocket ejector mode, and rocket ramjet mode of the RBCC engine operation, a rocket engine is required. Therefore, improving the thrust and specific impulse performance of the rocket engine can improve the overall performance of the RBCC engine in this mode. The rocket ejector mode is an important link in the mode transition of the RBCC engine. When the rocket engine maintains a large flow rate in the ejector mode, the thrust performance of the RBCC engine can be improved, but the overall specific impulse performance of the RBCC engine in the ejector mode cannot be improved. When the rocket engine maintains a small flow rate in the ejector mode, it often cannot meet the requirements of the engine's air entrainment ratio and thrust performance, and it is difficult to maintain flame stability, so it cannot reach an efficient combustion state. The independent rocket supply and ramjet supply circulation systems make it impossible for the heat in the cooling channel to return well to the combustion chamber thermodynamic cycle, resulting in a loss of engine thrust and specific impulse performance. In the ejector mode, if the waste heat of the ramjet combustion chamber wall is recycled into the ramjet combustion chamber, the kerosene combustion performance cannot be improved to a large extent. However, bringing the waste heat into the rocket combustion chamber to achieve the thermodynamic coupling cycle of the rocket and ramjet channels can further improve the kerosene combustion efficiency, increase the combustion chamber wall temperature, further promote kerosene cracking, and thus improve the engine thrust and specific impulse performance. Using a plasma generator to highly ionize air or oxygen to form some more active oxidant ions, which are mixed and burned with the kerosene cracking gas in the rocket combustion chamber, will further improve the mixing and combustion efficiency, increase the combustion temperature and pressure of the rocket engine, and further improve the rocket thrust and specific impulse.

[0003] In currently commonly used rocket combined engines, usually the ramjet combustion chamber and the built-in rocket share liquid kerosene, and liquid kerosene is also used for the cooling of the rocket and ramjet combustion chamber walls. Although high-density endothermic kerosene has a considerable physical heat sink, in order to improve the ejector performance of the engine, the combustion temperature of the rocket combustion chamber will be further increased, resulting in an increase in the combustion chamber wall temperature and the wall heat flux density. At this time, a larger cooling kerosene flow rate is required to achieve phase-change-free cooling. Summary of the Invention

[0004] The object of the present invention is to provide a method for plasma-enhanced combustion in the ejector mode of a rocket-based combined cycle engine, which can improve the combustion performance of the RBCC engine in the rocket ejector mode and the rocket ramjet mode on the premise of utilizing the waste heat of the combustion chamber wall, and further improve the thrust and specific impulse.

[0005] The present invention adopts the following technical solutions: A rocket-based combined cycle engine, comprising:

[0006] A ramjet combustion chamber body, which is a cavity structure with openings at both the front and the rear. Its front end is the combustion chamber inlet end and serves as the incoming air inlet.

[0007] A rocket combustion chamber, which is a cavity structure. Its rear end is connected to the side wall of the front end of the ramjet combustion chamber body and is in communication with the chamber of the ramjet combustion chamber body. A plurality of intake pipes are connected to its front end, and plasma generators are arranged on each intake pipe. The front ends of the intake pipes are used to be connected to a plasma gas source. The plasma generator is used to ionize the plasma gas source to form high-temperature active groups.

[0008] A kerosene cooling channel is arranged in the shells of the ramjet combustion chamber body and the rocket combustion chamber. The inlet end of the kerosene cooling channel is located at the rear end of the ramjet combustion chamber body and is used to be connected to the liquid kerosene storage tank pipeline. Its outlet end is located at the outlet end of the rocket combustion chamber, and the outlet end is in pipeline communication with the inner cavity of the rocket combustion chamber.

[0009] The kerosene cooling channel is used to carry kerosene to absorb the heat in the ramjet combustion chamber body and the rocket combustion chamber, and after absorbing heat, it is cracked into cracked gas, which is input into the rocket combustion chamber, mixed and burned with the high-temperature active groups to form a high-temperature jet, and then injected into the ramjet flow channel in the ramjet combustion chamber body to burn secondary with the incoming air and kerosene.

[0010] Further, a cracked gas supply valve is arranged on the pipeline between the outlet of the kerosene cooling channel and the rocket combustion chamber. The cracked gas supply valve is used to adjust the flow rate of the cracked gas supply.

[0011] Further, each of the plasma generators is connected to a plasma power source.

[0012] Further, the inner cavity of the ramjet combustion chamber body is in pipeline communication with the liquid kerosene pipeline.

[0013] The present invention also discloses a method for plasma-enhanced combustion in the ejector mode of a rocket-based combined cycle engine. The method is as follows:

[0014] Liquid kerosene flows into the kerosene cooling channel from the inlet end, absorbs the heat from the walls of the rocket combustion chamber and the ramjet combustion chamber body, and the kerosene cracks into cracked gas, which enters the rocket combustion chamber from the outlet end; at the same time, the plasma gas source enters the plasma generator through the pipeline, and the plasma generator ionizes it into active groups and introduces them into the rocket combustion chamber, where they burn and react with the kerosene cracked gas to form a high-temperature jet; the high-temperature jet is injected into the ramjet flow channel in the ramjet combustion chamber body and burns again with the oncoming air and kerosene in the ramjet combustion chamber body.

[0015] The beneficial effects of the present invention are as follows: 1. Utilize the high-temperature kerosene cracked gas and high-temperature active plasma jet in the rocket combustion chamber and the ramjet combustion chamber for mixing and combustion, improve the mixing and combustion efficiency in the narrow space of the rocket combustion chamber, thereby increasing the combustion temperature and pressure in the rocket combustion chamber and improving the specific impulse of the engine. It can directly increase the rocket specific impulse in the pure rocket mode. 2. Utilize the self-induced oxygen / air arc plasma to form high-temperature active gas. The cracked gas is a mixture of high-temperature small-molecule gases, which are mixed and burned with the high-temperature active groups of the plasma jet in the low-speed environment of the combustion chamber, increasing the combustion temperature and pressure in the rocket combustion chamber, and at the same time increasing the rocket jet velocity. In the rocket ejector mode, the ejector capacity can be increased to a greater extent, promoting the combustion organization in the ramjet flow channel. In the rocket-ramjet mode, a higher ejector ratio (air entrainment amount) can increase the kerosene injection amount in the ramjet flow channel, and a higher rocket jet temperature can improve the kerosene combustion efficiency in the ramjet flow channel, improving the thrust and specific impulse performance of the ramjet flow channel, and thus improving the overall performance of the RBCC engine. 3. Utilize normal-temperature liquid kerosene to actively cool the high-temperature walls of the rocket combustion chamber and the ramjet combustion chamber. The kerosene evaporates and cracks in the cooling channel to form combustible small-molecule gases. The kerosene cracked gas is controlled by the pipeline and its valve assembly and input into the rocket engine combustion chamber. Use liquid kerosene to cool the local high-temperature area to form kerosene cracked gas. The integrated cooling solution for the walls of the rocket combustion chamber and the ramjet combustion chamber can make the most of the waste heat of the shell, inject it into the thermal cycle of the RBCC engine combustion chamber to a greater extent, and at the same time concentrate the energy and release it in the rocket combustion chamber, which can increase the combustion efficiency to a greater extent, not only improving the rocket thrust and specific impulse performance, but also increasing the gain of the rocket's effect on the ramjet flow channel. 4. The plasma gas source is oxygen or air, which is convenient to store. Brief Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of a rocket-based combined cycle engine in the present invention;

[0017] Among them: 1. Ramjet combustion chamber body; 2. Plasma gas source; 3. Plasma power supply; 4. Cracked gas supply valve; 5. Plasma generator; 6. Rocket combustion chamber; 7. Kerosene cooling channel; 8. Liquid kerosene storage tank; 9. Injection support plate. Detailed Embodiments

[0018] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0019] The present invention discloses a rocket-based combined cycle engine, as Figure 1 shown, including:

[0020] A ram combustion chamber body 1, which is a cavity structure with openings at both the front and the rear. Its front end is the combustion chamber inlet end and serves as the inlet for the oncoming air. The inner cavity of the ram combustion chamber body 1 is connected to the liquid kerosene pipeline. Specifically, a jet plate 9 is arranged in the ram combustion chamber body 1, and the jet plate 9 is connected to the liquid kerosene storage tank 8 through a pipeline.

[0021] A rocket combustion chamber 6, which is a cavity structure. Its rear end is connected to the side wall of the front end of the ram combustion chamber body 1 and is in communication with the chamber of the ram combustion chamber body 1; its front end is connected with a plurality of intake pipes, and plasma generators 5 are arranged on each intake pipe; the front ends of the intake pipes are used to be connected to a plasma gas source 2; the plasma generators 5 are used to ionize the plasma gas source 2 to form high-temperature active groups, and each plasma generator 5 is connected to a plasma power supply 3. The plasma gas source is oxygen or air, which is convenient for storage; the plasma power supply is small in size and light in weight.

[0022] A kerosene cooling channel 7 is arranged in the shells of the ram combustion chamber body 1 and the rocket combustion chamber 6. The inlet end of the kerosene cooling channel 7 is located at the rear end of the ram combustion chamber body 1 and is used to be connected to the liquid kerosene storage tank 8 through a pipeline; its outlet end is located at the outlet end of the rocket combustion chamber 6, and the outlet end is in communication with the inner cavity of the rocket combustion chamber 6 through a pipeline.

[0023] The kerosene cooling channel 7 is used to carry kerosene inside to absorb the heat in the ram combustion chamber body 1 and the rocket combustion chamber 6, and after absorbing heat, it is cracked into cracked gas, which is input into the rocket combustion chamber 6, mixed and burned with the high-temperature active groups to form a high-temperature jet, and then injected into the ram flow channel in the ram combustion chamber body 1 to secondary combust with the oncoming air and kerosene in the ram combustion chamber body 1.

[0024] A cracked gas supply valve 4 is arranged on the pipeline between the outlet of the above-mentioned kerosene cooling channel 7 and the rocket combustion chamber 6. The cracked gas supply valve 4 is used to adjust the flow rate of the cracked gas supply, thereby controlling the thrust of the rocket engine.

[0025] The present invention also discloses a method for plasma-enhanced combustion in the ejector mode of a rocket-based combined cycle engine. The method is as follows:

[0026] Liquid kerosene flows into the kerosene cooling channel 7 from the inlet end, absorbs the heat from the walls of the rocket combustion chamber 6 and the ramjet combustion chamber body 1, and the kerosene cracks into cracked gas, which enters the rocket combustion chamber 6 from the outlet end; meanwhile, the plasma gas source 2 enters the plasma generator 5 through the pipeline, is ionized into active groups by the plasma generator 5, and is introduced into the rocket combustion chamber 6, where it undergoes a combustion reaction with the cracked gas of kerosene to form a high-temperature jet; the high-temperature jet is injected into the ramjet flow channel in the ramjet combustion chamber body 1 and undergoes a secondary combustion reaction with the incoming air and kerosene.

[0027] Since the pressure in the ejector rocket combustion chamber of RBCC is relatively low, while the pressure at the inlet end of the kerosene cooling channel 7 is as high as several megapascals, the cracked gas after heat exchange and cracking in the cooling channel 7 can also meet the pressure requirements of the rocket engine combustion chamber. Therefore, only relying on the pressure of the kerosene storage tank can meet the flow requirements, and no additional work components such as pumps are needed.

[0028] In this embodiment, the design pressure of the rocket combustion chamber 6 is 3 MPa. According to the flight state and mission requirements, the two-way flow is allocated. The first-way kerosene directly enters the ramjet combustion chamber body 1 to react and burn with the incoming air and the rocket jet in the rocket combustion chamber 6, and the second-way kerosene is input into the kerosene cooling channel 7 on the wall of the shell through the pipeline for cooling the wall of the ramjet combustion chamber body 1.

[0029] According to the engine size, the oxidizer demand, and the power of the plasma generator 5, two, four, or more plasma generators 5 are selected to be circumferentially distributed.

[0030] The plasma gas source 2 is input into the plasma generator 5 through the pipeline. Under the action of the high-voltage power supply, the gas between the positive and negative electrodes will be broken down to form an active plasma jet. The plasma jet reacts violently with the cracked gas in the rocket combustion chamber 6 to form high-temperature and high-pressure gas, which is injected into the flow channel in the ramjet combustion chamber body 1 through the rocket nozzle, and undergoes a combustion reaction with the incoming air and the kerosene injected by the strut, forming a high-speed jet, improving the anti-backpressure ability of the isolator, improving the ejector ability in the ejector mode, and improving the secondary combustion performance in the rocket-ramjet mode, and finally improving the overall performance of the engine.

[0031] The pressure of the liquid kerosene storage tank 8 > 10 Mpa. The kerosene undergoes heat exchange and evaporation through the kerosene cooling channel 7. The temperature of the kerosene in the kerosene cooling channel 7 continuously rises and exceeds 870 K, and the kerosene begins to crack until the outlet of the kerosene cooling channel 7, and the kerosene cracks into cracked gas. The cracked gas is injected into the rocket combustion chamber 6 through the cracked gas supply valve 5 on the premise of ensuring that the upstream pressure of the cracked gas > 3 MPa.

[0032] Under the action of the high-voltage electrode, the plasma generator 5 ionizes the working medium oxygen / air into high-temperature active groups. The oxidant active groups then react with the high-temperature pyrolysis gas by combustion, increasing the thrust and specific impulse of the rocket engine. In the rocket ramjet mode, the high-temperature rocket jet enhanced by plasma promotes the mixing, atomization, and combustion process of the liquid kerosene ejected from the injection strut 9, improving the combustion efficiency of kerosene in the ramjet combustion chamber body 1. In the pure rocket mode, based on the combustion enhancement effect of plasma, the combustion efficiency, temperature, and pressure of the rocket combustion chamber are increased, thereby increasing the thrust and specific impulse of the rocket engine. Due to the increase in the combustion temperature in the ramjet combustion chamber body 1, the temperature of the engine casing rises, increasing the heat transfer flux density of the kerosene in the kerosene cooling channel and further promoting the cracking of kerosene, enabling the entire thermodynamic cycle system to operate normally.

[0033] Kerosene cracking generally occurs at temperatures above 875K, and the cracking rate increases with increasing temperature. In the temperature range of 875K to 1050K, the kerosene cracking rate can gradually reach 100%. The variation of the kerosene cracking rate with temperature is shown in Table 1 below:

[0034] Table 1 Variation of Kerosene Cracking Rate with Temperature

[0035] Temperature / K 870 900 920 950 980 1050 Cracking rate of kerosene 0 3％ 5％ 20％ 60％ ～100％

[0036] Kerosene is a complex multi-component mixture, and the types of its cracking products are even more numerous. In theoretical and calculation processes, kerosene and its cracking products are usually quantitatively simplified to satisfy both physical and chemical properties and have simple components. Taking JP-10 as an example, its simplified cracking products are shown in Table 2 below:

[0037] Table 2 Cracking Products and Contents

[0038]

[0039] In this embodiment, the NASA CEA is selected for the theoretical calculation process to obtain the combustion chamber outlet temperature, gas components, and rocket ground and vacuum specific impulse performance corresponding to the chemical equilibrium state. The combustion process is assumed to be constant-pressure combustion, and it is also assumed that the pressure remains the same as that of JP-10 when calculating different fuels. When calculating, the reactant composition, temperature, and rocket combustion chamber pressure need to be given, and the kerosene cracking rate is obtained through different kerosene temperatures. Under different kerosene cracking rate conditions, the contents of each component in the kerosene cracking gas remain unchanged, and only the amount of kerosene cracking is increased or decreased. The rocket specific impulse gain brought by the kerosene cracking rate in the range of 0-50% (corresponding to the temperature range of 870K-975K) is calculated. According to the power of the plasma generator 5, the degree of oxygen ionization is theoretically calculated from 0-50%, and the theoretical specific impulse gain brought by different degrees of oxygen ionization is compared. When calculating the RBCC combustion process, the reactant components include rocket fuel, rocket oxidizer, incoming flow air, and secondary fuel. In the ejector mode calculation, only the rocket specific impulse gain is considered.

[0040] Theoretical calculations are carried out using chemical equilibrium reactions. The influence of the kerosene cracking rate on the rocket's theoretical specific impulse performance is exemplified by an oxygen ionization rate of 10% (2000K) and 5% (2500K), and a kerosene cracking rate of 50% (975K) and 5% (920K):

[0041] Condition 1:

[0042] When the kerosene cracking rate is 50%, the temperature of the cracked gas and JP-10 mixture is 975K; when the oxygen ionization rate is 10%, the design temperature is 2500K; the combustion chamber pressure is designed to be 3MPa. The equivalence ratio of the rocket combustion chamber 6 is 1.0, that is, the ratio of the content of gaseous JP-10 to the content of cracked gas is 1:1; the ratio of the oxygen content to the O* content is 9:1. Using chemical equilibrium combustion calculation, the theoretical combustion temperature of the combustion chamber is 4288.62K, the gas specific heat ratio is 1.1546, the vacuum specific impulse is 385.6s, and the ground specific impulse is 344.1s.

[0043] Condition 2:

[0044] When the kerosene cracking rate is 5%, the temperature of the cracked gas and JP-10 mixture is 920K; when the oxygen ionization rate is 10%, the design temperature is 2500K; the combustion chamber pressure is designed to be 3MPa. The equivalence ratio of the rocket combustion chamber 6 is 1.0, that is, the ratio of the content of gaseous JP-10 to the content of cracked gas is 19:1; the ratio of the oxygen content to the O* content is 9:1. Using chemical equilibrium combustion calculation, the theoretical combustion temperature of the combustion chamber is 4159.7K, the gas specific heat ratio is 1.1496, the vacuum specific impulse is 347.2s, and the ground specific impulse is 309.8s.

[0045] From the above two operating conditions, it can be concluded that when the kerosene cracking rate increases from 5% to 50%, the rocket specific impulse can be significantly improved. The vacuum specific impulse increases by about 38.4 s, and the sea-level specific impulse increases by about 34.3 s. When the plasma power is reduced and the degree of oxidizer ionization is reduced to 5%, the theoretical specific impulse performance under this operating condition is obtained:

[0046] Operating condition three:

[0047] When the kerosene cracking rate is 50%, the temperature of the cracked gas and JP-10 mixture gas is 975 K; when the oxygen ionization rate is 5%, the designed temperature is 2500 K; the designed combustion chamber pressure is 3 MPa. The equivalence ratio of the rocket combustion chamber is 1.0, that is, the ratio of the gaseous JP-10 content to the cracked gas content is 1:1; the ratio of the oxygen content to the O* content is 19:1. Using chemical equilibrium combustion calculation, the theoretical combustion temperature of the combustion chamber is 4206.9 K, the specific heat ratio of the gas is 1.1505, the vacuum specific impulse is 376.7 s, and the sea-level specific impulse is 336 s.

[0048] From the above operating condition one and operating condition three, it can be concluded that when the kerosene cracking rate is maintained at 50% and the degree of oxidizer ionization is reduced by half, the combustion temperature of the combustion chamber decreases by 80 K, the vacuum specific impulse decreases by 8.9 s, and the sea-level specific impulse decreases by 8.1 s. Relatively speaking, due to the plasma generator power should not be too large, the degree of oxidizer ionization is low, but the specific impulse increases. And the increase of the kerosene cracking rate can significantly increase the combustion temperature of the combustion chamber and the rocket specific impulse, which has an obvious effect.

Claims

1. A rocket-based combined cycle engine, characterized in that, Comprising: A ram combustion chamber body (1), which is a cavity structure with openings at both the front and the rear. Its front end is the combustion chamber inlet end and serves as the inlet for the oncoming air. A rocket combustion chamber (6), which is a cavity structure. Its rear end is connected to the side wall of the front end of the ram combustion chamber body (1) and is in communication with the chamber of the ram combustion chamber body (1). A plurality of intake pipes are connected to its front end, and plasma generators (5) are provided on each of the intake pipes. The front end of each intake pipe is used to be connected to a plasma gas source (2). The plasma generator (5) is used to ionize the plasma gas source (2) to form high-temperature active groups. A kerosene cooling channel (7) is provided inside the shells of the ram combustion chamber body (1) and the rocket combustion chamber (6). The inlet end of the kerosene cooling channel (7) is located at the rear end of the ram combustion chamber body (1) and is used for pipeline connection with a liquid kerosene storage tank (8). Its outlet end is located at the outlet end of the rocket combustion chamber (6), and the outlet end is in pipeline communication with the inner cavity of the rocket combustion chamber (6). In the kerosene cooling channel (7), kerosene is used to be carried therein to absorb the heat in the ram combustion chamber body (1) and the rocket combustion chamber (6), and after absorbing heat, it is cracked into cracked gas, which is input into the rocket combustion chamber (6), mixed and burned with the high-temperature active groups to form a high-temperature jet, and then injected into the ram flow channel in the ram combustion chamber body (1) to perform secondary combustion with the oncoming air and kerosene.

2. The combined cycle rocket-based engine according to claim 1, characterized in that A cracked gas supply valve (4) is provided on the pipeline between the outlet of the kerosene cooling channel (7) and the rocket combustion chamber (6). The cracked gas supply valve (4) is used to adjust the flow rate of the cracked gas supply.

3. The rocket-based combined cycle engine according to claim 2, characterized in that, Each of the plasma generators (5) is connected to a plasma power supply (3).

4. A rocket-based combined cycle engine according to claim 3, characterized in that, The inner cavity of the ram combustion chamber body (1) is in pipeline communication with the liquid kerosene pipeline.

5. Plasma enhanced combustion method for the ejector mode of a rocket-based combined cycle engine, characterized in that, The method is as follows: Liquid kerosene flows into the kerosene cooling channel (7) from the inlet end, absorbs the heat on the walls of the rocket combustion chamber (6) and the ram combustion chamber body (1), and the kerosene is cracked into cracked gas, which enters the rocket combustion chamber (6) from the outlet end. At the same time, the plasma gas source (2) enters the plasma generator (5) through the pipeline, is ionized into active groups by the plasma generator (5), and is introduced into the rocket combustion chamber (6) to react with the kerosene cracked gas by combustion to form a high-temperature jet. The high-temperature jet is injected into the ram flow channel in the ram combustion chamber body (1) to perform secondary combustion with the oncoming air and kerosene in the ram combustion chamber body (1).

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