Quick starting system and method for small turbofan engine

Abstract

The invention discloses a quick starting system and method for a small turbofan engine. The quick starting system and method are suitable for the quick starting requirement of the small turbofan engine under the high-altitude flight condition. The system comprises a gunpowder starting unit arranged at the turbine end and a smoke and fire ignition unit arranged at the gas compressor end, the gunpowder starting unit directly injects high-temperature and high-pressure gas to the tip of a turbine blade through a gas generator, a flow guide bent pipe and a starting jet nozzle penetrating through an outer culvert structure, and blowing starting of an engine rotor is achieved; the smoke and fire ignition unit introduces flames into a specific area of a combustion chamber through a solid gunpowder barrel and a flame transfer bent pipe, and ignition reliability is ensured. The method comprises the steps of starting preparation, gunpowder excitation, ignition triggering, starting termination and the like, and rapid and reliable starting of the engine is achieved through the synergistic effect of the two. By means of the design, the requirements of a low-cost small turbofan engine for small size, low cost, high reliability and high performance of a quick starting system are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of aviation engine starting control, and relates to engine rapid starting technology. Specifically, it provides a low-cost high-altitude rapid starting system and method for a small turbofan engine. The system can realize rapid and reliable starting of a small turbofan engine in a high-altitude environment under conditions of compact structure and limited space. Background Art

[0002] Small turbofan engines are widely used in low-cost, lightweight aviation platforms such as light UAVs, loitering missiles, target drones, and light general aviation aircraft. They offer significant advantages in terms of compactness, thrust-to-weight ratio, and cost control. As the demand for high performance and rapid deployment in related applications continues to increase, the ability of small turbofan engines to quickly and reliably start at high altitudes is becoming a key factor influencing the overall mission responsiveness and operational reliability of the aircraft.

[0003] Traditional aircraft engine starting systems primarily rely on electric starting, pneumatic starting, or auxiliary power unit (APU) starters. In medium-to-large turbojet or twin-shaft turbofan engines, a compressor shaft connected to an electric or pneumatic motor is often used to achieve ground or air starting. However, these systems are generally bulky, heavy, complex, expensive, and difficult to maintain, making them unsuitable for small platforms with limited space, power, and weight. Especially at high altitudes, low temperatures, and low pressures, factors such as limited battery capacity, reduced electric drive capability, and insufficient air compression energy exacerbate the inadequacy of traditional starting methods. Furthermore, existing research has largely focused on the design of rapid starting systems for traditional turbojet engines and high-cost twin-shaft turbofan engines. Research on the design of high-altitude rapid starting systems for low-cost small turbofan engines is limited, resulting in a near-complete lack of research on the design of high-altitude rapid starting systems for small turbofan engines. Furthermore, traditional starting methods and starting system designs are often difficult to directly apply.

[0004] From a structural integration perspective, small turbofan engines place strict constraints on the size and mass of their starting systems. These systems must be arranged within limited radial and axial space without negatively impacting the engine's aerodynamics, heat transfer, and structural integrity. However, some existing systems utilize a modular, external design, resulting in complex overall structures, difficult installation, and insufficient reliability. Furthermore, the system's maintainability and replaceability are often overlooked, increasing ongoing operational and maintenance costs.

[0005] Furthermore, from a cost perspective, the widespread use of low-cost turbofan engines in disposable or semi-reusable aircraft places higher demands on the economic efficiency of starting systems. The high-precision mechanical components, complex control systems, and high-cost materials used in traditional starting technologies are detrimental to the cost-effectiveness of these systems, making them unsuitable for large-scale deployment and rapid deployment.

[0006] In summary, existing technologies lack a rapid start system solution specifically designed for the characteristics of low-cost small turbofan engines, leaving gaps in starting torque optimization, spatial layout, and high-altitude ignition reliability. Therefore, research on high-altitude rapid start systems for low-cost small turbofan engines is crucial. Determining an in-flight rapid start system suitable for these low-cost aircraft engines, while also ensuring small size, low cost, high reliability, and adaptability to high-altitude environments, is a pressing technical challenge in this field. This system can provide support for rapid in-flight starts and high-altitude ignition of low-cost aircraft engines. Summary of the Invention

[0007] (1) Purpose of the invention

[0008] In response to the aforementioned shortcomings and deficiencies of the prior art, the present invention aims to provide a rapid starting system and method for a small turbofan engine. By installing a powder starting unit at the engine turbine end and employing a high-energy jet nozzle through a ducted structure, rapid rotation of the engine rotor is achieved at high altitudes. A pyrotechnic ignition unit is also installed at the compressor end, and a flame transfer elbow is used to precisely direct the flame into the combustion chamber, ensuring stable and reliable high-altitude ignition. This system combines structural compactness with integrated adaptability, enabling efficient placement of the starter and igniter within a limited radial space. A replaceable nozzle core design reduces maintenance costs and enhances system reusability, thereby enabling highly responsive, reliable, and rapid starting of small turbofan engines at high altitudes.

[0009] (2) Technical solution

[0010] In order to achieve the purpose of the invention and solve the technical problems, the present invention adopts the following technical solutions:

[0011] The first object of the present invention is to provide a rapid starting system for a small turbofan engine, which is used to achieve high-reliability, low-cost rapid starting of the small turbofan engine under high-altitude flight conditions, and includes a powder starting unit and a pyrotechnic ignition unit, wherein:

[0012] The propellant starting unit is arranged at the turbine end of the engine and includes a propellant gas generator, a guide bend, and a starting jet nozzle, wherein: the gas outlet of the propellant gas generator is connected to the gas inlet of the starting jet nozzle through the guide bend; the starting jet nozzle adopts a duct-through structure, and its overall design is to pass through the duct between the outer and inner casings of the engine, and its gas outlet is designed to be arranged toward the tip of the turbine blade. It is used to guide the high temperature and high pressure generated by the propellant gas generator through the guide bend, and then spray it through the starting jet nozzle and directly impact the tip of the turbine blade, thereby providing a blowing torque to achieve rapid start-up of the engine rotor;

[0013] The pyrotechnic ignition unit is arranged at the compressor end of the engine, and includes a solid powder cartridge and a flame transfer bend pipe. The solid powder cartridge is arranged in the outer annular space of the air intake casing to reduce the occupation of the radial structural space of the engine. The inlet end of the flame transfer bend pipe is connected to the outlet of the solid powder cartridge, and the outlet end extends into the evaporator tube combustion chamber, which is used to guide the high-temperature and low-pressure combustion gas generated after the solid powder cartridge is ignited to be transmitted to the inside of the combustion chamber in a predetermined direction, so as to ensure that the combustion chamber has good ignition performance and diffusion combustion boundary conditions in a high-altitude and low-pressure environment, while reducing the disturbance effect on the combustion chamber aerodynamic system.

[0014] A second object of the present invention is to provide a method for quickly starting a small turbofan engine. The method comprises at least the following steps:

[0015] SS1. Start preparation

[0016] In high-altitude flight, the system detects and confirms that the engine is in the required starting conditions, initializes the control instructions of the gunpowder starting unit and the pyrotechnic ignition unit, and completes the electronic control unlocking and gas channel pre-opening inspection;

[0017] SS2. Powder starting unit excitation

[0018] The propellant gas generator located at the turbine end is ignited, releasing high-temperature, high-pressure gas. This gas is then transported through a guide bend to a starting jet nozzle located in the engine duct. The gas is then directed toward the tip of the turbine blades. The high-temperature, high-pressure gas impacts the blade tips, generating an effective rotational torque that drives the engine rotor to rotate, achieving a rapid start.

[0019] SS3. Pyrotechnic ignition unit ignites

[0020] When the engine speed reaches the set starting speed range, the solid powder cartridge of the pyrotechnic ignition unit is triggered to ignite, causing it to burn and produce high-temperature, low-pressure combustion gas, which is guided along the flame transfer elbow to the preset flame position in the evaporator tube combustion chamber, forming an ignition core in the combustion chamber and igniting the oil-gas mixture, achieving reliable ignition and stable combustion of the engine;

[0021] SS4. Start process terminated

[0022] When the engine speed reaches the slow speed and the combustion is stable, the gunpowder starting unit and the pyrotechnic ignition unit stop operating, the engine enters the normal autonomous operation state, and the rapid starting process ends.

[0023] (3) Technical effects

[0024] Compared with the prior art, the low-cost small turbofan engine rapid starting system and method of the present invention have the following beneficial and significant technical effects:

[0025] (1) The starting jet nozzle of the gunpowder starting unit adopts a through-the-tube structure, which generates high-temperature and high-pressure combustion gas that impacts the tip of the turbine blade through the starting jet nozzle to rotate the turbofan engine rotor. Therefore, compared with the traditional starting turbine, this starter has a larger blowing radius and generates a larger starting torque, which can reduce the amount of gunpowder, thereby reducing the weight of the engine and reducing the cost of engine use; the starting jet nozzle flow channel is a zoom type, and the nozzle core inside the nozzle is replaceable, which reduces the cost of engine use and maintenance.

[0026] (2) The solid powder cartridge of the pyrotechnic ignition unit is arranged in the outer ring space of the air intake casing at the front end of the engine, which saves the radial installation space of the engine and reduces the cost of the engine body; the flame injection position of the flame transfer bend is 19% L (L is the full length of the combustion chamber) away from the head of the combustion chamber, while ensuring the high-altitude ignition boundary of the combustion chamber and reducing the impact on the engine pneumatic system.

[0027] (3) The above-mentioned design of the present invention meets the requirements of low-cost small turbofan engines for a fast start system with small size, low cost, high reliability and high performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute undue limitations thereon. The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0029] Figure 1 This is a schematic diagram of the structural arrangement of the gunpowder starting unit in the engine of the present invention;

[0030] Figure 2 This is a schematic diagram of the structural arrangement of the pyrotechnic ignition unit in the engine of the present invention;

[0031] Figure 3 It is a flow chart of the implementation of the quick starting method for a small turbofan engine of the present invention.

[0032] Description of reference numerals:

[0033] 1-engine outer casing, 2-engine inner casing, 3-turbine blades, 4-starting jet nozzle of the gunpowder starting unit, 5-replaceable starting nozzle core, 6-solid gunpowder cartridge of the pyrotechnic ignition unit, 7-flame transfer bend tube, 8-evaporation tube combustion chamber. DETAILED DESCRIPTION

[0034] The present invention is intended to provide a rapid starting system and method for a small turbofan engine. To further clarify the objectives, technical solutions, and advantages of the present invention, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The described embodiments are only a portion of the embodiments of the present invention, not all of them. The described embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] Example 1: Rapid start system for small turbofan engine

[0036] As a specific example, Figure 1 、 Figure 2 As shown, the low-cost small turbofan engine rapid start system of the present invention is used to achieve high reliability, low-cost rapid start of a small turbofan engine under high-altitude flight conditions. It includes a powder starting unit arranged at the engine turbine end and a pyrotechnic ignition unit arranged at the engine compressor end. Specifically:

[0037] The powder starting unit in the embodiment of the present invention is as follows: Figure 1 As shown, the system is integrated into the turbine end of the engine and comprises at least a pyrotechnic gas generator, a guide elbow, and a starting jet nozzle 4. The gas outlet of the pyrotechnic gas generator communicates with the gas inlet of the starting jet nozzle 4 via the guide elbow. The starting jet nozzle 4 adopts a duct-through structure, designed to pass through the duct between the engine's outer casing 1 and inner casing 2. Its gas outlet is designed to face the tips of the turbine blades 3. The high-temperature, high-pressure gas generated by the pyrotechnic gas generator is channeled through the guide elbow to the starting jet nozzle 4, where it impacts the tips of the turbine blades 3, providing a turning torque, thereby achieving a rapid start of the engine rotor.

[0038] Preferably, a replaceable starting nozzle core 5 is provided within the starting jet nozzle 4. If the starting nozzle core becomes structurally damaged or its performance degrades due to high-temperature, high-pressure erosion or gunpowder residue deposition, it can be replaced without replacing the entire nozzle assembly, thereby enabling multiple reuse of the gunpowder starting unit and reducing maintenance costs. Furthermore, the internal flow channel structure of the replaceable starting nozzle core 5 is designed as a zoom-in structure, comprising a contracting section and an expanding section. The contracting section is used to accelerate the high-temperature, high-pressure gas generated by the gunpowder gas generator, and the expanding section is used to further optimize the gas flow characteristics. Through the aerodynamic design of the zoom-in flow channel, the high-temperature, high-pressure gas generated by the gunpowder gas generator is accelerated to form a high-speed jet, thereby improving blowing efficiency and starting torque, enhancing starting efficiency and shortening starting time.

[0039] Further preferably, the gas outlet of the starting jet nozzle 4 is arranged at an optimized angle in spatial orientation relative to the tip of the turbine blade, so that the injection direction of the gunpowder gas forms an efficient impact angle with the tangential velocity direction of the blade, so as to increase the driving torque generated per unit mass of gas and optimize the energy efficiency ratio of the starter.

[0040] For the gunpowder gas generator in the gunpowder starting unit, high-energy solid propellant is preferably used, the main components of which include at least nitrocellulose, nitroglycerin and stabilizer. The formula is optimized to ensure that it has good combustion performance, stability, safety and low corrosion, and provides sufficient starting power in a very short time to meet the needs of rapid engine starting; the diversion elbow is made of high-temperature resistant and corrosion-resistant alloy material, and its inner wall is precisely processed and has a high surface finish to reduce the friction resistance of the gas during the flow process and improve the diversion efficiency.

[0041] The pyrotechnic ignition unit in the embodiment of the present invention is integrally arranged at the compressor end of the engine, and its main structure is as follows: Figure 2 As shown, it at least includes a solid powder cartridge 6 and a flame transfer bend 7. The solid powder 6 of the pyrotechnic ignition unit is preferably arranged in the outer annular space of the air intake casing at the front end of the engine, saving the radial installation size of the engine. The inlet end of the flame transfer bend 7 is connected to the outlet of the solid powder cartridge 6, and the outlet end extends to the evaporator tube combustion chamber 8. The flame injection position of the flame transfer bend 7 of the pyrotechnic ignition unit is preferably arranged at a position 19% L away from the head of the combustion chamber. The high-temperature and low-pressure combustion gas generated by the solid powder cartridge 6 passes through the flame transfer bend 7 and is transferred to the combustion chamber for ignition, ensuring that the combustion chamber has good ignition performance and diffusion combustion boundary conditions in a high-altitude and low-pressure environment, while reducing the disturbance effect on the combustion chamber pneumatic system.

[0042] Preferably, the flame jet nozzle of the flame transfer elbow 7 in the pyrotechnic ignition unit is positioned at a predetermined distance from the combustion chamber head, optimized according to the engine combustion chamber type, evaporator tube layout, and ignition boundary requirements. This ensures the high-altitude ignition boundary of the combustion chamber while minimizing the impact on the engine's aerodynamic system and avoiding adverse disturbances to the airflow within the combustion chamber caused by the ignition process. More preferably, the flame transfer elbow nozzle is positioned at a distance of 19%L±2%L from the combustion chamber head, where L is the axial length of the combustion chamber. This position is calibrated through CFD simulation and high-altitude ignition testing to ensure a stable mixing equivalence ratio between the flame jet and the evaporator tube fuel spray within the range of 0.7-1.3, an ignition delay time of ≤0.2s under a low-pressure environment of 0.01MPa, and an increase in the total pressure loss in the combustion chamber of ≤0.5%.

[0043] Furthermore, the solid powder cartridge 6 in the pyrotechnic ignition unit preferably utilizes smokeless gunpowder, whose primary components include at least nitrocellulose and a stabilizer, to reduce corrosion and carbon deposits on engine components and extend the engine's service life. The flame transfer elbow is made of a high-temperature, corrosion-resistant, and low-thermal-conductivity ceramic material to ensure it maintains good operating condition even under the long-term effects of high-temperature combustion gases. Furthermore, a thermal insulation layer is preferably provided within the outer annular space of the engine's intake casing to prevent heat generated by the solid powder cartridge from being transferred to other engine components, thereby preventing damage or performance degradation due to excessive temperatures. The tips of the turbine blades are provided with an anti-scouring coating to prevent damage or deformation due to long-term scouring, thereby extending the service life of the turbine blades.

[0044] In embodiments of the present invention, both the powder starting unit and the pyrotechnic ignition unit preferably utilize a dual- or multi-engine layout. Each unit is equipped with two or more independent operating systems, symmetrically arranged at corresponding positions on the engine. This provides redundant starting capability in the event of unit failure. If one system fails, the other system can still function normally, avoiding starting failures due to a single point of failure and improving the engine's adaptability and safety in complex high-altitude environments. This dual- or multi-engine redundant design can significantly improve the engine's starting success rate and is particularly suitable for military or emergency scenarios requiring strict high reliability. The dual- or multi-engine configuration also provides greater starting power and ignition energy.

[0045] The working principle of the quick starting system for the small turbofan engine of the present invention is as follows:

[0046] For the propellant starting unit, the propellant gas generator burns to produce high-temperature, high-pressure gas, which is then channeled through a guide bend to the starting jet nozzle. After acceleration in a convergent-divergent flow channel, it forms a high-speed jet. This high-speed jet passes through the duct and directly impacts the turbine blade tip. Because the impact radius is significantly larger than that of a traditional starting turbine, a greater starting torque is generated, thereby enabling rapid rotation of the engine rotor.

[0047] For the pyrotechnic ignition unit, the combustion of the solid powder cartridge generates high-temperature, low-pressure gas, which is then transferred to a specific location within the combustion chamber via a flame transfer elbow. The flame is ejected at a distance of 19% L from the combustion chamber head, achieving reliable ignition of the combustion chamber. This location not only meets the high-altitude ignition boundary requirements but also minimizes adverse effects on the engine's main combustion flow field and aerodynamic system.

[0048] The design of the through-the-duct structure enables the starting jet nozzle to bypass the geometric limitations of the outer duct and act directly on the tip of the turbine blade. Compared with the traditional starting turbine scheme, the starting blowing radius is increased and the starting torque is significantly improved. At the same time, the technical difficulties of installing the starting turbine in a limited radial space are avoided; the arrangement of the solid powder cartridge in the annular space outside the air intake casing effectively saves the radial installation space of the engine, reduces the outer diameter of the engine and the cost of the body, and meets the requirements of small turbofan engines for a compact structure.

[0049] Example 2: Rapid starting method for a small turbofan engine

[0050] Based on the detailed description of the structure and working principle of the quick start system for a small turbofan engine of the present invention in Example 1, this Example 2 further provides a specific quick start method of the system in actual application, aiming to demonstrate the whole process of realizing quick start of the engine under high-altitude flight conditions of the present invention through a clear step-by-step process, such as Figure 3 As shown, the method mainly includes the following implementation steps:

[0051] SS1. Start preparation

[0052] At high altitude, the system checks and confirms that the engine is in the starting condition. If it detects that the engine has stalled, has failed to idle, or requires restarting, it determines that the starting condition has been met and issues initialization instructions to the propellant starting unit and pyrotechnic ignition unit. The control system unlocks the electronic control logic and simultaneously performs a self-check on the trigger circuits of the propellant gas generator and solid propellant cartridge. The gas passages of the guide bend and flame transmission bend are simultaneously checked for airtightness and unobstructed flow, ensuring that the start-up preparation process is carried out in a safe and controlled state. Furthermore, the engine's fuel supply system must be checked to ensure that the fuel pump is functioning properly, the fuel nozzle is unobstructed, and sufficient fuel is being supplied to the combustion chamber.

[0053] SS2. Powder starting unit excitation

[0054] The starting control system issues a trigger command, igniting the propellant gas generator located at the engine's turbine end, causing it to release high-temperature, high-pressure gas in a very short period of time. This high-temperature, high-pressure gas is directed through an optimized, high-temperature-resistant guide bend to the starting jet nozzle located in the engine's outer duct. The gas is then directed toward the tip of the turbine blades, where it impacts the blade tips to generate an effective torque, driving the engine rotor to rotate and achieving a rapid start. During this process, the zooming flow channel structure of the starting jet nozzle effectively accelerates the gas, increasing its injection speed and impact force, thereby more effectively driving the turbine blades to rotate. Simultaneously, real-time monitoring of the engine speed is required to promptly trigger the pyrotechnic ignition unit once the preset speed is reached.

[0055] SS3. Pyrotechnic ignition unit ignites

[0056] When the engine speed reaches the set starting speed range (e.g., 10% to 15% of the engine's idle speed), the solid powder cartridge in the pyrotechnic ignition unit is triggered to ignite, generating high-temperature, low-pressure combustion gas. This gas is then transmitted via an optimally arranged flame transfer elbow to a preset flame position within the evaporator combustion chamber (e.g., 19%L ± 2%L axially from the combustion chamber head, where L is the total axial length of the combustion chamber). This forms an ignition core within the combustion chamber and ignites the fuel-gas mixture, achieving reliable engine ignition and stable combustion. During this process, the combustion chamber's temperature and pressure must be monitored in real time to determine if ignition is successful, and the fuel supply is adjusted as needed to maintain stable combustion.

[0057] SS4. Start process terminated

[0058] When the engine speed reaches idle speed (usually between 50% and 60% of rated speed) and combustion stabilizes, the propellant starting unit and pyrotechnic ignition unit cease operation, disconnecting the propellant source and the ignition control circuit. At this point, the engine enters normal autonomous operation, and the quick start process is complete. After the start process is complete, a comprehensive inspection of all engine parameters is required to ensure normal engine operation, with no abnormal vibration or noise, and that all component temperatures are within normal ranges.

[0059] In summary, through the description of the above embodiment 2, it can be seen that the small turbofan engine rapid starting method proposed in the present invention can be reliably implemented under various flight conditions, and is particularly suitable for various high-dynamic flight platforms that have strict requirements on starting response speed, system reliability and structural adaptability.

[0060] The above embodiments fully and effectively achieve the objectives of the present invention. Those skilled in the art will appreciate that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the above specific embodiments. Although the present invention has been described with reference to the embodiments currently considered to be the most practical and preferred, it should be understood that the present invention is not limited to the disclosed embodiments, and any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A quick start system for a small turbofan engine, characterized in that: It consists of a powder starting unit and a pyrotechnic ignition unit, wherein: The propellant starting unit is arranged at the turbine end of the engine and includes a propellant gas generator, a guide bend, and a starting jet nozzle, wherein: the gas outlet of the propellant gas generator is connected to the gas inlet of the starting jet nozzle through the guide bend; the starting jet nozzle adopts a duct-through structure, and its overall design is to pass through the duct between the outer and inner casings of the engine, and its gas outlet is designed to be arranged toward the tip of the turbine blade. It is used to guide the high temperature and high pressure generated by the propellant gas generator through the guide bend, and then spray it through the starting jet nozzle and directly impact the tip of the turbine blade, thereby providing a blowing torque to achieve rapid start-up of the engine rotor; The pyrotechnic ignition unit is arranged at the compressor end of the engine, and includes a solid powder cartridge and a flame transfer bend pipe. The solid powder cartridge is arranged in the outer annular space of the air intake casing. The inlet end of the flame transfer bend pipe is connected to the outlet of the solid powder cartridge, and the outlet end extends into the evaporator tube combustion chamber, which is used to guide the high-temperature and low-pressure combustion gas generated after the solid powder cartridge is ignited to be transmitted to the interior of the combustion chamber in a predetermined direction, so as to ensure that the combustion chamber has good ignition performance and diffusion combustion boundary conditions in a high-altitude and low-pressure environment, while reducing the disturbance effect on the combustion chamber aerodynamic system.

2. The rapid starting system for a small turbofan engine according to claim 1, characterized in that: The powder starting unit and the pyrotechnic ignition unit both adopt a dual or multi-shot arrangement structure. Each unit is provided with two or more independent working systems and are symmetrically arranged at corresponding positions of the engine. When one of the systems fails, the other system can still work normally, thus avoiding starting failure.

3. The quick start system for a small turbofan engine according to claim 1, characterized in that: In the gunpowder starting unit, a removable and replaceable starting nozzle core is provided inside the starting jet nozzle. When the performance of the starting nozzle core is degraded due to high-temperature and high-pressure erosion or gunpowder residue deposition, only the starting nozzle core needs to be replaced without replacing the entire nozzle assembly. The flow channel of the starting nozzle core adopts a zoom-type structural design, including a contraction section and an expansion section, wherein the contraction section is used to accelerate the high-temperature and high-pressure gas generated by the gunpowder gas generator, and the expansion section is used to further optimize the gas flow characteristics. The high-temperature and high-pressure gas generated by the gunpowder gas generator is accelerated through the zoom-type flow channel to form a high-speed jet.

4. The quick start system for a small turbofan engine according to claim 1, characterized in that: The gas outlet of the starting jet nozzle is arranged at an optimized angle relative to the tip of the turbine blade in spatial orientation, so that the injection direction of the gunpowder gas forms an efficient impact angle with the tangential velocity direction of the blade, thereby increasing the driving torque generated by unit mass of gas.

5. The quick start system for a small turbofan engine according to claim 1, characterized in that: In the pyrotechnic ignition unit, the flame injection port of the flame transfer bend is set at a preset distance from the combustion chamber head and is optimized according to the combustion chamber type, evaporation tube layout and / or ignition boundary requirements, while ensuring the high-altitude ignition boundary of the combustion chamber and reducing the impact on the engine pneumatic system.

6. The quick start system for a small turbofan engine according to claim 5, characterized in that: The injection port of the flame transfer bend is set at a position of 19%L±2%L from the head of the combustion chamber, where L is the full axial length of the combustion chamber. This position is calibrated through CFD simulation and high-altitude ignition test, so that the mixing equivalence ratio of the flame jet flow and the evaporator tube fuel spray is stabilized in the range of 0.7-1.3, the ignition delay time is ≤0.2s under a low-pressure environment of 0.01MPa, and the increase in the total pressure loss of the combustion chamber is ≤0.5%.

7. The quick start system for a small turbofan engine according to claim 1, characterized in that: In the gunpowder starting unit, the gunpowder gas generator uses high-energy solid propellant, and its formula is optimized to ensure good combustion performance and low corrosion; the diversion elbow is made of high-temperature resistant and corrosion-resistant alloy material, and its inner wall is precisely machined and has a high surface finish.

8. The quick start system for a small turbofan engine according to claim 1, characterized in that: In the pyrotechnic ignition unit, the solid gunpowder cartridge uses smokeless gunpowder, the main components of which include at least nitrocellulose and a stabilizer to reduce corrosion and carbon deposits on engine components; the flame transfer elbow is made of a high-temperature resistant, corrosion-resistant and low-thermal-conductivity ceramic material to ensure that it can maintain a good working condition under the long-term action of high-temperature gas.

9. The quick start system for a small turbofan engine according to claim 1, characterized in that: An insulating layer is provided in the outer annular space of the air intake casing to prevent the heat generated by the solid powder cartridge from being transferred to other parts of the engine; an anti-scouring coating is provided at the tip of the turbine blade to prevent the blade tip from being damaged or deformed due to long-term scouring, thereby extending the service life of the turbine blade.

10. A quick starting method for a small turbofan engine, based on the quick starting system for a small turbofan engine according to any one of claims 1 to 9, characterized in that: At least the following steps are included: SS1. Starting Preparation: While in high-altitude flight, the aircraft checks and confirms that the engine meets the starting requirements, initializes the control commands for the propellant starting unit and pyrotechnic ignition unit, and completes the electronic unlocking and gas channel pre-opening checks. SS2. Explosive Starting Unit Activation: The explosive gas generator located at the turbine end is ignited, releasing high-temperature, high-pressure gas. This gas is then transported through a guide bend to a starting jet nozzle located in the engine duct. The jet is then directed toward the tips of the turbine blades. The impact of the high-temperature, high-pressure gas on the blade tips generates an effective torque, driving the engine rotor for rapid engine start. SS3. Pyrotechnic Ignition Unit Ignition: When the engine speed reaches the set starting speed range, the solid powder cartridge in the pyrotechnic ignition unit is triggered to ignite, generating high-temperature, low-pressure combustion gas. This gas is then guided along the flame transfer elbow to the preset flame position within the evaporator combustion chamber, forming an ignition core within the combustion chamber and igniting the fuel-gas mixture, ensuring reliable engine ignition and stable combustion. SS4. Termination of the starting process: When the engine speed reaches the idle speed and the combustion is stable, the gunpowder starting unit and the pyrotechnic ignition unit stop operating, the engine enters the normal autonomous operation state, and the rapid starting process ends.

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