Method for reducing overshoot during start of open cycle forced start high altitude rocket engine

Abstract

This invention relates to a method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine. To improve engine reliability while ensuring start-up acceleration, the method reduces or eliminates start-up overshoot. The method includes the following steps: Step 1: Define a threshold value A1 for the relative amount of engine speed start-up overshoot during the first start and a threshold value A2 for the relative amount of engine speed start-up overshoot during the second start; Step 2: Start the engine for the first time, open two auxiliary valves at time t1, and calculate the relative amount B1 of engine speed start-up overshoot when engine start-up acceleration is satisfied; Step 3: If B1 < A1, proceed to Step 4; otherwise, delay t1 and return to Step 2; Step 4: Start the engine for the second time, open two auxiliary valves at time t2, and calculate the relative amount B2 of engine speed start-up overshoot during the second start-up when engine start-up acceleration is satisfied; Step 5: If B2 < A2, proceed to Step 6; otherwise, delay t2 and return to Step 4; Step 6: Record t1 and t2, thereby reducing the start-up overshoot of the open-cycle forced-start high-altitude rocket engine.

Description

Technical Field

[0001] This invention relates to high-altitude liquid rocket engines, and more specifically to a method for reducing start-up overshoot in open-cycle forced-start high-altitude rocket engines. Background Technology

[0002] The high-altitude liquid rocket engine with multiple start-up capabilities uses a propellant starter for ignition, driving the turbine to rotate, which is the initial power source for engine startup. By controlling the ignition timing of the gas generator, the gas generator and the propellant starter work in tandem. After the propellant has burned out, the gas generator works independently, enabling the engine to transition to the main stage operating state.

[0003] To ensure acceleration during startup, the current startup design involves an overlapping operating range between the propellant starter and the gas generator, resulting in significant engine speed overshoot beyond design limits and increased workload on components. This leads to increased internal pressure in components such as the assembly piping and thrust chamber, and increased stress on welds. Furthermore, the substantial increase in turbine speed during the parameter overshoot phase increases the workload on components such as end-face seals and bearings, making operating conditions more severe and negatively impacting engine reliability to some extent. Although extensive flight and test runs have shown that the current startup overshoot does not affect normal engine operation and the risk is manageable, measures should be taken to reduce or eliminate the startup overshoot while maintaining acceleration during startup to further improve engine reliability. Summary of the Invention

[0004] To further improve the reliability of engine operation, this invention proposes a method to reduce or eliminate start-up overshoot in an open-cycle forced-start high-altitude rocket engine. This method reduces overshoot by rationally controlling the operating time of the engine's subsystems and reducing the overlapping operating range of the propellant starter and the gas generator. In other words, this invention effectively reduces overshoot during engine start-up by simply changing the operating time of the subsystems without modifying the existing engine structure and while ensuring the development schedule.

[0005] The technical solution of the present invention is as follows:

[0006] A method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine, characterized by the following steps:

[0007] Step 1: Define the engine speed overshoot relative threshold as A1 for the first start and A2 for the second start;

[0008] Step 2: Starting the engine for the first time

[0009] When starting the engine once, two auxiliary valves are opened at time t1, and the engine speed overshoot relative amount B1 is calculated to meet the requirements of engine starting acceleration.

[0010] Step 3: If B1 < A1, proceed to step 4 to restart the engine a second time; otherwise, delay by t1 and return to step 2.

[0011] Step 4: Second start of the engine

[0012] When starting the engine for the second time, open the two auxiliary valves at time t2 and calculate the relative overshoot B2 of the engine speed during the second start-up while meeting the requirements for engine starting acceleration.

[0013] Step 5: If B2 < A2, then proceed to step 6; otherwise, postpone t2 and return to step 4.

[0014] Step 6: Record t1 and t2 to reduce the start-up overshoot of the open-cycle forced start high-altitude rocket engine.

[0015] Furthermore, step 2 specifically includes:

[0016] 2.1 When starting the engine for the first time, open both auxiliary valves at time t1;

[0017] 2.2 Obtain the starting acceleration performance of the engine under its current condition;

[0018] 2.3 If the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.4; otherwise, return to step 2.1 and decrease the time t1 until the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.4.

[0019] 2.4 Calculate the relative overshoot B1 of the engine speed during a single start-up.

[0020] Further, step 2.1 specifically includes:

[0021] 2.11 Before the engine's propellant starter is ignited, the two types of propellant components fill the engine cavity before the main valve and the engine cavity before the auxiliary valve, respectively, and keep both auxiliary valves closed.

[0022] 2.12. At 0 o'clock, the gunpowder starter is activated, and the turbine rotates under the pressure and flow of the gunpowder gas;

[0023] 2.13. At time t1, the two auxiliary valves are opened, allowing the two components of propellant to enter the engine gas generator for ignition. The propellant burns, producing gas that drives the turbine.

[0024] 2.14 After the gunpowder has burned out, the gas generator works independently and continues to drive the turbine, thus completing the engine starting process.

[0025] Furthermore, step 4 specifically includes:

[0026] 4.1 Under the premise that the relative overshoot of the engine speed during the first start is B1 < A1, when starting the engine for the second time, open the two auxiliary valves at time t2;

[0027] 4.2 Obtain the starting acceleration performance of the engine under its current condition;

[0028] 4.3 If the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 4.4; otherwise, return to step 4.1 and decrease the time t2 until the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 4.4.

[0029] 4.4 Calculate the relative overshoot B2 of the engine speed during secondary start-up.

[0030] Furthermore, the method of starting the engine a second time in step 4.1 is the same as the method of starting the engine a first time in step 2.1.

[0031] The beneficial effects of this invention are:

[0032] 1. In this invention, without modifying the existing structure of the engine and ensuring the development progress, the overshoot during engine start-up is effectively reduced simply by changing the working time of the subsystem.

[0033] 2. In this invention, based on the matching principle of the working relay time of the gas generator and the gunpowder starter with the speed overshoot (the shorter the working relay time, the smaller the speed overshoot), the problem of excessive system starting overshoot leading to high load on engine components and harsh working environment during the starting process is solved.

[0034] 3. The method proposed in this invention can reduce start-up overshoot by delaying the ignition time of the gas generator while meeting the requirements for start-up acceleration. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the existing engine control system.

[0036] Figure 2 This is a schematic diagram of a startup timing according to an embodiment of the present invention;

[0037] Figure 3 A comparison graph of dimensionless rotational speed curves before and after using the method of the present invention;

[0038] Figure 4This is a comparison chart of the turbine start-up overshoot curves before and after using the method of this invention;

[0039] In the diagram, 1--gunpowder starter, 2--gas generator, 3--subsidiary valve, 4--turbine, 5--pump. Detailed Implementation

[0040] Three-stage rocket engine system, such as Figure 1 As shown, it includes a gunpowder starter 1, a gas generator 2, a turbine 4, two auxiliary valves 3 and two pumps 5. The engine has the ability to start twice. The function of the starting system is to drive the turbine to rotate, so that the engine can transition to the main stage working state. Here, the two L represent the fuel and oxidizer inlets, respectively, and G represents the outlet.

[0041] The starting process is divided into two stages: In the first stage, the gunpowder starter 1 provides the initial power source, which is ignited by the electric detonator and drives the turbine 4 to rotate. In the second stage, the auxiliary system (two auxiliary valves 3, gas generator 2 and the pipeline between them) supplies propellant to the turbine 4, maintains the normal operation of the turbine 4, and continuously supplies propellant to the main system.

[0042] Analysis of the engine starting process reveals that the overlapping operating range between the propellant combustion time of the starting system and the auxiliary system supplying the working fluid to turbine 4 during ignition is the key factor contributing to starting overshoot. A longer overlapping operating range results in greater overshoot during starting, but also better acceleration. To reduce engine starting overshoot, the following solutions can be implemented: 1. Adjusting the parameters and structure of the auxiliary system, such as adding a starting valve to reduce the flow rate of the auxiliary system during starting; 2. Reducing the propellant combustion rate or combustion time; 3. Shortening the overlapping operating time between the propellant starter 1 and the gas generator 2.

[0043] Adjusting the parameters and structure of the subsystems alters engine performance and layout, increasing system complexity and requiring start-up simulation analysis and multiple ground tests for verification, which is time-consuming. Reducing the propellant burning rate or combustion time essentially changes the propellant charge or combustion energy; however, engine start-up acceleration is essentially linearly related to the propellant burning rate, so such adjustments may reduce engine start-up acceleration. After comprehensive consideration, optimizing the overlapping operating range of the propellant starter 1 and gas generator 2 to reduce start-up overshoot is considered a low-risk, easily implemented, and minimally impactful approach to the propulsion system. However, altering the overlapping operating range of the propellant starter 1 and gas generator 2 is primarily achieved by delaying the relay time between them, which also reduces engine start-up acceleration and, under extreme conditions, may lead to delayed ignition or even start-up failure. Therefore, the key to this improvement is to reduce the relative amount of start-up overshoot below a threshold while ensuring that the engine start-up acceleration does not exceed the mission requirements; that is, during ground testing, the engine's second start-up overshoot should be less than the predetermined threshold.

[0044] Based on the above, this invention proposes a method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine, comprising the following steps:

[0045] Step 1: Define the engine speed overshoot relative threshold for the first start as A1 and the overshoot relative threshold for the second start as A2, and confirm the engine's starting acceleration performance in advance.

[0046] Step 2: Starting the engine for the first time

[0047] When starting the engine once, two auxiliary valves 3 are opened at time t1, and the engine speed overshoot relative amount B1 is calculated to meet the requirements of engine starting acceleration.

[0048] 2.1, such as Figure 2 As shown, when the engine is started once, two auxiliary valves 3 are opened at time t1;

[0049] 2.11 Before the ignition of the propellant starter 1 of the engine, the two components of the engine propellant fill the engine cavity before the main valve and the engine cavity before the auxiliary valve 3 respectively, and keep the two auxiliary valves 3 in the closed state.

[0050] 2.12. At time 0, the gunpowder starter 1 is activated, and the turbine 4 rotates under the pressure and flow of the gunpowder gas;

[0051] 2.13. At time t1, the two auxiliary valves 3 are opened, allowing the two components of propellant to enter the engine gas generator 2 for ignition. The propellant burns, producing gas that drives the turbine 4 to move.

[0052] At time 2.14, after the gunpowder has burned out, the gas generator 2 operates independently and continues to drive the turbine 4, thus completing the engine starting process.

[0053] 2.2 Calculate the starting acceleration of the engine when both auxiliary valves 3 are open at time t1;

[0054] 2.3 If the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.4; otherwise, return to step 2.1 and shorten the time t1 until the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.4.

[0055] 2.4 Calculate the relative overshoot B1 of the engine speed during a single start-up;

[0056] Step 3: If B1 < A1, proceed to step 4 to start the engine a second time; otherwise, delay by t1 and return to step 2 until the engine speed overshoot of the first start is less than A1 under the requirement of satisfying the engine starting acceleration.

[0057] Step 4: Second start of the engine

[0058] When the engine is started for the second time, the two auxiliary valves 3 are opened at time t2, and the engine speed overshoot relative amount B2 is calculated under the condition of meeting the requirements of engine starting acceleration.

[0059] The method for starting twice in step 4 is the same as the method for starting once in step 2;

[0060] Step 5: If B2 < A2, proceed to step 6; otherwise, delay t2 and return to step 4 until the engine speed secondary start-up overshoot relative amount B2 < A2 under the requirement of satisfying engine starting acceleration.

[0061] Step 6: Record t1 and t2 to complete the overshoot reduction of the open-cycle forced start high-altitude rocket engine start.

[0062] The control method proposed in this invention has been verified through engine starting simulation. A dynamic simulation model was established for the open-loop forced starting process of an aerial work platform engine using this control method, and the calculation results are as follows. Figure 3 As shown, after adopting this control method, the maximum speed (dimensionless) during the engine's relative start-up process decreased from 1.18 to 1.04, meaning the overshoot decreased from 18% to 4%, achieving the goal of suppressing start-up overshoot. A comparison of the turbocharger start-up overshoot curves before and after implementing this method is provided. Figure 4 As shown in the figure, the overshoot is significantly reduced after using this method.

[0063] The simulation results of engine starting show that the starting overshoot reduction method proposed in this invention can effectively suppress the starting overshoot of open-cycle forced starting high-altitude engines without changing the engine structure.

Claims

1. A method of reducing start overshoot in an open cycle, positive start, high altitude rocket engine, the method comprising: Includes the following steps: Step 1: Define the engine speed overshoot relative threshold as A1 for the first start and A2 for the second start; Step 2: Starting the engine for the first time When the engine is started once, two auxiliary valves (3) are opened at time t1, and the engine speed overshoot relative amount B1 is calculated to meet the requirements of engine starting acceleration; the auxiliary valve (3) is a valve that controls the propellant to enter the gas generator (2); Step 3: If B1 < A1, proceed to step 4 to restart the engine a second time; otherwise, delay by t1 and return to step 2. Step 4: Second start of the engine When the engine is started for the second time, two auxiliary valves (3) are opened at time t2, and the engine speed overshoot relative amount B2 is calculated under the condition of meeting the requirements of engine starting acceleration. Step 5: If B2 < A2, then proceed to step 6; otherwise, postpone t2 and return to step 4. Step 6: Record t1 and t2 to reduce the start-up overshoot of the open-cycle forced start high-altitude rocket engine.

2. The method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine according to claim 1, characterized in that: Step 2 specifically involves: 2.1 When starting the engine for the first time, open the two auxiliary valves (3) at time t1; 2.2 Obtain the starting acceleration performance of the engine under its current condition; 2.3 If the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.4; otherwise, return to step 2.1 and decrease the time t1 until the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 2.

4. 2.4 Calculate the relative overshoot B1 of the engine speed during a single start-up.

3. The method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine according to claim 2, characterized in that: Step 2.1 specifically includes: 2.11 Before the ignition of the engine's propellant starter (1), the two components of the engine propellant fill the engine cavity before the main valve and the engine cavity before the auxiliary valve, respectively, and keep the two auxiliary valves (3) in the closed state. 2.

12. At time 0, the gunpowder starter (1) is activated, and the turbine (4) rotates under the pressure and flow of the gunpowder gas; 2.

13. At time t1, the two auxiliary valves (3) are opened, allowing the two component propellants to enter the engine gas generator (2) for ignition. The gunpowder burns, generating gas, which drives the turbine (4) to move. 2.14 After the gunpowder burns out, the gas generator (2) works independently and continues to drive the turbine (4), thus completing the engine starting process.

4. The method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine according to claim 3, characterized in that: Step 4 specifically involves: 4.1 Under the premise that the relative overshoot of the engine speed during the first start is B1 < A1, when starting the engine for the second time, open the two auxiliary valves (3) at time t2; 4.2 Obtain the starting acceleration performance of the engine under its current condition; 4.3 If the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 4.4; otherwise, return to step 4.1 and decrease the time t2 until the starting acceleration performance of the engine in its current state meets the requirements, then proceed to step 4.

4. 4.4 Calculate the relative overshoot B2 of the engine speed during secondary start-up.

5. The method for reducing start-up overshoot of an open-cycle forced-start high-altitude rocket engine according to claim 4, characterized in that: The method of starting the engine a second time in step 4.1 is the same as the method of starting the engine a first time in step 2.1.

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