A micro turbojet closed-loop starting control method based on multi-working condition boundary constraint
Patent Information
- Application Number
- CN202611365749.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-04
- Publication Date
- 2026-11-03
AI Technical Summary
Existing micro turbojet engine start-up control methods fail to comprehensively consider multiple safety boundaries and ambient temperature changes, making them prone to outputting extreme fuel commands, which can lead to overheating, surge, suspension, or stalling. Furthermore, they are not adaptable enough to the differences in the start-up phase, and relying on bench calibration tests is costly and risky.
A micro turbojet engine starting component-level model was established, multi-condition boundaries were calculated and a stable fuel supply range was generated, and a feedforward-PI closed-loop control was adopted to execute the starting process in stages. Combined with dynamic limiting and environmental adaptive boundary correction, the engine safety was monitored and protected in real time.
It enables stable engine starting under multiple operating conditions, avoids malfunctions caused by insufficient or excessive fuel supply, reduces R&D costs and engine damage risks, improves starting safety and adaptability, and ensures speed and smoothness.
Smart Images
Figure CN123028085A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of aero-engine control technology, and in particular to a micro turbojet closed-loop start-up control method based on multi-condition boundary constraints. Background Technology
[0002] The starting process of a micro turbojet engine from a stationary state to idle is a highly nonlinear transient process involving the coordinated operation of components such as the starter motor, igniter, auxiliary gas valve, and fuel pump. The starting phase requires not only a rapid increase in engine speed but also simultaneous stability of combustion, controlled exhaust temperature, and the compressor being kept away from the surge zone. If the starting fuel supply is too small, insufficient heat release in the combustion chamber will prevent the turbine's remaining power from sustaining rotor acceleration, easily leading to stalling or cold suspension. Conversely, if the fuel supply is too large, it can easily cause excessively high T5 exhaust temperatures and the compressor operating point to approach the surge boundary, resulting in hot suspension, overheating, or component damage. Simultaneously, ambient temperature alters air density, compressor flow rate, and combustion states, causing the same fuel supply pattern to have drastically different safety margins under different environmental conditions.
[0003] Existing micro turbojet engine starting methods typically employ fixed-sequence open-loop control or fixed-fuel-air ratio following control. Fuel control quantities rely heavily on repeated bench tests and engineering experience for calibration, resulting in high testing costs and a significant risk of engine damage. While some technical solutions utilize rotor acceleration (N-dot) as feedback for closed-loop control, these existing technologies still suffer from the following significant drawbacks:
[0004] (1) Existing closed-loop control usually does not simultaneously utilize the lean fuel boundary, T5 over-temperature boundary and compressor surge boundary to limit fuel command. When the controller is tracking the acceleration target, it is very easy to output too large or too small fuel command, resulting in over-temperature, surge or suspension, or engine shutdown.
[0005] (2) The existing starting rules are not adaptable enough to ambient temperature, individual engine differences and component performance degradation, and fail to correct the stable starting range according to changes in ambient temperature;
[0006] (3) The control objectives of the entire starting process (including the initial ignition stage, the oil accumulation combustion stage, the motor-assisted stage and the exit stage) are significantly different. Existing technologies using a single control law cannot simultaneously ensure ignition reliability, rapid start-up and smooth switching of operating conditions. Summary of the Invention
[0007] The present invention provides a micro turbojet engine closed-loop starting control method based on multi-condition boundary constraints, in order to solve the technical problems of existing micro turbojet engine starting control methods that do not comprehensively consider multiple safety boundaries and ambient temperature changes, rely solely on feedback control, are prone to outputting extreme fuel commands that lead to engine overheating, surge, suspension or stalling, and have poor adaptability to single control at different starting stages and are heavily dependent on bench calibration tests.
[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:
[0009] A closed-loop starting control method for a micro turbojet based on multi-condition boundary constraints includes:
[0010] A starting component-level model of a micro turbojet engine was established, and the lean fuel limit boundary, T5 over-temperature limit boundary, and compressor surge limit boundary of the micro turbojet engine were calculated under multiple calibrated ambient temperatures and different engine speeds.
[0011] Using the lean oil limiting boundary as the lower boundary and the smaller value of the T5 over-temperature limiting boundary and the compressor surge limiting boundary as the upper boundary, a stable oil supply range is formed, and the stable oil supply range is converted into a rotor acceleration N-dot stable control range.
[0012] A target N-dot control line is set within the rotor acceleration N-dot stable control range, and a feedforward fuel MAP is generated based on engine speed, actual ambient temperature, and the target N-dot control line.
[0013] The micro turbojet engine is subjected to phased start-up control; wherein, in the closed-loop acceleration phase, a feedforward-PI closed-loop fuel control is adopted, which provides a feedforward fuel command through the feedforward fuel MAP and is adjusted in conjunction with the PI feedback module to output the final fuel command; the final fuel command is subject to the dynamic limit of the stable fuel supply range.
[0014] Furthermore, the method for calculating the lean fuel limiting boundary, the T5 over-temperature limiting boundary, and the compressor surge limiting boundary specifically includes:
[0015] Establish a starting component-level model that includes the air intake, compressor, combustion chamber, turbine, and tail nozzle;
[0016] By coupling the solutions of mass conservation, flow continuity, pressure balance and rotor dynamics equations, the compressor operating point, turbine output power, compressor power consumption, T5 exhaust temperature and rotor acceleration N-dot are calculated under given ambient temperature, engine speed and fuel flow conditions.
[0017] For the multiple calibrated ambient temperatures, the minimum fuel flow rate required to maintain rotor power balance is calculated as the lean fuel limit boundary, the fuel flow rate when the T5 exhaust temperature reaches the maximum allowable temperature is calculated as the T5 over-temperature limit boundary, and the fuel flow rate when the compressor maintains a preset surge safety margin is calculated as the compressor surge limit boundary.
[0018] Furthermore, after obtaining the actual ambient temperature, when the actual ambient temperature is between two adjacent calibrated ambient temperatures, the lean oil limiting boundary, the T5 overheating limiting boundary, and the compressor surge limiting boundary are corrected by linear interpolation, spline interpolation, or radial basis function regression methods to obtain the boundary data at the current actual ambient temperature.
[0019] Furthermore, the phased start-up control of the micro turbojet engine specifically includes a preparation phase, a first phase, a second-first phase, a second-second phase, and a third phase executed sequentially; wherein the closed-loop acceleration phase includes the second-second phase and the third phase.
[0020] During the preparation phase, after receiving the oil unsealing command, the fuel pump is driven to unseal the oil circuit with the minimum oil supply. Then, the oil supply is shut off and the oil unsealing completion mark is set. The micro turbojet engine is then driven to the preset cold running speed for cold running by the starter motor.
[0021] In the first stage, the starter motor first drives the micro turbojet engine to the ignition preparation speed, opens the auxiliary gas valve and igniter for preheating and ignition; the starter motor continues to drive it to the first preset speed and starts fuel supply; when the T5 exhaust temperature exceeds the preset ignition success threshold, the fuel ignition is confirmed to be successful, and the igniter and auxiliary gas valve are closed.
[0022] In the first stage (II-1), an initial open-loop fuel supply control is adopted to keep the fuel quantity and starter motor control quantity constant, so that the fuel accumulated during the fuel circuit opening and ignition process is fully burned; when the engine speed rises to the second preset speed, the system switches to the second stage (II-2).
[0023] In the second stage, the starter motor continues to provide auxiliary torque and increases the output according to the pre-calibrated starter motor control line, wherein the target N-dot control line is 0.95 times the upper boundary of the rotor acceleration N-dot stable control range; when the engine speed reaches the starter motor disengagement speed, the starter motor disengages and enters the third stage.
[0024] In the third stage, the micro turbojet engine accelerates using only the remaining power of the turbine. The target N-dot control line is taken as 0.90 times the upper boundary of the rotor acceleration N-dot stable control range, and the target N-dot control line is gradually reduced to zero when approaching the idle speed.
[0025] Furthermore, during the phased start-up control process, the T5 exhaust temperature, engine speed, actual rotor acceleration N-dot, and fuel flow are monitored in real time, and over-temperature protection, cold suspension or stall protection, and hot suspension or surge risk protection are implemented.
[0026] When the engine speed reaches the idle threshold, the actual rotor acceleration N-dot approaches zero, and the T5 exhaust temperature is within the allowable range, the start-up control is discontinued and the idle speed closed-loop control is switched to the idle speed control.
[0027] Furthermore, the over-temperature protection includes: reducing the fuel command when the T5 exhaust temperature reaches the warning threshold; and performing emergency fuel reduction or shutdown when the T5 exhaust temperature reaches the maximum limit temperature or the temperature rise rate remains abnormal.
[0028] The cold suspension or engine shutdown protection includes: when the fuel flow is low and the actual rotor acceleration N-dot remains below the threshold, the engine speed does not increase for a long time, or the T5 exhaust temperature drops, increasing the fuel command to the stable fuel supply range or performing re-ignition; if the situation does not improve, stopping the start-up process.
[0029] The thermal suspension or surge risk protection includes: limiting or reducing fuel commands and maintaining starter motor assistance when the T5 exhaust temperature is too high, the actual rotor acceleration N-dot decreases, and the compressor operating point is close to the surge safety boundary; and executing a shutdown when the risk persists.
[0030] Compared with the prior art, the beneficial effects of the present invention are:
[0031] (1) The present invention calculates the lean fuel limit boundary, the T5 over-temperature limit boundary and the compressor surge limit boundary, thereby forming a stable fuel supply range, and dynamically limits the final fuel command during the closed-loop acceleration phase. This mechanism constrains the fuel command in real time through the three types of boundaries, so that the engine can ensure rotor acceleration while fundamentally avoiding stalling or cold suspension caused by insufficient fuel supply, as well as over-temperature, surge and hot suspension caused by excessive fuel supply.
[0032] (2) This invention plans the target N-dot control line within the safe range and generates a feedforward fuel MAP. The feedforward MAP provides the main control quantity, and PI feedback compensates for model error and individual differences. This feedforward-PI closed-loop control method not only reduces the adjustment burden of simple feedback control and improves tracking stability, but also enables the controller to balance speed and safety without touching the boundary limit value. It reduces the number of times the starting law needs to be calibrated by repeated test runs of physical objects, and reduces the R&D cost and risk of engine damage.
[0033] (3) This invention establishes a boundary database for multiple calibrated ambient temperatures and corrects the boundary data by interpolation or regression methods based on the actual ambient temperature during startup, thereby reducing the impact of high or low temperature environmental changes on startup safety margin and making the startup control logic highly adaptable to changes in environmental conditions and component degradation.
[0034] (4) The present invention divides the starting process into five stages and implements different control strategies for ignition, oil combustion, and closed-loop acceleration (motor-assisted and exit stages). In particular, the transition stage (stage II-1) retains the initial open-loop oil supply to allow the oil to burn fully before switching to feedforward-PI closed-loop acceleration (stages II-2 and III), avoiding the drawback of a single rule running through the entire process and achieving seamless and smooth switching of all operating conditions.
[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, embodiments of the present invention are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0037] Figure 1 This is the overall flowchart of the multi-boundary closed-loop starting method of the micro turbojet engine in the embodiment;
[0038] Figure 2 This is a logic diagram of the phased start-up control timing and operating condition switching in the embodiment. Detailed Implementation
[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.
[0040] The micro turbojet closed-loop starting control method based on multi-condition boundary constraints described in this invention relies on the electronic control system (including the electronic control unit ECU) of the micro turbojet engine. The system hardware mainly includes: ambient temperature sensor, speed sensor, T5 exhaust temperature sensor, fuel flow sensor, and other status acquisition devices, as well as actuators such as fuel pump, fuel solenoid valve, auxiliary gas valve, igniter, and starter motor. The ECU internally includes a starting state machine, an environmental boundary database, an N-dot calculation module, a feedforward fuel MAP, a PI feedback module, a dynamic limiting module, and a fault protection module.
[0041] Reference Figure 1 This invention provides a closed-loop starting control method for a micro turbojet engine, which mainly includes the following steps:
[0042] S1: Establish a starting component-level model and calculate multi-condition boundaries.
[0043] First, collect engine component characteristics, rotor inertia, T5 limiting temperature, surge safety margin, ambient temperature range, and actuator control characteristics to establish an engine starting component-level model (or a semi-physical model, lookup table model, or digital twin model corrected by test data) including the intake manifold, compressor, combustion chamber, turbine, and exhaust nozzle.
[0044] The component-level model is solved by coupling the principles of mass conservation, flow continuity, pressure balance, and rotor dynamics equations. Under given ambient temperature, engine speed, and fuel flow rate conditions, the compressor operating point, turbine output power, compressor power consumption, T5 exhaust temperature, and rotor acceleration (N-dot) are calculated.
[0045] For multiple calibration environmental temperature and rotational speed grids, the following three major constraint boundaries are calculated respectively:
[0046] (1) Lean fuel limit boundary: the minimum fuel flow required to maintain rotor power balance.
[0047] At a given engine speed, with a fixed intake air flow, the minimum fuel supply corresponding to the rotor acceleration N-dot being exactly equal to zero (i.e., the rotor power reaches critical equilibrium, and there is no reverse drag or stalling of the geared generator) is calibrated as the lean fuel limit boundary.
[0048] (2) T5 over-temperature limit boundary: that is, the fuel flow rate when the T5 exhaust temperature reaches the maximum allowable temperature.
[0049] At the same speed, as the fuel supply gradually increases, the heat released in the combustion chamber increases, causing the exhaust temperature T5 after the turbine to rise continuously. When the theoretically calculated value of T5 reaches the highest allowable temperature that the engine turbine blade material can withstand (e.g., 1050K), the corresponding fuel flow rate is the T5 over-temperature limit boundary.
[0050] (3) Compressor surge limit boundary: the fuel flow rate when the compressor maintains the preset surge safety margin.
[0051] As the fuel supply increases, the compressor back pressure rises, and its operating point moves toward the surge boundary line on the compressor characteristic diagram (MAP). A preset surge safety margin (e.g., 10% to 15%) is set. When the margin between the compressor operating point and the theoretical surge line decreases to the lower limit of this safety margin, the corresponding fuel flow rate is the compressor surge limit boundary.
[0052] S2: Generation of adaptive and stable control range for ambient temperature.
[0053] Boundary data at each calibrated ambient temperature are stored in the environmental boundary database. When the engine is actually started, the current actual ambient temperature is obtained. When the actual ambient temperature falls between two adjacent calibrated ambient temperatures, the ECU obtains the corrected lean fuel limit boundary, T5 over-temperature limit boundary, and compressor surge limit boundary at the current actual ambient temperature through linear interpolation (or spline interpolation, radial basis function, or other regression methods).
[0054] Subsequently, a stable fuel supply range is formed by using the lean fuel limit boundary as the lower boundary and the smaller value of the T5 over-temperature limit boundary and the compressor surge limit boundary as the upper boundary. This range of fuel flow dimension is then converted into a stable control range of rotor acceleration N-dot.
[0055] S3: Establish target control lines and feedforward fuel MAP.
[0056] To prevent the control target from closely adhering to the stability boundary, a target N-dot control line is set within the calculated rotor acceleration N-dot stability control range, with a safety margin reserved. The ECU generates a feedforward fuel MAP based on engine speed, actual ambient temperature, and the target N-dot control line, which is used to provide a reference feedforward fuel command in subsequent closed-loop control.
[0057] When the ambient temperature decreases, the air density increases significantly, resulting in a larger air mass flow rate drawn into the compressor. To maintain the same acceleration characteristics, more fuel is required. Conversely, in high-temperature environments, the air is thin, and the same fuel supply can easily lead to rich combustion and T5 overheating. Through interpolation correction using an environmental boundary database, this system can accurately reconstruct a stable control range that conforms to the current operating conditions before testing or at startup, based on the actual local weather conditions of the day.
[0058] After entering closed-loop control, the mathematical execution form of the feedforward-PI closed-loop fuel control and dynamic limiting logic used in this embodiment is as follows:
[0059] The final fuel command output by the system Base fuel quantity output by feedforward fuel MAP The adjustment amount of the PI feedback controller output It is formed by superposition, that is, basic instructions. .
[0060] The input to the PI feedback controller is the difference between the desired value on the target N-dot control line and the actual N-dot obtained by differentiating the current speed sensor.
[0061] Subsequently, the dynamic limiting module applies the basic commands. Strict upper and lower limit constraints are imposed:
[0062]
[0063] In the formula, Limiting boundaries for oil-poor areas, The upper limit is the smaller of the over-temperature and surge boundaries (i.e., the safe upper limit). Through this dynamic limiting mechanism, even if the PI controller generates excessive integral saturation or overshoot calculation values due to sensor noise or sudden speed changes, the final command output to the fuel pump or fuel solenoid valve will never exceed the physical safety boundary of the current speed and ambient temperature, fundamentally preventing the occurrence of dangerous operating conditions.
[0064] Meanwhile, the target N-dot control line is set at 0.95 times or 0.90 times the upper boundary, respectively. The technical consideration is to fully utilize the engine's acceleration potential to meet the requirements of rapid start-up (close to the upper limit), while reserving 5% to 10% control redundancy to prevent dynamic overshoot due to pipeline pressure build-up delay or actuator lag.
[0065] S4: Phased closed-loop start-up control.
[0066] Reference Figure 2 Based on the aforementioned feedforward fuel MAP and stable control range, a five-stage start-up control is implemented for the micro turbojet engine:
[0067] To more clearly illustrate the execution logic of the startup state machine, the specific control strategies, main actions, and stage switching conditions for each stage in this embodiment are shown in Table 1.
[0068] Table 1. Staged Start-up Control Logic Table Provided by Embodiments of the Invention
[0069]
[0070] Based on Table 1 above, the specific engineering physical execution logic of the five-stage start-up control is as follows:
[0071] (1) Preparation stage (fuel opening and cold run): After receiving the fuel opening command, the ECU drives the fuel pump at the minimum fuel supply and maintains it for a specified time (e.g., 5s) to fill the fuel line with fuel. Then, the fuel supply is shut off and the fuel opening completion mark is set. Subsequently, the starter motor drives the engine to the preset cold run speed (e.g., 2600rpm) and maintains it for a specified time (e.g., 5s) to check the status of the rotor, sensors and actuators, and to complete ventilation and cooling.
[0072] (2) Stage I (Initial Ignition Control): The starter motor first rotates the engine to the ignition preparation speed, at which point the combustion chamber is in the optimal ignition flow field. First, the auxiliary gas valve (introducing flammable gases such as propane or butane) and igniter are opened for preheating and ignition; then the starter motor continues to rotate to the first preset speed (e.g., 7800 rpm) and begins liquid fuel supply. Gas preheating can significantly improve the ignition success rate of kerosene. When the T5 exhaust temperature exceeds the preset ignition success threshold (e.g., 150°C), it indicates that the main fuel has been ignited. The system confirms successful ignition and closes the igniter and auxiliary gas valve, saving energy and gas.
[0073] (3) Stage II-1 (Initial Open-Loop Fuel Supply, Fuel Accumulation Combustion Stage): This stage is crucial for preventing hot suspension. Due to the initial opening of the fuel circuit and initial ignition, unburned liquid fuel accumulates in the combustion chamber and exhaust nozzle. If closed-loop acceleration is introduced immediately at this point, the controller will significantly increase fuel supply due to the slow initial speed increase, causing the existing fuel accumulation and the newly supplied fuel to combust simultaneously, resulting in a catastrophic surge in T5 temperature. Therefore, this stage forces the use of initial open-loop fuel supply, keeping the fuel quantity and starter motor control quantity essentially unchanged, giving the fuel accumulation a window for stable combustion and discharge with the airflow. When the speed reaches the second preset speed (e.g., 11000 rpm), and after confirming that the fuel accumulation is exhausted and the aerodynamic flow field is stable, the system safely switches to the next stage.
[0074] (4) Stage II-2 (Closed-loop acceleration with electric motor assistance): The engine enters the high-load acceleration period. As the speed increases, the torque output characteristics of the starter motor gradually decrease. At this time, feedforward-PI closed-loop fuel control is adopted, and the target N-dot control line is taken as 0.95 times the upper boundary of the stable control range. The decrease in the auxiliary torque of the starter motor is compensated by the increase in fuel, and is strictly controlled by the dynamic limiting module. When the engine speed reaches the disengagement critical point of the starter motor (e.g., 22828.8 rpm, disengaging the motor through a one-way clutch or electrical control), it enters Stage III.
[0075] (5) Stage III (Independent Turbine Acceleration and Smooth Transition): The starter motor is completely disengaged, and the engine relies entirely on the residual power generated by its own turbine to overcome compressor resistance for acceleration. Due to the loss of external auxiliary torque, the engine is more sensitive to changes in fuel supply. The ECU continues to perform feedforward-PI closed-loop control, but to enhance stability, the target N-dot control line is lowered to 0.90 times the upper boundary of the stable control range. In particular, as the engine speed gradually approaches the target idle speed, the algorithm actively causes the target N-dot control line to gradually decrease to zero along a smooth curve. This design effectively avoids violent overshoot when the engine speed reaches the idle point and the resulting sudden change in fuel supply (system anti-oscillation).
[0076] S5: Fault protection and slow-speed switching.
[0077] Throughout the entire startup process, parameters such as T5 exhaust temperature, engine speed, N-dot, and fuel flow are monitored in real time. If any abnormality is detected, the safety protection mechanism is immediately activated.
[0078] (1) Over-temperature protection: When the exhaust temperature of T5 reaches the warning threshold, reduce the fuel command; when T5 reaches or exceeds the maximum limit temperature (e.g., 1050K), or the temperature rise rate is abnormal, perform emergency fuel reduction or stop.
[0079] (2) Cold suspension or shutdown protection: When the fuel flow is low and N-dot is consistently below the threshold, the engine speed does not increase for a long time or T5 drops significantly, the fuel command will be increased to the safe fuel supply range or restart will be performed; if it still does not recover, the start will be stopped.
[0080] (3) Protection against hot suspension or surge risk: When T5 is high, N-dot is low and the compressor operating point is close to the surge safety boundary, limit or reduce fuel command and keep the starter motor assisting; if the risk persists, shut down.
[0081] (4) Ignition failure protection: In the first stage, if the T5 exhaust temperature does not exceed the ignition success threshold within the maximum ignition timeout period specified by the system, the ECU determines that the ignition has failed. At this time, the system immediately cuts off the main fuel and auxiliary gas supply, but keeps the starter motor running to perform the ventilation and cooling procedure to purge the residual fuel and gas in the combustion chamber until the safety conditions are met before allowing the next start command to be initiated.
[0082] (5) Sensor and actuator hardware protection: During the entire start-up state machine operation, the ECU performs high-frequency rationality verification on the signals of the speed, T5, fuel flow and ambient temperature sensors. Once a signal is detected to be seriously out of bounds (such as exceeding the range limit), a sudden change that is not physically regular (such as a step jump in the speed signal), or a signal loss or disconnection, and exceeds the anti-interference filtering window, or the actuator (such as the fuel pump PWM feedback) is unresponsive, the system determines that the hardware has failed, directly bypasses the closed-loop control logic, and enters the highest priority safe shutdown state.
[0083] When the engine speed reaches the idle threshold, N-dot approaches zero, and T5 is within the allowable range, it signifies that the starting state machine has been successfully completed, the system exits starting control, and switches to idle speed closed-loop control.
[0084] We conducted simulation and bench testing on the method of this invention:
[0085] The proposed method was simulated using the established component-level model at an ambient temperature of approximately 290.75 K. The results show that the engine started in approximately 16.98 s, and the engine remained within the stable control range throughout the start-up process, without any overheating or speed fluctuations.
[0086] The control method was programmed into the ECU for bench testing. The engine sequentially completed oil opening, cold running, preheating, ignition, closed-loop acceleration, and starter motor disengagement, entering idle condition in about 17.25 seconds. During startup, the maximum T5 value was about 1003K, which is lower than the limit temperature of 1050K, and the engine speed increase was smooth.
[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A closed-loop starting control method for a micro turbojet engine based on multi-condition boundary constraints, characterized in that, include: A starting component-level model of a micro turbojet engine was established, and the lean fuel limit boundary, T5 over-temperature limit boundary, and compressor surge limit boundary of the micro turbojet engine were calculated under multiple calibrated ambient temperatures and different engine speeds. Using the lean oil limiting boundary as the lower boundary and the smaller value of the T5 over-temperature limiting boundary and the compressor surge limiting boundary as the upper boundary, a stable oil supply range is formed, and the stable oil supply range is converted into a rotor acceleration N-dot stable control range. A target N-dot control line is set within the rotor acceleration N-dot stable control range, and a feedforward fuel MAP is generated based on engine speed, actual ambient temperature, and the target N-dot control line. The micro turbojet engine is subjected to phased start-up control; wherein, in the closed-loop acceleration phase, a feedforward-PI closed-loop fuel control is adopted, which provides a feedforward fuel command through the feedforward fuel MAP and is adjusted in conjunction with the PI feedback module to output the final fuel command; the final fuel command is subject to the dynamic limit of the stable fuel supply range.
2. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 1, characterized in that, The specific methods for calculating the lean fuel limit boundary, T5 over-temperature limit boundary, and compressor surge limit boundary include: Establish a starting component-level model that includes the air intake, compressor, combustion chamber, turbine, and tail nozzle; By coupling the solutions of mass conservation, flow continuity, pressure balance and rotor dynamics equations, the compressor operating point, turbine output power, compressor power consumption, T5 exhaust temperature and rotor acceleration N-dot are calculated under given ambient temperature, engine speed and fuel flow conditions. For the multiple calibrated ambient temperatures, the minimum fuel flow rate required to maintain rotor power balance is calculated as the lean fuel limit boundary, the fuel flow rate when the T5 exhaust temperature reaches the maximum allowable temperature is calculated as the T5 over-temperature limit boundary, and the fuel flow rate when the compressor maintains a preset surge safety margin is calculated as the compressor surge limit boundary.
3. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 1, characterized in that, After obtaining the actual ambient temperature, when the actual ambient temperature is between two adjacent calibrated ambient temperatures, the lean oil limit boundary, the T5 overheat limit boundary, and the compressor surge limit boundary are corrected by linear interpolation, spline interpolation, or radial basis function regression methods to obtain the boundary data at the current actual ambient temperature.
4. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 1, characterized in that, The phased start-up control of the micro turbojet engine specifically includes a preparation phase, a first phase, a second-first phase, a second-second phase, and a third phase executed sequentially; wherein the closed-loop acceleration phase includes the second-second phase and the third phase.
5. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 4, characterized in that, During the preparation phase, after receiving the oil unsealing command, the fuel pump is driven to unseal the oil circuit with the minimum oil supply. Then, the oil supply is shut off and the oil unsealing completion mark is set. The micro turbojet engine is then driven to the preset cold running speed for cold running by the starter motor. In the first stage, the starter motor first drives the micro turbojet engine to the ignition preparation speed, opens the auxiliary gas valve and igniter for preheating and ignition; the starter motor continues to drive it to the first preset speed and starts fuel supply; when the T5 exhaust temperature exceeds the preset ignition success threshold, the fuel ignition is confirmed to be successful, and the igniter and auxiliary gas valve are closed.
6. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 5, characterized in that, In the first stage (II-1), an initial open-loop fuel supply control is adopted to keep the fuel quantity and starter motor control quantity constant, so that the fuel accumulated during the fuel circuit opening and ignition process is fully burned; when the engine speed rises to the second preset speed, the system switches to the second stage (II-2).
7. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 6, characterized in that, In the second stage, the starter motor continues to provide auxiliary torque and increases the output according to the pre-calibrated starter motor control line, wherein the target N-dot control line is 0.95 times the upper boundary of the rotor acceleration N-dot stable control range; when the engine speed reaches the starter motor disengagement speed, the starter motor disengages and enters the third stage. In the third stage, the micro turbojet engine accelerates using only the remaining power of the turbine. The target N-dot control line is taken as 0.90 times the upper boundary of the rotor acceleration N-dot stable control range, and the target N-dot control line is gradually reduced to zero when approaching the idle speed.
8. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 1, characterized in that, During the phased start-up control process, the T5 exhaust temperature, engine speed, actual rotor acceleration N-dot and fuel flow are monitored in real time, and over-temperature protection, cold suspension or stall protection, and hot suspension or surge risk protection are implemented. When the engine speed reaches the idle threshold, the actual rotor acceleration N-dot approaches zero, and the T5 exhaust temperature is within the allowable range, the start-up control is exited and switched to the idle speed closed-loop control.
9. The micro turbojet closed-loop starting control method based on multi-condition boundary constraints according to claim 8, characterized in that, The over-temperature protection includes: reducing fuel command when the T5 exhaust temperature reaches the warning threshold; and performing emergency fuel reduction or shutdown when the T5 exhaust temperature reaches the maximum limit temperature or the temperature rise rate remains abnormal. The cold suspension or engine shutdown protection includes: when the fuel flow is low and the actual rotor acceleration N-dot remains below the threshold, the engine speed does not increase for a long time, or the T5 exhaust temperature drops, increasing the fuel command to the stable fuel supply range or performing re-ignition; if the situation does not improve, stopping the start-up process. The thermal suspension or surge risk protection includes: limiting or reducing fuel commands and maintaining starter motor assistance when the T5 exhaust temperature is too high, the actual rotor acceleration N-dot decreases, and the compressor operating point is close to the surge safety boundary; and executing a shutdown when the risk persists.