A method and system for testing the external characteristics of an aero-piston engine based on a high-altitude environmental cabin

Abstract

The application discloses a kind of based on high-altitude environment cabin's aviation piston engine external characteristic test method and system, it is related to aero-engine test technical field.The method relies on high-altitude environment cabin with temperature, humidity and pressure accurate simulation function, with full load condition as core, through six steps of test preparation, condition setting, environment cabin parameter regulation, full load condition regulation and data acquisition, multi-condition test cycle, data processing and curve drawing, obtains the power, torque and fuel consumption rate of engine under different high-altitude environment and other core external characteristic parameters and curve;Wherein environment cabin parameter regulation adopts the order of pressure first, temperature second, humidity third.This application also provides a test system for executing the above method.The application solves the problem that ground test bench cannot simulate high-altitude environment and high-altitude flight test is high in cost and difficult to control working condition, provides reliable technical means for the high-altitude performance evaluation and airworthiness certification of aviation piston engine.

Description

Technical Field

[0001] This invention relates to the field of aero-engine testing technology, specifically to a method and system for testing the external characteristics of an aero-engine based on a high-altitude environmental chamber, which is suitable for accurately evaluating the high-altitude performance of an aero-engine under full load conditions. Background Technology

[0002] The external characteristics of an aircraft piston engine refer to the changes in core performance parameters such as power, torque, and fuel consumption rate with engine speed under full load conditions (when torque reaches its maximum at a certain speed). These characteristics directly determine critical flight performance parameters of an aircraft, such as maximum speed, rate of climb, and payload capacity, and are the core basis for engine development optimization, performance evaluation, and airworthiness certification. Because the operating environment of an aircraft piston engine varies significantly with flight altitude, parameters such as low air pressure, low / high temperature, and low / high humidity in the high-altitude environment directly affect the engine's intake air density, combustion efficiency, and power output, thus significantly altering its external characteristics under full load. Therefore, accurately obtaining external characteristic data of the engine under full load conditions in different high-altitude environments is a crucial step in ensuring the engine's adaptability to high-altitude flight requirements and improving the safety and reliability of the aircraft.

[0003] Current external characteristic tests for aero-engines are mainly divided into two categories: ground bench tests and high-altitude flight tests. Ground bench tests are typically conducted under normal temperature and pressure conditions. While they can achieve full-load control, they cannot simulate the special environmental conditions at high altitudes. This results in a significant deviation between the full-load external characteristic data obtained from the tests and the engine's actual high-altitude operating conditions, making it difficult to accurately reflect its high-altitude full-load performance. High-altitude flight tests require the engine to be carried on a test aircraft for actual flight testing. Although they can simulate the high-altitude environment, they are not only costly and time-consuming, but also subject to limitations such as weather conditions and airspace control. Precise control under full-load conditions is difficult, the repeatability and stability of the test data are poor, and there are also flight safety risks.

[0004] To address the aforementioned issues, high-altitude environmental chambers equipped with temperature, humidity, and pressure simulation capabilities have emerged, allowing for the artificial adjustment of environmental parameters at different altitudes. CN111927623A discloses a high-altitude scavenging and power performance simulation test platform and method for a two-stroke aero-piston engine. This platform simulates low temperature and low pressure for the intake air and low pressure for the exhaust air, and can use an auxiliary supercharging system and an exhaust back pressure control system to simulate high-altitude supercharging boundary conditions when the engine is not equipped with a supercharger. However, this platform and method primarily focus on scavenging and power performance simulation of two-stroke aero-piston engines, with its testing emphasis on measuring scavenging performance indicators (capture rate and charging efficiency). It does not focus on specific tests of the engine's full-load external characteristics, nor does it address precise maintenance strategies for full-load operation or methods for coordinated control of multiple environmental parameters. CN115576257A, on the other hand, emphasizes a high-altitude simulation test device and method for the internal flow of aero-piston engines, employing a method that only simulates low temperature and low pressure for the engine intake air. Furthermore, the test apparatus disclosed in CN102023096A has a simple structure and lacks an auxiliary supercharging system. It cannot simulate the boundary pressure and temperature conditions of a supercharged system when the engine lacks a supercharger, and it can only simulate the engine's power performance at high altitudes, failing to acquire scavenging performance data. None of the aforementioned existing technologies offer a systematic solution for testing the full-load external characteristics of aero-piston engines, particularly exhibiting significant shortcomings in the precise maintenance of full-load operating conditions, the coordinated control of high-altitude environmental parameters and full-load operating conditions, and the targeted acquisition and processing of full-load external characteristic data.

[0005] The full-load external characteristic test of aero-piston engines presents the following specific technical challenges: First, full-load operation requires the engine to output its maximum torque at every speed, which places extremely high demands on the stability of fuel supply, the adequacy of intake air volume, and the heat dissipation capacity of the cooling system. Fluctuations in any of these aspects can lead to deviations from the full-load condition. Second, the extreme conditions of low pressure, low temperature, and low humidity in the high-altitude environment significantly affect the engine's combustion process and mechanical operation. There is a complex nonlinear coupling relationship between fluctuations in environmental parameters and the engine's full-load operating state. How to maintain the stability of the full-load condition while dynamically adjusting environmental parameters is a technical problem that urgently needs to be solved in this field. Third, external characteristic tests require data collection at multiple speed points, and stable full-load operation at each speed point requires a certain amount of time. How to efficiently complete test cycles at multiple altitudes and speeds within a limited time while ensuring data quality is also a practical difficulty that needs to be overcome.

[0006] Therefore, there is an urgent need for a special external characteristic test method based on a high-altitude environmental chamber that is specifically adapted to aero-piston engines and focuses on full-load operating conditions, to fill the existing technological gap and meet the core requirements of full-load high-altitude performance evaluation of engines. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies in high-altitude external characteristic testing of aero-piston engines, such as high cost, long cycle, poor data accuracy, and difficulty in controlling full-load conditions. This invention provides a method for testing the external characteristics of aero-piston engines based on a high-altitude environmental chamber. This method utilizes the temperature, humidity, and pressure simulation capabilities of the high-altitude environmental chamber to accurately simulate different high-altitude environmental conditions. Through precise control strategies under full-load conditions and a scientifically designed test procedure, it efficiently and accurately acquires external characteristic data of aero-piston engines under different high-altitude environments, providing reliable support for the full-load performance evaluation of the engine.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for testing the external characteristics of an aero-engine based on a high-altitude environmental chamber, wherein the high-altitude environmental chamber has precise simulation capabilities for temperature, humidity, and pressure, and can simulate environmental parameters at different altitudes. This method focuses on the full-load operating conditions of the engine and constructs a test system that can directly obtain target values ​​of performance parameters. The method includes the following steps:

[0010] S1. Experimental Preparation:

[0011] S1.1. Fix the aircraft piston engine to be tested on the test bench inside the high-altitude environmental chamber, and complete the connection between the engine and the test bench dynamometer system, fuel supply system, cooling system, intake system, and exhaust system. Among them, the dynamometer system is used to cooperate with the engine control system to achieve stable maintenance under full load conditions, and at the same time provide a stable operating condition basis for performance parameter testing; the fuel supply system adopts a high-precision metering device and a full-load pressure stabilizing device to ensure sufficient and stable fuel supply under full load conditions; the cooling system is used to maintain the temperature stability of the engine during full load operation; the intake system is connected to the gas circulation system of the high-altitude environmental chamber to ensure the intake requirements under full load; the exhaust system extends to the outside of the environmental chamber and is equipped with a pressure regulating device to prevent exhaust back pressure from affecting full load performance.

[0012] S1.2 Constructing a test system integrating power performance and economic performance testing functions: Sensors are deployed in the high-altitude environmental chamber and at key engine components, including environmental parameter sensors (temperature sensor, humidity sensor, pressure sensor) and engine performance parameter sensors (intake air temperature sensor, exhaust air temperature sensor, cylinder pressure sensor, fuel flow sensor, throttle opening sensor, torque sensor, etc.); all sensors and supporting data acquisition and processing equipment are connected to the data acquisition system to form a test system capable of directly acquiring target values ​​of performance parameters; where "capable of directly acquiring target values ​​of performance parameters" means that the torque sensor can directly measure the torque of the engine output shaft. Torque and power are directly calculated by multiplying torque and speed (both torque and speed are direct measurements, and the calculation process is a simple multiplication operation, requiring no model estimation or indirect inference). The fuel flow sensor can directly measure the volume or mass of fuel consumed per unit time. The above parameters are all core target parameters of the test and do not need to be inferred through indirect means such as intake volume and exhaust composition analysis. The torque and throttle opening sensors are used to monitor and confirm that the engine is under full load in real time. In conjunction with the dynamometer system, the engine torque, power and other power performance parameters can be directly collected or indirectly calculated as target values. The fuel flow sensor can directly collect the basic economic performance parameters such as fuel flow as target values.

[0013] S1.3 System Debugging and Pre-inspection: Conduct comprehensive debugging of the temperature control system, humidity control system, pressure control system, dynamometer system, integrated power and economic performance testing system, and data acquisition system of the high-altitude environmental chamber to ensure that each system operates normally, sensor data acquisition is accurate, and test equipment operates stably; perform pre-acquisition verification through the test system to confirm that the target values ​​of core performance parameters such as torque, power, fuel flow, and fuel consumption rate can be accurately obtained; at the same time, perform a pre-start check on the engine to confirm that the connection of each engine component is reliable and fault-free, and debug the engine control system to ensure that it can stably maintain full-load operation.

[0014] S2. Test Condition Settings:

[0015] Based on the experimental requirements, determine the range of altitudes to be simulated and the corresponding standard values ​​of environmental parameters (refer to the standard atmospheric model). The environmental parameters include ambient temperature, ambient humidity, and ambient pressure. For each target altitude, set the corresponding target values ​​of environmental parameters. At the same time, set the full-load speed range and speed gradient of the engine. The speed range covers the engine's idle speed to its maximum rated speed, and the speed gradient is set according to the experimental accuracy requirements. Clarify the full-load control standard: achieve the engine's maximum design load by adjusting the throttle opening or fuel supply to ensure that the engine is operating at full load under each speed condition.

[0016] The full-load threshold is determined as follows: According to the definition of the speed characteristics of an internal combustion engine, the external characteristic is the speed characteristic measured when the throttle is fully open (100% opening). However, in actual engineering tests, due to factors such as sensor measurement errors (typically ±0.5%), machining and assembly tolerances, and unavoidable minor fluctuations during engine operation, it is difficult to maintain a strictly 100% throttle-open state accurately and continuously in dynamic tests. Therefore, this invention uses 98% as the engineering-acceptable full-load threshold, which comprehensively considers the following factors:

[0017] (1) The measurement accuracy (±0.5%) of the high-precision throttle opening sensor allows for a deviation of no more than 0.5% between the measured value and the true value;

[0018] (2) The response delay and closed-loop regulation overshoot of the engine electronic control system are usually controlled within 1%-2%;

[0019] (3) The 98% threshold can effectively distinguish between full load and partial load (partial load usually refers to the condition where the throttle opening is less than 90%), avoid misjudgment caused by sensor noise or instantaneous fluctuations, and ensure that the test data can truly reflect the engine's limit power output performance.

[0020] S3, Environmental Chamber Parameter Control:

[0021] The control system of the high-altitude environmental chamber is activated, adopting a coordinated control sequence of "pressure first, then temperature, then humidity." Based on the target environmental parameter values ​​corresponding to a certain target altitude set in step S2, the environmental parameters inside the chamber are controlled. During the control process, the environmental parameters inside the chamber are monitored in real time through environmental parameter sensors, and a closed-loop control strategy is used to provide feedback adjustment to the control system until the temperature, humidity, and pressure inside the chamber stabilize within the target range and the fluctuation range meets the requirements. After the environmental parameters stabilize, they are maintained for a certain period of time to ensure that the environmental conditions are stable before starting the engine for full-load operation.

[0022] The physical principle behind the "pressure first, temperature second, humidity third" control sequence is as follows: The high-altitude environmental chamber is a sealed container, and the gas state inside follows the ideal gas law PV=nRT. The reason for controlling pressure P first is that pressure changes directly alter the gas density inside the chamber, thus affecting the convective heat transfer coefficient and thermal inertia during temperature control. If temperature is adjusted before pressure, pressure changes will cause significant drift in the already stable temperature field due to changes in gas density, requiring repeated adjustments to achieve convergence. The reason for controlling temperature T second is that temperature changes affect the saturated water vapor partial pressure of the gas inside the chamber (following the Clausius-Clapeyron equation), thus directly changing the relative humidity value at the same absolute humidity. If humidity is adjusted before temperature, temperature changes will cause significant fluctuations in relative humidity (for every 10°C change in temperature, the saturated water vapor pressure approximately doubles), requiring readjustment of humidity. Therefore, prioritizing pressure control, followed by temperature control, and then humidity control effectively avoids cross-coupling interference between parameters, achieving rapid convergence and precise stabilization of each environmental parameter.

[0023] S4. Engine Full-Load Condition Control and Data Acquisition:

[0024] S4.1 Full-load start-up and speed regulation: After the cabin environmental parameters stabilize, start the aircraft piston engine. After the engine idle speed stabilizes, adjust the fuel supply and throttle opening through the engine control system to bring the engine into full-load operation. After confirming that the full-load state is stable through real-time monitoring by the torque sensor, adjust the engine speed through the dynamometer system, gradually increasing it from the idle speed to the maximum rated speed according to the speed gradient set in step S2.

[0025] S4.2 Stable Operation and Parameter Acquisition: Under full load conditions at each target speed, the engine is kept running stably to ensure that the engine's full load performance parameters reach a stable state. During this period, the engine's target values ​​for power performance parameters such as speed, torque, and power, as well as target values ​​for basic economic performance parameters such as fuel flow, are directly acquired through a test system that integrates power and economic performance testing functions. At the same time, auxiliary performance parameters such as engine intake air temperature, exhaust air temperature, cylinder pressure, and throttle opening, as well as real-time ambient temperature, humidity, and pressure data in the test chamber, are simultaneously acquired through a data acquisition system. The acquisition duration and frequency at each target speed meet the test accuracy requirements to ensure that the true parameters under stable full load conditions can be captured.

[0026] S4.3, Cyclic Data Acquisition: After completing the data acquisition under full load conditions at a certain target speed, the engine speed is adjusted to the next target speed through the dynamometer system. The full load condition is maintained throughout the process, and the operation of step S4.2 is repeated until the data acquisition under all full load speed conditions corresponding to the target altitude is completed.

[0027] S5, Multi-condition test cycle:

[0028] Following the process of steps S3-S4, the environmental parameter adjustment and data acquisition of the engine under various full-load speed conditions corresponding to all target altitudes set in step S2 are completed sequentially. When switching target altitudes, the engine is first taken out of full load and reduced to idle speed. Then, the temperature, humidity and pressure of the environmental chamber are adjusted to the new target values. After the environmental parameters stabilize, the engine is switched to full load and the speed is adjusted to avoid the impact of sudden changes in environmental parameters or sudden changes in full load conditions on engine performance and the accuracy of test data.

[0029] S6. Full-load external characteristic data processing and curve plotting:

[0030] S6.1 Data Preprocessing and Validity Verification: The collected test data is preprocessed. First, the valid data segments under full load conditions are selected and the data that is not under full load conditions are removed. Abnormal data in the valid data segments are removed using the 3σ criterion. The average value of the valid full load data at each target speed and target altitude is calculated to obtain the average value of each parameter. A full load validity verification step is added. If the average throttle opening value under a certain speed condition does not reach the full load threshold, the data under that condition is determined to be invalid data and the test under that speed condition needs to be repeated.

[0031] S6.2 Parameter Calculation: Based on the target values ​​of power performance parameters such as full-load speed, torque, and power directly obtained from the test system, as well as the target values ​​of basic economic performance parameters such as fuel flow, calculate the fuel consumption rate (fuel consumption rate = fuel flow / power) of the engine at different full-load speeds at each target altitude.

[0032] S6.3 Plotting External Characteristic Curves: Using engine speed as the horizontal axis and power, torque, and fuel consumption rate as the vertical axes, plot the engine's external characteristic curves corresponding to each target altitude. This will provide complete external characteristic data of the aero-piston engine under full load in different high-altitude environments, providing a direct basis for full-load performance evaluation.

[0033] This invention also provides an external characteristic testing system for an aircraft piston engine based on a high-altitude environmental chamber, used to perform the above-described methods. The system includes:

[0034] The high-altitude environment chamber is equipped with precise simulation functions for temperature, humidity and pressure, and is used to provide environmental simulation spaces at different altitudes.

[0035] The bench dynamometer system, set up inside the high-altitude environmental chamber, is used to fix the aircraft piston engine to be tested and adjust its output shaft speed, working in conjunction with the engine control system to maintain stable operation under full load conditions.

[0036] The fuel supply system, connected to the engine, is equipped with a full-load pressure stabilizing device to provide sufficient and stable fuel with pressure fluctuations within a preset range under full-load conditions.

[0037] An integrated power and economic performance testing system is installed in the high-altitude environmental chamber and key parts of the engine. It includes environmental parameter sensors, throttle opening sensors, torque sensors and fuel flow sensors, which are used to monitor environmental parameters and engine performance parameters in real time. The torque sensor directly measures the engine torque and the fuel flow sensor directly measures the fuel flow.

[0038] The data acquisition and processing system is connected to the integrated power and economic performance testing system and various sensors, and is used to collect test data, perform data preprocessing, validity verification, parameter calculation and external characteristic curve plotting.

[0039] The central control unit is connected to the high-altitude environmental chamber, the bench dynamometer system, the fuel supply system, the integrated power and economic performance testing system, and the data acquisition and processing system, respectively. The central control unit is configured to execute each step of the test method for the external characteristics of an aero-piston engine based on the high-altitude environmental chamber described in this invention.

[0040] The mechanism of this invention is as follows:

[0041] The above-mentioned technical solution of the present invention includes the following three key technical means:

[0042] Technical approach 1: To address the technical challenge of mutual interference among the three physical parameters of temperature, humidity, and pressure in the high-altitude environmental chamber during the control process, a coordinated control approach of "pressure first, then temperature, and then humidity" is adopted.

[0043] Technical means two: precise control and stable maintenance under full load conditions;

[0044] Technical means three: Through an integrated testing system configured with high-precision sensors, the target values ​​of core performance parameters can be obtained directly, efficiently, and accurately.

[0045] The three key technologies mentioned above have the following synergistic effects:

[0046] Technical means one and technical means two form a synergistic relationship of "environmental protection - operating condition execution". The precision and stability of the environmental chamber parameter control directly determine the external boundary conditions for the engine to operate at full load. Only when the pressure, temperature, and humidity inside the chamber are stable within the target range can the engine's intake air density, intake air temperature, and combustion environment remain constant, and the power output under full load conditions be repeatable and comparable. Conversely, if the environmental parameters fluctuate too much, even if the engine control system maintains the throttle fully open, its actual output torque will drift due to changes in intake conditions, rendering the "full load" state ineffective. Therefore, technical means one provides a stable and repeatable environmental boundary for technical means two, while technical means two achieves precise execution of full load conditions under the environmental conditions created by technical means one. Both are indispensable.

[0047] Technical means two and three form a synergistic relationship of "operating condition maintenance - parameter acquisition". Stable maintenance of full-load operating conditions is a prerequisite for obtaining effective external characteristic data—if the full-load state cannot be continuously stabilized, the collected parameters such as torque and fuel flow will not reflect the engine's true limiting performance at that speed. Simultaneously, the high-performance testing system acquires data at high frequency and high precision, and can provide real-time feedback on the maintenance status of the full-load state (such as real-time monitoring data from the throttle opening sensor and torque sensor), providing a closed-loop correction basis for operating condition control. Technical means two ensures that "full-load data is measured," while technical means three ensures "accurate measurement, fast measurement, and feedback." The two support each other, jointly guaranteeing the validity and reliability of the test data.

[0048] Technical means three and technical means one form an indirect synergistic relationship of "parameter perception-environmental feedback". Environmental parameter sensors (temperature, humidity, and pressure sensors) in the testing system monitor the cabin environment in real time, providing feedback signals for the closed-loop control of the environmental chamber control system. Simultaneously, changes in engine performance parameters (such as intake air temperature, exhaust air temperature, and cylinder pressure) can indirectly reflect the effectiveness and deviation of environmental parameter control, assisting the control system in making fine-tuning adjustments. Technical means one creates the test environment, while technical means three senses the environment and performance status through a sensor network and feeds this information back to the control system of technical means one, forming a complete closed loop of "control-perception-re-control".

[0049] In summary, the three key technologies are not simply superimposed, but rather organically coordinated through a closed-loop link of "environmental protection → operational condition execution → parameter acquisition → environmental feedback," which together achieve high efficiency, accuracy, and reliability in full-load external characteristic testing under high-altitude conditions.

[0050] The beneficial effects of this invention are as follows:

[0051] 1. Precise Simulation and Scientific Control of Environmental Parameters: Utilizing the temperature, humidity, and pressure simulation functions of the high-altitude environment chamber, and combining a scientific control sequence of "pressure first, then temperature, then humidity," the system precisely simulates environmental conditions at different altitudes. This overcomes the limitation of traditional ground-based bench tests, which cannot simulate high-altitude environments, making the full-load test environment closer to the actual high-altitude operating conditions of the engine. This control sequence is based on the physical principles of the ideal gas law and the Clausius-Clapeyron equation, effectively avoiding cross-coupling interference between pressure, temperature, and humidity, and achieving rapid convergence and precise stabilization of various environmental parameters.

[0052] 2. Precise Control and Stable Maintenance under Full Load: This invention closely adheres to the core definition of the external characteristics of aero-piston engines (full load performance evaluation). By adding features such as real-time throttle opening monitoring and full-load fuel supply stabilization, it achieves precise control and stable maintenance under full load conditions, ensuring that the test data accurately reflects the engine's high-altitude performance under full load. The full load threshold is set at 98%, fully considering practical engineering factors such as sensor measurement errors, mechanical tolerances, and operational fluctuations, balancing test accuracy and engineering feasibility.

[0053] 3. Direct acquisition of performance parameters, improving efficiency and accuracy: This invention constructs a test system that integrates power and economic performance testing functions. It is equipped with high-precision dedicated sensors and supporting equipment for torque, power, fuel flow, etc. The torque sensor can directly measure the torque value, the power can be directly calculated by simply multiplying the torque and the speed, and the fuel flow sensor can directly measure the fuel consumption per unit time. The above core parameters do not need to be inferred from indirect means such as intake volume and exhaust composition analysis, which greatly improves the efficiency and accuracy of test data acquisition.

[0054] 4. Synergistic Technical Effects: The three key technical means work together organically through a closed-loop link of "environmental assurance → operational condition execution → parameter acquisition → environmental feedback," producing comprehensive technical effects that cannot be achieved by any single feature. Specifically: Feature 1 provides stable and repeatable environmental boundary conditions for Feature 2; Feature 2 provides an effective prerequisite for full-load data acquisition for Feature 3; Feature 3 uses a sensor network to perceive the environmental and performance status in real time and feeds the perceived information back to the control system of Feature 1 and the operational condition maintenance system of Feature 2, forming a complete closed-loop control. The synergistic effect of the three enables the entire test system to automatically adapt, execute accurately, and acquire data efficiently in different high-altitude environments, significantly improving the automation level, data consistency, and result reliability of the test—a technical effect that no single technical means could achieve alone.

[0055] 5. High efficiency and economy in testing: Compared with traditional high-altitude flight testing, this invention does not require the use of a test aircraft, which greatly reduces testing costs and shortens the testing cycle. Moreover, it is not limited by external factors such as weather conditions and airspace control under full load conditions, and can flexibly set test parameters according to needs, thus improving the flexibility and efficiency of testing. Attached Figure Description

[0056] Figure 1 This is a flowchart of the test method for the external characteristics of an aircraft piston engine based on a high-altitude environmental chamber, as described in this invention.

[0057] Figure 2 This is a flowchart for drawing the engine's full-load external characteristic curve in step S6. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to specific embodiments.

[0059] This embodiment uses a certain type of aircraft piston engine as the test object and conducts a full-load external characteristic test using a high-altitude environment chamber with temperature, humidity and pressure simulation functions.

[0060] The aviation piston engine external characteristic test system based on a high-altitude environmental chamber used in this embodiment mainly consists of the following subsystems: a high-altitude environmental chamber and its temperature, humidity, and pressure control subsystem; a bench dynamometer subsystem (an electric dynamometer is used in this embodiment); a fuel supply subsystem (including a high-precision fuel metering pump and a full-load pressure regulating valve); an integrated power and economic performance testing subsystem (including an environmental parameter sensor group, a throttle opening sensor, a torque sensor, a fuel flow sensor, and a matching data acquisition instrument); and a central control unit (an industrial computer and matching control software). Each subsystem is connected to the central control unit via fieldbus communication, and the central control unit performs centralized scheduling and coordinated control, forming a complete closed-loop test system of "environmental control—operating condition execution—parameter acquisition—data feedback".

[0061] like Figure 1 As shown, the specific experimental method is as follows:

[0062] 1. Experimental preparation:

[0063] 1.1 Device Connection:

[0064] The aircraft piston engine to be tested was installed and fixed on the electric dynamometer test bench inside the high-altitude environmental chamber. The engine was connected to the hydraulic dynamometer to ensure that the dynamometer could work with the engine control system to maintain stable operation under full load. The fuel supply system was connected, using a high-precision fuel metering pump and a full-load pressure regulating valve. The full-load fuel supply pressure was set to 0.3 MPa, with a fluctuation allowable value of ≤ ±0.05 MPa. The forced air cooling system was connected, and the engine cylinder temperature control range was set to 80-100℃ during full-load operation. The engine intake manifold was connected to the gas circulation system of the environmental chamber through a pipe with a flow regulating valve. The exhaust pipe was extended to the outside of the chamber and a pressure regulating valve was installed. The pressure regulating valve was linked with the environmental chamber pressure control system to ensure that the exhaust back pressure was stable within the design allowable range (≤5 kPa).

[0065] 1.2 Test System Construction:

[0066] Three temperature sensors, two humidity sensors, and two pressure sensors are evenly distributed within the high-altitude environment chamber. An intake air temperature sensor is placed at the engine intake manifold outlet, an exhaust air temperature sensor at the exhaust manifold, a cylinder pressure sensor on the cylinder head of cylinder #1, a high-precision fuel flow sensor (measurement accuracy ±0.3%) on the fuel supply pipeline, a throttle opening sensor (measurement accuracy ±0.5%) on the throttle shaft, and a high-precision torque sensor (measurement accuracy ±0.5%) at the connection between the engine output shaft and the dynamometer. All sensors and their associated data acquisition and processing equipment are connected to a computer via a data acquisition instrument, with the data acquisition frequency set to 1kHz. The completed integrated power and economic performance testing system can directly acquire target values ​​for core performance parameters such as torque, power, and fuel flow—torque is directly measured by a torque sensor, power is directly calculated from the product of torque and engine speed, and fuel flow is directly measured by a fuel flow sensor.

[0067] 1.3 System debugging and pre-checks:

[0068] The high-altitude environmental chamber control system was debugged, with temperature control range of -60℃ to 60℃ (accuracy ±1℃), humidity control range of 10%RH to 90%RH (accuracy ±5%RH), and pressure control range of 20kPa to 101kPa (corresponding to altitude of 0m to 12000m, accuracy ±2kPa). The electric dynamometer was debugged, with speed adjustment range covering engine idle speed (800r / min) to maximum rated speed (3600r / min), adjustment accuracy ±10r / min. The integrated power and economic performance testing system was debugged, and parameter pre-acquisition was performed to confirm accurate acquisition of target values ​​for core performance parameters such as torque, power, and fuel flow. The data acquisition system was started and sensor calibration was completed. The engine electronic control system was debugged, full-load control parameters were set and pre-tested to confirm stable maintenance under full load. A pre-start check of the engine was performed to ensure reliable connections in the oil circuit, air circuit, and electrical circuit, and to prevent leaks, short circuits, and other faults. At the same time, the scheduling program of the central control unit was tested to confirm that it could sequentially call the environmental chamber control commands, dynamometer speed commands and data acquisition system trigger commands according to the set process, so as to realize the fully automated test process.

[0069] Verification data for full-load fuel pressure stabilization supply parameters:

[0070] To verify the rationality of the full-load fuel pressure regulation parameters (supply pressure 0.3MPa, allowable fluctuation ≤ ±0.05MPa), a specific verification test on the impact of fuel supply pressure fluctuation on full-load torque output was conducted before the formal test. The test was conducted at an altitude of 0m and an ambient temperature of 15℃. A typical engine speed of 2400 r / min was selected, and fuel supply pressure fluctuation ranges were set to ±0.02MPa, ±0.05MPa, ±0.08MPa, and ±0.10MPa. Full-load torque values ​​were measured five times under each fluctuation range. The test results showed that when the fuel pressure fluctuation was ≤ ±0.05MPa, the relative standard deviation (RSD) of the full-load torque measurement was 0.8%, and the torque fluctuation amplitude was ≤ 1.2%. When the fuel pressure fluctuation increased to ±0.08MPa, the torque RSD rose to 2.5%, and the fluctuation amplitude reached 3.8%. When the fluctuation increased to ±0.10MPa, the torque RSD further increased to 4.2%, and the fluctuation amplitude reached 6.1%. The above data shows that controlling fuel supply pressure fluctuations within ±0.05 MPa can control full-load torque output fluctuations within 1.5%, effectively ensuring the stability of full-load operating conditions and the repeatability of external characteristic data. Therefore, setting the allowable value for full-load fuel supply pressure fluctuations to ≤±0.05 MPa in this embodiment is reasonable and necessary.

[0071] 2. Test condition settings:

[0072] The altitudes to be simulated are set to 0m (ground level), 2000m, 4000m, 6000m, 8000m, and 10000m. The corresponding target values ​​of environmental parameters are determined with reference to the standard atmospheric model. The specific parameters are shown in Table 1 below.

[0073] Table 1 Target values ​​of environmental parameters at different altitudes

[0074]

[0075] The engine's full-load speed range is set to 800 r / min (idle) to 3600 r / min (maximum rated speed), with a speed gradient of 100 r / min. The target speeds are 800 r / min, 1000 r / min, ..., 3600 r / min. The full-load control standard is ≥98% of the maximum design torque at each speed.

[0076] 3. Environmental chamber parameter control:

[0077] First, the environmental parameters at an altitude of 0m were adjusted: the environmental chamber pressure control system was activated to adjust the chamber pressure to 101.3kPa. After the pressure stabilized (fluctuation ≤ ±2kPa), the temperature control system was activated to adjust the chamber temperature to 15℃. After the temperature stabilized (fluctuation ≤ ±1℃), the humidity control system was activated to adjust the chamber humidity to 60%RH. After the humidity stabilized (fluctuation ≤ ±5%RH), the environmental parameters were maintained stable for 5 minutes.

[0078] Comparative experimental data of different regulatory sequences:

[0079] To verify the superiority of the "pressure first, then temperature, then humidity" control sequence, comparative experiments were conducted using three different control sequences under the same target environmental parameters (0m altitude: pressure 101.3kPa, temperature 15℃, humidity 60%RH). The total time required for the three environmental parameters to stabilize and the fluctuation range of the parameters after stabilization were recorded for each sequence. Each sequence was repeated 3 times. The results are shown in Table 2 below:

[0080] Table 2 Comparison of the effects of environmental parameter regulation in different regulation sequences

[0081]

[0082] Comparative data shows that using the sequence of "pressure first, then temperature, then humidity" results in the shortest average stabilization time for environmental parameters (18 minutes), and the fluctuation amplitude of each parameter after stabilization is minimal. When using the sequence of "temperature first, then pressure, then humidity," changes in gas density during pressure control cause significant drift in the already stabilized temperature field (temperature fluctuations of ±1.8℃), requiring repeated adjustments to converge, extending the total stabilization time to 32 minutes. When using the sequence of "humidity first, then temperature, then pressure," temperature changes alter the saturated water vapor partial pressure, causing significant fluctuations in the already stabilized relative humidity (humidity fluctuations of ±6.1%RH), and pressure control further interferes with the temperature and humidity fields, resulting in a total stabilization time as long as 41 minutes. These comparative data fully verify the significant advantages of the control sequence adopted in this invention in terms of convergence speed and steady-state accuracy.

[0083] Start the aircraft piston engine and allow it to idle for 3 minutes after warming up to confirm stable engine operation. Then, switch to full-load mode via the engine electronic control system and monitor the torque sensor data to confirm that the value reaches more than 98% of the maximum design value. Adjust the engine speed using an electric dynamometer, increasing it at a rate of 20 rpm / s to 1000 rpm (the first target speed), and maintain stable full-load operation for 2 minutes. During this period, directly acquire target values ​​for power performance parameters such as speed, torque, and power, as well as basic economic performance parameters such as fuel flow rate, through the integrated power and economic performance testing system. The system simultaneously collects target values ​​for intake air temperature, exhaust air temperature, cylinder pressure, throttle opening, and ambient temperature, humidity, and pressure data within the test chamber for 30 seconds. During this process, the throttle opening and the operating status of the test system are continuously monitored. If the actual value is lower than 98% of the maximum value or if abnormal test data is detected, immediate correction or shutdown for inspection is initiated. After completing data collection at 1000 r / min full load, the speed is adjusted at the same rate to the next target speed, repeating the stable operation and data collection steps until data collection at 3600 r / min full load is completed. Throughout the entire speed adjustment and data collection process, the central control unit automatically records all process data and monitors the operating status of each subsystem in real time to ensure the safety and data integrity of the test process.

[0084] 5. Multi-condition test cycle:

[0085] After completing all full-load speed condition tests at 0m altitude, the engine speed was reduced to 800 rpm (idle). Then, following the order of "pressure first, then temperature, then humidity," the environmental chamber parameters were adjusted to the target values ​​corresponding to 2000m altitude (pressure 79.5 kPa, temperature 1℃, humidity 50%RH). After the environmental parameters stabilized, the engine was switched back to full-load mode, and the speed adjustment and data acquisition operations in step 4 were repeated. All full-load speed condition tests at altitudes of 4000m, 6000m, 8000m, and 10000m were completed sequentially. During the switching of each operating condition, the central control unit automatically executed the switching operation according to the preset logic sequence of "stop / idle - adjust environment - restart / restore full load," avoiding data anomalies caused by improper timing of manual operation.

[0086] Verification instructions for the multi-condition switching operation sequence:

[0087] To verify the necessity of the multi-condition switching operation sequence of "first reduce idle speed, then adjust the environment, and finally restore full load," a comparative verification experiment was conducted when switching target altitudes. After completing full-load data acquisition at an altitude of 4000m, three different switching operation sequences were used to switch to an altitude of 6000m:

[0088] Sequence A (Solution of the present invention): First, remove the engine from full load and reduce it to idle speed → adjust the environmental chamber parameters to the new target value → after the environmental parameters stabilize, switch back to full load and adjust the speed.

[0089] Sequence B: Adjust the environmental chamber parameters directly under full load without reducing idle speed → Continue collecting data after the environmental parameters stabilize.

[0090] Sequence C: First, adjust the environmental chamber parameters to the new target value → After the environmental parameters stabilize, switch the engine to full load (without idling transition).

[0091] The test results show that: when using sequence B, the engine was still operating at full load and high power during the environmental parameter adjustment process. Rapid changes in cabin pressure caused fluctuations in intake air density, resulting in severe oscillations in engine torque output (instantaneous fluctuations of ±8%). Furthermore, the exhaust back pressure experienced impacts due to changes in cabin pressure, leading to engine stalling in both tests. When using sequence C, although the environmental parameters stabilized first, the engine directly switched from a stopped state to full load operation. Due to the significant difference between the low-temperature, low-oxygen environment inside the cabin and ground conditions, starting the engine was difficult and idling was unstable, requiring an average of three attempts to successfully switch to full load. When using sequence A (the scheme of this invention), the engine's sensitivity to environmental parameter changes was significantly lower in idling conditions than in full load conditions. The engine ran smoothly during environmental parameter adjustment, and after the environment stabilized, it smoothly transitioned from idling to full load without stalling or abnormal oscillations, achieving a 100% success rate. The above comparisons and verifications fully demonstrate the effectiveness of the multi-condition switching operation sequence adopted in this invention in ensuring experimental safety and data continuity.

[0092] 6. Full-load external characteristic data processing and curve plotting:

[0093] 6.1 Data Preprocessing and Validation:

[0094] Valid data segments with torque values ​​≥ 98% of the maximum design value were selected, and outliers were removed using the 3σ criterion. The average value of the valid data was then calculated.

[0095] Detailed steps for applying the 3σ criterion:

[0096] The specific steps for applying the 3σ criterion (also known as the Raida criterion) are as follows:

[0097] The first step is to calculate the arithmetic mean μ and sample standard deviation σ of each measured parameter (torque, power, fuel flow, etc.) for each target speed and target altitude full-load effective data segment. The calculation formula is as follows:

[0098]

[0099] Where n is the number of data points in the data segment, and xᵢ is the measurement value of the i-th data point.

[0100] The second step is to determine the threshold range for outlier data based on the 3σ criterion: the residuals of normal data should satisfy... That is, the data points should fall within the interval [μ-3σ, μ+3σ].

[0101] The third step is to examine each data point in the data segment in turn. If the absolute value of the residual of a data point is greater than 3σ, then the data point is determined to be outlier (gross error) and is removed.

[0102] The fourth step is to remove all outlier data points and then recalculate the arithmetic mean and standard deviation of the remaining valid data points as the final statistical results of each parameter under this operating condition.

[0103] The fifth step is to record the number of abnormal data points that are removed under each working condition. If the proportion of abnormal data under a certain working condition exceeds 5%, it is determined that the overall quality of the test data under that working condition is poor, and the status of the test system needs to be checked and the test under that working condition needs to be repeated.

[0104] In this embodiment, the aforementioned 3σ criterion was applied to remove outlier data for each target rotational speed and target altitude (collection time 30s, collection frequency 1kHz, totaling 30,000 data points). Actual processing results show that the percentage of outlier data points removed under each operating condition is typically between 0.5% and 1.2%, mainly due to occasional sensor noise spikes and transient electromagnetic interference. After removal, the data quality is significantly improved, with the relative standard deviation (RSD) of torque measurements decreasing from 1.5%-2.5% before removal to 0.6%-0.9% after removal.

[0105] 6.2 Parameter Calculation:

[0106] Based on the target values ​​of parameters such as torque and fuel flow directly obtained from the testing system, calculate the power and full-load fuel consumption rate under various operating conditions.

[0107] 6.3 Curve Plotting:

[0108] Plotting engine speed on the x-axis and power, torque, and fuel consumption rate on the y-axis, according to... Figure 2 The process shown uses Origin software to plot the engine's full-load external characteristic curves at various altitudes, obtaining complete external characteristic data of this type of aero-piston engine under full load in different high-altitude environments.

[0109] The above embodiments are one of the implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for testing the external characteristics of an aircraft piston engine based on a high-altitude environmental chamber, characterized in that, The high-altitude environment chamber has precise simulation capabilities for temperature, humidity, and pressure, and can simulate environmental parameters at different altitudes. This method focuses on the full-load operating conditions of the engine and includes the following steps: S1. Test Preparation: Fix the aircraft piston engine to be tested on the test bench in the high-altitude environmental chamber, and complete the connection between the engine and the dynamometer system, fuel supply system, cooling system, intake system and exhaust system; set up environmental parameter sensors and engine performance parameter sensors and connect them to the data acquisition system; debug each system and perform a pre-start check on the engine; S2. Test Condition Setting: Determine the multiple altitudes to be simulated and the corresponding target values ​​of environmental parameters, and set several targets under the full load condition of the engine; S3. Environmental Chamber Parameter Control: Activate the high-altitude environmental chamber control system to coordinate and control the temperature, humidity, and pressure inside the chamber until they stabilize within the target range and are maintained for a preset time; the coordinated control adopts the order of first adjusting the pressure, then adjusting the temperature, and finally adjusting the humidity. S4. Engine full-load condition control and data acquisition: After the engine is started and warmed up and the idle speed is stable, the speed is adjusted according to the set speed gradient, and the engine is operated stably under full-load conditions at each target speed and data is collected. S5. Multi-condition test cycle: Change the simulated altitude in sequence, repeat steps S3 and S4, and complete the environmental parameter adjustment and multi-speed full-load condition data acquisition for all target altitudes. S6. External characteristic data processing and curve plotting: Preprocess the collected data, calculate the power and fuel consumption rate, and plot the full-load external characteristic curves corresponding to each altitude.

2. The test method according to claim 1, characterized in that, In step S1, a test system integrating power performance and economic performance testing functions is constructed. This test system includes sensors for testing power performance and economic performance, as well as related data acquisition and processing equipment, specifically including a throttle opening sensor, a torque sensor, and a fuel flow sensor. The throttle opening sensor is used to monitor and confirm that the engine is under full load in real time. The torque sensor and fuel flow sensor, together with the related test equipment, can directly or indirectly obtain the target values ​​of power performance parameters and the target values ​​of basic economic performance parameters. The sensors in the testing system have high precision characteristics, and the torque measurement accuracy and fuel flow measurement accuracy are within the preset range.

3. The test method according to claim 1, characterized in that, The full-load condition refers to the maximum design torque reached by the engine at each target speed or the maximum torque achievable under test conditions; the target speed range covers the engine idle speed to the maximum rated speed.

4. The test method according to claim 1, characterized in that, In step S3, the coordinated regulation of environmental parameters is used to effectively avoid cross-coupling interference between parameters after the regulation has stabilized, so as to achieve rapid convergence and precise stabilization of each environmental parameter.

5. The test method according to claim 1, characterized in that, In step S4, the engine speed adjustment rate does not exceed the preset value, the stable operating time under full load at each target speed is within the preset range, the data acquisition duration is not less than the preset value, and the acquisition frequency is not less than the preset value; and the load status is continuously monitored during the speed adjustment process to ensure that the full load status is not interrupted and to correct it in time when it deviates from the full load.

6. The test method according to claim 1, characterized in that, In step S5, when switching the simulated target altitude, first remove the engine from full load and reduce it to idle speed, then adjust the environmental cabin parameters to the new target value, and after stabilization, adjust the speed and load to full load.

7. The test method according to any one of claims 1 to 6, characterized in that, In step S6, data preprocessing includes screening full-load valid data segments, using the 3σ criterion to remove outlier data, and then performing average statistics on the valid data.

8. The test method according to claim 7, characterized in that, It also includes a full load validity verification step: if the average load under a certain speed condition does not reach the preset threshold, it is determined to be invalid data and the test is repeated.

9. A test system for the external characteristics of an aircraft piston engine based on a high-altitude environmental chamber, characterized in that, include: The high-altitude environment chamber is equipped with precise simulation functions for temperature, humidity and pressure, and is used to provide environmental simulation spaces at different altitudes. The bench dynamometer system, set up inside the high-altitude environmental chamber, is used to fix the aircraft piston engine to be tested and adjust its output shaft speed, working in conjunction with the engine control system to maintain stable operation under full load conditions. A fuel supply system connected to the engine; An integrated power and economic performance testing system is installed in the high-altitude environmental chamber and key parts of the engine. It includes environmental parameter sensors, throttle opening sensors, torque sensors and fuel flow sensors, which are used to monitor environmental parameters and engine performance parameters in real time. The torque sensor directly measures the engine torque and the fuel flow sensor directly measures the fuel flow. The data acquisition and processing system is connected to the integrated power and economic performance testing system and various sensors, and is used to collect test data, perform data preprocessing, validity verification, parameter calculation and external characteristic curve plotting. The central control unit is connected to the high-altitude environmental chamber, the bench dynamometer system, the fuel supply system, the integrated power and economic performance testing system, and the data acquisition and processing system, respectively. The central control unit is configured to perform a test method for the external characteristics of an aero-engine based on a high-altitude environmental chamber as described in any one of claims 1 to 7.

10. The system according to claim 9, characterized in that: The fuel supply system has a full-load pressure stabilization function, which is used to provide sufficient and stable fuel with pressure fluctuations within a preset range under full-load conditions. The dynamometer test system uses an electric dynamometer.

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