Method for measuring the ventilation performance of two-stroke aviation piston engines using the tracer gas method

Abstract

The present invention discloses a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method. The method comprises the following steps: determining whether the engine operates stably during a period of time while the tracer gas is injected; if the engine operates stably, then after the tracer gas is injected for a period of time, causing a collection and analysis system to simultaneously collect intake air mixture in the intake manifold and exhaust air mixture in the exhaust manifold to obtain data of the intake and exhaust mixtures; calculating ventilation performance parameters using the obtained intake and exhaust mixture data; and after data collection under specific operating conditions is completed, stopping the tracer gas injection and determining whether the engine continues to operate stably during the period of time after the tracer gas injection is stopped. If the engine continues to operate stably, the collected data under the specific operating conditions is valid; otherwise, the collected data is invalid, and the test is stopped. The present invention has higher measurement accuracy and a more standardized process.

Description

Technical Field

[0001] The invention relates to the technical field of two-stroke aviation piston engines, in particular to a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method. Background Art

[0002] Two-stroke aviation piston engines are widely used power plants in general aviation aircraft and unmanned aerial vehicles (UAVs). They offer advantages such as high power per unit weight, high power-to-weight ratio, smooth torque variation, and good uniformity. Their ventilation process refers to the entire process by which fresh charge replaces the exhaust gas in the cylinder, starting from the moment the exhaust valve opens (for exhaust valve systems) or the exhaust port opens (for piston-controlled port systems) and ending when both the intake and exhaust ports (doors) close. Ventilation performance determines the extent of exhaust gas scavenging in two-stroke aviation piston engines and the amount of fresh charge remaining in the cylinder for combustion, thus significantly impacting engine power, fuel economy, and emissions. Therefore, accurate experimental methods for measuring the ventilation performance of two-stroke aviation piston engines are of great significance.

[0003] The tracer gas method is one of the main methods for measuring the ventilation performance of two-stroke engines. Figure 4 As shown in the figure, the principle of the tracer gas method is to continuously inject a small amount of tracer gas into the intake duct of a two-stroke engine to fully mix it with the intake air. The tracer gas trapped in the cylinder of the two-stroke engine is completely burned during the combustion process, and the tracer gas that has short-circuited the ventilation flows out with the exhaust. By measuring the concentration of tracer gas in the intake and exhaust air and the intake volume of the engine, the ventilation performance parameters such as the air supply ratio, capture rate and charging efficiency are calculated.

[0004] The tracer gas method requires no modification to two-stroke engines and is widely used in studies of breathing performance measurements. Commonly used tracer gases include methylamine, N₂O₂, butane, acetone, and methane (selected based on the specific characteristics of the engine), depending on the specific conditions of the two-stroke engine, such as in-cylinder combustion and exhaust temperatures. The tracer gas method is simple and offers excellent accuracy, making it widely used in measuring breathing performance in two-stroke engines, such as those used in automotive and marine applications. However, the tracer gas method currently has several limitations when applied to two-stroke aviation piston engines: a lack of standardized experimental methods to improve measurement accuracy. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one object of the present invention is to provide a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method, which has higher measurement accuracy and more standardized process.

[0006] A method for measuring the ventilation performance of a two-stroke aircraft piston engine using a tracer gas method according to an embodiment of the present invention is applied to a test device for measuring the ventilation performance of a two-stroke aircraft piston engine. The test device comprises an engine, an injection system, an intake system, a collection and analysis system, an intake manifold, and an exhaust manifold. The injection system is used to inject tracer gas into the intake system. The intake manifold is connected between the intake system and the engine. The exhaust manifold is connected to the engine. The collection and analysis system is connected to the intake manifold and the exhaust manifold, respectively.

[0007] The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method comprises the following steps:

[0008] S1: starting the engine to a specific operating condition;

[0009] S2: determining whether the engine has been operating stably for a period of time. If the engine has been operating stably for a period of time, after the engine has been operating stably for a period of time, causing the injection system to begin stably injecting tracer gas into the intake system to mix with fresh charge in the intake system to form an intake mixture, and the intake mixture enters the engine through the intake manifold.

[0010] S3: determining whether the engine operates stably during the period of time during which the tracer gas is injected. If the engine operates stably, after the tracer gas is injected for a period of time, causing the acquisition and analysis system to simultaneously acquire intake air mixture in the intake manifold and exhaust air mixture in the exhaust manifold to obtain data of the intake air mixture and the exhaust air mixture; and calculating the ventilation performance parameter using the acquired data of the intake air mixture and the exhaust air mixture;

[0011] S4: After the data collection under the specific working condition is completed, the tracer gas injection is stopped, and it is determined whether the engine continues to operate stably for a period of time after the tracer gas injection is stopped. If the engine continues to operate stably, the collected data under the specific working condition is valid; otherwise, it is invalid, and the test is stopped.

[0012] According to an embodiment of the present invention, a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method determines whether the engine is operating stably during a period of time when the tracer gas is injected and a period of time when the tracer gas injection is stopped. If the engine maintains a stable operating state, i.e., the injection and cessation of the tracer gas injection have no effect on the engine's operating state, the measurement experiment is performed without affecting the engine's operating state. As a result, the engine's ventilation process parameters obtained from the measurement experiment are almost identical to those obtained without the tracer gas injection, thereby improving the accuracy of the experimental results and standardizing the measurement experiment process.

[0013] According to some embodiments of the present invention, in step S2, determining whether the engine has been operating stably for a period of time further includes the following sub-steps:

[0014] If the engine does not operate stably, the engine is debugged until the engine operates stably for a period of time under the specific operating conditions, and then the injection of tracer gas is restarted.

[0015] According to some embodiments of the present invention, in step S3, determining whether the engine operates stably during the period of time during which the tracer gas is injected further includes the following sub-steps: if the engine does not operate stably, stopping the tracer gas injection, then sequentially debugging the engine and the two-stroke aviation piston engine ventilation performance test device until the engine operates stably for a period of time under the specific operating conditions, then resuming the tracer gas injection, and repeating step S3.

[0016] According to some embodiments of the present invention, determining whether the engine is operating stably in step S2, step S3, and step S4 specifically includes determining whether operating parameters of the engine have changed.

[0017] According to some embodiments of the present invention, the following steps are further included:

[0018] S5: If it is determined in step S4 that the collected data under the specific working condition is valid, the collection and analysis system is purged until the tracer gas concentration in the collection and analysis system returns to zero;

[0019] S6: then adjusting the engine to the next specific operating condition, repeating steps S2, S3 and S4 to complete the test under the next specific operating condition;

[0020] Steps S5, S6, S2, S3 and S4 are repeated in sequence until the last test under the specific working condition is completed.

[0021] According to some embodiments of the present invention, the method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method further includes the following steps: separately collecting the intake mixture and the exhaust mixture discharged by the acquisition and analysis system to perform static concentration analysis on the intake mixture and the exhaust mixture, respectively.

[0022] According to some embodiments of the present invention, in step S3, the calculation of the engine ventilation performance parameters using the obtained intake mixture and exhaust mixture data specifically includes the following sub-steps:

[0023] S301: Input a set of obtained test data and data of intake mixture and exhaust mixture;

[0024] S302: Calculating a relative deviation between the actual tracer gas concentration in the intake mixture and the theoretical tracer gas concentration when the tracer gas is completely mixed with the fresh charge;

[0025] S303: Determine whether the relative deviation is less than or equal to 3%. If so, further determine whether the maximum combustion temperature in the cylinder of the engine is greater than or equal to 600°C and there is no misfire. If so, further determine whether the exhaust temperature in the exhaust manifold is less than or equal to 500°C and there is no afterburning. If so, calculate the ventilation performance parameters.

[0026] According to some embodiments of the present invention, the determination of whether the relative deviation is less than or equal to 3% in step S303 further includes the following sub-steps: if the relative deviation is greater than 3%, the set of test data and the data of the intake mixture and the exhaust mixture are invalid.

[0027] According to some embodiments of the present invention, the step S303 of determining whether the maximum combustion temperature in the cylinder of the engine is greater than or equal to 600°C and there is no misfire further includes the following sub-steps: if the maximum combustion temperature in the cylinder is less than 600°C and there is misfire, calculating the in-cylinder reaction rate and misfire coefficient, and then further determining whether the exhaust temperature in the exhaust manifold is less than or equal to 500°C and there is no afterburning.

[0028] According to some embodiments of the present invention, the step S303 of determining whether the exhaust temperature in the exhaust manifold is less than or equal to 500°C and there is no afterburning further includes the following sub-steps: if the exhaust temperature in the exhaust manifold is greater than 500°C and afterburning occurs, calculating the exhaust reaction rate

[0029] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0031] Figure 1 This is a flowchart of a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to an embodiment of the present invention.

[0032] Figure 2 The figure is a schematic diagram of the structure of the test device for measuring the ventilation performance of a two-stroke aviation piston engine in the present invention.

[0033] Figure 3 This is a flowchart for calculating parameters of engine ventilation performance in an embodiment of the present invention.

[0034] Figure 4 Schematic diagram of the principle of the tracer gas method.

[0035] Reference numerals:

[0036] Test device 1000 for measuring the ventilation performance of two-stroke aviation piston engines

[0037] Engine 1

[0038] Injection system 2

[0039] Gas cylinder 201 Switch valve 202 Filter 203 Flow control valve 204

[0040] Tracer gas micro flow meter 205

[0041] Intake system 3

[0042] Pressure stabilizing mixing chamber 301 Air filter 302 Mechanical supercharging system 303 Intake air flow meter 304

[0043] Acquisition and analysis system 4

[0044] Gas analyzer 401 First sampling probe 402 First mixed gas filter 403

[0045] First vacuum pump 404 Second sampling probe 405 Condenser 406 Steam-water separator 407

[0046] Second mixed gas filter 408 Second air pump 409 Gas sampling bag 410

[0047] Intake manifold 5 First temperature sensor 501 First pressure sensor 502

[0048] Exhaust manifold 6 Second temperature sensor 601 Second pressure sensor 602

[0049] Dynamometer 7 Fresh charge A DETAILED DESCRIPTION

[0050] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0051] The following combination Figures 1 to 3 The method of measuring the ventilation performance of a two-stroke aviation piston engine using the tracer gas method of the present invention is described below.

[0052] like Figure 1 and Figure 2 As shown, the method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to an embodiment of the present invention is applied in a test device 1000 for measuring the ventilation performance of a two-stroke aviation piston engine. The test device 1000 for measuring the ventilation performance of a two-stroke aviation piston engine includes an engine 1, an injection system 2, an intake system 3, an acquisition and analysis system 4, an intake manifold 5, and an exhaust manifold 6.

[0053] Specifically, the engine 1 in the test device 1000 for measuring the ventilation performance of a two-stroke aviation piston engine of the present invention is a two-stroke aviation piston engine. The injection system 2 is used to inject tracer gas into the intake system 3. Figure 2 As shown, the injection system 2 includes a gas cylinder 201, an on-off valve 202, a filter 203, a flow control valve 204, and a tracer gas micro-flowmeter 205, which are sequentially connected via pipelines. The gas cylinder 201 is used to store tracer gas and has leak detection and alarm functions. The on-off valve 202 has a pressure-reducing function, allowing the gas cylinder 201 to output tracer gas at a specific pressure. The filter 203 is used to filter the tracer gas output from the gas cylinder 201 to prevent impurities from entering the output tracer gas. The flow control valve 204 and the tracer gas micro-flowmeter 205 are respectively used to control and monitor the flow rate of the tracer gas, ensuring that the concentration of the tracer gas after mixing with the fresh charge A is within the required range. It should be noted that all components in the injection system 2 can well meet the explosion-proof and anti-leakage safety requirements of two-stroke aviation piston engines, thereby improving the safety of the measurement experiment process.

[0054] The intake system 3 includes a pressure-stabilizing mixing chamber 301, to which the injection system 2 is connected. The pressure-stabilizing mixing chamber 301 stabilizes the intake pressure of the engine 1, ensures that the tracer gas is injected into the intake system 3 at a uniform rate, and ensures that the tracer gas and the fresh charge A are thoroughly and evenly mixed. The design of the pressure-stabilizing mixing chamber 301 eliminates the need for a long intake line for uniformly mixing the tracer gas and the fresh charge A, thereby simplifying the intake system 3. While ensuring safety, using the intake system 3 can make the intake state of the engine 1 closer to the actual intake state of the engine 1. Specifically, for a two-stroke aircraft piston engine with a displacement of 0.5L, the volume of the pressure-stabilizing mixing chamber 301 is greater than or equal to 0.8L, which effectively meets the requirement for uniform mixing.

[0055] The intake manifold 5 is connected between the intake system 3 and the engine 1. It can be understood that the intake mixture after the tracer gas and the fresh charge A are mixed in the pressure-stabilizing mixing chamber 301 enters the engine 1 from the intake manifold 5. The exhaust manifold 6 is connected to the engine 1. It can be understood that the exhaust mixture exhausted from the engine 1 is exhausted from the exhaust manifold 6. The collection and analysis system 4 is respectively connected to the intake manifold 5 and the exhaust manifold 6 to respectively collect and analyze the volume concentration of the tracer gas of the intake mixture in the intake manifold 5 and the volume concentration of the tracer gas of the exhaust mixture in the exhaust manifold 6 in real time.

[0056] Specifically, the collection and analysis system 4 includes a gas analyzer 401 and a first collection branch and a second collection branch connected to the gas analyzer 401. The gas analyzer 401 is used to analyze the volume concentration of the gas entering the gas analyzer 401. The first collection branch includes a first sampling probe 402, a first mixed gas filter 403 and a first air pump 404 connected in sequence. The first air pump 404 is connected to the sampling port of a detection path of the gas analyzer 401. The first sampling probe 402 is installed in the intake manifold 5 for collecting the intake mixture in the intake manifold 5. The first mixed gas filter 403 is used to filter impurities in the extracted intake mixture. The first air pump 404 is used to extract the intake mixture in the intake manifold 5.

[0057] The second collection branch includes a second sampling probe 405, a condenser 406, a steam-water separator 407, a second mixed gas filter 408 and a second air pump 409 connected in sequence. The second sampling probe 405 is installed in the exhaust manifold 6 and is used to collect the exhaust mixed gas in the exhaust manifold 6. The condenser 406 is used to cool the collected exhaust mixed gas to below the allowable temperature of the gas analyzer 401. The steam-water separator 407 is used to remove some oil and water vapor in the exhaust mixed gas. The second mixed gas filter 408 is used to filter impurities in the extracted exhaust mixed gas. The second air pump 409 is connected to the sampling port of another detection path of the gas analyzer 401. The second air pump 409 is used to extract the exhaust mixed gas. It should be noted that the flow rates of the first air pump 404 and the second air pump 409 are adjustable. According to the intake pressure and exhaust pressure of the engine 1 under different working conditions, the flow rates of the intake mixture and the exhaust mixture entering the gas analyzer 401 can be kept consistent by adjusting the flow rates of the first air pump 404 and the second air pump 409.

[0058] In addition, the test device 1000 for measuring the ventilation performance of a two-stroke aviation piston engine also includes a dynamometer element 7, and the intake system 3 also includes an air filter 302, a mechanical supercharger system 303 and an intake flowmeter 304 connected in sequence through pipelines, wherein the dynamometer element 7 is used to measure parameters such as the speed, torque, and power of the engine 1, the air filter 302 is used to filter impurities in the fresh charge A, and the mechanical supercharger system 303 is used to adjust the intake pressure of the engine 1. For example, the mechanical supercharger system 303 is a positive displacement Roots pump driven and controlled by an electric motor with a maximum speed of 3000 r / min, so that the intake pressure of the engine 1 can reach a maximum of 0.25 MPa. The intake flowmeter 304 is used to monitor the flow of the fresh charge A filled into the pressure-stabilizing mixing chamber 301. The intake manifold 5 is provided with a first temperature sensor 501 and a first pressure sensor 502, which are used to monitor the pressure and temperature in the intake manifold 5. The exhaust manifold 6 is provided with a second temperature sensor 601 and a second pressure sensor 602, which are used to monitor the pressure and temperature in the exhaust manifold 6.

[0059] The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method comprises the following steps:

[0060] S1: Start engine 1 to a specific operating condition;

[0061] S2: Determine whether the engine 1 has been operating stably for a period of time. If the engine 1 has been operating stably for a period of time, the injection system 2 starts to stably inject the tracer gas into the intake system 3 to mix with the fresh charge A in the intake system 3 to form an intake mixture. The intake mixture enters the engine 1 through the intake manifold 5.

[0062] S3: Determining whether the engine 1 operates stably during the period of time after the tracer gas is injected. If the engine 1 operates stably, then after the tracer gas is injected for a period of time, causing the acquisition and analysis system 4 to simultaneously collect intake air mixture in the intake manifold 5 and exhaust air mixture in the exhaust manifold 6 to obtain data on the intake air mixture and the exhaust air mixture; and calculating ventilation performance parameters using the obtained intake air mixture and exhaust air mixture data.

[0063] S4: After the data collection under the specific working condition is completed, the tracer gas injection is stopped, and it is determined whether the engine 1 continues to operate stably for a period of time after the tracer gas injection is stopped. If the engine 1 continues to operate stably, the collected data under the specific working condition is valid; otherwise, it is invalid and the test is stopped.

[0064] Specifically, the engine 1 is started to a specific operating condition to measure the ventilation performance of the engine 1 under the specific operating condition. The specific operating condition here includes different engine 1 speed conditions or different engine 1 intake pressure conditions. It will be understood that during the measurement experiment, the engine 1 will perform several working cycles under each specific operating condition.

[0065] It is determined whether the engine 1 has been operating stably for a period of time, for example, 2 minutes. If the engine 1 has been operating stably, the injection system 2 begins to steadily inject the tracer gas into the intake system 3 after the engine 1 has been operating stably for a period of time. The tracer gas is mixed with the fresh charge A in the intake system 3 to form an intake mixture, for example, in the pressure-stabilizing mixing chamber 301. The intake mixture then enters the engine 1 through the intake manifold 5. It will be appreciated that injecting the tracer gas after the engine 1 has been operating stably for a period of time can prevent the impact of unstable operation of the engine 1 on the analytical measurement experiment, thereby ensuring the accuracy of the measurement results.

[0066] During the period of tracer gas injection, it is determined whether the engine 1 operates stably, i.e., whether the injection of the tracer gas affects the operating state of the engine 1. If the engine 1 operates stably, i.e., the injection of the tracer gas does not affect the operating state of the engine 1, then after a period of tracer gas injection, for example, 5 minutes, the acquisition and analysis system 4 simultaneously collects the intake mixture in the intake manifold 5 and the exhaust mixture in the exhaust manifold 6 to obtain data on the intake and exhaust mixtures. It will be understood that the data on the intake and exhaust mixtures herein refer to the volume concentrations of the intake and exhaust mixtures. After the period of tracer gas injection, it is again observed whether the engine 1 operates stably, i.e., whether the injection of the tracer gas affects the operating state of the engine 1. If the injection of the tracer gas does not affect the stable operation of the engine 1, the acquisition and analysis system 4 is again activated to perform acquisition and analysis. In this way, the engine 1 can be measured under an operating state as close as possible to that without the injection of the tracer gas, thereby facilitating the measurement of the ventilation performance values closer to the actual ventilation performance values, i.e., making the measurement results more accurate and the experimental process more standardized. The ventilation performance parameter is calculated using the obtained intake and exhaust mixture data, thereby obtaining the ventilation performance of the engine 1. For example, the ventilation performance parameter here can be the charging efficiency η c , air supply ratio λ s and capture rate η tr .

[0067] After data collection under the specific operating conditions is completed, tracer gas injection is stopped, and a determination is made as to whether engine 1 continues to operate stably for a period of time, for example, 2 minutes, after tracer gas injection is stopped. If so, the collected data under the specific operating conditions is valid; otherwise, the data is invalid, and the test is stopped. By determining whether engine 1 continues to operate stably for a period of time after tracer gas injection is stopped, it is determined whether the operating state of engine 1 has changed. If engine 1 continues to operate stably, it indicates that the injection of tracer gas has not affected the operating state of engine 1, and that the operating state of engine 1 during the measurement experiment is substantially equivalent to that without tracer gas injection. As a result, the ventilation process of engine 1 during the measurement experiment of the present invention is substantially equivalent to that without tracer gas injection, thereby increasing the accuracy of the measurement experiment results.

[0068] According to an embodiment of the present invention, a method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method determines whether the engine 1 is operating stably during a period of time during which tracer gas injection is performed and a period of time during which tracer gas injection is stopped. If the engine 1 maintains a stable operating state, i.e., the injection and cessation of tracer gas injection have no effect on the operating state of the engine 1, the measurement experiment is performed without affecting the operating state of the engine 1. As a result, the ventilation process parameters of the engine 1 obtained in the measurement experiment can be made almost identical to those of the engine 1 without the tracer gas injection, thereby improving the accuracy of the experimental results and making the measurement experiment process more standardized.

[0069] According to some embodiments of the present invention, the connection between the collection and analysis system 4 and the intake manifold 5 is 0.3 to 1 meter away from the intake valve of the engine 1, and the connection between the collection and analysis system 4 and the exhaust manifold 6 is 0.3 to 1.5 meters away from the exhaust valve of the engine 1. In this way, on the one hand, the concentration of the intake mixture measured by the collection and analysis system 4 can be guaranteed to be the same as the concentration of the intake mixture entering the engine 1, and the concentration of the exhaust mixture measured by the collection and analysis system 4 can be guaranteed to be the same as the concentration of the exhaust mixture discharged from the engine 1. On the other hand, the installation location of the collection and analysis system 4 on the intake manifold 5 and the exhaust manifold 6 will not affect the operation of the engine 1 itself, which is conducive to ensuring the safe operation of the engine 1. On the other hand, the vibration caused by the movement of the intake and exhaust valves of the engine 1 has little impact on the first and second collection probes of the collection and analysis system 4, which is conducive to ensuring the normal use of the first sampling probe 402 and the second sampling probe 405.

[0070] Preferably, the tracer gas is methane, and the maximum pressure of the methane injected into the intake system does not exceed 0.4 MPa, thereby facilitating improved safety during the measurement experiment. It should be noted that all structures and pipelines in the injection system 2 are modified or customized based on the explosion-proof and anti-leakage requirements of methane at a maximum pressure of 0.4 MPa. The methane concentration range in the intake manifold 5 and the exhaust manifold 6 is controlled within the range of 500-2500 ppm. This, on the one hand, helps ensure the accuracy of the measurement results of the gas analyzer 401, and on the other hand, ensures that methane does not affect the safety and normal operation of the engine 1. Correspondingly, the gas analyzer 401 can achieve real-time concentration measurement, and the methane concentration range is 0-5000 ppm with a detection accuracy of ±1% FS. The concentration data collected and analyzed by the gas analyzer 401 can be transmitted in real time to the data acquisition system of the engine 1 to calculate the ventilation performance parameters.

[0071] Preferably, before performing step S1, safety inspection and protective work need to be performed. Specifically, before starting the engine 1, the injection system 2 needs to be leak monitored, and the method of leakage monitoring is the gas storage volume determination method, that is, the internal pressure of the injection system 2 does not drop for a long time and is considered to be leak-free. Leakage monitoring of the injection system 2 before the measurement experiment can well avoid the safety risks caused by leakage of the injection system 2, thereby helping to improve the safety of the experimental measurement process. Before starting the engine 1, the entire two-stroke aviation piston engine ventilation performance test device 1000 needs to be leak tested, and the leak detection method can adopt the soapy water leak detection method, and the leak detection process is carried out under the condition that the intake system 3 is running. During the entire experimental process, the experimental environment should be kept well ventilated, equipped with sufficient fire extinguishers, and the experimenters should wear protective masks and protective clothing.

[0072] According to some embodiments of the present invention, in step S2, determining whether the engine 1 is operating stably for a period of time further includes the following sub-steps:

[0073] If engine 1 is operating unstably, debug engine 1 until it has been operating stably for a period of time under specific operating conditions, and then restart tracer gas injection. In other words, starting tracer gas injection after engine 1 has been operating stably for a period of time ensures that engine 1 is operating normally, while also ensuring the safety of the measurement process and the accuracy of the experimental results.

[0074] According to some embodiments of the present invention, in step S3, determining whether the engine 1 operates stably during the period of tracer gas injection further includes the following sub-step: if the engine 1 is operating unstably, stopping the tracer gas injection, then sequentially debugging the engine 1 and measuring the two-stroke aviation piston engine ventilation performance test apparatus 1000. Debugging the engine 1 includes debugging the engine 1 to a stable operating state or shutting down the engine 1 to ensure safe operation of the engine 1. After sequentially debugging the engine 1 and measuring the two-stroke aviation piston engine ventilation performance test apparatus 1000, the tracer gas injection is resumed after the engine 1 has operated stably for a period of time under specific operating conditions, and step S3 is repeated. This ensures that the measurement experiment is conducted under the premise that the tracer gas injection does not affect the stable operation of the engine 1, thereby facilitating the accuracy of the measurement results and the safety of the measurement experiment process.

[0075] According to some embodiments of the present invention, determining whether engine 1 is operating stably in steps S2, S3, and S4 specifically involves determining whether engine 1's operating parameters have changed. This determination process is more accurate and feasible, facilitating automated measurement and experimental procedures. The operating parameters include engine 1's circulating coolant temperature, intake air flow, exhaust temperature, and fuel consumption. Specifically, during the test, engine 1's circulating coolant temperature is preferably maintained at (80±2)°C.

[0076] According to some embodiments of the present invention, the method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method further includes the following steps:

[0077] S5: If it is determined in step S4 that the collected data under the specific working condition is valid, the collection and analysis system 4 is purged until the tracer gas concentration in the collection and analysis system 4 returns to zero;

[0078] S6: Then adjust the engine 1 to the next specific operating condition, and repeat steps S2, S3 and S4 to complete the test under the next specific operating condition;

[0079] Steps S5, S6, S2, S3, and S4 are repeated in a loop until the last test under a specific operating condition is completed. Before conducting a test under the next specific operating condition, the tracer gas concentration in the acquisition and analysis system 4 is reset to zero. This effectively prevents residual tracer gas in the acquisition and analysis system 4 from the previous specific operating condition from interfering with the tracer gas concentration measurement in the next specific operating condition measurement experiment, thereby ensuring the accuracy of the tracer gas volume concentration measurement under the next specific operating condition. Furthermore, it will be appreciated that the measurement experiment can be performed continuously in a loop, allowing the ventilation performance of the engine 1 to be continuously measured under multiple operating conditions.

[0080] Specifically, for example, the measurement speeds that can be selected are 1200 rpm, 1300 rpm, 1400 rpm, and 1500 rpm. At each speed, the supercharger system 303 is adjusted to obtain five different sets of intake pressures, i.e., five different intake and exhaust pressure differentials, to study factors affecting the ventilation performance of the engine 1. For each operating condition, the tracer gas concentration measurement results for the intake and exhaust mixtures are averaged over 300 data points. For the intake and exhaust pressure change curves, the average is calculated over 200 cycles to ensure the accuracy and repeatability of the measurement results.

[0081] According to some embodiments of the present invention, the method for measuring the ventilation performance of a two-stroke aircraft piston engine using a tracer gas method further includes the following steps: collecting the intake and exhaust mixtures discharged by the collection and analysis system 4, respectively, to perform static concentration analysis on the intake and exhaust mixtures. It is understood that static concentration analysis provides more accurate results. If the real-time collection and analysis results obtained by the collection and analysis system 4 deviate significantly from the static concentration analysis results, the measurement experiment parameters may be adjusted, such as adjusting the tracer gas concentration, changing the installation location of the collection and analysis system 4 on the intake manifold 5 and the exhaust manifold 6, adjusting the time when the collection and analysis system 4 begins collection and analysis, etc., to bring the real-time collection and analysis results closer to the static concentration analysis results, thereby improving the accuracy of the real-time collection and analysis results of the collection and analysis system, and thereby improving the accuracy of the ventilation performance parameters obtained by the measurement and calculation.

[0082] Specifically, a gas sampling bag 410 is respectively connected to the two exhaust ports of the two detection paths of the gas analyzer. The gas sampling bag 410 is used to collect the intake mixture and exhaust mixture discharged from the exhaust ports of the two detection paths of the gas analyzer 401 under specific working conditions. The intake mixture and exhaust mixture in the gas sampling bag 410 are analyzed using a high-precision static gas analyzer (offline). The error between the real-time tracer gas concentration output by the gas analyzer 401 and the static tracer gas concentration output by the high-precision static gas analyzer is compared to verify the accuracy of this real-time method.

[0083] According to some embodiments of the present invention, in step S3, the parameters of the ventilation performance of the engine 1 are calculated using the obtained data of the intake mixture and the exhaust mixture, such as Figure 3 As shown, it specifically includes the following sub-steps:

[0084] S301: Input a set of test data and the data of the intake and exhaust mixtures. It should be noted that the test data here include the volume flow rate X of the tracer gas entering the intake manifold 5. tracer ; The volume flow rate of the fresh charge A into the intake manifold 5 X air ; Fuel-air ratio of engine 1 (F / A) ov , (F / A) ov Calculated based on the fuel consumption rate of engine 1 and the intake flow rate of engine 1; the maximum combustion temperature T in the cylinder of engine 1 c，max ; Exhaust temperature T of engine 1 exh ; Gas density of fresh charge in intake state ρ s The data of the intake mixture and the exhaust mixture are: the volume concentration of the tracer gas in the intake mixture obtained by the collection and analysis system 4 is X t,i, unit ppm; the volume concentration of the tracer gas in the exhaust gas mixture obtained by the collection and analysis system 4 is X t,e , unit: ppm.

[0085] S302: Calculate the actual tracer gas volume concentration X in the intake mixture t,i The relative deviation of the volume concentration of the tracer gas from the theoretical value when the tracer gas and the fresh charge A are completely mixed. Specifically, in the experiment, the fresh charge A and the tracer gas enter the pressure-stabilized mixing chamber 301 at the same time. The volume concentration of the tracer gas after the tracer gas and the fresh charge A are completely mixed can be calculated based on the data of the intake flow meter 304 and the tracer gas micro flow meter 205. The collection and analysis system 4 will collect the concentration of the tracer gas in the intake mixture X t,i , compare the concentration of tracer gas in the collected intake mixture X t,i The relative deviation of the tracer gas concentration from the theoretical completely mixed state can be used to determine whether the tracer gas and the fresh charge A have achieved uniform mixing. Specifically, when the relative deviation is less than 3%, it can be considered that they have been completely mixed. The specific calculation formula is as follows:

[0086]

[0087] Among them, X tracer is the volume flow of the tracer gas measured by the tracer gas micro flowmeter 205; X air is the volume flow of the fresh charge A measured by the intake flow meter 304; X t,i It is the volume concentration of the tracer gas in the intake mixture obtained by the collection and analysis system 4, in ppm.

[0088] S303: Determine whether the relative deviation is less than or equal to 3%. If the relative deviation is less than or equal to 3%, that is, sufficient mixing has occurred between the fresh charge A and the tracer gas, then further determine the maximum combustion temperature T in the cylinder of the engine 1. c，max Is it greater than or equal to 600℃ and there is no misfire? Misfire means that there is no combustion in the engine cylinder 1. If the maximum combustion temperature in the cylinder T c，max If the temperature is greater than or equal to 600°C and there is no misfire, the exhaust temperature T in the exhaust manifold 6 is directly determined. exh Is it less than or equal to 500℃ and there is no afterburning? Afterburning means that part of the fuel is still burned after the exhaust valve of the engine 1 is opened. If the exhaust temperature T exhIf the temperature is less than or equal to 500°C and there is no afterburning, the ventilation performance parameters are calculated. In other words, if the operation process of the engine 1 meets the ideal test conditions that the tracer gas trapped in the cylinder is completely burned or decomposed, the short-circuited tracer gas does not react when passing through the cylinder, and is completely and evenly mixed with the exhaust gas and does not react in the exhaust gas, then the air supply ratio λ can be calculated according to the following method. s , capture rate η tr and charging efficiency η c .

[0089] Air supply ratio λ s Defined as the total mass m of fresh charge A flowing through the intake valve of engine 1 per cycle i The ratio of the charge mass m0 to the fresh charge A that completely fills the effective working volume of the engine cylinder 1 in the intake state is:

[0090]

[0091] Among them, m s is the intake air flow rate measured by the intake air flow meter 304, kg / s; Δt is the time corresponding to one working cycle of the engine 1, s; V eg is the total effective displacement of engine 1, m 3 ρ s is the gas density of the fresh charge A, which can be obtained from the ideal gas state equation:

[0092]

[0093] Among them, p s is the intake pressure, Pa; T s is the intake air temperature, K; M is the relative molecular mass of the fresh charge A, n is the engine speed, r / min. s It reflects the amount of circulating air intake of the engine 1 and represents the intake capacity of the engine 1 under certain working conditions.

[0094] Capture rate η tr It is defined as the total mass m of the fresh charge A remaining in the cylinder at the end of the ventilation process. a The total mass of the charge flowing through the intake valve per cycle m i The calculation formula in the present invention is as follows:

[0095]

[0096] Among them, (F / A) ov is the global fuel-gas ratio, which is calculated based on the fuel consumption rate of the engine 1 measured in the test and the flow rate measured by the intake flow meter 304; X t,i and X t,eare the measured volume concentrations of tracer gas in the intake and exhaust mixtures, ppm; M air and M exh are the molar masses of the intake and exhaust mixtures, respectively, in g / mol. Capture rate η tr It indicates the proportion of fresh charge A remaining in the cylinder to participate in atomization combustion, which directly reflects the effective utilization rate of the fresh charge A, and can also reflect the proportion of fresh charge A lost in the form of short circuit and mixing.

[0097] Charging efficiency η c is the air supply ratio λ s and capture rate η tr The product of: η c =λ s ·η tr .

[0098] Air supply ratio λ s , capture rate η tr and charging efficiency η c The analysis results are obtained through a series of measurement steps. The error in each instrument measurement step will affect the analysis results, so error propagation analysis is necessary. The system error propagation formula needs to be used to calculate and ensure that the system propagation error is within a small range.

[0099] According to some embodiments of the present invention, determining whether the relative deviation is less than or equal to 3% in step S303 further includes the following sub-step: If the relative deviation is greater than 3%, the set of test data and the intake and exhaust mixture data are invalid. In other words, the fresh charge A and the tracer gas are not evenly mixed, and the changes in the tracer gas cannot accurately reflect the actual breathing process of the engine 1. Therefore, the measured data is invalid and should be discarded. The test parameters, such as the start time of data collection and analysis, should be readjusted to reduce the relative deviation to less than 3%.

[0100] The above air supply ratio λ s , capture rate η tr and charging efficiency η c The calculation method is based on ideal test conditions, where the tracer gas trapped in the cylinder is completely burned or decomposed, the short-circuited tracer gas does not react when passing through the cylinder, and is completely and evenly mixed with the exhaust gas, and the tracer gas does not react in the exhaust gas.

[0101] However, in reality, there may be three non-ideal test phenomena: first, the tracer gas does not react completely during the cylinder combustion process; second, the tracer gas is destroyed in the exhaust; third, misfire occurs in certain cycles of the engine 1 during the test, that is, no combustion occurs in the cylinder of the engine 1. Among them, the phenomenon that the tracer gas does not react completely during the cylinder combustion process may be caused by incomplete combustion and other reasons. The temperature of some areas in the main combustion period cannot reach the ignition temperature of the tracer gas; the phenomenon that the tracer gas is destroyed in the exhaust may be caused by factors such as afterburning, that is, some fuel in the engine 1 is still burned after the exhaust valve is opened; the factors that cause misfire in certain cycles of the engine 1 may be: the engine 1 has valve sealing problems in these cycles, or there is missed injection, etc., and no combustion occurs in the cylinder. Therefore, in the misfire cycle, the tracer gas trapped in the cylinder is also unreactive. These will affect the measurement results of the capture rate in the ventilation performance parameters. For these three non-ideal test phenomena, three quantifiable parameters can be defined respectively: the in-cylinder reaction rate ε cr , exhaust reaction rate f mf and misfire coefficient ε er .

[0102] Among them, the in-cylinder reaction rate ε cr Defined as the mass G of the burned and decomposed part captured in the tracer gas in the cylinder r The total mass G of the tracer gas captured in the cylinder z The ratio of:

[0103] Exhaust reaction rate f mf Defined as the reaction amount of tracer gas in the exhaust gas G r,exh The total amount of tracer gas entering the exhaust G z,exh The ratio of: In the case of afterburning, N er is the number of cycles in which afterburning occurs, N z is the total number of sampling cycles.

[0104] Misfire coefficient ε er Defined as the number of cycles N at which misfire occurs mf The total number of sampling cycles N z The ratio of:

[0105] According to some embodiments of the present invention, Figure 3As shown, step S303 of determining whether the maximum combustion temperature in the cylinder of the engine 1 is greater than or equal to 600°C and there is no misfire further includes the following sub-steps: if the maximum combustion temperature in the cylinder is less than 600°C and there is misfire, calculating the in-cylinder reaction rate and misfire coefficient, and then further determining whether the exhaust temperature in the exhaust manifold 6 is less than or equal to 500°C and there is no afterburning. It is understandable that the maximum combustion temperature in the cylinder is measured by a temperature sensor used to monitor the temperature in the cylinder. By monitoring the temperature in the cylinder of the engine 1, if its temperature throughout the entire main combustion period is greater than the ignition temperature of methane, 546°C, and the captured air-fuel (the ratio of the portion of the intake mixture captured in the cylinder to the short-circuited portion) is relatively large (e.g., greater than 25) and the concentration of the injected tracer gas is relatively low (e.g., less than 2500 ppm), it can be considered that the fuel and methane in the cylinder are completely burned, and the in-cylinder reaction rate is 1. In the case of extreme incomplete combustion, specifically, for example, the maximum combustion temperature in the cylinder is less than 600°C and misfire occurs, the in-cylinder pressure sensor can be used to monitor phenomena such as incomplete combustion, evaluate the combustion temperature, and thus calculate the in-cylinder reaction rate using the above formula. Engine 1 may experience several misfire cycles, with an average misfire coefficient of 0.02-0.04. The occurrence of misfire cycles can be determined by monitoring the changes in the transient exhaust pressure. In a misfire cycle, when the exhaust valve opens, there is no combustion in the cylinder, so the exhaust gas pressure does not spike. This can be clearly distinguished from a stable combustion cycle. Therefore, the misfire coefficient ε can be calculated using the above formula. er The embodiment of the present invention determines whether a non-ideal test state has occurred, and thus can reasonably correct the capture rate according to the actual situation, which is conducive to obtaining more accurate capture rate data.

[0106] According to some embodiments of the present invention, Figure 3 As shown, step S303 of determining whether the exhaust temperature in the exhaust manifold 6 is less than or equal to 500°C and there is no aftercombustion further includes the following sub-step: if the exhaust temperature in the exhaust manifold 6 is greater than 500°C and aftercombustion occurs, then calculating the exhaust reactivity. It should be noted that even if the exhaust temperature of the engine 1 is consistently below the ignition temperature of methane, if aftercombustion occurs under non-routine operating conditions (such as high altitude), methane may still be destroyed in the exhaust manifold 6 even if the exhaust temperature is below the ignition temperature of methane. Therefore, an exhaust transient pressure sensor is required to monitor the occurrence of aftercombustion in real time to calculate the corresponding exhaust reactivity. By determining whether a non-ideal test condition has occurred, the embodiment of the present invention can reasonably modify the capture rate based on actual conditions, thereby facilitating the acquisition of more accurate capture rate data.

[0107] When the maximum combustion temperature in the cylinder is less than 600°C and misfire occurs, the exhaust temperature in the exhaust manifold 6 is greater than 500°C and afterburning occurs, that is, the in-cylinder reaction rate ε needs to be considered at the same time. cr , exhaust reaction rate fmf and misfire coefficient ε er To correct the capture rate η tr The calculation formula for capture rate η tr The revised calculation formula is as follows:

[0108]

[0109] Among them, (F / A) ov is the global fuel-gas ratio, which is calculated based on the fuel consumption rate of the engine 1 measured in the test and the flow rate measured by the intake flow meter 304; X t,i and X t,e are the measured volume concentrations of tracer gas in the intake and exhaust mixtures, ppm; M air and M exh are the molar masses of the intake and exhaust mixtures, g / mol, respectively.

[0110] Throughout this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" indicate that the specific features, structures, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0111] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method, characterized in that: The invention is applied to a test device for measuring the ventilation performance of a two-stroke aviation piston engine, which comprises an engine, an injection system, an intake system, a collection and analysis system, an intake manifold, and an exhaust manifold. The injection system is used to inject tracer gas into the intake system, the intake manifold is connected between the intake system and the engine, the exhaust manifold is connected to the engine, and the collection and analysis system is connected to the intake manifold and the exhaust manifold respectively. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method comprises the following steps: S1: starting the engine to a specific operating condition; S2: determining whether the engine has been operating stably for a period of time. If the engine has been operating stably for a period of time, after the engine has been operating stably for a period of time, causing the injection system to begin stably injecting tracer gas into the intake system to mix with fresh charge in the intake system to form an intake mixture, and the intake mixture enters the engine through the intake manifold. S3: determining whether the engine operates stably during the period of time during which the tracer gas is injected. If the engine operates stably, after the tracer gas is injected for a period of time, causing the acquisition and analysis system to simultaneously acquire intake air mixture in the intake manifold and exhaust air mixture in the exhaust manifold to obtain data of the intake air mixture and the exhaust air mixture; and calculating the ventilation performance parameter using the acquired data of the intake air mixture and the exhaust air mixture; S4: After the data collection under the specific operating condition is completed, the tracer gas injection is stopped, and it is determined whether the engine continues to operate stably for a period of time after the tracer gas injection is stopped. If the engine continues to operate stably, the collected data under the specific operating condition is valid; otherwise, it is invalid and the test is stopped; In step S3, the engine ventilation performance parameters are calculated using the obtained intake mixture and exhaust mixture data, which specifically includes the following sub-steps: S301: Input a set of obtained test data and data of intake mixture and exhaust mixture; S302: Calculating a relative deviation between the actual tracer gas concentration in the intake mixture and the theoretical tracer gas concentration when the tracer gas is completely mixed with the fresh charge; S303: Determine whether the relative deviation is less than or equal to 3%. If so, further determine whether the maximum combustion temperature in the cylinder of the engine is greater than or equal to 600°C and there is no misfire. If so, further determine whether the exhaust temperature in the exhaust manifold is less than or equal to 500°C and there is no afterburning. If so, calculate the ventilation performance parameters.

2. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 1, characterized in that: In step S2, determining whether the engine has been operating stably for a period of time further includes the following sub-steps: If the engine does not operate stably, the engine is debugged until the engine operates stably for a period of time under the specific operating conditions, and then the injection of tracer gas is restarted.

3. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 2, characterized in that: In step S3, it is determined whether the engine operates stably during the period of time during which the tracer gas is injected. The method further includes the following sub-steps: if the engine does not operate stably, the tracer gas injection is stopped, and then the engine and the two-stroke aviation piston engine ventilation performance test device are debugged in sequence until the engine operates stably for a period of time under the specific operating conditions. Then, the tracer gas injection is restarted, and step S3 is repeated.

4. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 2, characterized in that: The determining whether the engine is operating stably in step S2, step S3 and step S4 specifically includes determining whether the operating parameters of the engine have changed.

5. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to any one of claims 1 to 4, characterized in that: The following steps are also included: S5: If it is determined in step S4 that the collected data under the specific working condition is valid, the collection and analysis system is purged until the tracer gas concentration in the collection and analysis system returns to zero; S6: then adjusting the engine to the next specific operating condition, repeating steps S2, S3 and S4 to complete the test under the next specific operating condition; Steps S5, S6, S2, S3 and S4 are repeated in sequence until the last test under the specific working condition is completed.

6. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to any one of claims 1 to 4, characterized in that: The method further includes the following steps: collecting the intake mixed gas and the exhaust mixed gas discharged by the collection and analysis system respectively, so as to perform static concentration analysis on the intake mixed gas and the exhaust mixed gas respectively.

7. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 1, characterized in that: The step S303 of determining whether the relative deviation is less than or equal to 3% further includes the following sub-steps: if the relative deviation is greater than 3%, the set of test data and the data of the intake mixture and the exhaust mixture are invalid.

8. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 1, characterized in that: The step S303 of determining whether the maximum combustion temperature in the cylinder of the engine is greater than or equal to 600°C and there is no misfire further includes the following sub-steps: if the maximum combustion temperature in the cylinder is less than 600°C and there is misfire, calculating the in-cylinder reaction rate and misfire coefficient, and then further determining whether the exhaust temperature in the exhaust manifold is less than or equal to 500°C and there is no afterburning.

9. The method for measuring the ventilation performance of a two-stroke aviation piston engine using a tracer gas method according to claim 8, characterized in that: The step S303 of determining whether the exhaust temperature in the exhaust manifold is less than or equal to 500° C. and there is no afterburning further includes the following sub-step: if the exhaust temperature in the exhaust manifold is greater than 500° C. and afterburning occurs, calculating the exhaust reactivity.

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