Method for measuring compression resistance moment of piston engine at low temperature and low air pressure

Abstract

The invention relates to the technical field of engine compression resistance moment measurement, discloses a method for measuring the compression resistance moment of a piston type engine at low temperature and low air pressure, comprehensively considers the great influence of environmental factors on the performance of the engine, and provides an effective and accurate measurement way. By means of the measuring method, accurate measurement of the compression resistance moment of the piston type engine under the low temperature and the low air pressure can be achieved, and then application and development of the engine under the extreme working condition are promoted; therefore, the scientificity and advancement of engine design can be improved, and meanwhile, a solid foundation is laid for using the engine in special environments such as high altitude, plateau and cold regions in the future.

Description

Technical Field

[0001] The invention relates to the technical field of engine compression resistance torque measurement, and in particular to a method for measuring the compression resistance torque of a piston engine under low temperature and low air pressure. Background Art

[0002] With the widespread use of drones, the impact of high-altitude environment on engine performance has gradually become a research hotspot. The premise of high-altitude delivery of drones is that the engine starts and ignites in a high-altitude environment and successfully enters the idle state. When the engine starts in a high-altitude, low-temperature and low-pressure environment, the starter generator acts as an external force to drive the engine to rotate. The resistance torque on the crankshaft is divided into three parts: friction resistance torque, compression resistance torque and inertia resistance torque. The friction resistance torque is only related to temperature, the compression resistance torque is related to both temperature and pressure, and the inertia resistance torque is not related to temperature and pressure.

[0003] Under normal conditions, the fluidity and combustion characteristics of the gas are relatively stable, but in a low-temperature and low-pressure environment, the dynamic behavior of the gas may show complex nonlinear characteristics, which in turn affects the gas flow, mixing and combustion process. When the altitude increases by about 1000m, the atmospheric pressure and atmospheric density decrease by about 11%, and the atmospheric temperature decreases by about 6°C. Since the air density and compression polynomial index will change accordingly, the air compression process in the engine cylinder will change due to changes in ambient temperature and atmospheric pressure, thereby affecting the overall compression resistance torque and compression loss of the engine. The compression resistance torque not only affects the overall resistance torque of the engine, but also affects the compression polynomial index, compression end pressure and compression end temperature of the engine. Only when the compression end temperature in the engine cylinder is greater than the fuel ignition point can the engine ignite.

[0004] Traditional methods for measuring engine compression resistance torque are mainly carried out under normal air pressure and temperature conditions. However, in low temperature and low pressure environments, these methods often cannot accurately predict the working state of the engine, resulting in safety hazards in engineering design and substandard performance. Therefore, in order to accurately evaluate the performance of the engine in low temperature and low pressure environments, new calculation models and methods need to be developed. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for measuring the compression resistance torque of a piston engine under low temperature and low pressure. Through a relatively realistic low temperature and low pressure high altitude environment simulation and a high-precision sensor and data acquisition system, as well as a new calculation model, it is possible to achieve accurate measurement of the compression resistance torque of a piston engine under low temperature and low pressure, thereby promoting the application and development of engines under extreme working conditions. The technical solution is as follows:

[0006] A method for measuring the compression resistance torque of a piston engine under low temperature and low pressure comprises the following steps:

[0007] Step 1: Install the engine in a high-altitude environment simulation test chamber to simulate the environment required for the test;

[0008] Step 2: Install a photoelectric encoder at the front end of the engine shaft to correspond the measured cylinder pressure to the engine crankshaft angle; remove the spark plugs at both ends of the engine cylinder head and replace them with cylinder pressure sensors to measure the engine cylinder pressure in real time; and collect and process the measured data;

[0009] Step 3: Cut off the fuel supply system and ignition system of the engine, and start the starter generator through the host ECU.

[0010] The starter generator drags the engine to a specific constant speed every time it is started, so as to ensure the same speed every time it is started;

[0011] Step 4: Set a temperature interval with a specific temperature interval, keep the ambient pressure unchanged, and measure the pressure in the engine cylinder at different set temperatures; set a pressure interval with a specific pressure interval, keep the ambient temperature unchanged, and measure the pressure in the engine cylinder at different set pressures; obtain N groups of operating parameters;

[0012] Step 5: Sort out the measured cylinder pressure data to determine the maximum pressure P in the engine cylinder max The relationship with ambient temperature and ambient pressure;

[0013] Step 6: Based on the above relationship and according to the pressure in the cylinder, calculate the compression resistance torque formed by the upward force of the piston acting on the upper surface of the piston and transmitted to the crankshaft through the crank-connecting rod mechanism when the piston moves toward the top dead center.

[0014] Furthermore, during the test, fuel is injected into the engine intake duct, and the injection pulse width is fixed at a constant value to prevent the engine from being damaged when suddenly started in a low temperature environment.

[0015] Furthermore, the step 6 is specifically as follows:

[0016] Without considering the gas flow inertia and gas viscous resistance, the compression resistance moment of a single-cylinder engine is obtained by multiplying the engine cylinder pressure, the piston equivalent area and the crankshaft connecting rod equivalent radius. The expression is as follows:

[0017] T p =A.P.J.

[0018] Where: T p is the engine compression resistance torque; A is the effective cross-sectional area of ​​the piston; P is the pressure in the cylinder; J is the instantaneous equivalent radius of the crank-connecting rod structure;

[0019] For the common crank-connecting rod mechanism of the engine, the expression of J is as follows:

[0020]

[0021] Where: Δ is the crankshaft eccentricity; α is the crankshaft angle; R is the crankshaft rotation radius; L is the connecting rod length;

[0022] For a two-stroke two-cylinder piston engine, the total compression resistance torque of the two cylinders is expressed as:

[0023]

[0024]

[0025] Among them: A piston is the piston top surface area, P(i) is the cylinder pressure of cylinder 1 or cylinder 2, and i is cylinder 1 or cylinder 2.

[0026] The beneficial effects of the present invention are:

[0027] The measuring method of the present invention can realize the accurate measurement of the compression resistance torque of the piston engine under low temperature and low pressure, thereby promoting the application and development of the engine under extreme working conditions; this not only helps to improve the scientificity and advancement of engine design, but also lays a solid foundation for the use of engines in special environments such as high altitude, plateau, cold areas, etc. in the future; it also has the following characteristics:

[0028] 1) Strong adaptability: The present invention is applicable to various types of piston engines, especially in special environments such as high altitude and high altitude, and can meet the needs of different application scenarios, thus broadening the application field of the technology;

[0029] 2) High accuracy: The present invention uses a relatively realistic low-temperature, low-pressure, high-altitude environment simulation and a new calculation model, which can more accurately measure the compression resistance torque of the engine than traditional methods; accurate measurement can provide important data information for engine design and optimization, ensuring that the performance of the engine under extreme conditions is more predictable;

[0030] 3) Convenient for working condition simulation: The present invention conducts dynamic analysis and mathematical modeling of the engine dragging working condition, which can provide a strong theoretical basis for the starter motor dragging the engine to start and the dynamic matching of the starting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the engine compression resistance torque test bench.

[0032] Figure 2 Schematic diagram of the engine compression resistance torque mechanical model. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The present invention proposes a novel method for measuring the compression resistance torque of a piston engine under low temperature and low pressure, which comprehensively considers the significant impact of environmental factors on engine performance and provides an effective and accurate measurement method. With the help of the measurement method of the present invention, it is possible to accurately measure the compression resistance torque of a piston engine under low temperature and low pressure, thereby promoting the application and development of engines under extreme working conditions. This not only helps to improve the scientificity and advancement of engine design, but also lays a solid foundation for the future use of engines in special environments such as high altitudes, plateaus, and cold regions.

[0035] The method for measuring the compression resistance torque of a piston engine under low temperature and low pressure of the present invention comprises the following steps:

[0036] 1) Install the engine in a high-altitude environment simulation test chamber, which can allow the engine performance test to reach a more realistic high-altitude environment, or simulate the special single environment or composite environment required for the test.

[0037] 2) Install a photoelectric encoder at the front end of the engine shaft to correspond the measured cylinder pressure to the engine crankshaft angle; remove the spark plugs at both ends of the engine cylinder head and replace them with cylinder pressure sensors to measure the pressure in the engine cylinder in real time; collect and process data through charge amplifiers, transmitters, data acquisition cards and other hardware and data storage and acquisition analysis programs.

[0038] 3) Cut off the fuel supply system and ignition system of the engine, and the upper computer ECU controls the starter generator to start. Each time the motor starts, it will drag the engine to a constant speed to ensure that the speed is consistent each time it starts. At the same time, the cylinder pressure sensor measures the cylinder pressure when the speed is stable.

[0039] Schematic diagram of engine compression resistance torque test bench Figure 1 shown.

[0040] 4) Set a certain temperature and pressure interval, such as -45°C to 15°C, every 15°C, 95kPa to 35kPa, every 20kPa. Keep the ambient pressure constant, measure the engine cylinder pressure at different set temperatures, keep the ambient temperature constant, measure the engine cylinder pressure at different set pressures, and obtain N groups of operating parameters.

[0041] 5) During the test, the lubricating oil of the engine may freeze in a low temperature environment, and the gap between the engine piston ring and the cylinder becomes smaller. Therefore, in order to prevent the engine from being damaged when suddenly started in a low temperature environment, a certain amount of oil is injected into the engine intake duct during the test, and the injection pulse width is fixed at a constant value.

[0042] 6) Sort out the cylinder pressure data obtained, and the maximum pressure in the engine cylinder P max It is linearly related to the ambient temperature and ambient pressure. In a low temperature and low pressure environment, as the ambient temperature decreases, the maximum pressure P in the cylinder max Gradually increases; as the ambient pressure decreases, the maximum pressure in the cylinder P max Gradually decrease.

[0043] 7) Calculate the compression resistance torque formed by the upward force of the piston acting on the upper surface of the piston and transmitted to the crankshaft through the crank-connecting rod mechanism. The expression is as follows:

[0044] Without considering the gas flow inertia and gas viscous resistance, the compression resistance torque of a single-cylinder engine is obtained by multiplying the engine cylinder pressure, the piston equivalent area and the crankshaft connecting rod equivalent radius, as shown in formula (1):

[0045] T p =A·P·J (1)

[0046] Where: T p is the engine compression torque; A is the effective cross-sectional area of ​​the piston; P is the pressure in the cylinder; J is the instantaneous equivalent radius of the crank-connecting rod structure.

[0047] The schematic diagram of the engine compression resistance torque mechanical model is as follows Figure 2 As shown, F p is the compression resistance generated when the piston is compressed. Therefore, for the common crank-connecting rod mechanism of the engine, the expression of J is as follows:

[0048]

[0049] Where: Δ is the crankshaft eccentricity; α is the crankshaft angle; R is the crankshaft rotation radius; L is the connecting rod length.

[0050] For a two-stroke two-cylinder piston engine, the total compression resistance torque of the two cylinders is expressed as (3):

[0051]

[0052] Among them: A piston is the piston top surface area, P(i) is the cylinder pressure of cylinder 1 or cylinder 2, and i is cylinder 1 or cylinder 2.

[0053] The sum of the compression resistance torque in this expression is a periodic function of the change in crankshaft angle. The maximum value in the dragging process occurs at the compression top dead center position and is related to the engine structural parameters. The engine compression resistance torque accounts for the largest proportion of all resistance torques. In a working cycle of a two-stroke piston engine, that is, within 360° of crankshaft torque, the compression resistance torque shows a periodic fluctuation characteristic. For every rotation of the engine crankshaft, the compression resistance torque will have two maximum fluctuations.

[0054] The relationship between engine compression torque and ambient temperature and ambient pressure: Due to the maximum pressure P in the cylinder max It increases with the decrease of ambient temperature and decreases with the decrease of ambient pressure, while the equivalent area of ​​the engine piston and the equivalent radius of the crankshaft connecting rod do not change with temperature and atmospheric pressure. Therefore, the maximum compression torque of the engine is T pmax It also increases with decreasing ambient temperature and decreases with decreasing ambient pressure.

Claims

1. A method for measuring the compression resistance torque of a piston engine at low temperature and low pressure, characterized in that: The following steps are involved: Step 1: Install the engine in a high-altitude environment simulation test chamber to simulate the environment required for the test; Step 2: Install a photoelectric encoder at the front end of the engine shaft to correspond the measured cylinder pressure to the engine crankshaft angle; remove the spark plugs at both ends of the engine cylinder head and replace them with cylinder pressure sensors to measure the engine cylinder pressure in real time; and collect and process the measured data; Step 3: Cut off the fuel supply system and ignition system of the engine, and control the starter generator to start through the upper computer ECU, so that the starter generator will drag the engine to a specific constant speed each time it starts, so as to ensure the same speed each time it starts; Step 4: Set a temperature interval with a specific temperature interval, keep the ambient pressure unchanged, and measure the pressure in the engine cylinder at different set temperatures; set a pressure interval with a specific pressure interval, keep the ambient temperature unchanged, and measure the pressure in the engine cylinder at different set pressures; Step 5: Sort out the measured cylinder pressure data to determine the maximum pressure P in the engine cylinder max The relationship with ambient temperature and pressure; Step 6: Based on the above relationship and according to the pressure in the cylinder, calculate the compression resistance torque formed by the upward force of the piston acting on the upper surface of the piston and transmitted to the crankshaft through the crank-connecting rod mechanism when the piston moves toward the top dead center.

2. The method for measuring the compression resistance torque of a piston engine at low temperature and low pressure according to claim 1, characterized in that: It also includes that during the test, fuel is injected into the engine intake duct, and the injection pulse width is fixed at a constant value to prevent damage to the engine when it is suddenly started in a low temperature environment.

3. The method for measuring the compression resistance torque of a piston engine at low temperature and low pressure according to claim 1, characterized in that: The step 6 is specifically as follows: Without considering the gas flow inertia and gas viscous resistance, the compression resistance moment of a single-cylinder engine is obtained by multiplying the engine cylinder pressure, the piston equivalent area and the crankshaft connecting rod equivalent radius. The expression is as follows: T p =A·P·J Where: T p is the engine compression resistance torque; A is the effective cross-sectional area of ​​the piston; P is the pressure in the cylinder; J is the instantaneous equivalent radius of the crank-connecting rod structure; For the common crank-connecting rod mechanism of the engine, the expression of J is as follows: Where: Δ is the crankshaft eccentricity; α is the crankshaft angle; R is the crankshaft rotation radius; L is the connecting rod length; For a two-stroke two-cylinder piston engine, the total compression resistance torque of the two cylinders is expressed as: Among them: A piston is the piston top surface area, P(i) is the cylinder pressure of cylinder 1 or cylinder 2, and i is cylinder 1 or cylinder 2.

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