A method for monitoring the state of an ultra-high pressure cylinder

Abstract

The present invention provides a state monitoring method for an ultra-high pressure cylinder, comprising monitoring the ultra-high pressure cylinder through finite strain monitoring, temperature monitoring, key phase monitoring and plunger strain test calibration; polishing the symmetrical outer surface of a pipeline near the inlet and exhaust ports of the ultra-high pressure cylinder and pasting a temperature self-compensating strain gauge to test the axial strain and axial strain of the pipeline respectively; pasting a resistive temperature sensor near the strain gauge to test the temperature change of the inlet and exhaust pipelines, calculating the increased axial strain of the pipeline after the pipeline is heated and expanded according to the temperature change of the inlet and exhaust pipelines and the equivalent material linear expansion coefficient of the ultra-high pressure pipeline, thereby obtaining the pressure change in the inlet and exhaust pipelines; pasting a temperature self-compensating strain gauge on the symmetrical outer surface of the plunger tail end to test the axial strain of the plunger when the ultra-high pressure cylinder is working; accurately identifying the PV diagram of the working process of the ultra-high pressure cylinder, and realizing online monitoring of the ultra-high pressure compressor.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high pressure compressors, and in particular to a state monitoring method for an ultra-high pressure cylinder. Background Art

[0002] For ultra-high-pressure compressors (i.e., exhaust pressures greater than 100 MPa), effectively identifying anomalies and diagnosing faults during the compression process is a crucial issue. When faults such as valve plate damage, packing leakage, and plunger wear occur within an ultra-high-pressure cylinder, monitoring the compression process (i.e., the PV diagram) is often sufficient for diagnosis. However, for equipment safety, small holes are typically not reserved in the ultra-high-pressure cylinder or near the cylinder inlet and outlet for installing invasive pressure sensors for monitoring the cylinder's condition.

[0003] The existing method is to monitor the compressor compression process by performing micro-strain detection on the piston rod running in the cylinder and reconstructing the PV diagram of the compressor cylinder. However, for ultra-high pressure compressors, if a wired strain test system is used for monitoring, as the plunger (i.e., piston rod) moves back and forth for a long time during operation, the wires transmitting the signal are prone to breaking due to alternating fatigue after a period of time, making long-term status monitoring impossible. If a wireless strain test system is used for monitoring, the risk of wire breakage can be avoided by fixing the acquisition node on the plunger so that it moves with it. However, the plunger of the ultra-high pressure cylinder is continuously flushed by high-temperature lubricating oil during operation, and the existing wireless strain test system cannot work continuously for a long time in high-temperature lubricating oil. In addition, the battery power of the acquisition node is limited and cannot work continuously, so long-term online monitoring is also impossible.

[0004] In order to achieve long-term online monitoring of ultra-high pressure cylinders, another safer and more reliable method is needed to complete the PV diagram monitoring of ultra-high pressure cylinders. Summary of the Invention

[0005] The main purpose of the present invention is to provide a state monitoring method for an ultra-high pressure cylinder to solve the problem that online PV diagram monitoring cannot be achieved during the compression process of the ultra-high pressure cylinder.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: monitoring the ultra-high pressure cylinder by including finite strain monitoring, temperature monitoring, key phase monitoring and correcting the monitoring error through plunger strain test calibration;

[0007] The symmetrical outer surface of the pipe near the inlet and exhaust ports of the ultra-high pressure cylinder is polished and a temperature self-compensating strain gauge is attached. The strain gauge is connected using a Wheatstone bridge to measure the micro-strain on the pipe surface, and the axial strain and axial strain of the pipe are measured respectively;

[0008] A resistance temperature sensor is attached near the strain gauge to measure the temperature change in the intake and exhaust ducts. Based on the temperature change in the intake and exhaust ducts and the equivalent material linear expansion coefficient of the ultra-high pressure duct, the increased axial strain in the duct due to thermal expansion is calculated, thereby deriving the pressure change in the ducts.

[0009] Temperature self-compensating strain gauges are attached to the symmetrical outer surface of the plunger tail end, and a full-bridge arrangement is used to test the axial strain of the plunger when it is working in an ultra-high pressure cylinder.

[0010] A metal protrusion is pasted at a fixed point on the crankshaft, and a wired eddy current sensor is used to align with the protrusion to test the time it takes for the compressor to rotate one circle.

[0011] In the preferred embodiment, according to the principles of elasticity, the isotropic generalized Hooke's law formula 1 is:

[0012]

[0013] in 、 、 is the strain in the three directions of the elastic element, 、 、 is the stress in three directions of the elastic body, E is the elastic modulus, is Poisson's ratio.

[0014] In the preferred solution, an ultra-high pressure pipeline model is established, a small three-dimensional unit in the model is taken, and the circumferential direction of the pipeline is , the radial direction of the pipe section is , the axial direction of the pipe is , 、 Specific data can be obtained through strain testing. When the pipeline is in a free state, the axial stress of the pipeline is , eliminate and , substituting this boundary condition into formula 1, we can get formula 2:

[0015]

[0016] Eliminate Formula 2 The conversion form is formula 3:

[0017]

[0018] Therefore, it can be deduced that:

[0019]

[0020] According to the balance equation, geometric equation and physical equation of thick-walled pipe unit, the internal pressure and pipe surface stress can be expressed as follows:

[0021]

[0022] in is the outer diameter of the pipe, is the inner diameter of the pipe, P is the internal pressure of the pipe, and by combining Formula 3 and Formula 4, we can know that the relationship between the internal pressure of the pipe and the strain on the outer surface of the pipe when both ends are in a free state is Formula 5:

[0023]

[0024] When the size and material of the ultra-high pressure pipeline are known, the circumferential strain in formula 5 can be and axial strain Calculate the pressure inside the pipe changes.

[0025] In the preferred embodiment, the temperature change of the inlet and exhaust pipes , according to the temperature change of the intake and exhaust pipes and the equivalent material linear expansion coefficient of the ultra-high pressure pipe , calculate the increased axial strain of the pipeline after the pipeline is thermally expanded ;

[0026] The pressure change in the intake and exhaust pipes is .

[0027] In the preferred embodiment, the axial strain of the test plunger when working in the ultra-high pressure cylinder is , then the plunger rod load is , where E is the elastic modulus of the plunger.

[0028] In the preferred solution, the reciprocating inertia force of the plunger is calculated by referring to the compressor design manual. and reciprocating damping force , then the gas pressure change in the ultra-high pressure cylinder is ,in is the cross-sectional area of ​​the plunger.

[0029] In the preferred embodiment, during one rotation of the crankshaft, the pressure changes The four working processes of the cylinder shown in the curve are intake, compression, exhaust, and expansion, and the time points are marked as ;

[0030] Respectively 、 、 、 The pressure change during a time period is named .

[0031] In the preferred embodiment, according to Find the intake and exhaust pipes at four time points The corresponding pressure changes in the two time periods , and according to the calculation formula of gas compression and expansion process, etc. .

[0032] In the preferred solution, the strain measurement system is used to calculate the error during the cylinder intake and exhaust process: , these two errors include the valve opening pressure difference , , system measurement error 、 Equal error, because the opening pressure difference of the gas valve , They are all constants and can be obtained by calibrating the valve individually. Therefore, the test can be carried out at multiple different inlet and exhaust pressures to summarize the law of the change of the system measurement error. , The change curve of the strain test system is used to test the corrected pressure The changes should be:

[0033] ;

[0034] Calculate the error during cylinder compression and expansion as , based on the test results of multiple different intake and exhaust pressures, the calculation formula of gas compression and expansion process is continuously adjusted The k value and the const value, until Or it can be ignored, then:

[0035] .

[0036] In the preferred solution, By time The PV diagram of the ultra-high pressure cylinder compression process is formed by combining them in sequence. Long-term monitoring of it can achieve the purpose of state monitoring of the ultra-high pressure cylinder working process.

[0037] The present invention provides a method for monitoring the status of an ultra-high-pressure cylinder. The method adopts wired strain monitoring, temperature monitoring, key phase monitoring, and plunger strain test calibration to correct monitoring errors to comprehensively realize long-term online monitoring of the ultra-high-pressure cylinder; the method can accurately identify the PV diagram of the ultra-high-pressure cylinder's working process and realize online monitoring of the ultra-high-pressure compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below with reference to the accompanying drawings and examples:

[0039] Figure 1 It is the principle diagram of the Wheatstone bridge of the present invention;

[0040] Figure 2 This is a schematic diagram of the strain gauge bonding of the present invention;

[0041] Figure 3 Schematic diagram of the stress-strain relationship of the elastic body unit of the present invention;

[0042] Figure 4 It is a pipeline model diagram of the present invention;

[0043] Figure 5 It is a trend diagram of the pressure and angle in the cylinder of the present invention; DETAILED DESCRIPTION

[0044] Example 1

[0045] like Figures 1 to 5 As shown in the figure, a condition monitoring method for ultra-high pressure cylinders is used to obtain the pressure changes of the cylinder intake and exhaust pipes through wired strain testing: the symmetrical outer surface of the pipe near the ultra-high pressure cylinder intake and exhaust ports is polished and a temperature self-compensating strain gauge is attached. The strain gauges are connected in a Wheatstone bridge manner to measure the micro-strain of the pipe surface. The testing principle is as follows: Figure 1 As shown, the pasting method is as follows Figure 2 As shown, the circumferential strain of the tested pipe is and axial strain :

[0046] According to the principles of elasticity, the isotropic generalized Hooke's law formula 1 is:

[0047]

[0048] in 、 、 is the strain in the three directions of the elastic element, 、 、 is the stress in three directions of the elastic body, E is the elastic modulus, is the Poisson's ratio, such as Figure 3 shown.

[0049] Establish an ultra-high pressure pipeline model such as Figure 4 As shown, take Figure 4 A tiny three-dimensional unit is shown in the box. Let the circumferential direction of the pipe be , the radial direction of the pipe section is , the axial direction of the pipe is , 、 Specific data can be obtained through strain testing. When the pipeline is in a free state, the axial stress of the pipeline is , eliminate and , substituting this boundary condition into formula 1, we can get formula 2:

[0050]

[0051] Eliminate Formula 2 The conversion form is formula 3:

[0052]

[0053] Therefore, it can be deduced that:

[0054]

[0055] According to the balance equation, geometric equation and physical equation of thick-walled pipe unit, the internal pressure and pipe surface stress can be expressed as follows:

[0056]

[0057] in is the outer diameter of the pipe, is the inner diameter of the pipe, P is the internal pressure of the pipe, and by combining Formula 3 and Formula 4, we can know that the relationship between the internal pressure of the pipe and the strain on the outer surface of the pipe when both ends are in a free state is Formula 5:

[0058]

[0059] When the size and material of the ultra-high pressure pipeline are known, the circumferential strain in formula 5 can be and axial strain Calculate the pressure inside the pipe changes.

[0060] Perform temperature testing to correct the pipeline pressure: Paste a resistance temperature sensor near the strain gauge to test the temperature changes of the intake and exhaust pipes respectively , according to the temperature change of the intake and exhaust pipes and the equivalent material linear expansion coefficient of the ultra-high pressure pipe , calculate the increased axial strain of the pipeline after the pipeline is thermally expanded ;

[0061] The pressure change in the intake and exhaust pipes is .

[0062] Plunger strain test (calibration test): Use the Figure 1The temperature self-compensating strain gauge is pasted by Figure 2 The method is to paste the piston in a full-bridge arrangement to test the axial strain of the piston when it is working in an ultra-high pressure cylinder. , then the plunger rod load is , where E is the elastic modulus of the plunger.

[0063] Pressure conversion: Refer to the compressor design manual to calculate the reciprocating inertia force of the plunger and reciprocating damping force , then the gas pressure change in the ultra-high pressure cylinder is ,in is the cross-sectional area of ​​the plunger.

[0064] Key phase test: stick a metal protrusion at a fixed point on the crankshaft, then use a wired eddy current sensor to align with the protrusion and test the time it takes for the compressor to rotate one circle. Assume that during the crankshaft rotation (360°), the pressure changes The time points of the four cylinder working processes (intake, compression, exhaust, and expansion) shown in the curve are marked as , Figure 5 As shown:

[0065] Respectively 、 、 、 The pressure change during a time period is named .

[0066] Find the pressure change in the intake and exhaust ducts: According to Find the intake and exhaust pipes at four time points The corresponding pressure changes in the two time periods , and according to the calculation formula of gas compression and expansion process, etc. .

[0067] Calculate the pressure change error based on the calibration results: The error in the cylinder intake and exhaust process calculated using the strain test system is: , these two errors include the valve opening pressure difference , , system measurement error 、 Equal error, because the opening pressure difference of the gas valve , They are all constants and can be obtained by calibrating the valve individually. Therefore, the test can be carried out at multiple different inlet and exhaust pressures to summarize the law of the change of the system measurement error. , The change curve of the strain test system is used to test the corrected pressure The changes should be:

[0068] ;

[0069] Calculate the error during cylinder compression and expansion as , based on the test results of multiple different intake and exhaust pressures, the calculation formula of gas compression and expansion process is continuously adjusted The k value and the const value, until Or it can be ignored, then:

[0070] .

[0071] Forming the PV diagram of the ultra-high pressure cylinder compression process: By time The PV diagram of the ultra-high pressure cylinder compression process is formed by combining them in sequence. Long-term monitoring of it can achieve the purpose of state monitoring of the ultra-high pressure cylinder working process.

[0072] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for monitoring the condition of an ultra-high pressure cylinder, characterized by: Including finite strain monitoring, temperature monitoring, key phase monitoring and plunger strain test calibration to correct monitoring errors for ultra-high pressure cylinder monitoring; The symmetrical outer surface of the pipe near the inlet and exhaust ports of the ultra-high pressure cylinder is polished and affixed with temperature self-compensating strain gauges. The strain gauges are connected using a Wheatstone bridge to measure the microstrain on the pipe surface, measuring the circumferential strain and axial strain of the pipe respectively. A resistance temperature sensor is attached near the strain gauge to measure the temperature change in the intake and exhaust ducts. Based on the temperature change in the intake and exhaust ducts and the equivalent material linear expansion coefficient of the ultra-high pressure duct, the increased axial strain in the duct due to thermal expansion is calculated, thereby deriving the pressure change in the ducts. Temperature self-compensating strain gauges are attached to the symmetrical outer surface of the plunger tail end, and a full-bridge arrangement is used to test the axial strain of the plunger when it is working in an ultra-high pressure cylinder. A metal protrusion is attached to a fixed point on the crankshaft, and a wired eddy current sensor is used to align with the protrusion to test the time it takes for the compressor to rotate one circle. According to the principles of elasticity, the isotropic generalized Hooke's law formula 1 is: in 、 、 is the strain in the three directions of the elastic element, 、 、 is the stress in three directions of the elastic body, E is the elastic modulus, is Poisson's ratio; Establish an ultra-high pressure pipeline model, take a small three-dimensional unit in the model, and let the circumferential direction of the pipeline be , the radial direction of the pipe section is , the axial direction of the pipe is , 、 Specific data can be obtained through strain testing. When the pipeline is in a free state, the axial stress of the pipeline is , eliminate and , substituting this boundary condition into formula 1, we can get formula 2: Eliminate Formula 2 The conversion form is formula 3: Therefore, it can be deduced that: According to the balance equation, geometric equation and physical equation of thick-walled pipe unit, the internal pressure and pipe surface stress can be expressed as follows: in is the outer diameter of the pipe, is the inner diameter of the pipe, P is the internal pressure of the pipe, and by combining Formula 3 and Formula 4, we can know that the relationship between the internal pressure of the pipe and the strain on the outer surface of the pipe when both ends are in a free state is Formula 5: When the size and material of the ultra-high pressure pipeline are known, the circumferential strain in formula 5 can be and axial strain Calculate the pressure inside the pipe changes; Temperature changes in the intake and exhaust ducts , according to the temperature change of the intake and exhaust pipes and the equivalent material linear expansion coefficient of the ultra-high pressure pipe , calculate the increased axial strain of the pipeline after the pipeline is thermally expanded ; The pressure change in the intake and exhaust pipes is .

2. The method for monitoring the state of an ultra-high pressure cylinder according to claim 1, wherein: Test the axial strain of the plunger when working in an ultra-high pressure cylinder , then the plunger rod load is , where E is the elastic modulus of the plunger.

3. The state monitoring method of an ultra-high pressure cylinder according to claim 2 is characterized in that: referring to Compressor Design Manual Calculation of the Reciprocating Inertia Force of the Plunger and reciprocating damping force , then the gas pressure change in the ultra-high pressure cylinder is ,in is the cross-sectional area of ​​the plunger.

4. The method for monitoring the state of an ultra-high pressure cylinder according to claim 1, wherein: During one crankshaft rotation, the pressure changes The four working processes of the cylinder shown in the curve are intake, compression, exhaust, and expansion, and the time points are marked as ; Respectively 、 、 、 The pressure change during a time period is named .

5. The method for monitoring the state of an ultra-high pressure cylinder according to claim 4, wherein: according to Find the intake and exhaust pipes at four time points The corresponding pressure changes in the two time periods , and according to the gas compression and expansion process calculation formula calculate .

6. The method for monitoring the state of an ultra-high pressure cylinder according to claim 5, characterized in that: The error in the cylinder intake and exhaust process calculated using the strain test system is: , these two errors include the valve opening pressure difference , , system measurement error 、 , because the opening pressure difference of the gas valve , They are all constants and can be obtained by calibrating the valve individually. Therefore, the test can be carried out at multiple different inlet and exhaust pressures to summarize the law of the change of the system measurement error. , The change curve of the strain test system is used to test the corrected pressure The changes should be: ； Calculate the error during cylinder compression and expansion as , based on the test results of multiple different intake and exhaust pressures, the calculation formula of gas compression and expansion process is continuously adjusted The k value and the const value, until Or it can be ignored, then: 。 7. The method for monitoring the state of an ultra-high pressure cylinder according to claim 6, characterized in that: Will By time The PV diagram of the ultra-high pressure cylinder compression process is formed by combining them in sequence. Long-term monitoring of it can achieve the purpose of state monitoring of the ultra-high pressure cylinder working process.

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