Device and method for accelerating acquisition of holding time of automotive LNG (Liquefied Natural Gas) cylinder

Abstract

The invention discloses a device and a method for accelerating acquisition of holding time of an automotive LNG (liquefied natural gas) cylinder, the device comprises a box body and a water cooling box, heat-conducting oil capable of immersing a to-be-detected cylinder is injected into the box body, a heating device and a thermometer are arranged in the box body, the heating device is used for heating the heat-conducting oil, and the thermometer is used for detecting the temperature of the heat-conducting oil; a temperature sensor and a pressure sensor are mounted in the to-be-detected gas cylinder and are respectively used for detecting the temperature and the pressure of an inner container of the to-be-detected gas cylinder; the bottom of the box body is connected with a cooling coil inlet in the water cooling box through a first pipeline, and a first stop valve is arranged on the first pipeline; an outlet of the cooling coil is connected with the box body through a second pipeline, and a circulating pump is arranged on the second pipeline. According to the invention, the LNG gas cylinder for the vehicle is uniformly heated by the conduction oil, the temperature is accurate and controllable, the theoretical pressure-time formula is further corrected by using the obtained data, the maintenance time data of the gas cylinder to be tested at normal temperature is obtained, and the whole test process is short in time consumption.

Description

Technical Field

[0001] The invention relates to a performance test of a vehicle LNG gas cylinder, and in particular to a device and a method for accelerating the acquisition of the maintenance time of a vehicle LNG gas cylinder. Background Art

[0002] The maintenance time test of vehicle LNG cylinders is designed to evaluate the ability of the cylinder to maintain working conditions under working conditions to ensure that its insulation performance can meet the requirements of maintaining the required pressure and temperature under long-term operation. The maintenance time test can optimize the structural design of vehicle LNG cylinders, improve insulation performance, and extend service life and efficiency. The maintenance time test is usually carried out at ambient temperature. During the test, the test piece is treated as a closed system (with neither medium input nor medium output). After the maximum volume of test medium allowed to be filled in the test piece (usually liquid nitrogen) is filled inside, the valve on the test piece pipeline that is connected to the atmosphere is closed, and the time it takes for the pressure in the inner tank of the test piece to rise from 0 to the action pressure of the pressure limiting device is recorded. The test process generally takes more than 10 days, which greatly prolongs the research and development cycle of vehicle LNG cylinders. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a device and method for accelerating the acquisition of the maintenance time of vehicle LNG cylinders in order to solve the problem that the maintenance time test of vehicle LNG cylinders takes a long time.

[0004] Technical solution: The device for accelerating the acquisition of the maintenance time of a vehicle LNG gas cylinder described in the present invention includes a box body and a water cooling box. Heat transfer oil capable of immersing the gas cylinder to be tested is injected into the box body. A heating device and a thermometer are arranged in the box body. The heating device is used to heat the heat transfer oil, and the thermometer is used to detect the temperature of the heat transfer oil. A temperature sensor and a pressure sensor are installed inside the gas cylinder to be tested, which are respectively used to detect the temperature and pressure of the inner tank of the gas cylinder to be tested. The bottom of the box body is connected to the cooling coil inlet in the water cooling box through a first pipeline, and a first stop valve is arranged on the first pipeline; the cooling coil outlet is connected to the box body through a second pipeline, and a circulating pump is arranged on the second pipeline.

[0005] Furthermore, a second stop valve and an oil storage tank are sequentially arranged on the second pipeline between the cooling coil outlet and the circulation pump.

[0006] Furthermore, circulating cooling water is connected to the water cooling box.

[0007] The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder of the present invention adopts the device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder, and the method comprises:

[0008] 1) The gas phase in the inner liner of the gas cylinder to be tested is simplified as an insulated fixed cavity filled with nitrogen, and the liquid phase is simplified as a gas source that absorbs external heat and vaporizes, and a theoretical model is established;

[0009] 2) The differential equations are derived:

[0010]

[0011] Among them, p is the pressure of the inner liner of the gas cylinder to be tested, which is obtained by the pressure sensor; θ is the temperature of the inner liner of the gas cylinder to be tested, which is obtained by the temperature sensor; t is the time; κ is the polytropic index, κ=1 in the isothermal process and κ=1.4 in the adiabatic process; G is the mass flow rate entering the cavity; R is the ideal gas constant; V is the volume of the gas phase space;

[0012] Substituting pressure, temperature and mass flow into the differential equations, we can obtain the theoretical pressure-time relationship p theory =f(t);

[0013] 3) The temperature of the heat transfer oil in the box is controlled to T1, the gas cylinder to be tested is immersed in the heat transfer oil, and the pressure data of the gas cylinder to be tested is collected at a time interval Δt during the process of the pressure increase Δp:

[0014] (t1, p 11 );(t2,p 12 );(t3,p 13 );(t4,p 14 );(t5,p 15 )……

[0015] Then through p theory =f(t), calculate the pressure data corresponding to the corresponding time under the theoretical state:

[0016] (t1, p 11 ');(t2,p 12 ');(t3,p 13 ');(t4,p 14 ');(t5,p 15 ')……

[0017] Take multiple sets of measured pressure-time data, and then take the pressure data at the corresponding time in the theoretical calculation, perform multi-point mapping, and calculate the mapping relationship p 1theory →p 1correction , and obtain the pressure-time correction formula p 1correction =f1(t);

[0018] According to the same method, the pressure-time correction formula p is obtained when the temperature of the heat transfer oil in the box is T2, T3... 2correction =f2(t);p 3correction =f3(t)……

[0019] 4) For any of the multiple pressure-time correction formulas, substitute the measured data of other groups at different temperatures for verification, and take the group with the smallest data fit. If the maximum error does not exceed the second set value, it is determined as the final pressure-time correction formula p correction =f(t); otherwise, return to step 3);

[0020] 5) Substitute the normal temperature data into the final pressure-time correction formula to obtain the maintenance time data of the gas cylinder to be tested at normal temperature.

[0021] Furthermore, in step 2), the derivation process of the differential equation system is as follows:

[0022] The state equation of nitrogen in the chamber is pV = mRθ, where m represents the mass of the gas;

[0023] Differentiating both sides of the state equation with respect to time yields in is the mass flow rate G entering the cavity, and the mass flow rate G can be reduced to the heat flow absorbed by the liquid phase And the latent heat of vaporization ΔHvap of liquid nitrogen is calculated; then the formula is expressed as:

[0024]

[0025] The state change of the gas in the cavity is a variable process. The original gas in the cavity is considered to be a closed mass system being compressed or expanded. Its state change is expressed as const is a constant; differentiate the formula and get:

[0026]

[0027] The differential equation group is obtained by combining equations (1) and (2) and then rearranging them.

[0028] Furthermore, the speed of liquid nitrogen vaporization is related to the heat flow absorbed by liquid nitrogen. related,

[0029] in The heat conduction between the cylinder shell and the inner liner, It is the radiant heat from the outside to the inner tank;

[0030]

[0031] Among them, λ is the thermal conductivity of the material between the shell and the liner, A is the thermal conductivity area, δ is the thermal conductivity thickness, ε is the emissivity of the object, and σ is the blackbody radiation constant. For the same gas cylinder to be tested, λ, A, δ, ε, and σ are all constants, and the heat flow Only the ambient temperature T0 and the temperature of the liquid nitrogen in the liner TN related;

[0032] The conversion formula of heat flow at different ambient temperatures is:

[0033]

[0034] in, is the heat flow at the test environment temperature; is the heat flow at the standard ambient temperature of 20°C; T0 is the test ambient temperature; T N The temperature of liquid nitrogen in the inner tank is -196℃.

[0035] Furthermore, in step 3), the method for controlling the temperature of the heat transfer oil includes: if the temperature of the heat transfer oil needs to be increased, turning on the heating device to heat the heat transfer oil; if the temperature of the heat transfer oil needs to be lowered, turning off the heating device, turning on the corresponding stop valve and the circulation pump, and allowing the heat transfer oil to circulate and cool through the water cooling box.

[0036] Furthermore, in step 3), the mapping relationship p is calculated 1theory →p 1correction ,include:

[0037] Solve the polynomial equation p 1correction =k 11 p theory +k 12 p theory 2 +k 13 p theory 3 +k 14 p theory 4 +k 15 p theory 5 …

[0038] Solve for the polynomial coefficient k 1n , n≤10, until p 1correction =f1(t) and the error between all the collected pressure data does not exceed the first set value. If the error exceeds the first set value, the next section of Δp pressure boost process data is taken and the data is reprocessed until the requirements are met.

[0039] Furthermore, the first set value is 3%.

[0040] Furthermore, Δp is 0.1 MPa; and the second set value is 5%.

[0041] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention uses heat transfer oil to uniformly heat the vehicle LNG cylinder, and the temperature is precisely controllable; further, the theoretical pressure-time formula is corrected using the obtained data to obtain the maintenance time data of the gas cylinder to be tested at room temperature. The entire test process is time-saving, easy to operate, and the test device can be reused. In addition to vehicle LNG cylinders, the present invention is also applicable to the maintenance time test of other vacuum insulation cryogenic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the structure of a device for accelerating acquisition of the maintenance time of a vehicle LNG cylinder provided by an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of a simplified model of a vehicle LNG cylinder liner according to an embodiment of the present invention;

[0044] Figure 3 This is a flowchart of a method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder provided by an embodiment of the present invention;

[0045] Figure 4 It is a pressure-time curve diagram of the inner liner of a theoretical model gas cylinder at a heat transfer oil temperature of 200° C. in an embodiment of the present invention;

[0046] Figure 5 It is a graph showing the change of the pressure data actually measured over time at a heat transfer oil temperature of 200° C. in an embodiment of the present invention;

[0047] Figure 6 It is a comparison diagram of the theoretical pressure rise curve and the measured pressure-time data at a heat transfer oil temperature of 200° C. in an embodiment of the present invention;

[0048] Figure 7 It is a pressure-time curve diagram of the inner liner of the modified model gas cylinder at a heat transfer oil temperature of 200° C. in an embodiment of the present invention;

[0049] Figure 8 It is a comparison diagram of the theoretical pressure rise curve and the measured pressure-time data at a heat transfer oil temperature of 100° C. in an embodiment of the present invention;

[0050] Fig. 9 It is a comparison diagram of the theoretical pressure rise curve and the measured pressure-time data at a heat transfer oil temperature of 300° C. in an embodiment of the present invention;

[0051] Fig.10 It is a theoretical boost curve diagram at standard ambient temperature (20° C.) in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the accompanying drawings.

[0053] Attached Figures 1 to 10 The reference numerals in the figures are as follows:

[0054] 1. Gas cylinder to be tested; 2. Temperature sensor; 3. Pressure sensor; 4. Box; 5. Heat transfer oil; 6. Thermometer; 7. Heating device; 8. First stop valve; 9. Water cooling box; 10. Second stop valve; 11. Oil storage tank; 12. Circulation pump.

[0055] like Figure 1 As shown, an embodiment of the present invention provides a device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder, comprising a box body 4 and a water cooling box 9, a heat transfer oil 5 capable of immersing the gas cylinder 1 to be tested is injected into the box body 4, a heating device 7 and a thermometer 6 are arranged in the box body 4, wherein the heating device 7 is used to heat the heat transfer oil 5, and the thermometer 6 is used to detect the temperature of the heat transfer oil 5. In this embodiment, the boiling point of the heat transfer oil 5 is 300°C, and the heating device 7 can be an electric heating wire.

[0056] A temperature sensor 2 and a pressure sensor 3 are installed inside the gas cylinder 1 to be tested, which are used to detect the temperature and pressure of the inner tank of the gas cylinder 1 to be tested respectively. The sensors are connected to a signal acquisition device (single chip microcomputer, PLC or data acquisition card) to record data.

[0057] The bottom of the box body 4 is connected to the cooling coil inlet in the water cooling box 9 through a first pipeline, a first stop valve 8 is provided on the first pipeline, and circulating cooling water is connected to the water cooling box 9. The cooling coil outlet is connected to the box body 4 through a second pipeline, and a second stop valve 10, an oil storage tank 11 and a circulating pump 12 are sequentially provided on the second pipeline.

[0058] The heat transfer oil 5 is initially pumped from the oil storage tank 11 to the box body 4 through the circulation pump 12. After the test, the heat transfer oil 5 in the box body 4 is discharged into the oil storage tank 11 for use in the next test. The circulation pump 12 is also used to realize the circulation cooling of the heat transfer oil 5 in the box body 4. The stop valve is used to realize the on-off of the corresponding pipeline.

[0059] During the test, if the temperature of the heat transfer oil 5 needs to be increased, the heating device 7 is turned on to heat the heat transfer oil 5; if the temperature of the heat transfer oil 5 needs to be reduced, the heating device 7 is turned off, the first stop valve 8, the second stop valve 10 and the circulation pump 12 are turned on, and the heat transfer oil 5 is circulated and cooled through the water cooling box 9. The temperature control process is realized by interlocking control based on the data detected by the thermometer 6.

[0060] like Figure 3 As shown, the embodiment of the present invention also provides a method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder, comprising the following steps:

[0061] 1) Establish a theoretical model

[0062] Figure 2The figure shows a simplified model schematic diagram of the inner liner of a vehicle LNG gas cylinder. The inside of the gas cylinder is divided into two parts: gas phase and liquid phase. Because the volume ratio of liquid nitrogen to nitrogen is 1:648, only a very small part of the liquid nitrogen needs to be vaporized to make the gas phase pressure reach the limited pressure for maintaining the experiment, and the compressibility of liquid nitrogen is very small, so the gas phase part in the inner liner of the gas cylinder 1 to be tested can be simplified to an insulated fixed cavity filled with nitrogen, and the liquid phase part can be simplified to a gas source that absorbs external heat and vaporizes.

[0063] 2) Calculate the theoretical data of the increase of internal pressure of the gas cylinder over time

[0064] The state equation of nitrogen in the cavity is pV=mRθ; p is the inner tank pressure of the gas cylinder 1 to be tested, which is obtained by the pressure sensor 3; V is the volume of the gas phase space, which is a fixed value for the same gas cylinder 1 to be tested; m represents the gas mass, m=nM, where n is the amount of substance and M is the molar mass; R is the ideal gas constant; θ is the inner tank temperature of the gas cylinder 1 to be tested, which is obtained by the temperature sensor 2;

[0065] Differentiating both sides of the state equation with respect to time yields in is the mass flow rate G entering the cavity, and the mass flow rate G can be reduced to the heat flow absorbed by the liquid phase And the latent heat of vaporization ΔHvap of liquid nitrogen (can be known through the latent heat of vaporization query table); then the formula is expressed as:

[0066]

[0067] When the state change of the gas in the cavity is a variable process, although the gas enters the control body (which is a cavity equivalent to the gas phase space), the original gas in the cavity can be considered as a closed mass system being compressed or expanded, and its state change is expressed as κ is a polytropic index, κ = 1 in isothermal process, κ = 1.4 in adiabatic process; const is a constant; differentiate the formula to obtain:

[0068]

[0069] After combining equations (1) and (2), we can get the differential equation system:

[0070]

[0071] Where, t is time;

[0072] It can be seen from the differential equations that the pressure rise rate is not only affected by the initial pressure p and the initial temperature θ, but also by the mass flow rate G entering the cavity. In the simplified theoretical model, the mass flow rate G is the gasification mass of liquid nitrogen in the liquid phase per unit time. The speed of liquid nitrogen vaporization is related to the heat flow absorbed by the liquid nitrogen. related,

[0073] Heat flow Mainly due to the heat conduction between the cylinder shell and the inner liner And the radiant heat from the outside to the inner tank composition:

[0074]

[0075] Among them, λ is the thermal conductivity of the material between the shell and the liner, A is the thermal conductive area, δ is the thermal conductive thickness, ε is the emissivity of the object, and σ is the blackbody radiation constant; for the same gas cylinder 1 to be tested, λ, A, δ, ε, and σ are all constants, so the heat flow Only the ambient temperature T0 and the temperature of the liquid nitrogen in the liner T N related.

[0076] The conversion formula of heat flow at different ambient temperatures is:

[0077]

[0078] in, is the heat flow at the test environment temperature; is the heat flow at the standard ambient temperature of 20°C; T0 is the test ambient temperature; T N The temperature of liquid nitrogen in the inner tank is -196℃.

[0079] The higher the ambient temperature T0, the greater the heat flow between the outside and the inner tank. The larger it is, the greater the nitrogen mass flow rate G entering the liquid phase cavity will be, which can accelerate the test.

[0080] Substituting pressure, temperature and mass flow into the differential equations, we can obtain the theoretical pressure-time relationship p theory =f(t).

[0081] 3) Obtain pressure change data through experiments, correct the theoretical pressure-time formula, and reduce experimental errors.

[0082] According to the above analysis, the pressure-time relationship in the gas cylinder under the theoretical model can be calculated through a group of differential equations. However, there is definitely a deviation between the theoretical calculation and the actual test results. Therefore, the theoretical data is corrected through test data to make the calculation formula results closer to the actual situation.

[0083] 3.1) The temperature of the heat transfer oil 5 in the box 4 is controlled to 200°C. Figure 4The pressure-time curve of the inner liner of the theoretical model gas cylinder at a heat transfer oil temperature of 200°C is shown, which is obtained through the aforementioned differential equations. The gas cylinder 1 to be tested is immersed in the heat transfer oil 5, and the pressure increase data of the inner liner of the gas cylinder 1 to be tested is collected at a time interval Δt during the process of the pressure increase of 0.1Mpa, as shown in Figure 5 shown. Figure 6 Shown Figure 4 and Figure 5 From the data combination, it can be seen that there is still a difference between the theoretical pressure rise curve and the actual pressure data, so the measured pressure value is taken:

[0084] (t1, p 21 );(t2,p 22 );(t3,p 23 );(t4,p 24 );(t5,p 25 )……

[0085] Then through p theory =f(t), calculate the pressure data corresponding to the corresponding time under the theoretical state:

[0086] (t1, p 21 ');(t2,p 22 ');(t3,p 23 ');(t4,p 24 ');(t5,p 25 ')……

[0087] Take multiple sets of measured pressure-time data, and then take the pressure data at the corresponding time in the theoretical calculation, perform multi-point mapping, and calculate the mapping relationship p 2theory →p 2correction , and obtain the pressure-time correction formula p 2correction =f2(t);

[0088] Solve the polynomial equation p 2correction =k 21 p theory +k 22 p theory 2 +k 23 p theory 3 +k 24 p theory 4 +k 25 p theory 5 …

[0089] Solve for the polynomial coefficient k 2n , n≤10, until p 2correction=f2(t) and the error between all the collected pressure data shall not exceed 3%. If the error exceeds 3%, continue to take the next 0.1Mpa pressure boost process data and reprocess the data until the requirements are met. Figure 7 The figure shows the pressure-time curve of the modified model gas cylinder liner at a heat transfer oil temperature of 200°C.

[0090] 3.2) Figure 8 The figure shows that the temperature of the heat transfer oil 5 in the box 4 is controlled to 100° C., and the time-pressure data of the gas cylinder liner under the actual state is compared with the theoretical pressure increase curve.

[0091] Take the measured pressure value:

[0092] (t1, p 11 );(t2,p 12 );(t3,p 13 );(t4,p 14 );(t5,p 15 )……

[0093] Then through p theory =f(t), calculate the pressure data corresponding to the corresponding time under the theoretical state:

[0094] (t1, p 11 ');(t2,p 12 ');(t3,p 13 ');(t4,p 14 ');(t5,p 15 ')……

[0095] Take multiple sets of measured pressure-time data, and then take the pressure data at the corresponding time in the theoretical calculation, perform multi-point mapping, and calculate the mapping relationship p 1theory →p 1correction , and obtain the pressure-time correction formula p 1correction =f1(t);

[0096] Solve the polynomial equation p 1correction =k 11 p theory +k 12 p theory 2 +k 13 p theory 3 +k 14 p theory 4 +k 15 p theory 5 …

[0097] Solve for the polynomial coefficient k 1n, n≤10, until p 1correction = The error between f1(t) and all the collected pressure data shall not exceed 3%. If the error exceeds 3%, the next 0.1Mpa pressure boost process data will be taken and the data will be reprocessed until the requirements are met.

[0098] 3.3) Fig. 9 It is shown that the temperature of the heat transfer oil 5 in the box 4 is controlled to 300° C., and the time-pressure data of the inner liner of the gas cylinder under the actual state is compared with the theoretical pressure increase curve.

[0099] Take the measured pressure value:

[0100] (t1, p 31 );(t2,p 32 );(t3,p 33 );(t4,p 34 );(t5,p 35 )……

[0101] Then through p theory =f(t), calculate the pressure data corresponding to the corresponding time under the theoretical state:

[0102] (t1, p 31 ');(t2,p 32 ');(t3,p 33 ');(t4,p 34 ');(t5,p 35 ')……

[0103] Take multiple sets of measured pressure-time data, and then take the pressure data at the corresponding time in the theoretical calculation, perform multi-point mapping, and calculate the mapping relationship p 3theory →p 3correction , and obtain the pressure-time correction formula p 3correction =f3(t);

[0104] Solving polynomial equations: p 3correction =k 31 p theory +k 32 p theory 2 +k 33 p theory 3 +k 34 p theory 4 +k 35 p theory 5 …

[0105] Solve for the polynomial coefficient k 3n , n≤10, until p 3correction=f3(t) and the error between all the collected pressure data shall not exceed 3%. If the error exceeds 3%, the next 0.1Mpa pressure boost process data shall be taken and the data shall be reprocessed until the requirements are met.

[0106] The corrected pressure-time relationship of the cylinder after the accelerated test at different temperatures is obtained:

[0107] p 1correction =f1(t)

[0108] p 2correction =f2(t)

[0109] p 3correction =f3(t)

[0110] 4) For any of the three pressure-time correction formulas, substitute the measured data of the other two groups at different temperatures for verification, and take the group with the smallest data fit. If the maximum error does not exceed 5%, it is determined as the final pressure-time correction formula p correction =f(t); otherwise, return to step 3);

[0111] 5) Substitute the normal temperature data into the final pressure-time correction formula to obtain the maintenance time data of the gas cylinder 1 to be tested at normal temperature.

[0112] Substituting the mass flow rate G, initial pressure p and initial temperature θ at room temperature into the modified model, the pressure-time relationship inside the gas cylinder at room temperature can be obtained, as follows: Fig.10 shown.

Claims

1. A device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder, characterized in that: The invention comprises a box (4) and a water cooling box (9), wherein heat transfer oil (5) capable of immersing a gas cylinder (1) to be tested is injected into the box (4), and a heating device (7) and a thermometer (6) are arranged in the box (4), wherein the heating device (7) is used to heat the heat transfer oil (5), and the thermometer (6) is used to detect the temperature of the heat transfer oil (5); a temperature sensor (2) and a pressure sensor (3) are installed inside the gas cylinder (1) to be tested, and are used to detect the temperature and pressure of the inner liner of the gas cylinder (1) to be tested respectively; the bottom of the box (4) is connected to the inlet of the cooling coil in the water cooling box (9) through a first pipeline, and a first stop valve (8) is arranged on the first pipeline; the outlet of the cooling coil is connected to the box (4) through a second pipeline, and a circulating pump (12) is arranged on the second pipeline.

2. The device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 1 is characterized in that: A second stop valve (10) and an oil storage tank (11) are sequentially arranged on a second pipeline between the cooling coil outlet and the circulation pump (12).

3. The device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 1 is characterized in that: Circulating cooling water is connected to the water cooling box (9).

4. A method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder, characterized in that: The device for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to any one of claims 1 to 3 is used, and the method comprises: 1) Simplify the gas phase part in the inner liner of the gas cylinder (1) to be tested into an insulated fixed cavity filled with nitrogen, and simplify the liquid phase part into a gas source that absorbs external heat and vaporizes, and establish a theoretical model; 2) The differential equations are derived: Wherein, p is the inner pressure of the gas cylinder (1) to be tested, which is obtained by the pressure sensor (3); θ is the inner temperature of the gas cylinder (1) to be tested, which is obtained by the temperature sensor (2); t is time; κ is the polytropic index, κ=1 in the isothermal process and κ=1.4 in the adiabatic process; G is the mass flow rate entering the cavity; R is the ideal gas constant; V is the volume of the gas phase space; Substituting pressure, temperature and mass flow into the differential equations, we can obtain the theoretical pressure-time relationship p theory =f(t); 3) The temperature of the heat transfer oil (5) in the box (4) is controlled to be T1, the gas cylinder (1) to be tested is immersed in the heat transfer oil (5), and the data of the pressure increase over time during the process of the inner tank pressure of the gas cylinder (1) to be tested increasing by Δp is collected at a time interval Δt: (t1,p 11 );(t2,p 12 );(t3,p 13 );(t4,p 14 );(t5,p 15 )…… Then through p theory =f(t), calculate the pressure data corresponding to the corresponding time under the theoretical state: (t1,p 11 ’);(t2,p 12 ’);(t3,p 13 ’);(t4,p 14 ’);(t5,p 15 ’)…… Take multiple sets of measured pressure-time data, and then take the pressure data at the corresponding time in the theoretical calculation, perform multi-point mapping, and calculate the mapping relationship p 1theory →p 1correction , and obtain the pressure-time correction formula p 1correction =f1(t); According to the same method, the pressure-time correction formula p is obtained when the temperature of the heat transfer oil (5) in the box (4) is T2, T3, etc. 2correction =f2(t);p 3correction =f3(t)…… 4) For any of the multiple pressure-time correction formulas, substitute the measured data of other groups at different temperatures for verification, and take the group with the smallest data fit. If the maximum error does not exceed the second set value, it is determined as the final pressure-time correction formula p correction =f(t); otherwise, return to step 3); 5) Substitute the normal temperature data into the final pressure-time correction formula to obtain the maintenance time data of the gas cylinder (1) to be tested at normal temperature.

5. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 4, characterized in that: In step 2), the derivation process of the differential equation system is as follows: The state equation of nitrogen in the chamber is pV = mRθ, where m represents the mass of the gas; Differentiating both sides of the state equation with respect to time yields in is the mass flow rate G entering the cavity, and the mass flow rate G can be reduced to the heat flow absorbed by the liquid phase And the latent heat of vaporization ΔHvap of liquid nitrogen is calculated; then the formula is expressed as: The state change of the gas in the cavity is a variable process. The original gas in the cavity is considered to be a closed mass system being compressed or expanded. Its state change is expressed as const is a constant; differentiate the formula and get: The differential equation group is obtained by combining equations (1) and (2) and then rearranging them.

6. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 5, characterized in that: The speed of liquid nitrogen vaporization and the heat flow absorbed by liquid nitrogen related, in The heat conduction between the cylinder shell and the inner liner, It is the radiant heat from the outside to the inner tank; Among them, λ is the thermal conductivity of the material between the shell and the liner, A is the thermal conductive area, δ is the thermal conductive thickness, ε is the emissivity of the object, and σ is the blackbody radiation constant. For the same gas cylinder to be tested (1), λ, A, δ, ε, and σ are all constants. The heat flux Only the ambient temperature T0 and the temperature of the liquid nitrogen in the liner T N related; The conversion formula of heat flow at different ambient temperatures is: in, is the heat flow at the test environment temperature; is the heat flow at the standard ambient temperature of 20°C; T0 is the test ambient temperature; T N The temperature of liquid nitrogen in the inner tank is -196℃.

7. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 4, characterized in that: In step 3), the method for controlling the temperature of the heat transfer oil (5) comprises: if the temperature of the heat transfer oil (5) needs to be increased, the heating device (7) is turned on to heat the heat transfer oil (5); if the temperature of the heat transfer oil (5) needs to be reduced, the heating device (7) is turned off, and the corresponding stop valve and the circulation pump (12) are turned on to allow the heat transfer oil (5) to be circulated and cooled through the water cooling box (9).

8. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 4, characterized in that: In step 3), the mapping relationship p is calculated 1theory →p 1correction ,include: Solve the polynomial equation p 1correction =k 11 p theory +k 12 p theory 2 +k 13 p theory 3 +k 14 p theory 4 +k 15 p theory 5 … Solve for the polynomial coefficient k 1n , n≤10, until p 1correction =f1(t) and the error between all the collected pressure data does not exceed the first set value. If the error exceeds the first set value, the next section of Δp pressure boost process data is taken and the data is reprocessed until the requirements are met.

9. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 8, characterized in that: The first set value is 3%.

10. The method for accelerating the acquisition of the maintenance time of a vehicle LNG cylinder according to claim 8, characterized in that: Δp is 0.1 MPa; the second set value is 5%.

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