A measurement method for measuring the methanol concentration in flexible fuels

Abstract

The invention relates to a measurement method for measuring the methanol concentration in flexible fuels. Through calibration, by setting multiple thresholds, by reducing the influence of the electric field time, and by reducing the influence of temperature. The ultimate beneficial effects achieved are: a large measurement range, no polarization deviation of the solution, small measurement error, no occurrence of incorrect data, and high measurement accuracy; during calibration, the calibration environment is simplified, the calibration time is greatly reduced, the use of raw materials is saved, the testers are prevented from being exposed to methanol for a long time, and at the same time, the resolution of the sensor can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of engine fuel control, and particularly to a method for measuring the methanol concentration in flexible fuel. Background Art

[0002] Flexible fuel (a blend solution of methanol and gasoline) vehicles can meet the national and social demands for energy security and diversification. To be able to use various blends of flexible fuels (blend solutions of methanol, ethanol, and gasoline) and meet the increasingly stringent national motor vehicle pollutant emission standards poses a severe challenge to engine control.

[0003] There are many methods for detecting methanol concentration in the prior art, mainly including physical methods and chemical methods. For example, sensors made based on phenomena such as the concentration, intensity, sound velocity, light refraction, heat capacity, and temperature rise of methanol solutions; sensors designed using various membrane materials according to the law of the change in the resistance of the magic membrane caused by the measurement of methanol; these solutions are either suitable for laboratory environments or in the form of instruments and meters, with complex structures, large volumes, and high production costs, and are not suitable for mass applications in the automotive industry.

[0004] With the large-scale use of ethanol fuel in countries such as Brazil, Continental Automotive Systems has developed a sensor for detecting ethanol concentration; after testing, if applied to methanol solutions, this sensor can only meet the concentration range of 0 - 75% of methanol mixtures. The excess part cannot be detected; from their patent documents, it is known that they use the dielectric constant of ethanol solutions to determine the solution concentration, but this solution cannot be applied to methanol solutions to detect methanol mixtures with a concentration of 0 - 100%.

[0005] The dielectric constant refers to the ratio of the capacitance of a capacitor with a certain substance as the dielectric to the capacitance of the same capacitor in a vacuum. According to the dielectric constant of a substance, the polarity of polymer materials can be discriminated. Therefore, we can use this index to determine the content of methanol in the fuel.

[0006] According to the relationship formula between the dielectric constant and capacitance The dielectric constant ε can be calculated by measuring the capacitance value of a capacitor constructed by immersing the solution to be measured.

[0007] Currently, there are many methods for detecting capacitance values: for example, the oscillation frequency method, the reactance method, the constant current integration method, the Kelvin bridge, the reactance bridge measurement, the constant current charging oscillation method, the constant voltage discharge method, the comparison method, etc.; all of them observe voltage or use laws related to frequency.

[0008] However, the above methods are respectively applicable to measurements with different capacities and different precision requirements. Some are only applicable to static measurements, some are only applicable to dynamic measurements, and some are applicable to both dynamic and static measurements.

[0009] However, if the capacitance of a solution is to be measured, phenomena such as solution polarization, capacitance effect, and temperature characteristics will all affect the measurement accuracy. Therefore, the measurement accuracy using the above methods is not high.

[0010] Therefore, our company has developed a new method for measuring the methanol concentration in flexible fuels to avoid adverse effects and thus greatly improve the measurement accuracy. Summary of the Invention

[0011] The object of the present invention is to overcome the shortcomings of the prior art and provide a measurement method for measuring the methanol concentration in flexible fuels, which can improve the measurement accuracy, simplify the calibration environment, greatly reduce the calibration time, save the use of raw materials, prevent testers from coming into contact with methanol for a long time, and at the same time improve the resolution of the sensor.

[0012] The object of the present invention is achieved through the following technical solutions: A measurement method for measuring the methanol concentration in flexible fuels,

[0013] including the following steps:

[0014] S1. Construct a methanol concentration sensor, which includes an RC circuit and a capacitance part, and the capacitance part is placed in the methanol solution;

[0015] S2. Calibrate;

[0016] Apply a time excitation voltage to the RC circuit, and set more than 2 threshold voltages for the excitation voltage;

[0017] Measure the charging time of the methanol solution at different temperatures and different methanol concentration gradients under different threshold voltage conditions;

[0018] According to the measured values, establish a three-dimensional table related to the methanol concentration gradient, temperature gradient, and charging time under different threshold voltage conditions;

[0019] The charging time, that is, the time constant, is the time required for the voltage to rise from 0 to the lower threshold voltage during charging;

[0020] S3. Apply an excitation voltage to the RC circuit, set more than 2 threshold voltages for the excitation voltage, and sequentially measure the charging time under different threshold voltages from small to large;

[0021] Calculate the capacitance through the charging time, and reflect the concentration value through the capacitance;

[0022] S4. Configure a temperature sensor in the solution of S2 to measure the solution temperature;

[0023] Through the measured solution temperature, correct the concentration value in S3 by interpolation according to the three-dimensional table in S2.

[0024] Further, in S2 and S3, each time the charging time is collected, the excitation is withdrawn immediately after each excitation feedback reaches the preset threshold;

[0025] That is, the excitation voltage is released to reduce the time for the solution to be placed in the electric field.

[0026] Further, in S1, when the capacitor part in the RC circuit is constructed, it includes a sleeved outer diode and inner diode;

[0027] The outer diode and the inner diode are axially arranged, and the length of the outer diode is greater than that of the inner diode;

[0028] The distance between the outer diode and the inner diode is set to form a capacitor.

[0029] Further, when the calibration experiment is carried out in S2, methanol is filled into the capacitor part, and the capacitor part is placed in a temperature-adjustable box.

[0030] Further, when the calibration experiment is carried out in S2, the steps include:

[0031] S201. Configure methanol solutions with different concentration gradients and divide the temperature range into multiple temperature gradients;

[0032] S202. Apply an excitation voltage to the RC circuit, measure the charging time at different temperatures with the same methanol concentration, and form a two-dimensional data table related to methanol concentration - charging time;

[0033] S203. Apply an excitation voltage to the RC circuit, measure the charging time at different methanol concentrations at the same temperature, and form a two-dimensional data table related to methanol concentration - charging time;

[0034] S204. Combine the corresponding two-dimensional data tables in S202 and S203 to obtain a three-dimensional data table related to the charging time at different methanol concentrations and different temperatures;

[0035] S205. Change the threshold voltage value of the excitation voltage and measure the three-dimensional data tables obtained in the manner of S202 - S204 under conditions of more than 2 threshold voltages.

[0036] Preferably, in S201, the methanol concentration increases by one gradient every 10%, that is, the methanol concentration gradients are 0%, 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%;

[0037] In S201, the temperature gradient increases by one gradient every 5°C, that is, it is divided into -30°C, -25°C, -20, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C.

[0038] Further, when calibrating in S2, each threshold voltage corresponds to a three-dimensional table;

[0039] In S4, select the three-dimensional table corresponding to the threshold voltage with the highest resolution to correct the concentration value;

[0040] The threshold voltage with the highest resolution means that when other conditions change under this level threshold, the charging time changes significantly.

[0041] Further, the methanol concentration sensor:

[0042] Nest the outer tube and the inner tube together and fix them in the middle through insulating materials;

[0043] The outer tube is connected to the ground on the PCBA through a bonding wire, and the inner tube is connected to the circuit on the PCBA through a bonding wire. The inner tube is the anode;

[0044] The solution to be measured flows through the gap in the middle of the tube;

[0045] The PCBA circuit sends an excitation voltage to the anode tube, and a high level is output from a pin PT of the microprocessor to charge the inner tube through a resistor R2;

[0046] Another analog-to-digital conversion pin PA of the microprocessor collects the voltage at the connection end of the resistor R2 and C1 / / R1. When this voltage reaches the preset threshold value, the charging port outputs a low level to discharge;

[0047] When the T port outputs a high level, the timer starts to record, and when the PT port output is pulled low, the timing ends, and the charging time is calculated.

[0048] Further, the microprocessor inside the methanol concentration sensor, i.e., the MCU, will internally store three-dimensional maps under multiple threshold conditions, namely the temperature-time constant-concentration three-dimensional map;

[0049] The microprocessor substitutes the collected time constant τ, temperature t, and the threshold v used into the preset temperature-time constant-concentration three-dimensional map and looks up the concentration value in the table;

[0050] Since multiple thresholds are used, multiple concentration values will be obtained;

[0051] According to the obtained concentration value range, find the threshold voltage with high resolution in calibration as the priority;

[0052] According to the found priority threshold voltage, determine the concentration value corresponding to this priority threshold voltage.

[0053] It should be noted that:

[0054] First, in this solution, according to the formula the dielectric constant ε can be calculated; if an RC circuit is constructed and the time constant τ (τ = RC) of the RC circuit is collected to calculate the capacitance C (C = τ / R), then there is a linear relationship between the time constant τ and the dielectric constant ε, and the solution concentration can be characterized only by the time constant τ;

[0055] Since the solution to be measured is determined (0 - 100% methanol solution), the relationship between the concentration and the time constant is formed into a data table through laboratory calibration and stored in the FLASH of the sensor; during application, the time constant τ of the solution flowing through the sensor is collected, and the solution concentration is obtained by looking up the table; the problems of small measurement range and easy polarization deviation of the solution in the conventional scheme are solved;

[0056] Second, since the waveform for collecting the charging time constant of the methanol solution is as Figures 5 - 7 shown, only at the position of the threshold where the waveform slope is large can the collection accuracy be guaranteed; if the slope is too small, as Figure 7 shown, the circuit, external noise or solution flow noise will have a great impact on the sampled data (t fluctuates greatly);

[0057] Third, the capacitance of the low-concentration solution is small ( Figure 4 -MO), and the capacitance of the high-concentration solution is large ( Figure 4 -M100); in order to obtain a higher-precision resolution in the low-concentration range, a large threshold voltage is required ( Figure 4 -v3); if the threshold voltage is low, the low concentration cannot be distinguished. In order to obtain a higher-precision resolution in the high-concentration region, a small threshold voltage is required ( Figure 4 -v1); if the threshold voltage is high, the sampling slope is too small (as Figure 7 , V3), and it is difficult to obtain a high-precision resolution in the high-concentration range;

[0058] Therefore, more than 3 comparison level thresholds are set, and they are collected and tested in ascending order one by one. A concentration value is calculated for each threshold, so that a high-precision data source can be ensured in the entire concentration range, such as Figures 8 - 10 (time constants at different concentrations and different temperatures); Figure 11 The time constants at different thresholds at -30 degrees are shown in ; it can be seen that v3 has a high resolution when the concentration is 0 - 35%, v2 has a high resolution when the concentration is 35% - 70%, and v3 has a high resolution when the concentration is 70 - 100%;

[0059] Moreover, the time constants of the methanol solution at different temperatures, different concentrations and different thresholds are obtained through preliminary calibration experiments (as Figures 6 - 8 shown), and the applicable concentration intervals are divided for the multiple calculated concentration values ( Figure 12 );

[0060] After collecting the time constants at v1 / v2 / v3, their respective concentrations can be obtained by looking up a table ( Figures 8 - 10 ), and then through the internal decision-making mechanism, look up the table ( Figure 12 ) to confirm the final output concentration;

[0061] IV. Since the dielectric constant of the liquid solution has a behavior that changes with temperature, the same solution has different dielectric constants at different temperatures, that is, the measured time constants are different (such as Figures 7 - 10 ), Figures 7 - 10 records the time constants measured at different temperatures; the higher the concentration, the greater the influence of temperature on the time constant (such as Figure 13 );

[0062] Therefore, a temperature sensor is configured in the solution to obtain the solution temperature, and the temperature is used to correct the concentration calculation value; the time constants varying with temperature at each concentration are calibrated through experiments (such as Figures 8 - 10 ), the data is stored in the sensor, and interpolation operations are performed through table lookup during application to determine the concentration;

[0063] V. Since the solution will have a polarization phenomenon in the electric field, resulting in inaccurate collected data. The longer the time in the electric field, the deeper the polarization degree, and the larger the collected time constant. The polarization degree is positively correlated with the electric field strength and time;

[0064] Therefore, in this solution, τ is collected during the rising stage of the charging voltage. When the collection threshold is reached, the applied voltage is released to reduce the time the solution is in the electric field, reduce the polarization degree of the solution, and improve the measurement accuracy (such as Figures 5 - 7 );

[0065] VI. Since the acquisition circuit in the solution uses a comparison circuit, an interrupt signal is output in real time when the voltage touches the punctuation point, with a short response time and avoiding data errors caused by jitter;

[0066] Therefore, multiple comparison thresholds are used in this solution. Each threshold is tested sequentially, and after obtaining the data, it is analyzed and matched with the calibrated data stored in the MCU; since the linearity of the dielectric constant of the solution at different concentrations is different, the measurement accuracy in each concentration range can be guaranteed through this solution;

[0067] VII. In the solution, columnar diodes are used to construct a cylindrical capacitor. This solution is suitable for the installation of the fuel supply system and greatly reduces the influence of edge effects on the data;

[0068] The columnar capacitor in the solution is constructed by two diodes with different diameters and lengths. The outer diode is grounded and its length is greater than that of the inner diode, which can effectively protect the internal circuit of the sensor and is connected in series into the pipeline as part of the fuel supply system; the outer diode is both the pipeline and one electrode of the capacitor.

[0069] The present invention has the following advantages:

[0070] (1) It solves the problems of small measurement range and easy polarization deviation of the solution in the conventional measurement scheme;

[0071] (2) Through multiple threshold levels and calibration experiments at multiple threshold levels, the accuracy of the final methanol concentration is improved;

[0072] (3) It is less affected by temperature;

[0073] (4) It is less affected by the polarization of the solution in the electric field, improving the measurement accuracy;

[0074] (5) The response time is short, avoiding false data caused by jitter;

[0075] (6) The design of the capacitance part is suitable for the installation of the fuel supply system and greatly reduces the influence of edge effects on data;

[0076] (7) During the calibration test, multiple comparison points are selected for multiple tests to select appropriate comparison points; at the same time, it provides an arbitration basis for formal measurement to reduce measurement errors;

[0077] This calibration test method does not require the construction of a methanol solution circulation device. Only the methanol-gasoline mixed solution with the configured concentration needs to be filled into the sensor diode and placed in a temperature chamber, occupying very little space, as long as the sensor can be placed; in this way, we can calibrate multiple concentrations of methanol-gasoline mixed solutions simultaneously. And during the entire calibration process, we will control the charging time of the sensor diode and will not cause the solution to polarize, improving the calibration accuracy and ensuring the resolution of the sensor;

[0078] This calibration test method can test multiple concentrations of methanol-gasoline mixed solutions simultaneously, which can shorten the calibration time by 90%, saving time costs;

[0079] During the calibration test process, it is not necessary to replace the solution in the diode multiple times. Filling it once can complete the test of the entire calibration process, saving the loss of raw materials and reducing the time for testers to contact methanol, preventing testers from being exposed to methanol for a long time during the test and causing damage to the human body. Description of the Drawings

[0080] Figure 1 It is a schematic cross-sectional view of the radial section of the capacitance part of the methanol sensor;

[0081] Figure 2 It is a schematic cross-sectional view of the axial section of the capacitance part of the methanol sensor;

[0082] Figure 3 It is a schematic circuit diagram of the methanol sensor;

[0083] Figure 4 Schematic diagram of the excitation response waveform of the methanol sensor;

[0084] Figure 5 Waveform diagram of port PA under the V1 threshold at the same concentration;

[0085] Figure 6 Waveform diagram of port PA under the V2 threshold at the same concentration;

[0086] Figure 7 Waveform diagram of port PA under the V3 threshold at the same concentration;

[0087] Figure 8 Time constants at different concentrations and temperatures under the V1 threshold;

[0088] Figure 9 Time constants at different concentrations and temperatures under the V2 threshold;

[0089] Figure 10 Time constants at different concentrations and temperatures under the V3 threshold;

[0090] Figure 11 Time constants at different concentrations under the three thresholds of V1, V2, and V3 at a temperature of -30 degrees;

[0091] Figure 12 Table for threshold priority selection;

[0092] Figure 13 Variation of time constant at different temperatures under the V2 threshold. Detailed implementation mode

[0093] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0094] A measurement method for measuring the methanol concentration in flexible fuel, comprising the following steps:

[0095] S1. Construct a methanol concentration sensor, which includes an RC circuit and a capacitor part, and the capacitor part is placed in the methanol solution;

[0096] S2. Calibration experiment, comprising the following steps:

[0097] S201. Configure methanol solutions with concentration gradients of 0%, 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, and divide the temperature gradient into -30°C, -25°C, -20, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C;

[0098] S202. Apply an excitation voltage to the RC circuit. The threshold of this excitation voltage is V1. Measure the charging time at different temperatures for the same methanol concentration to form a two-dimensional data table related to methanol concentration - charging time;

[0099] S203. Apply an excitation voltage to the RC circuit. The threshold of this excitation voltage is V1. Measure the charging time at the same temperature for different methanol concentrations to form a two-dimensional data table related to methanol concentration - charging time;

[0100] S204. Integrate the corresponding two-dimensional data tables in S202 and S203 to obtain a three-dimensional data table related to different methanol concentrations at different temperatures and charging time under the V1 threshold, as Figure 8 shown;

[0101] S205. Change the threshold voltage of the excitation voltage to V2. In a similar manner to S202 - S204, measure a three-dimensional data table related to different methanol concentrations at different temperatures and charging time under the V2 threshold, as Figure 9 shown;

[0102] S206. Change the threshold voltage of the excitation voltage to V3. In a similar manner to S202 - S204, measure a three-dimensional data table related to different methanol concentrations at different temperatures and charging time under the V3 threshold, as Figure 10 shown;

[0103] Apply time excitation voltage to the RC circuit, and set three threshold voltages V1, V2, and V3 for the excitation voltage;

[0104] The charging time mentioned above, that is, the time constant, is the time required for the voltage to rise from 0 to the threshold voltage during charging;

[0105] It should be noted that in the above S1 and S2, as Figures 1 - 3 shown, when constructing the capacitor part, an outer diode and an inner diode are selected. The two diodes are nested together and fixed in the middle through an insulating material; the outer diode is connected to the ground on the PCBA through a bonding wire; the inner diode is a positive diode, and the positive diode is connected to the circuit on the PCBA through a bonding wire;

[0106] The solution to be measured flows through the gap in the middle of the diode; the PCBA circuit sends an excitation voltage to the positive diode, as Figure 3 shown, a high level is output from a pin PT port of the microprocessor (such as Figure 4 S1 / S2 / S3) through a resistor R2 to charge the positive diode ( Figure 2 sensor diode sectional view); another analog - to - digital conversion pin PA of the microprocessor collects the voltage at the connection end of the resistor R2 and C1 / / R1;

[0107] S3. Apply an excitation voltage to the RC circuit. The excitation voltage is set with three threshold voltages V1, V2, and V3, and measure the charging times at different threshold voltages in ascending order.

[0108] Calculate the capacitance based on the charging time, and reflect the concentration value through the capacitance.

[0109] Specifically, according to the formula the dielectric constant ε can be calculated; if an RC circuit is constructed and the time constant τ (τ = RC) of the RC circuit is collected to calculate the capacitance C (C = τ / R), then there is a linear relationship between the time constant τ and the dielectric constant ε, and only the time constant τ is needed to characterize the solution concentration.

[0110] S4. Configure a temperature sensor in the solution of S2 to measure the solution temperature.

[0111] Based on the measured solution temperature, correct the concentration value in S3 by interpolation according to the three-dimensional table in S2.

[0112] When correcting, select the three-dimensional table corresponding to the threshold voltage with the highest resolution to correct the concentration value.

[0113] The threshold voltage with the highest resolution means that when other conditions change under this level threshold, the charging time changes significantly.

[0114] Specifically, in S4, for the methanol concentration sensor, its internal microprocessor, i.e., the MCU, will internally store a three-dimensional map under the three threshold conditions of V1, V2, and V3, namely the temperature-time constant-concentration three-dimensional map.

[0115] During operation: The microprocessor substitutes the collected time constant τ, temperature t, and the threshold v used into the pre-set temperature-time constant-concentration three-dimensional map to look up the concentration value; since 3 thresholds (v1 / v2 / v3) are used, 3 concentration values will be obtained.

[0116] When correcting: According to the obtained concentration value range, find the threshold voltage with high resolution in the calibration as the priority; according to the found priority threshold voltage, determine the concentration value corresponding to this priority threshold voltage.

[0117] It should be noted that the selection of the priority refers to the selection of the threshold voltage with high resolution. For example, according to Figures 8 - 10 , it is known that the priority threshold for the concentration gradient of 0% - 30% is V3, the priority threshold for the concentration gradient of 40% - 60% is V2, and the priority threshold for the concentration gradient of 70% - 100% is V1. Then a threshold selection table can be established, as shown in Figure 12 shown.

[0118] In this embodiment, in S2 and S3, each time the charging time is collected, the excitation is withdrawn immediately after each excitation feedback reaches the preset threshold; that is, the excitation voltage is released to reduce the time for the solution to be placed in the electric field.

[0119] In this embodiment, in S1, when constructing the capacitance part of the RC circuit, it includes a sleeved outer diode and an inner diode; the outer diode and the inner diode are arranged coaxially, and the length of the outer diode is greater than that of the inner diode; the distance between the outer diode and the inner diode is set to form a capacitance.

[0120] In this embodiment, when performing the calibration experiment in S2, methanol is filled into the capacitance part, and the capacitance part is placed in a temperature-adjustable box.

[0121] The above embodiments only represent relatively preferred implementation manners, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A measurement method for measuring the methanol concentration in flexible fuel, characterized in that: It includes the following steps: S1. Construct a methanol concentration sensor, which includes an RC circuit and a capacitance part, and the capacitance part is placed in a methanol solution; S2. Calibration; Apply an excitation voltage to the RC circuit, and set more than 2 threshold voltages for the excitation voltage; Measure the charging time of the methanol solution at different temperatures and different methanol concentration gradients under different threshold voltage conditions; According to the measured values, establish a three-dimensional table related to the methanol concentration gradient, temperature gradient, and charging time under different threshold voltage conditions; The charging time, that is, the time constant, is the time required for the voltage to rise from 0 to the threshold voltage during charging; S3. Apply an excitation voltage to the RC circuit, set more than 2 threshold voltages for the excitation voltage, and sequentially measure the charging time at different threshold voltages from small to large; Calculate the capacitance through the charging time, and reflect the concentration value through the capacitance; S4. Configure a temperature sensor in the solution in S2 to measure the solution temperature; Correct the concentration value in S3 by interpolation according to the three-dimensional table in S2 through the measured solution temperature.

2. The measurement method for measuring the methanol concentration in flexible fuel according to claim 1, characterized in that: In S2 and S3, each time the charging time is collected, after each excitation feedback reaches the preset threshold, the excitation is immediately withdrawn; That is, release the excitation voltage to reduce the time for the solution to be placed in the electric field.

3. A measurement method for measuring the methanol concentration in flexible fuel according to claim 1, characterized in that: In S1, when constructing the capacitance part in the RC circuit, it includes a sleeved outer tube and inner tube; The outer tube and the inner tube are arranged coaxially, and the length of the outer tube is greater than that of the inner tube; The distance between the outer tube and the inner tube is set to form a capacitance.

4. A measurement method for measuring the methanol concentration in flexible fuel according to claim 3, characterized in that: When conducting the calibration experiment in S2, load methanol into the capacitance part and place the capacitance part in a temperature-adjustable box.

5. A measurement method for measuring the methanol concentration in flexible fuel according to claim 1, characterized in that: When conducting the calibration experiment in S2, the steps include: S201. Configure methanol solutions with different concentration gradients, and divide the temperature range into multiple temperature gradients; S202. Apply an excitation voltage to the RC circuit, measure the charging time at different temperatures with the same methanol concentration, and form a two-dimensional data table related to methanol concentration - charging time; S203. Apply an excitation voltage to the RC circuit, measure the charging time at different methanol concentrations at the same temperature, and form a two-dimensional data table related to methanol concentration - charging time; S204. Integrate the corresponding two-dimensional data tables in S202 and S203 to obtain a three-dimensional data table related to the charging time at different temperatures with different methanol concentrations; S205. Change the threshold voltage value of the excitation voltage, and measure the three-dimensional data tables obtained in the manner of S202 - S204 under more than 2 threshold voltage conditions.

6. A measurement method for measuring the methanol concentration in flexible fuel according to claim 5, characterized in that: In S201, the methanol concentration increases by one gradient every 10%, that is, the methanol concentration gradients are 0%, 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%; In S201, for the temperature gradient, it increases by one gradient every 5°C, that is, it is divided into -30°C, -25°C, -20, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C.

7. A measurement method for measuring the methanol concentration in flexible fuel according to claim 1, characterized in that: When calibrating in S2, each threshold voltage corresponds to a three-dimensional table; In S4, select the three-dimensional table corresponding to the threshold voltage with the highest resolution to correct the concentration value. The threshold voltage with the highest resolution means that when other conditions change under this threshold voltage, the charging time changes significantly.

8. A measurement method for measuring the methanol concentration in flexible fuel according to claim 3, characterized in that: The methanol concentration sensor described above: The outer tube and the inner tube are nested together and fixed in the middle by insulating materials; The outer tube is connected to the ground on the PCBA through a bonding wire, and the inner tube is connected to the circuit on the PCBA through a bonding wire. The inner tube is the anode; The solution to be measured flows through the gap in the middle of the tube; The PCBA circuit sends an excitation voltage to the anode tube, and a high level is output from a pin PT port of the microprocessor to charge the inner tube through a resistor R2; Another analog-to-digital conversion pin PA of the microprocessor collects the voltage at the connection end of the resistor R2 and C1 / / R1. When this voltage reaches the preset threshold voltage value, the charging port outputs a low level to discharge; When the PT port outputs a high level, the timer starts to record, and when the PT port output is pulled low, the timing ends, and the charging time is calculated.

9. A measurement method for measuring the methanol concentration in flexible fuel according to claim 8, characterized in that: In the methanol concentration sensor described above, the microprocessor inside, that is, the MCU, will build a three-dimensional map under multiple threshold voltage conditions, namely the temperature-time constant-concentration three-dimensional map; The microprocessor substitutes the collected time constant τ, temperature t, and the used threshold voltage v into the preset temperature-time constant-concentration three-dimensional map and looks up the table to obtain the concentration value; Since multiple threshold voltages are used, multiple concentration values will be obtained; According to the obtained concentration value range, find the threshold voltage with high resolution in the calibration as the priority; According to the found priority threshold voltage, determine the concentration value corresponding to this priority threshold voltage.

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