CN106546632B - Device and method for measuring ion concentration distribution in combustion field - Google Patents
Device and method for measuring ion concentration distribution in combustion field Download PDFInfo
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Abstract
The device and the method for measuring the ion concentration distribution in the combustion field are based on measuring the ion current change distribution in the combustion field to obtain the ion concentration distribution at different positions in the combustion field, can well solve the problem of measuring the ion concentration distribution at different positions in the oscillatory combustion process, have low cost, small volume and convenient installation, and are suitable for various hydrocarbon fuel combustion devices. The device comprises an ion probe module and a measuring circuit module, wherein the ion probe module is used for acquiring an ion current signal of dynamic flame in a combustion field; and the measurement circuit module is used for measuring and processing the ion current signal acquired by the ion probe module and obtaining the change of the ion concentration in the combustion field by measuring the change of the ion current.
Description
Technical Field
The invention relates to a device and a method for measuring ion concentration distribution in a combustion field, which are mainly applied to monitoring the combustion process of combustion devices in various engine combustion chambers or other fields.
Background
In the development of rocket engines, aircraft engines, modern large gas turbines, or other large combustion devices, combustion instability problems are often encountered. Unstable combustion can cause extremely high combustion rate and heat transfer efficiency, resulting in burn-through of the wall surface of the combustion chamber; meanwhile, the vibration can cause violent vibration, damage the mechanical structure of the device and influence the normal work of a power system. There are difficulties in experimental measurement due to the complexity and unpredictability of the combustion instability problem. When unstable combustion occurs, physical and chemical parameters in flame can change rapidly along with time and space, so that a sensor with high frequency response and high space identification degree is needed to monitor a combustion field.
The main means used for monitoring the combustion field of the combustion chamber at present is optical measurement, but the optical measurement light path is complex, the device price is high, the requirements on the test environment and experimental operators are high, and the operation is inconvenient. Most optical measurements give average information on the measurement light path, and lack sufficient spatial discrimination, so a measurement technique with good spatial discrimination for the oscillating combustion field, simple operation and low cost is required. The invention has high frequency, small volume and simple structure, can be arranged at different positions in a combustion chamber, has better spatial identification, and has important significance for deeply researching the combustion instability mechanism and controlling the combustion instability phenomenon.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a device and a method for measuring the ion concentration distribution in a combustion field, which can well solve the problem of measuring the ion concentration distribution at different positions in the oscillating combustion process, have low cost, small volume and convenient installation and are suitable for various hydrocarbon fuel combustion devices.
The technical scheme of the invention is as follows:
1. a measuring device for ion concentration distribution in a combustion field is characterized by comprising an ion probe module and a measuring circuit module, wherein:
the ion probe module is used for acquiring an ion current signal of dynamic flame in a combustion field;
and the measurement circuit module is used for measuring and processing the ion current signal acquired by the ion probe module and obtaining the change of the ion concentration in the combustion field by measuring the change of the ion current.
2. The relation calculation formula of the ion current and the ion concentration acquired by the ion probe is as follows:
wherein [ H ]3O+]Is ion concentration, r is probe electrode radius, e is unit charge capacity, U is ion probe interelectrode voltage, δ is interelectrode gap,
is the mean free path of electrons in the gas, κ is the Boltzmann constant, T is the absolute temperature, meIs the electron mass.
3. The ion probe module comprises an ion probe, a probe insulating tube, an insulating tube sleeve and a probe mounting seat, wherein the ion probe is embedded into the probe insulating tube in an interference fit manner; the probe insulating tube is arranged in an insulating tube sleeve, and the insulating tube sleeve is fixed on the probe mounting seat through a fastening nut; the ion probe adopts a three-probe structure, wherein two probes are used as electrodes for measuring ion current, ion induction ends of the two probes extend out of a probe insulating tube, the other probe is used for eliminating the temperature difference potential of the probe, and the probe is sealed in the probe insulating tube and isolated from flame; the three probes have output leads at their ends for connection to a measurement circuit.
4. The ion probe and the probe insulating tube are cylindrical, and the length-to-outer diameter ratio of the probe insulating tube is larger than 10:1 so as to reduce the end effect as much as possible.
5. The diameter ratio of the length of the ion induction ends of the two probe electrodes extending out of the insulating tube and the insulating tube for measuring the ion current is not less than 1:10, the distance between the two probe electrodes is not more than 1mm, and the distance between the other probe electrode sealed in the insulating tube and the end face of the insulating tube for eliminating the temperature difference potential of the ion induction end electrode is not more than 2 mm.
6. The measuring circuit module comprises a preamplifier circuit and a filter circuit, and a measuring signal output by the ion probe is amplified by the preamplifier circuit and is connected to the filter circuit to eliminate noise.
7. The pre-amplification circuit comprises a measuring bridge and an instrument amplifier, wherein two ends of one bridge arm of the measuring bridge are respectively connected with output end leads of two probes for collecting ion current, and two output ends of the measuring bridge are respectively connected with a positive input end and a negative input end of the instrument amplifier; the output end lead of the third probe for eliminating the temperature difference potential is connected to the negative input end of the amplifier and is used for balancing the temperature difference potential generated by the two probes for collecting the ion current; the instrument amplifier is also externally connected with a gain adjusting resistor and used for amplifying the measuring signals collected by the ion probe.
8. The filter circuit comprises a power frequency wave trap and a low-pass filter, the power frequency wave trap is used for filtering power frequency interference, and a double-T-shaped circuit structure with adjustable quality factors is adopted; the low-pass filter is used for filtering broadband noise except for useful signals, and an active filter chip is adopted, so that the cut-off working frequency of the active filter chip is adjustable.
9. The method for measuring the ion concentration distribution in the combustion field by adopting the measuring device is characterized in that the method is used for obtaining the ion concentration distribution at different positions in the combustion field based on the measurement of the ion current change distribution in the combustion field, and comprises the following steps:
1) disposing a plurality of ion probe modules at different locations in a combustion field;
2) when combustion occurs, the ion probe module collects ion current change signals at different positions in a combustion field; the measurement circuit module amplifies and filters the ion current signal, and the ion current signal is output by data acquisition and display equipment to obtain ion current distribution at different positions in the combustion field;
3) and obtaining the spatial distribution of the ion concentration at different positions in the combustion field according to the relational expression of the ion current and the ion concentration.
10. The step 2) comprises the step of calibrating before the probe is used:
during calibration, a plurality of probes are placed in a small area in a combustion chamber for simultaneous measurement; FFT analysis is carried out on the measurement signal to obtain the amplitude of the ion concentration oscillation main frequency; obtaining the proportional relation of the ion concentration and amplitude results measured by different probes; by selecting one probe result as a standard, the measurement results of different probes can be unified.
The invention has the technical effects that:
the invention provides a device and a method for measuring ion concentration distribution in a combustion field, which can well solve the problem of measuring the ion concentration distribution at different positions in the oscillatory combustion process and are mainly used for monitoring the combustion process in various engine combustion chambers or combustion devices in other fields. The device is based on measuring ion current variation distribution in the combustion field to obtain ion concentration distribution at different positions in the combustion field. The measuring device consists of an ion probe and a measuring circuit, wherein the ion probe is used for collecting the change of ion current, and the measuring circuit is used for amplifying and filtering the collected signals. The device has the advantages of sensitive reaction to the combustion dynamic heat release process, high dynamic response speed, simple structure, low cost, small volume, convenient installation and good measurement effect, and is suitable for various hydrocarbon fuel combustion devices.
Drawings
FIG. 1 is a schematic view of the principle of the measuring device of the present invention
FIG. 2 Structure of ion Probe
FIG. 3 is a pre-amplifier circuit diagram
FIG. 4 circuit diagram of power frequency trap
FIG. 5 is a circuit diagram of a low pass filter
FIG. 6 is a schematic view showing the measurement of ion concentration distribution in a combustion chamber of a pulsating burner according to the present invention
FIG. 7 ion probe calibration installation diagram
FIG. 8 time series of pressure sensor and ion probe measurement signals
FIG. 9 FFT results of measurement signals of ion probe
The reference numbers are listed below: 1-ion probe, 2-probe insulating tube, 3-insulating tube sleeve, 4-probe mounting seat, 5-fastening nut and 6-output lead; 10-combustion chamber, 11-fuel nozzle, 12-fuel valve, 13-igniter, 14-air valve, 15-pressure regulator, 16-pressure sensor, 17-combustion chamber tail pipe, 18-blower, 19-ion probe module, 20-measuring circuit module.
Detailed Description
The following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings, but not intended to limit the scope of the invention.
A measurement device for ion concentration distribution in a combustion field, comprising an ion probe module and a measurement circuit module, wherein: the ion probe module is used for acquiring an ion current signal of dynamic flame in a combustion field; and the measurement circuit module is used for measuring and processing the ion current signal acquired by the ion probe module and obtaining the change of the ion concentration in the combustion field by measuring the change of the ion current.
Fig. 1 is a schematic diagram of the measuring device of the present invention. When the gas in the combustion chamber is combusted, the gas is ionized to generate a large amount of charged particles such as free electrons, positive ions, negative ions, free radicals and the like. When the ion probe with the bias voltage U is extended into the combustion field, a weak ion current is formed between the two probe electrodes. The change of the ion current is measured by a measuring circuit connected with the probe, so that the change rule of the concentration of the main ions in the combustion chamber can be obtained.
The calculation formula of the relationship between the ion current and the ion concentration is derived as follows:
for flames formed by combustion of hydrocarbon fuels:
the intermediate reaction process for forming ions in the process mainly comprises the following three steps:
wherein k is1，k2，k3The rate at which the reaction proceeds is characterized as the reaction constant. According to the magnitude of the reaction constant, CHO+After ion formation, the ions react rapidly to form H3O+. Thus, the ions in the hydrocarbon fuel flame are primarily H3O+In the form of (A), CHO+Relatively few. The final reaction is the process of neutralizing positive ions and electrons to generate electrically neutral particles.
Let positive ions and electrons in the electric field move dx respectively within dt timeiAnd dxeDistance, the variation of the surface charge density on the electrode is qiAnd q iseIs provided with
q＝qi+qe＝enidxi+enedxe
Wherein n isiIs the concentration of positively charged particles, neIs the negative particle concentration and e is the charge per unit. The current density at the x position from the cathode is then:
viis the migration velocity of positively charged particles, veThe negative ion mobility speed. The two electrodes extending into the flame are cylindrical in shape and have a radius r. Since the mobility of electrons is 3-4 orders of magnitude higher than that of ions, the ion current formed between the two electrodes is:
the migration rate of charged particles under the electric field intensity is mu-vdFor electrons, the migration rate μeA linear relationship with the electric field strength E exists:
wherein the content of the first and second substances,
is the average migration velocity of the electrons and,
is the mean free path of electrons in a gas, meIs the electron mass. Considering the diffusion movement of electrons in an electric field, there are the following relationships:
wherein D is the diffusion coefficient, k is the Boltzmann constant, and T is the absoluteVersus temperature. The average velocity of the electrons is:
the average kinetic energy of the electrons is:
then there is
Under the action of no electric field, the mixed gas is electrically neutral, i.e., [ H ]3O+]And [ e]At equal concentrations, there are:
ne＝[e]＝[H3O+]
setting the field intensity of an external uniform electric field as follows:
E＝U/δ
u is the applied voltage between the electrodes of the ion probe, and delta is the gap between the electrodes. Therefore, the final calculation formula of the relationship between the probe electrode ion current and the ion concentration is:
wherein [ H ]3O+]Is ion concentration, r is probe electrode radius, e is unit charge capacity, U is ion probe interelectrode voltage, δ is interelectrode gap,
is the mean free path of electrons in the gas, κ is the Boltzmann constant, T is the absolute temperature, meIs the electron mass.
For an ion probe to be used in a combustion field, it must have a certain rigidity to ensure easy fixed mounting at the measurement site during the measurement process, and its support portion in contact with the flame should be as small as possible because the support would leak charged particles to disturb the combustion parameter field. The length of the probe needs to be much greater than the probe diameter to ensure negligible end effects of the probe. The combustion chamber temperature will typically exceed 1000K, so the probe electrode needs to be resistant to high temperatures, resistant to sputtering, not participate in chemical reactions, have a high work function, and the secondary processes (e.g., electron emission due to ion collisions, metastable states, photons, probe temperature, etc.) should be as small as possible. In addition, since one end of the probe is disposed in the high-temperature combustion chamber and the other end is disposed outside the combustion chamber, a thermal electromotive force is generated between the two ends of the probe due to a large temperature difference, which may cause an inaccurate measurement signal. The use of conventional gas cooled hollow cylinder electrode structures, for example, can greatly increase the probe size. For a combustion field, the probe size should be as small as possible to minimize probe interference with the flame. Therefore, the invention introduces the ion probe with a three-probe structure, two probes are used as electrodes for detecting ion current in a combustion field, and the third probe is used for eliminating the thermoelectromotive force.
The structure of the ion probe module is shown in fig. 2, the ion probe module comprises an ion probe 1, a probe insulating tube 2, an insulating tube sleeve 3 and a probe mounting seat 4, and the ion probe 1 is embedded into the probe insulating tube 2 through interference fit; the probe insulating tube 2 is arranged in an insulating tube sleeve 3, and the insulating tube sleeve 3 is fixed on a probe mounting seat 4 through a fastening nut 5; the ion probe 1 adopts a three-probe structure, wherein two probes are used as electrodes for measuring ion current, ion induction ends of the two probes extend out of a probe insulating tube, the other probe is used for eliminating the temperature difference potential of the probe, and the probe is sealed in the probe insulating tube and isolated from flame; the ends of the three probes have output leads 6 for connection to a measurement circuit; wherein, the ion probe 1 is cylindrical, the probe insulating tube 2 embedded in the ion probe 1 is also cylindrical, and the length-to-outer diameter ratio is larger than 10:1 so as to reduce the end effect as much as possible. In the embodiment, the ion probe 1 is made of high-temperature-resistant metal material tungsten, and the probe insulating tube 2 is made of an alumina ceramic tube and is used as an external insulating medium of the probe; the length L of the ion probe 1 and the probe insulating tube 2 is 100mm, and the outer diameter D of the probe insulating tube 2 is 3 mm; three tungsten wire electrodes with the diameter D1 being 0.5mm are taken as ion probes 1 and are embedded into the alumina ceramic tube 2 through interference fit, wherein two probes are taken as electrodes for measuring ion current, and the electrode distance D is not more than 1 mm; in the embodiment, the length L1 of the ion induction ends of two probes used for measuring the ion current extending out of the ceramic tube is 0.5mm, the distance d between the two ends is 0.8mm, the other probe used for eliminating the temperature difference effect of the probe is sealed in the ceramic tube, and the distance L2 from the end part is 2 mm; the insulating tube sleeve 3 outside the insulating dielectric ceramic tube 2 is made of a stainless steel sleeve to improve the strength of the probe. The steel sleeve 3 fixes and determines the position of the ion probe 1 in the combustion chamber through a probe mounting seat 4. The steel sleeve 3 and the mounting seat 4 are fixed through a fastening nut 5. The output leads 6 of the three probe tips are connected to the measurement circuit module by shielded wires.
The measuring circuit module comprises a preamplifier circuit and a filter circuit, wherein a measuring signal output by the ion probe is amplified by the preamplifier circuit and then is connected to the filter circuit to eliminate noise.
The structure of the preamplifier circuit is shown in fig. 3. The preamplification circuit comprises a measuring bridge and an instrument amplifier, wherein the measuring bridge is used for measuring the gas resistance R between two probesxThe two ends of one bridge arm of the measuring bridge are respectively connected with output end leads of two probes for collecting ion current, and the resistance values of 4 bridge arms are R1. Wherein the relation between the gas resistance and the ion current between the probe electrodes is
In this embodiment, the bridge arm resistance R1The metal thin film resistor with an accuracy of 0.1% was selected as 100k Ω. The two output ends of the measuring bridge are respectively connected with the positive input end and the negative input end of the instrumentation amplifier, and are connected with a gas resistor R as shown in figure 3xThe output end (point A) of the bridge arm is connected with the anode of the input end of an instrumentation amplifier U6, and the other output end of the bridge arm is connected with the cathode of the output end of an amplifier U6; the output lead of the third probe for eliminating the temperature difference potential is also connected to the negative pole (point C) of the output end of the amplifier, and is used for balancing the temperature difference potential generated by the probe at the two points A, B in the figure 2. In this example, AD620 manufactured by Anglo-Design company was selected as the instrumentation amplifier. Because of the measured gas resistance RxIs a tiny amount, and needs to use an external gain adjustment resistor RGWherein R isGConnected between pins 1 and 8 of AD 620.In this example RGThe resistance value takes 1k omega. Gain adjusting resistor RGThe amplification factor of the instrumentation amplifier can be adjusted to convert the weak change of the gas resistance between A, B electrodes into the change of voltage.
The filter circuit consists of a power frequency wave trap and a low-pass filter. Fig. 4 shows a circuit diagram of a power frequency trap. The power frequency wave trap has a center frequency of 50Hz and adopts a double-T-shaped circuit structure with adjustable quality factor, and comprises an amplifier U1、U2、U3Wherein U is2Is the OUTPUT terminal OUTPUT2, U of the whole circuit3Being voltage followers, U3Is connected to the positive input end through a resistor R2Grounded while passing through a resistor R3Connect U2An output terminal of (a); by regulating R2、R3The ratio of (2) can change the quality factor Q of the wave trap, and the larger the Q value is, the narrower the trapped wave broadband is; amplifier U1Has a positive input connected with the OUTPUT terminal OUTPUT1, U of the pre-amplifying circuit1Through a resistor R connected in series4、R5Connecting amplifier U2Positive input terminal of, amplifier U1Through a capacitor C connected in series1、C2Is also connected with an amplifier U2Positive input terminal of, amplifier U3Respectively through a resistor R6Is connected to C1And C2And through a capacitance C3Is connected to a resistor R4And R5To (c) to (d); the resistance and the capacitance in the embodiment are respectively selected from a metal film resistance with the precision of 1% and a silver-plated mica capacitance with the precision of 2%. Wherein R is4＝R5＝2R6＝96.1kΩ，C1＝C2＝C3/2＝33nF，R2＝51Ω，R3The OPA277 manufactured by Burr-Brown was selected as the operational amplifier 953 Ω. The circuit structure of the low-pass filter in this embodiment is formed by taking a 4 th-order active filter chip MAX275 produced by MAXIM corporation as a core, as shown in fig. 5. The MAX275 comprises two second-order structures which are combined together to form a fourth-order low-pass filter; r7、R8、R9、R10Are peripheral resistors of a second order structure which determine fourPerformance of the order bandpass filter. Wherein R is7Determines the gain, R, of a fourth order low-pass filter8Determines the quality factor, R, of a fourth order low-pass filter9、R10The center frequency of the fourth order low pass filter is determined together, and the accuracy of the selection in this embodiment is 1% of the metal film resistance, where R is7＝R8＝755kΩ,R9＝R103.6M Ω. For the low-pass filter, since the pulsation burner is selected as the combustion chamber in this embodiment, and the natural combustion oscillation frequency is 89Hz, the cut-off frequency of the low-pass filter is designed to be 500Hz, and for the general burner, the cut-off frequency should not be lower than 5 times of the measurement frequency.
As shown in fig. 6, an embodiment of the present invention applied to the measurement of the ion concentration distribution in the combustion chamber of the pulse combustor is shown. The pulse combustor is an oscillation combustion heat release device well researching ion concentration distribution, and has fixed combustion oscillation frequency. In this embodiment, the natural combustion oscillation frequency of the pulsation burner is 89Hz, and in fig. 6, the pulsation burner includes a combustion chamber 10, a fuel nozzle 11, a fuel valve 12, an igniter 13, an air valve 14, a pressure regulator 15, a pressure sensor 16, a combustion chamber tail pipe 17, and a blower 18 for supplying air to the combustion chamber.
The measuring device of the invention is applied to the measuring method of the ion concentration distribution in the combustion chamber of the pulse combustor: based on measuring the ion current variation distribution in the combustion field to obtain the ion concentration distribution at different positions in the combustion field. Firstly, fixing a plurality of ion probe modules 19 at different positions in a combustion chamber through probe mounting seats; when the pulsating combustor generates oscillation combustion, the ion probe starts to acquire ion current change signals at different positions in a combustion field; the measurement circuit module 20 amplifies and filters the ion current signal, and outputs the amplified and filtered ion current signal through data acquisition and display equipment to obtain ion current distribution at different positions in the combustion field; and obtaining the spatial distribution of the ion concentration at different positions in the combustion field according to the deduced relation of the ion current and the ion concentration. FIG. 8 reflects the ion concentration in the pulsating burner versus the combustion chamber pressure over time. The solid line in fig. 8 shows the time-dependent profile of the combustion chamber pressure measured by the pressure sensor, and the dashed line in fig. 8 shows the time-dependent profile of the combustion chamber ion concentration. Fig. 9 shows FFT-processed results of the ion concentration versus time curve of fig. 8, with the abscissa reflecting 89Hz primary combustion oscillation frequency in the pulsed combustor combustion chamber, and the ordinate reflecting the oscillation amplitude of the ion concentration at this location, with different amplitudes of ion concentration at different locations.
Since the measurement results of the ion probe are very sensitive to the size of the electrode structure of the probe, different probes have different measurement results due to slight difference of the size of the electrode structure, and therefore the probe needs to be calibrated before being used. And a mutual calibration method is adopted for the ion probes to ensure that the measurement results of different probes are consistent. During calibration, a plurality of probes are placed in a small area in the combustion chamber for simultaneous measurement, and as shown in fig. 7, the ion sensing ends (point a in fig. 2) of the 4 probes are all pointed to the central point of the combustion chamber. The amplitude of the ion concentration oscillation is consistent in a tiny area, and the amplitude of the main frequency of the ion concentration oscillation can be obtained by performing FFT analysis on the measurement signal. The proportional relation of the ion concentration amplitude results measured among different probes can be obtained through a calibration test. The measurement results of one probe are selected as a standard, so that the measurement results of different probes can be unified.
It is pointed out here that the above description is helpful for the person skilled in the art to understand the invention, but does not limit the scope of protection of the invention. Any such equivalents, modifications and/or omissions as may be made without departing from the spirit and scope of the invention may be resorted to.
Claims (7)
1. A measuring device for ion concentration distribution in a combustion field is characterized by comprising an ion probe module and a measuring circuit module, wherein:
the ion probe module is used for acquiring an ion current signal of dynamic flame in a combustion field;
the measurement circuit module is used for measuring and processing the ion current signal acquired by the ion probe module and obtaining the change of the ion concentration in the combustion field by measuring the change of the ion current;
the ion probe module comprises an ion probe, a probe insulating tube, an insulating tube sleeve and a probe mounting seat, wherein the ion probe is embedded into the probe insulating tube in an interference fit manner; the probe insulating tube is arranged in an insulating tube sleeve, and the insulating tube sleeve is fixed on the probe mounting seat through a fastening nut; the ion probe adopts a three-probe structure, wherein two probes are used as electrodes for measuring ion current, ion induction ends of the two probes extend out of a probe insulating tube, the other probe is used for eliminating the temperature difference potential of the probe, and the probe is sealed in the probe insulating tube and isolated from flame; the tail ends of the three probes are provided with output leads for connecting with a measuring circuit module;
the measuring circuit module comprises a pre-amplifying circuit and a filter circuit, and a measuring signal output by the ion probe is amplified by the pre-amplifying circuit and then is connected to the filter circuit to eliminate noise;
the pre-amplification circuit comprises a measuring bridge and an instrument amplifier, and the resistance values of four bridge arms of the measuring bridge are R1Two ends of one bridge arm are respectively connected with output leads of two probes for collecting ion current, and a gas resistor R between the two probesxThe direct current bridge is connected to one bridge arm of the direct current bridge in parallel; connected with a gas resistor RxOne output end A of the bridge arm is connected with the anode of the input end of the instrument amplifier U6, and the other output end B is grounded; the output lead of the third probe for eliminating the temperature difference potential is connected to the negative electrode C of the input end of the instrument amplifier U6 and is used for balancing the temperature difference potential generated by the probes at A, B two points; the instrument amplifier U6 is also externally connected with a gain adjusting resistor RGGain adjusting resistor RGThe amplification factor of the instrumentation amplifier can be adjusted to convert the weak change of the gas resistance between A, B electrodes into the change of voltage.
2. The measurement device of claim 1, wherein the ion current collected by the ion probe is related to the ion concentration by the following formula:
wherein [ H ]3O+]Is ion concentration, r is probe electrode radius, e is unit charge capacity, U is ion probe interelectrode voltage, δ is interelectrode gap,
is the mean free path of electrons in the gas, κ is the Boltzmann constant, T is the absolute temperature, meIs the electron mass.
3. The measurement apparatus of claim 1 wherein the ion probe and probe insulator are cylindrical and the probe insulator length to outside diameter ratio is greater than 10:1 to minimize end effects.
4. The measuring device as claimed in claim 3, wherein the diameter ratio of the ion sensing ends of the two probe electrodes for measuring the ion current extending out of the insulating tube to the insulating tube is not less than 1:10, the distance between the two probe electrodes is not more than 1mm, and the distance between the probe electrode sealed in the insulating tube for eliminating the ion sensing end electrode temperature difference potential and the end face of the insulating tube is not more than 2 mm.
5. The measuring device according to claim 1, wherein the filter circuit comprises a power frequency wave trap and a low-pass filter, the power frequency wave trap is used for filtering power frequency interference, and a double-T-shaped circuit structure with adjustable quality factor is adopted; the low-pass filter is used for filtering broadband noise except for useful signals, and an active filter chip is adopted, so that the cut-off working frequency of the active filter chip is adjustable.
6. Method for measuring ion concentration distribution in a combustion field using a measuring device according to one of claims 1 to 5, based on measuring ion current variation distribution in the combustion field to obtain ion concentration distribution at different positions in the combustion field, comprising the steps of:
1) disposing a plurality of ion probe modules at different locations in a combustion field;
2) when the combustion field is combusted, the ion probe module collects ion current change signals at different positions in the combustion field; the measurement circuit module amplifies and filters the ion current signal, and the ion current signal is output by data acquisition and display equipment to obtain ion current distribution at different positions in the combustion field;
3) and obtaining the spatial distribution of the ion concentration at different positions in the combustion field according to the relational expression of the ion current and the ion concentration.
7. The measurement method according to claim 6, characterized in that in step 2) it comprises a step of calibration before use of the probe:
during calibration, a plurality of probes are placed in a small area in a combustion chamber for simultaneous measurement; FFT analysis is carried out on the measurement signal to obtain the amplitude of the ion concentration oscillation main frequency; obtaining the proportional relation of the ion concentration and amplitude results measured by different probes; by selecting one probe result as a standard, the measurement results of different probes can be unified.
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