CN104965001A - Flame heat release rate pulsation measuring device - Google Patents

Abstract

The invention discloses a flame heat release rate pulse measuring device, which belongs to the technical field of non-contact combustion diagnosis. It includes a filter, a photomultiplier tube, a negative high-voltage power supply, an amplifying circuit and a switching power supply; the filter is arranged on the light entrance of the photomultiplier tube, and the photomultiplier tube is respectively connected to the negative high-voltage power supply and the amplifying circuit. The amplifying circuit is connected with the switching power supply. The invention has simple structure, low price and cost, adopts non-contact measurement, has high sensitivity and reasonable measurement precision, and can perform real-time measurement on the flame heat release rate pulsation of the afterburner.

Description

Flame heat release rate pulse measuring device

technical field

The invention relates to a pulsation measurement device, in particular to a flame heat release rate pulsation measurement device, which belongs to the technical field of non-contact combustion diagnosis.

Background technique

The temperature in the afterburner of modern aero-engines can reach above 2000K, while the total residual gas coefficient is reduced to about 1.1, so it is easy to produce oscillating combustion. The study of oscillatory combustion manifestations requires real-time measurements of the heat release rate fluctuations in the combustor. The measurement of heat release rate and temperature are important parameters of oscillatory combustion phenomena. The engine combustion process, like most combustion phenomena, will produce a large number of intermediate components. These intermediate products are of great significance to the study of flame formation, development and measurement of heat release rate and temperature.

At present, the best technical method for optical measurement of temperature in the existing technology is planar laser-induced fluorescence (PLIF), which can not only detect some important combustion components (such as OH, O ₂ , NO, CH etc.) In addition to the two-dimensional component distribution in the combustion process, it can also quantitatively measure the combustion flame temperature field distribution. This technology has no interference to the combustion process, can carry out precise measurement, and has high spatial and temporal resolution (time resolution nanosecond, spatial resolution micron level), two-dimensional measurement, visibility and intuitive image. But this kind of equipment is expensive, and many colleges and universities engaged in combustion research cannot afford to buy it, and the equipment is complicated and cannot be produced in China.

The conventional measurement method is thermocouple, which is low in cost and suitable for popularization and application, but there are two major disadvantages of thermocouple. First of all, the thermocouple must be inserted into the flow field. Measuring the temperature at the recirculation area after the stabilizer in the combustion chamber will have a great impact on the flow field; second, it cannot measure dynamic temperature changes, and the thermocouple takes a long time to measure, that is It takes a long time to get a stable temperature output as the temperature changes.

On August 06, 2014, the Chinese invention patent application 201410225315.6 disclosed a non-contact flame temperature and OH group concentration measurement device and measurement method based on ultraviolet laser absorption spectrum. The measurement device includes Nd:YAG laser, tunable dye laser , aperture diaphragm, beam splitter, No. 1 photoelectric detector, No. 2 photoelectric detector, burner, oxygen cylinder, nitrogen gas cylinder, fuel gas cylinder, No. 1 flowmeter, No. 2 flowmeter, and No. 3 Flow meters, premix tanks, oscilloscopes, computers. This method can quantitatively measure the flame temperature and the OH radical concentration information in the flame at the same time, and because the dye laser has a very wide tuning range, it has the potential to measure the free radical components in a variety of flames, which enriches the measurement range of laser combustion diagnosis , providing a new technical means for the quantitative study of combustion. On December 1, 2010, Chinese invention patent CN101625269B disclosed a method for simultaneously monitoring the temperature field of combustion flame and the two-dimensional distribution of intermediate product concentration, including a flame detection device, a spectroscopic device, a filtering device, and a detection and processing device. The flame detection device includes a flame sighting device and a wide-angle mirror at its front end and a cooling sleeve. The flame radiated light is transmitted to the spectroscopic device through the spectroscopic device, and after the splitting, the filtering device obtains four channels of narrow-band optical signals with different center wavelengths. The invention can monitor the concentration of the flame intermediate product and the two-dimensional distribution of the flame temperature field in real time and simultaneously. However, the above devices and methods use a lot of equipment, such as lasers and CCD detectors, which are complicated to implement and expensive.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a flame heat release rate pulse measuring device with simple structure and low cost.

In order to solve the above-mentioned technical problems, a kind of flame heat release rate pulsation measuring device provided by the present invention comprises optical filter, photomultiplier tube, negative high-voltage power supply, amplifying circuit and switching power supply; On the light entrance, the photomultiplier tube is respectively connected to a negative high voltage power supply and an amplifying circuit, and the amplifying circuit is connected to a switching power supply.

In the present invention, the amplifying circuit includes a two-stage operational amplifier, the inverting input pin 2 of the first-stage operational amplifier is connected to a photomultiplier tube, the input pin 3 is grounded, and the output terminal of the first-stage operational amplifier is connected to a The feedback resistor R2 is connected between the pin 1 and the input pin 2, and the feedback capacitor C3 is connected in parallel on the feedback resistor R2; the output pin 1 of the first-stage operational amplifier is connected to the reverse input pin of the second-stage operational amplifier The output resistor R7 is connected between 2, the output resistor R7 is connected to one end of the resistor R9, the other end of the resistor R9 is connected to the output terminal pin 1 of the second-stage operational amplifier, and the input terminal pin 3 of the second-stage operational amplifier is grounded; the first-stage operational amplifier And pin 8 and pin 4 of the second-stage operational amplifier are respectively connected to the switching power supply.

In the present invention, the positive and negative power supply terminals of the first-stage operational amplifier and the second-stage operational amplifier are connected in series with RC decoupling filter sections.

In the present invention, the RC decoupling filter section includes a resistor, a first capacitor, and a second capacitor, one end of the resistor is connected to a power supply, and the other end is connected to a two-stage operational amplifier; the first capacitor is connected in parallel with the second capacitor, and its One end is connected to two stages of operational amplifiers, and the other end is grounded; the capacity of the first capacitor and the second capacitor are different.

In the present invention, the two ends of the output resistor R7 are respectively connected to one end of the capacitor C6 and the capacitor C7, and the other ends of the capacitor C6 and the capacitor C7 are grounded to form a π-type filter.

In the present invention, the central wavelength of the optical filter is 430nm, and the bandwidth is 10nm.

In the present invention, the photomultiplier tube is a side window type photomultiplier tube with a wavelength of 185nm-710nm.

The beneficial effects of the present invention are: (1), the present invention is simple in structure, low in price and cost, adopts non-contact measurement, has high sensitivity and reasonable measurement accuracy, and can perform real-time measurement of the flame heat release rate pulsation of the afterburner; (2) Connect the RC decoupling filter section to the positive and negative power supply terminals. Two capacitors, one large and one small, are connected in parallel; one capacitor is connected to each end of the output resistor to form a π-type filter to reduce the circuit size of each part of the amplifier. The parasitic coupling generated by the public DC power supply stabilizes the work of the amplifying circuit and prevents oscillation and interference; (3), using a side window type photomultiplier tube, its response efficiency to the spectrum of CH ions reaches 85%, which can The optical signal is converted into a microampere-level current signal; (4), the filter with a center wavelength of 430nm and a bandwidth of 10nm can efficiently pass through the spectrum of CH ions, and can filter out the spectra of other combustion intermediate products.

Description of drawings

Fig. 1 is the structure schematic diagram of flame heat release rate pulse measuring device of the present invention;

Figure 2 is the measured value when candles are used as the light source, picture (a) is the measured value when the distance is 50cm, and picture (b) is the measured value when the distance is 20cm;

Fig. 3 is the schematic diagram of amplifying circuit;

Fig. 4 is the detection waveform diagram of amplifying circuit;

Fig. 5 is a schematic diagram of CH ion measurement results.

Detailed ways

The present invention will be further described in detail below by taking the measurement of CH groups as an example in conjunction with the accompanying drawings.

As shown in FIG. 1 , the flame heat release rate pulse measurement device of the present invention includes a filter 4 , a photomultiplier tube 5 , a negative high voltage power supply 6 , an amplifier circuit 8 and a switching power supply 7 . The optical filter 4 is attached to the front light entrance of the photomultiplier tube 5, the photomultiplier tube 5 is connected to the negative high voltage power supply 6, the anode of the photomultiplier tube 5 is connected to the amplifying circuit 8, and the amplifying circuit 8 is connected to the switching power supply 7 and the acquisition computer 9. The switching power supply 7 adopts a power supply that can stably output a voltage of plus or minus 10V that is common in the prior art. During use, the photomultiplier tube 5 is assembled on the connection pipe 3 connected to the afterburner, the optical filter 4 is between the photomultiplier tube 5 and the connection pipe 3, and a Quartz viewing window 2, below the flame 1 in the combustion chamber, a flame stabilizer 10 is arranged.

It is known that the spectrum of CH ions is 431nm, and the concentration of CH ions with a peak wavelength of 435.3nm during combustion is directly proportional to the heat release rate per unit volume of the combustion zone. As long as the light radiation of this wavelength is measured, it can be measured by measuring the concentration of CH ions heat release rate. Therefore, in this embodiment, the filter 4 is selected as a filter with a center wavelength of 430 nm and a bandwidth of 10 nm. Because there are many intermediate products of hydrocarbon fuels, such as the characteristic wavelength of OH group is 280nm, and the characteristic wavelength of C2 is about 516nm, so the filter can effectively block the wavelength of other free radicals and pass the wavelength of CH ion. The narrower the bandwidth of the filter, the better the monochromaticity, and the stronger the filterability of the spectrum of other intermediate products. In addition, other combustion intermediate products can be measured by selecting filters with different central wavelengths to adapt to different application ranges; for example, when selecting a filter with a central wavelength of 280nm, the spectrum of OH radical ions can be measured.

In this embodiment, the photomultiplier tube 5 is an R5983 side-window photomultiplier tube with a response peak value of 410 nm and a response wavelength range of 185 nm to 710 nm. The photomultiplier tube has high sensitivity to the spectral response of CH ions, and the response efficiency reaches 85%, and can convert optical signals into microampere-level current signals. Responding to other intermediate products of hydrocarbon fuels can be realized by changing the type of the filter 4 .

The negative high-voltage power supply 6 can provide a strong electric field to the nine-level electron multiplier in the photomultiplier tube 5. When the light intensity is the same, the greater the negative high voltage applied, the larger the output current of the photomultiplier tube. The intensity of the luminescence is used to adjust the size of the negative high voltage, so as to achieve the effect of increasing or decreasing the output current of the photomultiplier tube. The output current of the photomultiplier tube 5 and the output characteristics under different light sources were measured, and it was found that under the negative high voltage of -350V, when candles were selected as the light source, the output current increased with the distance between the photomultiplier tube 5 and the light source. After conversion, it is about 2 microamps to 5 microamps, as shown in Figure 2. When the spray gun is the light source, the output current is about 10 microamps. In this embodiment, the negative high-voltage power supply selected by the negative high-voltage power supply 6 can provide a voltage of -1250V to 0V to measure other combustion intermediate products.

As shown in FIG. 3 , the amplifying circuit of the present invention converts the weak current output by the photomultiplier tube 5 into a voltage signal and amplifies the voltage signal. It includes the I/U conversion circuit of the first stage and the voltage amplification circuit of the second stage. The I/U conversion circuit includes a first-stage operational amplifier, the inverting input terminal pin 2 of the first-stage operational amplifier is connected to the anode of the photomultiplier tube 5, a resistor R3 is connected in series between the two, and the input terminal of the first-stage operational amplifier Pin 3 is grounded; a high-resistance feedback resistor R2 is connected between the output pin 1 and the input pin 2 of the first-stage operational amplifier, and the feedback capacitor C3 is connected in parallel with the feedback resistor R2, so that the output of the first-stage operational amplifier U1=Iin×R2. The resistance value of the feedback resistor R2 should make the output voltage of the first stage about 100mv. If the feedback resistor R2 is too small, the output voltage of the first stage is too small, which is easily disturbed by external noise. If the feedback resistor R2 is too large, the stability is too poor and interference is likely to occur; the feedback capacitor C3 is generally tens of pF, and the time at the input end The constant t≈R2×C3, when the feedback capacitor C3=10pF, if t=1μs. Due to the integral effect of the input resistance and capacitance, the output signal needs 5t to be stable when the input signal changes. So the measurement time of this circuit board is 5μs, and the measurement frequency is 200kHz. The pulse frequency of the flame is about 200Hz, so the amplifier circuit can meet the frequency requirements of the flame measurement team. The output terminal pin 1 of the first-stage operational amplifier is connected to the output resistor R7, the two ends of the output resistor R7 are respectively connected to one end of the capacitor C6 and the capacitor C7, and the other end of the capacitor C6 and the capacitor C7 is grounded to form a π-type filter. The input pin 8 of the first-stage operational amplifier is connected to one end of the resistor R1, the other end of the resistor R1 is connected to the positive pole of the switching power supply, the capacitor C1 and the capacitor C2 are connected in parallel, one end is connected to the input pin 8 of the first-stage operational amplifier, and the other end is grounded, forming RC decoupling filter section; in this embodiment, the capacity of the capacitor C1 is 0.01 μF, and the capacity of the capacitor C2 is 47 μF. Similarly, the input pin 4 of the first-stage operational amplifier is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the negative pole of the switching power supply, the capacitor C4 and the capacitor C5 are connected in parallel, one end of which is connected to the input pin 4 of the first-stage operational amplifier, and the other end is grounded , forming an RC decoupling filter section; in this embodiment, the capacity of the capacitor C4 is 0.01 μF, and the capacity of the capacitor C5 is 47 μF.

The voltage amplifying circuit includes a second-stage operational amplifier, the output resistor R7 is connected between the reverse input terminal pin 2 of the second-stage operational amplifier, and the output resistor R7 is connected to one end of the resistor R9 at the same time, and the other end of the resistor R9 is connected to the second-stage operational amplifier Output terminal pin 1, the signal is output from the output terminal pin 1 of the second-stage amplifier. The multiple of the resistor R9/output R7 is the magnification of the first-stage signal by the second-stage operational amplifier, and the general magnification is about 10 to 30 times. The pin 3 of the input terminal of the second-stage operational amplifier is connected to the resistor R6, and the resistor R6 is grounded. The input pin 8 of the second-stage operational amplifier is connected to one end of the resistor R8, and the other end of the resistor R8 is connected to the positive pole of the switching power supply. RC decoupling filter section; in this embodiment, the capacity of capacitor C8 is 0.01 μF, and the capacity of capacitor C9 is 47 μF. Similarly, the input terminal pin 4 of the second-stage operational amplifier is connected to one end of the resistor R5, the other end of the resistor R5 is connected to the negative pole of the switching power supply, the capacitor C10 and the capacitor C11 are connected in parallel, one end is connected to the input terminal pin 4 of the second-stage operational amplifier, and the other end is grounded , forming an RC decoupling filter section; in this embodiment, the capacity of the capacitor C10 is 0.01 μF, and the capacity of the capacitor C11 is 47 μF.

In this embodiment, both the first-stage operational amplifier and the second-stage operational amplifier are LM358 operational amplifiers. Connect the RC decoupling filter section with the switching power supply respectively. The capacitors are connected in parallel with one large capacitor and one small capacitor. The small capacitor has a good effect on high-frequency current pulse filtering; connect a capacitor at both ends of the output resistor R7 to form a π-type filter; The above settings can reduce the parasitic coupling generated by the public DC power supply between the parts of the amplifier, stabilize the operation of the amplifier circuit, and prevent oscillation and interference. Finally, the same kind of wire should be used as much as possible in the process, and the input section should use a cable with high insulation noise and be as short as possible. The circuit board and wires should avoid mechanical deformation.

The performance of the amplifier circuit directly determines the strength of the background noise and the size of the output signal. According to the range of the output current of the photomultiplier tube, we first select the size of the feedback resistor R2, and then select the size of the feedback capacitor C3 according to the measured frequency. As shown in Fig. 4, the amplifying circuit is detected by an oscilloscope, and it is found that the background noise of the amplifying circuit is about 0.1V, while the measuring range of the signal acquisition card on the acquisition computer 9 is 10V. According to the signal strength and the range of the acquisition card, the amplification factor of the second stage is selected to be 10 times, and the amplification circuit is substituted into the entire measurement system for inspection to meet the conversion amplification requirements.

As shown in Figure 1, the flame heat release rate pulsation measurement device is applied to the thermoacoustic coupling experimental bench of the afterburner, the filter 4 captures the flame through the quartz window 2 and blocks the wavelength of other free radicals and only passes through the CH ion wavelength, while the photomultiplier tube 5 responds to the spectrum of the CH ion, the negative high voltage power supply 6 applies a negative high voltage to the nine-stage electron multiplier in the photomultiplier tube 5 to control the output current of the photomultiplier tube; the amplifying circuit realizes the photoelectric multiplier The weak current output by the multiplier tube 5 is converted into a voltage signal, and the voltage signal is amplified and then output to the acquisition computer 9 for analysis and processing. As shown in Fig. 5, the CH ion waveform obtained by the acquisition computer 9 is basically consistent with the afterburner pressure waveform.

Above embodiment is only a kind of usage of this measurement device, can also measure other combustion intermediate products such as OH group by changing the filtering wavelength range of optical filter on its basis, or carry out spectroscopic analysis with spectroscopic equipment such as monochromator A similar effect can be achieved. Therefore, without departing from the principle of the present invention, improvements and modifications to the measuring device should also fall within the protection scope of the present invention.

Claims (7)

1. a flame heat release rate pulse measuring device is characterized in that: comprise optical filter, photomultiplier tube, negative high-voltage power supply, amplifying circuit and switching power supply; Described optical filter is arranged on the light entrance of photomultiplier tube, The photomultiplier tubes are respectively connected to a negative high voltage power supply and an amplifying circuit, and the amplifying circuit is connected to a switching power supply. 2. The flame heat release rate pulse measuring device according to claim 1, characterized in that: the amplifying circuit comprises a two-stage operational amplifier, and the inverting input terminal pin 2 of the first-stage operational amplifier is connected to a photomultiplier tube , the input terminal pin 3 is grounded, the feedback resistor R2 is connected between the output terminal pin 1 and the input terminal pin 2 of the first-stage operational amplifier, and the feedback capacitor C3 is connected in parallel on the feedback resistor R2; the output of the first-stage operational amplifier The output resistor R7 is connected between the terminal pin 1 and the reverse input terminal pin 2 of the second-stage operational amplifier, the output resistor R7 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the output terminal pin 1 of the second-stage operational amplifier. The pin 3 of the input terminal of the second-stage operational amplifier is grounded; the pins 8 and 4 of the first-stage operational amplifier and the second-stage operational amplifier are respectively connected to the switching power supply. 3. The flame heat release rate pulse measurement device according to claim 2, characterized in that: the positive and negative power supply terminals of the first-stage operational amplifier and the second-stage operational amplifier are connected in series with RC decoupling filter sections. 4. Flame heat release rate pulse measuring device according to claim 3, characterized in that: said RC decoupling filter section comprises a resistor, a first capacitor, and a second capacitor, one end of said resistor is connected to a power supply, and the other end is connected to A two-stage operational amplifier; the first capacitor and the second capacitor are connected in parallel, one end of which is connected to the two-stage operational amplifier, and the other end is grounded; the capacities of the first capacitor and the second capacitor are different. 5. The flame heat release rate pulse measuring device according to claim 2, 3 or 4, characterized in that: the two ends of the output resistor R7 are respectively connected to one end of the capacitor C6 and the capacitor C7, and the other end of the capacitor C6 and the capacitor C7 One end is grounded to form a π-type filter. 6. The flame heat release rate pulsation measuring device according to claim 5, characterized in that: the central wavelength of the filter is 430nm, and the bandwidth is 10nm. 7. The flame heat release rate pulsation measurement device according to claim 6, characterized in that: the photomultiplier tube is a side window type photomultiplier tube with a wavelength of 185nm-710nm.