CN117269008B - High-concentration soot volume fraction measuring device and method based on laser preheating - Google Patents
High-concentration soot volume fraction measuring device and method based on laser preheating Download PDFInfo
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Abstract
A high-concentration soot volume fraction measuring device and method based on laser preheating relate to a soot volume fraction measuring system. The time sequence controller is connected with the pulse laser and the detection system, laser emitted by the pulse laser is shaped into light sheets and then enters the burner, the detection system detects the area where the burner is located, laser emitted by the continuous laser is shaped into light sheets and then enters the burner, the 1/2 wave plate I is arranged behind the light outlet of the pulse laser, the 1/2 wave plate II is arranged behind the light outlet of the continuous laser, the emission spectrum measurement system measures the temperature of the carbon smoke particles, and the measurement result provides feedback for the output power of the continuous laser. The pulse laser and the continuous laser form a light source for laser-induced blazing measurement, and an emission spectrum measurement system is used for assistance, so that strong absorption of high-concentration soot to single-pulse laser energy is overcome, high-concentration soot particles are heated to the temperature of radiation blazing, and measurement accuracy is improved.
Description
Technical Field
The invention relates to a soot volume fraction measuring system, in particular to a high-concentration soot volume fraction measuring device and method based on laser preheating, and belongs to the technical field of laser spectrum application.
Background
The principle of the laser induced glow process (Laser Induced Incandescence, LII) is to heat the soot particles from the flame background temperature (about 2000K) to a near vaporization temperature (about 4000K) using a high energy laser, whereby the soot particles radiate intense glow outwardly. The intensity of the incandescent signal is proportional to the volume fraction of the soot, the decay rate of the incandescent signal is inversely proportional to the size of the soot particles, and accordingly, the information such as the volume fraction and the particle size of the soot particles can be obtained by detecting the incandescent signal.
The conventional LII experimental device generally comprises a laser system, a sheet light shaping and transmitting system, a time sequence control system, a detection system and a measured object, and is shown in the figure 1, laser emitted by the laser system is shaped into sheet light through the sheet light shaping and transmitting system and then is incident into the measured object, the sheet light is used for exciting carbon smoke particles in the measured object, incandescent light emitted by the carbon smoke particles is received by the detection system, and information such as two-dimensional distribution of the volume fraction of the carbon smoke can be obtained through later data analysis. However, the laser-induced blazing method is used as a non-invasive optical diagnosis method, and has the advantages of high space-time resolution, high signal-to-noise ratio and the like, but when high-concentration soot measurement is performed, the laser cannot excite all soot particles in a detection area due to strong scattering and absorption of the soot particles by the laser, so that errors are brought to measurement results. Therefore, for measuring the volume fraction of the high-concentration soot, the traditional LII experimental device and the traditional LII experimental method are required to be optimized and improved so as to solve the phenomenon that the soot is incompletely saturated and excited and improve the accuracy of experimental measurement results.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a high-concentration soot volume fraction measuring device and method based on laser preheating, which utilize a pulse laser and a continuous laser to form a laser-induced incandescent light measuring light source, and utilize an emission spectrum measuring system to assist, so that the strong absorption of high-concentration soot to single-pulse laser energy is overcome, high-concentration soot particles are heated to the temperature of radiation incandescent light, and the measuring accuracy is improved.
In order to achieve the above purpose, the invention adopts the following technical scheme:
The utility model provides a high concentration soot volume fraction measuring device based on laser preheats, includes pulse laser, piece light shaping and transmission system, combustor, time schedule controller, detecting system, continuous laser, additional piece light shaping and transmission system and emission spectrum measurement system, the combustor produces the flame that is surveyed, time schedule controller connects control pulse laser and detecting system, the laser that pulse laser sent is sent and is incident to the combustor after the piece light is formed into the piece through piece light shaping and transmission system, piece light shaping and transmission system includes beam expander I, collimating mirror, focusing mirror I and the speculum I that arranges in proper order, detecting system surveys the region that the combustor is located, the laser that continuous laser sent is incident to the combustor after additional piece light shaping and transmission system is formed into piece light, additional piece light shaping and transmission system includes beam expander II, focusing mirror II and the speculum II that arranges in proper order, arranges 1/2 wave plate I behind the pulse laser light outlet, continuous laser light outlet arranges 1/2 wave plate II behind the piece light outlet, emission system includes that the collimator is provided by connecting with the collimator and the spectral configuration is carried out to the measurement result of laser, the continuous laser particle is the power measurement is carried out to the optical fiber configuration, the laser is the collimator is provided.
A high-concentration soot volume fraction measuring method based on laser preheating comprises the following steps:
Step one: placing of laser light source and setting up of shaping light path
Arranging a pulse laser and a continuous laser according to requirements, arranging a 1/2 wave plate I and a plate light shaping and transmitting system in sequence after a light outlet of the pulse laser, arranging a 1/2 wave plate II and an additional plate light shaping and transmitting system in sequence after the light outlet of the continuous laser, mutually perpendicular to the polarization directions of the pulse laser and the continuous laser, and adjusting an optical path to ensure that two laser beams are in the same plane when being incident into flame to be measured of a burner;
Step two: focusing of a detection system
The detection system is arranged at a proper position away from the burner, the imaging result is required to be clear, and the size of the field of view is consistent with the size of the light of the pulse laser;
Step three: construction of emission spectrum measurement system
Arranging a spectrometer, a collimator and a focusing mirror III in an emission spectrum measurement system according to requirements, and ensuring that the focal point position of the focusing mirror III is positioned at the position irradiated by laser sheet light;
Step four: LII pre-measurement preparation
After confirming that each device runs normally, igniting the flame to be tested, opening the continuous laser to heat the temperature of the carbon smoke particles to 3000K, monitoring the temperature of the carbon smoke particles in real time by an emission spectrum measuring system during the period, and adjusting the output power of the continuous laser in real time by feedback;
step five: measurement of soot volume fraction
And (3) adjusting the time delay between the pulse laser and the detection system, heating the temperature of the soot particles to the temperature of the radiant incandescent light, ensuring that the excited incandescent light signals can be collected by the detection system, and obtaining the soot volume fraction according to the recorded incandescent light signals.
Compared with the prior art, the invention has the beneficial effects that: the invention uses pulse laser and continuous laser to form laser-induced blazing light measuring light source, to excite high concentration carbon smoke, the laser emitted by continuous laser is used to preheat carbon smoke, to heat carbon smoke particle from flame background temperature (about 2000K) to 3000K, the proposal can raise the temperature of high concentration carbon smoke, without the circumstance that the front carbon smoke particle absorbs heat excessively and the back carbon smoke particle absorbs heat or absorbs little heat excessively, to overcome the strong absorption of high concentration carbon smoke to single pulse laser energy, while the pulse laser is used as superposition excitation of blazing light signal, when the pulse laser reaches the measured flame, to heat carbon smoke particle temperature from 3000K to radiation blazing temperature (about 4000K), to ensure the heating effect of continuous laser, to use emission spectrum measuring system to assist, to improve the penetrability of pulse laser in high concentration carbon smoke field, to heat the high concentration carbon smoke particle in the whole measuring area to radiation blazing temperature, and improve the accuracy of high concentration carbon smoke volume fraction measurement.
Drawings
FIG. 1 is a schematic diagram of a conventional LII test apparatus in the background art;
fig. 2 is a schematic structural view of the measuring device of the present invention.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the invention, but not all embodiments, and all other embodiments obtained by those skilled in the art without making creative efforts based on the embodiments of the present invention are all within the protection scope of the present invention.
As shown in fig. 2, the high-concentration soot volume fraction measuring device based on laser preheating comprises a pulse laser, a sheet light shaping and transmitting system, a burner, a time sequence controller and a detection system, wherein the time sequence controller is connected with the pulse laser and the detection system, the time sequence controller adopts a DG645 time sequence controller, laser emitted by the pulse laser is shaped into sheet light through the sheet light shaping and transmitting system and then enters the burner, the burner generates measured flame, the sheet light shaping and transmitting system comprises a beam expander I, a collimating mirror, a focusing mirror I and a reflecting mirror I which are sequentially arranged, and the detection system adopts a ICMOS detector and detects the area where the burner is located. Because the basic principle of the laser-induced blazing method is to heat the soot particles by using laser, if only single pulse laser is used for heating the soot particles, for a measurement target of high-concentration soot, the temperature of the soot particles downstream of a light beam propagation path cannot be increased to a near vaporization temperature due to the absorption and scattering effects of the soot particles on the laser, so that the phenomenon of unsaturated excitation is generated, and a great error is caused to a volume fraction measurement result. Therefore, the measuring device of the invention adopts a pulse laser and a continuous laser to jointly form a laser-induced incandescent light measuring light source, laser emitted by the continuous laser is shaped into a piece of light through an additional piece of light shaping and transmitting system and then enters a burner, the additional piece of light shaping and transmitting system comprises a beam expander II, a focusing mirror II and a reflecting mirror II which are sequentially arranged, and meanwhile, in order to ensure that two beams of laser cannot interfere in the beam combining process, a 1/2 wave plate I is arranged behind a light outlet of the pulse laser, a 1/2 wave plate II is arranged behind a light outlet of the continuous laser, and the polarization directions of the two beams of laser are adjusted to be mutually perpendicular. Wherein, continuous laser and pulse laser output wavelength are 532nm or 1064nm, continuous laser is used for heating soot particle to 3000K from flame background temperature (about 2000K), pulse laser is used for further heating the soot particle of 3000K to radiation incandescent temperature (about 4000K), two bundles of laser heat soot particle in the flame to the outside radiation incandescent light when experimental, incandescent light signal is collected by the detection system on normal direction. It should be noted that, in order to ensure that the initial temperature of the activated soot particles is 3000K, the laser light emitted by the continuous laser needs to cover the flame region completely, while the laser light emitted by the pulse laser only needs to cover the measurement region, the laser light emitted by the continuous laser widens in the direction parallel to the flame, compresses in the direction perpendicular to the flame, and forms a divergent sheet light incident on the flame region, so that not only the soot particles in the measurement region can be heated, but also the upstream soot particles can be heated together, and the laser light emitted by the pulse laser forms a sheet light with a certain length, the length of the sheet light is equal to the width of the measurement region, and the measurement region is often located in the downstream part of the flame. In addition, in order to monitor the heating effect of the continuous laser on the soot particles, the measuring device is further provided with an emission spectrum measuring system, the emission spectrum measuring system comprises a spectrometer and a collimator which are connected through an optical fiber, the collimator is provided with a focusing mirror III, the temperature of the soot particles on a light beam propagation path is measured, and the measuring result provides feedback for the output power of the continuous laser, so that the output power of the continuous laser can be adjusted according to the measuring result.
The core of the measuring device of the invention is that: when high-concentration soot is measured, the single pulse laser is used for heating the soot particles, and a mode of combining one pulse laser and one continuous laser is adopted for heating the soot particles. By the aid of the method, the problem that a single pulse laser is insufficient in heating high-concentration soot is solved, the phenomenon that the soot in a measurement area is excited in an incomplete saturation mode is avoided, and accordingly the problem of deviation of measurement results is solved. The continuous laser heating mode provides a 'secondary heating' solution for complete and complete excitation of high-concentration soot, and continuous laser firstly heats the high-concentration soot in the whole measuring area from the flame background temperature to 3000K, so that the temperature range required to be increased by pulse laser heating is greatly reduced, and the pressure of the pulse laser for heating soot particles is reduced. Under the premise of ensuring continuous laser to heat the soot particles to 3000K, the pulse laser is utilized to heat the temperature of the whole soot particles from 3000K to 4000K, and preheated high-concentration soot emits glow outwards under the action of the pulse laser, so that all the soot particles in the whole measuring area can be heated to 4000K, and the accuracy of experimental measurement results is ensured.
Soot particulate endothermic and exothermic model
There are many models for performing simulation on a laser-induced blazing signal in a time dimension, and the basis of the models mainly focuses on an energy conservation equation and a mass conservation equation of the soot particles, wherein the energy conservation equation is mainly the energy conservation equation, namely the relationship between the energy conservation equation of the soot particles and the energy absorption and loss, and in a thermal equilibrium state, the energy conservation equation of the soot particles can be written as follows:
wherein: Representing the laser energy absorbed by the soot particles,/> Representing the internal energy change of soot particles,/>Representing the heat carried away by sublimation of soot particles,/>Representing the heat carried away by the heat conduction of the soot particles,/>Representing the energy of the soot particles to external radiation (source of glow signal);
wherein the laser energy absorbed by the soot particles The relation between the absorption cross section C abs of the soot particles and the laser intensity distribution F (t) over time can be written as:
The absorption cross section C abs of the soot particles can be written as:
Wherein: d represents the primary particle size of the soot, lambda ex represents the excitation laser wavelength, and E (m) represents the soot absorption function of the complex refractive index;
because of the heat carried away by sublimation of soot particles Expressed as:
wherein: Δh V,S represents the sublimation enthalpy of the soot particles, M V,S represents the molar mass of carbon atoms, and M p represents the mass of soot particles;
The last term in the equation represents the rate of sublimation of the mass of soot particles, which can be expressed as:
Wherein: m v represents the molar mass of the lost soot vapor, R represents the gas constant, T represents the absolute temperature, P * represents the reference pressure, and T * represents the corresponding temperature when the carbon vapor pressure is equal to the reference pressure;
Substituting formula (5) into formula (4) to obtain:
Heat carried away by heat conduction of soot particles Expressed as:
Wherein: k a represents the air heat conductivity coefficient, G represents the heat transfer factor, l represents the mean free path, and T 0 represents the ambient temperature;
Wherein the heat transfer factor G can be expressed as:
Wherein: f represents thermal conductivity, α T represents a heat fusion coefficient, and γ represents a specific heat rate;
the soot particles radiate energy outwards Expressed as:
wherein: epsilon represents emissivity and sigma represents boltzmann constant;
in general, the emissivity and absorptivity of the soot particles are approximately uniform, i.e. epsilon=c abs, so that:
Substituting the energy conversion process expressions into the original equation to obtain the energy conservation equation expression.
From the conservation of energy model of the soot particles, it can be seen that the source of the incandescent signal is the absorption of laser energy by the soot particles, particularly as a function of the change in light intensity (energy carried by the laser) over time, essentially the process of heating the soot particles with the laser.
Principle of emission spectrometry
The emission spectrum measurement principle used in the invention is based on a colorimetric method, the colorimetric temperature measurement technology is based on the Planckian law of blackbody radiation, and the spectral radiation emergent degree when the blackbody temperature is T in a thermodynamic equilibrium state is expressed as:
wherein: epsilon λ represents the spectral emissivity of the target, lambda represents the wavelength, and C 1、C2 represents the first and second radiation constants;
In the wavelength range of 240-800nm and the temperature of 500-5000K, C 2/λT > 1, the Planck's law can be approximated as Wen's law, then equation (11) can be further transformed to:
When the measured wavelength bandwidth is narrower than or equal to 10nm, and the central wavelengths of the two selected wave bands lambda 1 and lambda 2 are close, the ratio of the spectral emissivity can be approximately 1.
When the spectrometer is used for measuring the radiation of the flame, the relation between the spectral radiation emergence degree and the output signal of the spectrometer is as follows:
M(λ,T)＝Eλ·Rλ (13)
Wherein: e λ represents a spectrum intensity value acquired by a spectrometer, and R λ represents a responsivity coefficient;
selecting two wave bands lambda 1 and lambda 2 and comparing the radiation exitances of the two wave bands to obtain:
after finishing, the expression of T can be obtained as follows:
And (5) calculating according to the formula (15) to obtain the temperature information of the measured target.
The method for measuring the volume fraction of the high-concentration soot by the method comprises the following specific steps:
Step one: placing of laser light source and setting up of shaping light path
Arranging a pulse laser and a continuous laser according to requirements, arranging a 1/2 wave plate I and a plate light shaping and transmitting system in sequence after a light outlet of the pulse laser, arranging a 1/2 wave plate II and an additional plate light shaping and transmitting system in sequence after the light outlet of the continuous laser, mutually perpendicular to the polarization directions of the pulse laser and the continuous laser, and adjusting an optical path to ensure that two laser beams are in the same plane when being incident into flame to be measured of a burner;
Step two: focusing of a detection system
The detection system is arranged at a proper position away from the burner, the imaging result is required to be clear, and the size of the field of view is consistent with the size of the light of the pulse laser;
Step three: construction of emission spectrum measurement system
Arranging a spectrometer, a collimator and a focusing mirror III in an emission spectrum measurement system according to requirements, and ensuring that the focal point position of the focusing mirror III is positioned at the position irradiated by laser sheet light;
Step four: LII pre-measurement preparation
After confirming that each device runs normally, igniting the flame to be tested, opening the continuous laser to heat the temperature of the carbon smoke particles to 3000K, monitoring the temperature of the carbon smoke particles in real time by an emission spectrum measuring system during the period, and adjusting the output power of the continuous laser in real time by feedback;
step five: measurement of soot volume fraction
And (3) adjusting the time delay between the pulse laser and the detection system, heating the temperature of the soot particles to the temperature of the radiant incandescent light, ensuring that the excited incandescent light signals can be collected by the detection system, and obtaining the soot volume fraction according to the recorded incandescent light signals.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (4)
1. The utility model provides a high concentration soot volume fraction measuring device based on laser preheats, includes pulse laser, piece light shaping and transmission system, combustor, time schedule controller and detecting system, the combustor produces the flame that is surveyed, time schedule controller connects control pulse laser and detecting system, the laser that pulse laser sent is incident to the combustor after piece light shaping through piece light shaping and transmission system, piece light shaping and transmission system includes beam expander I, collimating mirror, focusing mirror I and the speculum I that arrange in proper order, detecting system detects the regional that the combustor is located, its characterized in that: the measuring device also comprises a continuous laser, an additional piece light shaping and transmitting system and an emission spectrum measuring system, wherein laser emitted by the continuous laser is shaped into piece light through the additional piece light shaping and transmitting system and then enters the burner, the additional piece light shaping and transmitting system comprises a beam expander II, a focusing mirror II and a reflecting mirror II which are sequentially arranged, a 1/2 wave plate I is arranged behind a light outlet of the pulse laser, a 1/2 wave plate II is arranged behind a light outlet of the continuous laser, the emission spectrum measuring system comprises a spectrometer and a collimator which are connected through optical fibers, the collimator is provided with the focusing mirror III, the emission spectrum measuring system measures the temperature of soot particles, and a measuring result provides feedback for the output power of the continuous laser, and the measuring method of the measuring device comprises the following steps:
Step one: placing of laser light source and setting up of shaping light path
Arranging a pulse laser and a continuous laser according to requirements, arranging a 1/2 wave plate I and a plate light shaping and transmitting system in sequence after a light outlet of the pulse laser, arranging a 1/2 wave plate II and an additional plate light shaping and transmitting system in sequence after the light outlet of the continuous laser, mutually perpendicular to the polarization directions of the pulse laser and the continuous laser, and adjusting an optical path to ensure that two laser beams are in the same plane when being incident into flame to be measured of a burner;
Step two: focusing of a detection system
The detection system is arranged at a proper position away from the burner, the imaging result is required to be clear, and the size of the field of view is consistent with the size of the light of the pulse laser;
Step three: construction of emission spectrum measurement system
Arranging a spectrometer, a collimator and a focusing mirror III in an emission spectrum measurement system according to requirements, and ensuring that the focal point position of the focusing mirror III is positioned at the position irradiated by laser sheet light;
Step four: LII pre-measurement preparation
After confirming that each device runs normally, igniting the flame to be tested, opening the continuous laser to heat the temperature of the carbon smoke particles to 3000K, monitoring the temperature of the carbon smoke particles in real time by an emission spectrum measuring system during the period, and adjusting the output power of the continuous laser in real time by feedback; the emission spectrum measurement system adopts a colorimetric method to measure the temperature, and based on the Planckian law of blackbody radiation, the spectral radiation emergent degree when the blackbody temperature is T is expressed as:
wherein: epsilon λ represents the spectral emissivity of the target, lambda represents the wavelength, and C 1、C2 represents the first and second radiation constants;
equation (11) can be further transformed to give:
when the spectrometer is used for measuring the radiation of the flame, the relation between the spectral radiation emergence degree and the output signal of the spectrometer is as follows:
M(λ,T)＝Eλ·Rλ (13)
Wherein: e λ represents a spectrum intensity value acquired by a spectrometer, and R λ represents a responsivity coefficient;
selecting two wave bands lambda 1 and lambda 2 and comparing the radiation exitances of the two wave bands to obtain:
The expression of T obtained by finishing is:
calculating according to a formula (15) to obtain temperature information of a measured target;
step five: measurement of soot volume fraction
And (3) adjusting the time delay between the pulse laser and the detection system, heating the temperature of the soot particles to the temperature of the radiant incandescent light, ensuring that the excited incandescent light signals can be collected by the detection system, and obtaining the soot volume fraction according to the recorded incandescent light signals.
2. The high concentration soot volume fraction measuring device based on laser preheating according to claim 1, wherein: the timing controller adopts DG645 timing controller.
3. The high concentration soot volume fraction measuring device based on laser preheating according to claim 1, wherein: the detection system employs ICMOS detectors.
4. The high concentration soot volume fraction measuring device based on laser preheating according to claim 1, wherein: the polarization directions of the two laser beams emitted by the pulse laser and the continuous laser are mutually perpendicular.
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