RU2805562C1 - Schlieren instrument for a flame with high time resolution - Google Patents

Abstract

FIELD: emission spectroscopy.

SUBSTANCE: relates to a schlieren instrument for a flame with a high temporal resolution. The schlieren instrument consists of a pulsed radiation source, collimators, an imaging diaphragm, an optical spectral-selective filter that forms an image of the optics, a strobe camera with a matrix photodetector connected by a strobe control line to a pulsed radiation source, and an optical emission spectrometer. The optical emission spectrometer consists of focusing optics and a broadband optical spectrometer connected to a pulsed radiation source and an optical spectral-selective filter by control communication channels for transmitting a control signal about the presence of interfering spectral components and configured to display the validity of the flame schlieren pattern on the display. The pulsed radiation source and the optical spectral-selective filter are frequency tunable.

EFFECT: providing the ability to maintain the contrast of the flame schlieren pattern with a high temporal resolution under dynamically changing conditions of the combustion process.

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Description

The invention relates to optical devices for shadow imaging and can be used to study unsteady combustion processes, including continuous monitoring with high time resolution of the shadow flow pattern with combustion.

One of the methods for visualizing high-speed flows with combustion is classical refractometric methods for studying transparent gas flows, for example, direct shadow, shadow and interferometric (www.cyberleninka.ru, article “Visualization of the structure of gas flows by shadow and interference methods” Inshakov S.I., Bulletin of the Samara State Aerospace University named after Academician S.P. Korolev, 2007).

All methods considered use a system that includes a radiation source and a recording camera. The classic radiation source is a broadband source in the form of halogen, mercury or deuterium lamps. The main disadvantage in the study of non-stationary structures is the insufficiently high time resolution of these systems. The relevance of the topic is due to the need for continuous monitoring of the shadow flow pattern with high time resolution.

To temporarily freeze the gas flow pattern, pulsed light sources are usually used. In the proposed shadow device, a pulsed radiation source was chosen as a solution, which is synchronized with a camera containing a matrix photodetector that records a continuous video stream. As is known, during combustion several types of optical radiation arise - a continuous spectrum of thermal radiation and spectrally discrete radiation of atomic lines and molecular bands (www.cyberleninka.ru, article “On the choice of the spectral interval when studying temperature fields in a flame using a thermal imager” by M.V. Agafontsev et al. Journal: Bulletin of Science of Siberia. 2015. Special issue (15), pp. 37-42). This radiation reduces the contrast of the shadow image until the shadow image of the object of study (flame) completely disappears. To reduce the influence of the object's own glow, two methods are used - temporal: reducing the exposure time, and spectral: using narrow-band spectral-selective filters.

There is a known patent application “High-Speed transient schlieren system for large wind turmel” (CN110207940A, IPC G01M 9/06, G02B 17/06, G02B 27/54, publication date 09/06/2019). In the application under consideration, a pulsed source of probing radiation is used to visualize the shadow pattern of high-speed flows.

The disadvantage of this system is the lack of spectral-selective and spectrometric systems, which does not allow shadow flame studies.

The invention “Device and method for measuring flame for and temperature synchronously” is known (patent CN107782463B, IPC G01B 11/00, G01B 11/24, G01K 11/003, publication date 04/28/2020). The patent describes a device for measuring flame shape using a high-speed shadow instrument and simultaneously measuring flame temperature using an absorption method using a diode laser. This device does not contain a module for spectral discrimination of the flame's own glow and an optical emission spectrometer.

The disadvantage of this device is the insufficient contrast of the shadow pattern of the flame, which leads to poor quality visualization.

A known system for studying the spatial structure of a flame is “System for researching flamecellular space structure based on three-dimensional Schlieren imaging technology” (patent CN111397907 B, IPC G01K 1/02, G01K 7/02, G01L 9/08, publication date 09.19.2021 G.). This system is based on a stereo-shadow device, and, moreover, shadow optical tomography. The system uses high-speed recording cameras, but there are no modules for spectral discrimination of the flame's own glow and an optical emission spectrometer.

The disadvantage of this device is the insufficient contrast of the shadow pattern of the flame, which leads to low-quality visualization due to the illumination of the shadow pattern by the flame’s own glow.

The prototype is a shadow device for studying high-speed flows with combustion (article by K.D. Kudryavtsev, A.N. Morozov, M.V. Rybakov, Materials of the Twentieth International School-Seminar, Moscow 2020, pp. 75-76).

The considered shadow device for a flame with high time resolution contains a source of probing radiation, a receiving system in the form of a gated camera with a matrix photodetector, an optical spectral-selective filter, and a synchronization system in the form of a strobe control line with a pulsed radiation source. A gate pulse signal (strobe) is used to synchronize the matrix exposure with the source radiation pulse using a small time window.

This shadow device does not provide the ability to continuously adjust the frequency of a pulsed radiation source and an optical spectral-selective filter in real time, which is its main disadvantage. To set up the device, a preliminary analysis of the emission spectra of the flow radiation is used to adjust the spectral region of the study, which limits the applicability of the shadow device in the case of changing parameters in terms of combustion temperature, and, consequently, in the chemical and spectral composition of the combustion process under study - thus, there are no wavelengths tunable measuring system components. Another disadvantage of the system is the lack of a continuous video data stream, since the video camera used in the work allows generating a sequence of images, but without the possibility of reverse synchronous control of the source of probing radiation.

The objective and technical result of the claimed invention is the development and creation of a flame shadow device with high time resolution, which allows maintaining the contrast of the shadow flame pattern with high time resolution under dynamically changing conditions of the combustion process.

The solution to the problem and obtaining a technical result is ensured due to the fact that the shadow device consists of a pulsed radiation source, collimators, a visualizing diaphragm, an optical spectral-selective filter, image-forming optics, a gated camera with a matrix photodetector connected by a strobe control line with a pulsed radiation source with function of transmitting data to the display, while the shadow device additionally contains an optical emission spectrometer consisting of focusing optics and a broadband optical spectrometer, while the optical emission spectrometer is connected to a pulsed radiation source and an optical spectral-selective filter by control communication channels, a pulsed radiation source and The optical spectral-selective filter is made tunable in frequency, and the optical emission spectrometer is designed to transmit an indication of the validity of the shadow flame pattern to the display.

The essence of the invention is illustrated by the following figures.

In fig. 1 shows the high time resolution shadow device described in the prototype.

In fig. Figure 2 shows the proposed shadow device with high temporal resolution.

List of elements:

1 - Pulsed radiation source

2 - Collimator 1

3 - Object of study (flame)

4 - Collimator 2

5 - Imaging diaphragm

6 - Optical spectral selective filter

7 - Imaging optics

8 - Gated camera with matrix photodetector

9 - Functional data output

10 - Display

11 - Strobe control line

12 - Focusing optics

13 - Broadband optical spectrometer

14 - Control communication channels

15 - Functional output indicating the validity of the shadow flame pattern.

The proposed flame shadow device with high time resolution consists of a pulsed radiation source, collimators, an imaging diaphragm, an optical spectral-selective filter, image-forming optics, a gated camera with a matrix photodetector, focusing optics, a broadband optical spectrometer and a display, which are rigidly fixed at using screws on the frame (not indicated in the figures). A bed is a fixed base, a frame on which individual parts of a device are mounted (S.I. Ozhegov, N.Yu. Shvedova. Ozhegov’s Explanatory Dictionary. 1949 - 1992).

The proposed shadow device for a flame with high time resolution contains: collimators 2 and 4, between which the object of study 3 (for example, a flame) is placed, a visualizing diaphragm 5 (for example, a cut-off filter, a Foucault knife), an optical spectral-selective filter 6 that forms the image optics 7, a gated camera with a matrix photodetector 8, which is connected by a control line of the strobe 11 with a pulsed radiation source 1 and with a functional data output 9 to the display 10, an optical emission spectrometer which consists of focusing optics 12 and a broadband optical spectrometer 13. Optical emission spectrometer The spectrometer is connected to a pulsed radiation source 1 and an optical spectral-selective filter 6 via control communication channels 14, and is configured with a functional display indicating the validity of the shadow flame pattern 15 on the display 10.

Strobe is an electronic method of selecting a time interval for monitoring control or subsequent processing (Dictionary-reference book of terms for normative and technical documentation www.academic.ru). A data transmission line is a means that is used in information networks to distribute signals in the desired direction; it can be a coaxial cable, twisted pair, wire, light guide (I.P. Norenkov, V.A. Trudonoshin. Telecommunication technologies and networks. MSTU im. Bauman, Moscow 1999, www.academic.ru). The strobe control line in this device means the line through which the strobe signal is transmitted.

The functional data output in this device is implemented in the form of a function for transmitting data to the display using a communication channel that connects the gated camera with a matrix photodetector 8 with a display 10. The communication channel is a means of one-way data transfer (I.P. Norenkov, V.A. Trudonoshin Telecommunication technologies and networks, MSTU named after N.E. Bauman, Moscow, 1999), while the communication channel can also be made in the form of a coaxial cable, twisted pair, wire or fiber.

A display is an electronic device designed to visually display information (ru.wikipedia.org).

The functional output for indicating the validity of the shadow flame pattern in this device is implemented as a function for transmitting an indication of the validity of the shadow flame pattern using a communication channel that connects the broadband optical spectrometer to the display.

Images of the object of study 3 using focusing optics 12 are recorded by a broadband optical spectrometer 13 with a functional output indicating the validity of the shadow flame pattern 15 on the display 10, while the broadband optical spectrometer 13 is connected by control communication channels 14 with the radiation source 1 and an optical spectral-selective filter 6. A spectrometer is an optical instrument used in spectroscopic studies to record the spectrum, its quantitative processing, and subsequent analysis (Wikipedia - ru.wikipedia.org).

In the proposed device, communication channels 14 are control channels and serve to transmit a control signal about the presence of interfering spectral components from the broadband optical spectrometer 13 to the radiation source 1 and the optical spectral-selective filter 6.

The proposed shadow device works as follows. Light from a pulsed radiation source 1 is converted into a beam of parallel rays using a collimator 2, then a beam of parallel rays passes through the object of study 3, while some of the rays are deflected, refracting at inhomogeneities in the density of the object of study 3, the refracted beam of rays is focused by the collimator 4 on the imaging diaphragm 5, allowing to obtain a shadow picture of the inhomogeneity of the densities of the object of study 3. The resulting shadow picture is recorded by a gated camera with a matrix photodetector 8, while the image of the shadow picture is obtained using image-forming optics 7. The intrinsic glow of the flow, which reduces the contrast of the shadow picture, is cut off using an optical spectral-selective filter 6. To match the light pulse from the pulsed radiation source 1 with the exposure time of the gated camera with matrix photodetector 8, the strobe control line 11 is used. In the proposed device, the gated camera with matrix photodetector 8 outputs a continuous video stream using functional data output 9 to display 10. In order to ensure synchronization of the video stream with a pulsed radiation source 1, the radiation pulse is controlled directly by a gated camera with a matrix photodetector 8.

As a result of the combustion process, the object of study 3 glows in a wide spectral range of the optical spectrum. This glow is a combination of both spectrum-continuous radiation (for example, thermal radiation from soot) and spectral-selective radiation produced by the excited atomic and molecular components of the flame of research object 3. To suppress the flame’s own radiation, two methods are used - temporal and spectral. As a temporary method, strobing of the recording chamber is used in temporal coordination with the source radiation pulse. Thus, with a short duration of the light pulse of the pulsed radiation source 1, the flame glow is suppressed in proportion to the duty cycle of the pulse sequence. As a spectral method for suppressing the flame's own glow, an optical spectral-selective filter 6 is used, the passband of which is adjusted to the radiation wavelength of the pulsed radiation source 1, while all flame glow is suppressed, the radiation wavelengths of which are outside the narrow spectral range of the optical spectral passband -selective filter 6.

A broadband optical spectrometer 13 records the emission spectrum of the object of study 3 using focusing optics 12. Information about intense spectral lines is supplied to a pulsed radiation source 1 and an optical spectral-selective filter 6, using control communication channels 14. When the wavelengths of intense spectral emission lines coincide object of study 3 with the wavelengths of the radiation of the pulsed radiation source 1 and the optical spectral-selective filter 6, the wavelengths of radiation and transmission are adjusted, respectively, which makes it possible to additionally effectively tune out from the own glow of the object of study 3. If it is impossible to tune out from the own glow of the object of study 3 using Functional output of the indication of the validity of the shadow flame pattern 15 on the display 10 provides information about the impossibility of displaying the correct shadow pattern.

The proposed shadow device allows, in contrast to devices with a continuous radiation source, to record non-stationary phenomena with high time resolution. It allows for continuous video recording of shadow patterns “frozen” in time. Also, the shadow device allows for discrimination of the own glow of the object of study 3 due to the short shutter speeds of the synchronized recording gated camera with a matrix photodetector 8 and the narrow spectral range of the passband of the optical spectral-selective filter 6.

The introduction of an optical emission spectrometer into the shadow device, consisting of focusing optics 12 and a broadband optical spectrometer 13, allows it to be used for dynamically changing conditions of the combustion process. Changes in combustion conditions can occur both in temperature and in chemical composition, which in turn leads to a change in the optical spectrum of the flame radiation. The flame's own radiation reduces the contrast of the shadow pattern until it completely disappears. The optical emission spectrometer used makes it possible to control the flame emission spectrum in real time, which makes it possible to use wavelength-controlled spectral-selective components - a pulsed radiation source 1 and an optical spectral-selective filter 6. Synchronous tuning in frequency (wavelength) of these shadow components The device allows for continuous shadow visualization of the flame. If it is not possible to register the shadow flame pattern due to the intense intrinsic glow of the flame in a wide spectral range, the broadband optical spectrometer uses a functional output indicating the validity of the shadow flame pattern 15 directly to the display 10.

A flame shadow device with high time resolution has been created, which allows maintaining the contrast of the flame shadow pattern with high time resolution under dynamically changing conditions of the combustion process.

Claims (1)

A flame shadow device with high time resolution, consisting of a pulsed radiation source, collimators, an imaging diaphragm, an optical spectral-selective filter, image-forming optics, a gated camera with a matrix photodetector, connected by a strobe control line to a pulsed radiation source, with a data transfer function to display, characterized in that the shadow device additionally contains an optical emission spectrometer consisting of focusing optics and a broadband optical spectrometer connected to a pulsed radiation source and an optical spectral-selective filter by control communication channels for transmitting a control signal about the presence of interfering spectral components from the broadband optical a spectrometer to a pulsed radiation source and an optical spectral-selective filter and made with a functional output indicating the validity of the shadow flame pattern to the display via a communication channel connecting a broadband optical spectrometer to the display, while the pulsed radiation source and the optical spectral-selective filter are made tunable in frequency, and the pulsed radiation source is controlled by a gated camera with a matrix photodetector.

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