The time-resolved measurement of gas components in the impact vibration environment such as combustion and explosion is of great significance for understanding the internal state and reaction process. In order to realize simultaneous detection of various gas components under impact vibration conditions, a method based on shock-resistant multi-reflection cavity is proposed to enhance spontaneous Raman scattering. The measurement system is divided into two parts: host subsystem and detection subsystem, which are connected by optical fiber. The host subsystem is far away from the impact site, while the detection subsystem is located at the measuring point, which can effectively improve the impact resistance by curing components and increasing shock absorption. At the same time, by means of signal enhancement, the measurement system can realize second-order time resolution and reliable measurement of gas components in strong impact vibration environment such as explosion. At the same time, by means of signal enhancement, the measurement system can realize second-order time resolution and reliable measurement of gas components in strong impact vibration environment such as explosion.
A technique that expands the OH-LIF thermometry range is developed. The PLIF of OH from dissociation of water in gas phase is used for temperature measurement both in flame and room air. The thermometry results from photo fragmentation laser induced fluorescence (PF-PLIF) at time delay from 200ns to 1ms after dissociation agree well with results from PLIF of OH from burning which are calibrated by CARS thermometry. And the results in room air agree with environment temperature at time delay from 50ns to 0.2ms. These two results validate the PF-PLIF thermometry method both in flame and room temperature, which allowing thermometry at low temperature or non-reaction region. At last the PF-PLIF was applied in a jet flow, and the temperature results from PF-PLIF, PLIF and CARS at different height of jet were compared.
KEYWORDS: Optimization (mathematics), Velocity measurements, Velocimetry, Combustion, Signal detection, Image segmentation, Image processing, Turbulence, Signal to noise ratio
The shape of OHp tagging signal line is complicated and changeable under the interaction of turbulence and combustion in HTV velocity measurement of scramjet combustion flow field. The light intensity distribution on the OHp tagging line is modulated, and the broadening degree is not consistent with the Gaussian distribution, so an optimal extraction method based on Hessian matrix is presented. Using the Hessian matrix, the gray distribution function on the cross-section of the tagging line is expanded in the normal direction by the second-order Taylor, and the precise position of the center line is obtained. Compared with line-by-line Gaussian fitting method, this method has better anti-distortion and anti-noise performance. The accurate extraction method of OHp molecular information is applied to the HTV velocity measurement technology in the scramjet combustion flow field, which improves the precision of the extraction and the accuracy of the HTV velocity measurement. It lays a foundation for the development and application of HTV.
In view of the surface temperature distribution and temperature rise measurement demand of metal target irradiated by high power laser, the thermosensitive phosphor surface temperature measurement technology was studied. The principle of two-color temperature measurement was introduced. After solving the key technologies of optical system optimization design, temperature distribution inversion calculation and high precision calibration, a compact thermosensitive phosphor surface temperature measuring system was developed. The temperature measurement range from room temperature to 1500 K, the space measurement range was greater than that of diameter 50mm, and the spatial resolution was better than 0.5mm. The thermosensitive phosphor surface temperature measurement technique was used to measure the surface temperature distribution and temperature rise of stainless steel targets irradiated by high power laser, and the results were compared with the results of thermocouple and numerical simulation. It is proved that the surface temperature measurement system can realize the measurement of surface temperature field distribution of high power laser irradiated target, and has high temperature measurement precision.
In order to improve extraction ability of the two-dimensional HTV grid experiment data and achieve rich flow field velocimetry data. In this paper, a two-dimensional grid extraction method combining cross ponits and grid lines is proposed. A template indirect correlation method was used to extract the position of cross ponits. Based on the vector position information of cross ponits, two-dimensional inversion of convective field velocity is achieved by using the method of skeleton extraction with directional template. This method not only can extend the inversion data, but also can be used in the scramjet combustion flow field, that the relative uncertainty of calculation speed is optimized from 0.8% to 0.17%.
In order to measure the 2-D velocimetry distribution without seed injection in the high-speed flow field of the engine, the 2-D HTV (hydroxyl tagging velocimetry) technique in the complex combustion field has been developed. The image processing method combining difference method with cross correlation method is presented. The background noise is suppressed by the difference method. The variable-template is used to perform cross correlation operation with experimental images, and the obtained correlation images is fitted with two-dimensional polynomial. Not only can the complex background interference be suppressed, but also can realize accurate extraction position of the tagging cross grid center.So the extraction accuracy is better than 0.25 pixels, when the image SNR is higher than 2. At the same time, based on Matlab software, the data processing program is written. The velocimetry distribution is gained by processing the experimental data in the flow field of the scramjet model. The speed calculation error is less than 5%, which meets the requirement of measurement accuracy of the system.
Stray light is the main noise source for planar imaging measurement technique, which can affect the accuracy of results directly. A method of Structured Laser Illumination Planar Imaging (SLIPI) was used to solve this issue. The key of SLIPI is periodic modulation of laser spatial intensity and implementation of post filtering algorithm. In this paper, cylindrical micro lens array was used to modulate the spatial intensity of laser periodically, which was compared with Ronchi ruling. The post filtering algorithm adopts phase-locked detection method. The signal results can be separated from the noisy image using only one measurement image by this method. SLIPI method has been used in Temperature Sensitive Paints measurement experiments. A diagnostic optical path combining cylindrical micro lens array and cylindrical mirror was designed for the need of surface light source irradiation. The results show that the method of SLIPI can be applied to most planar imaging measurement techniques, and the accuracy of two-dimensional parameter measurement can be further improved.
For the purpose of measuring the flow velocity in a scramjet test model, an special designed measurement system was established, including the strong vibration suppression, optical transport consideration, the movable device etc. The interference of the strong vibration to the velocity measurements was avoided by two ICCD cameras capturing the reference tag lines image and moved tag lines image together during an experiment. According to the tag lines image feature, data processing including correlation algorithm, data fitting by a Gauss function were used respectively to extract the positions of the reference tag lines and the moved tag lines. The velocity measurements were carried out at the isolation section and the cavity section. The results showed that the well SNR could be achieved in the H2/air combustion heating flow, but in the kerosene fuel combustion flow, the measurements images might be interfered by the strong OH background from the chemical reaction, and the signal intensity could be reduced due to the tag laser attenuation through the absorption by kerosene vapor. But when the combustor model was run at a low chemical equivalent, the interference could be suppressed to an accepted level.
KEYWORDS: Chemical species, Luminescence, Combustion, Liquids, Optical filters, Signal to noise ratio, Bioalcohols, Indium, Laser induced fluorescence, Signal generators
Nonlinear regime Two-line Atomic Fluorescence (NTLAF) is a promising technique for two-dimensional thermometry. A key challenge is seeding of indium atoms into flame. This work aims at investigating the mechanism of Indium LIF signal generation in a fuel-rich InCl3-ethanol premixed flame. Several types of images including natural emission of the flame itself, natural emission of CH, natural emission of OH, natural emission at 410 nm/451 nm of indium atom, and laser induced fluorescence at 410 nm/451 nm were obtained. The indium atom was generated in the flame front, and could survive in the post-flame zone for a while which is benefit for making NTLAF measurements. Further detail mechanism of fluorescence signals generation in InCl3-ethanol solution burning was investigated. The conclusion which probable to be drew is that to gain high NTLAF signals, the size of liquid droplets should be well controlled, neither to be too large nor to be gasified.
The key to improve Hydroxyl Tagging Velocimetry (HTV) Measurement precision in the laser supersonic combustion diagnosis research is to improve the effect of image processing. In terms of strong OH background and low signal-to-noise ratio (SNR) issues, the approach for HTV signal extraction in supersonic combustion filed is proposed. Firstly, the method of compensation-and-correction-window-filter and the progressive approach characteristic filtering window approach are adopted to remove background for image preprocessing. Then the algorithm combined image segmentation and the skeleton extraction is employed for signal extraction, that improves the signal identification ability in the interferences of fierce combustion zone of a mass of hydroxyl background, solves the insufficient precision problem of extracting hydroxyl effective signal, what's more, achieves the effective information of velocity distribution in combustion flow.
In order to obtain the velocity with high dependability at extreme combustion condition, a 2-D interferometric Rayleigh scattering (IRS) velocimetry based on detecting the Doppler frequency shift of molecular scattering with Fabry–Perot etalon was developed. The 2-D IRS measurement system was set up with a multi-beam probe laser, aspherical lens collection optics, and a solid Fabry-Perot etalon. A multi-beam probe laser with 0.5mm intervals was formed by collimating a laser sheet passing through a cylindrical microlens arrays. The aspherical lens was used to enhance the intensity of Rayleigh scattering signal. The 2-D velocity results of a Mach 1.5 air flow were obtained. The velocity in the flow center is about 450 m/s. The reconstructed results are in accordance with the characteristic of flow, which indicates the validity of this technique.
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