Plasma properties are diagnosed in parallel-plane electrodes under 1-15 kPa within input power of 0-25 W by coupling Optical Emission Spectroscopy (OES) and Planar Laser-induced fluorescence (PLIF). Electron excitation temperature (Te), electron density (Ne) are obtained based on the intensities and broadenings of atomic and ionic spectral lines of argon. The spatial resolution of Te and Ne are measured by a high-precision setup based on fiber. At the gas pressure of 1 kPa, Te reaches maximum of 8.745×103 K while the peak of Ne appears in 15 kPa, is 3.237×1016 cm-3 . Besides, spatial distribution of 1s5 metastable atoms (ArM) with transition scheme 4s( 2P0 3/2)2 -4p ( P (2P01/2)1-4s(2P03/2)1 are revealed by PLIF, as a complementary of plasma properties. The number density of ArM also shows a larger number density in 15 kPa. Combined with OES, Te, Ne and number of ArM are higher around the surface of anode within discharge area. The current experimental results are demonstration of optimal plasma state under different external parameters and validation of relevant discharge models
The model combustor of aircraft engine under fuel-lean condition is characterized by planar laser-induced fluorescence (PLIF) technique. By imaging the fluorescence from OH and CH2O simultaneously under various operation points, the transient structures of the reaction zone and preheat zone have been investigated. By the application of proper orthogonal decomposition (POD) and extended POD (EPOD) methods to the OH PLIF and CH2O PLIF data, the main dynamics modes of the swirling flame are extracted, as well as the CH2O PLIF signal distribution for each POD mode. The experimental results indicate that as the thermal power of the combustor increases, the time-averaged structure and dynamics modes experience notable transitions. At relatively high flow rate, local extinction occurs and unburnt fuel emerges in the external recirculation zone (ERZ).
Instantaneous measurement of flame spatial structure has been long desired for complicated combustion condition (gas turbine, ramjet et.). Three dimensional computed tomography of chemiluminescence (3D-CTC) is a potential testing technology for its simplicity, low cost, high temporal and spatial resolution. In most former studies, multi-lens and multi-CCD are used to capture projects from different view angles. In order to improve adaptability, only one CCD was utilized to build 3D-CTC system combined with customized fiber-based endoscopes (FBEs). It makes this technique more economic and simple. Validate experiments were made using 10 small CH4 diffusion flame arranging in a ring structure. Based on one instantaneous image, computed tomography can be conducted using Algebraic Reconstruction Technique (ART) algorithm. The reconstructed results, including the flame number, ring shape of the flames, the inner and outer diameter of ring, all well match the physical structure. It indicates that 3D combustion chemiluminescence could be well reconstructed using single camera.
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