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The spectroscopic analysis of plume emissions is a non-intrusive method which has been used to check for fatigue and possible damage throughout the pumps and other mechanisms in a rocket motor or engine. These components are made of various alloys. Knowing the composition of the alloys and for which parts they are used, one can potentially determin...
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... Some of the metals were chosen due to their presence in alloys used in certain engine components and because they appear to have produced molecular bands in previous combustion studies. [8,[10][11][12][13] Other metals were added to the study based on their tendency to oxidize easily, thus being likely to produce refractory particles in combustion. Fuel grains were made using R-45 HTPB resin and Desmodur N100 curative. ...
... Quantification studies have thus far focused only on the metal atomic emissions. [12,13] The goal of this study was to determine feasibility to quantitatively characterize molecular band emissions based on relative emission intensity. The emission detection system consisted of a quartz collection lens with a 100 mm focal length placed 20 inches (510 mm) from the exhaust plume axis and 6 inches (152 mm) behind the exit nozzle plane of the rocket motor. ...
A labscale hybrid rocket was used to study spectral bands produced by metal combustion. Bands in the ultraviolet-visible region (300– 750 nm) are of interest. The rubber-like fuel, hydroxyl-terminated polybutadiene (HTPB), was doped with a metallic salt for introduction into the plume during combustion. When introduced, the metals produce atomic line emissions as well as molecular bands due to excited forms of me-tallic molecules in combustion. The most likely molecular band emissions are from the excited states of metal oxides or metal hydroxides formed by these metals in the presence of the oxygen flow of the hybrid rocket. As the concentration of metallic dopants increases in the flame, the mo-lecular band emissions also increase. The fash-ion by which they increase is observed here. The high concentrations observed for these metals result in intensity versus concentration curves that diverge from the expected linear pro-gression for manganese, magnesium and stron-tium. The molecular band emissions observed for calcium, barium and copper in this study followed linear progression, as does the atomic line emis-sion for barium. The line emissions for manga-nese, strontium and calcium lean toward the con-centration axis. The curves are attributed to self-absorption or increased interactions among mix-ing species as metal concentration increases in the plume. This study indicates that molecular bands are useful for monitoring engine health and for plume diagnostics.
... The spectrograph system (for plume spectroscopy) has been described previously. [12] Figure 5. Picture of UV-Vis spectroscopic system. ...
... Molecular bands are present that appear to be similar to those in previous plume studies. [12] Further experiments are planned to fully characterize the baseline emissions in the combustion chamber. However, the current experiments validate the ability to extract useful information from the injector head mounted optics. ...
The oxygen injector head in UALR's labscale hybrid rocket motor has been redesigned to in- clude a coaxially located optical port. This port permits viewing directly into the space in front of the fuel grain where combustion is initiated. It is designed to allow a visible-imaging fiber optic, a UV-Vis fiber optic, or an infrared fiber optic to be aligned coaxially with the motor. The imaging fiber optic shows swirling and pulsating flow fields, which indicate that one-dimensional flow model assumptions are not valid. The quartz fi- ber optic is used with a UV-Vis spectrometer to perform spectral studies using fuels doped with metals. It is demonstrated that the same species that are seen in the plume can be detected in the combustion zone, which permits comparison of species at the two end points of the combustion process.
An instrumentation system was developed to measure the opacity of a hybrid rocket plume as a function of optical wavelength. The source consisted of collineated beams from two lasers, providing seven wavelengths in a single probe beam. Detection was accomplished with a spec- trograph equipped with a photodiode array. Previous work with a two-wavelength system demonstrated the ability to follow the changes in opacity level of a hybrid rocket plume during the various stages of a typical firing cycle. The present work was to investigate the feasibility of using a multiple wavelength system to acquire more detailed information about the particulates present in the hybrid rocket plume. Qualitative analysis of the plume particulates was done by comparison of the relative extinc- tion coefficients of the laser wavelengths with published extinction coefficient curves from Mie scattering theory. While it was found that light level fluctuations in the system prevent defini- tive conclusions, the data suggests that the par- ticulate matter in the plume may consist of some optically transparent material. This is in contrast to the absorbing, soot-like material that might be expected in a hybrid rocket plume.
