Date of Award
Ph.D. in Physics
Line-of-sight spectral observations in the near ultraviolet regime are made of the high-speed afterburning exhaust plume from a lab-scale rocket simulator which reacts gaseous H2 with gaseous O2. In the plume, afterburning results from energetic, unspent fuel (H2) reacting with the external Air. Hydroxyl (OH) is a dominant intermediate product in the reaction zone and is probed using broadband, near UV absorption spectroscopy to estimate the macrostate parameters of the exhaust plume. Molecular energy transition data from the HITRAN online database is used to model the absorption spectra as a bivariate function of the macrostate parameters temperature, T, and molecular column density, Nl. The reported macrostate builds the model spectrum which has the maximum probability in the posterior of a Bayesian estimator. Aluminum oxide (Al2O3) particles of nominal effective diameter 0.3 microns are injected into the rocket combustion chamber through the H2 fuel line with relatively low mass-loading and are carried along with the flow into the exhaust plume. The presence of these particles has a clearly broadband extinction effect on the transmission spectra. Separating this effect from the molecular absorption in a spectrum is achieved without any prior knowledge of the particle size distribution, provided the scattering spectrum has been characterized experimentally without any other spectral effects involved. In this way, broad band spectral measurements can be used to estimate the plume macrostate whether or not interstitial particulate is present. A bench top experiment with a vapor reference cell containing Oxygen gas (O2) at a known pressure and temperature is used to validate this procedure.
Herlan, Jonathan, "Influences of alumina particles on hydroxyl macrostate estimates in a high-speed, reacting flow" (2021). Electronic Theses and Dissertations. 2011.