Date of Award
2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical and Aerospace Engineering
Committee Chair
Kunning Xu
Committee Member
Robert Frederick Jr.
Committee Member
John Bennewitz
Committee Member
Robert Driscoll
Committee Member
Christopher Brophy
Research Advisor
Kunning Xu
Subject(s)
Rocket engines--Combustion, Injectors, Gas dynamics, Rotating Detonation Engine (RDE)
Abstract
Laser induced breakdown spectroscopy (LIBS) was developed for applications in the characterization of rocket engine injectors to evaluate the instantaneous, local gas concentration, or local mixture ratio of the injector flowfield. In this work, LIBS was tested in steady flows of premixed methane and air to create the correlation of the LIBS spectral species ratios H/O ratio, followed by a steady non-premixed flow to extract the localized mixing and shape of the flow field, then a transient study was performed to measure the development of the flow of the reactants in a pentad impingement injector previously used in RDE tests. This work tracks recovery on the basis of mixture concentration rather than bulk flow recovery to account for scenarios in which one reactant, usually the higher flow rate reactant, leads in recovery biasing the early development of the flowfield to be either too lean or rich. The results were supported using multiple methods, including plasma modeling, machine learning, and ANSYS simulations of steady and transient behavior. In steady premixed methane-air tests, a strong linear correlation between H/O spectral ratios and mixture equivalence ratio (R2 = 0.99 , MSE = 10E-04) is established and a linear regression model captures over 80% of variance in prediction of H/O spectral ratios with only five input variables (equivalence ratio, total flow rate, average laser pulse energy, ICCD gate delay, and ICCD gate width). For the non-premixed injector flowfields, the average equivalence ratio, and the highest percentage of the flowfield within +/- 10% of the target set mixture occurred at the highest flow rates (8800 sccm), or the highest injector momentum ratio tested, where the flowfield generally spreads further and more evenly. Extrapolating the sampled rows of the flowfield found that the concentration profiles mimic the velocity profiles of a turbulent jet in which the Gaussian fit has a steady stretch factor. The stretch factor of the concentration rows is 0.126. This result can be used to determine the flowfield mixture beyond the 1.75-inch sample area. Lastly, for transient tests, concentration-based flow recovery times, defined as the time the LIBS sees a signal to the time the H/O ratio reaches its steady state value, are location dependent and decrease with increasing flow rate. For flow rates of 4800, 6800, 8800, and 11000 sccm, the recovery times are 463, 417, 408, and 378 milliseconds, respectively. The exponential curve fit of the recovery times and flow rates to RDE operation flow rates found recovery times on the order of wave arrival times in a methane-oxygen propellant RDE. Understanding the flowfield mixedness and flow recovery times are critical in measuring the quality of performance of the injector that affects the overall rocket engine/RDE performance.
Recommended Citation
Hemming, Michaela Renee, "Rocket injector flowfield characterization through local, instantaneous gas composition tracing using laser induced breakdown spectroscopy" (2026). Dissertations. 495.
https://louis.uah.edu/uah-dissertations/495