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Daniel Guggenheim School of Aerospace Engineering

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search.filters.applied.f.advisor: Sun, Wenting × End date: 2023 × Start date: 2020 × search.filters.applied.f.isSeriesOfPublicationTitle: Aerospace Engineering Graduate Degree Program ×

Publication Search Results

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    Investigation of Ozone Initiated Ethylene Oxidation at Room Temperature: Chemistry and Flame Dynamics
    (Georgia Institute of Technology, 2021-08-24) Wu, Bin
    Ozone (O3) addition has been proved to be efficient and effective in combustion enhancement and control. For saturated fuels, it is recognized that the O3 decomposition at elevated temperatures dominantly contributes to the improvement. However, for unsaturated fuels, the knowledge is limited, due to the much more complicated kinetic pathways induced by direct reaction between fuel and O3, i.e., the ozonolysis reaction. In this dissertation, the O3 initiated ethylene (C2H4) oxidation is experimentally investigated at room temperature using multiple diagnostic methods. To accommodate the rapid reaction between C2H4 and O3, a novel flow reactor system with online fast-mixing feature is designed, manufactured, and deployed. By coupling the flow reactor system to 255 nm LED absorption technique, the global reaction rate constant of C2H4+O3 is measured at ambient conditions. Being supplementary to the results in previous studies, many new products and intermediates are rigorously identified in this chemical system of room-temperature C2H4 oxidation, using both gas chromatography and tunable photoionization mass spectrometry. Based on determined molecular structures by quantum chemistry calculations, the detected species can be mainly categorized into alcohol, aldehyde, and peroxide, while many of them have been widely considered as key intermediates in low-temperature oxidation chemistry. Additionally, the effect of ozonolysis reaction on laminar flame dynamics is studied. Stable C2H4 lifted flames are established with oxygen/nitrogen co-flow at reduced oxygen content conditions. By adding certain amounts of O3 into the oxidizer co-flow, non-monotonic flame dynamic behaviors are recorded. Depending on the initial value of the flame liftoff height before O3 is added, it is observed that the flame liftoff height could either increase or decrease. Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) measurement shows that prompt ozonolysis reaction between C2H4 and O3 produces large amounts of CH2O upstream of the flame. In contrast to previous studies of O3 addition on lifted flames—with saturated fuels in which O3 decomposition dominates—the ozonolysis reaction between C2H4 and O3 considerably changes the chemical composition of fuel jet even at room temperature. Such chemical reaction causes the simultaneous increase of both triple flame propagation speed of lifted flame and axial jet velocity along the stoichiometric contour, which also therefore changes the dynamic balance between these two values to stabilize the flame.
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    Numerical simulations of real-gas flows with phase-equilibrium thermodynamics
    (Georgia Institute of Technology, 2020-07-20) Tudisco, Principio
    Motivated by the complex physics of multi-component mixtures in strongly non-ideal, real-gas (RG) conditions reported in the field of chemical engineering, this work aims to address the behavior of multi-phase thermodynamics from a broader point of view. The focus is to evaluate the differences, as well as the possible sources of errors that would arise in a computational fluid-dynamics (CFD) simulation when conventional single-phase and multi-phase equilibrium RG thermodynamics are employed: an area of research that despite the active interest in many communities (especially CFD), has not been completely understood. Knowledge of the effects that multi-phase RG thermodynamics with the assumption of vapor-liquid equilibrium (VLE) can have on a flow dynamics is important because it establishes the relevance of the fully coupled CFD-VLE solver. In fact, this relevance may go beyond the stand-alone calculation of a multi-phase state, providing important insights about the physics that may not be captured if the single-phase assumption is invoked. This work provides an extensive study of RG mixtures from a physical and numerical point of view. The difficulties associated with their modeling are discussed in detail and solutions are provided accordingly. Emphasis is given to the occurrence and suppression of numerical noise in form of pressure oscillations that can pollute the simulation to the point that it cannot be performed. Extension of existing models to eliminate such problem is achieved by incorporating the effects of VLE thermodynamics in a consistent manner, ultimately forming a new and robust tool to investigate the physics further. The resulting model is applied to non-reacting and reacting flows in canonical setups where emphasis is devoted to the discussion of the differences and sources of errors that would occur if this multi-phase behavior is not taken into account. Results show that the different thermodynamic states reached by this advanced model can have an impact on the flow physics, especially in a non-reacting (or more in general cold) regime. In particular, the strong non-linear coupling between the VLE thermodynamics and the transport properties is identified as a key element of difference with respect to the single-phase model counterpart. These differences manifest into the occurrence of localized changes in the fluid properties (such as density) that affect the flow-field in their vicinity, causing visible discrepancies even when time-averaging is performed. Concurrently, results obtained on the reacting side and carried out (for the first time) with finite-rate kinetics suggest that any VLE formation between the products and the reactants may be considered of minor importance. The latter conclusion is supported by the analysis conducted on the multi-phase field which appears to be largely composed of the vapor solution, as expected, hence limiting the analogous effect observed the non-reacting system where a broader range of phase-separation appears instead.