Graduate Thesis Or Dissertation

Generalized Preconditioning to Accelerate Simulations with Large Multiphase Chemical Kinetics Models

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  • Combustion emissions produced from burning real transportation fuels have many environmental impacts. However, detailed chemistry across multiple phases, time scales, and thermodynamic conditions make predicting combustion emissions challenging. Detailed modeling of the gas phase alone is prohibitively expensive, due to the large size and stiffness of the kinetic models. The goals of this dissertation are to improve the current capability of numerical methods to model chemical kinetics and use the improved methods to simulate coupled combustion and atmospheric chemistry emissions simulations. Improving the current capability of methods to simulate large kinetics models can be achieved by leveraging preconditioning and system sparsity. Preconditioning is a method that can drastically improve simulation performance by accelerating the convergence of linear solvers particularly when sparse linear algebra can be leveraged. Semi-analytical and approximate Jacobian matrices for chemical kinetics are good candidates for sparse preconditioners, as chemical species usually only depend on a few others. However, improvements are limited by the standard mass or mole fraction representation of chemical systems. In this work, a preconditioning method was extended to a more-general mole-based state vector formulation applicable to generic reactor types and combinations of reactors. The method was also extended to systems of coupled reactors including both gas-and surface-phase chemistry. All developments made were rigorously performance tested and outperformed direct methods by up to several orders of magnitude. Additionally, they were reviewed and integrated into an open-source chemical kinetics and thermodynamics package for future research applications. Finally, the improved method was used to simulate a combined combustion and atmospheric model to study the emissions and the evolution of secondary organic aerosol precursors in the atmosphere resulting from the burning of sustainable aviation fuel blends with farnesane in a CFM56-5B jet engine. The emissions study showed that several factors influence the behavior of secondary organic aerosol precursors such as fuel composition, entrainment, ambient conditions, time of emissions, and initial emitted composition. The widely varying behavior and large uncertainty in combustion emissions estimates highlight the need for more-accurate simulation technology. Finally, the developed framework developed is openly available and can further be used to study complex coupled combustion--atmospheric chemistry scenarios.
  • KEYWORDS: Preconditioning, Atmospherics, Combustion, Numerical Methods
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  • This material is based upon work supported by the National Science Foundation under Grant Nos. 1931592 (OSU) and 1931391 (MIT).
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