Sub Topic: Chemical Kinetics 12 th U.S. National Combustion Meeting Organized by the Central States Section of the Combustion Institute May 24–26, 2021 College Station, Texas, USA Evaluating the Performance of Bath Gas Mixture Rules for General Implementation in Chemically Reacting Flow Codes: Tests for Multi-Well, Multi-Channel Reactions Lei Lei 1 and Michael P. Burke 2,* 1 Department of Mechanical Engineering, Columbia University, New York, NY, 10027, United States 2 Department of Mechanical Engineering, Department of Chemical Engineering, Data Science Institute, Columbia University, New York, NY, 10027, United States * Corresponding author: mpburke@columbia.edu Abstract: In most, if not all, realistic combustion environments, multiple species with distinct colli- sional energy-transfer characteristics are present in sufficient quantities to contribute to energy trans- fer in pressure-dependent reactions. The vast majority of rate constant data for pressure-dependent reactions are for pure bath gases, such that chemically reacting flow codes and experimental inter- pretations inevitably rely upon a “mixture rule” to calculate pressure-dependent rate constants in mixtures from available data for the constituent components when pure. Our previous studies have shown that the classic linear mixture rule yields errors in its estimates of pressure-dependent rate constants in mixtures that exceed an order of magnitude. On the contrary, we have found two new reduced-pressure-based mixture rules to be accurate within 30% and 10% for various single-well reaction systems across wide ranges of temperature, pressures, and mixture compositions of impor- tance to combustion. However, the nature of mixture effects and the performance of various mixture rules have yet to be explored for multi-well reactions. In the present paper, we investigate mixture effects in multi-well systems and the ways to appropriately represent such effects in combustion kinetics modeling – for use in fundamental and applied investigations of reacting mixtures and for implementation into reacting flow codes. Keywords: Mixture Rules, Pressure Dependence, Multi-Well Systems 1. Introduction Understanding and representing the kinetics of chemical reactions proceeding through rovibra- tionally excited complexes has been an important research area in combustion [1–9]. The fate of these rovibrationally excited complexes under the interplay of energy transferring collisions [8, 10–15], reactive collisions [7, 9, 16–18], and unimolecular reactions (unimolecular decompo- sition/isomerization [2, 19, 20]) governs the phenomenological behavior of a chemical system. In realistic chemical systems, the energy transfer process in “complex-forming” (or “pressure- dependent”) reactions almost always involves significant contributions from multiple components, each of which often possesses distinct energy transferring characteristics. However, the majority of available fundamental experiments and theoretical studies of rate coefficients of these complex- forming reactions almost all focus on pure bath gas environments. Therefore, for general ap- plications of chemical kinetics in either experimental interpretations of rate coefficients [15] or 1