Optimal Bayesian Experimental Design for Combustion Kinetics Xun Huan ∗ and Youssef Marzouk † Massachusetts Institute of Technology, Cambridge, MA, 02139, USA Experimental diagnostics play an essential role in the development and refinement of chemical kinetic models, whether for the combustion of common complex hydrocarbons or of emerging alternative fuels. Questions of experimental design—e.g., which variables or species to interrogate, at what resolution and under what conditions—are extremely important in this context, particularly when experimental resources are limited. This paper attempts to answer such questions in arigorous and systematic way. We propose a Bayesian framework for optimal experimental design with nonlinear simulation-based models. While the framework is broadly applicable, we use it to infer rate parameters in a combustion system with detailed kinetics. The framework introduces a utility function that reflects the expected information gain from a particular experiment. Straightforward evaluation (and maximization) of this utility function requires Monte Carlo sampling, which is infeasible with computationally intensive models. Instead, we construct a polynomial surrogate for the dependence of experimental observables on model parameters and design conditions, with the help of dimension-adaptive sparse quadrature. Results demonstrate the efficiency and accuracy of the surrogate, as well as the considerable effectiveness of the experimental design framework in choosing informative experimental conditions. I. Introduction An increasingly broad range of fuels, derived from diverse feedstocks, are shaping future transportation and power generation systems. In the realm of ground transportation, biofuels are entering the fuel supply in blends with conventional petroleum-derived fuels and as primary energy carriers. Alternative aviation fuels—synthesized through gasification and liquefaction processes from biomass, coal, natural gas, tar sands, and oil shale—are of great interest to engine and airframe manufacturers. Environmental requirements often dictate that these fuels be coupled with high-efficiency energy conversion technologies designed to minimize pollutant emissions. Emerging strategies include low-temperature combustion in homogeneous charge compression ignition (HCCI) engines, direct injection in spark-ignition (SI) engines, or staged ultra- lean combustion in gas turbines. Yet the consumption of alternative fuels in these systems involves chemical species and blends whose physical properties and combustion kinetics are poorly characterized. Additionally, new engines and propulsion technologies may operate in low temperature or extreme pressure regimes where current kinetic models—even for widely-used fuels, much less alternative fuels—are not validated. Myriad sources of data contribute to reaction mechanisms and thermophysical properties. Ignition ex- periments, flow reactor experiments, and flame speed measurements are important, yet indirect, targets for developing and validating kinetic mechanisms. Optical diagnostics are essential to focused experimental studies of gas-phase combustion kinetics, but high pressure environments and direct interrogation of large molecules present significant challenges. Ab initio calculations, on the other hand, are limited in scale, and results often must be extrapolated to larger species or to faraway pressures and temperatures, with unknown levels of confidence. The rapid development of new fuels and new conversion technologies urges more sys- tematic approaches to model development that synthesize all these sources of kinetic information, including indirect data such as ignition delays and flame speeds. ∗ Graduate Student, Department of Aeronautics and Astronautics, 77 Massachusetts Ave., 37-442, Cambridge, MA 02139, AIAA Student Member. † Assisstant Professor, Department of Aeronautics and Astronautics, 77 Massachusetts Ave., 33-305, Cambridge, MA 02139, AIAA Senior Memmber. 1 of 16 American Institute of Aeronautics and Astronautics 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 4 - 7 January 2011, Orlando, Florida AIAA 2011-513 Copyright © 2011 by Xun Huan and Youssef Marzouk. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.