From theoretical reaction dynamics to chemical modeling of combustion

The chemical modeling of combustion treats the chemical conversion of hundreds of species through thousands of reactions. Recent advances in theoretical methodologies and computational capabilities have transformed theoretical chemical kinetics from a largely empirical to a highly predictive science. As a result, theoretical chemistry is playing an increasingly significant role in the combustion modeling enterprise. The accurate prediction of the temperature and pressure dependence of gas phase reactions requires state-of-the-art implementations of a variety of theoretical methods: ab initio electronic structure theory, transition state theory, classical trajectory simulations, and the master equation. In this work, we illustrate the current state-of-the-art in predicting the kinetics of gas-phase reactions through sample calculations for some prototypical reactions central to combustion chemistry. These studies are used to highlight the success of theory, as well as its remaining challenges, through comparisons with experiments ranging from elementary reaction kinetics studies through to global observations such as flame speed measurements. The illustrations progress from the treatment of relatively simple abstraction and addition reactions, which proceed over a single transition state, through to the complexity of multiwell multichannel reactions that commonly occur in studies of the growth of polycyclic aromatic hydrocarbons. In addition to providing high quality rate prescriptions for combustion modelers, theory will be seen to indicate various shortcomings in the foundations of chemical modeling. Future progress in the fidelity of the chemical modeling of combustion will benefit from more widespread applications of theoretical chemical kinetics and from increasingly intimate couplings of theory, experiment, and modeling.