Developing chemical kinetic models for thermochemical applications

Abstract

A general procedure for the development of chemical kinetic models relevant to thermochemical applications (pyrolysis, gasification and combustion) is described. Here we present techniques that aim at producing models that are modular in structure, thoroughly validated, and applicable to a wide variety of conditions (generality), while balancing accuracy and computational burden. Starting from a core mechanism describing the pyrolysis and oxidation of light species, heavier compounds are added to the model in a hierarchical fashion, starting from archetypal species of each class of compounds. Using analogy rules derived from the archetypal species, a list of reactions and reaction rate parameters are compiled for molecules belonging to the classes of interest, obtaining detailed or semidetailed reaction mechanisms. The model is then validated using data available from the literature and/or novel experiments performed ad hoc. Depending on the applications of interest and on the size of the model, a mechanism reduction can be performed using a combination of lumping techniques and flux or sensitivity analyses. These procedures, although partially automated, still require some level of expert knowledge. The development of reaction rate rules and the identification of reaction pathways require indeed critical analysis and are most effective when the operator has previous experience in the field. A rigorously built mechanism, obeying the general principles presented here, provides high predictivity and permits extrapolating fuel behavior with greater confidence outside the range of validation conditions compared with models assembled from nonconsistently sourced submechanism from the literature, or based on limited datasets and empirical information.