The E ect of Flow and Mixture Inhomogeneity on the Dynamics of Strained Flames

Changes in ow strain and mixture composition on the order of a ame time scale are characteristic of many practical combustion processes. Accurately predicting the unsteady reponse of burning to these changes requires detailed modeling of species transport and chemical kinetics. This thesis formulates a detailed one-dimensional computational model for arbitrary unsteady conditions of strain and mixture, demonstrating its applicability to subgrid modeling of turbulent combustion. A novel numerical formulation, based on a globalized Newton iterative method and a preconditioned Krylov subspace linear solver, ensures e cient and robust convergence despite the sti ness of detailed chemistry. The model is validated via comparison with OPPDIF, a well-benchmarked steady-state strained ame code. The model is then used to characterize the fundamental interactions of ow and mixture inhomogeneity| examining the dynamic response of ame structure and burning to linear variations in mixture equivalence ratio, and capturing the e ect of unsteady strain on a ame surface interacting with a vortex in two dimensions. The latter example leads to a rede nition of the appropriate subgrid strain for ame embedding simulation of premixed turbulent combustion. Thesis Supervisor: Ahmed F. Ghoniem Title: Professor of Mechanical Engineering