Development and Evaluation of Reduced Kinetics Models for 1,3-Butadiene–Air Combustion

The present work details the development and evaluation of two-step and six-step finite-rate chemistry mechanisms for 1,3-butadiene oxidation in air, relevant for hypersonic airbreathing engines utilizing hydroxyl-terminated polybutadiene (HTPB). A sensitivity study was performed to calibrate the pre-exponential factor of the Arrhenius rate expressions for reproducing laminar counterflow-diffusion flame behavior and extinction strain rate. Evaluation of the calibrated mechanisms was performed for a model one-dimensional solid-fuel counterflow diffusion flame and two-dimensional axisymmetric large-eddy simulation of a solid-fuel ramjet combustor. A 20-species pressure comprehensive skeletal mechanism serves as a baseline for model evaluation. The simulations utilized interfacial solid–gas coupling to evaluate the influence of the reduced mechanisms on the regression rate of solid fuel and coupled flame dynamics. The results established that both two-step and six-step mechanisms are capable of predicting salient features of HTPB–air combustion, with the six-step mechanism providing superior accuracy in the prediction of flame temperatures, species mass fractions, and regression rates in time-resolved solid-fuel ramjet simulations. Although the reduced mechanisms have limited utility when it comes to capturing all relevant turbulence and chemistry interactions due to the lack of available chemical pathways, both reduced mechanisms showed significant computational speedup in comparison to the skeletal mechanism.