Propagation and extinction of premixed dimethyl-ether/air flames

Abstract

Laminar flame speeds and extinction strain rates of dimethyl-ether/air mixtures were measured at room temperature and atmospheric pressure over a wide range of equivalence ratios. The experiments were performed in the counterflow configuration, and included the use of digital particle image velocimetry and laser Doppler velocimetry. The laminar flame speeds were experimentally determined using a new nonlinear extrapolation technique, which utilizes simulations obtained using detailed chemistry and transport. Compared to literature experimental data, the measured laminar flame speeds were found to be in good agreement with the majority of measurements using spherically expanding flames, and they are lower compared to measurements reported by other groups using the stagnation flame technique. An updated kinetic model of dimethyl-ether oxidation is also proposed, which entails a number of adjustments to reactions involving methane chemistry. Compared to previous versions of the model, improved agreement was found with the experimental data. Simulations incorporated both the mixture-averaged and full multicomponent formulations to evaluate transport properties. Results revealed that the use of the mixture-averaged formulation results in negligible discrepancy in the calculated laminar flame speeds but can substantially overestimate the extinction strain rates particularly near stoichiometry. Sensitivity analyses with respect to reactions and binary diffusion coefficients were conducted to provide insight into the controlling physico-chemical processes. Additionally, reaction pathway analyses were used to interpret the results, and to identify the high-temperature reaction pathways of dimethyl-ether oxidation. Intermediates were shown to dominate high-temperature DME oxidation kinetics.