Chemistry effects in the wall quenching of laminar premixed DME flames

Abstract

Fundamental studies on Flame-Wall Interaction (FWI) are of the utmost importance to unravel the intricate coupling between chemistry and transport in the near-wall region, and to characterize the quenching dynamics. For this purpose, an accurate description of reaction kinetics is especially needed. In this work, the role of chemistry during the wall quenching of premixed dimethyl ether (DME) flames is numerically investigated, leveraging recently-obtained experimental data in a Side-Wall Quenching configuration (SWQ) in a variety of conditions. A detailed kinetic model describing the low-to-high temperature oxidation of DME is used as starting point. In order to accommodate it into 2D simulations, it is first reduced to a skeletal level, both accounting for (31 species and 140 reactions) and neglecting (20 species and 93 reactions) low-temperature chemistry, and successfully validated against the original model in predicting flame propagation and Head-On Quenching (HOQ). Using an established CFD framework, the SWQ features of DME are investigated in terms of flame structure, heat fluxes and thermochemical CO-T states. A good agreement with the available experimental data is observed in the operating space. In the near-wall region, the prediction of the thermochemical state is most critical, and it is found that diffusion is here the prevailing contribution in defining such state. In the same region, kinetic analysis shows that low-temperature chemistry affects the speciation of the quenching region to a good extent, which is modified with respect to a freely-propagating flame. Yet, due to the lower reactivity, SWQ thermal features are not significantly influenced. As a result, for the purposes of the wall quenching analysis, only high-temperature chemistry needs to be accounted for, and the 20-species mechanism can be safely considered as a consolidated milestone for future studies.