Theoretical insight into key reactions in DME/NH3 co-firing: A detailed kinetic study and implications for rational combustion modelling.

Dimethyl ether (DME) is promising as an additive for co-firing with ammonia (NH 3) to solve the problem of its low reactivity combustion. However, the combustion modeling of blended fuels is challenging, and previous efforts primarily relied on the adjustment of rate constants for key reactions to bridge the gap between experiments and simulations. In the present work, ab initio kinetic studies were performed for the key reactions of OH/HO 2 /NH 2 with DME in blended combustion. High-level theoretical calculations were carried out for all saddle points and a benchmark was implemented for accurate evaluation of the barrier heights. The direct dynamics calculations used variational transition state theory with interpolated single-point energies method. The kinetic studies took into account the small-curvature tunneling, low-pressure limit or pre-equilibrium model and the multistructural torsional anharmonicity effect. The calculated rate constants are in very good agreement with the available experimental kinetic data. The mechanism of Xiao et al. (Combust. Flame 245 (2022) 112372) was updated based on this kinetic study and the simulations of the ignition delay times with modified rate constants better agree with the measurements than with the original mechanism. Especially, the present model avoids decreasing the cross-reaction rate constants to improve the simulation results. This work provides detailed theoretical insights and updated models with good predictive performance based on ab initio kinetics, which have more rigorous theoretical significance. [ABSTRACT FROM AUTHOR]