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A theoretical kinetic study of the reactions of NH2 radicals with methanol and ethanol and their implications in kinetic modeling
Authors:Binod Raj Giri  Krishna Prasad Shrestha  Tam V-T Mai  Fabian Mauss  Lam K Huynh
Institution:1. Clean Combustion Research Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Makkah, 23955-6900 Saudi Arabia;2. Thermodynamics and Thermal Process Engineering, Brandenburg University of Technology, Siemens-Halske-Ring 8, Cottbus, Germany;3. Molecular Science and Nano-Materials Lab, Institute for Computational Science and Technology, Ho Chi Minh City, Vietnam;4. Vietnam National University, Ho Chi Minh City, Vietnam
Abstract:Amino (NH2) radicals play a central role in the pyrolysis and oxidation of ammonia. Several reports in the literature highlight the importance of the reactions of NH2 radicals with fuel in NH3-dual-fuel combustion. Therefore, we investigated the reactions of NH2 radicals with methanol (CH3OH) and ethanol (C2H5OH) theoretically. We explored the various reaction pathways by exploiting CCSD(T)/cc-pV(T, Q)Z//M06-2X/aug-cc-pVTZ level of theory. The reaction proceeds via complex formation at the entrance and exit channels in an overall exothermic process. We used canonical transition state theory to obtain the high-pressure limiting rate coefficients for various channels over the temperature range of 300–2000 K. We discerned the role of various channels in the potential energy surface (PES) of NH2 + CH3OH/C2H5OH reactions. For both reactions, the hydrogen abstraction pathway at the OH-site of alcohols plays a minor role in the entire T-range investigated. By including the title reactions into an extensive kinetic model, we demonstrated that the reaction of NH2 radicals with alcohols plays a paramount role in accurately predicting the low-temperature oxidation kinetics of NH3-alcohols dual fuel systems (e.g., shortening the ignition delay time). On the contrary, these reactions have negligible importance for high-temperature oxidation kinetics of NH3-alcohol blends (e.g., not affecting the laminar flame speed). In addition, we calculated the rate coefficients for NH2 + CH4 = CH3 + NH3 reaction that are in excellent agreement with the experimental data.
Keywords:amino radical  combustion  ethanol  kinetics  methanol  NH3-dual-fuel
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