A theoretical kinetic study of the reactions of NH₂ radicals with methanol and ethanol and their implications in kinetic modeling

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.

A Theoretical Study of NH2 Radical Reactions with Propane and Its Kinetic Implications in NH3-Propane Blends’ Oxidation

“…Our findings revealed that the kinetic model can only accurately capture the low-temperature oxidation data by including cross-reactions between the carbon and nitrogen families. Our recent work on NH 3 /CH 3 OH/C 2 H 5 OH [14] led us to a similar conclusion. Therefore, the cross-chemistry between carbon and nitrogen chemistry is of utmost importance for accurately modeling NH 3 dual-fuel combustion.…”

“…Similar to our earlier work on NH 2 + CH 3 OH/C 2 H 5 OH reactions [14], we optimized the geometry of all the stationary points for the NH 2 + C 3 H 8 reaction at the M06-2X//augcc-pVTZ level of theory. Our choice of the M06-2X level of theory is based on several earlier studies that reported the best suitability of the M06-2X//aug-cc-pVTZ level of theory for geometry optimizations, frequency calculations, and accurate energetics of many chemical systems [14,[26][27][28][29][30][31][32]. We characterized the identity of each stationary point in the potential energy surface (PES) of the NH 2 + C 3 H 8 reaction through normal model analysis.…”

“…Over the past few years, we have been exploring the combustion behavior of ammonia blended with reactive oxygenated fuels like dimethyl ether (DME) [10], diethyl ether (DEE) [8,12], dimethoxymethane (DMM) [7], methanol (CH 3 OH), and ethanol (C 2 H 5 OH) [14]. It is well-known that co-firing NH 3 with these reactive fuels increases the system's complexity.…”

Exploring the Effect of Different Reactivity Promoters on the Oxidation of Ammonia in a Jet-Stirred Reactor

“…Besides, Giri et al 75 have very recently updated the rate coefficients for the reactions NH 2 + CH 4 ⇄ NH 3 + CH 3 (R2) and NH 2 + CH 3 OH ⇄ NH 3 + CH 3 O/CH 2 OH (R3) by theoretical calculation. Since R2 and R3 are essential for predicting the oxidation of NH 3 /CH 4 and NH 3 /CH 3 OH fuel blends, respectively, it is worth seeing the effect of the updated rate coefficients on the model performance.…”

Laminar flame speed measurement and combustion mechanism optimization of methanol–air mixtures

“…Methanol is widely used as an alternative or additive to the traditional fossil fuels in combustion devices, due to the abundant sources and low emissions. [1][2][3][4] As the smallest member of the alcohol family, during the CH 3 OH oxidation, some important combustion intermediates (e.g., CH 3 O, CH 3 and CH 2 OH, etc.) can be easily formed and measured.…”