Effect of C-N cross-reactions on combustion dynamics in ammonia binary blends

• Published in: Fuel (Guildford) Vol. 373; p. 132061
• Main Authors: Liu, Zechang, He, Xu, Feng, Guangyuan, Zhao, Chengyuan, Zhou, Xiaoran, Wang, Zhi, Chen, Qingchu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2024
• Subjects: C-N cross reactions; Combustion characteristics; TRF/NH3; C-N cross reactions; Combustion characteristics; TRF/NH3
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2024.132061

•The study examined the effect of C-N cross-reactions on LFS, IDT, and species concentrations in binary NH3 blends mixtures.•And a small-scale CN cross-reaction mechanism with skeletal mechanism is proposed. The application of ammonia (NH3) in the transportation sector presents a practical approach to steer the automotive industry towards a more eco-friendly and sustainable trajectory. The study examined the effect of C-N cross-reactions on laminar flame speed (LFS), ignition delay time (IDT), and species concentrations in binary NH3 blends using methane/ammonia (CH4/NH3), toluene/ammonia (C7H8/NH3), dimethyl ether/ammonia (DME/NH3), and n-heptane/ammonia (NC7H16/NH3) fuel mixtures. The research indicates that although C-N cross-reactions have a minimal impact on LFS of most blends, they significantly reduce the predictive precision of models for mixtures of C7H8/NH3. Furthermore, the existence of C-N cross-reactions diminishes the anticipated IDT of the combinations, and this influence becomes more pronounced as the initial temperature (T0) decreases. Furthermore, although C-N cross-reactions have a negligible impact on fuel species concentrations, they exert an impact on the concentrations of nitroic oxide (NO) and nitrous oxide (N2O). The mechanism by which C-N cross-reactions affect IDT and species concentrations is similar, mainly attributed to methyl (CH3) related C-N cross-reactions, which can be illustrated as: (1) C-N cross-reaction effects the concentration of CH3, which subsequently affects the concentration of CH3O. CH3O plays a vital role as a reactant for hydroperoxyl radical (HO2) generation in the intermediate temperature range (CH3O + O2 = CH2O + HO2), consequently exerting an impact on IDT; (2) the reaction NO + HO2 = NO2 + OH denotes the principal consumption reaction of NO, which is affected by HO2, consequently affecting the concentration of NO. (3) The H-abstraction reaction between NH2 and fuel promoted the primarily oxidation of fuel. This study concludes that limiting the inclusion to nine categories of reactions in C-N cross-reactions results in a considerable reduction in the complexity of the mechanism. This reduction significantly improves the predictive capacity of the model regarding combustion characteristics.