TY - JOUR

T1 - Unraveling the positive ion chemistry in ammonia-methane flames

AU - Cherepanov, Andrey V.

AU - Kiselev, Vitaly G.

AU - Chernov, Anatoly A.

AU - Shmakov, Andrey G.

AU - Knyazkov, Denis A.

N1 - Andrey V. Cherepanov, Vitaly G. Kiselev, Anatoly A. Chernov, Andrey G. Shmakov, Denis A. Knyazkov, Unraveling the positive ion chemistry in ammonia-methane flames, Proceedings of the Combustion Institute, Volume 42, 2026, 106222, ISSN 1540-7489, https://doi.org/10.1016/j.proci.2026.106222. This work is supported by Russian Science Foundation (Project No: 24-19-00165, https://rscf.ru/en/project/24-19-00165/).

PY - 2026

Y1 - 2026

N2 - Ammonia-methane mixtures are considered promising low-carbon fuels for future power generation, yet the understanding of ion chemistry in such flames remains limited. This work presents the first comprehensive study of positive ion chemistry in laminar premixed NH3/CH4 flames at 1 atm by combining molecular beam mass spectrometry (MBMS), saturation current measurements, and detailed kinetic modeling supported by quantum chemistry calculations. Mass spectra recorded in the flame reaction zone identified a number of key flame cations, including H3O⁺, NH4⁺, NO⁺, HCNH⁺, CH2NH2⁺, CH3NH3⁺, C2H3NH3+, H2NCO⁺, CHN2H4⁺ and C2H5NH3+, as well as their ammonia and water clusters formed during sampling. Saturation current measurements confirmed the CH + O pathway as the primary route of chemiionization, leading to the selection of the Zhang et al. mechanism (Fuel 341 (2023) 127676) as the optimal neutral chemistry basis. Based on the experimental findings, a comprehensive ion-chemistry mechanism was constructed by merging previously developed models for hydrocarbon flames and for the carbon-free NH3/H2 system, and extending them with reactions for the identified nitrogen-carbon cations. The proposed mechanism reproduces the spatial profiles of the major cations and captures key experimental trends. Notably, the inclusion of HONO-mediated pathways proved essential for correctly predicting NO+ formation in the post-flame zone, a significant improvement over previous mechanisms that substantially underestimated NO+ abundance. These results provide detailed insight into the coupled N–C–H–O ion chemistry in ammonia-methane flames and establish a foundation for simulation of ion currents and behavior of electrified flames, and the development of ion-based diagnostics and control strategies for ammonia-fueled combustion systems. Novelty and significance statement This study presents the first comprehensive investigation of positive ion chemistry in NH3/CH4 flames. Multiple cations specific to ammonia-methane combustion are identified by molecular beam mass spectrometry, and their structural and thermochemical characterization is provided using high-accuracy quantum chemical calculations. An ion chemistry mechanism, validated against measured spatial distributions of ions and saturation currents, offers novel insights into ion formation pathways during the combustion of ammonia-methane blends. The significance of this work lies in enabling ion-based technologies for ammonia-methane combustion, a promising low-carbon energy solution. By identifying key ions and providing the first validated ion chemistry mechanism for an H-C-O-N system, we establish a direct path for developing advanced combustion diagnostics and control strategies. The mechanism enables reasonable prediction of ion currents, which is crucial for designing sensors to monitor flame stability and optimize combustion in real time, thereby facilitating the practical implementation and reliability of ammonia-fueled systems.

AB - Ammonia-methane mixtures are considered promising low-carbon fuels for future power generation, yet the understanding of ion chemistry in such flames remains limited. This work presents the first comprehensive study of positive ion chemistry in laminar premixed NH3/CH4 flames at 1 atm by combining molecular beam mass spectrometry (MBMS), saturation current measurements, and detailed kinetic modeling supported by quantum chemistry calculations. Mass spectra recorded in the flame reaction zone identified a number of key flame cations, including H3O⁺, NH4⁺, NO⁺, HCNH⁺, CH2NH2⁺, CH3NH3⁺, C2H3NH3+, H2NCO⁺, CHN2H4⁺ and C2H5NH3+, as well as their ammonia and water clusters formed during sampling. Saturation current measurements confirmed the CH + O pathway as the primary route of chemiionization, leading to the selection of the Zhang et al. mechanism (Fuel 341 (2023) 127676) as the optimal neutral chemistry basis. Based on the experimental findings, a comprehensive ion-chemistry mechanism was constructed by merging previously developed models for hydrocarbon flames and for the carbon-free NH3/H2 system, and extending them with reactions for the identified nitrogen-carbon cations. The proposed mechanism reproduces the spatial profiles of the major cations and captures key experimental trends. Notably, the inclusion of HONO-mediated pathways proved essential for correctly predicting NO+ formation in the post-flame zone, a significant improvement over previous mechanisms that substantially underestimated NO+ abundance. These results provide detailed insight into the coupled N–C–H–O ion chemistry in ammonia-methane flames and establish a foundation for simulation of ion currents and behavior of electrified flames, and the development of ion-based diagnostics and control strategies for ammonia-fueled combustion systems. Novelty and significance statement This study presents the first comprehensive investigation of positive ion chemistry in NH3/CH4 flames. Multiple cations specific to ammonia-methane combustion are identified by molecular beam mass spectrometry, and their structural and thermochemical characterization is provided using high-accuracy quantum chemical calculations. An ion chemistry mechanism, validated against measured spatial distributions of ions and saturation currents, offers novel insights into ion formation pathways during the combustion of ammonia-methane blends. The significance of this work lies in enabling ion-based technologies for ammonia-methane combustion, a promising low-carbon energy solution. By identifying key ions and providing the first validated ion chemistry mechanism for an H-C-O-N system, we establish a direct path for developing advanced combustion diagnostics and control strategies. The mechanism enables reasonable prediction of ion currents, which is crucial for designing sensors to monitor flame stability and optimize combustion in real time, thereby facilitating the practical implementation and reliability of ammonia-fueled systems.

KW - Ammonia-methane blend

KW - Cations

KW - Electrified flame

KW - Ion chemistry mechanism

KW - Saturation current

KW - Механизм ионной химии

KW - Смесь аммиака и метана

KW - Катионы

KW - Ток насыщения

KW - Электризованное пламя

UR - https://www.mendeley.com/catalogue/6a9e24c9-ae89-3580-b78a-5894a979238f/

UR - https://www.scopus.com/pages/publications/105043442463

U2 - 10.1016/j.proci.2026.106222

DO - 10.1016/j.proci.2026.106222

M3 - Article

VL - 42

JO - Proceedings of the Combustion Institute

JF - Proceedings of the Combustion Institute

SN - 1540-7489

M1 - 106222

ER -