Atomic-scale mechanism of electric-field-assisted NH₃/CH₄ combustion

The transition toward low-carbon energy has placed combustion research in a strange position—caught between deep tradition and urgent reinvention. Ammonia, once an industrial bystander, is now being reconsidered as a possible clean fuel and a dense hydrogen carrier. On paper, it looks ideal: no carbon atoms, easy storage, and mature production routes. In practice, though, it behaves awkwardly. It resists ignition, burns unevenly, and releases nitrogen oxides that undermine its environmental advantage. To tame these problems, researchers often mix it with small amounts of methane. The idea works to some degree—the flame becomes steadier, ignition easier—but the chemistry grows more complicated, and NOₓ emissions tend to climb again. Every gain seems to come with a compromise. Lately, another line of thought has emerged: perhaps electricity itself could guide the flame. Experiments show that applying an external field changes how ions drift and how radicals meet, almost as if the flame were being quietly steered by invisible hands. The so-called “ionic wind” explains some of this motion, yet the real story happens much deeper. Bonds stretch, charges shuffle, and reactions seem to follow slightly different routes. These microscopic adjustments remain difficult to capture, but understanding them may eventually let us tune combustion in real time—something earlier generations of engineers could only imagine. To this account, new research paper published in International Journal of Hydrogen Energy and conducted by Dr. Yingshan Hong, Professor Jing Wang, Dr. Yuqing Liu, and Professor Xi Zhuo Jiang from the School of Mechanical Engineering and Automation at Northeastern University, the researchers developed two coupled molecular-scale models: a ReaxFF-based simulation of NH₃/CH₄ combustion in air and a charge-tracking model centered on the newly defined “center of charge” descriptor.

The authors constructed an atomistic simulation cell containing NH₃, CH₄, O₂, and N₂ molecules confined at 5 atm within a cubic domain of 431 Å per side. After initial thermal equilibration at 300 K, the system was heated to 3000 K and subsequently subjected to direct-current electric fields ranging from 2 × 10¹ to 2 × 10⁶ V m⁻¹. ReaxFF parameters for H, C, O, and N systems were employed, ensuring that bond formation and dissociation could evolve naturally during combustion. The simulations revealed a striking non-linear response: moderate electric fields substantially shortened ignition delay and increased fuel consumption rates, whereas excessively strong fields produced complex, less predictable dynamics. The team also found the electric field elongated N–H bonds and compressed H–N–H angles within ammonia molecules, effectively weakening bond energy and facilitated early decomposition and these structural deformations coincided with a measurable rise in the system’s kinetic energy which confirmed that electrostatic acceleration enhances molecular motion and collision frequency. Additionally, the authors introduced a novel quantitative descriptor—the center of charge (COC)—to track charge redistribution under varying field strengths. The COC shifted along the field direction, which reveal polarization-induced asymmetry that altered radical trajectories and reaction localization.

The authors’ analysis of nitrogen-containing intermediates showed the pathways linking NH₃ decomposition to NOₓ formation with the dominant routes proceeded through HNO and NH radicals reacting with O, O₂, and OH species, but new reactions emerged exclusively under electric-field conditions. For instance, at 2 × 10⁴ V m⁻¹, CH₃O + HN → HNO + CH₃ appeared as a previously unreported path. Interestingly, a relatively weak field (~2 × 10² V m⁻¹) reduced NO₂ yield by about 20 %, which indicate that fine-tuned electrostatic control could inhibit rather than promote nitrogen-oxide generation. Moreover,  carbon emissions displayed a similar trend. When CH₄ oxidation accompanied ammonia combustion, the application of low-intensity fields decreased overall COₓ output by up to 9 %, with CO₂ specifically reduced by nearly 40 % compared to field-free simulations. Collectively, the data demonstrate that electric fields restructure the entire reaction network—from bond rupture to radical recombination—yielding altered kinetics, new intermediates, and in certain regimes, cleaner exhaust compositions.

In conclusion, Professor Xi Zhuo Jiang and colleagues developed novel models that capture both chemical reactivity and electrostatic polarization under applied electric fields. Their integration allows dynamic visualization of how electric forces distort molecular geometry, redirect radicals, and alter emission pathways which offer the first atomistic explanation of electric-field-modulated ammonia–methane combustion.  Indeed, the study for the first time establishes a mechanistic foundation for active emission control through applied fields by unraveling the atomic-scale dynamics of electrically assisted NH₃/CH₄ combustion. The findings reveal that electric fields act both as macroscopic stabilizers as well as microscopic catalysts and selectively steering reaction channels. A low-intensity field (≈10² V m⁻¹) proved optimal, simultaneously promoting ignition and suppressing pollutant formation which challenges the conventional assumption that stronger fields always enhance combustion. From a theoretical standpoint, the new work advances our understanding of how charge redistribution, molecular deformation, and radical transport interact during high-temperature oxidation. The proposed COC metric introduces a new lens for quantifying electrostatic influence on chemical kinetics. It also explains why certain intermediates, particularly HNO and NH, dominate NOₓ formation: their spatial dynamics and local charge environments are directly modulated by the external field.

Moreover, the results hint at a new generation of intelligent combustion systems in which external fields function as tunable “knobs” for efficiency and emissions. In future reactors, small-scale electric fields could be applied near flame fronts or within micro-combustors to adjust ignition timing or to minimize NOₓ without altering fuel composition. Moreover, this atomic insight bridges to broader energy transitions—ammonia-based propulsion, gas-turbine retrofits, and hybrid hydrogen-ammonia engines—where managing both carbon and nitrogen emissions is imperative. We also believe by combining ReaxFF-MD with detailed statistical pathway analysis, the authors provide a replicable computational protocol for exploring field–reaction coupling in other fuel systems, such as hydrogen or bio-derived molecules. This dual emphasis on molecular physics and environmental performance exemplifies a growing direction in combustion science which is to integrate reactive dynamics with external-field control to achieve sustainability.