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<p>The utilization of ammonia as an alternative fuel is of great significance in the carbon neutrality strategy. However, the ammonia flame extinction mechanism induced by growing oscillations with its cramped flammability range, sluggish propagation speed, and poor stability is still not studied in sufficient details. In this paper, the high-fidelity simulations with efficient continuation computation and detailed models are conducted to investigate the ammonia extinction dynamics as a function of hydrogen blending ratio, and to reveal the governing sub-processes in flame extinction and oscillation development. It is found that the extinction and onset of oscillatory instability in the ammonia/hydrogen spherical diffusion flame (SDF) derive from the interaction of competing chemistry with diffusive leakage losses. Chemical oscillations occurring at the maximum temperature iso-contour are primarily responsible for the near-limit flame oscillations. In the rich-side low-temperature region, although the local heat production is inappreciable, the strong diffusive losses with governing, adverse contributions to the ignition chemistry play a leading role in flame extinction. The reactions dominating the extinction limit are also important for the oscillation frequency; the reactions that help to extend the extinction limit also tend to increase the frequency, and vice versa. The extinction limit and frequency depend mainly on the major reactant diffusivities (including NH<sub>3</sub>, H<sub>2</sub>, and O<sub>2</sub>) and heat conduction, while the diffusivities of other radicals and products are fairly unimportant. Hydrogen addition could remarkably extend the steady-state and oscillatory extinction limits of ammonia SDFs, and reduce the oscillation frequency since the imaginary eigenvalue is depressed.</p>

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Extinction Dynamics with the Underlying Physics of Ammonia and Ammonia/Hydrogen Spherical Diffusion Flames in Micro-Gravitational Condition

  • 期刊论文

  • 发表日期：

    2025年7月14日

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  • Yinhu Kang,
  • Junkun Liu,
  • Xiaomei Huang,
  • Pengfei Wu,
  • Zhijing Jiang,
  • Jiuyi Zhang,
  • Xiaofeng Lu

摘要

The utilization of ammonia as an alternative fuel is of great significance in the carbon neutrality strategy. However, the ammonia flame extinction mechanism induced by growing oscillations with its cramped flammability range, sluggish propagation speed, and poor stability is still not studied in sufficient details. In this paper, the high-fidelity simulations with efficient continuation computation and detailed models are conducted to investigate the ammonia extinction dynamics as a function of hydrogen blending ratio, and to reveal the governing sub-processes in flame extinction and oscillation development. It is found that the extinction and onset of oscillatory instability in the ammonia/hydrogen spherical diffusion flame (SDF) derive from the interaction of competing chemistry with diffusive leakage losses. Chemical oscillations occurring at the maximum temperature iso-contour are primarily responsible for the near-limit flame oscillations. In the rich-side low-temperature region, although the local heat production is inappreciable, the strong diffusive losses with governing, adverse contributions to the ignition chemistry play a leading role in flame extinction. The reactions dominating the extinction limit are also important for the oscillation frequency; the reactions that help to extend the extinction limit also tend to increase the frequency, and vice versa. The extinction limit and frequency depend mainly on the major reactant diffusivities (including NH3, H2, and O2) and heat conduction, while the diffusivities of other radicals and products are fairly unimportant. Hydrogen addition could remarkably extend the steady-state and oscillatory extinction limits of ammonia SDFs, and reduce the oscillation frequency since the imaginary eigenvalue is depressed.