Plasma-Assisted Combustion

Ammonia (NH₃) is increasingly recognized as a promising carbon-free fuel. However, its adoption is hindered by challenging ignition properties, including high minimum ignition energy and narrow flammability limits. This study explores the ignition of NH₃-air mixtures using Nanosecond-Pulsed High-Frequency Discharge (NPHFD), which has shown potential for enhancing ignition efficiency in difficult-to-ignite conditions. The investigation focuses on the effects of key parameters such as equivalence ratio (φ), flow velocity (u), pulse number (N), and inter-pulse time (τ) on ignition probability (P_I) and flame kernel development. High-speed Schelien and high-speed inferred imaging are utilized to characterize flame kernels in terms of growth, temperature, and morphology. The results demonstrate that P_I decreases with a decreasing N, peaking at φ = 0.85; elevated u reduces P_I at φ ≤ 0.75; increasing τ improves P_I, consistent with behaviors observed in other fuel-air mixtures like methane and ethylene. Furthermore, flame kernel size and development are shown to be significantly affected by discharge conditions. This research has the potential to contribute to the broader understanding of NPHFD ignition mechanisms, offering insights that could facilitate the development of more efficient and reliable NH₃-based combustion systems. By systematically investigating these parameters, the study lays the groundwork for optimizing NPHFD technology to overcome the ignition challenges associated with NH₃, thus advancing its viability as a clean energy source.

Funding acknowledgement

Israel Science Foundation Personal Research Grants no. 2578/23