Spatiotemporal imaging of NH2 in plasma-assisted NH3 combustion via nanosecond pulsed discharge

Direct, time-resolved measurements of the amino radical (NH 2 ) are critical for understanding plasma-assisted ammonia (NH 3 ) combustion, in terms of both plasma-accelerated NH 3 decomposition and reduced NO x emission, yet such data remain scarce. The current study focuses on the spatiotemporal characteristics of NH 2 using laser-induced fluorescence (LIF) in a quasi-one-dimensional NH 3 /air flame subjected to a pin-to-pin nanosecond pulsed discharge (NPD), and comparatively analyzes the plasma effects in both the unburnt and burnt zones. In the unburnt zone for both lean and rich flames, a considerable amount of NH 2 is observed with signal intensities of 3–4 times that in the flame front without plasma, demonstrating the capability of NPD in enhancing NH 3 decomposition. The spatial and temporal dynamics of plasma-produced NH 2 are explored over timescales ranging from hundreds of nanoseconds to milliseconds following a single NPD pulse. The results indicate that NH 2 reaches its peak before 700 ns after the discharge initiation, highlighting the role of plasma kinetics in dissociating NH 3 through electrons, excited nitrogen molecules, and O( 1 D). The generated NH 2 subsequently undergoes an exponential decay with a characteristic lifetime of 3–4 μs. This consumption is mainly driven by combustion kinetics, where several diverging pathways are identified as possible reaction routes. Moreover, a “butterfly-like” distribution of plasma-produced NH 2 , is characterized by lower signals and faster decay in the center, both of which are attributed to the higher temperature within the center of discharge channel. In the burnt zone, NH 2 is only detected in the rich flame, and decays much faster (∼1.3 μs) compared to the unburnt zone. The unique experimental data of plasma-produced NH 2 provide valuable insights into plasma-assisted NH 3 combustion and deliver critical experimental data for the development and refinement of kinetic models.