An investigation into the impact of discharge pulse width on the performance of long Pulse-Width plasma ignition (LPWPI) systems

• A complete causal chain for LPWPI from circuit to combustion is built for the first time. • An optimal discharge pulse width of 1.72 ms for peak performance is identified. • Lean ignition limit is extended by up to 31.46% with robust flow adaptability. • The law of non − monotonic variation of jets with pulse width is revealed. • Diminishing marginal returns with increasing energy input are uncovered. Conventional aero-engine spark ignition (SI) systems exhibit limited ignition capability under high-speed lean-burn conditions due to instantaneous energy deposition and localized spark scale. The long pulse-width plasma ignition (LPWPI) system extends the ignition envelope by prolonging discharge duration to the millisecond level. This study aims to optimize system performance and elucidate the mechanism through which discharge pulse width influences ignition characteristics. By systematically constructing a complete causal chain from circuit parameters to discharge characteristics, and subsequently to jet evolution and combustion performance, results demonstrate that discharge pulse width increases monotonically with inductance, while its effects on jet characteristics and ignition performance exhibit non-monotonic behavior. Experimental findings confirm the existence of an optimal pulse width for achieving optimal matching between jet development and energy deposition. At an energy input of 12 J, a maximum jet penetration depth of 29.49 mm was achieved at t p = 1.72 ms. Ignition tests confirmed the optimal performance under these conditions. Within the flow rate range of 750–2550 SLM, LPWPI consistently outperformed SI, with significantly extended lean ignition limits, achieving a maximum extension of 31.46%, demonstrating excellent flow adaptability. Comparative studies from 3 to 20 J demonstrated LPWPI’s superior performance under all tested conditions, with performance improvement declining at 16 J and 20 J energy levels, revealing the phenomenon of diminishing marginal returns. This research identifies key optimization parameters as well as the synergy between pulse width and energy for LPWPI systems, providing both theoretical insights and practical foundations for their application in high-speed aero-combustion environments.