Plasma Resistance Control for Ignition Energy Improvements Under High-Speed Flow Conditions

Modern spark ignition (SI) systems tend to face a fuel-lean mixture of elevated density and intensified flow for improving engine efficiency and exhaust emission. A more effective ignition source, e.g., a properly modulated current profile of on-demand elevated energy is preferred to assist the flame kernel formation process and developments. The strong air motion blows the plasma channel away from the spark gap, causing the plasma channel to stretch, which leads to restrike events when stretched excessively. In this work, the impact of spark plasma stretching on the discharge processes has been investigated under various flow velocities and background densities. It is observed that the cross-flow may raise the deposition efficiency of discharge energy between the spark electrodes via plasma stretching, but the prolonged stretching may challenge the plasma stability. The mechanisms of restrike and blow-off events are investigated corresponding to plasma resistance and discharge voltage. Furthermore, a boosted current strategy is applied to study the effectiveness of discharge current modulation (50 mA–3 A) on the plasma resistance control under the flow conditions. The study comprehensively investigates the impacts of discharge current, flow velocity, and background pressure on plasma stretching and energy release efficacy.