The role of non-thermal transient plasma for enhanced flame ignition in C2H4-air

Transient plasma ignition, involving short ignition pulses (typically 10-50 ns), has been shown to effectively reduce ignition delays and improve engine performance for a wide range of combustion-driven engines relative to conventional spark ignition. This methodology is therefore potentially useful for many engine applications; however, at present there is limited understanding of the underlying physics. Evidence is presented here for two distinct phases of the plasma-ignition process: an initial non-equilibrium plasma phase, wherein energetic electrons transfer energy into electronically excited species that accelerate reaction rates, and a spatially distributed thermal phase, that produces exothermic fuel oxidation reactions that result in ignition. It is shown that ignition kernels are formed at the ends of the spatially separated streamer channels, at the cathode and/or anode depending on the local electric field strength, and that the temperature in the streamer channel is close to room temperature up to 100 ns after the discharge. (fast track communication)