Impact of the dielectric surface on the electric field in a 10-ns transient plasma in a CH₄-air mixture

Transient plasma ignition (TPI) initiated by nanosecond high-voltage pulses was shown to improve combustion efficiency and reduce the NO_x production due to its lean burn capability and the volumetric ignition effect [1]. Having a sufficiently large ignition kernel is important to reliably achieve successful combustion in extremely lean-fuel mixtures. A recent study showed that a repetitive nanosecond pulsed surface discharge could initiate sufficiently large ignition kernel without requiring an impractically high peak voltage and hence bear good economy in the ignition technology for internal combustion engines [1]. This study examines the transient electric field prior to the discharge breakdown or development of ignition kernel, and during the streamer mode of the discharge. We compare the field strength and distribution with and without the presence of a dielectric surface using a pin-to-pin electrode configuration in a CH₄/air mixture at the atmospheric pressure, obtained with the spatiotemporally-resolved, electric field-induced second harmonic generation (EFISH) method. Effects of the discharge modes and the time interval between pulses on the electric field in the surface discharge are also discussed.