Ignition delay times under the action of a high-voltage nanosecond discharge have been studied and compared with autoignition delays in a rapid compression machine (RCM) of Lille University. The nanosecond Surface Dielectric Barrier Discharge (SDBD) was initiated in a quasi-uniform radial geometry in the proximity of the end plate of the combustion chamber of the RCM. Experiments were performed for methane:oxygen and n-butane: oxygen mixtures diluted by Ar or N2 for temperatures and pressures at the end of compression respectively ranging from 650 to 1000 K and 6 to 16 bar. Decrease of the ignition delay time is observed, when compared to autoignition experiments: instead of tens and hundreds of milliseconds, a few milliseconds are registered between the discharge initiation and sharp pressure increase in the combustion chamber. Experiments with lean CH4:O2:Ar mixtures with different stoichiometry demonstrate that the observed ignition delay is a function of stoichiometry, that is that, at initial pressures 8
