A nanosecond surface dielectric barrier discharge at elevated pressures: Time-resolved electric field and efficiency of initiation of combustion

We study a nanosecond surface dielectric barrier discharge (SDBD) initiated by negative or positive polarity pulses 10-15kV in amplitude in a cable, 25-30ns FWHM, 5ns rise time, in the regime of a single shot or 3Hz repetitive frequency. Discharge parameters, namely spatial structure of the discharge and time- and space-resolved electric field are studied in a N ₂:O ₂=4:1 mixture for P=1-5atm. The possibility of igniting a combustible mixture with the help of an SDBD is demonstrated using the example of a stoichiometric C ₂H ₆:O ₂ mixture at ambient initial temperature and at 1atm pressure. Flame propagation and ignited volume as a function of time are compared experimentally for two discharge geometries: SDBD and pin-to-pin configurations at the same shape and amplitude of the incident pulse. It is shown that the SDBD can be considered as a multi-point ignition system with maximum energy release near the high-voltage electrode. Numerical modeling of the discharge and subsequent combustion kinetics for the SDBD conditions is performed. The discharge action leads to the production of atoms and radicals as well as to fast gas heating, due to the relaxation of electronic and vibrational degrees of freedom. The calculated ignition delay time is in reasonable agreement with the experimental results.