Ignition of Lean Air / Hydrocarbon Mixtures at Low Temperature by a Single Corona Discharge Nanosecond Pulse

A great number of experimental studies have demonstrated that non-thermal plasmas produced by high voltage pulse discharges, running at a given pulse repetition frequency, are able to ignite air / hydrocarbon mixtures at a low initial temperature and atmospheric pressure. In this paper, we show that ignition can also be achieved using a single nanosecond pulse corona discharge generated under a very strong overvoltage. Experiments were conducted in air / propane and air / n-heptane mixtures. For such a discharge, ignition of n-heptane requires less released electrical energy than propane and lean mixtures can be completely burnt with reasonable energy values of several tens of mJ. Extended flame kernels or several points of ignition can be induced. For n-heptane, we have developed a simplified combustion model using a reduced mechanism, enabling us to suggest a kinetic explanation for ignition at a low temperature. In particular, it appears that oxygen atoms produced in the plasma induce a significant reduction of the ignition time. This model lays the foundation for a more complete study, including the production of other active species by the discharge, such as the first excited state of the oxygen atom, or even dissociation products of the hydrocarbon molecule following electron collisions or quenching of the nitrogen excited states.