Flame kernel development with radiofrequency oscillating plasma ignition

Abstract

In this paper a radiofrequency oscillating plasma discharge is investigated under various initial pressures up to 5 atm in a constant-volume combustion chamber. The oscillating plasma is suppressed by elevated pressure, both in length and branch number. The ignition performance under elevated background pressure is investigated, and the results are compared with spark events with a similar ignition energy. Under ambient conditions, the oscillating plasma discharge generates multiple streamers that are much longer than a spark gap, resulting in a much bigger initial flame kernel. Under elevated background pressures, fewer streamers with much smaller sizes are observed, thus the advantage of an oscillating plasma discharge over a spark discharge is compromised. Prolonged duration of an oscillating plasma discharge consistently demonstrates a positive impact on flame propagation speed, but neither prolonged duration nor enhanced discharge current has a noticeable impact on flame kernel growth for the spark ignition cases. Both oscillating plasma and spark are used to treat non-combustible propane–air mixtures under background pressures from 1 to 5 atm.