Effects of pulse rise time and repetition frequency on nanosecond pulsed plasma ignition for combustion

Abstract

Transient plasma ignition (TPI) employs highly non-equilibrium plasmas driven by nanosecond high-voltage pulses for combustion ignition. The effects of rise time and pulse repetition frequency (PRF) on combustion ignition are evaluated when transient plasmas, powered by 10-ns, kilovolt pulses, are employed to initiate combustion of lean, stoichiometric, or rich methane-dry air mixtures at atmospheric pressure. It was found that the plasmas driven by high voltage pulses with a faster rise time and PRF between 6–10 kHz enhanced combustion with higher peak pressure and/or shorter ignition delay. A mode transition in the plasma, corresponding to the combustion initiation, was observed based on voltage and current waveforms of four consecutive pulsed plasmas driven by a pulse burst at kilohertz PRFs. Although benefits in combustion ignition from a shorter rise time and optimal PRF were observed for all three equivalence mixture ratios, the highest peak pressure and shortest ignition delay were associated with the stoichiometric mixtures. In addition, the gas temperature of the transient plasma was measured by determining the rotational temperature of the 2nd positive system of nitrogen to be ∼1000 K for the first pulse and increased up to 2000 K after the application of the 4th pulse in a four-pulse burst TPI.