A simplified analysis of turbulence effects on nanosecond pulsed discharge induced ammonia ignition

This study developed a perfectly stirred reactor (PSR) model that incorporates the discharge and the combustion reactions to investigate the effects of turbulence on the Nanosecond Pulsed Discharge (NSD) induced ignition of the NH3/O2/He mixture. Three NSD induced ignition states in the PSR can be distinguished as the NSD works continuously and thus the Equivalent Minimum Ignition Energy (EMIE) is defined for the characterization of NSD induced ignition processes. Afterwards, the effects of discharge frequency and flow velocity on EMIE are firstly analyzed. It is found that the EMIE increases rapidly with discharge frequency (fp) initially and then slows down with a critical transition frequency between 30 and 50 kHz. As fp is below 30 kHz, EMIE increases almost linearly with fp since the energy density of individual pulses determines EMIE, while as fp is above 50 kHz, EMIE increases quite slowly with fp since the so-called memory effect of discharge pulses works. Secondly, the effects of turbulence characteristics such as the turbulent fluctuation velocity (u') and frequency (ft) as well as the phase difference between the discharge pulse and the turbulent fluctuation on the EMIE are explored. EMIE is found to be greatly impacted by the phase matching between turbulent fluctuations and discharge pulses. When fp and ft are matched (i.e., fp is equal to or a multiple of ft), the phase effect can influence EMIE by up to 28 %. In contrast, when fp and ft are mismatched, EMIE is primarily determined by the amplitude and frequency of turbulent velocity fluctuation. The smaller ft or the larger u' results in the smaller EMIE. The proposed method is finally used to analyze the NSD induced ignition probability, which can be quite consistent with the reported experimental results. It confirms to be a useful approach for quickly studying NSD enhanced ignition and combustion characteristics in turbulence.