Ignition enhancement and deterioration by nanosecond repetitively pulsed discharges in a randomly-stirred lean n-butane/air mixture at various inter-electrode gaps

Shenqyang Steven Shy, Yi Rong Chen, Bo Liang Lin, Anatoly Maznoy

Research output: Contribution to journalArticlepeer-review

Abstract

At 38th Symposium, Shy and co-workers investigated a turbulence-facilitated-ignition (TFI) phenomenon via both conventional-single-spark-discharge (CSSD) and nanosecond-repetitively-pulsed-discharge (NRPD) at various pulsed-repetitive-frequency (PRF=5–70 kHz) using a fixed inter-electrode gap (dgap=0.8 mm) in a randomly-stirred lean n-butane/air mixture with Lewis number Le≈2.2 ≫ 1 over a range of r.m.s. turbulent fluctuating velocity (u′=0–2.1 m/s). It was found that the ignition probability (Pig) decreases significantly with increasing u′ for most PRFs, except at PRF=60 kHz having turbulent Pig,T = 37% at u′=0.5 m/s > laminar Pig,L = 34%, showing possible TFI. Using the same methodology, this paper presents two new Pig datasets at dgap=0.6 mm and 2.0 mm over wider ranges of PRF=1–90 kHz and u′=0–2.8 m/s. All NRPD experiments apply the same total ignition energy Etot≈23 mJ via a train of 11 pulses, each pulse having about 2.2 mJ except for the first pulse having about 1 mJ when using sufficiently high open-circuit-voltage of 28 kV. Note that Etot≈MIEL≈23 mJ at dgap=0.8 mm as a baseline for comparison; MIEL is the laminar minimum ignition energy measured by CSSD at 50% ignitability and MIEL=26.3 mJ/3.4 mJ at dgap=0.6 mm/2.0 mm. While TFI is noticeably observed at dgap=0.6 mm when PRF=60 kHz with Pig,T = 92% at u′=0.5 m/s > Pig,L = 78%, turbulence reclaims its dominating role when u′ > 1.4 m/s with Pig,T << Pig,L. At dgap=2.0 mm, there is no TFI; a Pig,T transition is found where the decrease of Pig,T with u′ changes from gradually to rapidly when u′ > u′c (critical u′ depending on PRF). We also discover that the curves of Pig,T versus PRF are highly non-monotonic with peaks around PRF=40 kHz for u′ > 1.4 m/s; too high PRFs are detrimental for spherical flame ignition. These results are explained by coupling effects of dgap, PRF, u′, and differential diffusion.

Original languageEnglish
Article number111506
JournalCombustion and Flame
Volume231
DOIs
StatePublished - Sep 2021

Keywords

  • Ignition probability enhancement and deterioration
  • Inter-electrode gap
  • Nanosecond repetitively pulsed discharge
  • Pulsed repetitive frequency
  • Synergistic effect
  • Turbulent ignition transition

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