Effect of non-equilibrium plasma on two-stage ignition of n-heptane

Sharath Nagaraja, Wenting Sun, Vigor Yang

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)

Abstract

The effect of pulsed nanosecond dielectric barrier plasma discharges on the ignition characteristics of n-heptane and air mixtures is investigated through self-consistent simulations in a plane-to-plane geometry at reduced pressures (20.3 kPa). The present work represents one of the first attempts in understanding the kinetic and thermal effects of nanosecond pulsed discharges on the two-stage ignition process of n-heptane. A plasma-fluid formulation is developed with ions and neutral species at gas temperature, and electrons in non-equilibrium. The work makes use of an optimized chemical kinetics mechanism consisting of 166 species and 611 reactions, obtained by combining a reduced n-heptane kinetic model, a non-equilibrium plasma chemistry scheme, and a NOx kinetic model. The catalytic effect from plasma-generated radicals on the first stage of the n-heptane ignition process has been identified. Production of radicals such as O, H and OH from the plasma initiates and accelerates the H abstraction of fuel molecules, and dramatically reduces the induction time of the exothermic cycle (RH → R → RO2 → OROOH) by a factor of 10. Furthermore, the plasma action on low temperature chemistry is found to be nearly independent of the equivalence ratio and more pronounced at lower temperatures (550-650 K). A staggered application of nanosecond voltage pulses (2-4 pulses at the beginning and 20-30 pulses after the first stage heat release) is shown to be optimal, resulting in a reduction of the ignition delay by approximately a factor of 2. NO production from the plasma via electron impact and quenching processes at low temperatures plays an important role in promoting chain-branching reactions and contributes to shortening the ignition delay by approximately 10%.

Original languageEnglish
Pages (from-to)3497-3504
Number of pages8
JournalProceedings of the Combustion Institute
Volume35
Issue number3
DOIs
Publication statusPublished - 2015

All Science Journal Classification (ASJC) codes

  • General Chemical Engineering
  • Mechanical Engineering
  • Physical and Theoretical Chemistry

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