Direct ignition and S-curve transition by in situ nano-second pulsed discharge in methane/oxygen/helium counterflow flame

Wenting Sun, Sang Hee Won, Yiguang Ju, Timothy Ombrello, Campbell Carter

Research output: Contribution to conferencePaper

1 Scopus citations

Abstract

A novel well-defined plasma assisted combustion system with an in situ discharge in a counterflow diffusion flame is developed to study the direct coupling kinetic effect of a nonequilibrium plasma on the flame ignition and extinction. Uniform discharge is generated between the two burner nozzles by placing porous metal electrodes at the nozzle exits. The ignition and extinction characteristics of CH4/O2/He diffusion flame are investigated by measuring the excited OH (OH*) emission intensity at constant strain rates and O2 concentrations on the oxidizer side while changing of the fuel mole fraction. It is found that ignition and extinction occur with an abrupt change of OH* emission intensity at lower O2 concentration, indicating the existence of the conventional S-curve in the flame regimes. However, at a higher O2 concentration, it is found that the in situ discharge can significantly modify the characteristics of ignition and extinction, create a new monotonic, and fully stretched S-curve. The transition from the conventional S-curves to a new stretched ignition curve indicates clearly that the active species generated by the plasma can change the chemical kinetic pathways of fuel oxidation at low temperature, thus resulting in the transition of flame stabilization mechanism from the extinction-controlled to the ignitioncontrolled regimes. The chemical kinetic model for plasma-flame interaction has been developed based on the assumption of constant electric field intensity in the bulk plasma region. Thus, the rate constants for electron impact ionization and dissociate reactions are calculated from the Boltzmann equation. The temperature profiles are measured experimentally by Rayleigh scattering technique and compared with the numerical modeling. Both show that the local maximum temperature in the reaction zone, where the ignition occurs, can be as low as 900 K. The reaction pathways analysis further reveals that atomic oxygen generated by the discharge is critical to controlling the radical production and modifying the branching ratio in the reaction zone for the low temperature ignition enhancement.

Original languageEnglish (US)
DOIs
StatePublished - Dec 1 2012
Event50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition - Nashville, TN, United States
Duration: Jan 9 2012Jan 12 2012

Other

Other50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
CountryUnited States
CityNashville, TN
Period1/9/121/12/12

All Science Journal Classification (ASJC) codes

  • Aerospace Engineering

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    Sun, W., Won, S. H., Ju, Y., Ombrello, T., & Carter, C. (2012). Direct ignition and S-curve transition by in situ nano-second pulsed discharge in methane/oxygen/helium counterflow flame. Paper presented at 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Nashville, TN, United States. https://doi.org/10.2514/6.2012-381