TY - CONF
T1 - Direct ignition and S-curve transition by in situ nano-second pulsed discharge in methane/oxygen/helium counterflow flame
AU - Sun, Wenting
AU - Won, Sang Hee
AU - Ju, Yiguang
AU - Ombrello, Timothy
AU - Carter, Campbell
N1 - Funding Information:
This work was supported by the MURI research grant from the Air Force Office of Scientific Research and the grant FA9550-07-1-0136 . Wenting Sun thanks James Michael and Dr. Tanvir Farouk from the Department of Mechanical and Aerospace Engineering, Princeton University for the help of the Rayleigh scattering measurement and numerical modeling, respectively.
PY - 2012
Y1 - 2012
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84872864629&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84872864629&partnerID=8YFLogxK
U2 - 10.2514/6.2012-381
DO - 10.2514/6.2012-381
M3 - Paper
AN - SCOPUS:84872864629
T2 - 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
Y2 - 9 January 2012 through 12 January 2012
ER -