Search

Combustion dynamics are investigated for plasma-enhanced methane–air flames in premixed and nonpremixed configurations using a transient arc dc plasmatron. Planar laser-induced fluorescence images of hydroxyl (OH) and carbon monoxide (CO) radicals are obtained over a range of equivalence ratios ( \phi = 0.7 - 1.3), flow rates (6–18 LPM), and plasma powers (100–900 mA) to monitor radical propagation and in situ fuel reforming. The flow rates presented here are outside the range of normal flame stability. In the nonpremixed mode, the fuel is injected separately as a coflow around the plasma discharge, resulting in a unique two-cone flame front geometry, and the flame stability is mainly dependent on the flow dynamics. For premixed flames, partial oxidation occurs inside the chamber, resulting in higher energy conversion efficiencies, and stability is shown to be sensitive to the combustion chemistry. Both configurations are significantly influenced by in situ fuel reforming at higher plasma powers. [ABSTRACT FROM AUTHOR]

This paper presents quantitative planar laser- induced fluorescence (PLIF) imaging of nitric oxide (NO) in a transient-arc direct-current plasmatron igniter using premixed air/fuel mixtures. Quantitative measurements of NO are reported as a function of gas flow rate (20-50 standard cubic feet per hour), plasma power (100-900 mA, 150-750 W), and equivalence ratio (0.7-1.3). Images were corrected for temperature effects by using 2-D temperature field measurements obtained with infrared thermometry and calibrated by a more accurate multiline fitting technique. The signals were then quantified using an NO addition method and spectroscopic laser-induced fluorescence modeling of NO. NO PLIF images and single-point NO concentrations are presented for both plasma-discharge-only and methane/air plasma-enhanced combustion cases. NO formation occurs predominantly through N2(υ) + O → NO + N for the plasma-discharge-only case without combustion. The NO concentration for the plasma-enhanced combustion case (500-3500 ppm) was an order of magnitude less than the plasma-discharge-only case (8000-15 000 ppm) due to the reduction of plasma reactions by the methane. Experiments show the linear decay of NO from equivalence ratio 0.8-1.2 under the same flow condition and discharge current. [ABSTRACT FROM AUTHOR]

Quantitative images of temperature and hydroxyl (OH) concentrations are presented in plasma-enhanced flames, where a nonthermal microwave plasma discharge is coupled directly with the reaction zone of the flame. The plasma jet is generated through a novel microwave (2.45 GHz) waveguide based a coaxial reactor system. Planar laser-induced fluorescence is used to generate the OH fields, and planar Rayleigh scattering thermometry is used for the temperature. Plasma-enhanced flames present new possibilities for ignition and flame holding under harsh operating conditions, including stabilization of combustion in hypersonic flame conditions. [ABSTRACT FROM AUTHOR]