Nitric Oxide Formation During Ignition and Combustion of a Transient Arc Plasmatron

Abstract

Spatially resolved nitric oxide (NO) concentrations in plasma-enhanced flames of a transient arc plasmatron are presented using planar laser-induced fluorescence (PLIF). Quantitative measurements of NO are made by comparing the laser-induced fluorescence (LIF) signal to a well defined flat-flame calibration torch and using a NO addition method based on sequentially increased seeding of NO. For correction of the LIF signal variation, temperature field measurements are made using a combination of IR thermometry and a more accurate multi-line fitting technique of multiple NO transitions. 2-D NO PLIF images and single point NO concentrations are presented for both plasma discharge only and methane/air plasma enhanced combustion. Measurements are reported as a function of gas flow rate (20 to 50 SCFH), plasma power (100 to 900 mA, 150 to 750 watt) and equivalent ratio (0.7 to 1.3). The NO concentration for the plasma coupled combustion (500 to 3500 ppm) case was an order of magnitude less than the plasma discharge only case (8000 to 15000 ppm) due to the reduction of NO from the hydrocarbon chemistry. NO concentration was observed to decrease with less discharge power, decreased flow rate and increased equivalence ratio.