Strategies for Laser-Induced Fluorescence Detection of Nitric Oxide in HighPressure Flames. II. A -X (0,1) Excitation

A-X (0,1) excitation is a promising new approach for NO laser-induced fluorescence (LIF) diagnostics at elevated pressures and temperatures. We present what to our knowledge are the first detailed spectroscopic investigations within this excitation band using wavelength-resolved LIF measurements in premixed methane /air flames at pressures between 1 and 60 bar and a range of fuel /air ratios. Interference from O2 LIF is a significant problem in lean flames for NO LIF measurements, and pressure broadening and quenching lead to increased interference with increased pressure. Three different excitation schemes are identified that maximize NO /O2 LIF signal ratios, thereby minimizing the O2 interference. The NO LIF signal strength, interference by hot molecular oxygen, and temperature dependence of the three schemes are investigated.