Abstract

Because NO is formed in a variety of combustion processes, concentration measurements using laser-induced fluorescence (LIF) have been widespread. Accurate measurements are needed at high temperatures to validate flame models, yet the fluorescence quantum yield, an essential factor relating optical signals to concentration, has previously been estimated using only quenching rates determined primarily at lower temperatures.¹,² We report rate coefficients for the deexcitation of NO (A²Σ, v′ = 0, N′ = 17) by NO, CO₂, Ar, and He at temperatures more representative of combustion environments. Output pulses (~10 ns) from a Nd:YAG-based laser system excited the A-X (0,0) R₁(17) transition of NO, which was nanometrically seeded in unreactive gas mixtures and then heated by incident shock waves. Filtered fluorescence in the (0,3) band was detected perpendicular to the laser beam and the gas flow and was recorded using a transient digitizer. Fluorescence decay rates obtained using different partial pressures of NO and NO/CO₂ in Ar or He/Ar allow us to extract collisional quenching rate coefficients at temperatures between 900 and 2200 K. These rates, together with additional rates at room temperature, are interpreted using collision models and discussed in terms of application to flame diagnostics using LIF.

© 1991 Optical Society of America