Journal of Physical Chemistry A, Vol.115, No.21, 5346-5353, 2011
NCO Quantitative Measurement in Premixed Low Pressure Flames by Combining LIF and CRDS Techniques
NCO is a short-lived species involved in NO formation. It has never been quantitatively measured in flame conditions. In the present study, laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CADS) were combined to measure NCO radical concentrations in premixed low-pressure flames (p = 5.3 kPa). NCO LIF excitation spectrum and absorption spectrum (using CADS) measured in a stoichiometric CH(4)/O(2)/N(2)O/N(2) flame were found in good agreement with a simulated spectrum using PGOPHER program that was used to calculate the high-temperature absorption cross section of NCO in the A(2)Sigma(+)-X(2)Pi transition around 440.479 nm. The relative NCO-LIF profiles were measured in stoichiometric CH(4)/O(2)/N(2)O/N(2) flames where the ratio N(2)O/O(2) was progressively decreased from 0.50 to 0.01 and in rich CH(4)/O(2)/N(2) premixed flames. Then, the LIE profiles were converted into NCO mole fraction profiles from the absorption measurements using CRDS in a N(2)O-doped flame.