NCO Quantitative Measurement in Premixed Low Pressure Flames by Combining LIF and CRDS Techniques

Abstract

NCO is a short-lived species involved in NO(x) formation. It has never been quantitatively measured in flame conditions. In the present study, laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CRDS) were combined to measure NCO radical concentrations in premixed low-pressure flames (p = 5.3 kPa). NCO LIF excitation spectrum and absorption spectrum (using CRDS) 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)Σ(+)-X(2)Π 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 LIF profiles were converted into NCO mole fraction profiles from the absorption measurements using CRDS in a N(2)O-doped flame.

NO formation in high pressure premixed flames: Experimental results and validation of a new revised reaction mechanism

“…In 2006, El Bakali et al [7] were the first to implement the new initiation reaction in their mechanism, namely the GDFkin ® 3.0_NCN (i.e., the hydrocarbon oxidation mechanism GDFkin ® 3.0 associated to the N-species sub-mechanism NOmecha1.0). Since then, Lamoureux et al have performed an extensive experimental and numerical study on the role of NCN in the prompt-NO mechanism in low pressure methane and acetylene flames with the measurements of species such as CH, NO, NCN [8][9][10], HCN, CN [11,12] and NCO [13] combining LIF (Laser Induced Fluorescence) and CRDS (Cavity Ring Down Spectroscopy) techniques. Recently, Lamoureux et al [14] proposed a final version of a new detailed NOx chemistry sub-mechanism, named NOmecha2.0, validated at high temperature on a large experimental database obtained in laminar premixed flames, jet-stirred and plug-flow reactors under sub-atmospheric and atmospheric pressure conditions.…”

The rate constant of the reaction NCN + H2 and its role in NCN and NO modeling in low pressure CH4/O2/N2-flames

“…The performance of the latter has been extensively validated and improved over the last few years by quantitative measurements and modeling of CH, NO and NCN concentration profiles in low-pressure CH 4 /O 2 /N 2 and C 2 H 2 /O 2 /N 2 flames of various fuel/air equivalent ratios. 12,14 Recently, corresponding NCO, CN and HCN profiles have been measured as well. 13 Whereas early versions of NCN submechanisms relied on rate constant estimates of Glarborg et al, 15 the more recent implementations are based on extensive rate constant data from the theoretical work performed by the M.C.…”

Quantitative NH measurements by using laser-based diagnostics in low-pressure flames

“…The temperature profiles were previously obtained by LIF thermometry according to a procedure described in [14]. They are reported in [10], except for flame CH4-N2O in which the temperature was measured equal to 1790 K at HAB=5.75 mm [9]. and recorded on a digital oscilloscope (Lecroy HDO4000, 12-bit vertical resolution, 1GHz bandwidth, 1.25 GS/s).…”

“…where the temperature was previously determined to be equal to 1790 K [9]. The absorption spectrum of the NH radical was recorded by using CRDS.…”

“…In our laboratory, we have previously shown the strong complementarities of LIF and CRDS to quantify trace species in premixed flames provided that they fluoresce. The LIF/CRDS coupling already allowed measuring species with mole fractions as low as a few ppb in the case of NCO [9].…”