Measurements and modelling of HCN and CN species profiles in laminar CH4/O2/N2 low pressure flames using LIF/CRDS techniques

In the present work, measurements of absolute mole fraction profiles of CN and HCN were jointly performed in low pressure (5.3 kPa) premixed CH4/O2/N2 flames of three equivalent ratios (ϕ = 0.8-1.25). These species were the missing link of the database comprising CH, NCN, NCO and NO species previously acquired in Lille to improve detailed mechanisms of prompt-NO formation. For that purpose, LIF and pulsed CRDS techniques were implemented to measure in the flames absolute mole fraction of CN by probing the B-X(1,0) vibrational band around 356 nm. This combination of techniques allows reaching a detection limit as low as tenth of ppbv that was necessary to measure CN in lean flame condition could be achieved. HCN molecules were measured by using cw-CRDS technique around 1.5 μm (in the (2 0 0)-(0 0 0) vibrational band) after gas probe sampling. The required sensitivity equal to 15 ppbv of HCN was achieved using a long absorption cell (about 1 m). These CN and HCN profiles were simulated by considering two detailed mechanisms of prompt-NO formation from literature (Konnov0.6 (Combust. Flame 156 (2009) 2093-2105) and GDFkin®3.0_NCN (Combust. Flame 157 (2010) 1929-1941)).