Quantitative Laser-Induced Fluorescence Measurements and Modeling of Nitric Oxide in High-Pressure (6–15 Atm) Counterflow Diffusion Flames

Abstract

Laser-induced fluorescence (LIF) measurements of NO concentration ([NO])have been obtained along the centerline of methane-air counterflow diffusion flames at 6 to 15 atm. This study is an extension of our previous work involving measurements of [NO] in similar flames at two to five atm, wherein we had used a counterflow premixed flame for calibration. For the flames studied here, a method based on computed overlap fractions is developed to calibrate [NO] measurements at higher pressures. The linear LIF measurements of [NO], which are corrected for variations in the electronic quenching rate coefficient, are compared with numerical predictions from an opposed-flow flame code utilizing two Gas Research Institute (GRI) chemical kinetic mechanisms (versions 2.11 and 3.0). The effect of radiative heat loss on code predictions is accounted for by using an optically thin radiation model. The revised GRI mechanism (version 3.0) offers a significant improvement in prompt-NO predictions for these flames compared to the older version (2.11), especially at pressures below eight atm. However, a consistent discrepancy remains in the comparisons, particularly at peak NO locations for pressures lower than six atm. The measurements display a continuing trend of decreasing NO concentration with increasing pressure at 6-15 atm as expected for flames dominated by prompt NO. The discrepancy between measurements and predictions decreases with rising pressure so that the revised GRI mechanism predicts [NO] with reasonable accuracy at pressures above six atm.

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

“…The complete understanding of the chemical kinetics involved in the production of NO at high pressure requires accurate in situ measurements of NO concentration. Most of the studies dedicated to NO measurements in laminar high pressure flames were performed using Laser Induced Fluorescence by the groups of N.M. Laurendeau [20][21][22][23][24][25][26][27][28][29][30] and R.K. Hanson [31][32][33][34][35].…”

“…The first NO LIF measurements in a counterflow burner configuration were performed by Thomsen et al [23,24] who presented an experimental and modeling study of NO formation in premixed CH4/air flames at equivalence ratios varying from 0.65 to 1.5 at atmospheric and high pressures. Further studies were performed in high pressure partially premixed and diffusion flames [25][26][27][28][29][30].…”

The Chemical and Physical Effect of Diluent H2O on NO and CO Emissions in Computational CH4 / Air Laminar Diffusion Flames

“…The chemical reaction mechanism GRI -mech 3.0 is generally used to calculate methane combustion, which consists of 325 chemical reactions involving 53 species. The mechanism can reasonably and reliably predicate NOX formation, but leads to an overestimation of prompt NOX when the thermal route dominates NOX formation [30][31]. However, solving the tens/hundreds of millions of Lagrangian particles clearly implies a long computational time when using the detailed mechanism, and a high computer configuration is required [32].…”

Advances in understanding combustion phenomena using non-premixed and partially premixed counterflow flames: A review

“…Several researchers have extensively investigated the prompt-NO route in counterflow diffusion flames using hydrocarbons such as methane and ethane. [160][161][162][163][164][165] The measurements initially showed a necessity in the improvement of prompt-NO initiation reactions used in GRI 2.11 mechanism especially for predictions below 6 bar. Predictions by GRI 3.0 were found to be in better agreement with the NO measurements at pressures below 8 bar.…”