Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1272192 | International Journal of Hydrogen Energy | 2014 | 13 Pages |
•Effect of pressure on NOx kinetics in H2/CO diffusion and premixed flames is studied.•Significant discrepancies among NOx predictions by various H2/CO mechanisms.•NNH pathways, N2O pathways are dominant in most mechanisms.•Prompt NO formation is unique to GRI 3.0.•Accurate OH, NO measurements are necessary for mechanism validation.
The present study provides an extensive and detailed numerical analysis of NOx chemical kinetics in low calorific value H2/CO syngas flames utilizing predictions by five chemical kinetic mechanisms available out of which four deal with H2/CO while the fifth mechanism (GRI 3.0) additionally accounts for hydrocarbon chemistry. Comparison of predicted axial NO profiles in premixed flat flames with measurements at 1 bar, 3.05 bar and 9.15 bar shows considerably large quantitative differences among the various mechanisms. However, at each pressure, the quantitative reaction path diagrams show similar NO formation pathways for most of the mechanisms. Interestingly, in counterflow diffusion flames, the quantitative reaction path diagrams and sensitivity analyses using the various mechanisms reveal major differences in the NO formation pathways and reaction rates of important reactions. The NNH and N2O intermediate pathways are found to be the major contributors for NO formation in all the reaction mechanisms except GRI 3.0 in syngas diffusion flames. The GRI 3.0 mechanism is observed to predict prompt NO pathway as the major contributing pathway to NO formation. This is attributed to prediction of a large concentration of CH radical by the GRI 3.0 as opposed to a relatively negligible value predicted by all other mechanisms. Also, the back-conversion of NNH into N2O at lower pressures (2–4 bar) was uniquely observed for one of the five mechanisms. The net reaction rates and peak flame temperatures are used to correlate and explain the differences observed in the peak [NO] at different pressures. This study identifies key reactions needing assessment and also highlights the need for experimental data in syngas diffusion flames in order to assess and optimize H2/CO and nitrogen chemistry.