The effect of hydrogen addition on flammability limit and NOx emission in ultra-lean counterflow CH4/air premixed flames

The effect of hydrogen addition to ultra lean counterflow CH₄/air premixed flames on the extinction limits and the characteristics of NO_x emission was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. The results show that the addition of hydrogen can significantly enlarge the flammable region and extend the flammability limit to lower equivalence ratios. If the equivalence ratio is kept constant, the addition of hydrogen increases the emission of NO in a flame due to the enhancement in the rate of the NNH or N₂O intermediate NO formation routes. The addition of hydrogen causes a monotonic decrease in the formation of NO₂ and N₂O, except flames near the extinction limits, where the emission of NO₂ and N₂O first increases, and then decreases with the increase in the fraction of hydrogen. Overall, hydrogen enrichment technology allows stable combustion under ultra lean conditions, resulting in significant CO₂ and NO emission reduction.     

Implementation of an advanced fixed sectional aerosol dynamics model with soot aggregate formation in a laminar methane/air coflow diffusion flame

An advanced fixed sectional aerosol dynamics model describing the evolution of soot particles under simultaneous nucleation, coagulation, surface growth and oxidation processes is successfully implemented to model soot formation in a two-dimensional laminar axisymmetric coflow methane/air diffusion flame. This fixed sectional model takes into account soot aggregate formation and is able to provide soot aggregate and primary particle size distributions. Soot nucleation, surface growth and oxidation steps are based on the model of Fairweather et al. Soot equations are solved simultaneously to ensure convergence. The numerically calculated flame temperature, species concentrations and soot volume fraction are in good agreement with the experimental data in the literature. The structures of soot aggregates are determined by the nucleation, coagulation, surface growth and oxidation processes. The result of the soot aggregate size distribution function shows that the aggregate number density is dominated by small aggregates while the aggregate mass density is generally dominated by aggregates of intermediate size. Parallel computation with the domain decomposition method is employed to speed up the calculation. Three different domain decomposition schemes are discussed and compared. Using 12 processors, a speed-up of almost 10 is achieved which makes it feasible to model soot formation in laminar coflow diffusion flames with detailed chemistry and detailed aerosol dynamics.     

Excited‐state hydrogen bonding dynamics of pyruvic acid and geminal‐diol, 2,2‐dihydroxypropanoic acid in aqueous solution: a DFT/TDDFT study

In this work, we present the optimized ground state geometrical structures, electronic excitation energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated Tce‐CH3COCOOH and Tce‐CH3C(OH)2COOH as well as their corresponding hydrogen‐bonded dimers Tce‐CH3COCOOH‐H2O and Tce‐CH3C(OH)2COOH‐H2O through time‐dependent density functional theory method. It is found that the intermolecular hydrogen bonds C=O···H‐O are strengthened in the electronically excited states of the hydrogen‐bonded dimers Tce‐CH3COCOOH‐H2O and Tce‐CH3C(OH)2COOH‐H2O, in that the excitation energies of the related excited states for the hydrogen‐bonded dimers are decreased compared with those of the corresponding monomers. The calculated results are consistent with the rules that are first demonstrated by Zhao on the excited‐state hydrogen bonding dynamics. Copyright © 2012 John Wiley & Sons, Ltd.