Quantitative Radar REMPI measurements of methyl radicals in flames at atmospheric pressure

Spatially resolved quantitative measurements of methyl radicals (CH₃) in CH₄/air flames at atmospheric pressure have been achieved using coherent microwave Rayleigh scattering from Resonance enhanced multi-photon ionization, Radar REMPI. Relative direct measurements of the methyl radicals were conducted by Radar REMPI via the two-photon resonance of the $ 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} $ state and subsequent one-photon ionization. Due to the proximity of the argon resonance state of 2s ²2p ⁵4f [7/2, J = 4](4+1 REMPI by 332.5 nm) with the CH₃ state of $ 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} $ (2+1 REMPI by 333.6 nm), in situ calibration with argon was performed to quantify the absolute concentration of CH₃. The REMPI cross sections of CH₃ and argon were calculated based on time-dependent quantum perturbation theory. The measured CH₃ concentration in CH₄/air flames was in good agreement with numerical simulations performed using detailed chemical kinetics. The Radar REMPI method has shown great flexibility for spatial scanning, large signal-to-noise ratio for measurements at atmospheric pressures, and significant potential to be straightforwardly generalized for the quantitative measurements of other radicals and intermediate species in practical and relevant combustion environments.     

Transient interactions between a premixed double flame and a vortex

The interaction between a laminar flame and a vortex is an important study for understanding the fundamentals of turbulent combustion. In the past, however, flame-vortex interactions have been investigated only for high-temperature flames. In this study, the impact of a vortex on a premixed double flame, which consists of a coupled cool flame and a hot flame, is examined experimentally and computationally using dimethyl ether/oxygen/ozone mixtures. The double flame is first shown to occur near the extinction limit of the hot flame. The differences between steady-state cool flames, double flames, and hot flames are explored in a one-dimensional counterflow configuration. The transient interactions between double flames and impinging vortices are then investigated experimentally using a micro-jet and numerically in two-dimensional transient modeling. It is seen that the vortex can extinguish the near-limit hot flame locally, resulting in a lone cool flame. At higher vortex intensities, the cool flame may also be extinguished after the extinction of the hot flame. It is found that there can be three different transient flame structures coexisting at the same time: an extinguished flame hole, a cool flame, and a double flame. Moreover, flame curvature is shown to play an important role in determining whether the vortex weakens or strengthens the cool flame and double flame.     

Soot emission reduction in oxygenated co-flow jet flames

A computational study was performed for ethylene/air non-premixed laminar co-flow jet flames using an axisymmetric CFD code to explore the effect of oxygenation on PAH and soot emissions. Oxygenated flames were established using N₂ diluted fuel stream along with O₂ enriched air stream such that the stoichiometric mixture fraction (Ζ_st) is varied but the adiabatic flame temperature is not materially changed. Simulations were carried out using a spatially and temporally accurate algorithm with detailed chemistry and transport. A detailed kinetic model involving 111 species and 784 reactions and a fairly detailed soot model were incorporated into the code. Two different approaches, one with constant flame height and other with constant inlet velocity are comprehensively examined to bring out the effects of changes in flame structure and residence time on soot emissions with respect to Z_st. With increase in Ζ_st, a drastic reduction in the formation of soot precursors (acetylene and benzene) and thus in soot emissions are observed. In the present study, oxygenated flames with Ζ_st ≥ 0.424 are considered as blue flames or completely soot free. For various oxygenated flames a C/O ratio between 0.45 and 0.6 is found to be most favorable for soot formation.     

Ionic Conductivity Studies in Yttrium-doped KCl Crystals

Ionic conductivity measurements have been made on Potassium Chloride crystals doped with different concentrations of Yttrium, in the temperature range 200 °C to 600 °C, to understand the nature of impurity vacancy (I–V) complexes, various types of their formation and to understand how these I–V complexes affect the conduction process. The conductivity-temperature plots of KCl: Y showed three distinct regions. These regions are explained on the basis of Dryfus and Nowick notation, formation and dissociation of yttrium impurity precipitates.     

Role of flow visualization in the development of UNICORN

This paper describes how visualizations have been used in the development and evaluation of a reacting-flow-simulation model known as UNICORN (UNsteady Ignition and COmbustion with ReactioNs). UNICORN, which solves full Navier-Stokes equations, has evolved over a 6-year period and is perhaps one of the most thoroughly evaluated codes of its kind. It evolved hand-in-hand with experiments that have been conducted to test its ability to predict ignition, extinction, and the dynamic characteristics of diffusion and premixed flames of hydrogen, methane, and propane fuels and that are stabilized in different ways. This paper also describes how UNICORN has been used, in conjunction with experiments, to provide new insights into combusting flows. Also, predictions of unobserved phenomena that were later confirmed by experiments are described. This paper demonstrates that the judicious use of a well-validated simulation in conjunction with laser based diagnostics is an effective way of understanding complex combusting flows.     

Microwave assisted synthesis of 4-methyl-3-arylpyrano[2,3-f]chromen-2(8H)-one derivatives,evaluation of antiproliferative,and antimicrobial activities

A series of new 4-methyl-3-arylpyrano[2,3-f]chromen-2(8H)-one derivatives were designed and synthesized through an efficient, an eco-friendly manner under microwave irradiation and conventional heating methods. Structures of final compounds established based on IR, NMR and mass spectral analysis. The final target compounds were screened for their in vitro antiproliferative activity by taking cisplatin as a reference, Further, antibacterial activity by taking strains such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia and Escherichia coli. Furthermore, antifungal activity screened with Aspergillus niger, Aspergillus flavus and Fusarium oxysporum strains. Many compounds results good activity.     

A mild and simple regioselective iodination of activated aromatics with iodine and catalytic ceric ammonium nitrate

Molecular iodine in the presence of a catalytic amount of CAN has been utilized efficiently for regioselective iodination of activated aromatic compounds under mild reaction conditions.     

A simple and efficient method for α-bromination of carbonyl compounds using N-bromosuccinimide in the presence of silica-supported sodium hydrogen sulfate as a heterogeneous catalyst

α-Bromination of carbonyl compounds (cyclic and acyclic ketones, amides and β-ketoesters) has been achieved efficiently by treatment with N-bromosuccinimide (NBS) and catalyzed by silica-supported sodium hydrogen sulfate (NaHSO₄·SiO₂). The products were formed in high yields under mild reaction conditions and in short reaction times.