Global sensitivity analysis of detailed chemical kinetic schemes for DME oxidation in premixed flames

Detailed chemical kinetic investigations on dimethylether oxidation in one-dimensional premixed flat flames were performed. Local and global sensitivities of the reaction rate constants within selected chemical kinetic schemes were studied using maximum flame temperature, and peak methane and formaldehyde concentrations as predictive target quantities. The global sensitivity analysis was based on the application of high dimensional model representations using quasi-random sampling. First- and second-order sensitivity indices of important reaction steps were determined for fuel rich (Φ = 1.49) and fuel lean (Φ = 0.67) conditions. Differences in the importance ranking for key reactions were found to exist between the selected schemes, highlighting the influence of differences in the key rate constants. Whilst the peak flame temperature was predicted with fairly low uncertainty by both schemes, significant uncertainties were identified in the prediction of the target minor species. Key reaction rates requiring better quantification in order to improve the prediction of methane and formaldehyde concentrations are identified

Characterization of megahertz X ray laser beams by multishot desorption imprints in PMMA

Proper diagnostics of intense free electron laser FEL X ray pulses is indisputably important for experimental data analysis as well as for the protection of beamline optical elements. New challenges for beam diagnostic methods are introduced by modern FEL facilities capable of delivering powerful pulses at megahertz MHz repetition rates. In this paper, we report the first characterization of a defocused MHz 13.5 nm beam generated by the free electron laser in Hamburg FLASH using the method of multi pulse desorption imprints in poly methyl methacrylate PMMA . The beam fluence profile is reconstructed in a novel and highly accurate way that takes into account the nonlinear response of material removal to total dose delivered by multiple pulses. The algorithm is applied to experimental data of single shot ablation imprints and multi shot desorption imprints at both low 10 Hz and high 1 MHz repetition rates. Reconstructed response functions show a great agreement with the theoretical desorption response function mode

Modelling accidental releases of dangerous gases into the lower troposphere from mobile sources

The article reports the results of different methods of modelling releases and dispersion of dangerous gases or vapours in cases of major accidents from road and rail transportation in urban zones. Transport accidents of dangerous substances are increasingly frequent and can cause serious injuries in densely inhabited areas or pollution of the environment. For quantitative risk assessment and mitigation planning, consequence modelling is necessary. The modelling of dangerous substance dispersion by standard methods does not fully represent the behaviour of toxic or flammable clouds in obstructed areas such as street canyons. Therefore the predictions from common software packages as ALOHA, EFFECTS, TerEx should be augmented with computational fluid dynamics (CFD) models or physical modelling in aerodynamic tunnels, and further studies are planned to do this. The goal of this article is to present the results of the first approach of modelling using these standard methods and to demonstrate the importance of the next development stage in the area of transport accident modelling of releases and dispersions of dangerous substances in urban zones in cases of major accident or terrorist attacks

Millimetre-wave and infrared spectroscopy of Br13CN : anharmonic force field of cyanogen bromide from spectroscopic data and ab initio calculations

The rotational spectra of 79Br13C14aNn d s1Br13C14Nin the low-lying 01'0, 10°O, 02OO and 02'0 vibrational states were observed in the millimetre-wave region, and the v3 fundamental band of the 13C containing species was recorded from 21 10 to 2170 cm-' with a diode laser spectrometer. The anharmonic force field of cyanogen bromide was calculated using the data obtained together with those already known for the normal and I5N isotopomers. The experimental determination of the force field was supported by an ab initio calculation of the intramolecular potential energy surface, which was obtained by the CASSCF method. A further refinement of the equilibrium structure was made using the equilibrium rotational constants of six different isotopomers

ANALYSIS OF THE ν2\nu_2 BAND OF THE FCO2_2 RADICAL: PRELIMINARY RESULTS

Kolesnikova, Varga, Beckers, Simeckova, Zelinger, Nova Striteska, Kania, Willner, and Urban, J. Chem Phys 128, 224 (2008)Author Institution: Laboratoire Inter Universitaire des Systemes Atmospheriques; CNRS, Universites Paris 12 et 7, 61 Av du General de Gaulle, 94010 Creteil; Cedex France; VSB-Technical University of Ostrava, Faculty of; Safety Engineering, Lum\irova 13, CZ-70030, Ostrava 3 - Vyskovice, Czech Republic; Institute of Thermomechanics, v.v.i., Academy of Sciences of the Czech Republic, Dolejskova 5; CZ-18200 Prague 8, Czech Republic; Inorg. Chemistry, University of Wuppertal, D-42119 Wuppertal, GERMANY; J. Heyrovsky Institute of Physical; Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, CZ-18223 Prague 8; Czech Republic; VSB-Technical University of Ostrava, Faculty; of Safety Engineering, Lum\irova 13, CZ-70030, Ostrava 3 - Vyskovice, Czech Republic; Institute of Thermomechanics, v.v.i, Academy of Sciences of the Czech Republic, Dolejskova 5; CZ-18200 Prague 8, Czech Republic.The unique fluoroformyloxyl radical (FCO$_2$) is assumed to participate in atmospheric processes such as the degradation of hydrofluorocarbons that have been considered as chlorofluorocarbon substitutes. Despite this atmospheric interest, the molecular and spectroscopic properties of FCO$_2$ have not yet sufficiently been explored. The high resolution FT IR gas phase spectrum of the fluoroformyloxyl (FCO$_2$) radical was recorded in the 650 - 1500~cm$^{-1}$ spectral range at the University of Wuppertal. Using this spectrum and the ground state parameters achieved recently we carried out the first high resolution study of the $\nu_2$ $A$-type band (C-F stretching mode) centered at 970.209 cm$^{-1}$. The analysis was difficult because the band is congested. In addition the spin doublets are difficult to identify except for high K$_a$ values. However, we could take advantage of the fact that only K$_a$=odd values are observable for symmetry reasons. The line position calculation accounts for the spin rotation doubling and for the Fermi-type resonances linking the 2$^1$ and 5$^2$ spin rotation energy levels

Experimental investigations and numerical simulations of methane cup-burner flame

Pulsation frequency of the cup-burner flame was determined by means of experimental investigations and numerical simulations. Simplified chemical kinetics was successfully implemented into a laminar fluid flow model applied to the complex burner geometry. Our methodical approach is based on the monitoring of flame emission, fast Fourier transformation and reproduction of measured spectral features by numerical simulations. Qualitative agreement between experimental and predicted oscillatory behaviour was obtained by employing a two-step methane oxidation scheme