Intramolecular vibrational energy flow in excited bridged azulene-anthracene compounds is investigated by time-resolved pump-probe laser spectroscopy. The bridges consist of molecular chains and are of the type (CH(2))(m) with m up to 6 as well as (CH(2)OCH(2))(n) (n=1,2) and CH(2)SCH(2). After light absorption into the azulene S(1) band and subsequent fast internal conversion, excited molecules are formed where the vibrational energy is localized at the azulene side. The vibrational energy transfer through the molecular bridge to the anthracene side and, finally, to the surrounding medium is followed by probing the red edge of the azulene S(3) absorption band at 300 nm and/or the anthracene S(1) absorption band at 400 nm. In order to separate the time scales for intramolecular and intermolecular energy transfer, most of the experiments were performed in supercritical xenon where vibrational energy transfer to the bath is comparably slow. The intramolecular equilibration proceeds in two steps. About 15%-20% of the excitation energy leaves the azulene side within a short period of 300 fs. This component accompanies the intramolecular vibrational energy redistribution (IVR) within the azulene chromophore and it is caused by dephasing of normal modes contributing to the initial local excitation of the azulene side and extending over large parts of the molecule. Later, IVR in the whole molecule takes place transferring vibrational energy from the azulene through the bridge to the anthracene side and thereby leading to microcanonical equilibrium. The corresponding time constants tau(IVR) for short bridges increase with the chain length. For longer bridges consisting of more than three elements, however, tau(IVR) is constant at around 4-5 ps. Comparison with molecular dynamics simulations suggests that the coupling of these chains to the two chromophores limits the rate of intramolecular vibrational energy transfer. Inside the bridges the energy transport is essentially ballistic and, therefore, tau(IVR) is independent on the length.

Intra- and intermolecular vibrational energy flow in vibrationally highly excited bridged azulene-(CH2) n -aryl (n = 0,1,3; aryl = benzene or anthracene) compounds is observed using time-resolved pump−probe laser spectroscopy. Light absorption in the azulene S1-band, followed by fast internal conversion, leads to vibrational excitation at the azulene side of the molecules. Subsequent energy flow through the aliphatic chain to the aryl group at the other side of the molecules and vibrational energy transfer into a surrounding liquid solvent bath are measured either by probing the red edge of the azulene S3-absorption band at 300 nm and/or the anthracene S1-absorption band at 400 nm. The data are analyzed by representing the intramolecular energy flux as a diffusion process and using hot absorption spectra of the two chromophores of the compounds for measuring their energy contents. A fit to all of the experimental signals leads to an energy conductivity of a single C−C bond of κ CC = (10 ± 1) cm-1 K-1 ps-1 (with energies measured in cm-1). Depending on the substituent and the length of the chain, this models yield intramolecular energy transfer times of 1.2−4 ps. Energy transfer to the solvent 1,1,2-trichloro-trifluoro-ethane, on the other hand, is characterized by an exponential loss profile with a cooling time constant of (21 ± 2) ps, independent of the substituent and the same as for bare azulene.

Power generation by using oxyfuel combustion in a gas turbine cycle is a promising option to reduce carbon dioxide (CO 2 ) emission, while using fossil fuels. In order to use this process some significant changes to the gas turbine are required, regarding which open questions still exist. An important question is whether reliable operation with oxyfuel combustion under gas turbine conditions is possible. The paper describes experiments on partiallypremixed swirl stabilized oxyfuel flames carried out in a gas turbine model combustor at atmospheric pressure. To characterize the behaviour of the oxyfuel flames a systematic parameter study for oxidisers consisting of 20 % -40 % oxygen (O 2 ), equivalence ratios from 0.5 to 1, and powers of 10 kW to 30 kW was carried out. OH * -chemiluminescence imaging was used to visualise the flame structure and stability. The results show a strong influence of the O 2 concentration on the combustion behavior in contrast to the equivalence ratio which has only a very small effect. To obtain quantitative results, laser Raman scattering has been used on selected flames to measure simulta- neously the major species concentrations, mixture fraction and temperature.The results reveal differences in the flame stabilisation mechanism, compared to methane (CH 4 )/air flames in the same burner.

The structure and stabilization of heated hydrogen jet flames in heated cross-flows was experimentally investigated in a configuration that is analogous to terrestrial gas turbine components. Three flames, with jet velocities ranging from 100-200 m/s, were investigated using particle image velocimetry and OH planar laser induced fluorescence in a total of 11 x − y and y − z planes. Additionally, laser Raman scattering was performed in the 200 m/s jet to characterize the thermo-chemical state. In all cases, the flame along the jet centerline plane consisted of two branches, one stabilized in the jet lee and one lifted above the jet trajectory. The positional stability of the lee-stabilized branch was greater in the higher jet velocity cases due to the larger and stronger recirculation zones created downstream of the injection point. The lifted flame branch was much more dynamic, with measured flame base axial positions ranging from the jet near field to the flame tip. This flame branch instantaneously resided downstream of regions with high extensive principal strain-rate, and the strain-rate significantly affected the thermo-chemical state. The Raman measurements indicated that the base of the lifted flame branch existed in locations where both tribrachial and/or stratified premixed flame behaviors are expected, depending on the instantaneous flame location. Accurately modeling these complex flame structures and flow-flame interactions therefore is necessary to properly simulate jet flames in cross-flows.

An experimental analysis of confined premixed turbulent methane/air and hydrogen/air jet flames is presented. A generic lab scale burner for high-velocity preheated jets equipped with an optical combustion chamber was designed and set up. The size and operating conditions were configured to enable flame stabilization by recirculation of hot combustion products. The geometry of the rectangular confinement and an off-center positioning of the jet nozzle were chosen to resemble one burner nozzle of a FLOX V Rbased combustor. The off-center jet arrangement caused the formation of a pronounced lateral recirculation zone similar to the one in previously investigated FLOX V R -combustors (Lückerath et al., 2007. "FLOX V R Combustion at High Pressure with Different Fuel Compositions," ASME J. Eng. Gas Turbines Power, 130(1), pp. 011505; Lammel et al., 2010. "FLOX V R Combustion at High Power Density and High Flame Temperatures," ASME J. Eng. Gas Turbines Power, 132(12), p. 121503ff). The analysis was accomplished by different laser measurement techniques. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. Results of measurements in two confined jet flames are shown. The mixing of fresh gas with recirculating combustion products and the stabilization of the methane flame are discussed in detail. The presented findings deliver important information for the understanding of confined jet flames operated with different fuels. The obtained data sets can be used for the validation of numerical simulations as well.

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An experimental analysis of confined premixed turbulent methane/air and hydrogen/air jet flames is presented. A generic lab scale burner for high-velocity preheated jets equipped with an optical combustion chamber was designed and set up. The size and operating conditions were configured to enable flame stabilization by recirculation of hot combustion products. The geometry of the rectangular confinement and an off-center positioning of the jet nozzle were chosen to resemble one burner nozzle of a FLOX®-based combustor. The off-center jet arrangement caused the formation of a pronounced lateral recirculation zone similar to the one in previously investigated FLOX®-combustors [1, 2]. The analysis was accomplished by different laser measurement techniques. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. Results of measurements in two confined jet flames are shown. The mixing of fresh gas with recirculating combustion products and the stabilization of the methane flame are discussed in detail. The presented findings deliver important information for the understanding of confined jet flames operated with different fuels. The obtained data sets can be used for the validation of numerical simulations as well.

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