Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence

Bittner J, Lawitzki A, Meier U, Kohse-Höinghaus K. Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence. Applied Physics, B. 1991;52(2):108-116.Nitrogen atoms have been detected in stoichiometric flat premixed H2/O2/N2 flames at 33 and 96 mbar doped with small amounts of NH3, HCN, and (CN)2 using two-photon laser excitation at 211 nm and fluorescence detection around 870 nm. The shape of the fluorescence intensity profiles versus height above the burner surface is markedly different for the different additives. Using measured quenching rate coefficients and calibrating with the aid of known N-atom concentrations in a discharge flow reactor, peak N-atom concentrations in these flames are estimated to be on the order of 10 12–5×10 13 cm –3; the detection limit is about 1×10 11 cm –3

Laser-induced fluorescence determination of flame temperatures in comparison with CARS measurements

Lawitzki A, Plath I, Stricker W, Bittner J, Meier U, Kohse-Höinghaus K. Laser-induced fluorescence determination of flame temperatures in comparison with CARS measurements. Applied Physics, B. 1990;50(6):513-518.Temperature profiles in several premixed low pressure H2/O2/N2 flames and in an atmospheric pressure CH4/air flame were determined by laser-induced fluorescence (LIF) and by CARS experiments. In the LIF study, temperatures were derived from OH excitation spectra, CARS temperatures were deduced from N2 Q-branch spectra. The present study is the first quantitative comparison of these two methods for temperature determination in flames burning at pressures up to 1 bar. The resulting temperatures showed good agreement

Using Variant Selection to Facilitate Accurate Fitting of γ″ Peaks in Neutron Diffraction

γ″ diffraction peaks are hard to discern in neutron/X-ray diffraction patterns, hindering studies on the γ″-strengthened superalloys using in-situ diffraction. In this study, we propose a variant selection method to increase the intensity of γ″ peaks and to facilitate accurate fitting. The specific variants of γ″ are controlled by applying a 300 MPa tensile stress during aging at 790 °C for 5 hours. The interaction energy between the applied stress and the transformation strain of each γ″ variant differs, leading to an increase in the amount of the variants with a greater energy reduction at the expense of other variants. The enhanced variants result in greater γ″ peak intensities in neutron diffraction patterns, allowing both the Pawley refinement and single peak fitting to be performed. Lattice parameters of γ″ and γ phases, and lattice misfit between the two phases and volume fraction of γ″ are acquired. The uncertainties associated with the fitting maintain an acceptable level corresponding to 150 microstrains. The proposed variant selection method shows potential for studying the role of γ″ phase in Ni-base superalloys