Determination of spatial temperature distributions in a laminar premixed ethylene/air flame by laser-induced atomic fluorescence

A quick and simple detection system for spatially resolved temperature measurements in flames based on laser-induced thermally assisted atomic line fluorescence of seeded rubidium atoms is described. The fluorescence light from two atomic states is dispersed and simultaneously recorded by a CCD camera. The fluorescence ratio distributions lead directly to absolute temperature distributions. The practical use, the spatial and temperature resolution and error limits of the method are discussed and compared with other procedures for temperature measurements.     

Exhaust-gas imaging via planar laser- induced fluorescence of sulfur dioxide

The potential use of planar laser-induced fluorescence (PLIF) of sulfur dioxide (SO₂) for visualization of exhaust-gas distributions is outlined and demonstrated. Strong absorption features in the UV spectral range allow excitation of SO₂ with the fourth harmonic of a Nd:YAG laser at 266 nm. Fluorescence emissions are mostly red-shifted and can be easily detected in single-shot imaging arrangements with a good signal-to-noise ratio. This study uses a premixed methane/air flame that is doped with SO₂ to demonstrate the technique. The signal strength has a pronounced temperature dependence for excitation at 266 nm. Received: 14 January 2002 / Revised version: 30 January 2002 / Published online: 14 March 2002     

Time-resolved two-color LII: size distributions of nano-particles from gas-to-particle synthesis

A two-color LII technique for in situ measurements of particle size distributions is described. The technique is based on the simultaneous detection of time-resolved LII signals at two different wavelengths with one-dimensional spatial resolution using a newly developed experimental setup. The ratio of both LII signals yields particle temperatures as a function of time and location. Measured particle temperature decays are numerically simulated based on a detailed cooling model for particle ensembles. Particle size distributions are obtained by fitting simulated particle temperature decays to measured ones using multi-dimensional non-linear regression. The two-color LII technique for particle sizing can be applied to a wide range of materials because it is independent of the optical properties of the particle material. Exemplarily, the measuring technique is applied to investigate the synthesis of nanoscaled metal oxide particle in a laser vaporization reactor.     

Characterization of premixed swirling methane/air diffusion flame through filtered Rayleigh scattering

Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering (FRS). Three operating conditions are investigated with the equivalence ratios of the methane/air flame covering a range of 0.67—0.83. Under each condition, single-shot and averaged FRS images over a region measured 39.3×65.6 mm² at seven cross sections of the flame are collected to demonstrate the flame behavior. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements. Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions. The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The gradient of the instantaneous FRS images clearly illustrates the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behavior of turbulent flames.     

双层材料光热偏转光谱的定量研究

从三线传热方程出发,给出了双层材料的光热偏转光谱的理论模型,讨论了光热偏转信号的特征及其在扫描成象应用中的意义.     

Diode laser atomic fluorescence temperature measurements in low-pressure flames

Temperature measurements have been performed in a low-pressure flame by the technique of diode laser induced atomic fluorescence. The experiments were done in a near-stoichiometric flat-flame of premixed methane, oxygen and nitrogen, at a pressure of 5.3 kPa. Indium atoms were seeded to the flame and probed using blue diode lasers; the lineshapes of the resulting fluorescence spectra were used to determine the flame temperature at a range of heights above the burner plate. The particular issues associated with the implementation of this measurement approach at low pressure are discussed, and it is shown to work especially well under these conditions. The atomic fluorescence lineshape thermometry technique is quicker to perform and requires less elaborate equipment than other methods that have previously been implemented in low-pressure flames, including OH-LIF and NO-LIF. There was sufficient indium present to perform measurements at all locations in the flame, including in the pre-heat zone close to the burner plate. Two sets of temperature measurements have been independently performed by using two different diode lasers to probe two separate transitions in atomic indium. The good agreement between the two sets of data provides a validation of the technique. By comparing thermocouple profiles recorded with and without seeding of the flame, we demonstrate that any influence of seeding on the flame temperature is negligible. The overall uncertainty of the measurements reported here is estimated to be ±2.5% in the burnt gas region.     

Measurement of temperature, fuel concentration and equivalence ratio fields using tracer LIF in IC engine combustion

A technique based on planar laser-induced fluorescence of 3-pentanone, for measurements of absolute concentration, temperature and fuel/air equivalence ratios in turbulent, high-pressure combustion systems such as an internal combustion engine is presented. Quasi-simultaneous excitation with 248 nm and 308 nm of 3-pentanone that is used as a fluorescence tracer doped to iso-octane, yields pairs of strongly temperature-dependent fluorescence images. Previous investigations have resulted in information on temperature and pressure dependence of absorption cross-sections and fluorescence quantum yields. Using these data the ratio of corresponding fluorescence images can be converted to temperature images. Instantaneous temperature distribution fields in the compression stroke and in the unburned end-gas of an SI engine were measured. The temperature fields obtained from the two-line technique are used to correct the original tracer-LIF images in order to evaluate quantitative fuel distributions in terms of number densities and fuel/air equivalence ratio. Received: 10 March 2000 / Revised version: 19 April 2000 / Published online: 16 August 2000     

Analysis of the correction factor in the spreading-resistance technique for monitoring epitaxial silicon

The range of applicability of the mixed-boundary-value method for calculating spreading resistance for a homogeneous slab with an effective contact-radius source and backed by a substrate of arbitrary but finite resistivity is investigated. Solutions are presented in terms of the correction factor and the source current density distributions for a slab of varying thickness and with various high-resistivity substrates. The correction factors for different schemes of calculation are correctly obtained by means of introducing an additional current source of opposite sign, but with the same absolute value, located at the drain point contact. This combination of source and drain currents gives the true value for the potential distribution along the surface of the semiconductor. This, in turn, leads to new terms in the equations obtained for the correction factors, which have been omitted in previously published works. A comparison between several schemes of calculation is presented. Within the framework of “uniform” and “variable” current distributions underneath the contact probe, there are two limits for the correction factor. A model based on a combination of these approaches is discussed, and a comparison between the proposed method and the Schumann–Gardner formulation is made. Received: 30 January 2002 / Accepted: 30 January 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +7-095/531-83-54, E-mail: telkom@df.ru     

Inelastic relaxation and noise temperature in S/N/S junctions

We studied electronic relaxation in long diffusive superconductor/normal metal/superconductor (S/N/S) junctions by means of current noise and transport measurements down to very low temperature (100mK). Samples with normal metal lengths of 4, 10 and 60μm have been investigated. In all samples the shot noise increases very rapidly with the voltage. This is interpreted in terms of enhanced heating of the electron gas confined between the two S/N interfaces. Experimental results are analyzed quantitatively taking into account electron-phonon interaction and heat transfer through the S/N interfaces. Transport measurements reveal that in all samples the two S/N interfaces are connected incoherently, as shown by the reentrance of the resistance at low temperature. The complementarity of noise and transport measurements allows us to show that the energy dependence of the reentrance at low voltage is essentially due to the increasing effective temperature of the quasiparticles in the normal metal. Received 5 February 2002 / Received in final form 6 September 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: hoffmann@drfmc.ceng.cea.fr     

Quantitative laser-induced fluorescence of CH in atmospheric pressure flames

Absolute number densities of the CH radical were determined in a partially premixed methane/air flame (equivalence ratio was 1.36) at atmospheric pressure by exciting a predissociating level via the CH B–X(1,0) transition using a quasi-linear laser-induced fluorescence scheme. The peak number density was (1.0±0.4)×10¹³ cm^-3 or 2.4±1 ppm at 1900 K, with a flame-front width of 250 μm (FWHM). Rotational energy transfer must be considered for correct laser-induced fluorescence signal interpretation. Competition between optical pumping and rotational relaxation in both excited and ground states produces a signal that varies almost linearly with laser pulse energy even for large pumping rates. For these conditions, the population of the initial ground-state rotational level is depleted by optical pumping, and rotational energy transfer collisions rapidly repopulate the level during the laser pulse. Deviations from linear behavior are less than 20%. The effects of spatial resolution and polarization of the fluorescence on the absolute measurements are also discussed. Received: 27 March 2002 / Revised version: 22 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Present address: Lam Research Corporation, Fremont, CA 94538, USA RID="**" ID="**"Present address: Mechanical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands RID="***" ID="***"Present address: Mechanical Engineering Dept., Stanford University, Stanford CA 94305, USA RID="****" ID="****"Corresponding author. Fax: +1-650/859-6196, E-mail: smith@mplvax.sri.com     

Quantitative oxygen imaging in an engine

Simultaneous imaging of laser-induced fluorescence of toluene and 3-pentanone was used to determine the local absolute oxygen and residual gas concentrations present within an engine. The technique utilizes the different sensitivities of the laser-excited molecules to quenching by molecular oxygen as a means to determine quantitative images of in-cylinder oxygen concentrations. The difference in the amount of oxygen available between two operating conditions was investigated. Results are in agreement with measurements in the exhaust gas. Received: 4 June 2002 / Published online: 8 August 2002     

Measurement of the η production in proton-proton collisions with the COSY time-of-flight spectrometer

The reaction pp → ppη was measured at excess energies of 15 and 41 MeV at an external target of the Jülich Cooler Synchrotron COSY with the time-of-flight spectrometer. About 25000 events were measured for the excess energy of 15 MeV and about 8000 for 41 MeV. Both protons of the process ppη were detected with an acceptance of nearly 100% and the η was reconstructed by the missing-mass technique. For both excess energies the angular distributions are found to be nearly isotropic. In the invariant-mass distributions strong deviations from the pure phase space distributions are seen. Received: 24 May 2002 / Accepted: 20 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: e.roderburg@fz-juelich.de Communicated by M. Gar?on     

Optical extinction resonance of Au and Ag clusters formed by ion irradiation in SiO2 and Al2O3

Three methods based on ion-beam irradiation were used to fabricate Ag and Au colloids in silica and alumina. Their surface-plasmon resonance in the visible was characterised by transmittance measurements and interpreted on the basis of transmission electron microscope observations. Despite their bimodal size distribution, particles formed by ion-beam mixing of sandwich layers exhibit much narrower resonances than those obtained by ion implantation. This unusual effect of an inhomogeneity in cluster size is ascribed to the spatial organisation of these clusters. Irradiation of supersaturated solid solutions at much lower ion fluences produces colloids with more uniform size and spatial distributions, and equally strong resonances. Received: 17 March 2001 / Accepted: 31 July 2001 / Published online: 11 February 2002     

Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. II. Rotational Raman line widths

Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures and atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5–9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S₁-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert–Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved. Received: 18 February 2002 / Revised version: 9 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +46-46/2224542, E-mail: mikael.afzelius@forbrf.lth.se     

Anisotropic velocity distributions in 3D dissipative optical lattices

We present a direct measurement of velocity distributions in two dimensions by using an absorption imaging technique in a 3D near resonant optical lattice. The results show a clear difference in the velocity distributions for the different directions. The experimental results are compared with a numerical 3D semi-classical Monte-Carlo simulation. The numerical simulations are in good qualitative agreement with the experimental results. Received 3 September 2002 / Received in final form 25 October 2002 Published online 11 February 2003     

Magnetic properties of Ni:SiO<Subscript>2</Subscript> nanocomposites synthesized by a modified sol–gel method

Ni nanoparticles embedded in an amorphous SiO₂ matrix were produced by a modified sol–gel method. This method resulted in nanocomposites with a controlled size distribution and good dispersion of the metallic particles. The particle-size distributions were found to have an average radius of ∼3 nm, as inferred from transmission electron microscopy, X-ray-diffraction analysis, and magnetic measurements. Magnetic characterizations revealed that samples exhibit superparamagnetic behavior above the blocking temperature T_B, 20 K≤T_B≤40 K, and absence of a shift along the field axis on hysteresis loops measured at T≤T_B, indicating that the metallic nanoparticles are also free from an oxide layer. Received: 7 October 2002 / Accepted: 9 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +55-11/3091-6984, E-mail: rjardim@if.usp.br     

Nuclear-matter distributions of halo nuclei from elastic proton scattering in inverse kinematics

Proton-nucleus elastic scattering at intermediate energies, a well-established method for probing nuclear-matter density distributions of stable nuclei, was applied for the first time to exotic nuclei. This method is demonstrated to be an effective means for obtaining accurate and detailed information on the size and radial shape of halo nuclei. Absolute differential cross-sections for small-angle scattering were measured at energies near 700 MeV/u for the neutron-rich helium isotopes ⁶He and ⁸He, and more recently for the lithium isotopes ⁶Li, ⁸Li, ⁹Li and ¹¹Li, using He and Li beams provided by the fragment separator FRS at GSI Darmstadt. Experiments were performed in inverse kinematics using the hydrogen-filled ionization chamber IKAR which served simultaneously as target and recoil-proton detector. For deducing nuclear-matter distributions, differential cross-sections calculated with the aid of the Glauber multiple-scattering theory, using various parametrizations for the nucleon density distributions as input, were fitted to the experimental cross-sections. The results on nuclear-matter radii and matter distributions are presented, and the significance of the data for a halo structure is discussed. Nuclear-matter distributions obtained for ⁶He and ⁸He conform with the concept that both nuclei compose of α-particle like cores and significant neutron halos. The matter distribution in ¹¹Li exhibits, as expected from previous reaction cross-section studies with nuclear targets, the by far most extended halo component of all nuclei being investigated. In addition the present data allow a quantitative comparison of the structure of the He and Li isobares of either the mass number A = 6 or A = 8. The measured differential cross-sections have also been used for probing density distributions as predicted from various microscopic calculations. A few examples are presented. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: p.egelhof@gsi.de     

Study of range distribution parameters for bismuth-ion implantation in silver gallium diselenide

Range distributions for bismuth ions implanted in AgGaSe₂ in the energy range 80–300 keV were investigated by using 2.1-MeV He²⁺ Rutherford backscattering spectrometry (RBS). A convolution calculation method was used to extract the true distributions of bismuth from the measured RBS spectra. The range distribution parameters, R_p and ΔR_p, were obtained and compared with those obtained from Monte Carlo simulation. The experimental R_p values agree with the Monte Carlo simulation values very well, but the experimental ΔR_p values are systematically larger than those from the theoretical simulation. Received: 28 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-531/856-5167, E-mail: xdliu@sdu.edu.cn     

Negligibility of temporal laser wing effects in saturated LIF diagnostics

The temporal influence of a laser pulse on saturated laser-induced fluorescence is investigated by means of numerical solutions of rate equations describing dynamical models of two- and four-level molecular systems. It turns out that temporal wings of the laser become negligible if the saturated fluorescence power from the entire pulse is monitored instead of the total energy obtained from the integrated fluorescence. The negligibility is evaluated relative to the saturation status obtained with temporal sampling of the fluorescence signal as is commonly adopted in the time-resolved technique. The advantages and the limitations of power measurements are discussed with reference to the experimental feasibility of pulse acquisitions for the determination of the flawless saturation degree. Received: 4 December 2002 / Revised version: 14 February 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +39-06/3048-4811, E-mail: michele.marrocco@casaccia.enea.it     

Multi-species detection in spray flames with tunable excimer lasers

Planar imaging with tunable excimer-laser sheet illumination is used to determine spatial distributions of different species in liquid-fuelled spray flames of commercial oil burning furnaces. Two burner configurations, which differ only in the fuel/air mixing devices, are investigated to understand why one configuration yields 30% less NO_x emission. Iso-octane and n-heptane fuels are used. To understand the origin for NO_x reduction spatial distributions of reactants (fuel, O₂), the reaction intermediate OH and the pollutant NO are recorded. OH and O₂ are measured by LIPF, NO by LIF. Fuel distributions are determined by another broad-band emission, whose origin is not yet identified. Both single shot and averaged distributions are recorded. The averaged distributions are extremely reproducible and depend sensitively on details of the burner geometry and the fuel/air mixing device. They can clearly be used to distinguish fine details in different injection systems. The spatial distribution of different species relative to each other yield considerable insight in the differences between the two combustion processes. On the basis of purely qualitative visualization it is possible to understand the origin for NO_x reduction: it results from faster injection of air in the one fuel/air mixing device.