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721.
Evaporating Diesel sprays are studied by laser Rayleigh scattering measurements in an optically accessible high-pressure/high-temperature
cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a Diesel engine during injection.
n-Decane is injected into the vessel using a state-of-the-art near-production three-hole nozzle. Global images of the distributions
of the liquid and vapor phases of the injected fuel are obtained using a combined Schlieren and Mie scattering setup. More
details about the evaporation are revealed when the spray is illuminated by a laser light sheet: laser light can be scattered
by molecules in the gas phase (Rayleigh scattering) or comparably large fuel droplets (Mie scattering). The former is seen
in regions where the fuel has completely evaporated, and the latter is dominant in regions with high droplet concentrations.
Studying the polarization of the signal light allows the distinction of three different regions in the spray that are characterized
by a moderate, low or negligible concentration of liquid fuel droplets. The characteristics of fuel evaporation are investigated
for different observation times after the start of injection, chamber conditions and injection pressures. For the quantification
of the fuel concentration measurements based on Rayleigh scattering, a calibration method that uses propane as a reference
gas is presented and tested. At high ambient temperatures, the accuracy of the concentration measurements is limited by pyrolysis
of the fuel molecules.
This paper was originally presented at the 14th International Symposium on Applications of Laser Techniques to Fluid Mechanics,
Lisbon, 2008. 相似文献
722.
723.
Takayuki Fuyuto Helmut Kronemayer Burkhard Lewerich Jan Brübach Taketoshi Fujikawa Kazuhiro Akihama Thomas Dreier Christof Schulz 《Experiments in fluids》2010,49(4):783-795
A detailed understanding of transport phenomena and reactions in near-wall boundary layers of combustion chambers is essential
for further reducing pollutant emissions and improving thermal efficiencies of internal combustion engines. In a model experiment,
the potential of laser-induced fluorescence (LIF) was investigated for measurements inside the boundary layer connected to
flame-wall interaction at atmospheric pressure. Temperature and species distributions were measured in the quenching boundary
layer formed close to a cooled metal surface located parallel to the flow of a premixed methane/air flat flame. Multi-line
NO-LIF thermometry provided gas-phase temperature distributions. In addition, flame species OH, CH2O and CO were monitored by single-photon (OH, CH2O) and two-photon (CO) excitation LIF, respectively. The temperature dependence of the OH-LIF signal intensities was corrected
for using the measured gas-phase temperature distributions. The spatial line-pair resolution of the imaging system was 22 μm
determined by imaging microscopic line pairs printed on a resolution target. The experimental results show the expected flame
quenching behavior in the boundary layer and they reveal the potential and limitations of the applied diagnostics techniques.
Limitations in spatial resolution are attributed to refraction of fluorescence radiation propagating through steep temperature
gradients in the boundary layer. For the present experimental arrangements, the applied diagnostics techniques are applicable
as close to the wall as 200 μm with measurement precision then exceeding the 15–25% limit for species detection, with estimates
of double this value for the case of H2CO due to the unknown effect of the Boltzmann fraction corrections not included in the data evaluation process. Temperature
measurements are believed to be accurate within 50 K in the near-wall zone, which amounts to roughly 10% at the lower temperatures
encountered in this region of the flames. 相似文献
724.
Hanjun Sun Ibrahim Halil
ner Tao Wang Tao Zhang Oleksandr Selyshchev Christof Neumann Yubin Fu Zhongquan Liao Shunqi Xu Yang Hou Andrey Turchanin Dietrich R. T. Zahn Ehrenfried Zschech Inez M. Weidinger Jian Zhang Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(30):10476-10482
Conjugated polymers featuring tunable band gaps/positions and tailored active centers, are attractive photoelectrode materials for water splitting. However, their exploration falls far behind their inorganic counterparts. Herein, we demonstrate a molecular engineering strategy for the tailoring aromatic units of conjugated acetylenic polymers from benzene‐ to thiophene‐based. The polarized thiophene‐based monomers of conjugated acetylenic polymers can largely extend the light absorption and promote charge separation/transport. The C≡C bonds are activated for catalyzing water reduction. Using on‐surface Glaser polycondensation, as‐fabricated poly(2,5‐diethynylthieno[3,2‐b]thiophene) on commercial Cu foam exhibits a record H2‐evolution photocurrent density of 370 μA cm?2 at 0.3 V vs. reversible hydrogen electrode among current cocatalyst‐free organic photocathodes (1–100 μA cm?2). This approach to modulate the optical, charge transfer, and catalytic properties of conjugated polymers paves a critical way toward high‐activity organic photoelectrodes. 相似文献
725.
726.
Cyganik P Buck M Wilton-Ely JD Wöll C 《The journal of physical chemistry. B》2005,109(21):10902-10908
Self-assembled monolayers of omega-(4'-methylbiphenyl-4-yl) alkane thiols CH3(C6H4)2(CH2)(n)SH (BPn, n = 2, 3, and 5) on Au(111) substrates, prepared at room and elevated temperatures, were studied using scanning tunneling microscopy. In contrast to the biphenyl thiol analogues with n = 0 or 1, ordered domains of large size are formed which exhibit small, periodic height variations on a length scale of several nanometers. These are attributed to solitons (or domain walls), resulting from structural mismatch between the molecular adlayer and the gold substrate. The implications of these results for the design of aromatic thiols to cope with stress and yield low-defect density self-assembled monolayers are discussed. 相似文献
727.
728.
Anja-Carina Schulte Adrian Görler Christof Antz Klaus-Peter Neidig Hans Robert Kalbitzer 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,129(2):165-172
Automated or semiautomated pattern recognition in multidimensional NMR spectroscopy is strongly hampered by the large number of noise and artifact peaks occurring under practical conditions. A general Bayesian method which is able to assign probabilities that observed peaks are members of given signal classes (e.g., the class of true resonance peaks or the class of noise and artifact peaks) was proposed previously. The discriminative power of this approach is dependent on the choice of the properties characterizing the peaks. The automated class recognition is improved by the addition of a nonlocal feature, the similarities of peak shapes in symmetry-related positions. It turns out that this additional property strongly decreases the overlap of the multivariate probability distributions for true signals and noise and hence largely increases the discrimination of true resonance peaks from noise and artifacts. 相似文献
729.
Christof Külske 《Probability Theory and Related Fields》2003,126(1):29-50
We consider diffraction at random point scatterers on general discrete point sets in ℝν, restricted to a finite volume. We allow for random amplitudes and random dislocations of the scatterers. We investigate
the speed of convergence of the random scattering measures applied to an observable towards its mean, when the finite volume
tends to infinity. We give an explicit universal large deviation upper bound that is exponential in the number of scatterers.
The rate is given in terms of a universal function that depends on the point set only through the minimal distance between
points, and on the observable only through a suitable Sobolev-norm. Our proof uses a cluster expansion and also provides a
central limit theorem.
Received: 10 October 2001 / Revised version: 26 January 2003 /
Published online: 15 April 2003
Work supported by the DFG
Mathematics Subject Classification (2000): 78A45, 82B44, 60F10, 82B20
Key words or phrases: Diffraction theory – Random scatterers – Random point sets – Quasicrystals – Large deviations – Cluster expansions 相似文献
730.