共查询到20条相似文献,搜索用时 31 毫秒
1.
F. Migliorini S. De Iuliis S. Maffi F. Cignoli G. Zizak 《Applied physics. B, Lasers and optics》2009,96(4):637-643
Theoretical papers predict that prompt LII signals are weakly dependent on the soot size due to the fact that larger particles
reach higher temperatures during the heating process by nanosecond laser pulses. This question is of crucial importance for
establishing LII as a practical technique for soot volume fraction measurements. In this work two-color prompt LII measurements
have been performed in several locations of diffusion and rich premixed ethylene-air flames. The experimental apparatus was
carefully designed with a probe volume of uniform light distribution and sharp edges, a 4 ns integration time around the signal
pulse peak and narrow spectral bandwidth. Measurements did not confirm the theoretical predictions concerning an increase
of temperature for larger particles. On the contrary, larger particles in richer premixed flames exhibit a lower 400/700 signal
ratio. This can probably be attributed to small differences in the refractive index of soot. 相似文献
2.
F. Liu D. R. Snelling K. A. Thomson G. J. Smallwood 《Applied physics. B, Lasers and optics》2009,96(4):623-636
The sensitivity and relative sensitivity of soot temperature and soot volume fraction inferred from the two-color laser-induced
incandescence technique to different variables were systematically investigated to quantitatively understand how the detection
wavelengths affect the behavior of the detection system. The effects of signal shot noises on the derived soot temperature
and soot volume fraction were also analyzed. The detection wavelengths are in general between about 400 nm for the lower band
and near infrared for the upper one. Numerical calculations were conducted for seven detection wavelength selections commonly
used in two-color laser-induced incandescence experiments reported in the literature. To achieve a better accuracy for soot
temperature and volume fraction measurements, it is desirable to use a shorter lower detection wavelength and a longer upper
detection wavelength in the spectral range of about 400 nm to near infrared. The lower detection wavelength has a stronger
impact on the detection system performance than the upper one. The sensitivity and shot noise analyses are valuable tools
to assess the relative performance of different detection wavelengths and should be used in combination with other considerations
to design an optimal detection system in a two-color laser-induced incandescence experiment. 相似文献
3.
M. Köhler K. P. Geigle W. Meier B. M. Crosland K. A. Thomson G. J. Smallwood 《Applied physics. B, Lasers and optics》2011,104(2):409-425
Computational fluid dynamics (CFD) modelers require high-quality experimental data sets for validation of their numerical
tools. Preferred features for numerical simulations of a sooting, turbulent test case flame are simplicity (no pilot flame),
well-defined boundary conditions, and sufficient soot production. This paper proposes a non-premixed C2H4/air turbulent jet flame to fill this role and presents an extensive database for soot model validation. 相似文献
4.
J. M. Headrick F. Goulay P. E. Schrader H. A. Michelsen 《Applied physics. B, Lasers and optics》2011,104(2):439-450
We have measured time-resolved laser-induced incandescence of flame-generated soot under high-vacuum conditions (4.1×10−6 mbar) at an excitation wavelength of 532 nm with laser fluences spanning 0.06–0.5 J/cm2. We generated soot in an ethylene/air diffusion flame, introduced it into the vacuum system with an aerodynamic lens, heated
it using a pulsed laser with a spatially homogeneous and temporally smooth laser profile, and recorded LII temporal profiles
at 685 nm. At low laser fluences LII signal decay rates are slow, and LII signals persist beyond the residence time of the
soot particles in the detection region. At these fluences, the temporal maximum of the LII signal increases nearly linearly
with increasing laser fluence until reaching a plateau at ∼0.18 J/cm2. At higher fluences, the LII signal maximum is independent of laser fluence within experimental uncertainty. At these fluences,
the LII signal decays rapidly during the laser pulse. The fluence dependence of the vacuum LII signal is qualitatively similar
to that observed under similar laser conditions in an atmospheric flame but requires higher fluences (by ∼0.03 J/cm2) for initiation. These data demonstrate the feasibility of recording vacuum LII temporal profiles of flame-generated soot
under well-characterized conditions for model validation. 相似文献
5.
R. Hiers 《Applied physics. B, Lasers and optics》2008,92(4):635-641
This paper considers the unsteady energy equation for a particle undergoing processes relevant to laser-induced incandescence.
The energy equation is derived using both an integral control volume formalism and a differential approach. Confusion in the
previous literature over the form of the energy equation is traced to the evaluation of the energy flux terms to and from
the particle surface. Terms such as the heat of sublimation or heat of combustion are shown to arise naturally in both the
control volume and differential derivations. Problems associated with the confusion regarding the flux terms resulting in
incorrect energy equations are also identified. 相似文献
6.
J. Yon R. Lemaire E. Therssen P. Desgroux A. Coppalle K. F. Ren 《Applied physics. B, Lasers and optics》2011,104(2):253-271
The refractive index of soot is an essential parameter for its optical diagnostics. It is necessary for quantitative interpretation
of LII (Laser Induced Incandescence) signals, light scattering or extinction measurements as well as for emissivity calculations.
The most cited values have been determined by intrusive methods or without taking into account the soot size distribution
and its specific morphology. In the present study, soot generated by the combustion of diesel and diesel/rapeseed methyl ester
(RME) mixture (70% diesel and 30% RME) are extensively characterized by taking into account the morphology, the aggregate
size distribution, the mass fraction and the spectral dispersion of light. The refractive index m for wavelengths λ between 300 and 1000 nm is determined for diesel and diester fuels by both in-situ and ex-situ methods. The ex-situ method
is based on the interpretation of extinction spectra by taking into account soot sizes and fractal morphology with the RDG-FA
(Rayleigh–Debye–Gans for Fractal Aggregate) theory. The in-situ approach is based on the comparison of the LII signals obtained
with two different excitation wavelengths. The absorption function E(m) and the scattering function F(m) are examined. This study reveals similar optical properties of soot particles generated by both studied fuels even at ambient
and flame temperatures. The function E(m) is shown to reach a maximum for λ=250 nm and to tend toward a plateau-like behavior close to E(m)=0.3 for higher wavelength (600<λ (nm)<1000). The function F(m) is found to be quite constant for 400<λ (nm)<1000 and equal to 0.31. 相似文献
7.
G. Cléon T. Amodeo A. Faccinetto P. Desgroux 《Applied physics. B, Lasers and optics》2011,104(2):297-305
In this work, the two-excitation wavelength laser induced incandescence (LII) method has been applied in a low-pressure premixed
methane/oxygen/nitrogen flame (equivalence ratio 2.32) to determine the variation of the ratio of the soot absorption functions
at 532 nm and 1064 nm E(m,532 nm)/E(m,1064 nm) along the flame. This method relies on the comparison of LII signals measured upon two different excitation wavelengths
(here 532 nm and 1064 nm) and with laser fluences selected in such a way that the soot particles are equally laser-heated.
The comparison of the laser fluences at 532 nm and 1064 nm leads to an easy determination of E(m,532 nm)/E(m,1064 nm). The reliability of the method is demonstrated for the first time in a low pressure flame in which the soot nucleation
zone can be spatially resolved and which contains soot particles acting differently with the laser fluence according to their
residence time in the flame. The method is then applied to determine the profile of E(m,532 nm)/E(m,1064 nm) along the flame. A very important decrease of this ratio is observed in the region of nascent soot, while the ratio
remains constant at high distance above the burner. Implication on temperature determination from spectrally resolved measurement
of flame emission is studied. 相似文献
8.
The effect of sub-nanosecond fluence fluctuations and triggering on time-resolved laser-induced incandescence (LII) from soot
has been studied using an injection-seeded pulsed Nd:YAG laser that produces a smooth laser temporal profile. Without injection
seeding, this multi-mode laser generates pulses with large intensity fluctuations with sub-nanosecond rise times. The experimental
results described here demonstrate that at fluences below 0.6 J/cm2 LII signals are insensitive to fluence fluctuations on nanosecond time scales. At fluences above 0.6 J/cm2 fluctuations in the laser profile cause the rising edge of the LII profile to move around in time relative to the center
of the laser pulse causing a broader average profile that shifts to earlier times. Such fluctuations also lead to a decrease
in the average LII temporal profile by up to 12% at a fluence of 3.5 J/cm2. A timing jitter on the trigger of the data acquisition, such as that produced by triggering on the laser Q-switch synchronization
pulse, has a negligible effect on the shape and temporal maximum of the LII signal. Additional jitter, however, considerably
reduces the peak of the LII temporal profiles at fluences as low as 0.15 J/cm2. Neither fast fluence fluctuations nor trigger jitter have a significant effect on gated LII signals, such as those used
to infer soot volume fraction. 相似文献
9.
S. De Iuliis S. Maffi F. Cignoli G. Zizak 《Applied physics. B, Lasers and optics》2011,102(4):891-903
In this work, a three-angle scattering and extinction technique has been applied in order to study soot formation and growth in a rich ethylene/air premixed flame (Φ=2.34). The Rayleigh–Debye–Gans theory together with the fractal-like approach has been applied to derive soot parameters, in terms of volume concentration and morphology. A mathematical procedure is presented to obtain the radius of gyration by considering scattering signals collected at two supplementary angles. TEM measurements, carried out at different locations on the flame axis, are used to derive some parameters, such as fractal prefactor, fractal dimension and size distribution, to be entered in the mathematical treatment of optical data. The radius of gyration and the primary particle size as obtained by TEM and by optical measurements are compared. Good agreement has been found in the upper part of the flame investigated. Discrepancies observed low in the flame are discussed. 相似文献
10.
Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive
technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy
of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is
recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward
to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle
sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile
on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides
online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed
in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically
sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some
influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this
effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient. 相似文献
11.
Billy Kaldvee Christian Brackmann Marcus Aldén Joakim Bood 《Applied physics. B, Lasers and optics》2014,115(1):111-121
A novel concept for remote in situ detection of soot emissions by a combination of laser-induced incandescence (LII) and light detection and ranging (lidar) is presented. A lidar setup based on a picosecond Nd:YAG laser and time-resolved signal detection in the backward direction was used for LII measurements in sooty premixed ethylene–air flames. Measurements of LII–lidar signal versus laser fluence and flame equivalence ratio showed good qualitative agreement with data reported in literature. The LII–lidar signal showed a decay consisting of two components, with lifetimes of typically 20 and 70 ns, attributed to soot sublimation and conductive cooling, respectively. Theoretical considerations and analysis of the LII–lidar signal showed that the derivative was proportional to the maximum value, which is an established measure of soot volume fraction. Utilizing this, differentiation of LII–lidar data gave profiles representing soot volume fraction with a range resolution of ~16 cm along the laser beam propagation axis. The accuracy of the evaluated LII-profiles was confirmed by comparison with LII-data measured simultaneously employing conventional right-angle detection. Thus, LII–lidar provides range-resolved single-ended detection, resourceful when optical access is restricted, extending the LII technique and opening up new possibilities for laser-based diagnostics of soot and other carbonaceous particles. 相似文献
12.
Paul Sorensen 《The European Physical Journal C - Particles and Fields》2009,61(4):829-833
Recent data from heavy ion collisions at RHIC show strong near-side correlations extending over several units of rapidity.
This ridge-like correlation exhibits an abrupt onset with collision centrality. In this talk, I argue that the centrality
and beam-energy dependence of these near-angle correlations could provide access to information about the Quark Gluon Plasma
phase boundary and the Equation of State of nuclear matter. A beam-energy-scan at RHIC will better reveal the true source
of these correlations and should be a high priority at RHIC. 相似文献
13.
Sukanta Dutta Ashok Goyal Mamta 《The European Physical Journal C - Particles and Fields》2009,63(2):305-315
We study the one-loop new physics effects to the CP even triple neutral gauge boson vertices γ
⋆
γ
Z, γ
⋆
Z
Z, Z
⋆
Z
γ and Z
⋆
ZZ in the context of Little Higgs models. We compute the contribution of the additional fermions in Little Higgs models in the
framework of direct product groups where [SU(2)×U(1)]2 gauge symmetry is embedded in SU(5) global symmetry and also in the framework of the simple group where SU(N)×U(1) gauge symmetry breaks down to SU(2)
L
×U(1). We calculate the contribution of the fermions to these couplings when T parity is invoked. In addition, we re-examine the MSSM contribution at the chosen point of SPS1a′ and compare with the SM
and Little Higgs models. 相似文献
14.
M. Miyabe M. Oba H. Iimura K. Akaoka Y. Maruyama I. Wakaida 《Applied Physics A: Materials Science & Processing》2010,101(1):65-70
A cerium oxide sample was ablated by 2nd harmonic radiation of Nd:YAG laser at a power density of 0.1 GW/cm2. Time evolution of the ablation plume was investigated by laser absorption time-of-flight (TOF) measurement. It was found
that the ablated ionic plume in vacuum consisted of two components having different velocities whereas the ablated neutral
atoms had mainly a single component. The flow velocity perpendicular to the sample surface in vacuum was determined to be
3.5 km/s for neutral atoms, and 4.7 km/s and 9.3 km/s for singly charged ions. From the detailed plume evolution in ambient
atmosphere with several pressures we obtained some experimental conditions suitable for isotope analysis of atomic cerium. 相似文献
15.
A. Bolshakova I. Boyko G. Chelkov D. Dedovitch A. Elagin M. Gostkin S. Grishin A. Guskov Z. Kroumchtein Yu. Nefedov K. Nikolaev A. Zhemchugov F. Dydak J. Wotschack A. De Min V. Ammosov V. Gapienko V. Koreshev A. Semak Yu. Sviridov E. Usenko V. Zaets 《The European Physical Journal C - Particles and Fields》2009,62(4):697-754
We report on double-differential inclusive cross-sections of the production of secondary protons and charged pions, in the
interactions with a 5% λ
abs thick stationary beryllium target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20° <θ<125°. 相似文献
16.
M. Hauer V. V. Begun M. I. Gorenstein 《The European Physical Journal C - Particles and Fields》2008,58(1):83-110
The aim of this paper is to introduce a new technique for the calculation of observables, in particular multiplicity distributions,
in various statistical ensembles at finite volume. The method is based on Fourier analysis of the grand canonical partition
function. A Taylor expansion of the generating function is used to separate contributions to the partition function in their
power in volume. We employ Laplace’s asymptotic expansion to show that any equilibrium distribution of multiplicity, charge,
energy, etc. tends to a multivariate normal distribution in the thermodynamic limit. A Gram–Charlier expansion additionally
allows for the calculation of finite volume corrections. Analytical formulas are presented for the inclusion of resonance
decay and finite acceptance effects directly into the partition function of the system. This paper consolidates and extends
previously published results of the current investigation into the properties of statistical ensembles. 相似文献
17.
Carlo Cafaro 《International Journal of Theoretical Physics》2008,47(11):2924-2933
A new information-geometric approach to chaotic dynamics on curved statistical manifolds based on Entropic Dynamics (ED) is
proposed. It is shown that the hyperbolicity of a non-maximally symmetric 6N-dimensional statistical manifold ℳ
s
underlying an ED Gaussian model describing an arbitrary system of 3N degrees of freedom leads to linear information-geometric entropy growth and to exponential divergence of the Jacobi vector
field intensity, quantum and classical features of chaos respectively. 相似文献
18.
D. Nodop J. Rothhardt S. H?drich J. Limpert A. Tünnermann 《Applied physics. B, Lasers and optics》2009,94(3):399-401
We present a Q-switched microchip laser emitting 1064-nm pulses as short as 100 ps synchronized to a cavity dumped femtosecond
laser emitting 800-nm pulses as short as 80 fs. The synchronization is achieved by presaturating the saturable absorber of
the microchip laser with femtosecond pulses even though both lasers emit at widely separated wavelengths. The mean timing
jitter is 40 ps and thus considerably shorter than the pulse duration of the microchip laser. 相似文献
19.
André Mischke 《The European Physical Journal C - Particles and Fields》2009,61(4):807-809
We report measurements of the azimuthal angular correlation distribution of heavy-quark decay electrons and open charmed mesons
in pp collisions at
GeV in the STAR experiment at RHIC. This measurement in combination with current theoretical model calculations allows to
extract the relative bottom contribution to the heavy-quark decay electrons, which is important for the interpretation of
the observed strong suppression of the high-p
T electron yield in central Au+Au collisions. 相似文献
20.