| 1. |
- Michelsen, H. A., et al.
(författare)
-
Modeling laser-induced incandescence of soot: a summary and comparison of LII models
- 2007
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 87:3, s. 503-521
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed a comparison of ten models that predict the temporal behavior of laser-induced incandescence (LII) of soot. In this paper we present a summary of the models and comparisons of calculated temperatures, diameters, signals, and energy-balance terms. The models were run assuming laser heating at 532 nm at fluences of 0.05 and 0.70 J/cm(2) with a laser temporal profile provided. Calculations were performed for a single primary particle with a diameter of 30 nm at an ambient temperature of 1800 K and a pressure of 1 bar. Preliminary calculations were performed with a fully constrained model. The comparison of unconstrained models demonstrates a wide spread in calculated LII signals. Many of the differences can be attributed to the values of a few important parameters, such as the refractive-index function E(m) and thermal and mass accommodation coefficients. Constraining these parameters brings most of the models into much better agreement with each other, particularly for the low-fluence case. Agreement among models is not as good for the high-fluence case, even when selected parameters are constrained. The reason for greater variability in model results at high fluence appears to be related to solution approaches to mass and heat loss by sublimation.
|
|
| 2. |
- Oliveira, M. H. de Andrade, et al.
(författare)
-
Soot, PAH and OH measurements in vaporized liquid fuel flames
- 2013
-
Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 112, s. 145-152
-
Tidskriftsartikel (refereegranskat)abstract
- Qualitative measurements of both OH and polycyclic aromatic hydrocarbons (PAH) as well as quantitative data of soot volume fraction f(v) have been obtained in vaporized liquid fuels, with the main goal of providing experimental data for combustion models and numerical mechanism validation. Measurements were carried out in a laminar coflow burner which was designed, built and integrated with an evaporation system, enabling the combustion of vaporized liquid fuels at pressures of up to 3.0 MPa to be studied. The fuels n-heptane and n-decane, referred to in the literature as being important surrogate fuels, were selected for measurements at atmospheric pressure that were carried out in the experimental setup described, making use of a combination of the Laser Induced Fluorescence (LIF) and Laser Induced Incandescence (LII) techniques. Partially premixed flames of n-heptane and n-decane showed similar combustion characteristics in the range of 1.9 < phi < 3.7. For both of the fuels the threshold for soot formation was found to be at about phi similar to 3.3. Comparison of the LIF and LII measurements for the n-heptane flames within the range of 3.7 <= phi <= 8.5 indicated the maximum PAH LIF signal to be a good predictor of f(vmax) obtained from LII. Excitation at 266 nm using delayed detection was found to result in the signals obtained showing a close linear correlation with the soot volume fraction obtained from LII when prompt detection at 1064 nm excitation was used. Neither the effects of any additional photo-chemical processes making use of high laser power at 266 nm nor the effects of particle size on the delayed gate times appeared to be of any significance for the flame conditions studied here. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
| 3. |
- Brackmann, Christian, et al.
(författare)
-
Simultaneous vibrational and pure rotational coherent anti-Stokes Raman spectroscopy for temperature and multispecies concentration measurements demonstrated in sooting flames
- 2002
-
Ingår i: Applied Optics. - 2155-3165. ; 41:3, s. 564-572
-
Tidskriftsartikel (refereegranskat)abstract
- The potential of measuring temperature and multiple species concentrations (N-2, O-2, CO) by use of combined vibrational coherent anti-Stokes Raman spectroscopy (CARS) and pure rotational CARS has been investigated. This was achieved with only one Nd:YAG laser and one dye laser together with a single spectrograph and CCD camera. From measurements in premixed sooting C2H4-air flames it was possible to evaluate temperatures from both vibrational CARS and rotational CARS, spectra, O-2 concentration from the rotational CARS spectra, and CO concentration from the vibrational CARS spectra. Quantitative results from premixed sooting C2H4-air flames are presented, and the uncertainties in the results as well as the possibility of extending the combined CARS technique fur probing of additional species are discussed. (C) 2002 Optical Society of America.
|
|
| 4. |
- Nordström, Emil, et al.
(författare)
-
Fourier-based approach to overcome anomalies in high-resolution spectra of vibrational CARS measurements of gases
- 2014
-
Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 45:7, s. 489-494
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we report on an unconventional experimental procedure useful for thermometric measurements on the basis of high-resolution vibrational coherent anti-Stokes Raman scattering (CARS) generated using conventional lasers. The high spectral dispersion of 0.02 cm(-1)/pixel is achieved by means of some specific spectral arrangements (single-mode pump laser and diffraction grating providing spectra at the sixth order) and is further strengthened by the use of a relay lens system mounted before the charge-coupled device camera. Surprisingly, at the high spectral dispersion of our measurements, a significant and persistent thermometric inaccuracy is observed. The effect arises from an inevitable spectral modulation of defined frequency hidden in the main CARS signal of the gas under study, and to secure a good thermometric evaluation, we describe a Fourier approach that is experimentally demonstrated for the typical nitrogen CARS spectrum measured at room temperature. Copyright (C) 2014 John Wiley & Sons, Ltd.
|
|
| 5. |
- Walewski, Joachim, et al.
(författare)
-
Soot visualisation by use of laser-induced soot vapourisation in combination with polarisation spectroscopy
- 2003
-
Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 77:4, s. 447-454
-
Tidskriftsartikel (refereegranskat)abstract
- A novel approach to the visualisation of soot is presented. It relies on a combination of laser-induced soot vapourisation and consecutive polarisation spectroscopy. Upon soot vapourisation, molecular fragments (for example, C-2) emerge, and may serve as effective tracers for soot. In this study we demonstrate that saturated polarisation spectroscopy on photoinduced C-2 can be exploited for soot detection. Signal maps featuring high signal-to-noise ratios were readily recorded in ethyne-rich flames and any spurious background, for example, caused by Rayleigh scattering, was successfully suppressed by means of spatial filtering. Additionally, investigations were carried out addressing how the attained signals correlate with local soot volumne fractions. For this purpose, height profiles of C-2 number densities inferred from the polarisation spectroscopy signal maps were compared with profiles of the soot volumne fraction inferred from measurements with laser-induced incandescence. For low soot volumne fractions, the shapes of the height profiles from our approach agree rather well with the latter; they do not agree for higher soot volumne fractions. Further investigation is required to resolve this discrepancy. Scattering from particles in the Mie scattering range may hamper the application of this approach, and avenues are suggested for extending the applicability of the approach presented to large soot particles.
|
|
