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Indirect Spectral Hard Modeling for the Analysis of Reactive and Interacting Mixtures

We present an indirect hard modeling (IHM) approach for the quantitative analysis of reactive multicomponent mixtures with intermolecular interaction. It can be used when it is not possible to obtain calibration data in the composition region of interest. The goal of this work, specifically, is to analyze reactive systems, although the validation of the method is done with nonreactive systems. Compared to conventional hard modeling, the new approach reduces the manual work required for modeling and renders unnecessary the assignment of bands in mixture spectra to individual components. It is based on parametric models of the pure component spectra that are made just flexible enough to fit the spectra of the unknown mixtures, and it only requires small calibration data sets that may lie in different regions of the composition space. The application to infrared (IR) and Raman spectra of multicomponent systems is discussed.

Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

A new method based on Raman spectroscopy is presented for noninvasive, quantitative determination of the spatial polymer distribution in alginate beads of approximately 4 mm diameter. With the experimental setup, a two-dimensional image is created along a thin measuring line through the bead comprising one spatial and one spectral dimension. For quantitative analysis of the Raman spectra, the method of indirect hard modeling was applied to make use of the information contained in the entire recorded spectra. For quantification of the alginate signals from within the beads, a calibration curve acquired from sodium alginate solutions was used after it was shown that only negligible differences occur between signals from alginate solutions and alginate gels. The distribution of alginate over the bead gel matrix was acquired with high spatial (51 μm) and time (12 s) resolution. The inhomogeneous distribution obtained using the new measuring technique is qualitatively in excellent agreement with data from the literature. In contrast to known measuring techniques, correct quantitative information about the spatial polymer distribution within the matrix was derived. It gave an alginate mass fraction of approximately 0.045 g/g at the edges and 0.02 g/g in the center of the beads. Next to the determination of mere polymer concentrations, the excellent time resolution of the presented method will enable investigation of the dynamic process of gel formation and it will also serve as a basis for investigation of mass transfer of small diffusing molecules in alginate matrices.

Time-Resolved Measurement of Concentrations in Mixing Processes Using Raman Spectroscopy

Optical measurement techniques are more and more widely used to investigate the mixing processes in small and medium scale mixers. Most of these techniques (including LIF based techniques) suffer from principle problems when investigating and quantifying reacting processes. Within this work a Raman scattering test-bench has been set-up to investigate dynamic processes in more than one dimension. While the Raman scattering approach allows investigating concentrations of several components simultaneously in reacting and non-reacting fluids with high accuracy, it is normally restricted to one-dimensional measurements, which is not sufficient for characterization of mixing processes. So the technique was improved to a pseudo two-dimensional multipoint technique. This article deals in detail with the advantages, disadvantages and limitations of different approaches. Furthermore the technical details of the developed Raman scattering set-up are described.

The influence of ignition and in-cylinder flow on the combustion of highly diluted mixtures in SI engines

The efficiency of SI engines at part load can be improved by lean burn and EGR. However, the maximum dilution rate of the air/ fuel mixture and therefore the potential of fuel consumption reduction is limited by increasing cyclic combustion variations. This article reports on investigations of the suitability of various ignition and intake systems for increasing the maximum charge dilution.

Evaluation of Noisy Coherent Anti-Stokes Raman Spectra by Evolutionary Algorithms

Coherent Anti-Stokes Raman Spectroscopy (CARS) is frequently the method of choice for non-intrusive temperature measurements in combustion systems. The temperature determination requires a comparison of measured spectra with theoretically calculated ones. Conventional gradient-based least squares fitting of experimental data with a library of theoretical spectra usually leads to sensible results, as long as the spectrum shapes behave well and the noise level is low.