Three-step approach for prediction of limit cycle pressure oscillations in combustion chambers of gas turbines

Currently, gas turbine manufacturers frequently face the problem of strong acoustic combustion driven oscillations inside combustion chambers. These combustion instabilities can cause extensive wear and sometimes even catastrophic damages to combustion hardware. This requires prevention of combustion instabilities, which, in turn, requires reliable and fast predictive tools. This work presents a three-step method to find stability margins within which gas turbines can be operated without going into self-excited pressure oscillations. As a first step, a set of unsteady Reynolds-averaged Navier–Stokes simulations with the Flame Speed Closure (FSC) model implemented in the OpenFOAM® environment are performed to obtain the flame describing function of the combustor set-up. The standard FSC model is extended in this work to take into account the combined effect of strain and heat losses on the flame. As a second step, a linear three-time-lag-distributed model for a perfectly premixed swirl-stabilized flame is extended to the nonlinear regime. The factors causing changes in the model parameters when applying high-amplitude velocity perturbations are analysed. As a third step, time-domain simulations employing a low-order network model implemented in Simulink® are performed. In this work, the proposed method is applied to a laboratory test rig. The proposed method permits not only the unsteady frequencies of acoustic oscillations to be computed, but the amplitudes of such oscillations as well. Knowing the amplitudes of unstable pressure oscillations, it is possible to determine how these oscillations are harmful to the combustor equipment. The proposed method has a low cost because it does not require any license for computational fluid dynamics software.     

A generalization of von Neumann's assignment problem and K. Fan optimization result

Summary In this paper we generalize the assignment problem in higher dimensions, referring at to another study by the authors. The hide-and-seek game, which is intimately related to the assignment problem, is extended, and an elegant result due to K. Fan about extrema is generalized.     

Photoreduction of Thiosulfate in Semiconductor Dispersions

Conduction band electrons produced by band gap excitation of TiO₂-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO₂-electrodes. The valence band process in alkaline TiO₂-dispersions involves oxidation of S₂O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur.     

High-performance liquid chromatographic/tandem mass spectrometric identification of the phototransformation products of tebuconazole on titanium dioxide

Tebuconazole is a widely used fungicide. The formation of by-products on irradiated titanium dioxide as a photocatalyst was evaluated. Several species derived from tebuconazole degradation were identified and characterized by HPLC/MS(n). A pattern of reactions accounting for the observed intermediates is proposed. Different parallel pathways are operating (and through these pathways the transformation of the molecule proceeds), leading to a wide range of intermediate compounds. All these molecules are more hydrophylic than tebuconazole. The main steps involved are (1) the hydroxylation of the molecule with the formation of three species having [M + H](+) 324; the hydroxylation occurs on the C-1 carbon and on the aromatic ring in the two ortho-positions; (2) the cleavage of a C--C bond with the release of the tert-butyl moiety and the formation of a species having m/z 250; analogously to step 1, also on this species a further hydroxylation reaction occurs; (3) through the loss of the triazole moiety with the formation of a structure with m/z 257.     

A boxmodel development to study the relationships between the photo-oxidants and the particles formation in the troposphere

The model BAGS (Boxmodel for Aerosol and Gasphase Simulations) has been developed. It is composed of two major modules: the first one describes the system of the chemical reactions in the gaseous phase, the second one calculates the aerosol chemical composition and the dimensional distribution of the particles. The boxmodel has been developed with the introduction of new chemical and physical processes, not previously included, in particular the formation of Secondary Organic Aerosol. The other implemented processes are a module for the dynamic of the particle population, nucleation, coagulation and dry deposition. The last phase of the work has been a check of the BAGS capabilities by a series of tests, that have permitted to compare it with other models (MAPS and MADM). The tests in particular have concerned the aerosol water content prediction, the photochemistry, the condensation of the inorganic compounds and the formation of Secondary Organic Aerosol.     

Measurement of the carbonaceous component in the Milan urban particulate matter

The carbonaceous component in the Milan urban particulate matter, i.e. the two components black carbon (BC) and organic carbon (OC), has been measured by means of a thermogravimetric analyzer combined with an infrared spectrophotometer (TGA/FT-IR). While black carbon may be considered a primary pollutant, organic carbon includes both primary emissions and secondary organic aerosols. Since carbonaceous aerosol (including a small quantity of inorganic carbon, too) makes up roughly from 25% to 50% of the average annual PM 2.5 mass concentration, a deeper understanding of this component is required. The TGA/FT-IR technique, employed for the first time to our knowledge for the quantification of the particulate matter carbonaceous component, allows, thought the results here presented are preliminary, to assess the two components BC and OC in a simple way especially if compared with the methods reported in the literature. The total carbon (TC) determinations performed by TGA/FT-IR on Milan urban particulate matter are in good agreement with the results obtained by a total organic carbon (TOC) analyzer operating directly on the solid sample.     

Evaluation by chemical parameters of the pollution state of the agricultural-industrial settlement of the Fucino Plain

In the present work are reported the results of a monitoring on a vast scale, carried out through evaluation of opportune chemical parameters, of the pollution state of the agricultural-industrial settlement of the Fucino Plain. The parameters took into consideration have been the presence of wide consumption pesticides and of ionic species as Cl-, NO2-, NO3-, NH4+, the quantification of the dissolved oxygen, of the temperature, of the conductivity, of pH and eH. Collected data are used for chemometric elaboration. The water systems examined, by means of drawing campaigns carried out at regular intervals in winter, spring, summer, and autumnal seasons, are represented by superficial waters constituting a network of irrigation canals fed by stratum and meteoric waters. In this work are reported the results relative to the drawing campaigns.