Methodology for the numerical prediction of pollutant formation in gas turbine combustors and associated validation experiments

International audienceFor aircraft engine manufacturers the formation of pollutants such as NOx or soot particles is an important issue because the regulations on pollutant emissions are becoming increasingly stringent. In order to comply with these regulations, new concepts of gas turbine combustors must be developed with the help of simulation tools. In this paper we present two different strategies, proposed by ONERA and DLR respectively, to simulate soot or NOx formation in combustors. The first one is based on simple chemistry models allowing significant effort to be spent on the LES description of the flow, while the second one is based on more accurate, but also more expensive, models for soot chemistry and physics. Combustion experiments dedicated to the validation of these strategies are described next: The first one, performed at DLR, was operated at a semi-technical scale and aimed at very accurate and comprehensive information on soot formation and oxidation under well-defined experimental conditions; the second one, characterized at ONERA, was aimed at reproducing the severe conditions encountered in realistic gas turbine combustors. In the third part of the paper the results of combustion simulations are compared to those of the validation experiments. It is shown that a fine description of the physics and chemistry involved in the pollutant formation is necessary but not sufficient to obtain quantitative predictions of pollutant formation. An accurate calculation of the turbulent reactive flow interacting with pollutant formation and influencing dilution, oxidation and transport is also required: when the temperature field is correctly reproduced, as is the case of the ONERA simulation of the DLR combustor, the prediction of soot formation is quite satisfactory while difficulty in reproducing the temperature field in the TLC combustor leads to overestimations of NOx and soot concentrations.Pour les constructeurs de moteurs d’avion, la formation de polluants comme les NOx ou les particules de suies est une question importante car la réglementation sur les émissions polluantes est de plus en plus sévère. Pour respecter cette réglementation, de nouveaux concepts de foyers de turbine à gaz doivent être développés avec l’aide d’outils de simulation. Dans cet article, nous présentons deux stratégies différentes proposées par l’ONERA et le DLR pour simuler la formation des suies et des NOx dans les chambres de combustion. La première est basée sur des modèles chimiques simples permettant de faire porter l’effort de calcul sur la description LES de l’écoulement, tandis que la seconde est basée sur des modèles physico-chimiques de formation des suies plus précis mais aussi plus coûteux en temps de calcul. Des expériences de combustion conçues pour la validation de ces stratégies sont ensuite décrites : La première, réalisée au DLR, reproduit la combustion à une échelle semi-industrielle et a pour but de donner une information très précise et complète sur les mécanismes de formation des suies et leur oxydation dans des conditions expérimentales parfaitement maîtrisées ; la seconde, réalisée à l’ONERA, a pour but de reproduire de façon réaliste les conditions sévères rencontrées dans les foyers de turbine à gaz industrielles. Dans la troisième partie du papier, les résultats des simulations de combustion sont comparés à ceux des expériences de validation. Il est démontré que la description précise de la physique et de la chimie intervenant dans la formation des polluants est nécessaire mais non suffisante pour simuler correctement les quantités de polluants formés. Un calcul précis de l’écoulement turbulent réactif interagissant avec les mécanismes de formation, de dilution, d’oxydation et de transport des polluants est également nécessaire : Lorsque le champ de température est correctement reproduit comme c’est le cas pour la simulation ONERA du foyer DLR, la simulation de la formation des suies est assez satisfaisante, alors qu’une difficulté pour reproduire le champ de température dans le foyer TLC conduit à une surestimation des concentrations de NOx et de suies

Expansion of human mesenchymal stem cells in a fixed-bed bioreactor system based on non-porous glass carrier – Part A: Inoculation, cultivation, and cell harvest procedures

Human mesenchymal stem cells (hMSC) are a promising cell source for several applications of regenerative medicine. The used cells are either autologous or allogenic, whereas the latter enables, especially by using of stem cell lines, a production of cell therapeutic or tissue engineered implants in stock. Therefore, the usually small initial cell number has to be increased. For that purpose bioreactors are demanded, which offer the controlled expansion of the hMSC under GMP-conform conditions. In this study, divided in part A and B, a fixed bed bioreactor system based on non-porous borosilicate glass spheres for the expansion of hMSC, demonstrated with the model cell line hMSC-TERT, is introduced. The system offers a comfortable automation of the inoculation, cultivation, and harvesting procedures. Furthermore the bioreactor owns a simple design which benefits the manufacturing as disposable. Part A is focused on the inoculation, cultivation, and harvesting procedures. Cultivations were performed in lab scales up to a bed volume of 300 cm3. It could be shown that the fixed bed system, based on 2-mm borosilicate glass spheres, as well as the inoculation, cultivation, and harvesting procedures are suitable for the expansion of hMSC with high yield and vitality

Degradation and Recondensation of Metal Oxide Nanoparticles in Laminar Premixed Flames

The behavior of technical nanoparticles at high temperatures was measured systematically to detect morphology changes under conditions relevant to the thermal treatment of end-of-life products containing engineered nanomaterials. The focus of this paper is on laboratory experiments, where we used a Bunsen-type burner to add titania and ceria particles to a laminar premixed flame. To evaluate the influence of temperature on particle size distributions, we used SMPS, ELPI and TEM analyses. To measure the temperature profile of the flame, we used coherent anti- Stokes Raman spectroscopy (CARS). The comprehensible data records show high temperatures by measurement and equilibrium calculation for different stoichiometries and argon admixtures. With this, we show that all technical metal oxide nanoparticle agglomerates investigated reform in flames at high temperatures. The originally large agglomerates of titania and ceria build very small nanoparticles (<10 nm/“peak 2”) at starting temperatures of <2200 K and <1475 K, respectively (ceria: Tmelt = 2773 K, Tboil = 3873 K/titania: Tmelt = 2116 K, Tboil = 3245 K). Since the maximum flame temperatures are below the evaporation temperature of titania and ceria, enhanced vaporization of titania and ceria in the chemically reacting flame is assumed

Therapeutic concentrations of glucagon-like peptide-1 in cerebrospinal fluid following cell-based delivery into the cerebral ventricles of cats

<p>Abstract</p> <p>Background</p> <p>Neuropeptides may have considerable potential in the treatment of acute and chronic neurological diseases. Encapsulated genetically engineered cells have been suggested as a means for sustained local delivery of such peptides to the brain. In our experiments, we studied human mesenchymal stem cells which were transfected to produce glucagon-like peptide-1 (GLP-1).</p> <p>Methods</p> <p>Cells were packed in a water-permeable mesh bag containing 400 polymeric microcapsules, each containing 3000 cells. The mesh bags were either transplanted into the subdural space, into the brain parenchyma or into the cerebral ventricles of the cat brain. Mesh bags were explanted after two weeks, and cell viability, as well as GLP-1 concentration in the cerebrospinal fluid (CSF), was measured.</p> <p>Results</p> <p>Viability of cells did not significantly differ between the three implantation sites. However, CSF concentration of GLP-1 was significantly elevated only after ventricular transplantation with a maximum concentration of 73 pM (binding constant = 70 pM).</p> <p>Conclusions</p> <p>This study showed that ventricular cell-based delivery of soluble factors has the capability to achieve concentrations in the CSF which may become pharmacologically active. Despite the controversy about the pharmacokinetic limitations of ventricular drug delivery, there might be a niche in this for encapsulated cell biodelivery of soluble, highly biologically-effective neuropeptides of low molecular weight like GLP-1.</p