Experimental and numerical study of the accuracy of flame-speed measurements for methane/air combustion in a slot burner

Measuring the velocities of premixed laminar flames with precision remains a controversial issue in the combustion community. This paper studies the accuracy of such measurements in two-dimensional slot burners and shows that while methane/air flame speeds can be measured with reasonable accuracy, the method may lack precision for other mixtures such as hydrogen/air. Curvature at the flame tip, strain on the flame sides and local quenching at the flame base can modify local flame speeds and require correc- tions which are studied using two-dimensional DNS. Numerical simulations also provide stretch, dis- placement and consumption flame speeds along the flame front. For methane/air flames, DNS show that the local stretch remains small so that the local consumption speed is very close to the unstretched premixed flame speed. The only correction needed to correctly predict flame speeds in this case is due to the finite aspect ratio of the slot used to inject the premixed gases which induces a flow acceleration in the measurement region (this correction can be evaluated from velocity measurement in the slot section or from an analytical solution). The method is applied to methane/air flames with and without water addition and results are compared to experimental data found in the literature. The paper then discusses the limitations of the slot-burner method to measure flame speeds for other mixtures and shows that it is not well adapted to mixtures with a Lewis number far from unity, such as hydrogen/air flames

Effects of hydrogen and steam addition on laminar burning velocity of methane–air premixed flame: Experimental and numerical analysis

Effects of hydrogen enrichment and steam addition on laminar burning velocity of methaneeair premixed flame were studied both experimentally and numerically. Measurements were carried out using the slot burner method at 1 bar for fresh gases temperatures of 27 °C and 57 °C and for variable equivalence ratios going from 0.8 to 1.2. The hydrogen content in the fuel was varied from 0% to 30% in volume and the steam content in the air was varied from 0 to 112 g/kg (0e100% of relative humidity). Numerical calculations were performed using the COSILAB code with the GRI-Mech 3.0 mechanism for one-dimensional premixed flames. The calculations were implemented first at room temperature and pressure and then extended to higher temperatures (up to 917 K) and pressures (up to 50 bar). Measurements of laminar burning velocities of methanee hydrogeneair and methaneeairesteam agree with the GRI-Mech calculations and previous measurements from literature obtained by different methods. Results show that enrich- ment by hydrogen increases of the laminar burning velocity and the adiabatic flame temperature. The addition of steam to a methaneeair mixture noticeably decreases the burning velocity and the adiabatic flame temperature. Modeling shows that isentropic compression of fresh gases leads to the increase of laminar burning velocity

Coupled study of the film and spray on a basic annular prefiming airblast atomizer

[EN] One way to increase efficiency and reduce pollution in transport and energetic domain is designing fuel injectors with better atomization. In this work, experiments were performed on a prefilming airblast atomizer often used in gas turbine engines. For this purpose, a new injector was designed to visualize the prefilming zone and the primary atomization together. The flow configuration corresponds to an annular liquid film sheared by inner high velocity airflows. High speed Shadowgraphy was used to observe film and spray, liquid film frequency, wave velocity and wave deformation, primary breakup regime. Finally, a link between liquid film and the primary atomization are shown first qualitatively and after quantitatively.Gosselin, V.; Ferret, B.; Bazile, R. (2017). Coupled study of the film and spray on a basic annular prefiming airblast atomizer. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 505-512. https://doi.org/10.4995/ILASS2017.2017.4626OCS50551

Stabilization of a premixed laminar flame on a rotating cylinder

This paper investigates the stabilization of a laminar premixed flame on a rotating cylinder. Experiments and DNS are combined to analyze the effects of rotation on the flow topology and flame stabilization. Both experiment and simulation reveal that the usual stabilization pattern (two symmetric flame roots on both sides of the cylinder) is strongly affected by rotation. The flame roots positions on the upper and lower sides of the cylinder are modified with increasing rotation speeds. One of the two flame roots is quenched over a long region. The distance of the flame roots to the flameholder changes with the rotation speed until a bifurcation takes place: at a critical rotation speed, the flame roots merge, and the flame stabilizes upstream of the cylinder. DNS results are used to explain the flame topologies observed experimentally

Étude expérimentale de l'évaporation de gouttelettes bicomposant

Nous souhaitons affiner la compréhension de phénomènes qui ont lieu dans une chambre de combustion, dans laquelle des gouttes de carburant sont injectées. On souhaite mieux comprendre l’influence du caractère multicomposant des carburants sur l’évaporation des gouttes et on s’intéresse particulier à l’effet de la présence d’un alcool dans le mélange liquide. Un travail expérimental est nécessaire afin de constituer une base de données utile à l’amélioration des modèles d’évaporation. Une expérience modèle pour l’étude d’écoulements diphasiques turbulents a été conçue à cet effet. Le banc expérimental permet de générer dans un canal un écoulement d’air chauffé fortement turbulent et présentant des propriétés de turbulence homogène isotrope. Un spray de gouttelettes poly-dispersées de liquide bi-composant acétone/éthanol est généré dans cet écoulement. Un large accès optique permet de suivre l’évolution de l’écoulement diphasique le long du canal, et notamment la dispersion et l’évaporation des gouttes et le mélange de la vapeur et de l’air. Une campagne expérimentale de fluorescence induite par plan laser (PLIF) a été entreprise afin de caractériser les régimes d’évaporation en fonction de la composition du mélange liquide. Les concentrations instantanées de la phase vapeur d’acétone sont extraites de cette campagne. Des résultats encourageants montrent que la présence de l’alcool accélère l’évaporation des gouttes. L’influence de paramètres de l’écoulement sera étudiée afin de mieux comprendre cet effet de l’alcool sur l’évaporation, tandis que les résultats de calculs LES (simulation aux grandes échelles) en cours seront présentés à titre de comparaison. Références : Moreau F., Bazile R. (2012) Evaporation of bi-component droplets in a heated, highly turbulent flow. Experiments in Fluids, 53:331-342. Cochet M., Bazile R., Ferret B., Cazin S. (2009) Evaporation of polydispersed droplets in a highly turbulent channel flow. Experiments in Fluids, 47:379–394

Mesenteric lymph node cells from neonates present a prominent IL-12 response to CpG oligodeoxynucleotide via an IL-15 feedback loop of amplification

At birth, the immune system is still in development making neonates more susceptible to infections. The recognition of microbial ligands is a key step in the initiation of immune responses. It can be mimicked to stimulate the immune system by the use of synthetic ligands recognising pattern recognition receptors. In human and mouse, it has been found that neonatal cytokine responses to toll-like receptor (TLR) ligands differ in many ways from those of adults but the relevant studies have been limited to cord blood and spleen cells. In this study, we compared the responses in neonate and adult sheep to CpG oligodeoxynucleotides (ODN), a TLR9 ligand, in both a mucosal and a systemic organ. We observed that in response to CpG-ODN more IL-12 was produced by neonatal than adult sheep cells from mesenteric lymph nodes (MLN) and spleen. This higher IL-12 response was limited to the first 20 days after birth for MLN cells but persisted for a longer period for spleen cells. The major IL-12-producing cells were identified as CD14+CD11b+. These cells were poor producers of IL-12 in response to direct stimulation with CpG-ODN and required the cooperation of other MLN cells. The difference in response to CpG-ODN between neonates and adults can be attributed to both a higher proportion of CD14+CD11b+ cells in neonate lambs and their higher capacity to produce IL-15. The IL-15 increases IL-12 production by an amplifying feedback loop involving CD40

Geometrical structure of an iron epilayer on Si (111) : an X-ray standing wave analysis

dépôt d'une copie effectué avec l'aimable autorisation de EDP SciencesThe structure of an iron film, deposited at low temperature (50 °C) upon a silicon (111) substrate, has been determined by means of X-ray Standing Wave experiments performed at LURE (Orsay, France). Experimental results are coherent with the model of an abrupt interface between the adsorbate and the surface : the first site of adsorption terminates the bulk silicon and a body-centred iron layer epitaxially grows on the substrate with a preferential growth orientation

Effect of Cold Pressor Test on the Internal Diameter of the Radial Artery

The aim of this study was to investigate in normal subjects the effect of a cold pressor test on the caliber of the radial artery, a muscular artery of medium size. The internal diameter of this artery was measured continuously using a recently developed ultrasonic device. Immersion of one hand in ice water for two minutes increased blood pressure from 115/75 ± 3/2 (Mean±SEM) to 136/90 ± 6/2 mm Hg (P <.001) and decreased the internal diameter of the radial artery from 2.82 ± 0.12 to 2.60 ± 0.09 mm ( P <.01). These data therefore indicate that the vasoconstriction induced by the cold pressor test involves not only arterioles, but also medium-size arteries. Am J Hypertens 1989; 2:727-72

Plasma membrane proteomes of differentially matured dendritic cells identified by LC-MS/MS combined with iTRAQ labelling

AbstractDendritic cells (DCs) play a pivotal role in polarising Th lymphocyte subsets but it is unclear what molecular events occur when DCs generate Th2-type responses. Here, we analysed plasma membrane-enriched fractions from immature, pro-Th1 and pro-Th2 DCs and used a combination of iTRAQ labelling and LC–MS/MS to quantify changes in the proteomes. Analysis was performed on triplicate biological samples and changes verified by flow cytometry. MHC class II molecules and CD29 were up-regulated in pro-Th1 DCs whilst CD18 and CD44 were up-regulated in pro-Th2 DCs. One of the most down-regulated molecules in pro-Th1 DCs was YM-1 whilst the greatest decrease in pro-Th2 DCs was NAP-22. Other molecules up-regulated in pro-Th2 DC compared to pro-Th1 DCs included some potentially involved in protein folding during antigen processing (clathrin and Rab-7), whilst other non-membrane proteins such as enzymes/transporters related to cell metabolism (malate dehydrogenase, pyruvate kinase, and ATPase Na+/K+) were also recorded. This suggests that pro-Th2 DCs are more metabolically active while pro-Th1 DCs have a mature ‘end state’. Overall, although several molecules were preferentially expressed on pro-Th2 DCs, our proteomics data support the view of a ‘limited maturation’ of pro-Th2 DCs compared to pro-Th1 DCs

Cellular and Molecular Mechanisms Underlying the Strong Neonatal IL-12 Response of Lamb Mesenteric Lymph Node Cells to R-848

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