Experimental investigation of the unsteady response of premixed flame fronts to acoustic pressure waves

International audienceUsing OH chemiluminescence, we measure the experimental unsteady response of a 1–D premixed flame to an acoustic pressure wave for a range of frequencies below and above the inverse of the flame transit time. We find that the response is positive and, at low frequency the order of magnitude is comparable with existing theoretical analyses. However, if it is supposed that the chemiluminescence is proportional to the mass consumption rate, despite some uncertainty in the interpretation of the chemiluminescence signal we find that the frequency dependence of the measured response is not compatible with the predictions of the standard flame model for one-step Arrhenius kinetics. A better, but not perfect, correlation is obtained for the heat release rate. We conclude that the standard model does not provide an adequate description of the unsteady response of real flames, and that it is necessary to investigate more realistic chemical models

Experimental and numerical investigations of the relation between OH* emission, flame speed and mass consumption rate

6 PagesWe investigate the relation between the intensity of the luminous emission of the excited OH* radical and the mass consumption rate of lean planar premixed methane-air flames. The flames were maintained perfectly flat using parametric acoustic stabilization in an imposed acoustic field. The consumption rate of the flames was varied by changing both the equivalence ratio and the temperature of the unburned mixture. We also compare our experimental measurements to the results of numerical simulations, using detailed chemical kinetics. For lean flames, we find that the OH* emission intensity is linear with mass consumption rate but, not proportional. Consequently, the relative fluctuation in mass consumption rate is not linearly related to the relative fluctuation in OH* emission intensity

The response of premixed flames to pressure oscillations

International audienceRecent measurements of the direct response of premixed flames to acoustic pressure fluctuations have shed doubt on the validity of analytical models that use irreversible one-step chemistry, and suggest that more realistic chemical kinetic models are needed to fully describe the unsteady dynamics of premixed flames. However, in the analysis of the experimental results some doubts subsisted concerning the exact relation between the intensity of emission from the excited OH* radical, used to determine the flame response, and the unsteady reaction rate given by the theoretical analyses. Combining experimental and numerical approaches on premixed methane-air flames, we propose corrections to give more confidence in the experimental results and to confirm the need for further investigations on the dynamics of unsteady premixed flames

Premixed flames propagating freely in tubes

International audienceThis paper reports an experimental investigation of premixed propane and methane-air flames propagating freely in tubes 1.5 m long and with diameters 54 and 94 mm. Two regimes of propagation are distinguished by correlating the flame speed and the radius of curvature at the flame tip. The characteristic lengths are then related to the cut-off wavelengths estimated from linear theories and compared to previous results of Michelson-Sivashinsky simulations

Self-Turbulent Flame Speeds

International audienceThis paper reports an experimental investigation of premixed propane andmethane-air flames propagating freely in tubes 1.5 m long and with diameters rangingfrom 26 to 141 mm. The thermo-acoustic instability was eliminated by means of anovel acoustic absorber placed at the closed end of the tube. We first remark that theflame can adopt different shapes either quasi-axisymmetric and normal to the meandirection of propagation, or inclined with a larger propagation speed because of theincrease in flame surface area. The minima of the propagation speeds, correspondingto non-tilted flame propagation, are then analyzed using analytical models for theself-turbulent flame propagation. The concept of a cut-off wavelength appears to berelevant to explain the different behaviors observed on the rich side of methane-ai

Diversité génétique individuelle, différenciation morphologique et comportementale entres les sexes, patterns d'appariement et paramètres démographiques chez une espèce d'oiseau tropicale et monogame, la tourterelle à queue carrée, Zenaida Aurita

La recherche en écologie comportementale est affectée par un biais notoire en faveur des oiseaux des zones tempérées, en dépit de la plus grande diversité des espèces tropicales et des conditions naturelles radicalement éloignées qui rendent les connaissances sur les espèces tempérées peu pertinentes pour les espèces tropicales.Nous proposons de combler le manque d informations concernant les oiseaux tropicaux via l étude d une espèce socialement monogame, se reproduisant et défendant un territoire toute l année, la Tourterelle à queue carrée, Zenaida aurita. Pour commencer, nous avons cherché à déterminer le caractère sexuellement mono- ou dichromatique de la coloration du plumage et si celui-ci reflétait la qualité individuelle. Nous avons ensuite exploré les patterns d appariements au sein des couples selon le degré d hétérozygotie et la taille du corps. Afin d établir la force des liens du couple, nous avons évalué le taux de divorce, les hypothèses pouvant expliquer les cas répertoriés, et les conséquences du changement de partenaire. Ceci a été suivi par la caractérisation des rôles des sexes au sein des couples selon diverses activités. Des analyses de capture-marquage-recapture ont permis d estimer le taux de survie ainsi que l influence du degré d hétérozygotie et de la taille de l aile sur la survie. La Tourterelle à queue carrée paraît suivre les spécificités comportementales, écologiques et démographiques caractérisant les espèces tropicales à monogamie pérenneResearch in avian behavioral ecology is affected by a known bias in favour of temperate species despite the greatest diversity of tropical species and the radically remote natural conditions which make knowledge of temperate species hardly relevant to tropical species.We propose to reduce the lack of information about tropical birds through the study of a socially monogamous species, reproducing and defending an all-purpose territory all year round, the Zenaida dove, Zenaida aurita. We used monitoring data from a population of ringed birds in Barbados for six years. First, we focused on plumage coloration both to ascertain their sexually mono- or dichromatic nature and whether plumage colour reflects individual quality. We then explored pairing patterns in relation to genome-wide heterozygosity and body size (tarsus length, wing chord). To determine the strength of pair bonding, we assessed divorce rate, evaluated which hypotheses could explain divorce cases and listed the consequences of mate loss and mate switching. It was followed by the characterization of sex roles within pairs during various activities (singing, nest building, juvenile care, territorial defence). Capture-mark-recapture analysis allowed us to estimate survival rate as well as influence of heterozygosity degree and wing chord on individual survival. Zenaida dove appears to conform to the behavioral, ecological and demographic features characterizing tropical species with perennial monogamyDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Experimental two dimensional cellular flames

International audienceThe propagation of very unstable cellular flames (also called self-turbulent flames) is studied experimentally in a Hele-Shaw cell. This quasi-two dimensional configuration allows for quantitative image analysis. The dynamics of the premixed flame is controlled in these conditions by the creation or merging of the cusps that appear on the front

Conductance switching at the nanoscale of diarylethene derivatives self-assembled monolayers on La0.7_{0.7}Sr0.3_{0.3}MnO3_3

We report on the phosphonic acid route for the grafting of functional molecules, optical switch (dithienylethene diphosphonic acid, DDA), on La0.7Sr0.3MnO3 (LSMO). Compact self-assembled monolayers (SAMs) of DDA are formed on LSMO as studied by topographic atomic force microscopy (AFM), ellipsometry, water contact angle and X-ray photoemission spectroscopy (XPS). The conducting AFM measurements show that the electrical conductance of LSMO/DDA is about 3 decades below that of the bare LSMO substrate. Moreover, the presence of the DDA SAM suppresses the known conductance switching of the LSMO substrate that is induced by mechanical and/or bias constraints during C-AFM measurements. A partial light-induced conductance switching between the open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip molecular junctions (closed/open conductance ratio of about 8). We show that, in the case of long-time exposition to UV light, this feature can be masked by a non-reversible decrease (a factor of about 15) of the conductance of the LSMO electrode.Comment: Full paper with supporting informatio

Real-time control of distributed batteries with blockchain-enabled market export commitments

Recent years have seen a surge of interest in distributed residential batteries for households with renewable generation. Yet, assuring battery assets are profitable for their owners requires a complex optimisation of the battery asset and additional revenue sources, such as novel ways to access wholesale energy markets. In this paper, we propose a framework in which wholesale market bids are placed on forward energy markets by an aggregator of distributed residential batteries that are controlled in real time by a novel Home Energy Management System (HEMS) control algorithm to meet the market commitments, while maximising local self-consumption. The proposed framework consists of three stages. In the first stage, an optimal day-ahead or intra-day scheduling of the aggregated storage assets is computed centrally. For the second stage, a bidding strategy is developed for wholesale energy markets. Finally, in the third stage, a novel HEMS real-time control algorithm based on a smart contract allows coordination of residential batteries to meet the market commitments and maximise self-consumption of local production. Using a case study provided by a large UK-based energy demonstrator, we apply the framework to an aggregator with 70 residential batteries. Experimental analysis is done using real per minute data for demand and production. Results indicate that the proposed approach increases the aggregator’s revenues by 35% compared to a case without residential flexibility, and increases the self-consumption rate of the households by a factor of two. The robustness of the results to uncertainty, forecast errors and to communication latency is also demonstrated