Reduced kinetic mechanisms for modelling LPP combustión in gas turbines

Reduced kinetic mechanisms for modelling LPP combustión in gas turbine

Simplified approach to the numerical description of methane-air diffusion flames

Starting with a three-step reduced chemistry description that employes H2 and CO as the only intermediates not in steady state, a simplified formulation aimed at facilitating numerical computations of non-premixed methane-air systems is developed. The analysis retains finite rates for radical recombination and CO oxidation but assumes infinitely fast fuel consumption taking place in a diffusion-controlled manner in an infinitely thin reaction sheet. To remove stiffness associated with the fast fuel consumption, the conservation equations for the major species and the temperature are written in terms of generalized coupling functions that for predictive accuracy permit species diffusivities that differ from the thermal diffusivity. The resulting formulation, which automatically determines the position of the fuel-consumption layer without necessity of front tracking or further interface approximations, can be used for analytical, computational, and modeling studies of both laminar and turbulent flows, removing stiffness difficulties associated with highly disparate chemical time scales. Comparisons of results of the simplified formulation in the counterflow mixing layer with those obtained with detailed chemistry and transport descriptions indicate that the proposed formulation applies with good accuracy to strain conditions ranging from weakly strained, robust flames to near-extinction flames

Modelling and Simulation of Moored Devices for Ocean Currents Energy Harnessing

The main objective of this paper is the presentation of modelling solutions off loating devices that can be used for harnessing energy from ocean currents. It has been structured into three main parts. First, the growing current interest in marine renewable energy in general, and in extracting energy from currents in particular, is presented, showing the large number of solutions that are emerging and some of the most significant types. GESMEY generator is presented in second section. It is based on a new concept that has been patented by the Universidad Politécnica de Madrid and which is currently being developed through a collaborative agreement with the SOERMAR Foundation. The main feature of this generator is that on operation is fully submerged, and no other facilities are required to move to floating state for maintenance, which greatly increases its performance. Third part of the article is devoted to present the modelling and simulation challenges that arise in the development of devices for harnessing the energy of marine currents, along with some solutions which have been adopted within the frame of the GESMEY Project, making particular emphasis on the dynamics of the generator and its contro

Beta-lactam resistance in enterobacteria isolated from animal and water

The susceptibility to β-lactam antibiotics was analysed in thirty seven strains of enterobacteria from both animals and non-chlorinated water of rural areas from Corrientes, North-eastern Argentina. Twenty nine were isolated from animals: Klebsiella pneumoniae (n=9), Klebsiella oxytoca (n=1), Proteus mirabilis (n=7), Escherichia coli (n=12), and 8 from non-chlorinated water: E. coli (n=5), K. pneumoniae (n=2), K. oxytoca (n=1). The antibiograms were performed by the Kirby-Bauer technique using antibiotic discs of ampicillin, cefotaxime, cefepime, piperacillin and with β-lactamases inhibitors: clavulanic acid-amoxicillin, sulbactam- cefoperazone and tazobactam-piperacillin. Carbapenems with an EDTA disc as metallo β-lactamases inhibitor were also used. Neither phenotypically ESBL (extended-spectrum beta-lactamases) nor carbapenemase were detected. It can be inferred that the resistance observed in this assay may be attributed to a different source

Ausencia de beta– lactamasas en Pseudomonas aeruginosa de origen animal y agua

In order to know the susceptibility to carbapenems (imipenem and meropenem), ceftazidime and aztreonam as phenotypical indicator substrates of β–lactamases, 30 strains of Pseudomonas aeruginosa (18 from animal clinical samples and 12 from non–chlorinated water) were analysed. There were not synergism indicating their production, and the results differ from those of human where prevalence of resistance is a great problem when instauring treatment.Con el fin de conocer la sensibilidad a carbapenems (imipenem y meropenem), ceftazidime y aztreonam como indicadores fenotípicos de sustratos de β–lactamasas, se analizaron 30 cepas de Pseudomonas aeruginosa (18 de muestras clínicas animales y 12 de aguas no clorinadas). No se halló sinergismo indicador de su producción. Estas estirpes se diferencian de las aisladas de seres humanos, donde alcanzan un alto grado de resistencia que dificulta considerablemente el tratamiento

Combustion theory and modeling

In honor of the fiftieth anniversary of the Combustion Institute, we are asked to assess accomplishments of theory in combustion over the past fifty years and prospects for the future. The title of our article is chosen to emphasize that development of theory necessarily goes hand-in-hand with specification of a model. Good conceptual models underlie successful mathematical theories. Models and theories are discussed here for deflagrations, detonations, diffusion flames, ignition, propellant combustion, and turbulent combustion. In many of these areas, the genesis of mathematical theories occurred during the past fifty years, and in all of them significant advances are anticipated in the future. Increasing interaction between theory and computation will aid this progress. We hope that, although certainly not complete in topical coverage or reference citation, the presentation may suggest useful directions for future research in combustion theory

The reduced kinetic description of lean premixed combustion

Lean premixed methane-air flames are investigated in an effort to facilitate the numerical description of CO and NO emissions in LP (lean premixed) and LPP (lean premixed prevaporized) combustion systems. As an initial step, the detailed mechanism describing the fuel oxidation process is reduced to a four-step description that employs CO, H2, and OH as intermediates not following a steady-state approximation. It is seen that, under conditions typical of gas-turbine combustion, this mechanism can be further simplified to give a two-step reduced description, in which fuel is consumed and CO is produced according to the fast overall step CH4 + 3/2 O2 CO + 2H2O, while CO is slowly oxidized according to the overall step CO + 1/2 O2 CO2. Because of its associated fast rate, fuel consumption takes place in a thin layer where CO, H2, and OH are all out of steady state, while CO oxidation occurs downstream in a distributed manner in a region where CO is the only intermediate not in steady state. In the proposed description, the rate of fuel consumption is assigned a heuristic Arrhenius dependence that adequately reproduces laminar burning velocities, whereas the rate of CO oxidation is extracted from the reduced chemistry analysis. Comparisons with results obtained with detailed chemistry indicate that the proposed kinetic description not only reproduces well the structure of one-dimensional unstrained and strained flames, including profiles of CO, temperature, and radicals, but can also be used to calculate NO emissions by appending an appropriate one-step reduced chemistry description that includes both the thermal and the N2O production paths. Although methane is employed in the present study as a model fuel, the universal structure of the resulting CO oxidation region, independent of the fuel considered, enables the proposed formulation to be readily extended to other hydrocarbons

The New Political Economy of EU State Aid Policy

Despite its importance and singularity, the EU’s state aid policy has attracted less scholarly attention than other elements of EU competition policy. Introducing the themes addressed by the special issue, this article briefly reviews the development of EU policy and highlights why the control of state aid matters. The Commission’s response to the current economic crisis notably in banking and the car industry is a key concern, but the interests of the special issue go far beyond. They include: the role of the European Commission in the development of EU policy, the politics of state aid, and a clash between models of capitalism. The special issue also examines the impact of EU policy. It investigates how EU state aid decisions affect not only industrial policy at the national level (and therefore at the EU level), but the welfare state and territorial relations within federal member states, the external implications of EU action and the strategies pursued by the Commission to limit any potential disadvantage to European firms, and the conflict between the EU’s expanding legal order and national

The quasi-cylindrical description of submerged laminar swirling jets

TThe quasi-cylindrical approximation is used to describe numerically the structure of a submerged swirling jet for subcritical values of the swirl ratio S<Sc . The emerging flow structure is affected by the swirling motion, which enhances the entrainment rate of the jet and induces an adverse pressure gradient that reduces its momentum flux. The effect is more pronounced as the swirl ratio S is increased, yielding for sufficiently large values of S a jet with an annular structure. The integration describes the smooth transition towards the far-field self-similar solution for all values of S smaller than a critical value S5Sc , at which the numerical integration fails to converge at a given downstream location. The comparisons with previous experimental results confirm the correspondence between the onset of vortex breakdown and the failure of the quasi-cylindrical approximation

How Much Education Is Needed to Delay Women's Age at Marriage and First Pregnancy?

Background: Early childbirth is associated with adverse maternal and child health outcomes. In South Asia, where women generally marry before having children, public health efforts need to focus on delaying marriage. Female education is widely considered the primary means to achieve this. However, it remains unclear how much education is required to delay marriage to the universal minimum age of 18 years, or what predicts marriage age in women lacking any education. This is crucial to address in the Terai region of Nepal which has the highest proportion of children out of school and where girls marry and have their first pregnancy early. Methods: We analyzed data from 6,406 women aged 23-30 years from a cluster-randomized trial in lowland Terai Nepal. Using Kaplan-Meier survival analysis, multivariable logistic and Cox proportional hazards regression models, we investigated associations between women's education level and age at marriage and first pregnancy, and the interval between these events. Among the uneducated women, we investigated associations of husband's education level with the same outcomes. Results: Compared to uneducated women, educated women had a greater probability of delaying marriage until the age of 18 years and of pregnancy until 20 years. Women needed to complete grade 9, and ideally 11, to substantially increase their odds of marrying after 18 years. Delaying first pregnancy to 20 years was largely due to marrying later; education had little extra effect. The association of marriage with first pregnancy age worked independently of education. However, later-marrying women, who generally had completed more education, had their first pregnancy sooner after marriage than earlier marrying women. Most uneducated women, regardless of their husbands' level of education, still married under the legal age of marriage. Conclusion: Delaying marriage to majority age requires greater efforts to ensure girls get to school in the first place, and complete secondary education. Since currently only 36% of girls in the Terai attend secondary school, parallel efforts to delay marriage are crucial to prevent early childbearing. Sexual and reproductive health programmes in school and in women's groups for married and uneducated adolescents may help prepare for marriage and pregnancy