Laser ignition and flame characteristics of pulsed methane jets in homogeneous isotropic turbulence without mean flow

The influence of turbulence on the minimum ignition energy (MIE) and ignited flame characteristics is investigated for pulsed methane diffusion jets ignited by laser-induced plasma. The methane jet is injected in a volume of homogeneous and isotropic air turbulence without mean flow, with the level of turbulence being controlled independently. The study is carried out for a range of fuel jet (Rejet) Reynolds number, namely 1000, 2000, and 3000, and a range of turbulent (Reλ) Reynolds number, namely 0–207. The results show that the position of the maximum intensity of flame emission was randomly scattered due to the fact that the ignited flame is deflected from the nozzle axis by the turbulent velocity fluctuations. The effect is more profound at higher Rejet. The value of the MIE, determined according to 50% ignitibility of mixture, increases by a factor of 2 for an increase of Reλ from 0 to 207 and by a factor of 5 for an increase of Rejet from 1000 to 3000. Two trends are observed on MIE with Reλ. For low Reλ, MIE is independent of Reλ. Past a critical value of Reλ, MIE increases as a linear function of Reλ. This transition occurs at critical values of Reλ,c = 158, 197 and 202 for Rejet= 1000, 2000 and 3000, respectively. The mean value of MIE for ignition before and after transition is a linear function of Rejet. The difference between the mean value of MIE before transition and after transition is around 5 mJ for all considered Rejet

Laser-induced spark ignition of pulsed methane jets in homogeneous and isotropic turbulence without mean flow

The influence of surrounding air turbulence on laser-induced spark ignition of a pulsed methane jet was investigated in an air environment where the turbulence is homogeneous and isotropic without mean flow. The methane jet Reynolds number (Rejet) was set at 160, while the surrounding air turbulent Reynolds number was varied in the range of Reλ = 0 - 220. Minimum Ignition Energy (MIE) was evaluated at four ignition locations by measuring the ignition probability and correlated with the local equivalence ratio (Φ) measured at three ignition locations using Laserinduced Breakdown Spectroscopy (LIBS) technique. The relationship between MIE and the local equivalence ratio obtained in quiescent air environment was similar to that reported in premixed methane/air mixtures. The impact of the surrounding air turbulence on MIE varies for different ignition locations, because the turbulence not only affects the mixing process and thereby the local equivalence ratio, but also increases the heat loss from the ignition point. The MIE decreased with increasing level of air turbulence, when the effect of local mixture composition becoming closer to stoichiometry was more significant than the adverse effect of increasing heat loss. Otherwise, the MIE increased with the level of air turbulence due to the dominance of the enhanced heat loss. The rate of increase in MIE became higher, if the local mixture composition moved further away from stoichiometry when turbulence was present. Successful ignition was also observed at locations where the mixture is relatively difficult to be ignited (Φmean = 2.38 and Φmean = 0.02), which may be attributed to the finite size of the plasma

Effect of liquid viscosity on the aerodynamic breakup of non-spherical droplets

This paper studies the effect of liquid viscosity on the atomisation regimes of initially spherical and non-sphericaldroplets and also kinematic characteristics of non-spherical droplets. The droplets consisted of water-glycerolsolutions with viscosities ranging from 6.3 to 697 mPa s, and the initial aspect ratio was 1<AR<2. The range of Wenumber was from 10 to 200 and of the Oh number from 0.01 to approximately 4. The experimental findings showedthat the equivalent Weeq and Oheq numbers, proposed in previous work [1] for water droplets, are also applicableto spherical and non-spherical droplets in the range of Oh numbers of this study in order to classify the breakupregimes on the existing morphological charts. The kinematic characteristics of the centre of mass for droplets withAR=1.2 are evaluated and the role of viscosity examined in the no breakup and bag-stamen regimes

Towards S-NAMO: Socially-aware Navigation Among Movable Obstacles

International audienc

Navigating paediatric virology through the COVID‑19 era (Review).

The present review article presents the key messages of the 8th Workshop on Paediatric Virology organised virtually by the Institute of Paediatric Virology based on the island of Euboea in Greece. The major topics covered during the workshop were the following: i) New advances in antiviral agents and vaccines against cytomegalovirus; ii) hantavirus nephropathy in children; iii) human rhinovirus infections in children requiring paediatric intensive care; iv) complications and management of human adenovirus infections; v) challenges of post‑coronavirus disease 2019 (COVID‑19) syndrome in children and adolescents; and vi) foetal magnetic resonance imaging in viral infections involving the central nervous system. The COVID‑19 era requires a more intensive, strategic, global scientific effort in the clinic and in the laboratory, focusing on the diagnosis, management and prevention of viral infections in neonates and children

Measuring sub-mm structural displacements using QDaedalus: a digital clip-on measuring system developed for total stations

The monitoring of rigid structures of modal frequencies greater than 5 Hz and sub-mm displacement is mainly based so far on relative quantities from accelerometers, strain gauges etc. Additionally geodetic techniques such as GPS and Robotic Total Stations (RTS) are constrained by their low accuracy (few mm) and their low sampling rates. In this study the application of QDaedalus is presented, which constitutes a measuring system developed at the Geodesy and Geodynamics Lab, ETH Zurich and consists of a small CCD camera and Total Station, for the monitoring of the oscillations of a rigid structure. In collaboration with the Institute of Structural Engineering of ETH Zurich and EMPA, the QDaedalus system was used for monitoring of the sub-mm displacement of a rigid prototype beam and the estimation of its modal frequencies up to 30 Hz. The results of the QDaedalus data analysis were compared to those of accelerometers and proved to hold sufficient accuracy and suitably supplementing the existing monitoring techniques

Evaluation of natural and tracer fluorescent emission methods for droplet size measurements in a diesel spray

The final publication is available at Springer via http://dx.doi.org/10.1007/s12239-012-0070-zSpray sizing that records fluorescent emission and scattered light has been widely applied to spray diagnostics over the last two decades. Different experimental strategies have been developed, but comparing the different solutions offered has remained of interest to experimentalists. In this work, a comparison of two fluorescence strategies for measuring droplet size in the liquid phase of a last-generation DI diesel spray is conducted. The natural fluorescent emission of a commercial diesel fuel and the fluorescence emitted by a tracer (Rhodamine B) are compared using theoretical and experimental approaches. The LIF/Mie ratio commonly called Planar Droplet Sizing (PDS) technique is applied in two different ways to elucidate the possible advantages of using a fluorescent dopant. The sprays were injected under non-evaporative conditions into a constant pressure vessel that simulates densities present at the moment of injection in currently used passenger car diesel engines. Characterization of the signal properties was performed by measuring the absorption coefficient, fluorescence emission spectrum, quantum yield and lifetime of both configurations. The scattered light and fluorescence intensities were calculated to verify the dependencies of the droplet surface and volume. When applying the two techniques to quantify droplet size in dense diesel sprays, the results show that signal weakness and lack of control over the properties of natural fluorescence produce distortion in the shape of the spray and cause measurements to be unreliable. © 2012 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.This research has been funded in the frame of the project PROFUEL reference TRA2011-26293 from Ministerio de Ciencia e Innovacion. 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