A new analytical approach of the impact of jitter on continuous time delta sigma converters

International audienceThe performances of continuous time delta sigma converters are severely affected by clock jitter and no generic technique to predict the corresponding degradations is nowadays available. This paper presents a new analytical approach to quantify the power spectral density of jitter errors. This generic computational method can be applied to all kind of delta sigma converters. Furthermore, clock imperfections are described by means of phase noise spectrum, consequently all possible type of jitters can be taken into account. This paper also describes the temporal non ideal clock models that have been created to simulate the impact of jitter on delta sigma converters and validate the theoretical results

Experimental study of laminar and turbulent flame speed of a spherical flame in a fan-stirred closed vessel for hydrogen safety application

International audienceThe aim of this paper is to report new experimental results on the effect of turbulence on the propagation speed of hydrogen/air flames. To do so, a new experimental setup, called the spherical bomb, has been designed and built at CNRS-ICARE laboratory. With this new setup, the effect of a given and well-characterized turbulence intensity on the increase of hydrogen/air flame speed can be investigated. This new facility consists of a spherical vessel equipped (563 mm internal diameter) equipped with 8 motors which are linked to fans inside the bomb. Fan actuation induces the generation of a turbulent flow inside the vessel prior to any ignition. The spherical bomb is equipped with 4 quartz windows (200 mm optical diameter) that allow the use of a Particle Image Velocimetry diagnostic in order to characterize the turbulence level inside the bomb. The flame propagation was recorded using a high speed camera at 19,002 frames per second. These experiments were performed for lean to stoichiometric hydrogen/air mixtures (16–20% of H2 in air), initially at ambient temperature and pressure, and for a rotation speed from 1000 to 5000 rpm. The PIV measurements showed that a homogeneous and isotropic turbulence is created with a fluctuation speed that can reach 4 m/s at 5000 rpm. © 2016 Elsevier B.V

Effects of water sprays on flame propagation in hydrogen/air/steam mixtures

Different aspects of the interaction between droplets and flame propagation have been studied. First, flammability limits of H2/air/steam mixtures at 100 kPa for 3 temperatures between 358 and 383 K. the flammability domain was marginally modified by increasing the temperature. The mixtures were not flammable for H2O mol% ≥ 55. The presence of water mist in initially dry H2/air mixtures at 100 kPa and 298 K did not shift the lower flammability limit as long as the droplets density number was below a critical value. The slight shift in the limit was essentially due to the saturated water vapor pressure. The effect of dispersed large droplets (SMD = 200-250 μm) on laminar H2/air flames was also marginal except when the droplet velocity is of the same order of magnitude as the flame speed in the same direction. Non-flammable H2/air/steam mixtures at 358 K and 383 K were made explosive by aspersion with cold water spray. However, the pressure increase was limited when ignition occurred for mixtures close to the flammability limit. In this case, the burned gas bubble was rapidly dragged downward by the spray. The water mist effect on the deflagration of H2/air mixtures were studied for various equivalence ratios. With droplets diameter <10 μm, the violence of explosion was mitigated except for lean mixtures in the domain where the combustion was not complete. In this case, the turbulence generated by the spray was sufficient to increase the combustion rate. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved