11 results found
Garcia Gonzalez C, Ueda M, Spikes H, et al., 2021, Temperature dependence of Molybdenum dialkyl dithiocarbamate (MoDTC) tribofilms via time-resolved Raman spectroscopy, Scientific Reports, Vol: 11, Pages: 3621-3621, ISSN: 2045-2322
Molybdenum dialkyl dithiocarbamate (MoDTC) is a friction reducing additive commonly used in lubricants. MoDTC works by forming a low-friction molybdenum disulphide (MoS<sub>2</sub>) film (tribofilm) on rubbed surfaces. MoDTC-induced MoS<sub>2</sub> tribofilms have been studied extensively ex-situ; however, there is no consensus on the chemical mechanism of its formation process. By combining Raman spectroscopy with a tribometer, effects of temperature and shear stress on MoS<sub>2</sub> tribofilm formation in steel-steel contacts were examined. Time-resolved Raman spectra of the tribofilm were acquired, together with the instantaneous friction coefficient. The tribofilm is constantly being formed and removed mechanically during rubbing. Increasing shear stress promotes MoS<sub>2</sub> formation. The nature of the tribofilm is temperature-dependent, with high-temperature tribofilms giving a higher friction than lower temperature films. Below a critical temperature T<sub>c</sub>, a small amount of MoS<sub>2</sub> gives significant friction reduction. Above T<sub>c,</sub> a patchy film with more MoS<sub>2</sub>, together with a substantial amount of amorphous carbon attributed to base oil degradation, forms. The composition of this tribofilm evolves during rubbing and a temporal correlation is found between carbon signal intensity and friction. Our results highlight the mechanochemical nature of tribofilm formation process and the role of oil degradation in the effectiveness of friction modifier MoDTC.
Liu A, Garcia CE, Sewerin F, et al., 2020, Population balance modelling and laser diagnostic validation of soot particle evolution in laminar ethylene diffusion flames, Combustion and Flame, Vol: 221, Pages: 384-400, ISSN: 0010-2180
Laminar diffusion flames present an elementary configuration for investigating soot formation and validating kinetic models before these are transferred to turbulent combustors. In the present article, we present a joint experimental and modelling investigation of soot formation in a laminar co-flow burner. The diffusion flames are analysed with the aid of laser diagnostic techniques, including elastic light scattering (ELS), planar laser-induced fluorescence of OH (OH-PLIF) and line-of-sight attenuation (LOSA), to measure the spatial distribution of soot, gas phase species and the line-of-sight integrated soot volume fraction (ISVF), respectively. The experimental dataset is supplemented by location-specific TEM images of thermophoretically sampled soot particles. The simulation of the sooting flames is carried out with a recently developed discretisation method for the population balance equation (Liu and Rigopoulos, 2019, Combust. Flame 205, 506-521) that accomplishes an accurate prediction of the particle size distribution, coupled with an in-house CFD code. By minimising numerical errors, we ensure that the discrepancies on the modelling side are mainly due to kinetics and are able to carry out an investigation of alternative models. We include a complete set of soot kinetics for PAH-based nucleation and condensation, HACA-based surface growth and oxidation as well as size-dependent aggregation, and consider three different gas phase reaction mechanisms (ABF, BBP and KM2). Based on predictions of the gas phase composition and particle size distribution of soot, modelled counterparts of the laser diagnostic signals are computed and compared with the experimental measurements. The approach of directly predicting signals circumvents the difficulties of explicitly representing the OH concentration in terms of the measured OH-PLIF data and avoids using ‘hybrid’ modelled and measured values to approximate the OH concentration. Moreover, the LOSA signal is
Neuber G, Kronenburg A, Stein OT, et al., 2020, Sparse-Lagrangian PDF Modelling of Silica Synthesis from Silane Jets in Vitiated Co-flows with Varying Inflow Conditions, FLOW TURBULENCE AND COMBUSTION, Vol: 106, Pages: 1167-1194, ISSN: 1386-6184
Neuber G, Garcia CE, Kronenburg A, et al., 2019, Joint experimental and numerical study of silica particulate synthesis in a turbulent reacting jet, PROCEEDINGS OF THE COMBUSTION INSTITUTE, Vol: 37, Pages: 1213-1220, ISSN: 1540-7489
Garcia Gonzalez CE, Sewerin F, Liu A, et al., 2017, Predicting and measuring soot formation and particle size distributions in a laminar diffusion flame, European Combustion Meeting 2017, Publisher: The Combustion Institute
We present the results from a joint experimental and modelling investigation of a laminar diffusion flame on a Santoroburner. The experimental techniques include laser diagnostic measurements and extractive thermophoretic sampling.In order to predict the spatial evolution of the primary soot particle size distribution throughout the flame, we employa detailed population balance model. From the model predictions, “modelled” laser diagnostic signals are obtainedwhich we directly compare with the experimental laser diagnostic images. This allows us to assess the validity ofthe model with reduced uncertainty by reducing the set of assumptions commonly made when recovering physicalmagnitudes from experimental signals.
Güemes A, García CE, López del Cerro F, 2011, Comportamiento a fuego de laminados carbono-epoxy, Girona, IX Congreso Nacional de Materiales Compuestos
García González CE, Güemes Gordo JA, 2011, Determinación del coeficiente de expansión térmica en materiales compuestos utilizando sensores de fibra óptica, Girona, IX Congreso Nacional de Materiales Compuestos
García CE, Güemes JA, Fernández A, 2011, High Sampling Rate Fiber-optic Extensometry for Ultrasonic Wave Detection, 8th International Workshop on Structural Health Monitoring, Publisher: DEStech Publications, Inc, Pages: 1620-1627
Güemes A, Garcia-Gonzalez CE, Gonzalez-Requena I, et al., 2011, Monitoring the degradation by fire of composite laminates by embedded FBG sensors, 8th International Workshop on Structural Health Monitoring, Pages: 525-530
García González CE, Güemes A, 2010, Compensation for Temperature and Static Strain in Lamb Wave Propagation, Fifth European Workshop on Structural Health Monitoring, Publisher: DEStech Publications, Inc, Pages: 736-741
Trex Enterprises Corporation has developed a full body passive millimeter-wave security screening imager. The system images naturally occurring W-band blackbody radiation, which penetrates most types of clothing. When operated indoors, the primary mechanism for image formation is the contrast between body heat radiation and the room temperature radiation emitted or reflected by concealed objects that are opaque at millimeter-wave wavelengths. Trex Enterprises has previously demonstrated that an imager noise level of 0.25 to 0.5 K is necessary to detect and image small concealed threats indoors. Achieving this noise level in a head-to-toe image required image collection times of 24 seconds using the previous imager design. This paper first discusses the measurement of the noise temperature of the MMW detectors employed. The paper then explores reducing the image collection times through a new front-end amplifier design and the addition of more imaging units. By changing the orientation and direction of travel of the imaging units, the new design is able to employ more detectors and collect imagery from a subject’s front and sides. The combination of lower noise amplifiers and a new scanning architecture results in an imager appropriate for high throughput security screening scenarios. Imagery from the new configuration is also presented.
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