The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
F Escudero - One of the best experts on this subject based on the ideXlab platform.
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effects of Oxygen Index on soot production and temperature in an ethylene inverse diffusion flame
Experimental Thermal and Fluid Science, 2016Co-Authors: R. Demarco, F Escudero, A Fuentes, J L Consalvi, J C Elicercortes, C FernandezpelloAbstract:Abstract An experimental study was conducted to investigate the effects of the Oxygen Index (OI) in an ethylene laminar inverse diffusion flame (IDF). The OI was varied from 21% to 37% and its influence was measured in terms of the flame height, soot volume fraction, soot temperature and radiant fraction. The stoichiometric flame height was measured by the spontaneous emission of CH ∗ radicals and was found to decrease when the OI increases. In contrast, the luminous flame height increases with OI because soot can still form and grow beyond the reaction zone. Radial profiles of soot volume fraction and soot temperature were obtained by means of a Modulated Absorption/Emission (MAE) technique. The line-of-sight intensities, integrated along the optical path and captured by ECCD camera at two wavelengths were inverted using deconvolution and regularization techniques in order to obtain radial profiles of soot volume fraction and temperature. The increase in OI enhances soot volume fraction due to higher temperatures and soot formation rates. Both the local and integrated soot quantities increase with OI. The radiant fraction of IDF increases with the OI in a similar way to the integrated soot volume fraction.
C Fernandezpello - One of the best experts on this subject based on the ideXlab platform.
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effects of Oxygen Index on soot production and temperature in an ethylene inverse diffusion flame
Experimental Thermal and Fluid Science, 2016Co-Authors: R. Demarco, F Escudero, A Fuentes, J L Consalvi, J C Elicercortes, C FernandezpelloAbstract:Abstract An experimental study was conducted to investigate the effects of the Oxygen Index (OI) in an ethylene laminar inverse diffusion flame (IDF). The OI was varied from 21% to 37% and its influence was measured in terms of the flame height, soot volume fraction, soot temperature and radiant fraction. The stoichiometric flame height was measured by the spontaneous emission of CH ∗ radicals and was found to decrease when the OI increases. In contrast, the luminous flame height increases with OI because soot can still form and grow beyond the reaction zone. Radial profiles of soot volume fraction and soot temperature were obtained by means of a Modulated Absorption/Emission (MAE) technique. The line-of-sight intensities, integrated along the optical path and captured by ECCD camera at two wavelengths were inverted using deconvolution and regularization techniques in order to obtain radial profiles of soot volume fraction and temperature. The increase in OI enhances soot volume fraction due to higher temperatures and soot formation rates. Both the local and integrated soot quantities increase with OI. The radiant fraction of IDF increases with the OI in a similar way to the integrated soot volume fraction.
Walter Wilhelm Focke - One of the best experts on this subject based on the ideXlab platform.
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effect of hydrated fillers and red phosphorus on the limiting Oxygen Index of poly ethylene co vinyl actate poly vinyl butyral and low density polyethylene poly ethylene co vinyl alcohol blends
Journal of Vinyl & Additive Technology, 2008Co-Authors: Mara Burns, Berndt Kretzschmar, Udo Wagenknecht, Walter Wilhelm FockeAbstract:The limiting Oxygen Index (LOI) values of EVA-PVB and low density polyethylene (LDPE)-poly(ethylene-co-vinyl alcohol) (EVOH) polymer blends containing hydrated filler-type flame retardants and red phosphorus were measured. When used as the sole flame retardant, magnesium hydroxide [Mg(OH)2] and alumina trihydrate (ATH) performed best in EVA and PVB, respectively. Magnesium hydroxide addition had a limited effect on the LOI of plasticized PVB, and addition of red phosphorus made little difference. This result is attributed to a mismatch between the decomposition temperature of Mg(OH)2 and the temperature at which the PVB plasticizer vaporizes. Otherwise, low-level addition of red phosphorus significantly improved LOI values. The presence of hydroxyl groups on the polymer backbone had a beneficial effect with respect to LOI values in ATH-filled blends. An LOI value of 30 was achieved in EVOH with as little as 32% of ATH and 3% of red phosphorus. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers
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Effect of hydrated fillers and red phosphorus on the limiting Oxygen Index of poly(ethylene‐co‐vinyl actate)‐poly(vinyl butyral) and low density polyethylene‐poly(ethylene‐co‐vinyl alcohol) blends
Journal of Vinyl & Additive Technology, 2008Co-Authors: Mara Burns, Berndt Kretzschmar, Udo Wagenknecht, Walter Wilhelm FockeAbstract:The limiting Oxygen Index (LOI) values of EVA-PVB and low density polyethylene (LDPE)-poly(ethylene-co-vinyl alcohol) (EVOH) polymer blends containing hydrated filler-type flame retardants and red phosphorus were measured. When used as the sole flame retardant, magnesium hydroxide [Mg(OH)2] and alumina trihydrate (ATH) performed best in EVA and PVB, respectively. Magnesium hydroxide addition had a limited effect on the LOI of plasticized PVB, and addition of red phosphorus made little difference. This result is attributed to a mismatch between the decomposition temperature of Mg(OH)2 and the temperature at which the PVB plasticizer vaporizes. Otherwise, low-level addition of red phosphorus significantly improved LOI values. The presence of hydroxyl groups on the polymer backbone had a beneficial effect with respect to LOI values in ATH-filled blends. An LOI value of 30 was achieved in EVOH with as little as 32% of ATH and 3% of red phosphorus. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers
A Fuentes - One of the best experts on this subject based on the ideXlab platform.
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Oxygen Index effect on the structure of a laminar boundary layer diffusion flame in a reduced gravity environment
Proceedings of the Combustion Institute, 2016Co-Authors: Jorge E. Contreras, J L Consalvi, A FuentesAbstract:Forty-five experimental flames established over a flat plate were analyzed. A diffusion flame generated from a porous ethylene burner discharging into a parallel oxidizer flow provided a laminar boundary layer. All experiments were conducted in parabolic flights that provide twenty-two seconds of microgravity conditions. Soot production was tracked using the laser-induced incandescence technique, while the spontaneous emission of OH* was used in order to identify the reaction zone. The study was focused on the influence of the Oxygen Index, the oxidizer flow velocity, and the fuel injection velocity on the flame geometry, characterized by the stand-off distance, flame length and the soot production. A dimensionless procedure of transport equations and a scaling analysis were carried out in order to interpret the experimental results and to understand the flame extinction process at the trailing edge. The stand-off distance is found to exhibit three regimes as the distance from the burner leading edge increases: a convection-controlled regime close to the burner leading edge, followed by a diffusion-controlled regime and then a third regime at the burner trailing edge due to the appearance of tridimensional effects. Experimental results shows that the flame length decrease with the Oxygen Index and increases with the fuel injection velocity and the oxidizer velocity. This latter evolution is opposite to that observed in ‘closed-tip’ diffusion flame, showing that the flame length is controlled by radiant quenching at the flame trailing edge. Concerning soot production, it is observed that the characteristic length scale of soot volume fraction evolves in an opposite manner with the flame length, showing that this latter is not relevant to define the soot residence time. A residence time based on the integrated soot volume fraction and on the oxidizer flow was found appropriate to study soot formation processes.
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The Oxygen Index on Soot Production in Propane Diffusion Flames
Combustion Science and Technology, 2014Co-Authors: R Henriquez, J L Consalvi, R. Demarco, A FuentesAbstract:An experimental study of the effect of Oxygen Index (OI) on soot formation in laminar coflow propane diffusion flames is presented. The OI was defined as the Oxygen volumetric concentration in the oxidizer flow, O2/(O2+N2), which was varied from 21% to 37%. The influence of the OI was quantified by means of three variables: the flame height, the soot volume fraction, and the vertical distribution of radiative heat flux. The flame height was based on CH* spontaneous emission and found to vary inversely with the OI, following the classical theory of Roper. As the OI increases, the rates of soot growth and soot oxidation are enhanced, and the maximum soot volume fraction and the peak of integrated soot volume fraction also increase. Moreover, the evolution of the peak of radiative heat flux and the maximum soot volume fraction are found to follow the same evolution with the OI.
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experimental and numerical study of the effects of the Oxygen Index on the radiation characteristics of laminar coflow diffusion flames
Combustion and Flame, 2013Co-Authors: A Fuentes, R Henriquez, Fatiha Nmira, J L ConsalviAbstract:Abstract The Oxygen concentration in the oxidizer stream (O2 + N2) of laminar coflow ethylene diffusion flames is varied from 17% to 35% in order to study its influence on the flame height, the soot formation/oxidation processes, the smoke point characteristics, and the vertical distributions of radiative flux at a distance of 6.85 cm from the flame axis. Measured values for all the investigated parameters are compared with the predictions provided by a numerical model based on a two-equation semiempirical acetylene-based soot model and on the statistical narrow-band correlated-k model to compute thermal radiation. Predictions are in overall reasonable agreement with the experiments for Oxygen indices in the range 19–35%, whereas all the investigated parameters are significantly underestimated for an Oxygen Index of 17%. Measured flame heights based on CH∗ emission below, at, or slightly above the smoke point, as well as predicted stoichiometric flame heights, are found to be proportional to ζ = V ˙ f [ D ∞ ln ( 1 + 1 / S ) ] - 1 ( T ∞ / T ad ) 0.67 , where V ˙ f , D∞, S, and Tad are the volumetric flow rate of ethylene, the diffusion coefficient at ambient temperature, the stoichiometric molecular air-to-fuel ratio, and the adiabatic flame temperature. Soot formation processes are found to increase with the Oxygen Index, leading to higher values of the maximum soot volume fraction and the peak integrated soot volume fraction. In addition, the latter is reached at a nondimensional height (normalized by ζ of approximately 0.05, regardless of the Oxygen Index within the investigated range. Two regimes are evidenced: The first regime, occurring for Oxygen indices lower than 25%, is dominated by soot oxidation and is characterized by an enhancement in both the maximum soot volume fraction and the fuel flow rate at the smoke point with the Oxygen Index. The second regime, occurring for Oxygen indices higher than 25%, is dominated by soot formation; the rate of increase in the maximum soot volume fraction with the Oxygen concentration is lower than in the first regime, whereas the fuel flow rate at the smoke point decreases. Finally, the peak of radiative flux increases with the Oxygen Index, but its rate of increase is also found to be considerably reduced for Oxygen indices greater than 25%.
Peter J Kirkpatrick - One of the best experts on this subject based on the ideXlab platform.
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tissue Oxygen Index thresholds for cerebral ischemia using near infrared spectroscopy
Stroke, 2006Co-Authors: Pippa G Alrawi, Peter J KirkpatrickAbstract:Background and Purpose— To date, the clinical application of near infrared spectroscopy in the adult brain has been limited. The NIRO 300 (Hamamatsu Photonics) provides a continuous measurement of tissue Oxygen Index (TOI) using spatially resolved spectroscopy. Although TOI reflects cerebral Oxygenation to a high degree of sensitivity and specificity, to become a useful clinical tool, thresholds for cerebral ischemia need to be defined. This study has attempted to identify a quantifiable TOI threshold for ischemia in the adult brain. Methods— One hundred sixty-seven patients undergoing carotid endarterectomy were studied. The NIRO 300 was incorporated into an established multimodal monitoring system enabling observations of cerebral hemodynamic changes under highly controlled conditions. Changes in TOI (%ΔTOI) on clamping the internal carotid artery were compared with intracranial blood flow (middle cerebral artery flow velocity) and cerebral function monitoring to identify and quantify periods of cerebra...
