Interaction soot-SO2. Experimental and kinetic analysis

This study aims to evaluate the capability of SO2 to interact with soot and to determine the kinetics of this reaction under conditions of interest for combustion. The conditions of the soot reactivity experiments were: 1% SO2 with nitrogen to balance, around 10 mg of soot, and different reaction temperatures for each run: 1275, 1325, 1375, 1425, and 1475 K. Results demonstrate that SO2 does interact with soot. The evaluation of the soot reactivity has been based on the calculation of the time for the complete conversion of carbon through the employment of the Shrinking Core Model equations for decreasing size particle with chemical reaction control. The reactivity of soot with SO2 increased by a factor of about 3 when increasing the reaction temperature of the test from 1275 K to 1475 K. Kinetics in terms of Arrhenius parameters showed that the activation energy of the interaction of soot with SO2 was around 82 kJ/mol

Analysis of the regional pattern of sea level change due to ocean dynamics and density changes for 1993-2099 in observations and CMIP5 AOGCMs

Predictions of twenty-first century sea level change show strong regional variation. Regional sea level change observed by satellite altimetry since 1993 is also not spatially homogenous. By comparison with historical and pre-industrial control simulations using the atmosphere–ocean general circulation models (AOGCMs) of the CMIP5 project, we conclude that the observed pattern is generally dominated by unforced (internal generated) variability, although some regions, especially in the Southern Ocean, may already show an externally forced response. Simulated unforced variability cannot explain the observed trends in the tropical Pacific, but we suggest that this is due to inadequate simulation of variability by CMIP5 AOGCMs, rather than evidence of anthropogenic change. We apply the method of pattern scaling to projections of sea level change and show that it gives accurate estimates of future local sea level change in response to anthropogenic forcing as simulated by the AOGCMs under RCP scenarios, implying that the pattern will remain stable in future decades. We note, however, that use of a single integration to evaluate the performance of the pattern-scaling method tends to exaggerate its accuracy. We find that ocean volume mean temperature is generally a better predictor than global mean surface temperature of the magnitude of sea level change, and that the pattern is very similar under the different RCPs for a given model. We determine that the forced signal will be detectable above the noise of unforced internal variability within the next decade globally and may already be detectable in the tropical Atlantic

Influence of the temperature and 2,5-dimethylfuran concentration on its sooting tendency

The sooting tendency of 2,5-dimethylfuran (2,5-DMF), as a proposed fuel or fuel additive, has been studied in a flow reactor at different reaction temperatures (975, 1075, 1175, 1275, 1375, and 1475 K) and inlet 2,5-DMF concentrations (5000, 7500, and 15,000 ppm) under pyrolytic conditions. The quantification of soot and light gases has been done. Additionally, the experimental results of the light gases have been simulated with a detailed gas-phase chemical kinetic model. The experimental results indicate that the temperature has a great influence on both the soot and gas yields, as well as on the concentration of the light gases of pyrolysis. The inlet 2,5-DMF con- centration influences the soot yield, whereas no significant effect is observed on the gas yield

Global, Diffuse, Direct, and Ultraviolet Solar Irradiance Recorded in Malta and Atmospheric Component Influences

AbstractGlobal and diffuse shortwave (SW) and global erythemal (UVER) irradiances were measured in Malta, in the middle of Mediterranean Sea. The effect of solar zenith angle on these irradiances is studied using the measurements and simulations developed with a radiative transfer model. The role of ozone, scattering by gases, and aerosols is analyzed. Results show that ozone and Rayleigh scattering are the main drivers responsible for the behavior of UVER variations with SZA. In the case of global and diffuse irradiance, the role of aerosols is the principal determinant

High pressure oxidation of dimethoxymethane

The oxidation of dimethoxymethane (DMM) has been studied under a wide range of temperatures (373-1073 K), pressures (20-60 bar) and air excess ratios (¿ = 0.7, 1 and 20), from both experimental and modeling points of view. Experimental results have been interpreted and analyzed in terms of a detailed gas-phase chemical kinetic mechanism for describing the DMM oxidation. The results show that the DMM oxidation regime for 20, 40 and 60 bar is very similar for both reducing and stoichiometric conditions. For oxidizing conditions, a plateau in the DMM, CO and CO2 concentration profiles as a function of the temperature can be observed. This zone seems to be associated with the peroxy intermediate, CH3OCH2O2, whose formation and consumption reactions appear to be important for the description of DMM conversion under high pressure and high oxygen concentration conditions

Dimethoxymethane oxidation in a flow reactor

The simultaneous reduction of NOx and soot emissions from diesel engines is a major research subject and a challenge in today’s world. One prospective solution involves diesel fuel reformulation by addition of oxygenated compounds, such as dimethoxymethane (DMM). In this context, different DMM oxidation experiments have been carried out in an atmospheric pressure gas-phase installation, in the 573–1373 K temperature range, from pyrolysis to fuel-lean conditions. The results obtained have been interpreted by means of a detailed gas-phase chemical kinetic mechanism. Results indicate that the initial oxygen concentration slightly influences the consumption of DMM. However, certain effects can be observed in the profiles of the main products (CH4, CH3OH, CH3OCHO, CO, CO2, C2H2, C2H4, and C2H6). Acetylene, an important soot precursor, is only formed under pyrolysis and reducing conditions. In general, a good agreement between experimental and modeling data was observed

Study of the conversion of CH4/H2S mixtures at different pressures

Due to the different scenarios where sour gas is present, its composition can be different and, therefore, it can be exploited through different processes, being combustion one of them. In this context, this work deals with the oxidation of CH4 and H2S at different pressures and under a wide variety of conditions. The oxidation has been evaluated experimentally in two different flow reactor set-ups, one working at atmospheric pressure and another one operating from atmospheric to high pressures (40 bar). Different CH4/H2S mixtures have been tested, together with different oxygen concentrations and in the temperature range of 500–1400 K. The experimental results obtained show that the oxidation of the CH4/H2S mixtures is shifted to lower temperatures as pressure increases, obtaining the same trends at atmospheric pressure in both experimental set-ups. H2S oxidation occurs prior to CH4 oxidation at all conditions, providing radicals to the system that promote CH4 oxidation to lower temperatures (compared to neat CH4 oxidation). This effect is more relevant as pressure increases. H2S oxidation is inhibited by CH4 at atmospheric pressure, being more noticeable when the CH4/H2S ratio is higher. At higher pressures, the H2S conversion occurs similarly in the absence or presence of CH4. The experimental results have been modeled with an updated kinetic model from previous works from the literature, which, in general, matches well the experimental trends, while some discrepancies between experimental and modeling results at atmospheric pressure and 40 bar are found in the conversion of H2S and CH4

Oxidación de compuestos orgánicos oxigenados usados como combustibles y su efecto sobre las emisiones de contaminantes

El consumo de combustibles fósiles, derivado del uso de vehículos con motores diésel, tiene un impacto significativo sobre el cambio climático y las emisiones de contaminantes. Las emisiones más importantes son la materia particulada (hollín) y los óxidos de nitrógeno. La preocupación medioambiental y la legislación cada vez más restrictiva, hacen necesario el desarrollo de motores más eficientes y combustibles más limpios. Entre estos últimos destacan los combustibles oxigenados derivados de biomasa, como algunos alcoholes, éteres y ésteres. Numerosos estudios demuestran que usar compuestos oxigenados como combustibles, bien como combustibles alternativos o bien como aditivos al gasóleo, puede reducir la formación de hollín en los motores diésel sin efectos significativos sobre las emisiones de NOx. Sin embargo, se desconoce si la disminución de partículas se debe a la reducción de la formación de hollín o a la oxidación del mismo. En ocasiones, la combustión de estos compuestos puede dar lugar a la formación de contaminantes tóxicos, como por ejemplo aldehídos. En este contexto y con el objetivo de conocer el comportamiento de algunos compuestos oxigenados con distinto contenido en oxígeno y distinto grupo funcional (etanol, dimetoximetano, dimetilcarbonato), se lleva a cabo un estudio tanto experimental como de modelado de la oxidación de estos compuestos a distintas presiones y temperaturas, en distintos regímenes de oxidación y en presencia y ausencia de NO. Estos estudios proporcionarán información sobre la oxidación y los caminos de reacción de los compuestos considerados, con el objeto de minimizar la formación de hollín y otros contaminantes