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Metamorphic P-T evolution of granulites in the central Ribeira Fold Belt, SE Brazil
Telmo Santos,José M. Munhá,Colombo C.G. Tassinari,Paulo E. Fonseca,Coriolano Dias Neto 한국지질과학협의회 2011 Geosciences Journal Vol.15 No.1
Pseudosections, geothermobarometric estimates and careful petrographic observations of gneissic migmatites and granulites from Neoproterozoic central Ribeira Fold Belt (SE Brazil) were performed in order to quantify the metamorphic P-T conditions during prograde and retrograde evolution of the Brasiliano Orogeny. Results establish a prograde metamorphic trajectory from amphibolite facies conditions to metamorphic peak (T = 850 ± 50 °C; P = 8 ± 1 kbar) that promoted widespread dehydration-melting of 30 to 40% of the gneisses and high-grade granitization. After the metamorphic peak, migmatites evolved with cooling and decompression to T 500 °C and P 5 kbar coupled with a_(H2O) increase, replacing the high-grade paragenesis plagioclase–quartz–K-feldspar–garnet by quartz–biotite–sillimanite–(muscovite). Cordierite absence, microtextural observations and P-T results constrain the migmatite metamorphic evolution in the pseudosections as a clockwise P-T path with retrograde cooling and decompression. High-temperature conditions further dehydrated the lower crust with biotite and amphibole-dehydration melting and granulite formation coupled with 10% melt generation. Granulites can thus be envisaged as middle to lower crust dehydrated restites. Granulites were slowly (nearly isobarically) cooled, followed by late exhumation/retrograde rapid decompression and cooling, reflecting a two step P-T path. This retrograde evolution, coupled with water influx, chemically reequilibrated the rocks from granulite to amphibolite/greenschist facies, promoting the replacement of the plagioclase–quartz–garnet–hypersthene peak assemblage by quartz–biotite–K-feldspar symplectites.
Internal modifications to reduce pollutant emissions from marine engines. A numerical approach
M.I. Lamas,C.G. Rodríguez,J.D. Rodríguez,J. Telmo 대한조선학회 2013 International Journal of Naval Architecture and Oc Vol.5 No.4
Taking into account the increasingly stringent legislation on emissions from marine engines, this work aims to analyze several internal engine modifications to reduce NOx (nitrogen oxides) and other pollutants. To this end,a numerical model was employed to simulate the operation cycle and characterize the exhaust gas composition. After a preliminary validation process was carried out using experimental data from a four-stroke, medium-speed marine engine,the numerical model was employed to study the influence of several internal modifications, such as water addition from 0 to 100% water to fuel ratios, exhaust gas recirculation from 0 to 100% EGR rates, modification of the overlap timing from 60 to 120°, modification of the intake valve closing from 510 to 570°, and modification of the cooling water temperature from 70 to 90 oC. NOx was reduced by nearly 100%. As expected, it was found that, by lowering the combustion temperature, there is a notable reduction in NOx, but an increase in CO (carbon monoxide), HC (hydrocarbons)and consumption.
Internal modifications to reduce pollutant emissions from marine engines. A numerical approach
Lamas, M.I.,Rodriguez, C.G.,Rodriguez, J.D.,Telmo, J. The Society of Naval Architects of Korea 2013 International Journal of Naval Architecture and Oc Vol.5 No.4
Taking into account the increasingly stringent legislation on emissions from marine engines, this work aims to analyze several internal engine modifications to reduce $NO_x$ (nitrogen oxides) and other pollutants. To this end, a numerical model was employed to simulate the operation cycle and characterize the exhaust gas composition. After a preliminary validation process was carried out using experimental data from a four-stroke, medium-speed marine engine, the numerical model was employed to study the influence of several internal modifications, such as water addition from 0 to 100% water to fuel ratios, exhaust gas recirculation from 0 to 100% EGR rates, modification of the overlap timing from 60 to $120^{\circ}$, modification of the intake valve closing from 510 to $570^{\circ}$, and modification of the cooling water temperature from 70 to $90^{\circ}C$. $NO_x$ was reduced by nearly 100%. As expected, it was found that, by lowering the combustion temperature, there is a notable reduction in $NO_x$, but an increase in CO (carbon monoxide), HC (hydrocarbons) and consumption.