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저온 디젤 연소에서 스월비에 따른 CO 배출 및 연비 변화
국상훈(Sanghoon Kook),Paul C. Miles(Paul C. Miles),Michael Bergin(Michael Bergin),배충식(Choongsik Bae) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_1
Engine-out CO emission was measured over a wide range of swirl ratios and injection timings on low-temperature diesel combustion regime in a small~bore single-cylinder diesel engine. Our previous work has shown that late-cycle mixing plays an important role even in so-called dilution-controlled low-temperature combustion systems. In this study. we employ multi-dimensional numerical simulation to characterize the flow structures and their impact on CO emissions. 65% exhaust gas recirculation is simulated with additional N₂ and CO₂, The CO emission shows optimal values at swirl ratio of 2.59 and limited ranges of injection timings. The numerical simulations show that the formed CO is trapped inside bowl at high swirl of 7.12. while CO is lifted out due to an enhanced reverse squish flow with a swirl ratio of 2.59. For a lower swirl ratio of 1.44, the existence of a single, large bulk flow structure limits the mixing process. The measured fuel conversion efficiency shows maximum value at low swirl ratio. The source of the maxima is clarified by the analysis of the work conversion efficiency, combustion efficiency, and heat transfer loss. Results show heat loss plays important role in determining the fuel conversion efficiency.
THE SOLAR NEBULA ON FIRE: A SOLUTION TO THE CARBON DEFICIT IN THE INNER SOLAR SYSTEM
Lee, Jeong-Eun,Bergin, Edwin A.,Nomura, Hideko IOP Publishing 2010 ASTROPHYSICAL JOURNAL LETTERS - Vol.710 No.1
<P>Despite a surface dominated by carbon-based life, the bulk composition of the Earth is dramatically carbon poor when compared to the material available at formation. Bulk carbon deficiency extends into the asteroid belt representing a fossil record of the conditions under which planets are born. The initial steps of planet formation involve the growth of primitive sub-micron silicate and carbon grains in the Solar Nebula. We present a solution wherein primordial carbon grains are preferentially destroyed by oxygen atoms ignited by heating due to stellar accret on at radii <5 AU. This solution can account for the bulk carbon deficiency in the Earth and meteorites, the compositional gradient within the asteroid belt, and for growing evidence for similar carbon deficiency in rocks surrounding other stars.</P>
Timescales for the evolution of oxygen isotope compositions in the solar nebula
Lyons, J.R.,Bergin, E.A.,Ciesla, F.J.,Davis, A.M.,Desch, S.J.,Hashizume, K.,Lee, J.E. Pergamon Press ; Elsevier Science Ltd 2009 Geochimica et cosmochimica acta Vol.73 No.17
We review two models for the origin of the calcium-, aluminum-rich inclusion (CAI) oxygen isotope mixing line in the solar nebula: (1) CO self-shielding, and (2) chemical mass-independent fractionation (MIF). We consider the timescales associated with formation of an isotopically anomalous water reservoir derived from CO self-shielding, and also the vertical and radial transport timescales of gas and solids in the nebula. The timescales for chemical MIF are very rapid. CO self-shielding models predict that the Sun has Δ<SUP>17</SUP>O<SUB>SMOW</SUB> ∼ -20%% (Clayton, 2002), and chemical mass-independent fractionation models predict Δ<SUP>17</SUP>O<SUB>SMOW</SUB> ∼0%%. Preliminary Genesis results have been reported by McKeegan et al. (McKeegan K. D., Coath C. D., Heber, V., Jarzebinski G., Kallio A. P., Kunihiro T., Mao P. H. and Burnett D. S. (2008b) The oxygen isotopic composition of captured solar wind: first results from the Genesis. EOS Trans. AGU 89(53), Fall Meet. Suppl., P42A-07 (abstr)) and yield a Δ<SUP>17</SUP>O<SUB>SMOW</SUB> of ∼ -25%%, consistent with a CO self-shielding scenario. Assuming that subsequent Genesis analyses support the preliminary results, it then remains to determine the relative contributions of CO self-shielding from the X-point, the surface of the solar nebula and the parent molecular cloud. The relative formation ages of chondritic components can be related to several timescales in the self-shielding theories. Most importantly the age difference of ∼1-3My between CAIs and chondrules is consistent with radial transport from the outer solar nebula (>10AU) to the meteorite-forming region, which supports both the nebular surface and parent cloud self-shielding scenarios. An elevated radiation field intensity is predicted by the surface shielding model, and yields substantial CO photolysis (∼50%) on timescales of 0.1-1My. An elevated radiation field is also consistent with the parent cloud model. The elevated radiation intensities may indicate solar nebula birth in a medium to large cluster, and may be consistent with the injection of <SUP>60</SUP>Fe from a nearby supernova and with the photoevaporative truncation of the solar nebula at KBO orbital distances (∼47AU). CO self-shielding is operative at the X-point even when H<SUB>2</SUB> absorption is included, but it is not yet clear whether the self-shielding signature can be imparted to silicates. A simple analysis of diffusion times shows that oxygen isotope exchange between <SUP>16</SUP>O-depleted nebular H<SUB>2</SUB>O and chondrules during chondrule formation events is rapid (∼minutes), but is also expected to be rapid for most components of CAIs, with the exception of spinel. This is consistent with the observation that spinel grains are often the most <SUP>16</SUP>O-rich component of CAIs, but is only broadly consistent with the greater degree of exchange in other CAI components. Preliminary disk model calculations of self-shielding by N<SUB>2</SUB> demonstrate that large δ<SUP>15</SUP>N enrichments (∼ +800%%) are possible in HCN formed by reaction of N atoms with organic radicals (e.g., CH<SUB>2</SUB>), which may account for <SUP>15</SUP>N-rich hotspots observed in lithic clasts in some carbonaceous chondrites and which lends support to the CO self-shielding model for oxygen isotopes.
Tobin, John J.,Bergin, Edwin A.,Hartmann, Lee,Lee, Jeong-Eun,Maret, Sé,bastien,Myers, Phillip C.,Looney, Leslie W.,Chiang, Hsin-Fang,Friesen, Rachel IOP Publishing 2013 The Astrophysical journal Vol.765 No.1
<P>We present a study on the spatial distribution of N2D+ and N2H+ in 13 protostellar systems. Eight of thirteen objects observed with the IRAM 30 m telescope show relative offsets between the peak N2D+ (J = 2 -> 1) and N2H+ (J = 1 -> 0) emission. We highlight the case of L1157 using interferometric observations from the Submillimeter Array and Plateau de Bure Interferometer of the N2D+ (J = 3 -> 2) and N2H+ (J = 1 -> 0) transitions, respectively. Depletion of N2D+ in L1157 is clearly observed inside a radius of similar to 2000 AU (7 '') and the N2H+ emission is resolved into two peaks at radii of similar to 1000 AU (3 ''.5), inside the depletion region of N2D+. Chemical models predict a depletion zone in N2D+ and N2H+ due to destruction of H2D+ at T similar to 20 K and the evaporation of CO off dust grains at the same temperature. However, the abundance offsets of 1000 AU between the two species are not reproduced by chemical models, including a model that follows the infall of the protostellar envelope. The average abundance ratios of N2D+ to N2H+ have been shown to decrease as protostars evolve by Emprechtinger et al., but this is the first time depletion zones of N2D+ have been spatially resolved. We suggest that the difference in depletion zone radii for N2H+ and N2D+ is caused by either the CO evaporation temperature being above 20 K or an H-2 ortho-to-para ratio gradient in the inner envelope.</P>
THE ORIGINAL ENVIRONMENT OF THE SOLAR SYSTEM INFERRED FROM THE OXYGEN ISOTOPE ANOMALIES
Lee, Jeong-Eun,Bergin, Edwin A.,Lyons, James R. The Korean Astronomical Society 2007 Journal of The Korean Astronomical Society Vol.40 No.4
The original environment of the solar system can be inferred by studying the oxygen isotope ratios in the Sun as well as in primitive meteorites and comets. The oxygen isotopic fractionation measured in primitive meteorites is mass-independent, which can be explained by the isotopic-selective photodissociation of CO. The isotopic-selective photodissociation model in a collapsing cloud by Lee et al. (2007) imply the birth of the Sun in a stellar cluster with an enhanced radiation field, which is consistent with the inferred presence of $^{60}Fe$.