The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Magnus Sjoberg - One of the best experts on this subject based on the ideXlab platform.
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High-speed imaging of spray-guided DISI engine Combustion with near-TDC injection of E85 for ultra-low NO and soot
Proceedings of the Combustion Institute, 2013Co-Authors: Magnus Sjoberg, David L. ReussAbstract:Abstract Using E85 fuel, this work demonstrates the use of near-TDC injection and highly turbulent Combustion to achieve ultra-low emissions of NO and soot from a DISI engine with a spray-guided, stratified-charge Combustion system. Despite the low NO emissions, both Combustion efficiency and stability remain relatively high. One striking aspect of engine operation with near-TDC injection is the need to initiate the spark prior to fuel injection. Using E85 fuel, such early spark timing leads to stable ignition. For gasoline, however, such early spark timing leads to misfire under the conditions studied, thereby prEventing the use of near-TDC fuel injection to achieve low exhaust emissions of NO. High-speed imaging shows that the early spark timing for E85 allows the spark plasma to develop prior to interacting with one of the fuel jets adjacent to the spark plug, and this contributes to misfire-free operation. The spark-spray interactions generate a very fast spread of either weak or thin flames throughout a large fraction of the piston bowl prior to the main Combustion Event. The short delay between the near-TDC fuel injection and the Combustion Event are believed to enhance the mixing rates during the Combustion compared to the use of earlier injection, which may contribute to the low NO emissions.
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on the potential of ethanol fuel stratification to extend the high load limit in stratified charge compression ignition engines
Fuel, 2012Co-Authors: Alex Krisman, Evatt R Hawkes, Sanghoon Kook, Magnus SjobergAbstract:Abstract A multi-zone model is applied to investigate the potential of ethanol fuel stratification to reduce the problematic high rates of pressure-rise that can occur in homogeneous-charge compression-ignition (HCCI) engines. The model is first validated against published experimental data. Novel techniques for inducing in-cylinder stratification are then identified, that involve exploiting the high latent heat of vaporisation of ethanol to induce thermal stratification. This stratification introduces a range of induction times into the cylinder, leading to a staged Combustion Event. The impact of water content in the fuel is also investigated. This study finds that ethanol fuel stratification has the potential to provide significant improvements relative to the nominally homogeneous operating condition. Significant reductions in pressure-rise rates are attainable, providing the potential for extending the possible operating regime to higher loads. The trade-off between reduced pressure-rise rate and increased NO emissions is discussed. Mixing the fuel with quantities of water, which has cost and overall energy efficiency advantages, is found to significantly reduce the NO production and slightly accentuate the reductions of pressure-rise rate.
David L. Reuss - One of the best experts on this subject based on the ideXlab platform.
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an experimental and simulation study of early flame development in a homogeneous charge spark ignition engine
Oil & Gas Science and Technology-revue De L Institut Francais Du Petrole, 2017Co-Authors: Yajuvendra Shekhawa, David L. Reuss, D C Haworth, Alessandro Dadamo, Fabio Erni, Stefano Fontanesi, Philipp Schiffma, Volke SickAbstract:An integrated experimental and Large-Eddy Simulation (LES) study is presented for homogeneous premixed Combustion in a spark-ignition engine. The engine is a single-cylinder two-valve optical research engine with transparent liner and piston: the Transparent Combustion Chamber (TCC) engine. This is a relatively simple, open engine configuration that can be used for LES model development and validation by other research groups. Pressure-based Combustion analysis, optical diagnostics and LES have been combined to generate new physical insight into the early stages of Combustion. The emphasis has been on developing strategies for making quantitative comparisons between high-speed/high-resolution optical diagnostics and LES using common metrics for both the experiments and the simulations, and focusing on the important early flame development period. Results from two different LES turbulent Combustion models are presented, using the same numerical methods and computational mesh. Both models yield Cycle-to-Cycle Variations (CCV) in Combustion that are higher than what is observed in the experiments. The results reveal strengths and limitations of the experimental diagnostics and the LES models, and suggest directions for future diagnostic and simulation efforts. In particular, it has been observed that flame development between the times corresponding to the laminar-to-turbulent transition and 1% mass-burned fraction are especially important in establishing the subsequent Combustion Event for each cycle. This suggests a range of temporal and spatial scales over which future experimental and simulation efforts should focus.
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High-speed imaging of spray-guided DISI engine Combustion with near-TDC injection of E85 for ultra-low NO and soot
Proceedings of the Combustion Institute, 2013Co-Authors: Magnus Sjoberg, David L. ReussAbstract:Abstract Using E85 fuel, this work demonstrates the use of near-TDC injection and highly turbulent Combustion to achieve ultra-low emissions of NO and soot from a DISI engine with a spray-guided, stratified-charge Combustion system. Despite the low NO emissions, both Combustion efficiency and stability remain relatively high. One striking aspect of engine operation with near-TDC injection is the need to initiate the spark prior to fuel injection. Using E85 fuel, such early spark timing leads to stable ignition. For gasoline, however, such early spark timing leads to misfire under the conditions studied, thereby prEventing the use of near-TDC fuel injection to achieve low exhaust emissions of NO. High-speed imaging shows that the early spark timing for E85 allows the spark plasma to develop prior to interacting with one of the fuel jets adjacent to the spark plug, and this contributes to misfire-free operation. The spark-spray interactions generate a very fast spread of either weak or thin flames throughout a large fraction of the piston bowl prior to the main Combustion Event. The short delay between the near-TDC fuel injection and the Combustion Event are believed to enhance the mixing rates during the Combustion compared to the use of earlier injection, which may contribute to the low NO emissions.
Edward Lester - One of the best experts on this subject based on the ideXlab platform.
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petrographic characterization of coals as a tool to detect spontaneous Combustion potential
Fuel, 2014Co-Authors: Claudio Avila, Tao Wu, Edward LesterAbstract:Abstract Textural features of 25 worldwide coals were studied after slow oxidation processing (0.5 °C min−1 from 20 to 250 °C in air) using oil immersion microscopy and image analysis techniques. The characterization of samples, before and after oxidation, showed important changes in vitrinite reflectance with high reactive coals, which also related to their intrinsic self-oxidation potential. The morphology of the coal particles was also altered after the oxidation, to produce at least six different morphotypes. Particles with ‘homogeneous change of reflectance’ and particles with ‘oxidation rims’ were predominant in the samples studied, which related to boundary reactive conditions (kinetic and diffusion control of the reaction respectively). These textural characteristics indicate how particles interacted with oxygen at low temperatures, which could be used to predict the most probable pathway during the early stages of oxidation which could then lead to a spontaneous Combustion Event. The magnitude of the reflectance change and the morphological characteristics of samples studied were also related to the reactivity properties, providing an additional source of information to identify coals prone to spontaneous Combustion.
Kihong Park - One of the best experts on this subject based on the ideXlab platform.
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Mixing State of Size-Selected Submicrometer Particles During Photochemical and Combustion Events Measured with the Tandem System
Aerosol Science and Technology, 2013Co-Authors: Jaeseok Kim, Shila Maskey, Young Jun Yoon, Kihong ParkAbstract:A tandem differential mobility analyzer (TDMA) was applied to determine the mixing state of size-resolved submicrometer particles, in an urban area of Gwangju in Korea, when enhanced concentrations of particles were observed (e.g., photochemical and Combustion Events). The existence of a nonvolatile core was identified after removing volatile species with increasing temperature up to ∼250°C. Data showed that in the Combustion Event, the accumulation mode particles (137–139 nm) increased significantly and they had a nonvolatile core coated with volatile species, while in the photochemical Event, the nucleation mode (15–30 nm) particles enhanced and there was no such nonvolatile core (i.e., they were completely evaporated below 250°C). When hygroscopic growth factor (HGF) of the core particles was measured in the Combustion Event, their values were close to one, suggesting that they consist of nonvolatile and nonhygroscopic species like black carbon. In the photochemical Event, the nucleation mode particles...
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Measurements of hygroscopicity and volatility of atmospheric ultrafine particles during ultrafine particle formation Events at urban, industrial, and coastal sites.
Environmental science & technology, 2009Co-Authors: Kihong Park, Jaeseok Kim, Seungho ParkAbstract:The tandem differential mobility analyzer (TDMA) technique was applied to determine the hygroscopicity and volatility of atmospheric ultrafine particles in three sites of urban Gwangju, industrial Yeosu, and coastal Taean in South Korea. A database for the hygroscopicity and volatility of the known compositions and sizes of the laboratory-generated particles was first constructed for comparison with the measured properties of atmospheric ultrafine particles. Distinct differences in hygroscopicity and volatility of atmospheric ultrafine particles were found between a “photochemical Event” and a “Combustion Event,” as well as among different sites. At the Gwangju site, ultrafine particles in the “photochemical Event” were determined to be more hygroscopic (growth factor (GF) = 1.05−1.33) than those in the “Combustion Event” (GF = 1.02−1.12), but their hygroscopicity was not as high as pure ammonium sulfate or sulfuric acid particles in the laboratory-generated database, suggesting they were internally mixed...
Rolf D. Reitz - One of the best experts on this subject based on the ideXlab platform.
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evaluating temperature and fuel stratification for heat release rate control in a reactivity controlled compression ignition engine using optical diagnostics and chemical kinetics modeling
Combustion and Flame, 2015Co-Authors: Sage L Kokjohn, Mark P. B. Musculus, Rolf D. ReitzAbstract:We investigated the Combustion process in a dual-fuel, reactivity-controlled compression-ignition (RCCI) engine using a combination of optical diagnostics and chemical kinetics modeling to explain the role of equivalence ratio, temperature, and fuel reactivity stratification for heat-release rate control. An optically accessible engine is operated in the RCCI Combustion mode using gasoline primary reference fuels (PRF). A well-mixed charge of iso-octane (PRF = 100) is created by injecting fuel into the engine cylinder during the intake stroke using a gasoline-type direct injector. Later in the cycle, n-heptane (PRF = 0) is delivered through a centrally mounted diesel-type common-rail injector. This injection strategy generates stratification in equivalence ratio, fuel blend, and temperature. The first part of this study uses a high-speed camera to image the injection Events and record high-temperature Combustion chemiluminescence. Moreover, the chemiluminescence imaging showed that, at the operating condition studied in the present work, mixtures in the squish region ignite first, and the reaction zone proceeds inward toward the center of the Combustion chamber. The second part of this study investigates the charge preparation of the RCCI strategy using planar laser-induced fluorescence (PLIF) of a fuel tracer under non-reacting conditions to quantify fuel concentration distributions prior to ignition. Themore » fuel-tracer PLIF data show that the Combustion Event proceeds down gradients in the n-heptane distribution. The third part of the study uses chemical kinetics modeling over a range of mixtures spanning the distributions observed from the fuel-tracer fluorescence imaging to isolate the roles of temperature, equivalence ratio, and PRF number stratification. The simulations predict that PRF number stratification is the dominant factor controlling the ignition location and growth rate of the reaction zone. Equivalence ratio has a smaller, but still significant, influence. Lastly, temperature stratification had a negligible influence due to the NTC behavior of the PRF mixtures.« less
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SIMULTANEOUS OPTICAL DIAGNOSTIC IMAGING OF LOW-TEMPERATURE, DOUBLE-INJECTION Combustion IN A HEAVY-DUTY DI DIESEL ENGINE
Combustion Science and Technology, 2007Co-Authors: Satbir Singh, Rolf D. Reitz, Mark P. B. Musculus, Thierry LachauxAbstract:Abstract A highly diluted, low-flame-temperature diesel engine Combustion strategy with two separate fuel-injections per cycle was investigated using simultaneous optical diagnostics at a low-load operating condition. In-cylinder processes were visualized with a suite of laser/imaging diagnostics. The cool flame first-stage ignition reactions occur along the entire length of the jet for the first Combustion Event. For both injections, the second-stage ignition reactions occur after the end of injection, primarily in the downstream regions of the jet. OH is found throughout the cross-section of the jet, indicating greater mixing and leaner mixtures than observed for conventional diesel Combustion. For the first Combustion Event, very little soot is formed and it is found in small pockets near the tip of the jet. For the second Combustion Event, much more soot is formed throughout the downstream jet cross-section. Finally, Sandia's conceptual model of diesel Combustion has been extended to describe this ope...