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| 2. |
- Eismark, Jan, 1962, et al.
(author)
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Reduced soot emissions by piston bowl-shape guided late cycle oxidation in low-swirl heavy-duty diesel engine combustion
- 2018
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In: SIA POWERTRAIN ROUEN 2018 The New Compression Ignition Engine, Electrification and Sustainable Fuels for Passenger Cars and Commercial Vehicles. ; , s. 265-276
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Conference paper (peer-reviewed)abstract
- Reduced soot emissions by piston bowl-shape guided late cycle oxidation in low-swirl heavy-duty diesel engine combustion. Late cycle soot oxidation in heavy-duty diesel engine low-swirl combustion was investigated using single-cylinder engine and spray-chamber experiments supported by engine combustion computational fluid dynamics (CFD) simulations. The in-cylinder flow situation during interaction between adjacent flames (flame-flame event) was shown to have a large impact on the combustion late in the cycle. In order to modify the flame-flame flow-situation, a new piston bowl shape having wave-shaped protrusions (waves) for guiding of the near-wall flow, was developed. This resulted in a significant reduction of soot emissions and also increased fuel efficiency. The waves were observed to enhance the late cycle mixing which manifested as an increased apparent rate of heat release after the end of injection. Combustion simulations were used to show that the increased mixing was driven by the enhanced intensity of side-vortices leading to the creation of a radial mixing zone. This radial mixing zone extended further into the centre of the piston bowl where unused ambient gas is available, which promotes oxidation. This flame-interaction effect was isolated and further studied using an optical spray-chamber with a two-hole fuel injector nozzle and a wall interaction. Finally, the influence of bowl geometry on the flow field was investigated and coupled to observed late cycle soot oxidation efficiency.
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| 3. |
- Eismark, Jan, 1962, et al.
(author)
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Role of formation and transportation of hydroxyl radicals for enhanced late soot oxidation in a low emissions heavy-duty diesel engine.
- 2010
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In: Thiesel 2010 conference on Thermo-and fluid dynamic processes in Diesel Diesel Engines. - 9788469350096 ; , s. 173-190
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Conference paper (peer-reviewed)abstract
- In previous research enhancement of late soot oxidation by increased mixing rates has been identified as an important measure to decrease engine-out soot emissions. Additionally, the availability of oxidants, especially hydroxyl radicals (OH) in the mixing zones, is considered as essential for an effective fuel and soot burn-out process. The objective of this study was to combine experimental and computational methods to identify the role of OH for late soot oxidation. Experimental data from a high pressure/high temperature spray chamber and a heavy-duty single cylinder engine were analysed using combustion CFD. The formation, lifetime and transportation of OH were studied together with other important in-cylinder parameters. The soot formation and oxidation processes were analysed for a dataset of engine results with equal NOx emissions but having a large variation of engine-out soot emissions. The spray chamber experimental set-up includes a flame divider designed to enable studies of the OH history in the leading edge of the flame vortex. The engine combustion CFD results could be compared with CFD analysis of the spray chamber results regarding the behaviour of OH. From this study, it is suggested that the fluctuating interface between the soot leading edge and the important soot oxidant specie OH is influenced by interactions between local turbulent flame movements and the availability of OH. The soot and OH interface was observed to develop smoothly in a strongly re-directed side of a flame as well as on the free side of the same flame. According to experimental observations and analysis of CFD source terms of soot formation and oxidation rates, both the OH radical pool and the soot oxidation reach farther downstream in the flame than the soot formation. The study gave an increased understanding of limiting factors for enhanced late soot oxidation during diesel engine operation.
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| 4. |
- Eismark, Jan, 1962, et al.
(author)
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Role of fuel properties and piston shape in influencing soot oxidation in heavy-duty low swirl diesel engine combustion
- 2019
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 254
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Journal article (peer-reviewed)abstract
- The presented study evaluated effects on soot emissions of important diesel fuel properties (e.g. volatility T95, hydrogen to-carbon ratio H/C and oxygen content O/C) in a heavy-duty, low-swirl, direct injection diesel engine operated with cooled exhaust gas recirculation to control the emissions of nitrogen oxides. Variation of injection pressure was conducted in three representative operation points in the single-cylinder engine including conventional and wave piston bowl types. Additionally, detailed optical combustion studies were performed in a high pressure/high temperature combustion chamber with an engine-like flame-wall interaction geometry. The fuel properties mainly influenced parameters relating to events near the nozzle, such as the ignition delay, flame lift-off distance and spray air entrainment. Oxygenation of the fuel reduced soot formation (a known effect of spray-jet dilution), but the fuels’ H/C and T95 also influenced soot emissions. Viscosity, heating value and density, treated as secondary fuel parameters, affected the injected fuel's kinetic energy, and hence mean flow field and local turbulent mixing late in the combustion cycle. The results suggested that fuel effects on soot oxidation during late phases of combustion are mainly governed by parameters related to the fuel injection profile under the specific cylinder gas conditions. With an oxygenated fuel, flow structures (local turbulent side vortices) which are typical for the investigated engine type were found to form in a similar way as with a reference fuel. Hence, improved internal flow using a wave piston in combination with a low-sooting oxygenated fuel gave additional reductions in net soot emissions.
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| 5. |
- Eismark, Jan, 1962, et al.
(author)
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Role of late soot oxidation for low emission combustion in a diffusion-controlled, High-EGR, heavy duty diesel engine
- 2009
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Journal article (peer-reviewed)abstract
- Soot formation and oxidation are complex and competing processes during diesel combustion. The balance between the two processes and their history determines engine-out soot values. Besides the efforts to lower soot formation with measures to influence the flame lift-off distance for example or to use HCCI-combustion, enhancement of late soot oxidation is of equal importance for low-λ diffusion-controlled low emissions combustion with EGR. The purpose of this study is to investigate soot oxidation in a heavy duty diesel engine by statistical analysis of engine data and in-cylinder endoscopic high speed photography together with CFD simulations with a main focus on large scale in-cylinder gas motion. Results from CFD simulations using a detailed soot model were used to reveal details about the soot oxidation. A particular objective of the present study was to investigate the importance of enhancing soot oxidation after End of Injection (EOI) when temperature and NOx formation rapidly decreases. Geometrical measures to control flame propagation and different flame interactions were investigated. Such measures contribute to conserve available kinetic energy until late in the combustion period in an efficient way. Based on this combustion strategy it is possible to reach near zero engine-out soot emissions. Copyright © 2009 SAE International.
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| 6. |
- Eismark, Jan, 1962, et al.
(author)
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Role of Piston Bowl Shape to Enhance Late-Cycle Soot Oxidation in Low-Swirl Diesel Combustion
- 2019
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In: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 12:3
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Journal article (peer-reviewed)abstract
- Late-cycle soot oxidation in heavy-duty (HD) diesel engine low-swirl combustion was investigated using single-cylinder engine and spray chamber experiments together with engine combustion simulations. The in-cylinder flow during interactions between adjacent flames (flame-flame events) was shown to have a large impact on late-cycle combustion. To modify the flame-flame, a new piston bowl shape with a protrusion (wave) was designed to guide the near-wall flow. This design significantly reduced soot emissions and increased engine thermodynamic efficiency. The wave’s main effect was to enhance late-cycle mixing, as demonstrated by apparent rate of heat release after the termination of fuel injection. Combustion simulations showed that the increased mixing is driven by enhanced flow re-circulation, which produces a radial mixing zone (RMZ). The leading edge of the RMZ extends toward the center of the piston bowl, where unused ambient gas is available, promoting oxidation. The wave also enhances mixing in the trailing edge of the RMZ when it detaches from the wall, accelerating the burn-out of the RMZ. This flame interaction effect was isolated and studied further using a new optical setup in a spray chamber with a 2-hole nozzle fuel injector. A conceptual model relating piston bowl geometry to soot oxidation efficiency was developed to explain late-cycle soot oxidation in low-swirl HD engines.
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| 7. |
- Eismark, Jan, 1962, et al.
(author)
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Role of spray chamber experiments in understanding flame-flame interaction events in heavy-duty diesel engine combustion.
- 2018
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In: SAE International Journal of Engines. - 1946-3944 .- 1946-3936.
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Journal article (peer-reviewed)abstract
- Combustion in spray-controlled heavy-duty (HD) engines is characterized by gas-phase interactions between the ignited fuel jets (flames) and piston walls rather than liquid fuel impingement on the walls. In the research on HD engine emissions and fuel consumption, enhancement of mixing late in the combustion cycle is important. Mixing late in the cycle depends on development of the flow field in the cylinder, which in turn is affected by phenomena such as turbulent flow near a stagnation point during jet-wall impingement, wall-jet development along the piston walls and flame-flame interactions. Optical diagnostics in single-cylinder engines and combustion computational fluid dynamics (CFD) simulations are well-known methods for studying in-cylinder flow events. Detailed optical experiments conducted in high temperature/high pressure spray chambers (SCs) with single-hole fuel nozzles are now widely used for generating validation data for modeling a freely developing single spray. However, to date, very few SC setups have included flame-flame interactions. In this paper, a new SC setup is presented comprising a HD double-hole nozzle and different wall geometries. The setup enabled detailed optical analysis of the aforementioned interaction events. Imaging of soot luminosity, OH chemiluminescence and laser soot shadow imaging were used to compare late-cycle mixing in a conventional bowl geometry with a new piston type able to lower soot emissions considerably (referred to as a wave piston). Together with combustion CFD simulations, the new experimental setup yielded useful results for understanding flame-flame interaction effects on late-cycle mixing in HD engine combustion.
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| 8. |
- Eismark, Jan, 1962, et al.
(author)
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Role of turbulence for mixing and soot oxidation for an equivalent diesel gas jet during wall interaction studied with LES.
- 2012
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In: Proceeding of THIESEL 2012.
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Conference paper (peer-reviewed)abstract
- Using Large Eddy Simulations (LES), turbulent properties were studied of an equivalent diesel fuel gas jet having a vapour phase penetration equal as for a diesel spray. Half side of the jet was forced to sharply change direction by impinging upon a curved wall. The other side of the jet developed freely acting as a reference case. It was shown how turbulent structures of various scales develop along the jet and after wall impingement. The turbulent eddies contribute strongly to air entrainment into the jet resulting in an increasing rate of dilution of the jet core downstream of the fuel nozzle. Calculations of the instantaneous fuel concentration were used to study the total surface area and the kinetic energy of the wrinkled stoichiometric zones. Both the resolved kinetic energy and the sub-grid scale turbulent kinetic energy of the stoichiometric zones were found to increase on the wall side. Statistics of turbulent quantities were computed across interesting sections showing relations between velocity gradients, turbulent velocity field, turbulence production and dissipation. The findings were used for a reasoning about the role of turbulence for soot oxidation in a real diesel flame. Previous observations in a high temperature, high pressure combustion chamber experiment that turbulent eddies sweep fresh gas into the free jet core were confirmed by the simulations. As observed in the experiments, the LES results indicate that also non-fresh gases, especially on the wall side, may be swept into the jet side. As a result, soot oxidation rate can either increase if oxidant radicals are supplied by the turbulent flow or decrease if the in-rushing gases mainly consist of inert combustion products.
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| 9. |
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| 10. |
- Saccullo, Michael, 1984, et al.
(author)
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High Pressure Ethanol Injection under Diesel-Like Conditions
- 2017
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2017-March:March
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Journal article (peer-reviewed)abstract
- Laws concerning to emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are therefore needed to satisfy these new legal requirements and reduce fossil fuel dependency. One way to achieve both objectives is to partially replace fossil fuels with alternatives that are more sustainable with respect to emissions of greenhouse gas, particulates and NOx. As a first step towards the development of a direct injected dual fuel engine using diesel fuel and renewable alcohols such as methanol or ethanol, we have studied ethanol (E100) sprays generated with a standard high pressure diesel fuel injection system in a high pressure/temperature spray chamber with optical access. The experiments were performed at a gas density of ∼27kg/m3 at ∼550 °C and ∼60 bar, representing typical operating conditions for a HD engine at low loads. High speed video images of the developing sprays were recorded, enabling measurement of spray parameters such as the liquid cone angle, liquid penetration length and vapor penetration at injection pressures between 500 and 2200 bar. The results obtained provide insight into the fuel-air mixing process. Moreover, they serve as a proof-of-concept demonstrating that ethanol can be used successfully in a high pressure Diesel injection system.
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| 11. |
- Zhang, Tankai, 1988, et al.
(author)
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Effects of a wave-shaped piston bowl geometry on the performance of heavy duty Diesel engines fueled with alcohols and biodiesel blends
- 2020
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In: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 148, s. 512-522
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Journal article (peer-reviewed)abstract
- The effects of a new wave-shaped piston bowl design on combustion characteristics and engine out emissions were tested in a heavy duty Diesel engine fueled with conventional Diesel and fossil-free blends containing n-butanol, n-octanol, 2-ethylhexanol, hydrotreated vegetable oil, and rapeseed methyl ester. The compositions of the blends were chosen such that their cetane numbers matched that of fossil Diesel. Engine experiments were performed at four operating points from the European Stationary Cycle, with no modification of engine settings when switching between different fuels. A standard piston with omega geometry was tested using fossil Diesel and the fossil-free nBu30H (30% n-butanol and 70% hydrotreated vegetable oil by volume) blend, and the results obtained were compared to those achieved with the wave piston. In general, the fossil-free blends yielded significantly lower soot emissions than fossil Diesel but slightly higher NOx emissions. Relative to the standard piston, the wave piston accelerated the combustion of both Diesel and fossil-free blends, especially the diffusion combustion. The wave piston's positive effects on thermal efficiency and soot emissions were more pronounced for conventional Diesel fuel than for oxygenated nBu30H.
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