| 1. |
- Franken, T., et al.
(författare)
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Multi-objective optimization of water injection in spark-ignition engines using the stochastic reactor model with tabulated chemistry
- 2019
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Ingår i: International Journal of Engine Research. - : SAGE Publications. - 1468-0874 .- 2041-3149. ; 20:10, s. 1089-1100
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Tidskriftsartikel (refereegranskat)abstract
- Water injection is investigated for turbocharged spark-ignition engines to reduce knock probability and enable higher engine efficiency. The novel approach of this work is the development of a simulation-based optimization process combining the advantages of detailed chemistry, the stochastic reactor model and genetic optimization to assess water injection. The fast running quasi-dimensional stochastic reactor model with tabulated chemistry accounts for water effects on laminar flame speed and combustion chemistry. The stochastic reactor model is coupled with the Non-dominated Sorting Genetic Algorithm to find an optimum set of operating conditions for high engine efficiency. Subsequently, the feasibility of the simulation-based optimization process is tested for a three-dimensional computational fluid dynamic numerical test case. The newly proposed optimization method predicts a trade-off between fuel efficiency and low knock probability, which highlights the present target conflict for spark-ignition engine development. Overall, the optimization shows that water injection is beneficial to decrease fuel consumption and knock probability at the same time. The application of the fast running quasi-dimensional stochastic reactor model allows to run large optimization problems with low computational costs. The incorporation with the Non-dominated Sorting Genetic Algorithm shows a well-performing multi-objective optimization and an optimized set of engine operating parameters with water injection and high compression ratio is found.
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| 2. |
- Mueller, Michael, et al.
(författare)
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Microstructural, mechanical, and thermo-physical characterization of hypereutectic AlSi40 fabricated by selective laser melting
- 2019
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- The powder bed additive manufacturing process selective laser melting (SLM) enables designers and engineers to overcome restrictions of conventional manufacturing technologies. The potential of fabricating complex lightweight structures and processing advanced materials is a key feature for enhancing further development of high performance components for space applications. Due to a high specific stiffness and a thermal expansion coefficient very close to electroless nickel, which is an advantageous optical coating material, the hypereutectic aluminum-silicon alloy AlSi40 shows great potential for the manufacturing of optical mirrors for space applications. In prior investigations, Hilpert et al.showed the feasibility to process AlSi40 by SLM [E. Hilpert and S. Risse, Materials Science & Technology Conference and Exhibition MS&T'15, Columbus, Ohio, 4–8 October 2015(Association for Iron & Steel Technology, Warrendale, PA, 2015) and E. Hilpert, “Struktur und Eigenschaften von additiv gefertigten hypereutektischen Aluminum-Siliciumlegierungen,” in Werkstoffwoche 2017, Dresden, Germany, 28 September 2017 (Deutsche Gesellschaft für Materialkunde e.V., Berlin, 2017)]. Nevertheless, in order to qualify this material for space applications, the manufacturing process and fabricated samples need to be thoroughly investigated in terms of microstructural, mechanical, as well as thermo-physical characterization. The authors present results of the SLM process development for manufacturing dense AlSi40 samples with a relative density above 99.50%. The effect of various process parameters, such as hatch distance, preheating, and scanning strategy, on the formation of defects was investigated by destructive [e.g., optical microscopy (OM)] and nondestructive (e.g., computed tomography) testing. In addition, the effect of several thermal post-treatments on the AlSi40 microstructure was profoundly analyzed by multiple methods such as OM, scanning electron microscopy, and energy dispersive x-ray spectroscopy analysis. Moreover, mechanical and thermo-physical testing of manufactured specimens was conducted to provide material characteristics for component design. In conclusion, the determined material properties of AlSi40 samples fabricated by SLM were compared to bulk material properties. The gained knowledge and testing data were evaluated in order to identify correlations and dependencies.
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| 3. |
- Seidel, André, et al.
(författare)
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Intrinsic Heat Treatment Within Additive Manufacturing of Gamma Titanium Aluminide Space Hardware
- 2019
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Ingår i: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 71:4, s. 1513-1519
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Tidskriftsartikel (refereegranskat)abstract
- A major part of laser additive manufacturing focuses on the fabrication of metallic parts for applications in the space and aerospace sectors. Especially, the processing of the very brittle titanium aluminides can be particularly challenging because of their distinct tendency to lamellar interface cracking. In the present paper, a gamma titanium aluminide (γ-TiAl) nozzle, manufactured via electron beam melting, is extended and adapted via hybrid laser metal deposition. The presented example considers a new field of application for this class of materials and approaches the process-specific manipulation of the composition and/or microstructure via the adjustment of processing temperatures, temperature gradients and solidification conditions. Furthermore, intrinsic heat treatment is investigated for electron beam melting and laser metal deposition with powder, and the resulting influence is releated to conventional processing.
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