In-flame soot particle structures and in-cylinder flow fields in direct-injection spark-ignition engines

To enhance fundamental knowledge of the soot formation and flow field development inside the cylinder of a direct-injection spark-ignition engine, two innovative optical diagnostic methods are developed and implemented for various engine operating conditions. For in-flame soot, a thermophoresis-based particle sampling and subsequent transmission electron microscope imaging achieve quantitative and statistical analysis of particle morphology and internal structure. This new sampling technique is analysed for uncertainty and then applied for various injection timings and pressures in a single-cylinder full optical engine. For flow field, new endoscopic high-speed particle image velocimetry (eHS-PIV) method is developed in the same single-cylinder engine before it is applied to multi-cylinder high-tumble production engines. The complex in-cylinder flow field measurement is achieved for various engine speeds and intake valve closing timings. Using these new methods, major findings have been achieved. The early injection leads to piston wetting, which produces larger soot primary particles and soot aggregates. The internal carbon-layer fringe structures indicate more mature and carbonised soot, which is due to more significant and widely distributed pool fire and thus longer soot residence time. With higher injection pressure, soot particles are at a more reactive status evidenced by less defined core-shell boundaries and higher fringe separation resulting in enhanced soot oxidation. Regarding the flow field in a high-tumble engine, a strong tumble vortex is measured during the piston compression with the flow directed towards the exhaust side. As the piston reaches top dead centre, a complex flow breakup occurs resulting in lateral flow vectors travelling back towards the intake side. The flow fields become more complex due to higher engine speed or more advanced intake valve closure timing, and from the comparison between the flow and flame data, a strong positive correlation is found between the flow direction and spark plasma stretch, and subsequently the flame propagation direction. The enhanced knowledge about the in-flame soot formation and in-cylinder flow fields achieved in this study creates a science base needed for the development of cleaner and higher efficiency spark-ignition engines

Fracture behavior of brittle ceramics at the nanoscale

In spite of the excellent properties such as high hardness, low thermal expansion, enhanced resistance to chemical degradation and superior mechanical behavior at elevated temperature, ceramic materials usually suffer from the brittle fracture and catastrophic failure, which restrict them from being used for structural applications. While a number of researchers have strived to overcome this drawback of ceramic materials by constructing the microstructures that interfere with crack growth, recent theoretical and computational studies proposed another effective method to suppress the rapid crack propagation by reducing the specimen size down to the nanometer scale. In this study, we investigated the mechanical properties of brittle ceramics by changing sample sizes from bulk to nanoscale with particular focus on their fracture failure. For the ease of analysis, we chose the isotropic, homogeneous and purely brittle material, i.e., diamond-like carbon. In-situ fixed-ends bending experiments were conducted with different beam thicknesses and lengths, 1μm ~ 100nm and 3μm ~ 6μm, respectively. Additionally, in order to demonstrate the feasibility to intactly transfer the superior properties emergent only at the nanoscale to the macroscopically available form, we fabricated the large-area 3D hierarchical hollow ceramic nano-architectures using proximity nano-patterning technique

Uncovering the Active Galactic Nuclei in Low-Ionization Nuclear Emission-Line Regions with Spitzer

The impact of active galactic nuclei on low-ionization nuclear emission-line regions (LINERs) remains a vigorous field of study. We present preliminary results from a study of the mid-infrared atomic emission lines of LINERs with the Spitzer Space Telescope. We assess the ubiquity and properties of AGN in LINERs using this data. We discuss what powers the mid-infrared emission lines and conclude that the answer depends unsurprisingly on the emission line ionization state and, more interestingly, on the infrared luminosity.Comment: To appear in ASP Vol. 373, The Central Engine of Active Galactic Nuclei, ed. Luis C. Ho and Jian-Min Wang; 4 pages, 2 figure

Lyotropic Liquid Crystallinity of Linear and Cyclic Amylose Derivatives : Amylose Tris(n-octadecylcarbamate) in Tetrahydrofuran and 2-Octanone

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Macromolecules, copyright © American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.macromol.9b01917

Context-Preserving Two-Stage Video Domain Translation for Portrait Stylization

Portrait stylization, which translates a real human face image into an artistically stylized image, has attracted considerable interest and many prior works have shown impressive quality in recent years. However, despite their remarkable performances in the image-level translation tasks, prior methods show unsatisfactory results when they are applied to the video domain. To address the issue, we propose a novel two-stage video translation framework with an objective function which enforces a model to generate a temporally coherent stylized video while preserving context in the source video. Furthermore, our model runs in real-time with the latency of 0.011 seconds per frame and requires only 5.6M parameters, and thus is widely applicable to practical real-world applications.Comment: 5 pages, 3 figures, CVPR 2023 Workshop on AI for Content Creatio