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Volume 5 • Issue 3 • Jun. 2019 • Pages 351 -593
News & Highlights
Editorial
Topic Insights
Research Robotics—Article
Views & Comments
News & Highlights
Engineering Achievements
Research Engines and Fuels—Article
Research Engines and Fuels—Review
Research Engines and Flues—Article
Research Deep Matter & Energy—Review
Research Deep Matter & Energy—Article
Research Green Chemical Engineering—Article
Research Drop-on-Demand Printing—Article
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Editorial
News & Highlights
News & Highlights
A New Lander on Mars
Marcus Woo
Engineering . 2019, 5 (3): 355 -356 .   https://doi.org/10.1016/j.eng.2019.04.005
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More Super Supercomputers
Jane Palmer
Engineering . 2019, 5 (3): 357 -358 .   https://doi.org/10.1016/j.eng.2019.04.007
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Wearable Sweat Sensors
Elizabeth K. Wilson
Engineering . 2019, 5 (3): 359 -360 .   https://doi.org/10.1016/j.eng.2019.04.008
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Redefining the Kilogram
Chris Palmer
Engineering . 2019, 5 (3): 361 -362 .   https://doi.org/10.1016/j.eng.2019.04.004
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Views & Comments
The Deep Carbon Observatory: A Ten-Year Quest to Study Carbon in Earth
Craig M. Schiffries, Andrea Johnson Mangum, Jennifer L. Mays, Michelle Hoon-Starr, Robert M. Hazen
Engineering . 2019, 5 (3): 372 -378 .   https://doi.org/10.1016/j.eng.2019.03.004
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Engineering Achievements
Topic Insights
Prospects of Reciprocating Engines and Fuels
Michael J. Brear
Engineering . 2019, 5 (3): 395 -396 .   https://doi.org/10.1016/j.eng.2019.04.003
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Research Deep Matter & Energy—Review
Data-Driven Discovery in Mineralogy: Recent Advances in Data Resources, Analysis, and Visualization
Robert M. Hazen, Robert T. Downs, Ahmed Eleish, Peter Fox, Olivier C. Gagné, Joshua J. Golden, Edward S. Grew, Daniel R. Hummer, Grethe Hystad, Sergey V. Krivovichev, Congrui Li, Chao Liu, Xiaogang Ma, Shaunna M. Morrison, Feifei Pan, Alexander J. Pires, Anirudh Prabhu, Jolyon Ralph, Simone E. Runyon, Hao Zhong
Engineering . 2019, 5 (3): 397 -405 .   https://doi.org/10.1016/j.eng.2019.03.006
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Abstract

Large and growing data resources on the diversity, distribution, and properties of minerals are ushering in a new era of data-driven discovery in mineralogy. The most comprehensive international mineral database is the IMA database, which includes information on more than 5400 approved mineral species and their properties, and the mindat.org data source, which contains more than 1 million species/locality data on minerals found at more than 300 000 localities. Analysis and visualization of these data with diverse techniques—including chord diagrams, cluster diagrams, Klee diagrams, skyline diagrams, and varied methods of network analysis—are leading to a greater understanding of the co-evolving geosphere and biosphere. New data-driven approaches include mineral evolution, mineral ecology, and mineral network analysis—methods that collectively consider the distribution and diversity of minerals through space and time. These strategies are fostering a deeper understanding of mineral co-occurrences and, for the first time, facilitating predictions of mineral species that occur on Earth but have yet to be discovered and described.

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Ophiolite-Hosted Diamond: A New Window for Probing Carbon Cycling in the Deep Mantle
Dongyang Lian, Jingsui Yang
Engineering . 2019, 5 (3): 406 -420 .   https://doi.org/10.1016/j.eng.2019.02.006
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Abstract

As reported in our prior work, we have recovered microdiamonds and other unusual minerals, including pseudomorph stishovite, moissanite, qingsongite, native elements, metallic alloys, and some crustal minerals (i.e., zircon, quartz, amphibole, and rutile) from ophiolitic peridotites and chromitites. These ophiolite-hosted microdiamonds display different features than kimberlitic, metamorphic, and meteoritic diamonds in terms of isotopic values and mineral inclusions. The characteristic of their light carbon isotopic composition implies that the material source of ophiolite-hosted diamonds is surface-derived organic matter. Coesite inclusions coexisting with kyanite rimming an FeTi alloy from the Luobusa ophiolite show a polycrystalline nature and a prismatic habit, indicating their origin as a replacement of stishovite. The occurrence in kyanite and coesite with inclusions of qingsongite, a cubic boron nitride mineral, and a high-pressure polymorph of rutile (TiO2 II) point to formation pressures of 10–15 GPa at temperatures ∼1300 °C, consistent with depths greater than 380 km, near the mantle transition zone (MTZ). Minerals such as moissanite, native elements, and metallic alloys in chromite grains indicate a highly reduced environment for ophiolitic peridotites and chromitites. Widespread occurrence of diamonds in ophiolitic peridotites and chromitites suggests that the oceanic mantle may be a more significant carbon reservoir than previously thought. These ophiolite-hosted diamonds have proved that surface carbon can be subducted into the deep mantle, and have provided us with a new window for probing deep carbon cycling.

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First-Principles Methods in the Investigation of the Chemical and Transport Properties of Materials under Extreme Conditions
John S. Tse
Engineering . 2019, 5 (3): 421 -433 .   https://doi.org/10.1016/j.eng.2019.01.008
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Abstract

Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.

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A Breakthrough in Pressure Generation by a Kawai-Type Multi-Anvil Apparatus with Tungsten Carbide Anvils
Takayuki Ishii, Zhaodong Liu, Tomoo Katsura
Engineering . 2019, 5 (3): 434 -440 .   https://doi.org/10.1016/j.eng.2019.01.013
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Abstract

Expansion of the pressure range of Kawai-type multi-anvil presses (KMAPs) with tungsten carbide (WC) anvils is called for, especially in the field of Earth science. However, no significant progress in pressure generation has been made for 40 years. Our recent studies have expanded the pressure generation of a KMAP with WC anvils to 65 GPa, which is the world record for high-pressure generation in this device and is more than 2.5 times higher than conventional pressure generation. We have also successfully generated pressures of about 50 GPa at high temperatures. This work reviews our recently developed technology for high-pressure generation. High-pressure generation at room temperature and at high temperature was attained by integration of the following techniques: ① a precisely aligned guide-block system, ② a high degree of hardness of the second-stage anvils, ③ tapering of the second-stage anvil faces, ④ a high-pressure cell consisting of materials with a high bulk modulus, and ⑤ high thermal insulation of the furnace. Our high-pressure technology will facilitate investigation of the phase stability and physical properties of materials under the conditions of the upper part of the lower mantle, and will permit the synthesis and characterization of novel materials.

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Development of High-Pressure Multigrain X-Ray Diffraction for Exploring the Earth’s Interior
Li Zhang, Hongsheng Yuan, Yue Meng, Ho-Kwang Mao
Engineering . 2019, 5 (3): 441 -447 .   https://doi.org/10.1016/j.eng.2019.02.004
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Abstract

The lower mantle makes up more than a half of our planet’s volume. Mineralogical and petrological experiments on realistic bulk compositions under high pressure–temperature (PT) conditions are essential for understanding deep mantle processes. Such high PT experiments are commonly conducted in a laser-heated diamond anvil cell, producing a multiphase assemblage consisting of 100 nm to submicron crystallite grains. The structures of these lower mantle phases often cannot be preserved upon pressure quenching; thus, in situ characterization is needed. The X-ray diffraction (XRD) pattern of such a multiphase assemblage usually displays a mixture of diffraction spots and rings as a result of the coarse grain size relative to the small X-ray beam size (3–5 μm) available at the synchrotron facilities. Severe peak overlapping from multiple phases renders the powder XRD method inadequate for indexing new phases and minor phases. Consequently, structure determination of new phases in a high PT multiphase assemblage has been extremely difficult using conventional XRD techniques. Our recent development of multigrain XRD in high-pressure research has enabled the indexation of hundreds of individual crystallite grains simultaneously through the determination of crystallographic orientations for these individual grains. Once indexation is achieved, each grain can be treated as a single crystal. The combined crystallographic information from individual grains can be used to determine the crystal structures of new phases and minor phases simultaneously in a multiphase system. With this new development, we have opened up a new area of crystallography under the high PT conditions of the deep lower mantle. This paper explains key challenges in studying multiphase systems and demonstrates the unique capabilities of high-pressure multigrain XRD through successful examples of its applications.

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Tracing the Deep Carbon Cycle Using Metal Stable Isotopes: Opportunities and Challenges
Sheng-Ao Liu, Shu-Guang Li
Engineering . 2019, 5 (3): 448 -457 .   https://doi.org/10.1016/j.eng.2019.03.007
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Abstract

The subduction of marine carbonates and carbonated oceanic crust to the Earth’s interior and the return of recycled carbon to the surface via volcanism may play a pivotal role in governing Earth’s atmosphere, climate, and biosphere over geologic time. Identifying recycled marine carbonates and evaluating their fluxes in Earth’s mantle are essential in order to obtain a complete understanding of the global deep carbon cycle (DCC). Here, we review recent advances in tracing the DCC using stable isotopes of divalent metals such as calcium (Ca), magnesium (Mg), and zinc (Zn). The three isotope systematics show great capability as tracers due to appreciable isotope differences between marine carbonate and the terrestrial mantle. Recent studies have observed anomalies of Ca, Mg, and Zn isotopes in basalts worldwide, which have been interpreted as evidence for the recycling of carbonates into the mantle, even into the mantle transition zone (410–660 km). Nevertheless, considerable challenges in determining the DCC remain because other processes can potentially fractionate isotopes in the same direction as expected for carbonate recycling; these processes include partial melting, recycling of carbonated eclogite, separation of metals and carbon, and diffusion. Discriminating between these effects has become a key issue in the study of the DCC and must be considered when interpreting any isotope anomaly of mantle-derived rocks. An ongoing evaluation on the plausibility of potential mechanisms and possible solutions for these challenges is discussed in detail in this work. Based on a comprehensive evaluation, we conclude that the large-scale Mg and Zn isotope anomalies of the Eastern China basalts were produced by recycling of Mg- and Zn-rich carbonates into their mantle source.

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Theoretical Progress and Key Technologies of Onshore Ultra-Deep Oil/Gas Exploration
Xusheng Guo, Dongfeng Hu, Yuping Li, Jinbao Duan, Xuefeng Zhang, Xiaojun Fan, Hua Duan, Wencheng Li
Engineering . 2019, 5 (3): 458 -470 .   https://doi.org/10.1016/j.eng.2019.01.012
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Abstract

Oil/gas exploration around the world has extended into deep and ultra-deep strata because it is increasingly difficult to find new large-scale oil/gas reservoirs in shallow–middle buried strata. In recent years, China has made remarkable achievements in oil/gas exploration in ultra-deep areas including carbonate and clastic reservoirs. Some (ultra) large-scale oil and gas fields have been discovered. The oil/gas accumulation mechanisms and key technologies of oil/gas reservoir exploration and development are summarized in this study in order to share China’s experiences. Ultra-deep oil/gas originates from numerous sources of hydrocarbons and multiphase charging. Liquid hydrocarbons can form in ultra-deep layers due to low geothermal gradients or overpressures, and the natural gas composition in ultra-deep areas is complicated by the reactions between deep hydrocarbons, water, and rock or by the addition of mantle- or crust-sourced gases. These oils/gases are mainly stored in the original high-energy reef/shoal complexes or in sand body sediments. They usually have high original porosity. Secondary pores are often developed by dissolution, dolomitization, and fracturing in the late stage. The early pores have been preserved by retentive diageneses such as the early charging of hydrocarbons. Oil/gas accumulation in ultra-deep areas generally has the characteristics of near-source accumulation and sustained preservation. The effective exploration and development of ultra-deep oil/gas reservoirs depend on the support of key technologies. Use of the latest technologies such as seismic signal acquisition and processing, low porosity and permeability zone prediction, and gas–water identification has enabled the discovery of ultra-deep oil/gas resources. In addition, advanced technologies for drilling, completion, and oil/gas testing have ensured the effective development of these fields.

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Research Deep Matter & Energy—Article
Composition of Hydrocarbons in Diamonds, Garnet, and Olivine from Diamondiferous Peridotites from the Udachnaya Pipe in Yakutia, Russia
Nikolay V. Sobolev, Anatoly A. Tomilenko, Taras A. Bul'bak, Alla M. Logvinova
Engineering . 2019, 5 (3): 471 -478 .   https://doi.org/10.1016/j.eng.2019.03.002
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Abstract

Volatile components in diamonds, associated garnet (pyrope), and olivine from two extremely rare xenoliths of diamondiferous peridotites recovered from the Udachnaya kimberlite pipe in Yakutia, Russia, were analyzed by gas chromatography–mass spectrometry (GC–MS) using a Focus DSQ II Series Single Quadrupole GC–MS (Thermo Scientific, USA). These xenoliths are pyrope lherzolite and pyrope dunite based upon compositions of coexisting minerals. Unlike the pyrope lherzolite, which contained pyrope with moderate calcium (Ca)-component content (about 15 mol%), the dunite contained subcalcic chromium (Cr)-pyrope with low Ca-component content (less than 10 mol%). All investigated minerals contained dominating hydrocarbons and their derivatives represented by aliphatic (paraffins, olefins), cyclic (naphthenes, arenes), oxygenated (alcohols, ethers), and heterocyclic (dioxanes, furans) hydrocarbons; nitrogenated, chlorinated, and sulfonated compounds; carbon dioxide (CO2); and water (H2O). The relative concentration (rel%) of total hydrocarbon was 79.7 rel% for diamonds, 69.1 rel% for garnet, and 92.6 rel% for olivine, with a general amount of components ranging from 161 to 206. New data on volatiles in diamonds, associated garnet, and olivine suggest the presence of a wide spectrum of hydrocarbons along with nitrogen (N2), CO2, and H2O in some upper mantle areas.

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Applications for Nanoscale X-ray Imaging at High Pressure
Wendy L. Mao, Yu Lin, Yijin Liu, Jin Liu
Engineering . 2019, 5 (3): 479 -489 .   https://doi.org/10.1016/j.eng.2019.01.006
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Abstract

Coupling nanoscale transmission X-ray microscopy (nanoTXM) with a diamond anvil cell (DAC) has exciting potential as a powerful three-dimensional probe for non-destructive imaging at high spatial resolution of materials under extreme conditions. In this article, we discuss current developments in high-resolution X-ray imaging and its application in high-pressure nanoTXM experiments in a DAC with third-generation synchrotron X-ray sources, including technical considerations for preparing successful measurements. We then present results from a number of recent in situ high-pressure measurements investigating equations of state (EOS) in amorphous or poorly crystalline materials and in pressure-induced phase transitions and electronic changes. These results illustrate the potential this technique holds for addressing a wide range of research areas, ranging from condensed matter physics and solid-state chemistry to materials science and planetary interiors. Future directions for this exciting technique and opportunities to improve its capabilities for broader application in high-pressure science are discussed.

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Carbonation of Chrysotile under Subduction Conditions
Mihye Kong, Yongjae Lee
Engineering . 2019, 5 (3): 490 -497 .   https://doi.org/10.1016/j.eng.2019.01.007
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Abstract

In order to understand the role of serpentine minerals in the global carbon cycle, high-pressure X-ray diffraction (XRD) experiments were performed on chrysotile (Mg3Si2O5(OH)4) using carbon dioxide (CO2) as a pressure medium. Synchrotron XRD patterns revealed the formation of magnesite and high-pressure chrysotile after heating at 170 °C for 1 h at 2.5(1) GPa. The Rietveld refinement suggests that the unit cell composition of the original chrysotile changes to Mg2.4(1)Si2O5(OH)2.4(1) upon the formation of magnesite, which appears to be driven by the dehydrogenation of the innermost hydroxyl group, OH3, and the rearrangement of magnesium (Mg) at the M1 site, leading to the formation of metastable monodehydroxylated chrysotile. Metastable chrysotile is observed up to 5.0(1) GPa and 500 °C, which corresponds to the slab Moho geotherms for the South Sumatra and Ryukyu subduction zone. After recovery to ambient conditions, the characteristic fibrous morphology of the original chrysotile was found to have changed to an earthy form. These results can help us to understand deep carbon cycling along the subduction zones, and may prompt the design of a novel method of asbestos detoxification using pressure and temperature.

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Core Metabolic Features and Hot Origin of Bathyarchaeota
Xiaoyuan Feng, Yinzhao Wang, Rahul Zubin, Fengping Wang
Engineering . 2019, 5 (3): 498 -504 .   https://doi.org/10.1016/j.eng.2019.01.011
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Abstract

The archaeal phylum Bathyarchaeota comprises highly diversified subgroups and is considered to be one of the most abundant microorganisms on earth. The metabolic features and evolution of this phylum still remain largely unknown. In this article, a comparative metabolic analysis of 15 newly reconstructed and 36 published metagenomic assembled genomes (MAGs) spanning 10 subgroups was performed, revealing the core metabolic features of Bathyarchaeota—namely, protein, lipid, and benzoate degradation; glycolysis; and the Wood–Ljungdahl (WL) pathway, indicating an acetyl-CoA-centralized metabolism within this phylum. Furthermore, a partial tricarboxylic acid (TCA) cycle, acetogenesis, and sulfur-related metabolic pathways were found in specific subgroups, suggesting versatile metabolic capabilities and ecological functions of different subgroups. Intriguingly, most of the MAGs from the Bathy-21 and -22 subgroups, which are placed at the phylogenetic root of all bathyarchaeotal lineages and likely represent the ancient Bathyarchaeota types, were found in hydrothermal environments and encoded reverse gyrase, suggesting a hyperthermophilic feature. This work reveals the core metabolic features of Bathyarchaeota, and indicates a hot origin of this archaeal phylum.

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Structural Studies on the Cu–H System under Compression
Jack Binns, Miriam Peña-Alvarez, Mary-Ellen Donnelly, Eugene Gregoryanz, Ross T. Howie, Philip Dalladay-Simpson
Engineering . 2019, 5 (3): 505 -509 .   https://doi.org/10.1016/j.eng.2019.03.001
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Abstract

Hydrogen chemistry at extreme pressures is currently subject to extensive research due to the observed and predicted enhanced physical properties when hydrogen is incorporated in numerous binary systems. Despite the high reactivity of hydrogen, the noble metals (Cu, Ag, and Au) display an outstanding resilience to hydride formation, with no reports of a stable compound with a hydrogen molar ratio ≥ 1 at room temperature. Here, through extreme compression and in situ laser heating of pure copper in a hydrogen atmosphere, we explore the affinity of these elements to adopt binary compounds. We report on the phase behavior and stabilities in the Cu–H system, analyzed via synchrotron X-ray diffraction, up to pressures of 50 GPa. We confirm the existence of the previously reported γ0-CuH0.15, γ1-CuH0.5, and ε-Cu2H phases. Most notably, we report the highest hydrogen-content noble-metal hydride stable at room temperature to date: γ2-CuH0.65, which was synthesized through laser heating. This study furthers our understanding of hydrogen-transition metal chemistry and may find applicability in future hydrogen-storage applications.

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Research Engines and Fuels—Review
Development of Fuel/Engine Systems—The Way Forward to Sustainable Transport
Gautam Kalghatgi
Engineering . 2019, 5 (3): 510 -518 .   https://doi.org/10.1016/j.eng.2019.01.009
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Abstract

The global demand for transport energy is large, growing, and primarily met by petroleum-derived liquid fuels powering internal combustion engines (ICEs). Moreover, the demand for jet fuel and diesel is projected to grow faster than the demand for gasoline in the future, and is likely to result in low-octane gasoline components becoming more readily available. Significant initiatives with varying motivations are taking place to develop the battery electric vehicle (BEV) and the fuel cell as alternatives to ICE vehicles, and to establish fuels such as biofuels and natural gas as alternatives to conventional liquid fuels. However, each of these alternatives starts from a very low base and faces significant barriers to fast and unrestrained growth; thus, transport—and particularly commercial transport—will continue to be largely powered by ICEs running on petroleum-based liquid fuels for decades to come. Hence, the sustainability of transport in terms of affordability, energy security, and impact on greenhouse gas (GHG) emissions and air quality can only be ensured by improving ICEs. Indeed, ICEs will continue to improve while using current market fuels, through improvements in combustion, control, and after-treatment systems, assisted by partial electrification in the form of hybridization. However, there is even more scope for improvement through the development of fuel/engine systems that can additionally leverage benefits in fuels manufacture and use components that may be readily available. Gasoline compression ignition (GCI), which uses low-octane gasoline in a compression ignition engine, is one such example. GCI would enable diesel-like efficiencies while making it easier to control nitrogen oxides (NOx) and particulates at a lower cost compared with modern diesel engines. Octane on demand (OOD) also helps to ensure optimum use of available fuel anti-knock quality, and thus improves the overall efficiency of the system.

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The Possibility of Active Attitude Control for Fuel Spray
Masataka Arai
Engineering . 2019, 5 (3): 519 -534 .   https://doi.org/10.1016/j.eng.2019.04.010
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Abstract

The internal combustion engine (ICE) is an attractive power source for automobiles, with its superior storability, transportability, and suppliability of liquid fuel with high energy density. Compact ICEs with high performance and a low environmental load are greatly needed. In the future, smart active control of combustion by means of fuel spray injection must be considered as a breakthrough technology to address serious issues related to conventional ICEs, such as emissions. A designed fuel injection rate and spray pattern during the injection period have been technically developed, and combustion can be partially controlled in the conventional ICE. However, spatial fuel distribution is not progressing as desired in the field of combustion; thus, new and effective active control technologies for fuel spray are very necessary for the smart control of combustion. Cavitation, flash boiling, spray-to-spray interaction, spray-to-wall interaction, and air flow have potential as a basis for active attitude control of fuel spray. This article uses evidence from the literature to discuss the possibility of active spray attitude control for future fuel spray combustion technology in a smart compact ICE.

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A High-Efficiency Two-Stroke Engine Concept: The Boosted Uniflow Scavenged Direct-Injection Gasoline (BUSDIG) Engine with Air Hybrid Operation
Xinyan Wang, Hua Zhao
Engineering . 2019, 5 (3): 535 -547 .   https://doi.org/10.1016/j.eng.2019.03.008
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Abstract

A novel two-stroke boosted uniflow scavenged direct-injection gasoline (BUSDIG) engine has been proposed and designed in order to achieve aggressive engine downsizing and down-speeding for higher engine performance and efficiency. In this paper, the design and development of the BUSDIG engine are outlined discussed and the key findings are summarized to highlight the progress of the development of the proposed two-stroke BUSDIG engine. In order to maximize the scavenging performance and produce sufficient in-cylinder flow motions for the fuel/air mixing process in the two-stroke BUSDIG engine, the engine bore/stroke ratio, intake scavenge port angles, and intake plenum design were optimized by three-dimensional (3D) computational fluid dynamics (CFD) simulations. The effects of the opening profiles of the scavenge ports and exhaust valves on controlling the scavenging process were also investigated. In order to achieve optimal in-cylinder fuel stratification, the mixture-formation processes by different injection strategies were studied by using CFD simulations with a calibrated Reitz–Diwakar breakup model. Based on the optimal design of the BUSDIG engine, one-dimensional (1D) engine simulations were performed in Ricardo WAVE. The results showed that a maximum brake thermal efficiency of 47.2% can be achieved for the two-stroke BUSDIG engine with lean combustion and water injection. A peak brake toque of 379 N·m and a peak brake power density of 112 kW·L−1 were achieved at 1600 and 4000 r·min−1, respectively, in the BUSDIG engine with the stoichiometric condition.

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Research Engines and Fuels—Article
Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions
Hyunwook Park, Euijoon Shim, Choongsik Bae
Engineering . 2019, 5 (3): 548 -557 .   https://doi.org/10.1016/j.eng.2019.03.005
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Abstract

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

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Research Engines and Flues—Article
An Experimental Investigation on Low Load Combustion Stability and Cold-Firing Capacity of a Gasoline Compression Ignition Engine
Lei Zhou, Jianxiong Hua, Haiqiao Wei, Yiyong Han
Engineering . 2019, 5 (3): 558 -567 .   https://doi.org/10.1016/j.eng.2018.12.010
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Abstract

Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties; however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warm-up conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating; thus, this method is appropriate for engine cold-start and warm-up.

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Research Engines and Fuels—Article
Evaluation of H2 Influence on the Evolution Mechanism of NOx Storage and Reduction over Pt–Ba–Ce/γ-Al2O3 Catalysts
Pan Wang, Jing Yi, Chuan Sun, Peng Luo, Lili Lei
Engineering . 2019, 5 (3): 568 -575 .   https://doi.org/10.1016/j.eng.2019.02.005
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Abstract

In this investigation, Pt–Ba–Ce/γ-Al2O3 catalysts were prepared by incipient wetness impregnation and experiments were performed to evaluate the influence of H2 on the evolution mechanism of nitrogen oxides (NOx) storage and reduction (NSR). The physical and chemical properties of the Pt–Ba–Ce/γ-Al2O3 catalysts were studied using a combination of characterization techniques, which showed that PtOx, CeO2, and BaCO3, whose peaks were observed in X-ray diffraction (XRD) spectra, dispersed well on the γ-Al2O3, as shown by transmission electron microscope (TEM), and that the difference between Ce3+ and Ce4+, as detected by X-ray photoelectron spectroscopy (XPS), facilitated the migration of active oxygen over the catalyst. In the process of a complete NSR experiment, the NOx storage capability was greatly enhanced in the temperature range of 250–350 °C, and reached a maximum value of 315.3 μmol·gcat−1 at 350 °C, which was ascribed to the increase in NO2 yield. In a lean and rich cycling experiment, the results showed that NOx storage efficiency and conversion were increased when the time of H2 exposure (i.e., 30, 45, and 60 s) was extended. The maximum NOx conversion of the catalyst reached 83.5% when the duration of the lean and rich phases was 240  and 60 s, respectively. The results revealed that increasing the content of H2 by an appropriate amount was favorable to the NSR mechanism due to increased decomposition of nitrate or nitrite, and the refreshing of trapping sites for the next cycle of NSR.

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Research Green Chemical Engineering—Article
Laminar-to-Turbulence Transition Revealed Through a Reynolds Number Equivalence
Xiao Dong Chen
Engineering . 2019, 5 (3): 576 -579 .   https://doi.org/10.1016/j.eng.2018.09.013
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Abstract

Flow transition from laminar to turbulent mode (and vice versa)—that is, the initiation of turbulence—is one of the most important research subjects in the history of engineering. Even for pipe flow, predicting the onset of turbulence requires sophisticated instrumentation and/or direct numerical simulation, based on observing the instantaneous flow structure formation and evolution. In this work, a local Reynolds number equivalence γ (ratio of local inertia effect to viscous effect) is seen to conform to the Universal Law of the Wall, where γ = 1 represents a quantitative balance between the abovementioned two effects. This coincides with the wall layer thickness (y+ = 1, where y+ is the dimensionless distance from the wall surface defined in the Universal Law of the Wall). It is found that the characteristic of how the local derivative of γ against the local velocity changes with increasing velocity determines the onset of turbulence. For pipe flow, γ ≈ 25, and for plate flow, γ ≈ 151.5. These findings suggest that a certain combination of γ and velocity (nonlinearity) can qualify the source of turbulence (i.e., generate turbulent energy). Similarly, a re-evaluation of the previous findings reveals that only the geometrically narrow domain can act locally as the source of turbulence, with the rest of the flow field largely being left for transporting and dissipating. This understanding will have an impact on the future large-scale modeling of turbulence.

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Research Robotics—Article
A Micro Peristaltic Pump Using an Optically Controllable Bioactuator
Eitaro Yamatsuta, Sze Ping Beh, Kaoru Uesugi, Hidenobu Tsujimura, Keisuke Morishima
Engineering . 2019, 5 (3): 580 -585 .   https://doi.org/10.1016/j.eng.2018.11.033
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Abstract

Peristalsis is widely seen in nature, as this pumping action is important in digestive systems for conveying sustenance to every corner of the body. In this paper, we propose a muscle-powered tubular micro pump that provides peristaltic transport. We utilized Drosophila melanogaster larvae that express channelrhodopsin-2 (ChR2) on the cell membrane of skeletal muscles to obtain light-responsive muscle tissues. The larvae were forced to contract with blue light stimulation. While changing the speed of the propagating light stimulation, we observed displacement on the surface of the contractile muscle tissues. We obtained peristaltic pumps from the larvae by dissecting them into tubular structures. The average inner diameter of the tubular structures was about 400 μm and the average outer diameter was about 750 μm. Contractions of this tubular structure could be controlled with the same blue light stimulation. To make the inner flow visible, we placed microbeads into the peristaltic pump, and thus determined that the pump could transport microbeads at a speed of 120 μm·s−1.

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Research Drop-on-Demand Printing—Article
Multi-Objective Optimization Design through Machine Learning for Drop-on-Demand Bioprinting
Jia Shi, Jinchun Song, Bin Song, Wen F. Lu
Engineering . 2019, 5 (3): 586 -593 .   https://doi.org/10.1016/j.eng.2018.12.009
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Abstract

Drop-on-demand (DOD) bioprinting has been widely used in tissue engineering due to its high-throughput efficiency and cost effectiveness. However, this type of bioprinting involves challenges such as satellite generation, too-large droplet generation, and too-low droplet speed. These challenges reduce the stability and precision of DOD printing, disorder cell arrays, and hence generate further structural errors. In this paper, a multi-objective optimization (MOO) design method for DOD printing parameters through fully connected neural networks (FCNNs) is proposed in order to solve these challenges. The MOO problem comprises two objective functions: to develop the satellite formation model with FCNNs; and to decrease droplet diameter and increase droplet speed. A hybrid multi-subgradient descent bundle method with an adaptive learning rate algorithm (HMSGDBA), which combines the multi-subgradient descent bundle (MSGDB) method with Adam algorithm, is introduced in order to search for the Pareto-optimal set for the MOO problem. The superiority of HMSGDBA is demonstrated through comparative studies with the MSGDB method. The experimental results show that a single droplet can be printed stably and the droplet speed can be increased from 0.88 to 2.08 m·s−1 after optimization with the proposed method. The proposed method can improve both printing precision and stability, and is useful in realizing precise cell arrays and complex biological functions. Furthermore, it can be used to obtain guidelines for the setup of cell-printing experimental platforms.

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