1,720,964 research outputs found
대향류 연소 해석을 통한 고체연료의 후퇴율 및 연소 특성 예측에 관한 연구
No full textThis study investigates the regression rate and combustion characteristics of solid fuel using a simple one-dimensional counterflow diffusion flame analysis. A coupled computational framework was developed by integrating gas-phase and condensed-phase reaction models. Simulation results were validated using regression rates from counterflow combustion experiments. Furthermore, the effects of oxygen concentration, ambient pressure, and oxidizer momentum flux on the combustion behaviors of solid fuel were systematically examined. The predicted regression rates showed good agreement with experimental data across the range of conditions tested in this study, although discrepancies were observed at lower pressures. An increase in oxygen concentration, ambient pressure, and oxidizer momentum flux was found to enhance the regression rate. In particular, the increase in momentum flux and pressure shifts the peak temperature location closer to the fuel surface. This proximity intensifies heat feedback to the solid surface, thereby accelerating the pyrolysis process and increasing the regression rate. Furthermore, the correlation analysis identified the oxygen mass fraction as the most influential of the three examined parameters affecting the regression rate. These findings offer fundamental insight into the pyrolysis and combustion of solid fuel relevant to air-breathing solid fuel propulsion systems.
Atomistic insights into catalytic role of platinum-graphene nanostructures in decomposition of high-energy-density fuels
No full textTo advance the cooling performance critical for hypersonic vehicles, high-energy-density fuels have emerged as promising candidates, with platinum-graphene (Pt@FGS) nanocatalysts demonstrating significant potential for enhancing their regenerative cooling efficiency. However, the underlying catalytic mechanisms of these nanocatalysts, particularly their influence on reaction pathways and carbonization processes, remain insufficiently understood. This study employs a ReaxFF-based hybrid simulation approach to investigate the effects of Pt@FGS nanocatalysts on the decomposition of exo-tetrahydrodicyclopentadiene (exo-THDCPD) across a broad temperature range (900-2000 K). The Pt@FGS nanocatalysts were modeled as a partially oxidized graphene structure with six platinum atoms anchored at defect sites. ReaxFF molecular dynamics (MD) simulations were performed to capture real-time pyrolysis pathways and nanocatalyst-fuel interactions at the atomic scale. To extend the timescale and observe low-temperature pyrolysis relevant to experimental conditions, the collective variabledriven hyperdynamics (CVHD) method was employed. Nudged elastic band (NEB) calculations quantified key bond dissociation energy barriers, providing insight into catalytic dehydrogenation mechanisms. The MD results revealed that Pt@FGS nanocatalysts reduce the activation energy by approximately 33 % compared to neat fuel, significantly enhancing fuel conversion rates by up to a factor of four through catalytic dehydrogenation. Heat sink capacity improvements were observed at lower temperature ranges, attributed to nanocatalyst-promoted dehydrogenation, as confirmed by NEB analysis. The CVHD approach enabled pyrolysis simulations under experimentally relevant conditions, yielding activation energies and product distributions consistent with those obtained from high-temperature MD simulations. Interestingly, additional MD simulations demonstrated Pt@FGS nanocatalysts can delay carbonization onset effectively suppressing the formation of carbon deposits. By combining MD, CVHD, and NEB analyses, we elucidated the reaction mechanisms of exo-THDCPD decomposition over Pt@FGS nanocatalysts. The results demonstrate at the atomistic scale that Pt suppresses coke formation by interacting with intermediates and hindering aromatic ring closure, providing insights into the design of fueldispersible catalysts for regenerative fuel cooling.
Exploring mechanical performance in Al-Pt binary alloys through molecular dynamics simulations
No full textThis study systematically explores the impact of environmental factors on the mechanical properties of an Al-Pt binary alloy using molecular dynamics simulations. By varying Pt content and examining key conditions such as temperature, strain rate, and vacancy defects, we delve into their combined effects on the alloy's fracture behavior and overall mechanical performance. Our simulations demonstrate that increasing strain rates enhance fracture strength, while higher temperatures and vacancy concentrations notably reduce it. In contrast, the elastic modulus remained relatively insensitive to these environmental changes. Furthermore, our study highlights the crucial role of point vacancies in accelerating fracture initiation, providing new insights into the failure mechanisms of Al-Pt alloys. These findings have significant implications for the design and optimization of highperformance alloy materials, particularly for applications requiring resilience under extreme operational conditions. The detailed analysis of fracture strength across various environmental scenarios offers a pathway to developing alloys with improved durability and mechanical integrity.
ReaxFF molecular dynamics simulations of high-energy-density fuel combustion catalyzed by Pt-graphene hybrids
No full textThe enhancement of combustion performance and ignition characteristics of high-energy-density fuels is crucial for the advancement of hypersonic propulsion systems. In particular, addressing long ignition delay times and incomplete fuel oxidation remains a key challenge. This study investigates the combustion reaction mechanisms of exo-tetrahydrodicyclopentadiene (exo-THDCPD) dispersed with Pt-graphene nanocatalysts using ReaxFF molecular dynamics simulations. Simulations were conducted at various temperatures to analyze the effects of Pt-graphene on fuel decomposition, ignition delay, and intermediate species formation. The results demonstrate that the presence of Pt-graphene significantly reduces ignition delay by accelerating radical formation and enhancing early-stage oxidation reactions. Additionally, the nanocatalyst promotes more complete combustion by facilitating CO oxidation to CO2 and suppressing intermediate hydrocarbon accumulation. Reaction pathway analysis further confirms that Pt-graphene shifts fuel breakdown mechanisms toward oxidation-driven pathways, resulting in improved fuel consumption and combustion efficiency. These findings provide valuable insight into the role of nanocatalysts in optimizing fuel performance for high-speed propulsion applications.
Spatial control of silane layer formation on boron nanoparticles via diverse methods for high-energetic nanofuel applications
No full textThis study presents a spatial control strategy of silane layer thickness using injection and dropwise methods to enhance the dispersion stability and combustion efficiency of energetic boron nanoparticles (BNs) in hydro-carbon fuels. Dropwise addition enables uniform silane coating through controlled hydrolysis and condensation,while rapid injection results in deposits of low-density siloxane on BNs. The dropwise silane-coated reduced BNs (DrBNOs) exhibit improved dispersion stability, low sedimentation, and enhanced compatibility with hydro-carbon fuels. Additionally, the long-chain silane coating effectively passivates nanoparticle surface, thereby increasing oxidation resistance and enabling faster ignition, complete combustion, and optimized energy release. Bomb calorimetry and droplet combustion analysis confirmed that DrBNOs deliver high calorific values with minimal residual soot. These findings highlight the importance of silane layer thickness in maximizing com-bustion performance, with the spatial control strategy offering a promising approach for developing advanced energetic nanoadditives for scramjet engine fuels.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
