Journal articles on the topic 'Early ignition phase'
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1
PITT, P. L., R. M. CLEMENTS, and D. R. TOPHAM. "The Early Phase of Spark Ignition." Combustion Science and Technology 78, no. 4-6 (August 1991): 289–314. http://dx.doi.org/10.1080/00102209108951753.
2
Yossefi, D., S. J. Maskell, S. J. Ashcroft, and M. R. Belmont. "Ignition source characteristics for natural-gas-burning vehicle engines." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 214, no. 2 (February 1, 2000): 171–80. http://dx.doi.org/10.1177/095440700021400206.
Abstract:
Natural gas is a promising alternative fuel to petrol for vehicles. However, one of the factors hampering the design of natural gas burning engines for domestic cars is the long delay from the time of ignition to the commencement of significant heat release. This is mainly due to the substantially endothermic phase during the early development of the combustion in natural gas. It is well known that high-energy, extended or multiple ignition sources can reduce this problem. The present article uses a large-scale computer simulation of a natural gas engine to examine the issues affecting the optimization of such ignition sources.
3
Tornatore, C., P. Sementa, and S. S. Merola. "Optical investigations of the early combustion phase in spark ignition boosted engines." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 225, no. 6 (June 2011): 787–800. http://dx.doi.org/10.1177/2041299110394915.
4
Hatai, Keigo, and Taiichi Nagata. "Quantitative Clarification of Stable Ignition Region for HKP110 Green Hypergolic Bipropellant." Aerospace 9, no. 3 (March 2, 2022): 129. http://dx.doi.org/10.3390/aerospace9030129.
Abstract:
As a candidate for a green hypergolic bipropellant, the combination of highly concentrated hydrogen peroxide and fuel with dissolved sodium borohydride has been widely studied. In this study, a drop test using such a green hypergolic bipropellant was conducted to investigate the stable ignition region in terms of the mixture ratio. As a result, stagnation phenomena of flame growth were observed in high mixture ratio conditions. In addition, impinging-jet tests using a windowed chamber were conducted with the green hypergolic bipropellant to observe the ignition phenomena inside the combustion chamber. As a result, unstable ignition phenomena were observed in oxidizer-lead injection cases. Besides the unstable ignition, hard starts occurred several times during the test series. Data analysis demonstrated that controlling the transient mixture ratio in the early phase of injection is essential for preventing unstable ignition and hard starts. The quantitative threshold of mixture ratio for stable ignition was clarified based on the test results.
5
Andreassi, L., S. Cordiner, and V. Rocco. "Modelling the early stage of spark ignition engine combustion using the KIVA-3V code incorporating an ignition model." International Journal of Engine Research 4, no. 3 (June 1, 2003): 179–92. http://dx.doi.org/10.1243/146808703322223379.
Abstract:
The evolution of early stages of homogeneous mixture combustion in spark ignition (SI) engines represents a critical period that greatly affects the whole combustion process. A proper description of this critical phase represents a major issue, which could strongly influence the overall model predictive capability (i.e. model ability to reproduce the real engine behaviour for a large range of operating conditions without any major tuning). Such requirements become even more important for the simulation of last-generation gasoline direct injection or lean stratified engines, where ignition could determine the functionality of the engine itself. In this paper, after a detailed analysis of the ignition physical process and its modelling issues, the predictive capability of the KIVA-3V code has been improved by substituting the original ignition procedure with a more detailed kernel evolution model based on the one presented by Herweg and Maly in 1992. The ignition model introduced in a KIVA-3V version already modified by the authors (re-zoning algorithm, combustion and turbulence models, cylinder wall heat transfer, etc.) has then been tested in order to assess its level of accuracy in describing this complex phenomenon, by varying the most critical engine operating conditions and keeping combustion tuning parameters unchanged. After comparing ignition model results with the corresponding ones presented by Herweg and Maly, a specific application of the overall model (KIVA-3V + ignition model + turbulent combustion model) has been made to perform an analysis of a compressed natural gas (CNG) fuelled engine for heavy-duty applications. To this aim, the in-cylinder combustion history and the related processes as the temperature distribution and NOx formation have been calculated and verified with reference to the experimental data measured in a wide range of operating conditions of an IVECO turbocharged engine.
6
FIEDKIEWICZ, Łukasz, and Ireneusz PIELECHA. "Optical analysis of the gas flame development in a RCM using a high-power ignition system." Combustion Engines 173, no. 2 (May 1, 2018): 47–54. http://dx.doi.org/10.19206/ce-2018-208.
Abstract:
The combustion process quality is determined by several factors: the composition of the fuel-air mixture in the vicinity of the spark plug and the discharge conditions on the spark plug. This article assesses a high-power ignition system using optical gas flame propaga-tion analyzes. The tests were carried out in a rapid compression machine, using a fast camera for filming. The spark plug discharge quality assessment was determined indirectly by the flame propagation conditions after the ignition of the mixture (during methane combustion). The size of the flame surface and the rate of its change were assumed as a comparative criterion. It has been found that when using an ignition system with high discharge power the rate of flame development is 14% higher with respect to conventional ignition systems. In addition, the shorter development time of the early flame phase after discharge when using the new ignition system was confirmed. Based on the obtained test results and analyzes, modifications of engine operation settings were indicated, resulting from the use of a high discharge power system.
7
Bangerter, R. O., A. Faltens, and P. A. Seidl. "Accelerators for Inertial Fusion Energy Production." Reviews of Accelerator Science and Technology 06 (January 2013): 85–116. http://dx.doi.org/10.1142/s1793626813300053.
Abstract:
Since the 1970s, high energy heavy ion accelerators have been one of the leading options for imploding and igniting targets for inertial fusion energy production. Following the energy crisis of the early 1970s, a number of people in the international accelerator community enthusiastically began working on accelerators for this application. In the last decade, there has also been significant interest in using accelerators to study high energy density physics (HEDP). Nevertheless, research on heavy ion accelerators for fusion has proceeded slowly pending demonstration of target ignition using the National Ignition Facility (NIF), a laser-based facility at Lawrence Livermore National Laboratory. A recent report of the National Research Council recommends expansion of accelerator research in the US if and when the NIF achieves ignition. Fusion target physics and the economics of commercial energy production place constraints on the design of accelerators for fusion applications. From a scientific standpoint, phase space and space charge considerations lead to the most stringent constraints. Meeting these constraints almost certainly requires the use of multiple beams of heavy ions with kinetic energies >1 GeV. These constraints also favor the use of singly charged ions. This article discusses the constraints for both fusion and HEDP, and explains how they lead to the requirements on beam parameters. RF and induction linacs are currently the leading contenders for fusion applications. We discuss the advantages and disadvantages of both options. We also discuss the principal issues that must yet be resolved.
8
Soler, Anna, Nicolau Pineda, Helen San Segundo, Joan Bech, and Joan Montanyà. "Characterisation of thunderstorms that caused lightning-ignited wildfires." International Journal of Wildland Fire 30, no. 12 (2021): 954. http://dx.doi.org/10.1071/wf21076.
Abstract:
This work studies the characteristics of thunderstorms that cause lightning-caused wildfires in Catalonia, north-east Iberian Peninsula, using lightning and weather radar data. Although thunderstorms produce ~57 000 cloud-to-ground (CG) flashes yearly in Catalonia, only 1 in 1000 end up as a flaming wildfire. Characterisation of thunderstorms that ignite wildland fires can help fire weather forecasters identify regions of increased ignition potential. Lightning data and radar products like maximum reflectivity, echo tops heights and equivalent liquid content were obtained over a 7-year period. Characteristics of thunderstorms that ignite wildfires are examined including storm motion, duration, morphology and intensity. It was found that most probable ignition candidates are lightning associated with cellular thunderstorms and non-linear systems. Radar reflectivity values for lightning that ignites wildfires were found to be below average, these morphological types favouring the occurrence of lightning outside regions of high reflectivity, where precipitation reaching the ground is low or non-existent. Thunderstorms that ignite wildfires are typically of low intensity, with a CG flash rate below average. Most ignitions occur during the maturity phase when the CG flash rate is the highest. A better scientific understanding of the thunderstorms that cause lightning wildfires will help improve early firefighting response.
9
Wu, Taoyang, Jixu Liu, Chunling Wu, Xiaojun Jing, Jiajia Liu, Guomin Pang, Xiangyang Guo, and Yachen Guo. "Experimental study on the factors influencing performance and emissions of hydrogen internal combustion engines." E3S Web of Conferences 522 (2024): 01009. http://dx.doi.org/10.1051/e3sconf/202452201009.
Abstract:
Hydrogen internal combustion engines (H2-ICEs) have advantages such as clean combustion and zero carbon emissions, and have become one of the important technical routes for decarbonization in the internal combustion engine industry. In this paper, several key factors affecting the performance and emissions of hydrogen internal combustion engines, such as ignition timing, excess air coefficient, and hydrogen injection timing, were systematically studied on a spark ignition multi-point injection (MPI) hydrogen internal combustion engine bench. The experimental results indicate that the ignition timing controls the combustion phase of hydrogen. Moderate early ignition can improve the brake thermal efficiency (BTE) while having little impact on the NOX emissions. Excess air coefficient(λ) can significantly affect the performance and emissions of H2-ICE. Along with the increase of the λ, the NOX emissions first increases and then continues to decline. When the λ reaching 2.1 or above, near zero emissions of NOX can be achieved. The advance of hydrogen injection timing will slightly increase the peak of cylinder pressure and instantaneous heat release rate. However, overall, the impact of hydrogen injection timing on BTE and NOX emissions is not significant on MPI H2-ICE.
10
Strozzi, Camille, Moez Ben Houidi, Julien Sotton, and Marc Bellenoue. "Analysis of ECN spray A ignition in a Rapid Compression Machine using simultaneous OH* chemiluminescence and formaldehyde PLIF." Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 75 (2020): 38. http://dx.doi.org/10.2516/ogst/2020036.
Abstract:
The canonical diesel spray A is characterized in an optical Rapid Compression Machine (RCM) at high temperature and density conditions (900 K and 850 K, ρ = 23 kg/m3) using simultaneous high-speed OH* chemiluminescence and two-pulse 355 nm Planar Laser Induced Fluorescence (PLIF). The focus is on the time evolution and the repeatability of the early stages of both cool flame and hot ignition phenomena, and on the time evolution of the fluorescing formaldehyde region in between. In particular, time resolved data related to the cool flame are provided. They show the development of several separated kernels on the spray sides at the onset of formaldehyde appearance. Shortly after this phase, the cool flame region expands at high velocity around the kernels and further downstream towards the richer region at the spray head, reaching finally most of the vapor phase region. The position of the first high temperature kernels and their growth are then characterized, with emphasis on the statistics of their location. These time-resolved data are new and they provide further insights into the dynamics of the spray A ignition. They bring some elements on the underlying mechanisms, which will be useful for the validation and improvement of numerical models devoted to diesel spray ignition.
11
Balles, E. N., and J. B. Heywood. "Spray and Flame Structure in Diesel Combustion." Journal of Engineering for Gas Turbines and Power 111, no. 3 (July 1, 1989): 451–57. http://dx.doi.org/10.1115/1.3240275.
Abstract:
The diesel combustion process in direct-injection diesel engines consists of four distinct stages: an ignition delay, a premixed phase, a mixing-controlled phase, and a late combustion phase. This paper uses geometric information from high-speed direct and shadowgraph movies and corresponding combustion chamber pressure histories, taken in a rapid compression machine study of direct-injection diesel combustion, for a coupled analysis of the diesel flame geometry and energy or heat release to develop our understanding of the diesel spray and flame structure during the ignition delay period and premixed combustion phase. It is shown that each fuel spray from a multihole fuel-injector nozzle consists of a narrow liquid-containing core centered within a much larger fuel-vapor air region, which has a distinct boundary. The liquid core does not penetrate to the chamber periphery, while the vapor containing spray interacts strongly with the boundary. Ignition occurs part way along each growing spray. Once combustion starts, the outer boundary of the fuel-vapor-containing region expands more rapidly due to the combustion energy release. Very high initial spreading rates of the luminous region boundary are observed. A comparison of enflamed areas and volumes, and burned gas volumes, indicates that the luminous region during the early stages of combustion (assumed stoichiometric) is around 1 cm thick and does not fill the full height of the chamber. During the premixed combustion phase, the burned gas volume is one-half the enflamed volume, indicating the presence of a substantial unburned (rich) fuel-vapor/air core within the luminous region of each fuel spray. A close correspondence of flame geometry to spray geometry is evident throughout the combustion process.
12
Wang, Xiang-Yu, Xiao-Kun Wang, Kai Zhao, Yong-Xin Liu, and You-Nian Wang. "Experimental study on the ignition process of a pulsed capacitively coupled RF discharge: Effects of gas pressure and voltage amplitude." Physics of Plasmas 29, no. 5 (May 2022): 053501. http://dx.doi.org/10.1063/5.0087182.
Abstract:
The effects of gas pressure and voltage amplitude on the ignition process of a pulse capacitively coupled RF argon discharge are experimentally investigated. The electron density is measured by a hairpin probe, the spatiotemporal distribution of the electron impact excitation dynamics is determined by phase resolved optical emission spectroscopy, and the electrical parameters are obtained by analyzing the measured current and voltage waveforms. In this work, the pulse plasma is ignited with few initial electrons, so the ignition process behaves like gas breakdown. Based on the measured RF breakdown curve, the gas pressures and voltage amplitudes are selected, and then different characteristics of ignition processes are compared and discussed in detail. Particularly, the spatiotemporal pattern of the electron impact excitation rate obtained within the selected pressure range, as well as other results, aid the intuitive understanding of a typical “V-shaped” RF breakdown curve. At lower pressures, the excitation pattern exhibit shorter and tilted regions, ending at electrodes during the early ignition stage, implying a substantial electron energy loss, while at relatively high pressures, the excitation pattern becomes wider and less tilted, and the proportion of electron energy consumed by excitation processes increases. In addition, by increasing the voltage amplitude, the ignition is advanced and becomes more significant, manifesting a faster increase in discharge current and a stronger overshoot of RF power deposition. Meanwhile, at high voltage amplitude, the excitation pattern exhibits complex spatiotemporal distribution due to enhanced local electric field when the plasma emission intensity overshoots.
13
Howard, Stephen L., Lang‐Mann Chang, and Douglas E. Kooker. "Thermocouple sensor for rapid temperature measurements during ignition and early phase combustion of packed propellant beds." Review of Scientific Instruments 66, no. 8 (August 1995): 4259–66. http://dx.doi.org/10.1063/1.1145379.
14
Cheney, NP, and JS Gould. "Fire Growth and Acceleration." International Journal of Wildland Fire 7, no. 1 (1997): 1. http://dx.doi.org/10.1071/wf9970001.
Abstract:
The use of the terms "growth" and "acceleration" appears to be inconsistent in the literature and we believe this inconsistency has hindered our understanding of behaviour in the early stages of a fire. The development of a fire from a point ignition to some equilibrium state and the associated increase in fire size and intensity has been referred to variously as the fire growth (Pyne 1984); build-up (Luke and McArthur 1978); or acceleration (Chandler et al. 1983) phase of the fire. More specifically the "acceleration phase" has been used to describe the increase in rate of spread from ignition to a quasi-steady rate of spread (Luke and McArthur 1978, McAlpine and Wakimoto 1991). Characteristic curves showing the increase in rate of spread are illustrated for different fuel and weather conditions (Luke and McArthur 1978). Hypothetical models to describe these curves have been proposed by Cheney and Bary (1969), Van Wagner (unpublished) and McAlpine and Wakimoto (1991). They have been called acceleration curves and acceleration models. The terms growth and acceleration, however, represent different concepts that are not interchangeable. We would like to clarify these concepts and discuss the practical implications for fire managers.
15
BRET, ANTOINE, and CLAUDE DEUTSCH. "Density gradient effects on beam plasma linear instabilities for fast ignition scenario." Laser and Particle Beams 24, no. 2 (June 2006): 269–73. http://dx.doi.org/10.1017/s0263034606060411.
Abstract:
In the fast ignition scenario for inertial fusion, a relativistic electron beam is supposed to travel from the side of the fusion pellet to its core. One one hand, a relativistic electron beam passing through a plasma is a highly unstable system. On the other hand, the pellet core is denser than its side by four orders of magnitude so that the beam makes its way through a important density gradient. We here investigate the effect of this gradient on the instabilities. It is found that they should develop so early that gradient effects are negligible in the linear phase.
16
Gold, M. R., C. Arcoumanis, J. H. Whitelaw, J. Gaade, and S. Wallace. "Mixture preparation strategies in an optical four-valve port-injected gasoline engine." International Journal of Engine Research 1, no. 1 (February 1, 2000): 41–56. http://dx.doi.org/10.1243/1468087001545254.
Abstract:
The mixture formation in a single-cylinder, optical port-injected gasoline engine was investigated for both closed- and open-valve injection strategies with a combination of phase Doppler anemometry, laser-induced fluorescence and Mie scattering and correlated with combustion development and exhaust emissions. Detailed crank angle resolved data of the flow and mixture distribution during induction and compression have revealed the advantages of early open-valve injection, in terms of extending the lean limit and maintaining satisfactory engine performance and HC/NOx emissions, achieved through charge stratification in the vicinity of the spark plug at the time of ignition.
17
Merola, S., A. Irimescu, B. M. Vaglieco, S. Di Iorio, and P. Sementa. "Spectroscopy Based Tool for Temperature Evaluation during the Spark Discharge." SAE International Journal of Advances and Current Practices in Mobility 2, no. 2 (January 24, 2020): 966–78. http://dx.doi.org/10.4271/2019-32-0502.
Abstract:
<div class="section abstract"><div class="htmlview paragraph">In this work, a new tool is proposed and tested to investigate the early phase of spark ignition (SI) processes. The diagnostic tool is based on Spark-Induced Breakdown Spectroscopy (SIBS), a consolidated technique in which the plasma formed by spark generation between two electrodes is used as the excitation source for optical emission spectroscopy (OES).</div><div class="htmlview paragraph">The spark discharge of a commercial ignition system was analyzed through OES to correlate the characteristic evolution of the discharge with the formation of reactive species inside the activated volume. Specifically, an open-source spectrum simulation program (Lifbase) together with the NIST database was used for defining relations between the ultraviolet emission bands of nitrogen first negative system (FNS_N<sub>2</sub>) in the glow phase for different plasma temperature and pressure values.</div><div class="htmlview paragraph">Besides plasma density and ion energy, electron and gas temperatures are important parameters that govern the reaction rate of active species generation through dissociation, excitation, and ionization processes and thus influence the chemistry of the spark discharge. It is well known that the electrical discharge occurring between the spark plug electrodes can be divided into three phases (breakdown, arc and glow discharge), characterized by different time scales. The breakdown occurrence causes the gas molecules in the ignition area to break into atoms and ions. Molecular recombination starts after some hundreds nanoseconds from breakdown, thus leading to significantly different spectral emissions. Consequently, if measurements are triggered after the time at which breakdown occurs, molecule and molecular radical bands will be dominating in the spectral emission instead of the atomic lines.</div><div class="htmlview paragraph">The proposed methodology takes advantage of the peculiarity of N<sub>2</sub> molecules to exchange rotational and translational energy with heavy particles faster than with electrons. For this reason it is possible that rotational distributions quickly achieve thermodynamic equilibrium with the bulk gas. Therefore, a convenient way to determine the gas temperature is through the measurement of the roto-vibrational band spectrum of nitrogen.</div><div class="htmlview paragraph">The validation of the developed tool was performed by considering the emission of excited species detected in ambient conditions. Successively, the methodology was applied in an optically accessible combustion chamber of a spark ignition research engine under motored and fired conditions, and further validated by temperature evaluations based on CN and OH emission bands ratio. The proposed tool allowed obtaining deeper insight into the complex physical and chemical phenomena underlying the ignition event.</div></div>
18
Xu, Bo Yan, De Zhi Sun, Yun Liang Qi, Yong Wei Zheng, Hai Ying Tian, and Shao Li Cai. "Study on Mixture Formation of Liquid LPG for a Center Injection DISI Engine." Advanced Materials Research 201-203 (February 2011): 622–26. http://dx.doi.org/10.4028/www.scientific.net/amr.201-203.622.
Abstract:
Center injection in pentroof combustion chamber can reduce wall wetting and unburned hydrocarbon emission in wall guided combustion system, which is generally employed in DISI (Direct Injection Spark Ignition) engines. Once liquid phase LPG (Liquefied Petroleum Gas) is injected at a high pressure, flash boiling occurs severely, promotes mixing and reduces wall wetting in wall guided engine. Based on validating the feasibility of the models, this paper numerically simulates the mixing process of a center injection wall guided DISI engine in different conditions. The results show that a stratified charge can obtained at part load with late injection, whereas at high load the early injection can achieve a homogeneous mixture at the end of compression stroke.
19
Oghenevweta, J. E., D. Wexler, and A. Calka. "Early stages of phase formation before the ignition peak during mechanically induced self-propagating reactions (MSRs) of titanium and graphite." Scripta Materialia 122 (September 2016): 93–97. http://dx.doi.org/10.1016/j.scriptamat.2016.05.028.
20
Rossi, Eleonora, and Yanina Prystauka. "Oscillatory brain dynamics of pronoun processing in native Spanish speakers and in late second language learners of Spanish." Bilingualism: Language and Cognition 23, no. 5 (January 29, 2020): 964–77. http://dx.doi.org/10.1017/s1366728919000798.
Abstract:
AbstractA longstanding question in the second language acquisition literature is whether late second language (L2) learners process grammatical structures in a native-like manner. Here, we use Time Frequency Representation (TFR) analysis to test morpho-syntactic processing of clitic pronouns in native and late L2 learners of Spanish. The TFR results show overall similar power decreases in theta, alpha, and beta frequencies in both groups. Critically, the observed oscillatory effects persisted in time for native Spanish speakers, but declined earlier for L2 learners. We discuss the results using cell-assembly theory models for language processing (e.g., Pulvermüller, 1999) that posit a biphasic time-course for neural assemblies consisting of an early ignition (recognition) and a later reverberation (re-processing) phase. We propose a working hypothesis for L2 processing in tune with a cell-assembly theory suggesting that the length of the reverberation phase could be a distinguishing feature between native and L2 processing.
21
Boyd, B., A. Smith Clark, A. C. Calder, D. M. Townsley, and M. Zingale. "Sensitivity of 3D Convective Urca Simulations to Changes in Urca Reactions." Journal of Physics: Conference Series 2742, no. 1 (April 1, 2024): 012001. http://dx.doi.org/10.1088/1742-6596/2742/1/012001.
Abstract:
Abstract A proposed setting for thermonuclear (Type Ia) supernovae is a white dwarf that has gained mass from a companion to the point of carbon ignition in the core. There is a simmering phase in the early stages of burning that involves the formation and growth of a core convection zone. One aspect of this phase is the convective Urca process, a linking of weak nuclear reactions to convection that may alter the composition and structure of the white dwarf. Convective Urca is not well understood and requires 3D fluid simulations to realistically model. Additionally, the convection is relatively slow (Mach number less than 0.005) so a low-Mach method is needed to make simulating computationally feasible. Using the MAESTROeX low-Mach hydrodynamics code, we investigate recent changes to how the weak reactions are modeled in the convective Urca simulations. We present results that quantify the changes to the reaction rates and their impact on the evolution of the simulation.
22
Zhdanova, Alena, Roman Volkov, Aleksandr Sviridenko, Geniy Kuznetsov, and Pavel Strizhak. "Influence of Compartment Fire Behavior at Ignition and Combustion Development Stages on the Operation of Fire Detectors." Fire 5, no. 3 (June 17, 2022): 84. http://dx.doi.org/10.3390/fire5030084.
Abstract:
This paper presents experimental research findings for those involved in the early phase of fire in office buildings. Class A model fires with a reaction area from 5 cm2 to 300 cm2 were chosen for investigation. To mock up a fire, the following combustible materials typical of offices were used: wood pieces, heat-insulated linoleum, paper and cardboard. The main characteristics of a model fire were recorded: temperature in the combustion zone, heat release, time of complete burnout and concentration of flue gas components. Typical trends and histograms of changes of these characteristics over time were presented; stages of ignition, flame combustion and smoldering were illustrated. The key characteristics of fire detector activation at different stages of model fire combustion were analyzed. Dead bands and operation conditions of a group of detectors (smoke, heat, optical, flame), their response time and errors were identified. It has been established that the most effective detectors are flame and smoke detectors. Specific operational aspects of detectors were established when recording the ignition of different types of model fires. The viability of combining at least two detectors to record fire behavior was established. Recommendations were made on using the obtained findings when optimizing the systems for detecting and recording the start of a compartment fire.
23
Pospelov, Boris, Yuliia Bezuhla, Oleksandr Yashchenko, Batyr Khalmuradov, Olena Petukhova, Stella Gornostal, Yurii Kozar, Kateryna Tishechkina, Olga Salamatina, and Zhanna Ihnatenko. "Revealing the features of the third order phase spectrum of the main dangerous parameters of the gas medium." Eastern-European Journal of Enterprise Technologies 6, no. 10 (120) (December 30, 2022): 63–70. http://dx.doi.org/10.15587/1729-4061.2022.268437.
Abstract:
The object of this study is the dynamics of hazardous parameters of the gas environment when materials are ignited in the premises. The task addressed was the early detection of fires in the premises. It is proposed to resolve this issue on the basis of using an assessment of the coherence of frequency components in the third-order spectrum relative to the dynamics of hazardous parameters of the gas environment. The results indicate the nonlinear nature of the dynamics of hazardous parameters of the gas environment both in the absence and in the presence of fires. It was established that the assessment of the coherence of the frequency components relative to the considered triplets in the third-order spectrum contains information on the ratio of order to chaos in the dynamics of hazardous parameters of the gas environment. This information can be used to reliably detect fires. It was found that when the test materials in the form of alcohol, paper, wood, and textiles are ignited, the ratio of order to chaos in the temperature and CO dynamics in a gaseous medium is halved. It was established that the average values for frequency indices from 0 to 20 of the coherence of the frequency components of the dynamics of hazardous parameters on the ignition interval of test materials are in the range from +0.005 to –0.187. At the same time, in the interval of absence of ignition of test materials, the average values of the coherence assessment for frequency indices from 0 to 20 are in the range from +0.48 to +0.022. The reported results generally indicate the prospects and further development of studies into the coherence of the frequency components of the third-order spectrum for the dynamics of hazardous parameters of the gas environment in order to detect fires in the premises
24
Guo, Peng Jiang, Xi Yan Gao, and Yun Bang Tang. "Analysis of Combustion Characteristics and Influencing Factors of Space Dispersed Double-Wall-Jet Combustion System." Advanced Materials Research 308-310 (August 2011): 1302–13. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.1302.
Abstract:
Based on the ideas of wall-guiding-spray and spatial dispersion, A new type of diesel engine double-wall-jet combustion system is designed. The effect of speed, load and injection condition on the double-wall-jet combustion system is researched by testing, on the double-wall-jet combustion system, the combustion modes for whole working condition is analyzed, the comparison of combustion and performance between the original machine with the new one is carried out. The results showed that: Instantaneous heat release rate of double-wall-jet combustion system shows a single peak. As the speed increases, the corresponding crank angle of ignition retards, the peak outbreak pressure increases and then decreases, the peak instantaneous heat release rate, the peak average temperature, the peak cylinder pressure rise ratio, and the cumulative heat release per unit mass of working gas is reduced. As the load increases, the corresponding crank angles of peak cylinder pressure and gravity center of heat release rate are postponed. With the load increasing, the ignition crank angle corresponds early at low speed, and the ignition point does not change significantly with the load at high speed. The effect of the injector hole diameter/number on the cylinder pressure and instantaneous heat release rate curve is not significant at high speed and large loads, but at low speed and large loads is significant. Cylinder pressure of 6-Φ21 injector is higher than 5-Φ25, the instantaneous heat release rate of 6-Φ21 injector has a trend of a single peak, the instantaneous heat release rate of 5-Φ25 injector has a trend of a double peak and the focus of the heat release rate postponed. With the advancing of injection timing, the ignition crank angle and combustion phase advances, the peak cylinder pressure increases. Injection pressure has little effect on the combustion characteristics. By comparison with the original machine, while maintaining the power performance of the same circumstances, the cylinder pressure and NOx emissions of double-wall-jet engine are reduced in degree, fuel consumption rate is not almost changed, and the same plane rather, smoke intensity is improved at low speed, smoke intensity at high speed smoke high-speed only deteriorates of 0.2-0.3 BSU.
25
Ndiaye, Mamadou, Peter Myler, and Baljinder K. Kandola. "Thermoplastic Composites: Modelling Melting, Decomposition and Combustion of Matrix Polymers." Journal of Composites Science 6, no. 1 (January 12, 2022): 27. http://dx.doi.org/10.3390/jcs6010027.
Abstract:
In thermoplastic composites, the polymeric matrix upon exposure to heat may melt, decompose and deform prior to burning, as opposed to the char-forming matrices of thermoset composites, which retain their shape until reaching a temperature at which decomposition and ignition occur. In this work, a theoretical and numerical heat transfer model to simulate temperature variations during the melting, decomposition and early stages of burning of commonly used thermoplastic matrices is proposed. The scenario includes exposing polymeric slabs to one-sided radiant heat in a cone calorimeter with heat fluxes ranging from 15 to 35 kW/m2. A one-dimensional finite difference method based on the Stefan approach involving phase-changing and moving boundary conditions was developed by considering convective and radiative heat transfer at the exposed side of the polymer samples. The polymers chosen to experimentally validate the simulated results included polypropylene (PP), polyester (PET), and polyamide 6 (PA6). The predicted results match well with the experimental results.
26
Abalyaev, Andrey Yu, and Alexander B. Lyukhter. "Influence of the Mg/MoO<sub>3</sub> additive to diesel fuel on heat output." Tractors and Agricultural Machinery 90, no. 3 (September 14, 2023): 245–55. http://dx.doi.org/10.17816/0321-4443-529698.
Abstract:
BACKGROUND: The study results of influence of the Mg/MoO3 composite nanoadditive on the combustion process in the 4Ch10.5/12 diesel engine are given. It is shown that the heat output process in diesel engines divides into two phases: kinetic and diffusive combustion. The review of simulation methods for the heat output process in a diesel engine considering kinetic and diffusive combustion based on the I.I. Vibes method is presented. The review of methods of indicator diagram processing helping to obtain parameters of the Vibes heat output law for the two-phase combustion for the sake of following simulation and working process analysis is made. The heat output analysis of the 4Ch10.5/12 diesel engine indicator diagram processing using the Mg/MoO3 composite nanoadditive is made.
AIMS: Research of the influence of the Mg/MoO3 composite nanoadditive to fuel on the heat output process in a diesel engine.
METHODS: The 4Ch10.5/12 air-cooled diesel engine with factory-built fuel supply system was tested at the engine test rig. During the research, influence of the Mg/MoO3 composite nanoadditive to fuel on the heat output process was studied.
RESULTS: It is found that using the nanoadditive leads to decreasing hardness of combustion process, reduction of self-ignition time delay, increasing the maximal temperature of working body in a combustion chamber, reduction of amount of heat output at the kinetic combustion. Working body temperature increase and simultaneous maximal cycle pressure decrease testify the growth of pre-expansion degree. Parameters of diffusive combustion remain almost stable no matter of mass fraction of the nanoadditive in diesel fuel.
CONCLUSIONS: It was revealed that nanoparticles of the Mg/MoO3 additive serve as a homogenizer helping to destroy drops of the sprayed fuel and to intensify the evaporation process. Moreover, the nanoparticles serve as self-ignition centers at early stages of the combustion process.
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Karakas, Amanda I., Giulia Cinquegrana, and Meridith Joyce. "The most metal-rich asymptotic giant branch stars." Monthly Notices of the Royal Astronomical Society 509, no. 3 (November 9, 2021): 4430–47. http://dx.doi.org/10.1093/mnras/stab3205.
Abstract:
ABSTRACT We present new stellar evolutionary sequences of very metal-rich stars evolved with the Monash Stellar Structure code and with mesa. The Monash models include masses of 1–8 M⊙ with metallicities Z = 0.04 to Z = 0.1 and are evolved from the main sequence to the thermally pulsing asymptotic giant branch (TP-AGB). These are the first Z = 0.1 AGB models in the literature. The mesa models include intermediate-mass models with Z = 0.06 to Z = 0.09 evolved to the onset of the TP phase. Third dredge-up only occurs in intermediate-mass models Z ≤ 0.08. Hot bottom burning shows a weaker dependence on metallicity, with the minimum mass increasing from 4.5 M⊙ for Z = 0.014 to ≈5.5 M⊙ for Z = 0.04, 6 M⊙ for 0.05 ≤ Z ≤ 0.07 and above 6.5 M⊙ for Z ≥ 0.08. The behaviour of the Z = 0.1 models is unusual; most do not experience He-shell instabilities owing to rapid mass-loss on the early part of the AGB. Turning off mass-loss produces He-shell instabilities, however thermal pulses are weak and result in no TDU. The minimum mass for carbon ignition is reduced from 8 M⊙ for Z = 0.04 to 7 M⊙ for Z = 0.1, which implies a reduction in the minimum mass for core-collapse supernovae. mesa models of similarly high metallicity (Z = 0.06–0.09) show the same lowering of the minimum mass for carbon ignition: carbon burning is detected in a 6 M⊙ model at the highest metallicity (Z = 0.09) and in all 7 M⊙ models with Z ≥ 0.06. This demonstrates robustness of the lowered carbon burning threshold across codes.
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Ra, Y., E. J. Hruby, and R. D. Reitz. "Parametric study of combustion characteristics in a direct-injection diesel homogeneous charge compression ignition engine with a low-pressurefuel injector." International Journal of Engine Research 6, no. 3 (June 1, 2005): 215–30. http://dx.doi.org/10.1243/146808705x7392.
Abstract:
Homogeneous charge compression ignition (HCCI) combustion is an alternative to current engine combustion systems and is used as a method to reduce emissions. It has the potential nearly to eliminate engine-out NOx emissions while producing diesel-like engine efficiencies, when a premixture of gas-phase fuel and air is burned spontaneously and entirely by an autoignition process. However, when direct injection is used for diesel fuel mixture preparation in engines, the complex in-cylinder flow field and limited mixing times may result in inhomogeneity of the charge. Thus, in order to minimize non-uniformity of the charge, early injection of the fuel is desirable. However, when fuel is injected during the intake or early compression stroke, the use of high-pressure injection is limited by the relatively low in-cylinder gas pressure because of spray impingement on the cylinder walls. Thus, it is also of interest to consider low-pressure injectors as an alternative. In the present paper, the parametric behaviour of the combustion characteristics in an HCCI engine operated with a low-pressure fuel injector were investigated through numerical simulations and engine experiments. Parameters including the start-of-injection (SOI) timing and exhaust gas recirculation were considered, and diesel and n-heptane fuels were used. The results show good agreement of behaviour trends between the experiments and the numerical simulations. With its lower vaporization rates, significant effects of the SOI timing and intake gas temperature were seen for diesel fuel due to the formation of wall films. The modelling results also explained the origin of high-temperature NO x-producing regions due to the effect of the gas density on the spray.
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Djamari, Djati Wibowo, Muhammad Idris, Permana Andi Paristiawan, Muhammad Mujtaba Abbas, Olusegun David Samuel, Manzoore Elahi M. Soudagar, Safarudin Gazali Herawan, et al. "Diesel Spray: Development of Spray in Diesel Engine." Sustainability 14, no. 23 (November 29, 2022): 15902. http://dx.doi.org/10.3390/su142315902.
Abstract:
Research and development in the internal combustion engine (ICE) has been growing progressively. Issues such as air pollution, fuel cost, and market competitiveness have driven the automotive industry to develop and manufacture automobiles that meet new regulation and customers’ needs. The diesel engine has some advantages over the gasoline or spark ignition engine, including higher engine efficiency, greater power output, as well as reliability. Since the early stage of the diesel engine’s development phase, the quest to obtain better atomization, proper fuel supply, and accurate timing control, have triggered numerous innovations. In the last two decades, owing to the development of optical technology, the visualization of spray atomization has been made possible using visual diagnostics techniques. This advancement has greatly improved research in spray evolution. Yet, a more comprehensive understanding related to these aspects has not yet been agreed upon. Diesel spray, in particular, is considered a complicated phenomenon to observe because of its high-speed, high pressure, as well as its high temperature working condition. Nevertheless, several mechanisms have been successfully explained using fundamental studies, providing several suggestions in the area, such as liquid atomization and two-phase spray flow. There are still many aspects that have not yet been agreed upon. This paper comprehensively reviews the current status of theoretical diesel spray and modelling, including some important numerical and experimental aspects.
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Heller, René, Jan-Peter Duda, Max Winkler, Joachim Reitner, and Laurent Gizon. "Habitability of the early Earth: liquid water under a faint young Sun facilitated by strong tidal heating due to a closer Moon." PalZ 95, no. 4 (November 24, 2021): 563–75. http://dx.doi.org/10.1007/s12542-021-00582-7.
Abstract:
AbstractGeological evidence suggests liquid water near the Earth’s surface as early as 4.4 gigayears ago when the faint young Sun only radiated about 70% of its modern power output. At this point, the Earth should have been a global snowball if it possessed atmospheric properties similar to those of the modern Earth. An extreme atmospheric greenhouse effect, an initially more massive Sun, release of heat acquired during the accretion process of protoplanetary material, and radioactivity of the early Earth material have been proposed as reservoirs or traps for heat. For now, the faint-young-Sun paradox persists as an important problem in our understanding of the origin of life on Earth. Here, we use the constant-phase-lag tidal theory to explore the possibility that the new-born Moon, which formed about 69 million years (Myr) after the ignition of the Sun, generated extreme tidal friction—and therefore, heat—in the Hadean and possibly the Archean Earth. We show that the Earth–Moon system has lost $${\sim }3~{\times }~10^{31}$$ ∼ 3 × 10 31 J (99% of its initial mechanical energy budget) as tidal heat. Tidal heating of $${\sim }10\,\mathrm{W\,m}^{-2}$$ ∼ 10 W m - 2 through the surface on a time scale of 100 Myr could have accounted for a temperature increase of up to $$5\,^\circ $$ 5 ∘ C on the early Earth. This heating effect alone does not solve the faint-young-Sun paradox but it could have played a key role in combination with other effects. Future studies of the interplay of tidal heating, the evolution of the solar power output, and the atmospheric (greenhouse) effects on the early Earth could help in solving the faint-young-Sun paradox.
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Bozza, Roberto, Vincenzo De Bellis, Stefano Fantoni, and Donato Colangelo. "CFD 3D Analysis of Charge Motion and Combustion in a Spark-Ignition Internal Combustion Engine under Close-to-Idle Condition." E3S Web of Conferences 197 (2020): 06011. http://dx.doi.org/10.1051/e3sconf/202019706011.
Abstract:
The increasingly stringent limitations on noxious missions of transport sector highly affect the development of new engines. The operating conditions of the engine at low-load and idle play a relevant role along the regulatory homologation cycles, contributing to overall emissions. In this work, the effectiveness of some solutions to improve the behaviour under close-to-idle operation of a Spark-Ignition motorcycle engine are compared by 3D CFD analyses. Specifically, the effects of two designs of the intake port and of the opening direction of the throttle valve, either clockwise or counterclockwise, are investigated. Multi-cycle simulations are carried out, under motored and fired conditions, for a single close-to-idle operating point. The various designs are compared in terms of capability to generate a stable tumble vortex during the intake phase and to produce an adequate turbulence level at the beginning of the combustion process. The analyses revealed that a clockwise throttle opening can produce enhanced turbulence levels at the end of the compression stroke, especially in a close-to-spark region (increase of about 5% and 27 % at the TDC at a global and local level, respectively, compared to the base configuration). Additional limited improvements are obtained with the high tumbling design, where, however, a penalty on the maximum power output could emerge. The flow and turbulence motion differences among the tested geometries reflect on combustion development in its early stage, and on its degree of completeness at the exhaust valve opening. A clockwise opening of the throttle valve leads to an increase of the mass fraction burned of 5 percent points, compared to the base configuration.
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Bos, Johanna A. A., and Bas van Geel. "Palaeoenvironmental reconstruction based on the Early Holocene Haelen sequence, near Roermond (southeastern Netherlands)." Netherlands Journal of Geosciences 96, no. 2 (September 14, 2016): 115–30. http://dx.doi.org/10.1017/njg.2016.35.
Abstract:
AbstractHigh-resolution Early Holocene palynological records from the middle Meuse River valley were missing until recently. In order to investigate environmental and inferred climate changes during the Preboreal, sediments from a former residual channel of the Meuse River near Haelen were studied. Detailed multi-proxy analyses, including microfossils, macroremains and loss-on-ignition measurements, were carried out at a high temporal resolution. An accurate chronology of the >1000-year-long record was provided by accelerator mass spectrometry (AMS)14C wiggle-match dating.The channel was abandoned during the late Younger Dryas, when accumulation started with gyttja. This period was characterised by an open landscape with herbaceous vegetation and dwarf shrubs. Patches of birch were present on the floodplains around depressions and (oxbow) lakes. Some pines survived the cold in sheltered locations. In the residual channel the water was flowing temporarily and aquatic plant communities developed with predominantly submerged taxa and algae. The shores were fringed by willows and sedges and were probably used as a watering place by large herbivores.Following the Late-glacial/Holocene climate warming, dated in the Haelen record around 11,520 cal BP, birch woodlands expanded on the river floodplains and slopes of terraces during the Friesland Phase. Open vegetation with herbs and juniper remained present on the nearby terraces. An increase in the water level of the oxbow lake and seepage of groundwater occurred. Along the shores herbaceous vegetation was present. Around 11,420 cal BP, birch expansion was interrupted by the dry continental Rammelbeek Phase. On the river floodplain and terrace slopes, open grassland vegetation developed and on the terraces, grasslands and open grounds were abundant. In the residual channel the water became stagnant and floating-leaved vegetation developed. At the start of the Late Preboreal, around 11,270 cal BP, a sudden shift to a more humid climate took place and birch forests expanded again on the river floodplains and terrace slopes. Poplar became more abundant in these forests, and birch and poplar swamp forests were present near the site. Pine expanded atc. 11,160 cal BP on the higher sandy and gravelly terraces. During the Late Preboreal a reed swamp developed on the shores of the residual channel.At the onset of the Boreal, around 10,710 cal BP, woodlands, initially with hazel, but later also with oak, elm and lime, started to develop, while pine forest remained present on the higher terraces. Hazel shrubs were growing on the terrace slopes. Birch and poplar forests occurred on moist parts of the floodplains. Around the residual channel they formed a zone behind the reed swamps surrounding the oxbow lake. Vegetation with water lilies was present in open water.The Haelen record shows, despite a lack of archaeological evidence, indications for the presence of Mesolithic people in the area during the Preboreal. These include the occurrence of (natural or man-made) fires, in combination with the presence of trampled areas and disturbed grounds and possibly consumption of Nymphaeaceae seeds and tubers.
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Paredi, Davide, Tommaso Lucchini, Gianluca D’Errico, Angelo Onorati, Lyle Pickett, and Joshua Lacey. "Validation of a comprehensive computational fluid dynamics methodology to predict the direct injection process of gasoline sprays using Spray G experimental data." International Journal of Engine Research 21, no. 1 (August 22, 2019): 199–216. http://dx.doi.org/10.1177/1468087419868020.
Abstract:
A detailed prediction of injection and air–fuel mixing is fundamental in modern direct injection, spark-ignition engines to guarantee a stable and efficient combustion process and to minimize pollutant formation. Within this context, computational fluid dynamics simulations nowadays represent a powerful tool to understand the in-cylinder evolution of spray and air–fuel charge. To guarantee the accuracy of the adopted multidimensional spray sub-models, it is mandatory to validate the computed results against available experimental data under well-defined operating conditions. To this end, in this work, the authors proposed the calibration and validation of a comprehensive set of spray sub-models by means of the simulation of the Spray G experiment, available in the context of the engine combustion network. For a suitable validation of the proposed numerical setup in addition to the baseline condition, gasoline direct injection operating points typical of early injection with homogeneous operation, late injection with high ambient density and flash boiling with enhanced fuel evaporation were also simulated. Numerical computations were validated against a wide set of available experimental data by means of an accurate post-processing analysis taking into account axial liquid and vapor penetrations, gas-phase velocity between spray plumes, droplet size, plume liquid velocity, direction and mass distribution. Satisfactory results were achieved with the proposed setup, which is able to predict gasoline spray evolution under different operating conditions.
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Nhumaio, Geraldo C. S., and A. Paul Watkins. "Predictions of Charge Drift in a Concept Electrosprayed DISI Engine." Journal of Fluids Engineering 128, no. 5 (January 31, 2006): 903–12. http://dx.doi.org/10.1115/1.2243299.
Abstract:
Limited to nonvaporizing spray cases, this work discusses the transport of charged droplets within a cylinder of a motored axisymmetric model electrosprayed direct injection spark ignition (eDISI) engine with electrified walls. The concept engine investigated here is assumed to operate with an electrostatic atomizer previously studied for application in fuel burners [Yule et al., 1994, Fuel, 74(7), pp. 1094–1103]. A split/multiple injection strategy is employed in which three pulses of 5mg each are made at crank angles of 80, 150 and 300 deg ATDC of the intake, which fall within the intervals for stable combustion of either early or late injection modes of operation of DISI engines [Jackson et al., 1997, SAE Paper No. 970543]. The direct Simulation Monte Carlo (DSMC) approach embodied in an in-house CFD research code is used to simulate the discrete phase flow with the electrical charge distribution for different instants within the computational cells being computed by simple addition of the droplet charges residing in particular cells at particular instants of time. It is shown in the half engine cycle investigated that the use of charged sprays in eDISI engines may help to reduce the in-cylinder wall-wetting phenomenon. In addition, pockets of highest electrical charge are found to populate the region near the spark plug by 345 deg CA, which may be a path for improved combustion efficiency.
35
Pospelov, Boris, Vladimir Andronov, Evgenіy Rybka, Mikhail Samoilov, Olekcii Krainiukov, Igor Biryukov, Tetiana Butenko, Yuliia Bezuhla, Kostiantyn Karpets, and Eduard Kochanov. "Development of the method of operational forecasting of fire in the premises of objects under real conditions." Eastern-European Journal of Enterprise Technologies 2, no. 10 (110) (April 30, 2021): 43–50. http://dx.doi.org/10.15587/1729-4061.2021.226692.
Abstract:
A method for operational forecasting of fires is proposed that enables the sequential implementation of five procedures. The method development is necessary to predict early fires in premises in order to take measures to prevent them from escalating into an uncontrolled combustion phase ‒ a fire. As a result of research, it was found that a short-term forecast of the recurrence of increments of the air conditions by one step, based on the current measure of recurrence, is an effective indicator of early fires in premises. At the same time, it was found that before the moment of ignition of the material, the state of the air environment is characterized by dynamic stability, which is described by an irregular and time-dependent random change in the recurrence of the states of the vector of current increments of the state of the air environment. The values of the indicated levels of recurrence of the state increments are determined by the probability levels of 0.67 and 0.1, respectively. The probability of recurrence of state increments of 0.67 is characteristic of a larger number of measured states. When the material is ignited, the dynamics of the probability of recurrence of state increments change abruptly. There is a transition from two to one level of recurrence, close to zero probability ‒ the loss of dynamic stability (in the region of count 250). Further dynamics are characterized by the appearance of separate random recurrent increments corresponding to the instability of the air environment in the premises. In the course of the experiment, it was found that the accuracy of predicting a fire by the proposed method ranges from 4.48 % to 12.79 %, which generally indicates its efficiency. The obtained data prove useful in the development of new systems that early warn of fire in premises, as well as in the modernization of existing systems and means of fire protection of premises
36
Cui, Xiang, Wenbin Zhu, and F. Jourdan. "Subduction-related subcontinental lithospheric mantle metasomatism and crustal thickening: origin for superchondritic Nb/Ta in mafic dykes." Journal of the Geological Society 178, no. 1 (August 19, 2020): jgs2020–120. http://dx.doi.org/10.1144/jgs2020-120.
Abstract:
Superchondritic Nb/Ta is rarely reported in terrestrial reservoirs and is usually attributed to carbonatite metasomatism or accessory rutile in the residue phase. Previously documented high Nb/Ta in rocks derived from subcontinental lithospheric mantle indicated a predominance of carbonatite metasomatism. This study evaluates Nb/Ta in conjunction with other trace elements of Neoproterozoic mafic dykes exposed in the eastern segment of the Jiangnan Orogen, where early subduction existed before the amalgamation of South China. These mafic dykes show mostly superchondritic Nb/Ta ratios from 19.6 to 24.5. Partial melting modelling suggested low-degree melting of rutile-bearing subcontinental lithospheric mantle for these mafic dykes. A literature review of Neoproterozoic mafic–intermediate rocks throughout the Jiangnan Orogen shows sporadically but coincidently superchondritic Nb/Ta near or beneath the Shuangxiwu arc, indicating rutile stability in the relict sub-arc mantle. Rutile in the lherzolite was formed sometime after Neoproterozoic subduction initiation in South China but contemporaneous with crustal thickening at c. 860 Ma. This study brings direct evidence to bear on the mechanism of rutile formation in the mantle wedge, as well as the link between crustal thickening and superchondritic Nb/Ta of mafic products derived from the metasomatized mantle.Supplementary material: Major and trace element compositions, photomicrographs of samples, and figures illustrating geochemistry, REE and incompatible trace element patterns and loss on ignition versus Nb/Ta and La/Yb are available at https://doi.org/10.6084/m9.figshare.c.5093535
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Shin, Hyeon-Ji, Jun Tae Kim, and Hun-Gi Jung. "Degradation Behavior of Layered Structure Cathode in Sulfide Based All-Solid-State Batteries." ECS Meeting Abstracts MA2023-01, no. 6 (August 28, 2023): 1072. http://dx.doi.org/10.1149/ma2023-0161072mtgabs.
Abstract:
With declaration of carbon zero in response to climate change, the importance is also being bandied about developing large-scale energy storage system, especially for electric vehicle (EV). Commercialized EV with a highest development lithium-ion batteries (LIB) could operate over 300 miles per single charging, but liquid electrolyte-based LIB gives rise to a huge risk concerning about ignition and explosion. All-solid-state batteries (ASSBs) is considered to alternative next-generation battery that have high safety advantageous with removal the risk of ignition by applying non-combustible inorganic solid-electrolytes (SEs). In case of sulfide-based ASSBs, there were progressed in performance itself at cell capacity increase and cycling characteristic due to advance in cell configuration, composite cathode, and cell fabrication technique compared to early works. Nevertheless, it is still demanded improvement related to the cathode-electrolyte interface stability, and its dominant causes are electrochemical- and chemo-mechanical problems. Therefore, most of researchers have tried to figure out the behavior of all-solid-state batteries by providing external pressure, and then resolve degradation issues including contact loss and resistive layer formation. However, in practical and commercialization aspects, the external pressured cell can be a stumbling block to scale-up from lab to large-scale ASSBs stage. In this study, we evaluated electrochemical performance using by general coin cell to investigate behavior of ASSBs, which is consisted with LiNi0.5Co0.2Mn0.3O2/Li6PS5Cl/VGCF|Li6PS5Cl|In-Li. The ASSB coin cell showed a significant capacity degradation having 59 % of capacity retention in 50th cycles, as expected. Herein, the main cause of the rapid capacity decrease is likely to be due to the accelerated physical contact loss. In addition to this, we have expanded the scope of analysis to investigate if there are other causes entire range including cell- and material level. The degradation in cell level is the inhomogeneous electrochemical reaction, that is within composite cathode, resulting from analysis of electrochemical impedance spectroscopy, cross-sectional scanning electron microscopy, x-ray diffraction, and X-ray photoelectron spectroscopy. This induces more severe degradation on close to SE separator, resulting in intensification of SE deterioration accompanied by damage implying a phase transformation of the active material. Furthermore, even though the contact loss problem has improved through re-pressing, the capacity was not recovered, which is because the material itself has deteriorated. Moving on to the material level, many cracks are observed inside of the active material, and sulfur infused into grain-boundary of active materials that confirmed by energy dispersive X-ray spectroscopy. In addition, through analyzing transmission electron microscopy, the phase transformation both mixed and rock-salt phase was confirmed the cathode surface of not only secondary particle but also primary particle of interior cathode. For more specifically affirmed this, various analysis including Raman spectroscopy and inductively coupled plasma optical emission spectroscopy were conducted, and we confirmed that the major cause is due to depletion of the Li source. Therefore, the loss of active Li by infused sulfur caused acceleration of deterioration cathode making poor capacity retention. This study is meaningful in providing another guideline that should be regarded for practical all-solid-state batteries through a new consideration in cathode degradation.
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Kearney, Kevin, Benjamin Gearey, Susan Hegarty, Suzi Richer, Carla Ferreira, Ellen O’Carroll, Derek Hamilton, et al. "A multi-proxy Holocene palaeoenvironmental record of climate change and prehistoric human activity from Lough Cullin, southeast Ireland." Holocene 32, no. 4 (January 11, 2022): 262–79. http://dx.doi.org/10.1177/09596836211066593.
Abstract:
A multiproxy (pollen, microcharcoal, loss-on-ignition, magnetic susceptibility and geochemistry) sequence from Lough Cullin, southeast Ireland, supported by a high-resolution radiocarbon chronology, modelled using Bayesian approaches, provides a record of environmental change for much of the Holocene. Following the establishment of mixed deciduous woodland, climatic deterioration was likely responsible for pronounced vegetation change and erosion, 7615–6500 cal. BC to 6245–5575 cal. BC, evidence for the ‘8.2 Kyr’ BP climate event. The so-called ‘elm decline’ is dated to 4220–3980 cal. BC and whilst there are possible indications of an anthropogenic cause, clear evidence of woodland clearance with cereal pollen is recorded at 3900–3700 cal. BC, 3790–3580 cal. BC and 3760–3650 cal. BC, during a period of clearance and farming of 320–450 years duration. A reduction in farming/settlement and woodland regeneration during the Middle Neolithic parallels the archaeological record, with low levels of activity during the Late Neolithic/Chalcolithic after 2960–2525 cal. BC, prior to increases during the Bronze Age then woodland clearance and agriculture between 1500–1410 and 1275–1000 cal. BC, corresponding with the archaeological evidence. A subsequent ‘step-wise’ reduction in human activity follows, from the latter date to 815–685 cal. BC, and a brief but pronounced cessation at 690–535 cal. BC. Renewed woodland clearance and agriculture commenced until 415–250 cal. BC. From the latter date until cal. AD 390–540, the Late Iron Age/Early Medieval period, a phase of woodland recovery is attested, followed by renewed landscape disturbance and arable agriculture in particular, continuing to the close of the record at cal. AD 780–1035.
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Ahmed, Muhammad, Tola Mirza, and Stavros Kalaitzidis. "Petrography and Geochemistry of the Baska Piwaza Ore Mineralization, Halgurd Mountain, Iraqi Kurdistan Region: Insights on the Genesis." Iraqi Geological Journal 56, no. 2B (August 31, 2023): 114–36. http://dx.doi.org/10.46717/igj.56.2b.9ms-2023-8-18.
Abstract:
This paper is the first attempt to study the mineralogical and geochemical features of mineralization hosted within the volcanic rocks of the Baska Piwaza section, at Halgurd Mountain, which is the highest mountain in Kurdistan and the whole of Iraq. The host lithologies in the studied section represent mostly volcanic rocks (basalts to andesites), and secondary sedimentary lithologies, such as radiolarian chert. There are two main stages of oxide and sulfide mineralization that can be recognized under three-time epochs which are early, middle and late stages that caused the formation of oxide and sulfides ore minerals. The most dominant oxide mineral is hematite, with minor contribution of magnetite, goethite, and rutile. In terms of sulfides, pyrite is the predominant mineral phase with secondary contribution of chalcopyrite. The petrographic study and XRD data of the host volcanic rocks reveal that the most abundant minerals are plagioclase, K-feldspar, pyroxene, and amphibole, while the secondary minerals are quartz, calcite, clinochlore, sericite, prehnite, pumpellyite, and muscovite. Additionally, the radiolarian chert is comprised by quartz, hematite, calcite, ankerite, clay minerals, and apatite which is characterized by low silica content and high iron oxide. Low concentration of TiO2 ,and Fe2O3 are suggesting the quartz vein occurred with the volcanic rocks are formed due to low hydrothermal fluid. Field observation, petrographical and geochemical data indicate that the rocks of the Baska Piwaza section are influenced by hydrothermal alteration, due to the high value of Loss On Ignition (LOI) and the high ratio of alkalis (Na2O+K2O). Moreover, evidences of chloritization and sericitization of the mafic minerals, and feldspar minerals respectively support the hydrothermal impact.
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OVCHINNIKOV, E. V., S. YU UYUTOV, and V. A. KRYUCHKOV. "SUPPLY SYSTEM OF LIQUID GAS-ENGINE FUEL TO DIESEL ENGINE COMBUSTION CHAMBER." Vestnik of Ulyanovsk state agricultural academy 230 (September 25, 2021): 26–33. http://dx.doi.org/10.18286/1816-4501-2021-3-26-33.
Abstract:
The existing methods of diesel engine start up using gas engine fuel imply either introduction of design changes to implement spark ignition, or maintaining the supply of a certain proportion of diesel fuel in the air-gas mixture. The second method is more preferable, since it leaves the possibility of an easy return to the initial state, allows work only on the diesel process and does not require significant changes in the design. This method attracts the greatest attention of modern researchers, however, the final technical solutions and methods of work on such a gas-diesel process have not yet been developed, and the existing practices are expensive to implement or are not effective enough. The issues of ensuring high ecological parameters also remain in abeyance. Studies show that in order to reduce nitrogen oxide emissions, it is necessary to achieve the elimination of residual oxidant in combustion products, which is possible due to formation of a stoichiometric mixture in the cylinder. For this purpose, as well as to increase the overall combustion efficiency and improve the thermal balance of the engine, the authors propose a system for injecting gas in the liquid phase directly into the combustion chamber at the compression stroke. The described system assumes the maximum usage of standard engine components of MMZ D-245 type with seats for glow plugs in the cylinder head, where nozzles for supplying liquid gas will be installed. In this case, gas injection is possible by standard means of the Common rail system. Concurrently, there are already the necessary technical solutions that improve the operation control of the injection pump and ensure prevention of detonation combustion. The appropriate balance of the amount of both fuel types is calculated according to the known relationships. The analysis of the results of early studies showed that such a scheme deserves attention. Thus, the authors substantiated the currently absent approach, which makes it possible to improve the environmental performance of an engine operating on a gas-diesel process, implemented by available means.
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Nguyen, Minh Tien, and Shenqyang (Steven) Shy. "A Transition of Ignition Kernel Delay Time at the Early Stages of Lean Premixed n-Butane/Air Turbulent Spherical Flame Propagation." Applied Sciences 12, no. 8 (April 13, 2022): 3914. http://dx.doi.org/10.3390/app12083914.
Abstract:
This paper explores the effects of root-mean-square turbulence fluctuation velocity (u′) and ignition energy (Eig) on an ignition kernel delay time (τdelay) of lean premixed n-butane/air spherical flames with an effective Lewis number Le ≈ 2.1 >> 1. Experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence with negligible mean velocities using a pair of cantilevered electrodes with sharp ends at a fixed spark gap of 2 mm. τdelay is determined at a critical flame radius with a minimum flame speed during the early stages of laminar and turbulent flame propagation. Laminar and turbulent minimum ignition energies (MIEL and MIET) are measured at 50% ignitability, where MIEL = 3.4 mJ and the increasing slopes of MIET with u′ change from gradual to drastic when u′ > 0.92 m/s (MIE transition). In quiescence, a transition of τdelay is observed, where the decrement of τdelay becomes rapid (modest) when Eig is less (greater) than MIEL. For turbulent cases, when applying Eig ≈ MIET, the reverse trend of MIE transition is found for τdelay versus u′ results with the same critical u′ ≈ 0.92 m/s. These results indicated that the increasing u′ could reduce τdelay on the one hand, but require higher Eig (or MIET) on the other hand. Moreover, the rising of Eig in a specific range, where Eig ≤ MIE, could shorten τdelay, but less contribution as Eig > MIE. These results may play an important role to achieve optimal combustion phases and design an effective ignition system on spark ignition engines operated under lean-burn turbulent conditions.
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Benoit, Roland, Nesrine Belhadj, Maxence Lailliau, and Philippe Dagaut. "On the similarities and differences between the products of oxidation of hydrocarbons under simulated atmospheric conditions and cool flames." Atmospheric Chemistry and Physics 21, no. 10 (May 22, 2021): 7845–62. http://dx.doi.org/10.5194/acp-21-7845-2021.
Abstract:
Abstract. Atmospheric oxidation chemistry and, more specifically, photooxidation show that the long-term oxidation of organic aerosol (OA) progressively erases the initial signature of the chemical compounds and can lead to a relatively uniform character of oxygenated organic aerosol (OOA). This uniformity character observed after a long reaction time seems to contrast with the great diversity of reaction mechanisms observed in the early stages of oxidation. The numerous studies carried out on the oxidation of terpenes, and more particularly on limonene for its diversity of reaction sites (endo- and oxocyclic), allow this evolution to be studied. We have selected, for their diversity of experimental conditions, nine studies of limonene oxidation at room temperature over long reaction times to be compared to the present data set obtained at elevated temperature and short reaction time in order to investigate the similarities in terms of reaction mechanisms and chemical species formed. Here, the oxidation of limonene–oxygen–nitrogen mixtures was studied using a jet-stirred reactor at elevated temperature and atmospheric pressure. Samples of the reacting mixtures were collected and analyzed by high-resolution mass spectrometry (Orbitrap) after direct injection or after separation by reverse-phase ultra-high-pressure liquid chromatography and soft ionization, i.e., (+/-) HESI and (+/-) APCI. Unexpectedly, because of the diversity of experimental conditions in terms of continuous-flow tank reactor, concentration of reactants, temperature, reaction time, mass spectrometry techniques, and analysis conditions, the results indicate that among the 1138 presently detected molecular formulae, many oxygenates found in earlier studies of limonene oxidation by OH and/or ozone are also produced under the present conditions. Among these molecular formulae, highly oxygenated molecules and oligomers were detected in the present work. The results are discussed in terms of reaction pathways involving the initial formation of peroxy radicals (RO2), isomerization reactions yielding keto-hydroperoxides, and other oxygenated intermediates and products up to C25H32O17, products which could derive from RO2 autoxidation via sequential H shift and O2 addition (C10H14O3,5,7,9,11) and products deriving from the oxidation of alkoxy radicals (produced by RO2 self-reaction or reaction with HO2) through multiple H shifts and O2 additions (C10H14O2,4,6,8,10). The oxidation of RO2, with possible occurrence of the Waddington mechanism and of the Korcek mechanism, involving H shifts is also discussed. The present work demonstrates similitude between the oxidation products and oxidation pathways of limonene under simulated atmospheric conditions and in those encountered during the self-ignition of hydrocarbons at elevated temperatures. These results complement those recently reported by Vereecken and Nozière and confirm for limonene the existence of an oxidative chemistry of the alkylperoxy radical beyond 450 K based on the H shift (Nozière and Vereecken, 2019; Vereecken and Nozière, 2020).
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Zhao, Le, Yu Zhang, Yuanjiang Pei, Anqi Zhang, and Muhsin M. Ameen. "CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation." Sustainability 13, no. 23 (November 26, 2021): 13096. http://dx.doi.org/10.3390/su132313096.
Abstract:
A closed-cycle, three-dimensional (3D) computational fluid dynamics (CFD) analysis campaign was conducted to evaluate the performance of using spark plugs to assist gasoline compression ignition (GCI) combustion during cold idle operations. A conventional spark plug using single-sided J-strap design was put at a location on the cylinder head to facilitate spray-guided spark assistance. Ignition was modeled with an L-type energy distribution to depict the breakdown and the arc-to-glow phases during the energy discharge process. Several key design parameters were investigated, including injector clocking, number of nozzle holes, spray inclusion angle, number of fuel injections, fuel split ratio, and fuel injection timings. The study emphasized the region around the spark gap, focusing on flame kernel formation and development and local equivalence ratio distribution. Flame kernel development and the ignition process were found to correlate strongly with the fuel stratification and the flow velocity near the spark gap. The analysis results showed that the flame kernel development followed the direction of the local flow field. In addition, the local fuel stratification notably influenced early-stage flame kernel development due to varying injection spray patterns and the fuel injection strategies. Among these design parameters, the number of nozzle holes and fuel injection timing had the most significant effects on the engine combustion performance.
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Cai, Kaiyuan, Yi Liu, Qingchu Chen, Yunliang Qi, Li Li, and Zhi Wang. "Combustion Behaviors and Unregular Emission Characteristics in an Ammonia–Diesel Engine." Energies 16, no. 19 (October 9, 2023): 7004. http://dx.doi.org/10.3390/en16197004.
Abstract:
Ammonia is considered one of the attractive alternatives for fossil fuels to realize carbon neutralization. However, low chemical reactivity limits its use in compression ignition (CI) engines. This study investigated dual-fuel combustion, involving the use of ammonia for port fuel injection (PFI) and diesel for direct injection (DI) in a heavy-duty engine. Unregular emissions, specifically HCN, were studied for the first time in an ammonia–diesel engine. The combustion and emission performance of the engine with pure diesel mode was also studied to reveal the influence on ammonia addition. The engine was consistently operated at a fixed condition of 0.556 MPa IMEP and 800 r/min. The findings reveal the successful achievement of stable dual-fuel combustion in the tested engine. The addition of ammonia led to delayed ignition and an extended combustion duration. Implementing early pilot injection timing (SOI1) strategies significantly improved ammonia combustion efficiency, elevating it from 74% to 89%. This enhancement could be attributed to the diesel injected during pilot injection, which facilitated ammonia decomposition. However, early pilot injection had adverse effects on emissions, including CO, THC, NOx, N2O, and HCN. Advancing the main injection timing (SOI2) within the early SOI1 strategies accelerated the oxidation processes for CO, THC, N2O, and HCN. Nevertheless, this adjustment resulted in increased thermal NOx emissions. The highest HCN emission detected in this study was 9.2 ppm. Chemical kinetics analysis indicated that HCN production occurred within the temperature range of 1000 K to 1750 K under fuel-lean conditions. Furthermore, H2CN played a significant role in HCN formation as temperatures increased. More HCN was formed by H2CN as temperature rose. Strategies such as increasing pilot injection fuel quantity, raising premixed gas intake temperature, or advancing combustion phases close to TDC could potentially reduce HCN emissions.
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Miettinen, O. "What did the seahorse swallow? APEX 170 GHz observations of the chemical conditions in the Seahorse infrared dark cloud." Astronomy & Astrophysics 639 (July 2020): A65. http://dx.doi.org/10.1051/0004-6361/202037817.
Abstract:
Context. Infrared dark clouds (IRDCs) are useful target sources for the studies of molecular cloud substructure evolution and early stages of star formation. Determining the chemical composition of IRDCs helps to constrain the initial conditions and timescales (via chemical clocks) of star formation in these often filamentary, dense interstellar clouds. Aims. We aim to determine the fractional abundances of multiple different molecular species in the filamentary IRDC G304.74+01.32, nicknamed the Seahorse IRDC, and to search for relationships between the abundances and potential evolutionary trends. Methods. We used the Atacama Pathfinder EXperiment (APEX) telescope to observe spectral lines occurring at about 170 GHz frequency towards 14 positions along the full extent of the Seahorse filament. The sample is composed of five clumps that appear dark in the mid-IR, eight clumps that are associated with mid-IR sources, and one clump that is already hosting an H II region and is, hence, likely to be in the most advanced stage of evolution of all the target sources. We also employed our previous 870 μm dust continuum imaging data of the Seahorse. Results. Six spectral line transitions were detected (≥3σ) altogether, namely, SO(NJ = 44−33), H13CN(J = 2−1), H13CO+(J = 2−1), SiO(J = 4−3), HN13C(J = 2−1), and C2H(N = 2−1). While SO, H13CO+, and HN13C were detected in every source, the detection rates for C2H and H13CN were 92.9 and 85.7%, respectively. Only one source (SMM 3) showed detectable SiO emission (7.1% detection rate). Three clumps (SMM 5, 6, and 7) showed the SO, H13CN, H13CO+, HN13C, and C2H lines in absorption. Of the detected species, C2H was found to be the most abundant one with respect to H2 (a few times 10−9 on average), while HN13C was found to be the least abundant species (a few times 10−11). We found three positive correlations among the derived molecular abundances, of which those between C2H and HN13C and HN13C and H13CO+ are the most significant (correlation coefficient r ≃ 0.9). The statistically most significant evolutionary trends we uncovered are the drops in the C2H abundance and in the [HN13C]∕[H13CN] ratio as the clump evolves from an IR dark stage to an IR bright stage and then to an H II region. Conclusions. The absorption lines detected towards SMM 6 and SMM 7 could arise from continuum radiation from an embedded young stellar object and an extragalactic object seen along the line of sight. However, the cause of absorption lines in the IR dark clump SMM 5 remains unclear. The correlations we found between the different molecular abundances can be understood as arising from the gas-phase electron (ionisation degree) and atomic carbon abundances. With the exception of H13CN and H13CO+, the fractional abundances of the detected molecules in the Seahorse are relatively low compared to those in other IRDC sources. The [C2H] evolutionary indicator we found is in agreement with previous studies, and can be explained by the conversion of C2H to other species (e.g. CO) when the clump temperature rises, especially after the ignition of a hot molecular core in the clump. The decrease of [HN13C]∕[H13CN] as the clump evolves is also likely to reflect the increase in the clump temperature, which leads to an enhanced formation of HCN and its 13C isotopologue. Both single-dish and high-resolution interferometric imaging of molecular line emission (or absorption) of the Seahorse filament are required to understand the large-scale spatial distribution of the gas and to search for possible hot, high-mass star-forming cores in the cloud.
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Giannattasio, Pietro, Marco Pretto, and Enrico De Betta. "A phenomenological model for predicting the early development of the flame kernel in spark-ignition engines." Journal of Physics: Conference Series 2648, no. 1 (December 1, 2023): 012070. http://dx.doi.org/10.1088/1742-6596/2648/1/012070.
Abstract:
Abstract This work presents a simple and effective phenomenological model for the prediction of the early growth of the flame kernel in SI engines, including its initiation as a result of the electrical breakdown of the fuel/air mixture between the spark plug electrodes. The present model aims to provide an improved description of the ignition-affected early phases of flame kernel development compared to the majority of models currently available in literature. In particular, these models focus on electrical energy supply and turbulence, whereas the stretch-induced kernel growth slowdown is quantified with linear models that are inconsistent with the small kernel radius. For the flame kernel initiation, this model replaces the current methods that rely on 1D heat diffusion within a plasma column with a more consistent analysis of post-breakdown conditions. Concerning the kernel growth, the present model couples the mass and energy conservation equations of a spherical kernel with the species and temperature profiles outside of it. This combination leads to a non-linear description of the flame stretch, according to which the kernel development is controlled by the Lewis-number-dependent balance between the heat gained via combustion and the heat lost via thermal diffusion. As a result, the kernel temperature differs from the adiabatic flame temperature, causing the laminar flame speed to change from its adiabatic value and ultimately affecting the overall kernel development. Kernel growth predictions are conducted for laminar flames and compared to literature data, showing a satisfactory agreement and highlighting the ability to describe the stretch-induced kernel slowdown, up to its possible extinction. A good agreement with literature data is also obtained for kernel expansions under moderately turbulent conditions, typical of internal combustion engines. The simple formulation of the present model enables swift integration into phenomenological combustion models for sparkignition engines, while simultaneously offering useful insight into the early kernel development even for CFD-based approaches.
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Selby, Katherine A., Jane Wheeler, and Sally Derrett. "Disentangling Holocene Climate Change and Human Impact from Palaeoenvironmental Records from the Scottish West Coast." Quaternary 6, no. 1 (January 3, 2023): 2. http://dx.doi.org/10.3390/quat6010002.
Abstract:
Phases of rapid climate change throughout the early to mid Holocene coincide with regional human population expansion in Scotland and North-West Europe. Palaeoenvironmental signals of climate and anthropogenically driven vegetation changes can therefore be difficult to separate. To identify whether it is possible to distinguish potential signatures of anthropogenic clearance and agricultural activities from climatic drivers of landscape change in the early to mid Holocene in the region, two topographically contrasting sites on the Isle of Skye and the Isle of Bute were investigated. A multiproxy approach including pollen, spore, microcharcoal, loss on ignition and particle size analyses was adopted to investigate changes in vegetation and climate. There are subtle indications that the 8200 cal BP climate event had an effect on the vegetation composition at both sites. Signals of anthropogenic woodland clearance are apparent early in the sequence at Peat Hill (Bute), indicated by a peak in Poaceae (grass) cereal-type (7–14%) at 8592–8793 cal BP, alongside a decrease in arboreal pollen, which could not be associated with a regional episode of climate change. Early to mid Holocene vegetation changes at Lyndale House (Skye) occur alongside regional changes in precipitation and sea level and therefore cannot be readily separated. Continuous declines in arboreal pollen from ca. 5000 cal BP at Lyndale House indicates the onset of widespread clearance on Skye via felling and sustained grazing pressures.
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Kim, Hansol, Chenglin Cui, Yelim Kwon, Jungho Lee, and JI Man Kim. "Monitoring of Energy Storage Mechanism of Zn/Meso-MnO2 Battery System Using X-Ray Absorption Fine Structure." ECS Meeting Abstracts MA2023-02, no. 4 (December 22, 2023): 749. http://dx.doi.org/10.1149/ma2023-024749mtgabs.
Abstract:
As energy storage systems, LIBs, which are most frequently used, have excellent capacity, power, and long lifespan performance [1]. However, as the reserves of the raw minerals used—lithium and cobalt—are exhausted, prices are escalating. A further issue with LIB is that it heats up to a high temperature during charging, which leads to a string of fire or explosion catastrophes. To solve these safety or cost challenges, various next-generation batteries are being developed, and we are exploring about aqueous zinc ion battery (AZIB), which attracting attention as the next-generation battery due to outstanding safety and cost competitive advantage. Generally, zinc metal acting as an anode, has a high theoretical capacity of 820mAh/g as it is gives two electrons (2e-). Also, because of its sparse reactivity with water and ability to employ water-based electrolytes with strong ion conductivity and low ignition risk, it is particularly advantageous in terms of safety. There have been a variety of cathode materials utilized, such as manganese oxide, vanadium oxide, Prussian blue analogues (PBAs), polyanion compounds, and Chevrel phase compounds [2-4]. Especially, manganese dioxide (MnO2) has been addressed by prior studies that Zn2+ can be inserted into crystal structure because it exhibits several crystal structures (α, β, γ, δ, and λ) with tunnel-type or layer-type structure. Mn4+ ions occupying octahedral holes formed by hexagonal close-packed (hcp) oxide ions compose the fundamental unit of the crystal structure of MnO2 polymorphs. To construct a [MnO6] octahedral unit, each Mn4+ ion is precisely surrounded by six oxygen neighbors, and these units are connected by the edges and/or corners [5]. Understanding the energy storage mechanisms is essential for the one-step evolution of cathode materials for AZIB. However, these polymorphs significantly affect the electrochemical reaction, thus involving complex reaction mechanisms [5-7]. Additionally, it is extremely challenging to research the mechanisms of AZIB since protons (H+) are known to participate in the reaction by acting as charge transfer as well as Zn2+ ions. Therefore, while several efforts are being conducted to unveil the exact reaction mechanism, a mesoporous nanostructured material with a large specific surface area is adopted, which can more precisely grasp the electrochemical reaction studies of electrode/electrolyte surface [8,9]. X-ray absorption fine structure (XAFS) is a powerful technique used for the analysis of nanostructured materials, widely used in the field of battery research [10]. It involves the measurement of the absorption of X-ray by the material, which can provide information about oxidation state, chemical bonding of the materials and the local geometry structure during charge/discharge process. This analysis method gives great insight into the complex energy storage pathway of MnO2 materials with various polymorphs. Based on this knowledge, we synthesized ordered mesoporous β-MnO2 through nano-casting method by using KIT-6 as hard-template and used it as the cathode active material. As depicted in Figure 1, we performed ex-situ XAFS analysis at the states of charge during 2nd cycle to monitor energy storage mechanisms. The oxidation state changes could be quantitatively estimated by edge energy analysis by comparing the reference MnO2 and Mn2O3 samples. It was also possible to unveil further about the reaction mechanism at each voltage by examining the structural change in the local geometry of [MnO6] unit through a careful analysis of pre-edge region and EXAFS spectra. During discharge process, insertion mechanism, which causes relatively larger distortion in the local geometry compared to conversion mechanism, results in a increment of pre-edge intensity, which opposes the decline in pre-edge intensity due to the reduction of the oxidation state. This fact demonstrates that although H+ conversion could not have a significant effect on pre-edge intensity in the early discharge stage, Zn2+ insertion was the phenomenon responsible for the rise in pre-edge intensity during late discharge stage. In addition, through EXAFS spectra analysis, the irreversible change in corner sharing Mn-Mn bond distance during charge/discharge process could be seen that an irreversible phase transition of MnO2 occurred due to Zn2+ insertion, indicating clue to identify the cause of capacity fading. These findings contribute to further understanding of the reaction mechanisms and capacity fading phenomenon and suggest practical strategies for next-generation zinc-ion batteries. References [1] ACS Energy Lett. 2018, 3, 10, 2480-2501. [2] Angew. Chem. 2012,124, 957 –959. [3] Adv. Energy Mater 2015, 5, 1400930 [4] Mater. Chem. Phys. 2015, 149–150, 601– 606. [5] Chem. Mater. 27.10 (2015): 3609-3620. [6] Small 14.13 (2018): 1703850. [7] Nat. commun. 8.1 (2017): 405. [8] J. Energy Chem. 53 (2021): 276-284. [9] J. Power Sources 493 (2021): 229682. [10] J. Phys. D: Appl. Phys. 50 (2017) 074001 Figure 1
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Perrolas, Gonçalo, Milad Niknejad, Ricardo Ribeiro, and Alexandre Bernardino. "Scalable Fire and Smoke Segmentation from Aerial Images Using Convolutional Neural Networks and Quad-Tree Search." Sensors 22, no. 5 (February 22, 2022): 1701. http://dx.doi.org/10.3390/s22051701.
Abstract:
Autonomous systems can help firefighting operations by detecting and locating the fire spot from surveillance images and videos. Similar to many other areas of computer vision, Convolutional Neural Networks (CNNs) have achieved state-of-the-art results for fire and smoke detection and segmentation. In practice, input images to a CNN are usually downsized to fit into the network to avoid computational complexities and restricted memory problems. Although in many applications downsizing is not an issue, in the early phases of fire ignitions downsizing may eliminate the fire regions since the incident regions are small. In this paper, we propose a novel method to segment fire and smoke regions in high resolution images based on a multi-resolution iterative quad-tree search algorithm , which manages the application of classification and segmentation CNNs to focus the attention on informative parts of the image. The proposed method is more computationally efficient compared to processing the whole high resolution input, and contains parameters that can be tuned based on the needed scale precision. The results show that the proposed method is capable of detecting and segmenting fire and smoke with higher accuracy and is useful for segmenting small regions of incident in high resolution aerial images in a computationally efficient way.
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Peti, Leonie, and Paul C. Augustinus. "Micro-XRF-inferred depositional history of the Orakei maar lake sediment sequence, Auckland, New Zealand." Journal of Paleolimnology 67, no. 4 (February 7, 2022): 327–44. http://dx.doi.org/10.1007/s10933-022-00235-y.
Abstract:
AbstractLake sediment records offer insights into past climate and environmental changes. There are, however, few continuous lake sediment records from the Southern Hemisphere mid-latitudes that span the last glacial interval (LGI) and have the requisite chronological control and sampling resolution. Orakei maar paleolake in the Auckland Volcanic Field, New Zealand, is an exception, as it contains a high-resolution record of continuous lacustrine sedimentation from its formative phreatomagmatic eruption ~ 130 ka, until post-glacial sea-level rise breached the crater tuff rim and connected the lake to the sea ~ 9 ka. We used micro-XRF core scanning, dry bulk density, loss-on-ignition and visual facies descriptions to investigate the depositional history of Orakei maar lake as a response to regional and global drivers of climate change, and to erosional events in the lake catchment. The climate history of the lake was divided into six depositional phases: (I) Early warming with frequent in-wash events, followed by climate fluctuations coeval with marine isotope stages (MIS) 5e to mid-5c, (II) Warm, quiescent depositional conditions during mid-MIS 5c to 5a, (III) A colder, windier interval during MIS 4, (IV) Warmer conditions with dominantly autochthonous sedimentation during MIS 3, (V) Cold conditions followed by a slow temperature increase and the onset of sea-level rise during late MIS 2, (VI) Warm conditions that culminated in formation of a peat unit at the top of the Orakei lacustrine sediment sequence, which was terminated by an influx of massive marine muds into the basin at 9.75 ka. Comparison of the inferred climate evolution at Orakei with climate inferences from the global marine benthic MIS record during LGI shows general agreement, though inferred climate changes consistently occur earlier at Orakei than in the MIS. There is also general agreement in temperature changes inferred from the Orakei record and from other regional lake sediment records, but more detailed comparison requires additional proxy climate data such as pollen, organic geochemistry and biomarkers, to better understand discrepancies between some records. This study demonstrated the great potential of the Orakei record for paleoclimate inference and the applicability of micro-XRF core scanning data for addressing questions about paleoclimate and paleoenvironment. It also highlighted past intervals that require further study.