Combustion Conditions Research Articles

Emission Factors From Wildfires in the Western US: An Investigation of Burning State, Ground Versus Air, and Diurnal Dependencies During the FIREX‐AQ 2019 Campaign

AbstractEmission factors (EFs) are crucial in understanding the effects of wildfire emissions on air quality. We examined the variability of EFs of three wildfires (Nethker, Castle, and 204 Cow) during the 2019 Western US wildfire season using the Aerodyne Mobile Laboratory (AML) and compared them to previous studies. The AML sampling captured the high degree of variability present in wildfires, and we report results for a range of combustion conditions that is more extensive than previous field and laboratory studies. For instance, we captured emissions from freshly started flaming fuels and we report rare EF measurements at very high modified combustion efficiencies (MCEs); MCEs >0.9. Differences in emissions between AML‐observed wildfires were attributed to burning state/MCE rather than fuel type. A comparison of EFs versus MCE was made and linear fits were compared to previous observations to reveal important differences that incorporate these high MCEs. For some species, there remains an EF dependence on MCE at these high values, while others reach a minimum value and exhibit either no or a weak dependence above it. EF differences were found for many of the studied compounds when comparing ground‐based and airborne observations, with generally greater airborne EFs possibly due to photochemical oxidation. The largest differences were from monoterpenes and acetaldehyde. Comparisons were made between AML‐observed wildfires, aircraft observations, and the values in literature for EFs and emission ratios, with mixed agreement due to the high degree of variability caused by differences in MCE. Differences in MCE drove the diurnal EF differences.

Regulation of open straw burning and residential coal burning around urbanized areas could achieve urban air quality standards in the cold region of northeastern China

Air quality issues in Northeast China are concerning due to the significant seasonal atmospheric pollution and typical climatic, geographic and industrial structure characteristics of the area. However, urban air quality managers are having great difficulty achieving targeted pollution control goals in the time allotted due to limited studies in the region. In this study, using the city of Siping in Jilin Province as a case study, we analysed the cause of seasonal atmospheric pollution, developed a high-resolution emissions inventory for major atmospheric pollutants and simulated urban air quality improvements under projected emission control scenarios to select a reasonable source control scheme to inform urban air quality management planning in the region. Years with available air quality data (2014–2020) were divided into three periods, i.e., a weak control period (WCP: 2014–2017), an enhanced control period (ECP: 2018–2019) and the COVID-19 period (CDP: 2020). The annual PM2.5, PM10, SO2 and NOx emissions varied by 62∼46 μg·m−3, 103∼76 μg·m−3, 27∼22 μg·m−3 and 46∼41 μg·m−3, respectively, during the WCP; the emissions decreased to 37 μg·m−3, 69 μg·m−3, 11 μg·m−3 and 34 μg·m−3, respectively, during the ECP and to 33 μg·m−3, 61 μg·m−3, 11 μg·m−3 and 33 μg·m−3, respectively, during the CDP, which reached the limits of the Ambient Air Quality Standard of China (level II, 35 μg·m−3, 70 μg·m−3, 60 μg·m−3 and 50 μg·m−3). The PM2.5 and PM10 indices exceeded the standards, mainly in late autumn (October and November) and in the middle of winter (January and February). Based on comprehensive data analysis of the spatiotemporal air quality and the local high-resolution emissions inventory, straw burning, stationary combustion (especially for coal burning) and vehicle emissions were the main pollution sources in late autumn, and continuous adverse weather conditions were the dominant factors in severe pollution days during the middle of winter. In addition, the urban air quality of Siping was also affected by pollutant transport from the northwest (the city of Songyuan in Jilin Province), northeast (the city of Changchun in Jilin Province) and south (the city of Tieling in Liaoning Province) according the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Strict straw-burning policy was implemented in autumn during the ECP and CDP, which significantly improved the air quality from that of the WCP, with an AQI reduction of 31.58 %. However, the planned burning policy was not well-implemented, resulting in more days of moderate or heavy pollution. Using 2017 as the base year, scenarios were simulated in which feasible source control measures were set (namely, straw-burning control, the elimination of small boilers in urbanized areas, staggered peak heating measures and a 50 % reduction in residential bulk coal burning around urbanized areas and suburban areas), and the concentrations of PM2.5 and PM10 were projected to decline by more than 29.79 %, meeting the urban air quality standards. This study highlights the importance of combining straw burning regulation in no-burning areas, limited burning areas and residential coal-burning substitution around urbanized areas to improving the air quality in cold regions.

Allylic-alkylic C-C bond decomposition in 1-butene and 1-pentene

1-Butene and 1-pentene are critical intermediates in the oxidation and pyrolysis of larger alkanes and alcohols. Their thermal decomposition plays important role in fuel consumption under combustion conditions, yet seldom investigated. In this work, we studied the title reactions behind reflected shock waves over temperatures of 1178 – 1416 K and pressures near 1.2 bar. We monitored absorbance time-history of the product allyl radicals by employing a sensitive UV diagnostic scheme at a wavelength of 220 nm. We extracted the target rate coefficients by simulating the measured absorbance profiles with detailed kinetic models. Our determined rate coefficients of 1-butene (k1) and 1-pentene (k2) thermal decomposition may be expressed as (unit s−1):k1(1C4H8→CH3+aC3H5)=1.52×1016e(−37937T)k2(1C5H10→C2H5+aC3H5)=3.84×1014e(−31434T)We believe the current work provides the first direct measurements of these reactions. Our 1-butene thermal decomposition rate coefficients exhibit a positive Arrhenius temperature dependence. Around 1350 K and 1 bar, 1-butene decomposition proceeds ∼ 4.5 times faster than n-butane, and ∼ 66 times faster than 1,3-butadiene. Our work extends the literature measurements of 1-butene decomposition to temperatures higher than 1310 K. Literature measurements above 1000 K underestimate our rate coefficients by ∼ 20 %. Additionally, our 1-butene rate coefficients provide an analogy to bio-derived molecules containing similar allylic-alkylic C-C bonds, such as methyl-3-hexenoate. For 1-pentene thermal decomposition, we observed the product allyl radicals starting from 1178 K compared to 1213 K in 1-butene measurements. Thus 1-pentene decomposition proceeds 2 – 6 times faster than 1-butene, and shows a gentler Arrhenius temperature dependence. The current literature models exhibit a range of rate values that vary by an order of magnitude, resulting in noticeable discrepancies. Our study addresses this issue by providing much-needed clarity and precision. Furthermore, we implemented our rate coefficients in literature kinetic models and evaluated their influence on ignition delay time (IDT) and speciation measurements. The results indicate that our rate coefficients generally improved the model performance.

Evaluation of Minimum NOx Emission From Ammonia Combustion

Abstract Ammonia (NH3) is being explored as a hydrogen carrier with no carbon emissions. However, if burned directly as NH3, rather than being completely decomposed back to N2/H2, the fuel-bound nitrogen comes with a potentially significant NOx emissions penalty. Indeed, several existing studies are showing ammonia combustion NOx emissions that exceed current natural gas fueled, DLN technologies by one to two orders of magnitude. Therefore, it is important to establish the theoretical minimum NOx emissions for an ammonia combustor, to determine how much NOx levels can be reduced via further technology development. In other words, the purpose of this work is not to analyze the performance of a specific combustor but, rather, the fundamental limits of what is achievable. This study quantifies this minimum NOx level for a two-stage combustor system for a given combustor exit temperature and residence time, with a constraint on unburned fuel levels. As expected, the optimum configuration is a rich front end combustor to burn and crack ammonia with significant H2 production, followed by an NO relaxation reactor, followed by a lean stage that consumes the remaining H2. The optimum residence time and stoichiometry of each zone are determined in the fast mixing limit, which essentially balances between NOx production in the primary and secondary zones. These results show minimum NOx levels are in 200–400 ppm range at 1 bar, but drop to levels of ∼25 ppm at 20 bar. These NOx emissions are dominated by NOx production in the primary stage which relaxes to equilibrium levels quite slowly. As processes controlling NOx relaxation to equilibrium in the primary stage dominate overall NO emission levels, combustor NOx sensitivities are essentially opposite that of natural gas fired, DLN systems. Specifically, NOx values drop with increased combustor residence time, increased pressure, and increased combustor exit temperature. These results also suggest that the most important strategy for NOx minimization is to provide sufficient relaxation time after the primary zone for NOx to approach equilibrium—this can be done via kinetic means to accelerate this relaxation rate, such as enhancing pressure or temperature, or increasing residence times. Indeed, this work shows that low pressure combustors specifically optimized for ammonia will have residence times that are one to two orders of magnitude larger than current natural gas systems. By doing so, NOx levels below 10 ppm may be achievable. Finally, we discuss the sensitivity of these values to uncertainties in ammonia kinetics.

The carbon footprint of a Dutch academic hospital-using a hybrid assessment method to identify driving activities and departments.

The healthcare sector is responsible for 7% of greenhouse gas (GHG) emissions in the Netherlands. However, this is not well understood on an organizational level. This research aimed to assess the carbon footprint of the Erasmus University Medical Center to identify the driving activities and sources. A hybrid approach was used, combining a life cycle impact assessment and expenditure-based method, to quantify the hospital's carbon footprint for 2021, according to scope 1 (direct emissions), 2 (indirect emissions from purchased energy), and 3 (rest of indirect emissions) of the GHG Protocol. Results were disaggregated by categories of purchased goods and services, medicines, specific product groups, and hospital departments. The hospital emitted 209.5 kilotons of CO2-equivalent, with scope 3 (72.1%) as largest contributor, followed by scope 2 (23.1%) and scope 1 (4.8%). Scope 1 was primarily determined by stationary combustion and scope 2 by purchased electricity. Scope 3 was driven by purchased goods and services, of which medicines accounted for 41.6%. Other important categories were medical products, lab materials, prostheses and implants, and construction investment. Primary contributing departments were Pediatrics, Real Estate, Neurology, Hematology, and Information & Technology. This is the first hybrid analysis of the environmental impact of an academic hospital across all its activities and departments. It became evident that the footprint is mainly determined by the upstream effects in external supply chains. This research underlines the importance of carbon footprinting on an organizational level, to guide future sustainability strategies.

Formation of five-membered ring structures via reactions of o-benzyne

The formation of five-membered ring structures is important for the generation of curved and bowl-shaped polycyclic aromatic hydrocarbons (PAHs) under combustion conditions. Here, we report the identification of the indenyl (C9H7) radical – the simplest aromatic hydrocarbon radical carrying an adjacent five- and six-membered ring, as the major product of the o-benzyne (o-C6H4) reaction with propargyl (C3H3). Because real flames exhibit a complex chemistry, elucidation of a specific reaction is very challenging. Instead, we studied the o-C6H4 + C3H3 reaction in a resistively heated microtubular SiC reactor at controlled conditions of 1150 K and a pressure near 10–20 Torr. To this end, the reactants o-benzyne and propargyl were pyrolytically generated from benzoyl chloride and propargyl bromide. We identified the reactants and the indenyl radical isomer-selectively utilizing photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). The experimentally observed predominant formation of indenyl radicals finally confirms the theoretical predictions of Matsugi and Miyoshi [Phys. Chem. Chem. Phys. 14 (2012), 9722–9728] and highlights a versatile route for the formation of five-membered rings and curved PAHs via reactions of o-benzyne that favor the formation of multiring species over aliphatically substituted aromatic species.

Insights into the role of the H-abstraction reaction kinetics of amines in understanding their degeneration fates under atmospheric and combustion conditions.

Amines, a class of prototypical volatile organic compounds, have garnered considerable interest within the context of atmospheric and combustion chemistry due to their substantial contributions to the formation of hazardous pollutants in the atmosphere. In the current energy landscape, the implementation of carbon-neutral energy and strategic initiatives leads to generation of new amine sources that cannot be overlooked in terms of the emission scale. To reduce the emission level of amines from their sources and mitigate their impact on the formation of harmful substances, a comprehensive understanding of the fundamental reaction kinetics during the degeneration process of amines is imperative. This perspective article first presents an overview of both traditional amine sources and emerging amine sources within the context of carbon peaking and carbon neutrality and then highlights the importance of H-abstraction reactions in understanding the atmospheric and combustion chemistry of amines from the perspective of reaction kinetics. Subsequently, the current experimental and theoretical techniques for investigating the H-abstraction reactions of amines are introduced, and a concise summary of research endeavors made in this field over the past few decades is provided. In order to provide accurate kinetic parameters of the H-abstraction reactions of amines, advanced kinetic calculations are performed using the multi-path canonical variational theory combined with the small-curvature tunneling and specific-reaction parameter methods. By comparing with the literature data, current kinetic calculations are comprehensively evaluated, and these validated data are valuable for the development of the reaction mechanism of amines.

Systematic characterization of selenium speciation in coal fly ash.

Millions of tons of coal fly ashes (CFAs) are produced annually during coal combustion in the U.S., which are commonly beneficially used in the concrete industry or disposed of in ash ponds. CFAs contain trace amounts of a range of toxic heavy metals including selenium (Se). Because the toxicity of Se is dependent on its speciation, investigating Se speciation in CFAs as affected by coal source and combustion conditions can help understand the related environmental and human health impacts during disposal or beneficial reuse. In this study, a set of representative CFA samples were characterized for Se speciation using synchrotron X-ray absorption spectroscopy (XAS) and micro-X-ray fluorescence spectromicroscopy (μ-XRF/XAS). Se-containing particles were highly heterogeneous, and individual particles might contain multiple oxidation states including Se(0), Se(IV), and Se(VI). Principal component analysis was performed for sample characteristics including Al2O3, SiO2, CaO, FeO, loss on ignition, average particle size, Se concentration, and Se oxidation state. Selective catalytic reduction (SCR), which is used to limit nitrogen oxide (NOx) emissions during coal combustion, was found to be associated with the presence of reduced Se oxidation states, with up to 90% Se(0) observed in samples with SCR. Alongside SCR, FeO content may also influence Se speciation.

Effect of Compression Ratio on the Performance of Direct-Injection Hydrogen Engines

Direct injection of hydrogen into the cylinder can avoid abnormal combustion such as backfire, and the hydrogen engine can operate in a wider range of excess air coefficient. However, direct injection hydrogen engines still have problems such as high NOx emissions under high load conditions, reduced power output due to lean combustion, and low thermal efficiency. This paper adopts a variable compression ratio structural design to study the impact of compression ratio changes on the comprehensive performance of direct injection hydrogen engines. The results show that under the same working conditions, as the engine compression ratio increases, the turbulence in the engine cylinder becomes more intense, increasing the back pressure in the cylinder, inhibiting the diffusion of hydrogen, making the hydrogen distribution more concentrated and the combustion conditions in the cylinder better. The overall performance of the engine is significantly improved.

Simulation study on effect of nozzle geometry on flameless combustion of non-preheated methane gas

In this paper, the effects of different burner configurations on the characteristics of flameless combustion were evaluated by comparing the temperature field, NOx, OH, and H2CO at different burner inlet velocity and angles through a combination of experimental and numerical simulations. The results show that increasing the burner inlet angle and gas velocity is imperative in achieving the flameless combustion, increasing the re-circulation rate in the furnace, making the temperature distribution in the furnace uniform, and reducing the emission of NOx at the end of the furnace. During the simulation of flameless combustion, it was found that OH radicals and H2CO radicals were well correlated with the reaction exothermic zone, and the Reynolds number was positively correlated with the re-circulation rate in the furnace. With the increase of Reynolds number, the entrainment rate of flue gas increases, and the combustion state is closer to flameless combustion. When re-circulation rate Kv >2, combustion becomes flameless. Through the summary analysis of the data, it can be found that there is a critical Reynolds number for the burner to achieve flameless combustion, and flameless combustion occurs only when the Reynolds number is greater than 1.0?104.

Key technologies of two-phase pulse detonation combustor

The pulse detonation combustor is a new type of power device based on periodic high-temperature and high-pressure gas generated by detonation combustion as thrust. Due to its extremely fast heat release rate, detonation combustion has the characteristics of high thermal efficiency, low fuel consumption and low pollutant emissions. In recent years, relevant institutions have conducted extensive research on pulse detonation combustors. However, most research results focus on single studies where the fuel and oxidant are in the gas phase. Based on the vision of engineering application of pulse detonation combustors, the research progress of two key pulse detonation technologies, fuel atomization blending technology and rapid short-distance low-resistance detonation technology, as well as the research status of two-phase pulse detonation combustion based on kerosene are introduced. Regarding fuel atomization and blending technology, this paper mainly introduces the fuel atomization mechanism of two-phase detonation, fuel atomization technology and oil and gas blending technology. Regarding rapid short-distance low-resistance detonation technology, it mainly introduces obstacle-assisted detonation technology, spark plug ignition technology, hot jet ignition technology, pre-detonation tube ignition technology, shock wave focusing detonation technology and plasma ignition technology.

Energy, economic and environmental benefits of Demand Response for improving building energy flexibility

The increasing penetration of intermittent renewable sources in power generation at local and building-level poses growing issues in balancing generation and demand. To avoid imbalances, it is therefore necessary to ensure adequate levels of flexibility in the building energy system. This can be done both on the generation side, through the coupling of different energy carriers (cogeneration, power-to-heat solutions) and/or the integration of storage systems, and on the demand side, through smart “demand response” programs. This paper considers a tourist facility located in central Germany as a case study to evaluate the energy, economic and environmental benefits that can be obtained from the application of appropriate demand response strategies. The electrical demand data of the facility are monitored at both aggregate and individual load levels and made available by means of a cloud platform. The facility includes two stationary combined heat and power internal combustion engines powered by natural gas and a photovoltaic system. The results show how, thanks to appropriate load management, it is possible, on the one hand, to increase the self-consumption of PV-generated energy and, on the other hand, to keep more constant the load of the engines, which can therefore operate with better efficiencies. This results in both a reduction in energy expenses and a decrease in carbon dioxide emissions attributable to the building.

Spatio-temporal dynamics of methane concentration and its association to climatic and vegetation parameters: a case study of the Northern Cape Province, South Africa

Methane (CH4) is the second most abundant anthropogenic greenhouse gas after carbon dioxide (CO2), accounting for about 20% of global emissions. CH4 anthropogenic emission sources include landfills, oil and natural gas systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment and certain industrial processes. In this work, we examine the spatio-temporal dynamics of CH4 and its relationship to climatic and vegetation parameters in the Northern Cape province in South Africa. Various datasets from the TROPOspheric Monitoring Instrument, Moderate Resolution Imaging Spectroradiometer, Atmospheric Infrared Sounder and the Global Precipitation Climatology Project were used. The results show an increasing trend of CH4 concentration throughout the entire province. The greatest increase in CH4 concentration is observed in the western parts of the province during June–July–August (JJA) season. CH4 concentration shows negligible correlation with most climatic parameters, i.e. Temperature (Temp), Precipitation (Precip) and NDVI for both seasons. The Temp–NDVI relationship shows high correlation values of r = –0.71 and r = 0.82 for the DJF and JJA seasons, respectively. Seasonality plays a critical role in the relationships of the CH4 to climatic and vegetation parameters. This study shows that we are in a crisis, and robust mitigation strategies are needed to combat this.

Investigation of atmospheric VOCs sources and ozone formation sensitivity during epidemic closure and control: A case study of Zhengzhou

This study investigates the pollution characteristics of volatile organic compounds (VOCs) and their impact on ozone formation in the urban area of Zhengzhou. The analysis is based on the air quality data collected during the epidemic control period (P3) from July 20 to August 22, 2021, as well as the same period in 2019 and 2020 (P1 and P2). The results reveal a decreasing trend in the O3 precursors, namely NO2 and VOCs, from 2019 to 2021. During the P3 period, the mean concentrations of NO2 and VOCs were 19 μg/m3 and 56 μg/m3, respectively, a decline of 32% and 36% compared to the levels in P2. However, the mean MDA8 concentration in P3 was 142 μg/m3, 25% higher than that in P2, and ozone-polluted days was 12 d, 6 days more than that in P2. The VOCs composition profiles were similar across three periods, with alkanes accounting for 34%, 36%, and 39% of TVOC, respectively. Six kinds of VOCs sources were quantified by positive matrix factorization (PMF), among which vehicle emissions contributed the most (29%), followed by solvent usage (23%) and industrial processes (22%). The contribution of industrial processes and vehicle emissions declined significantly in P3, while that of stationary combustion and LPG/NG sources increased. The net production rate P(Ox) increased in P3 compared to that in P2, getting closer to the ridge line, indicating that O3 formation was gradually transiting from VOCs control zone to synergistic control zone. Therefore, VOCs and NOx emissions should be reduced synchronously.

Enhancing pure NH3 combustion: Impacts of O2 enrichment under MILD conditions in a 20-kW semi-industrial scale furnace

This experimental work provides insights into the effects of oxygen (O2) enrichment on pure ammonia (NH3) combustion in a 20-kW semi-industrial scale furnace featuring an industrial-grade burner operated under MILD/Flameless conditions. The impact of O2 enrichment on the NH3 combustion stabilization, the flame and furnace temperature, the exhaust emissions, and the OH* chemiluminescence were explored. The tests were conducted by varying O2 concentration in the oxidizer stream from 21 % to 50 % and using two different oxidizer injectors to achieve average inlet velocities of 80 m/s and 150 m/s while keeping the inlet power and the total oxidizer mass flow rate constant. Stable flameless combustion with a distributed reaction zone and a consistent and uniform temperature profile throughout the combustion chamber was achieved with O2 enrichments higher than 34 %. Nevertheless, high levels of NH3 slips were observed, which were drastically reduced to negligible concentrations at higher O2 enrichments. On the contrary, NO emissions increased with the O2 fraction with an opposite non-linear trend compared to that of NH3 slip. An optimum trade-off between NOx emissions and NH3 slip was achieved by co-firing NH3 with O2=37 % with ID16 and 36 % with ID20 injector. This study also compares the behavior of pure O2-enriched NH3 combustion under flame and MILD combustion conditions to highlight the advantages of oxygen-enhanced NH3 flameless combustion. While operating in flame mode ensured a stable ammonia oxidation process already at low O2 enrichment=30 %, NO emissions and NH3 slips were significantly higher than those measured under MILD conditions. Finally, the impact of varying industrial load and the related heat balance on the NH3 slip was assessed at different levels of O2 enrichments at a fixed equivalence ratio. The overall results show that O2-enriched flameless ammonia combustion can simultaneously expand the range of stable combustion and reduce NO and NH3 emissions.

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC).

Plumes from wildfires are transported over large distances from remote to populated areas and threaten sensitive ecosystems. Dense wildfire plumes are processed by atmospheric oxidants and complex multiphase chemistry, differing from processes at typical ambient concentrations. For studying dense biomass burning plume chemistry in the laboratory, we establish a Photochemical Large Aerosol Chamber (PHOTO-LAC) being the world's largest aerosol chamber with a volume of 1800 m3 and provide its figures of merit. While the photolysis rate of NO2 (jNO2) is comparable to that of other chambers, the PHOTO-LAC and its associated low surface-to-volume ratio lead to exceptionally low losses of particles to the walls. Photochemical ageing of toluene under high-NOx conditions induces substantial formation of secondary organic aerosols (SOAs) and brown carbon (BrC). Several individual nitrophenolic compounds could be detected by high resolution mass spectrometry, demonstrating similar photochemistry to other environmental chambers. Biomass burning aerosols are generated from pine wood and debris under flaming and smouldering combustion conditions and subsequently aged under photochemical and dark ageing conditions, thus resembling day- and night-time atmospheric chemistry. In the unprecedented long ageing with alternating photochemical and dark ageing conditions, the temporal evolution of particulate matter and its chemical composition is shown by ultra-high resolution mass spectrometry. Due to the spacious cavity, the PHOTO-LAC may be used for applications requiring large amounts of particulate matter, such as comprehensive chemical aerosol characterisation or cell exposures under submersed conditions.

Theoretical investigation of electron-impact ionization of W<sup>6+</sup> ion

<sec>Due to its unique characteristics, metal tungsten has been selected as the wall material for the tokamak magnetic confinement fusion device. The wall material directly interacts with the plasma for a long time, thus causing tungsten atoms and ions to be sputtered and ionized into different charge states, which then enter the tokamak device as plasma impurities. To ensure stable plasma combustion conditions, highly complex model is currently being used to evaluate the behavior of tungsten impurities and their influence on the tokamak plasma. This requires various high-precision atomic data for tungsten atoms and different ionized states of tungsten ions. Electron collision ionization, as a fundamental atomic physical process, is widely encountered in laboratory and astrophysical plasma environments. The parameters such as electron collision ionization cross-sections and rate coefficients are crucial for plasma radiation transport simulations and state diagnostics.</sec><sec>Electron-impact single-ionization (EISI) cross sections of the ground state and metastable state for W<sup>6+</sup> ions are calculated by using the level-to-level distorted-wave (LLDW) method. The contributions of direct ionization (DI) cross section and excited autoionization (EA) cross section to the total EISI cross section are primarily considered.</sec><sec>Comparison of our calculation results with the experimental data from Stenke et al. (Stenke M, Aichele K, Harthiramani D, Hofmann G, Steidl M, Volpel R, Salzborn E <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://iopscience.iop.org/article/10.1088/0953-4075/28/13/021">1995 <i>J. Phys. B: At. Mol. Opt. Phys.</i> <b>28</b> 2711</ext-link>) reveals that the EISI cross section considering only the ground state is significantly smaller than the experimental result. Therefore, it is imperative to take into account the contribution from the metastable state. To determine the fraction of ions in long-lived energy levels within the parent ion beam, three models are employed.</sec><sec>Our results, which include the contribution of metastable states, accord well with the experimental results of Stenke et al. Compared with the theoretical calculation result of Pindzola et al. our calculaiton provides a more comprehensive understanding of the electron-impact single-ionization process for W<sup>6+</sup> ions. The comparison is illustrated in the attached figure.</sec>

Flame Propagation Dynamics in Open Tubes: Factors Influencing Combustion Conditions and Practical Implementations

Flame Propagation Dynamics in Open Tubes: Factors Influencing Combustion Conditions and Practical Implementations

Molecular simulation of CO production and adsorption in a coal-kaolinite composite gangue slit model.

To reveal the mechanism of CO gas generation and adsorption in coal gangue slits at the microscopic level, a new composite kaolinite-coal-kaolinite (KCK) slit model was constructed by combining the Hongqingliang (HQL) coal molecular model and the Bish kaolinite model to characterize the crack structure of the gangue. It is compared with the kaolinite model (TriK) commonly used in gangue research. Molecular dynamics was used to study the production of CO in different oxygen environments and variation in the adsorption amount, adsorption sites and diffusion coefficient in the temperature range from 293.15 K to 333.15 K. The results indicate that CO mainly comes from the decomposition of ether and phenol in organic structures, and the lower the oxygen concentration, the lesser the CO production time. The KCK model has a higher average adsorption capacity and weaker diffusion capacity mainly due to the additional adsorption sites provided by the carbon-containing structural layer, and CO is mainly adsorbed near the oxygen-containing functional groups. Although kaolinite exhibits bonding adsorption on the Al-O plane, its adsorption site is limited to the surface. The slit model with the carbon structure can better reflect the complex conditions of gas motion in the gangue, thus providing a reference to determine the spontaneous combustion conditions of the gangue hill via the index gas.

Color and multi-band imaging of a cavity-based flameholder in supersonic flow

Utilizing time-resolved CH*/C2* and multi-angle color flame imaging recorded at 1 kHz/22.5 kHz frequencies, this study investigates the dynamics and stabilization of supersonic flames in a cavity flameholder combustor at Mach 2, with ethylene fuel and air. A stagnation pressure of 289 kPa was used for the stable cavity burning experiments with fuel flow rates of 30, 60, and 90 slpm and 483 kPa for ignition transient experiments with fuel flow rates of 55 and 90 slpm, injecting fuel at the closeout ramp. The stagnation temperature was 597 K. Chemiluminescence analysis focused on the equivalence ratio (ER) and combustion intensity, while a fiber-based endoscope captured color flame image, informing on premixedness, flame structure, and flame surface density. Results from transient ignition showed that a progression from lean to stoichiometric, and ultimately to fuel-rich conditions was observed, with marked transitions occurring along the cavity floor. High-intensity CH* regions were consistently associated with fuel-rich zones. Digital flame coloration discrimination (DFCD) analysis provided insights into the mixing efficiency, affecting the flame color and structure. Despite reduced fuel flow rates significantly altering flame characteristics, such as thickness and the persistence of a 'W' flame structure, the shear layer remained a focal point for optimal combustion conditions. The study demonstrated that the shear layer's intense turbulent mixing is crucial for flame stability and structure, with chemiluminescence surface density (CSD) profiles suggesting balanced combustion at 60 and 90 slpm flow rates. However, an asymmetry of CSD at 30 slpm indicated a shift towards fuel-rich conditions at the burning surface, indicating potential instability and elevated blowout.