記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Energies  

This study investigates the effects of diffusion modeling and swirl intensity on flow fields and NO emissions in CH<inf>4</inf>/NH<inf>3</inf> non-premixed swirling flames using large eddy simulations (LESs). Simulations are performed for a 50/50 ammonia–methane blend at three global equivalence ratios of 0.77, 0.54, and 0.46 and two swirl numbers of 8 and 12, comparing the unity Lewis number (ULN) and mixture-averaged diffusion (MAD) models against the experimental data includes OH-PLIF and ON-PLIF reported in a prior study by the KAUST group. Both models produce similar flow fields, but the MAD model alters the flame structure and species distributions due to differential diffusion (DD) and limitations in its Flamelet library. Notably, the MAD library lacks unstable flame branch solutions, leading to extensive interpolation between extinction and stable branches. This results in overpredicted progress variable source terms and reactive scalars, both within and beyond the flame zone. The ULN model better reproduces experimental OH profiles and localizes NO formation near the flame front, whereas the MAD model predicts broader NO distributions due to nitrogen species diffusion. Higher swirl intensities shorten the flame and shift NO production upstream. While a low equivalence ratio provides enough air for good mixing, lower ammonia and higher NO contents in exhaust gases, respectively.

DOI： 10.3390/en18153921

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出版者・発行元：Fuel  

The flamelet/progress variable (FPV) approach has been formulated to perform large eddy simulation (LES) modeling on a research gasifier at the Central Research Institute of Electric Power Industry (CRIEPI). The FPV approach employs a precomputed flamelet chemtable that stores all reactive scalars accessible through a limited number of tracking parameters. Three fuel streams that result from the gasification process are defined by their respective mixture fractions, and the mixing among them has been determined using mixing parameters. Separate flamelet chemtables are generated for each oxidizer stream, including primary air, secondary gas stream, and pure CO<inf>2</inf>/N<inf>2</inf> injected into the combustor, and these libraries are subsequently integrated into a single library. An oxidizer weighting factor represents the contribution of each library when accessing data from the flamelet library. Two cases have been examined to investigate the influence of CO<inf>2</inf> injection on gasification performance: in case 1, CO<inf>2</inf> has been injected as a gasifying agent, while in case 2, N<inf>2</inf> replaced CO<inf>2</inf>. The results indicate that the FPV–LES approach demonstrates strong concordance with experimental measurements of gas temperature and product gas yield in both cases. Case 1, in which CO<inf>2</inf> is injected as a gasifying agent, exhibited a lower combustor zone temperature compared to case 2. This reduction in temperature has been attributed to the higher heat capacity of the mixture, which absorbs more energy, leading to decreased temperatures.

DOI： 10.1016/j.fuel.2025.134887

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出版者・発行元：International Journal of Hydrogen Energy  

Understanding the explosion characteristics and flame behaviors of hydrogen related aerosol mixtures is an important subject for the safety maintenance of various hydrogen production and supply chain. As such, in present work, an extensive explosion experiment was conducted in a 5 L duct for gasoline spray/H<inf>2</inf> mixture with varying H<inf>2</inf> and gasoline concentrations. The explosion pressure and transient flame morphology of gasoline spray/H<inf>2</inf> aerosol were investigated, accompanied by a comprehensive analysis of chemical kinetics to elucidate the elementary reaction sensitivity and reaction paths that govern the combustion mechanism of mixed fuel. Results indicate that for median gasoline concentration, the peak explosion pressure of aerosol mixture first increases and then decreases when hydrogen component increases. Meanwhile, the peak explosion pressure shifts towards the lower hydrogen regime as gasoline concentration increases. The flame propagation of aerosol mixture with low gasoline concentration is close to that of gaseous fuel, which is characterized by a uniform combustion and is controlled by chemical dynamics. On the contrary, for higher gasoline concentration, the explosive mixture exhibits a heterogenous combustion, controlled by the multiphase devolatilization. Moreover, the reactions of O<inf>2</inf>+H[dbnd]O + OH and H<inf>2</inf>+OH[dbnd]H + H<inf>2</inf>O are the main pathways for hydrogen to participate in gasoline combustion and explosion, which improve the production rate of H, O, OH radicals and promote the reactivity of the hydrogen dual-fuel flame.

DOI： 10.1016/j.ijhydene.2025.04.498

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出版者・発行元：Fuel  

Furan groups play significant roles in the combustion of low-rank coal. We employed ReaxFF MD to investigate the pyrolysis and oxidation processes of furan (FR) and benzofuran (BFR) under various oxygen contents and temperatures. The results show that the initial reaction of FR groups pyrolysis is FR/BFR → R-unstable carbon chain + CO, with all oxygen-containing components converting to CO during pyrolysis. The aggregation of numerous unstable carbon chains leads to the formation of soot particles. Decreasing temperature and increasing oxygen content both reduce the size of the soot particles. We discovered a new mechanism for the formation of PAHs from FR molecules or unstable carbon chains, termed recombination cyclization of the unsaturated carbon chains from ring-opening (RCCRO). Soot particle evolution tends from 5-membered-carbon-ring to 6-membered-carbon-ring structures. During oxidation, oxygen-containing radicals attack carbon chains to extract carbon components, forming hydroxyl and aldehyde groups at the molecular ends. With increasing oxygen content, H<inf>2</inf>O, CO, and CO<inf>2</inf> production increases. Hydrogen is an important product during the oxidation and pyrolysis processes, with higher temperatures and lower oxygen content leading to increased hydrogen production. The similarities in the pyrolysis and oxidation mechanisms of FR and BFR further emphasize the effectiveness of studying FR group reactions in coal.

DOI： 10.1016/j.fuel.2024.134138

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出版者・発行元：Renewable Energy  

Thermochemical hydrogen production from carboxylic acids plays a significant role in the utilization of biofuels. We employed ReaxFF molecular dynamics simulations to investigate the pyrolysis mechanisms of formic acid and acetic acid in O<inf>2</inf>/H<inf>2</inf>O environments. There are two reaction channels in formic acid pyrolysis: the dehydration reaction (HCOOH→H<inf>2</inf>O+CO) and the decarboxylation reaction (HCOOH→H<inf>2</inf>+CO<inf>2</inf>), with the dehydration reaction predominating, where the major pathway is HCOOH→CHO→CO. For the pyrolysis of acetic acid, the primary pathway involves the sequential steps: CH<inf>3</inf>COOH→CH<inf>3</inf>→CH<inf>3</inf>OH→HCHO→CO. The initial major reactions are CH<inf>3</inf>COOH→CH<inf>3</inf>CO+OH, CH<inf>3</inf>CO→CH<inf>3</inf>+CO, and CH<inf>3</inf>+OH→CH<inf>3</inf>OH, followed by successive dehydrogenation reactions of CH<inf>3</inf>OH to form CO. During oxidation of formic acid, as the oxygen content increases, the production of H<inf>2</inf> and CO decreases, while the production of H<inf>2</inf>O and CO<inf>2</inf> increases. The water-catalyzed pyrolysis generates the most H<inf>2</inf> by inhibiting dehydration and enhancing decarboxylation, with elevated temperatures further increasing the yield. H<inf>2</inf> formation occurs through H-abstraction reactions on acids, H<inf>2</inf>O, and intermediate products by H radicals. Constructing reaction kinetic models for these processes. The decomposition activation energies are in good agreement with experimental data reported in the previous literature. The carboxyl group plays a more predominant role than the methyl group in the initial pyrolysis process.

DOI： 10.1016/j.renene.2024.122186

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Hydrogen Energy  

A thorough understanding of the Differential Diffusion (DD) effect is necessary for properly predicting combustion processes fueled by NH<inf>3</inf>/H<inf>2</inf>, especially because of the higher diffusivity of H<inf>2</inf> compared with thermal diffusivity and diffusivities of O<inf>2</inf> and NH<inf>3</inf>. It is a common practice in turbulent combustion simulations to ignore the effects of DD by assuming that turbulent mixing overweighs the diffusion mixing, hence simplifying the modeling process. However, it is important to understand that, despite this assumption being valid for hydrocarbon fuels, it loses significance when it comes to the burning of H<inf>2</inf> because of the significant influence of DD. In this work, two direct numerical simulations (DNS) of a turbulent NH<inf>3</inf>/H<inf>2</inf> non-premixed flame in the mixing layer are conducted, one considers the DD and the other assumes the Unity Lewis Number (ULN) to investigate the DD effect. It is found that DD allows more fuel to diffuse toward the flame front, significantly enhancing flame stability compared to the ULN assumption. It also keeps the scalar dissipation rate (SDR) at lower levels than in ULN due to smoother species distribution from enhanced diffusion. This supports the partially premixed and premixed combustion modes as well alongside non-premixed combustion, influenced by both ammonia's low reactivity and its higher diffusion flux. The tendency of ammonia to favor partially premixed and premixed modes offers insights into the causes of ammonia slip in emissions while burning in non-premixed mode. The fuel species diffusion angle measured from the flame front's normal direction is strongly influenced by the SDR, a higher SDR increases diffusion potential in the normal direction, resulting in a smaller diffusion angle, and vice versa. While the tangential diffusion magnitude is strongly influenced by the divergence of the diffusion flux, which is affected by the flame front curvature and reaction rates.

DOI： 10.1016/j.ijhydene.2024.12.434

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Combustion Science and Technology  

The flame–turbulence interaction and statistical behavior of the surface density function (SDF; i.e. magnitude of the reaction progress variable gradient) in the vicinity of the wall for a stoichiometric methane-air flame are investigated using a three-dimensional direct numerical simulation of a turbulent premixed V-flame interacting with an isothermal inert wall in a fully developed turbulent channel flow at a friction Reynolds number (Formula presented.). The results show that the mean SDF significantly decreases in the viscous sublayer in comparison to the corresponding values for the same reaction progress variable in the unstretched laminar flame. Moreover, the mean values of SDF for a given value of reaction progress variable decrease in the downstream direction with the progress of flame quenching in all zones of turbulent boundary layer. The effective normal strain rate (Formula presented.) ((Formula presented.)), which acts to reduce the SDF as it increases, is much higher in the viscous sublayer than in the other layers. In the viscous sublayer, the contribution of the gradient of displacement speed in the flame-normal direction ((Formula presented.)) to (Formula presented.) has been shown to dominate the fluid-dynamic normal strain rate ((Formula presented.)). This tendency is qualitatively similar to the previous findings for a V-flame interacting with an isothermal inert wall at (Formula presented.). However, the maximum mean value of (Formula presented.) at (Formula presented.) is approximately twice of that at (Formula presented.), which causes a sharper drop in the SDF in the viscous sublayer at higher (Formula presented.).

DOI： 10.1080/00102202.2022.2150971

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出版者・発行元：Energy  

Formaldehyde (HCHO), typically known as an industrial waste gas, can be recycled to generate syngas. Our study focuses on the high-temperature and high-pressure treatment of formaldehyde, including pyrolysis, oxidation, and supercritical H2O/CO2 (scH2O/scCO2) co-pyrolysis via reactive molecular dynamics. Results showed that in the pyrolysis, the primary final products are H2 and CO. The formation of CO occurs through the double dehydrogenation of HCHO, and H-abstraction reaction leads to the formation of H2. In the oxidation, scH2O and scCO2 co-pyrolysis systems, the corresponding global reactions vary. HCHO can be oxidized to HCOOH, ultimately producing CO2. Another pathway for CO2 generation involves the formation of the COOH radical from CO. Oxidative treatment is more powerful in handling formaldehyde pollutants, while the supercritical condition is more effective in producing syngas. The order of carbon emission is oxidation > scH2O > pyrolysis. In the scCO2 system, scCO2 participates in the reaction, increasing CO production. Moreover, reaction kinetics models are proposed and agree well with experimental results. Under high-temperature conditions, the reaction rate in the oxidation system is the highest. Based on the activation energy for formaldehyde consumption and the energy barriers of the sub-reactions, the pyrolysis process is the easiest, whereas the oxidation process is the most difficult.

DOI： 10.1016/j.energy.2024.133725

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Combustion and Flame  

Preferential diffusion plays an important role especially in hydrogen flames. Flame stretch significantly affects the flame structure and induces preferential diffusion. A problematic phenomenon occurring in real combustion devices is flashback, which is influenced by non-adiabatic effects, such as wall heat loss. In this paper, an extended flamelet-generated manifold (FGM) method that explicitly considers the preferential diffusion, flame stretch, and non-adiabatic effects is proposed. In this method, the diffusion terms in the transport equations of scalars, viz. the progress variable, mixture fraction, and enthalpy, are formulated employing non-unity Lewis numbers that are variable in space and different for each chemical species. The applicability of the extended FGM method to hydrogen flames is investigated using two- and three-dimensional numerical simulations of hydrogen-air flame flashback in channel flows. The results of the extended FGM method are compared with those of detailed calculations and other FGM methods. The two-dimensional numerical simulations show that considering both preferential diffusion and flame stretch improves the prediction accuracy of the mixture fraction distribution and flashback speed. The three-dimensional numerical simulations show that the prediction accuracy of the flashback speed, backflow region, and distributions of physical quantities near the flame front is improved by employing the extended FGM method, compared with the FGM method that considers only the heat loss effect. In particular, the extended FGM method successfully reproduced the relationship between the reaction rate and curvature. These results demonstrate the effectiveness of the extended FGM method. Novelty and Significance Statement The novelty of this research is the development of a flamelet-generated mani-fold (FGM) method that explicitly considers preferential diffusion, flame stretch, and non-adiabatic effects. To the best of the authors’ knowledge, no studies have performed numerical simulations of pure hydrogen flames using such an FGM method. The developed FGM method was applied to numerical simula- tions of hydrogen-air premixed flame flashback at an equivalence ratio of 0.5 and reproduced the flashback speed of lean hydrogen-air premixed flame. The applicability of the FGM method to the numerical simulation of hydrogen-air flashback is reported first. This research is significant because the FGM method is one of the most widely used combustion models for premixed combustion, and the development of an accurate FGM method will contribute to the engineering field. The accurate prediction of the flame flashback attempted in this study is particularly important for the development of hydrogen-fueled combustion devices.

DOI： 10.1016/j.combustflame.2024.113718

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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Fluids  

In this study, a semi-implicit pressure-based scheme which can suppress the spurious pressure oscillations is developed for real fluid flows. Conservation properties relevant to the proposed scheme are investigated through one-dimensional numerical simulations of the nitrogen interface advection. The efficiency and validity of this scheme are carefully examined with two- and three-dimensional numerical simulations of cryogenic nitrogen jets. From the one-dimensional simulation results, the conservation properties are well conserved as the past studies. The two-dimensional simulation results show that the developed scheme can reduce the computational cost by more than 92% (13-14 times faster) compared with the conventional density-based explicit solver employing the double flux model. It is also found that, through the three-dimensional simulation results, the developed scheme can predict the structure of the nitrogen jet under both transcritical and supercritical conditions, while taking into account the effects of real fluid properties on the mixing and spatiotemporal evolution of this jet, with excellent accuracy.

DOI： 10.1063/5.0231255

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出版者・発行元：Energy  

To uncover the microscopic reaction mechanisms of dimethyl ether (DME) pyrolysis and oxidation, reactive molecular dynamics simulations were employed to investigate the reaction processes under various O2/DME ratios and impurity environments at 2200 K–3200 K. The results show that DME pyrolysis begins with a decomposition reaction of CH3OCH3 → CH3O + CH3, ultimately leading to the formation of CO, H2 and PAHs. The reaction pathways of DME oxidation contain light gas conversion and combustion. In fuel rich conditions, the oxidation produces mainly H2 and CO, while in fuel lean conditions, the oxidation products tend to be H2O and CO2. The carbon components of DME are completely converted into CO2 and CO regardless of O2 content. In the presence of impurities H2O or CO2, the oxidation reaction pathway is altered, causing consumption and transformation of these impurities into active radicals such as OH, further promoting the progress of the reaction. The top three light gases produced are hydrogen, methanol and methane, and increasing H2 production in the DME oxidation process can be achieved through both oxygen subtraction and water addition. The rate of formaldehyde generation during pyrolysis is higher than that during oxidation. However, a higher oxygen content leads to increased formaldehyde production.

DOI： 10.1016/j.energy.2024.131013

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1299/jtst.24-00087

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Energy and Fuels  

The combustion characteristics of cracked NH3 flames are investigated experimentally and numerically. The one-dimensional (1D) calculations are performed to validate the accuracy of the reaction mechanisms in cracking conditions and to understand the fundamental characteristics of the cracked NH3 flames. In the experiments, the local distributions of OH and NO and the species emissions of NO, NO2, N2O, and NH3 are measured using hydroxyl radical planar laser-induced fluorescence (OH-PLIF), NO* chemiluminescence, and Fourier transform infrared (FTIR) spectroscopy, respectively. The effects of partial cracking on the flame structure and emission characteristics are investigated. In addition, the large eddy simulations (LESs) with flamelet-generated manifold (FGM) methods, which consider the preferential diffusion effect, are conducted to understand the validity of the LES and to further elucidate the effects of the cracking ratio (Cr) on cracked NH3 flames. The 1D calculation results show that reaction mechanisms by Mei et al. ( Mei, B. ; Zhang, J. ; Shi, X. ; Xi, Z. ; Li, Y. Enhancement of ammonia combustion with partial fuel cracking strategy: Laminar flame propagation and kinetic modeling investigation of NH3/H2/N2/air mixtures up to 10 atm. Combust. Flame 2021, 231, 111472, 10.1016/j.combustflame.2021.111472), Shrestha et al. ( Shrestha, K. P. ; Lhuillier, C. ; Barbosa, A. A. ; Brequigny, P. ; Contino, F. ; Mounaïm-Rousselle, C. ; Seidel, L. ; Mauss, F. An experimental and modeling study of ammonia with enriched oxygen content and ammonia/hydrogen laminar flame speed at elevated pressure and temperature. Proc. Combust. Inst. 2021, 38, 2163−2174, 10.1016/j.proci.2020.06.197), and Otomo et al. ( Otomo, J. ; Koshi, M. ; Mitsumori, T. ; Iwasaki, H. ; Yamada, K. Chemical kinetic modeling of ammonia oxidation with improved reaction mechanism for ammonia/air and ammonia/hydrogen/air combustion. Int. J. Hydrogen Energy 2018, 43, 3004−3014, 10.1016/j.ijhydene.2017.12.066) have acceptable accuracies for predicting combustion characteristics of cracked NH3 flames. As the cracking ratio increases, the ignition delay time (tig) and laminar flame speed (Sl) are shortened and accelerated, respectively, and the effect of Cr on Sl becomes evident in higher ϕ conditions. The NO emissions exhibit a tendency to achieve peaks around Cr = 0.6-0.9, irrespective of ϕ. The experimental results show that the partial cracking significantly changes the NH3 swirl flame structure. As Cr increases, the flames changed from “V” to “M” shape and the OH and NO* signals are enhanced. While OH and NO* signals show a strong positive correlation in a pure NH3 flame, the correlation gradually weakens when Cr increases. As Cr increases, the NO and NO2 emissions increase, whereas the NH3 emissions decrease. As a result, the optimal condition for minimizing global emissions is considered to be Cr = 0.2. By comparison of the velocity and OH fields to the experiments, it is verified that the present LESs coupled with the FGM combustion model, considering the preferential diffusion effect, capture the general feature of the cracked NH3 swirl flames well. The heat release rate (HRR) is enhanced as a result of partial cracking. A higher Cr enables the flame to stabilize even in highly strained areas of the flame front. As Cr increases, the amount of both fuel NO and thermal NO increases as a result of higher O and OH and higher temperature. However, these are reduced by increasing ϕ and enhancing heat loss through walls.

DOI： 10.1021/acs.energyfuels.4c00312

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1299/mej.23-00400

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Computational Physics  

A new semi-implicit pressure-based solver considering the real gas effect is developed and tested. The advantage of the semi-implicit solver is that it can take a large time step, which makes the calculation speed faster than the classical density-based explicit solver. The comparison of the calculation speed between the explicit density-based solver and the new semi-implicit pressure-based solver is conducted by performing two-dimensional numerical simulations of a cryogenic nitrogen planar jet. Moreover, the developed pressure-based solver is validated by comparing the numerical results of a three-dimensional large-eddy simulation of a cryogenic nitrogen jet under the supercritical pressure condition with the experimental result. Results show that the developed pressure-based solver can calculate more than five times faster than the classical explicit density-based solver and accurately predict the jet behavior under the supercritical pressure condition.

DOI： 10.1016/j.jcp.2024.112782

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applications in Energy and Combustion Science  

Importance of the considerations of preferential diffusion and flame stretch effects in the flamelet-generated manifold (FGM) method on the prediction accuracy is investigated by two-dimensional numerical simulations of cylindrical NH3/air premixed flames, under the conditions of an unburnt gas temperature of 673 K, an ambient pressure of 2 MPa, and equivalence ratios of 0.8 to 1.2. Results of the numerical simulations using the detailed chemistry, in which 32 species and 204 reactions are directly solved in the physical space without the FGM method, show that the mixture fraction in the burnt gas increases from the unburnt gas value when considering the preferential diffusion effect, whereas it remains flat when assuming the unity Lewis number. This means that assuming the unity Lewis number causes the underprediction and overprediction of the burnt gas temperature under fuel-lean and fuel-rich conditions, respectively. Results of the numerical simulations using the FGM methods show that considering the preferential diffusion and flame stretch effects in the FGM method is important for accurate prediction of the flame propagating speed, and the effectiveness is more evident for the flame stretch effect than for the preferential diffusion effect for the NH3/air premixed flames.

DOI： 10.1016/j.jaecs.2024.100253

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Gas Turbine, Propulsion and Power Systems  

To design a low-emission hydrogen-fired gas turbine combustor, prevention of flashback is one of key issues. However, the detailed measurement of flashback is difficult and expensive, especially at the actual operation condition. Therefore, the high-precision numerical simulation technology is important to study the mechanism and countermeasures of flashback. In this study, a large eddy simulation (LES) using a non-adiabatic flamelet-generated manifold (NA-FGM) approach, considering the effects of heat loss, is applied to simulate hydrogen-air premixed flame propagating in a rectangular channel. Then, the validity of predicting flashback limits is examined. The results show that the NA-FGM approach quantitatively well captures the flashback limits variation observed in the experiments. This indicates that accounting for the influence of heat loss is crucial in achieving precise prediction of the flashback in developing a low-emission hydrogen gas turbine combustor.

DOI： 10.38036/jgpp.15.1_40

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the Combustion Institute  

Direct numerical simulation with a detailed chemical reaction mechanism is performed for detonation-turbulence interaction in a stoichiometric hydrogen/oxygen mixture. Three turbulences are introduced into detonation with different intensities which are defined by turbulent Reynolds number and turbulent Mach number. The results show that turbulent flow corrugates both shock and flame fronts and makes cellular structures obscure and randomized. The strongest turbulence distorts the shock so strongly that the transverse wave is unclear and cellular structure is destroyed. Time-averaged one-dimensional profiles demonstrate that turbulence promotes the reaction progress. Stronger turbulence produces more intermediate species, by which the chemical reaction reaches completion more rapidly. The turbulent combustion regime indicates that small eddies intrude the flame structure, for which unburned gas pockets are broken into pieces and consumed rapidly. It is consistent with the tendency of the probability density function of induction length, which has only one peak in a smaller value under stronger turbulences, whereas two peaks under the weakest turbulence and without turbulence. Turbulence increases the peak pressure on one-dimensionally averaged structure except for the case where the cellular structure is destroyed. Averaged detonation velocity is strongly correlated with the magnitude of peak pressure, which is the lowest in the strongest turbulence, whereas its deviation increases with turbulent intensities. The absence of the cellular structure, which has been confirmed in optical measurements of rotating detonation engines, could be attributed to the collapse of the cellular structure observed in the strongest turbulence.

DOI： 10.1016/j.proci.2024.105337

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出版者・発行元：International Exchange and Innovation Conference on Engineering and Sciences  

The primary focus of this work is to examine the differential diffusion effect for flames fueled by H<inf>2</inf>/NH<inf>3</inf>. For a non-premixed turbulent flame, two Direct Numerical Simulations (DNS) have been implemented in two-dimensional domain, one is considering the differential diffusion (DD) of each species pair and the other assumes Unity Lewis Number (ULN). Two Flamelet libraries are created based on ULN and Constant Lewis Number (CLN) assumptions, they are validated through priori tests based on the DNS results. Significant difference between the two DNS cases, the DD case is more resistible for quenching than ULN case, meaning ULN assumption for DNS is not suitable. Furthermore, significant variations in the chemistry states are also evident in ULN library results, suggesting that differential diffusion should be considered in the Flame let model, additionally, equal diffusivities is inappropriate for an H<inf>2</inf>/NH<inf>3-</inf>fueled flame, while CLN library exhibits more consistent chemistry states with the DD DNS.

DOI： 10.5109/7323262

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1299/jtst.23-00279

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Hydrogen Energy  

A flamelet-generated manifold (FGM) method that explicitly considers the preferential diffusion effect, referred to as FGM-PD method, is employed for large-eddy simulations (LESs) of a lean-premixed H2/air low-swirl lifted flame, and the validity is examined by comparing with the experiment. First, the applicability of the FGM-PD method is investigated by one-dimensional numerical simulations of planar laminar premixed H2/air flames. Next, LESs of a lean-premixed H2/air low-swirl lifted flame are performed employing the FGM-PD and conventional FGM methods. Results of the one-dimensional numerical simulations show the importance of considering preferential diffusion to accurately predict species concentrations near the flame front. The FGM-PD method accurately predicts this, and therefore, reproduces the laminar burning velocity and spatial distributions of temperature and mixture fraction. Three-dimensional LES results confirm that the prediction accuracy of the velocities near the flame front is improved by employing this FGM-PD method. Additionally, the OH mass fraction distribution predicted by the FGM-PD method exhibits the inhomogeneous finger-like structure, which has been observed in previous experiments. This inhomogeneity of OH mass fraction distribution, which corresponds to that of the reaction rate, predicted by the FGM-PD method, strongly affects the flame front structure.

DOI： 10.1016/j.ijhydene.2022.12.164

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Fluids  

Direct numerical simulation is conducted to address the detonation-turbulence interaction in a stoichiometric hydrogen/oxygen/argon mixture. The argon dilution rate is varied so that the mixture composition is 2H2 + O2 + 7Ar and 2H2 + O2 + Ar to discuss the effects of cell regularity on the sensitivity to turbulence. Turbulent Reynolds number and turbulent Mach number are taken to be common for both mixtures. The results show that the shock and flame of detonation in both mixtures are significantly deformed into corrugated ones in the turbulent flow, producing many small unburned gas pockets. However, one-dimensional time-averaged profiles reveal the different sensitivity of the mixtures: in the highly diluted mixture (2H2 + O2 + 7Ar), the reaction progress is not much influenced by turbulence, whereas in the less-diluted mixture (2H2 + O2 + Ar), the reaction takes place more rapidly with turbulence. Analysis of the properties of turbulence and turbulent fluctuations in the detonations clarifies that the direct contribution of turbulence to the flame front is weaker; there is no clear correlation between the heat release and the curvature of the flame. On the other hand, a broader Mach number distribution just upstream of the shock front creates more hot spots in the less-diluted mixture, which results in a shorter induction length. These results indicate that the main contribution of turbulence is creation of different shock strength, which could lead to different reaction rates depending on the cell regularity.

DOI： 10.1063/5.0144624

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the Combustion Institute  

This work presents a detailed numerical investigation of dilute spray lifted flames experimentally studied by O'Loughlin and Masri at the University of Sydney (O'Loughlin and Masri, Combust. Flame 2011), with a focus on understanding the mechanism that governs flame stabilization under the influence of sprays. Two ethanol flames with varied spray mass loading and degree of partial-premixing at the inlet are simulated by large eddy simulation (LES) combined with the dynamically thickened flame (DTF) model with finite-rate chemistry. Chemical explosive mode analysis (CEMA) is employed which helps identify the prominent role of an entrainment-based ignition process along the shear layer; this process dominates the flame anchoring of the downstream partially-premixed reaction zone. Thus, a higher spray loading can intensify the entrainment, leading to a faster formation of ignition kernels. Furthermore, in present flames, the stabilization point appears to be sustained in a purely gaseous zone with the most reactive mixture fraction and low scalar dissipation rate. Results show that the premixed flamelet can adequately represent flame structures at the leading-edge that are primarily controlled by the inlet partial-premixing, whereas the upstream evolving pre-ignition mixtures are fit for the diffusion flamelet. Moreover, both flamelet configurations fail in capturing downstream structures with a direct spray - flame interaction because the larger droplets produce a less homogeneous mixture with a higher scalar dissipation rate. This is more evident in the lean spray flame.

DOI： 10.1016/j.proci.2022.07.127

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the Combustion Institute  

Large-eddy simulation (LES) employing a flamelet/progress-variable approach that considers the real gas effect is applied to liquid oxygen/ gaseous hydrogen (LOX/GH2) supercritical combustion, and the breakup mechanism of the LOX core is investigated in detail by comparing it to that in the inert case. The results show that in the reactive case, O2 is injected into the chamber in the liquid state; that is, LOX, successively shifts to the supercritical and gas states and then reacts with H2 in the gas state. The present LES in the reactive case generally succeeds in predicting the LOX core breakup location in the experiment. In the reactive case, the LOX core breakup location is observed to be further downstream than in the inert case. This is because in the inert case, the turbulent vortices that are produced around the injector exit act to break the LOX core, whereas in the reactive case, the turbulent vortices are suppressed by the volume dilatation and viscous forces around the LOX core. In the reactive case, the LOX core tends to be compressed and thinned by the thermal expansion caused by the combustion reaction around the LOX core, and at the same time, is stretched and broken by the shear forces caused by the thermal expansion.

DOI： 10.1016/j.proci.2022.07.208

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.jaecs.2022.100083

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.combustflame.2021.111615

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.energy.2021.121352

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.egyai.2021.100076

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.jaecs.2020.100022

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.38036/jgpp.11.3_8

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1299/jtst.2020jtst0033

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.applthermaleng.2020.115947

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.ijmultiphaseflow.2020.103216

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.jngse.2020.103158

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1016/j.energy.2019.07.101

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開催年月日： 2024年10月

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開催年月日： 2024年10月

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開催地：Kyushu University (Kasuga)   国名：日本国  

開催年月日： 2024年10月

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開催年月日： 2024年5月

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開催地：Kyoto Terrsa   国名：日本国  

開催年月日： 2024年5月

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開催地：Kyoto Terrsa   国名：日本国  

開催年月日： 2024年5月

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開催地：Kyoto Terrsa   国名：日本国  

開催年月日： 2023年11月 - 2023年12月

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開催地：Kyoto International Conference Center (Kyoto city)   国名：日本国  

開催年月日： 2023年11月 - 2023年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Kyoto International Conference Center (Kyoto city)   国名：日本国  

開催年月日： 2023年11月 - 2023年12月

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開催地：Kyoto International Conference Center (Kyoto city)   国名：日本国  

開催年月日： 2023年11月

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開催年月日： 2023年11月

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開催年月日： 2023年11月

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開催年月日： 2023年11月

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国名：日本国  

開催年月日： 2023年11月

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開催年月日： 2017年11月

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開催年月日： 2017年10月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Okinawa Convention Center (Okinawa)   国名：日本国