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Your search keyword '"Hayakawa, Akihiro"' showing total 217 results
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217 results on '"Hayakawa, Akihiro"'

12. Gene expression and protein localization of Cl− transporters, Slc26a6 and Cftr, in the gill ionocytes of rainbow trout.

Author

Kikuchi, Taisei, Inokuchi, Mayu, Hayakawa, Akihiro, Adachi, Umi, Ido, Atsushi, Otani, Maki, Suetake, Hiroaki, and Watanabe, Soichi

Subjects
ION transport (Biology), RAINBOW trout, ACTIVE biological transport, GENE expression, CYSTIC fibrosis transmembrane conductance regulator
Abstract

Euryhaline fishes acclimate to various osmotic environments by changing the direction of water and ion transport between body fluids and environmental waters. Ionocytes in the gills are one of the most important cells for the active ion transport. This study aimed to identify the molecules responsible for apical Cl− transport in rainbow trout ionocytes. Tissue distribution and time-course changes after seawater transfer were analyzed for mRNA expression of slc26a6, cftr1, and cftr2. slc26a6 was specifically expressed in the freshwater gills and decreased after seawater transfer. Both cftr genes were expressed in the gills and higher in seawater; however, the magnitude of expression increase after seawater transfer was greater in cftr1 than in cftr2. These results suggest that Cftr1 is mainly functioned in hypo-osmoregulation and that Cftr2 may also be involved in ion transport under freshwater conditions, such as acid–base regulation. Slc26a6 was localized at the apical membrane of Nkcc1-negative ionocytes only in freshwater-acclimated trout. Apical Cftr1 localization was also identified in most of ionocytes in seawater-acclimated fish. These results indicate that Slc26a6 in freshwater and Cftr1 in seawater contribute to osmoregulatory Cl− transport across the apical membrane of ionocytes in rainbow trout. [ABSTRACT FROM AUTHOR]

Published
2024
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29. Experimental and numerical study of product gas and N2O emission characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow

Author

Hayakawa, Akihiro, primary, Hayashi, Masao, additional, Kovaleva, Marina, additional, Gotama, Gabriel J., additional, Okafor, Ekenechukwu C., additional, Colson, Sophie, additional, Mashruk, Syed, additional, Valera-Medina, Agustin, additional, Kudo, Taku, additional, and Kobayashi, Hideaki, additional

Published
2023
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34. Experimental and Numerical Investigation of Laminar Burning Velocities of Artificial Biogas Under Various Pressure and CO2 Concentration

Author

Anggono Willyanto, Hayakawa Akihiro, Okafor Ekenechukwu C., and Gotama Gabriel Jeremy

Subjects
combustion characteristics, dilution ratio, renewable fuel, sustainable fuel, Environmental sciences, GE1-350
Abstract

As a renewable and sustainable fuel made from digestion facility, biogas is composed predominantly of methane (CH4) and carbon dioxide (CO2). CO2 in biogas strongly affects its combustion characteristics. In order to develop efficient combustors for biogas, fundamental flame characteristics of biogas require extensive investigation. In understanding the influence of CO2 concentration and mixture pressure on biogas combustion, the effects of CO2 concentration on the laminar burning velocity of methane/air mixtures were studied at different pressures. The studies were conducted using both numerical and experimental methods. The experiment was conducted using a constant volume high pressure combustion chamber. The propagating flames were recorded with a high speed digital camera by employing Schlieren photography technique. The numerical simulation was carried by utilizing CHEMKIN-PRO with GRI-Mech 3.0 employed as the chemical kinetics model. The results show that the laminar burning velocity of methane-air mixtures decreased with an increase in CO2 concentration and mixture pressure. Therefore, the burning velocity of biogas mixtures may decrease as the amount of CO2 in the gas increases.

Published
2019
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37. Start-Up Process of 50kW-Class Gas Turbine Firing Ammonia Gas

Author

Kurata, Osamu, additional, Iki, Norihiko, additional, Fan, Yong, additional, Matsunuma, Takayuki, additional, Inoue, Takahiro, additional, Tsujimura, Taku, additional, Furutani, Hirohide, additional, Kawano, Masato, additional, Arai, Keisuke, additional, Okafor, Ekenechukwu C., additional, Hayakawa, Akihiro, additional, and Kobayashi, Hideaki, additional

Published
2021
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38. Turbulent flame propagation limits of ammonia/methane/air premixed mixture in a constant volume vessel

Author

Hashimoto, Genya, Hadi, Khalid, Xia, Yu, Hamid, Aainaa, Hashimoto, Nozomu, Hayakawa, Akihiro, Kobayashi, Hideaki, 1000010183930, Fujita, Osamu, Hashimoto, Genya, Hadi, Khalid, Xia, Yu, Hamid, Aainaa, Hashimoto, Nozomu, Hayakawa, Akihiro, Kobayashi, Hideaki, 1000010183930, and Fujita, Osamu

Abstract

Ammonia is one of promising energy carriers that can be directly used as carbon-neutral fuel for combustion applications. However, because of the low-burning velocity of ammonia, it is challenging to introduce ammonia to practical combustors those are designed for general hydrocarbon fuels. One of ways to enhance the combustibility of ammonia is by mixing it with other hydrocarbon fuels, such as methane, with a burning velocity is much higher than the burning velocity of ammonia. In this study, we conducted flame propagation experiments of ammonia/methane/air using a fan-stirred constant volume vessel to clarify the effect of methane addition to ammonia on the turbulent flame propagation limit. From experimental results, we constructed the flame propagation maps and clarified the flame propagation limits. The results show that the flame propagation limits were extended with an increase in mixing a fraction of methane to ammonia. Additionally, ammonia/methane/air mixtures with the equivalence ration of 0.9 can propagate at the highest turbulent intensity, even though the peak of the laminar burning velocity is the fuel-rich side because of the diffusional-thermal instability of the flame surface. Furthermore, the Markstein number of the mixture obtained in this research successfully expressed the strength of the diffusional-thermal instability effect on the flame propagation capability. The turbulence Karlovitz number at the flame propagation limit monotonically increases with the decreasing Markstein number.

Published
2021

41. Laminar Burning Velocity and Markstein Length of CH₄/CO₂/Air Premixed Flames at Various Equivalence Ratios and CO₂ Concentrations Under Elevated Pressure

Author

Anggono, Willyanto, Hayakawa, Akihiro, Okafor, Ekenechukwu C., Gotama, Gabriel Jeremy, Wongso, Stevan, and School of Mechanical and Aerospace Engineering

Subjects
Mechanical engineering [Engineering], Biogas, Methane
Abstract

Biogas is a renewable fuel predominantly composed of carbon dioxide (CO₂) and methane (CH₄) in varying proportions. The effects of the varying CO₂ proportion need to be clarified for the development of engines. The laminar burning velocity and the burned gas Markstein length of premixed CH₄/CO₂/Air were measured with CO₂ concentration ranging from 0.3 to 0.7 dilution ratios. The equivalence ratio was varied from 0.8 to 1.2, the initial pressure was set at 0.5 MPa, and the temperature was set to 298 K. The experiment was performed using a high-pressure constant volume combustion chamber. One-dimensional simulation of the flames was conducted using GRI-Mech 3.0. The results showed a reduction in the laminar burning velocity of CH₄/CO₂/Air mixtures with an increase in CO₂ dilution ratio. A non-monotonic relationship was discovered between measured Markstein length and CO₂ dilution ratio with different equivalence ratios. It was found that an increase in the CO₂ dilution increased the response of the flames to stretch. For the lean and stoichiometric flames, the Markstein length was nearly constant with CO₂ dilution of 0–0.5 and decreased with CO₂ dilution of 0.7, suggesting an increase in susceptibility of the flame to the intrinsic flame instability. This was found to be mainly due to an increase in the Zel’dovich number and a decrease in the effective Lewis number with CO₂ dilution. The Markstein length of the rich flame increased with CO₂ dilution as it was more sensitive to CO₂ dilution. Thermo-diffusive effects and pure stretch effects had similar influences on the burning velocity of the rich flames with an increase in stretch rate.

Published
2020

42. Experimental and Numerical Study of NH3/CH4 Counterflow Premixed and Non-premixed Flames for Various NH3 Mixing Ratios

Author

Colson, Sophie, Hirano, Yuta, Hayakawa, Akihiro, Kudo, Taku, Kobayashi, Hideaki, Galizzi, Cédric, and Escudié, Dany

Abstract

Ammonia is a promising sustainable fuel, however, its low reactivity creates challenges in industrial applications. In this study, ammonia/methane mixtures were considered for premixed and non-premixed counterflow flames. The extinction stretch rate was measured over a wide range of ammonia/methane mixing ratios and compared to 1D numerical results from four different mechanisms. Additionally, for counterflow premixed twin flames, quantitative analysis based on the comparison of experimental and numerical FWHM of OH and NO profiles was performed. Results showed that in premixed flames, all the mechanisms investigated were inadequate for predicting the extinction stretch rate, specifically for lean flames. In non-premixed flames, Okafor’s mechanism was accurately predicting the extinction stretch rate. For the FWHM analysis, the numerical mechanisms overpredicted both OH and NO apparition in the flame, except for Tian’s mechanism which underpredicted OH apparition. GRI Mech 3.0 performed well for small quantities of ammonia but failed to reproduce the pure ammonia case. Okafor’s and UCSD mechanisms gave better predictions of experimental trends, though overestimated both OH and NO apparition. In the FWHM analysis of both OH and NO, the lower R2 values in the lean region suggest that the lean region should be the focus for mechanism improvement.

Published
2020
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