Tohoku University · Engineering
Professor Yuki Murakami's research lab specializes in combustion science and materials physics, focusing on the fundamental oxidation mechanisms of alternative fuels such as ammonia, dimethyl ether, and methane, particularly in mixtures with hydrogen and other hydrocarbons. The lab develops detailed and reduced chemical kinetic mechanisms to predict combustion behavior under various conditions, while also investigating the microstructural and magnetic properties of functional materials like shape memory alloys and spinels. Experimental and computational approaches, including micro-flow reactors, electron holography, and transmission electron microscopy, are employed to explore reaction kinetics, phase transformations, and defect evolution in materials under thermal and mechanical stress.
Figures are computed from collected data and may differ slightly.
Effects of mixture composition and equivalence ratios on oxidation and reactivity of dimethyl ether (DME)/ammonia (NH3) mixtures are investigated based on weak flame responses observed in a micro flow reactor with a controlled temperature profile (MFR). For observations, the NH3 fractions in fuel blends are varied as 0–50%. Three equivalence ratios (ϕ = 0.5, 1.0 and 1.2) are examined. A combined chemical reaction model for DME/NH3 mixtures is developed and used to simulate oxidation of DME/NH3 m
In this study, experimental and analytical estimation of residual flexural strength of RC beams with reinforcement corrosion was carried out. As a result, it is noted that the factors, which influence on residual flexural strength and failure behavior of RC beams were not only corrosion rate, bond stress behavior but also the corrosive crack characteristics of concrete. Moreover, it seems impossible to estimate the characteristics of bond splitting failure along reinforcement and sudden drop of
TEM studies have revealed the temperature dependence of the magnetic domain structure in the crystal MnV${}_{2}$O${}_{4}$, which has attracted considerable attention because of the intriguing coupling of structural orders (magnetism, orbital, and lattice) and potential applications of these phenomena. Although this crystal forms well-defined magnetic domains because of long-range ferrimagnetic order, in both the cubic and the tetragonal phases, the magnetic information is dramatically reduced at
Based on our latest detailed chemical reaction mechanism, C3MechV4.0, we have developed two reduced reaction mechanisms—C3MechLite and C3MechCore—targeting C 0 –C 3 chemical species including NH₃. C3MechLite (61 species), contains a number of species comparable to GRI-Mech (53 species), that can accurately predict the combustion characteristics of hydrogen, carbon monoxide, ammonia, methane, natural gas, nitrogen oxides, and their mixtures for a wide range of conditions. C3MechCore (118 species)
This paper reports a macroscopic pattern formation that occurs before the onset of a martensitic transformation in a ferromagnetic shape memory alloy, Ni51Fe22Ga27. Electron holography studies reveal that the magnetic flux pattern in the parent (cubic) phase changes dramatically with cooling. Interestingly, the flux pattern developed in the parent phase is inherited by the martensitic (monoclinic) phase. Observations of the diffuse electron scattering indicate that the change in the magnetic flu
The extinction limits of non-premixed counterflow flames of methane (CH 4 )/ammonia (NH 3 )/nitrogen (N 2 ) versus high-temperature air ( T Air = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH 4 /NH 3 mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH 4 /NH 3 mixtures, espec
The effects of CO/H2/CH4 mixture compositions on the reactivity are investigated based on weak flame responses in a micro flow reactor with a controlled temperature profile (MFR). The ratios of H2 and CH4 are varied widely at a constant fraction of CO and the effects of variations in the compositions on the reactivity of the stoichiometric CO/H2/CH4 mixtures are evaluated both experimentally and computationally at atmospheric pressure. The results show that a weak flame is stabilized at the high
The impact of mechanical stress on the morphology of crystallographic and magnetic domains in shape-controlled specimens of an orbital-spin-coupled system, MnV2O4, was examined by cryogenic Lorentz microscopy. Because of the difference in thermal expansion coefficients of MnV2O4 and the supporting Mo mesh, compression on the order of 0.01% was applied to the thin-foil specimens near the structural/magnetic phase transformation temperatures. The extent of compression was comparable to the lattice
本研究では，曲げ破壊先行型RC梁部材において鉄筋腐食が残存耐力性状に及ぼす影響評価を実施するため，主鉄筋の応力伝達や抜出し抑制に対するせん断補強筋や定着筋の効果に着目した実験を実施した．引張主鉄筋が比較的均一に腐食した場合，せん断補強筋の定着領域の残存量が十分であれば，その拘束により引張主鉄筋の付着が保持され曲げ破壊を呈する．一方，せん断補強筋の定着領域がその性能を発揮できない程に過度に腐食した場合には主鉄筋の定着領域まで荷重が伝達され，主鉄筋の定着性能が残存耐力性状に極めて支配的な影響を及ぼす．また，作用モーメントの大きい領域で主鉄筋が局所的に腐食を生じた場合，その領域において変形が局在化し，せん断補強筋の腐食程度によらず曲げ破壊性状を示すことが明らかとなった．
本研究では，鉄筋腐食により主鉄筋の定着不良を生じたRCはり部材の曲げ耐荷性状およびせん断耐荷性状評価を目的として，断面諸元，鉄筋腐食レベルなどが異なるRCはり部材に対して曲げ載荷実験を実施した．主鉄筋軸方向ひずみ分布性状に基づき，設計時からの耐荷機構の遷移や耐荷性状について検討を行った結果，主鉄筋の付着劣化に伴い，主鉄筋を介して，荷重が支点外側の領域まで伝達した場合，はりの耐荷機構が梁機構からアーチ機構に変化した．その際の耐荷性状は定着性能およびa/dに大きく影響することが明らかとなった．また，定着不良を考慮した腐食RCはり部材の残存耐力算定式を提案し，断面諸元，荷重条件によらず既往の実験結果を概ね評価可能であることを示した．
地震による石垣構造物の崩壊を防ぐためには，事前に耐震性能を把握し，その性能が不十分な場合は，適切な耐震補強を実施することが不可欠である．そこで本研究では，2次元拡張個別要素法を用いて石垣構造物の地震動応答解析を行い，その結果を踏まえて，耐震補強策を検討した．具体的には，道路橋示方書の地震動データを用いて解析し，その時の石垣の挙動を把握した．耐震補強策として，施工範囲の短縮と景観の維持を優先して，石垣に対する耐震補強法としてアンカー補強を選択した． その結果，無補強時とアンカー補強時の比較に加え，アンカー補強の違いによるパターン分けで，石垣構造物に対する耐震補強の必要性と補強パターンによる地震動応答の変化の傾向を示し，アンカー補強の有効性を確認した．
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