In this paper, an incremental formulation of pressure based method for fluid-rigid body interaction using intermediate variable is presented. The present method is based on the method proposed by Matsumoto and Kawahara in previous studies. In their method, the pressure Poisson equation equivalent to the incompressibility constraint is derived by using the intermediate fluid velocity and the approximation of enough small error between the intermediate fluid velocity and the fluid velocity. In the present method, all terms appear in the coupled equation system are evaluated in the same time instant, and unknown variables are solved incrementally by iterative solution procedure in each time step so as to satisfy the coupled equation system defined in the time instant. The present formulation is required when structural nonlinearity such as large deformation should be considered. The present method is applied for the free vibration of a rigid circular cylinder in a quiescent fluid to verify its performance.

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This paper describes a numerical solution to the shape optimization problems of viscous flow fields. The drag minimization problem and lift maximization problem for an isolated body in uniform flow were formulated in the domain of steady-state viscous flow fields. The shape gradient of the shape optimization problems were derived theoretically using the adjoint variable method, the Lagrange multiplier method and the formulae of the material derivative. Reshaping was accomplished using a traction method that was proposed as a solution to domain optimization problems. The validity of the proposed method was confirmed by results of 2D numerical analyses using finite element method.

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In this paper, pressure propagations generated by liquid-gas interactions were investigated by using a newly proposed model of the finite difference lattice Boltzmann method. The model which based on a constitutive equation of pressure allows us to consider the sound speeds for gas and liquid phases. As for the liquid-gas flow with the density ratio of about 1 000, the liquid drop impacting against a thin liquid film in the two-dimensional space was compared with other calculations. Pressure propagations in the case of the two-dimensional drop falling to a deep liquid on a gravity field were clarified by using the same model. The pressure fluctuation was 10^-6 times smaller than the reference pressure had the unique directivity.

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We present a number-density advection based method designed to calculate the condensation/ evaporation of cloud droplets. An Eulerian-in-radius discretization scheme is adopted, making the present model suitable for use in the spectral bin method for cloud microphysics. The mass advection equation is solved using the constrained interpolated profile-conservative semi-Lagrangian with rational function (CIP-CLSR) scheme. In order to evaluate the present method based on the CIP-CSLR scheme, we performed a condensation growth calculation using the present method and conventional methods, and then compared the results. The comparison revealed the advantages of the present method in numerical accuracy, numerical stability, conservation and computational cost.

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The flow characteristics of a dilute polymer solution and distilled water near the wall surface were clarified experimentally using evanescent wave illumination. Based on the integrated value of the particle tracking velocimetry data in the illumination, the velocity profile near the wall surface was obtained. Fluorescent particles with a diameter of 100 nm were used as tracer particles. The test polymer is polyethylene-oxide (Peo 15) solution at 5 ppm. The results obtained for the velocity profile of distilled water was found to agree well with the two-dimensional Poiseuille velocity profile at 100nm<z<250nm. On the other hand, the velocity profile of the dilute polymer solution decreased significantly compared with that of distilled water within 250nm of the wall surface. In addition, the particle diffusion of polymer solution decreased in flow conditions comparing that of distilled water, thought there were few differences for quiescent condition.

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The mechanism of mass transfer due to a single droplet impinging on the air-water interface was investigated using PIV and LIF techniques. Velocity and CO₂ concentration fields in the liquid side after the impingement of a single droplet were visualized. The radius and the velocity of the surfacerenewal vortex induced by the droplet impingement were estimated. It is found that CO₂ near the free surface goes downward due to the surface-renewal vortex induced by the impinging droplet, and both the radius and velocity of the vortex increase with increasing the vertical momentum of the droplet. This suggests that the droplet impinging on the free surface promotes mass transfer across the air-water interface.

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In this study, the flow features of vortex shedding from a pair of parallel arranged circular cylinders oscillating along the direction of the flow were observed by visualizing water flow experiment at the ranges of the frequency ratio f/f_k=0-7, amplitude ratio 2a/d=0.125, 0.25, 0.5 and 0.75, gap ratio G/d=0.25, 0.75 and 1.75, and Reynolds numbers Re=470-670 (towing water tank test) and 700-750 (closed circuit water channel test). The variations of mean vortex shedding frequency from each oscillating cylinder were investigated. As a result of the experiments, typical flow patterns of lock-in state or un-lock-in state were shown every gap ratio G/d. Although the cylinder oscillation frequency f is lower than the natural Karman vortex's frequency f_k, the lock-in phenomenon can be seen. It was found that the measurement result depended on the observation point because the rearrangement of vortex formation had changed the characteristics of the flow. When the cylinders were oscillated to the direction of flow, the flow pattern of bias gap flow became not seen. The map of lock-in state in the lock-in range was obtained. It was found that the lock-in range and the lock-in form were more different from the case of single oscillating cylinder.

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Pulsating jets are very common and sometimes useful in industrial fields, due to some differences in basic characteristics from steady jets. In this research, the authors focus upon the mechanism of the frequency effect on a finite-amplitude pulsating jet. Experiments are conducted at a Reynolds number of 5000, Strouhal numbers of 0.13, 0.20 and 0.27, and a velocity-amplitude ratio of 0.5. Using olive-oil smoke, the authors visualise the flow from a nozzle exit with a circular cross section, and get quantitative information by a PIV technique. As a result, the authors have succeeded in defining the locations of main and subsidiary ring vortices. And, the authors have revealed the vortices' convection manners at three frequencies. Besides, the instantaneous measurements on entraining flow with a conditional-sampling technique have shown the complexity of the frequency effect, which is affected by two factors in a trade-off relation.

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This is the first part of a pair of the studies which report the vertical sloshing, that is, the liquid surface motion in container oscillating in the vertical direction, concerning various equilateral-polygonal-section containers : namely, octagonal, heptagonal, hexagonal, pentagonal, square and trianglar containers together with a circular container, in order to generalise their sloshing modes. As a result, the authors classify the sloshing modes based on the circular-container sloshing modes, referring to computational and experimental results. This modal classification has some advantages over that based on the square-section-container sloshing modes. The present computation is based on the discrete singularity method. In the second part, the proposed modal classification is shown to be useful to predict the eigen frequencies.

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This is the second part of a pair of the studies which report the vertical sloshing, that is, the liquid surface motion in container oscillating in the vertical direction, concerning various equilateral-polygonal-section containers : namely, octagonal, heptagonal, hexagonal, pentagonal, square and trianglar containers together with a circular container, in order to generalise their sloshing modes. As a result, the stability diagrams for all the polygonal-section containers are investigated by both experiments and computations. Furthermore, it is found that the equivalent diameter d_el based on the hydraulic mean depth is the most adequate as a characteristic length scale to classify all the sloshing modes. The authors show an unified formula to predict the eigen frequencies, using d_el together with the modal classification proposed in the first part.

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Entrapment of non-wetting phase in porous media has been observed in variety of fields such as petroleum engineering, geological storage of carbon dioxide, and remediation of ground. We investigated the residual gas trapping from a microscopic point of views. High-resolution, three-dimensional images of pore structure and trapped gas bubbles in Berea, Tako, and Shirahama sandstones were obtained using a micro-focused X-ray CT scanner. The trapped bubbles consist of two-type; one occupies the center of pore with a pore-scale size and the other has a pore-network scale size. Even in the pore with a trapped gas bubble, wetting-phase imbibes into the pore through its corner depending on the structure and surface roughness. The maximum pore diameter and the maximum trapped bubble diameter were estimated from CT images. The maximum trapped bubble diameter is in the range from 10 to several hundreds as large as the median of pore throat diameter. Finally, the specific area ratios of pores and bubbles were estimated.

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We have investigated sedimentation phenomena of a colloidal dispersion composed of ferromagnetic spherical particles in the gravity field, by means of Brownian dynamics simulations. In concrete, we have attempted to clarify the influences of the magnetic field strength, magnetic interactions between particles and volumetric fraction of particles on sedimentation phenomena of such magnetic particles. In order to discuss quantitatively the sedimentation process and the internal structures of particle aggregates after the sedimentation, we have concentrated our attention on the time change in the local number density of particles and local radial distribution function of each layer. The main results obtained here are summarized as follows. For the case of a weak magnetic field and a weak magnetic force between particles, layered structures are formed. As the magnetic field increases, clusters are formed in upright formation along the gravity or the magnetic field direction. As magnetic particle-particle interactions increase, particles combine with each other to form aggregates in other directions, and new types of clusters are formed in the bottom area. In this situation, therefore, the upright-standing clusters come to disappear. For a dilute case, relatively small clusters are formed apart from each other in almost equal space. As the volumetric fraction increases from such a situation, clusters with voids in the center area of the clusters come to be observed, but such formation disappears and layered structures are formed with further increasing the volumetric fraction.

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Spectroscopic measurements of micro-air plasma-jets were performed at an atmospheric pressure in the wavelength region of 280 to 420 nm where N⁺₂1-and N₂2+ bands were predominant. The spectra were measured at many radial and axial points to obtain its radiative characteristics in detail. Abel inversion method was applied to all the experimental data measured laterally to obtain true spectral intensity distribution at all radial points. The comparison of the experimental and Abel-inverted spectra showed that the experimental data could not be used directly to deduce temperatures without the Abel inversion except around the flow axis. Temperatures of the plasma-jets were estimated by applying the spectral matching method to N⁺₂1-bands. Rotational temperature for N⁺₂1-bands was about 8000 K, and was almost independent of radial positions. Vibrational temperature was about 28000 K in the core region with much higher in the outermost region.

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In our previous experimental and numerical studies, we developed accurate submicron-particle classifiers using an almost rigidly rotating flow. In the present paper, with the final aim of improving the classification performance and devising new better classifiers on the numerical and theoretical bases of fluid and particle motions, we have ingeniouly performed a linear analysis of the steady and axisymmetric flow of attached and detached Stewartson layers developing at a step of a lower wall between rigidly rotating upper and lower walls shaped arbitrarily. We have used a singular perturbation method and boundary layer approximations, and have used, as boundary conditions, the theoretical linear solutions of Ekman layers and interior regions derived in our previous study. Consequently, we have derived theoretical linear solutions of E^1/4- and E^1/3-Stewartson layers and their Ekman extensions containing arbitrary additive constants that cannot be obtained by the conventional analysis following Van Heijst. The conventional solutions disagree with numerical solutions, but there is every possibility that the additive constants make the present solutions agree with numerical solutions qualitatively.

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Althought it is well-known that the swirl strength of a turbulent swirling flow in a straight pipe decays downstream and eventually becomes a non swirling pipe flow, few studies on the flow change in a weak swirling flow have been reported. In this study, changes in the flow pattern and the angular momentum in a weak swirling flow are described. Experiments are performed at a Reynolds number of Re=10⁵, which is based on the pipe inner diameter and the axial mean velocity under the condition that a guide-vane swirl generator, in which the guide vane angle is set at 5 degrees, is employed. As a result, it is confirmed that the combined vortex formed upstream in a straight pipe changes into a forced vortex far downstream. Both the swirl number and the swirling angle at γ/R=0.95, which are employed to define the swirl strength, exponentially decrease downstream. Also, the radial distribution and contours of the local angular momentum, which do not change in the entrance region, change considerably in the annular region far downstream.

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This paper describes the performance of a micro vertical-axis wind turbine with variable-pitch straight blades. The proposed variable-pitch angle mechanism has an eccentric point that is different from the main rotational point. A feature of the mechanism is to be able to vary the pitch angle of blades according to the azimuth angle of the main-links, without actuators. The performance of wind turbines was measured by using an open circuit type wind tunnel. The performance of the vertical axis wind turbines with this mechanism was better than that those with fixed pitch blades. The wind turbine with variable-pitch straight blades has directivity for the wind. It was found that the performance of the wind turbine is dependent on the offset of blade pitch angle, the amplitude of the pitch angle, the size of the turbine, the number of blades and the airfoil profiles.

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The final purpose of this study is to clarify the relation between the static pressure fluctuation between fan blades and the noise emitted to the outside of the fan. For this purpose, first of all, a new micro probe for the measurement of the static pressure fluctuation has been developed. The measurement of the static pressure fluctuation between the blades has been performed, and the intensity of sound source was quantified from the second derivative of phase averaged static pressure fluctuation signal (Ribner ⁽²⁾ ). It is shown that the intensity of sound source becomes largest when the blade approaches to the tongue. The difference between the cooling mode and the heating mode are also investigated. It is found that the sound source for cooling mode shows the larger value than that for heating as a whole.

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The objective of the study is to elucidate the contribution of micro-layer on heat transfer in nucleate pool boiling of isolated bubble region on the basis of the measurement of configuration of micro-layer. The distribution of micro-layer thickness formed under a growing bubble was measured by laser extinction method using specially devised system with a thin optical fiber in thin tube and gas blowing in the previous report. In this report, the dominant factors determining the characteristics of micro-layer such as micro-layer thickness distribution, duration of micro-layer existence, size of micro-layer area on the heat transfer surface and so-forth were expressed by nondimensional form based on the similarity of bubble growth rate. Finally, the contribution of evaporation from micro-layer in nucleate boiling of isolated bubble region was shown by using the relations among dominant factors.

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In the present study, the authors consider a control of the flow past a semi-infinite plate with a blunt front. The flow is one of the simplest separated-and-reattaching flows, and can be a model such as heat exchangers and flow straighteners commonly seen inside power plants, chemical plants and household appliances. As a control device, a rotating object, which is a small flat plate, is placed in the upstream of the semi-infinite plate. In a wind tunnel, the authors conduct flow-velocity-fluctuation measurements using a hot-wire anemometer for various control-object positions and rotation speeds, showing (1) root-mean-squared values near the leading edge of the semi-infinite plate and (2) dominant frequencies in the downstream. The present test range of the control-object rotation speed is low ; specifically, the object's tip velocity is less than the uniform main stream velocity. Referring to such results, we can classify the controlled flow into four regions. Moreover, in order to clarify the characteristics for each region, the authors carry out (1) flow visualisations with particle-image-velocimetry analyses, and (2) velocity-profile measurements concerning time-mean and turbulence-intensity values.

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There has been some interest in the flow drag and heat transfer reduction effects of brine flow with drag reduction surfactants in order to achieve the effective energy consumption in an industrial cooling system. Therefore, there have been our previous investigations of brine flow (Ethylene Glycol (EG) solution for organic brine) with drag reduction surfactant (Oleyldihydroxyetyl Amine Oxide (ODEAO) of non-ion surfactant) showing the flow drag and heat transfer reduction effect. But some technical issues are that EG is an environmentally harmful brine and the use of EG will be restricted in the future. Whereas, Propylene Glycol (PG) and Potassium Acetate (=PA) are expected to be environmentally friendly brines. But, there have been few studies on the flow drag and heat transfer reduction effects of PG or PA solution with drag reduction surfactants. This present paper shows that the flow friction coefficient and mean forced convection heat transfer coefficient of the PG, or PA solution with ODEAO in a straight pipe were measured for each parameter of concentration of brines, concentration of ODEAO and temperature of the brine with ODEAO. Finally, useful non-dimensional correlative equations for maximum flow resistance and heat transfer reduction effect are derived in terms of various non-dimensional parameters, and these experimental results of PG solution with ODEAO were compared with that of EG solution with ODEAO.

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Effect of non uniform heat transfer coefficient around the surface of horizontal circular cylinders on melting of phase change material (PCM) filled in the cylinders was studied by experiment and numerical analysis. Results of the numerical analysis performed on the basis of the uniform and non-uniform heat transfer coefficient with and without consideration of natural convection were compared with the experiment with water and tetradecane as PCM and acrylic resin and copper as cylindrical materials. Results show that heat conduction with the non-uniform heat transfer coefficient is dominant for the case of small cylinders. Effect of natural convection can not be neglected for the diameter more than 20 mm. Effect of the non-uniform heat transfer coefficient on flow of the natural convection was increased with increase in the diameter in conduction-dominant region. For case of acrylic cylinder. However the difference in the melting time is at most 5%. In natural convection dominant region, the diameter larger than 40 mm, the effect of the non-uniform heat transfer coefficient on the natural convection was reduced with increase in Rayleigh number in inner cylinder. For case of the copper cylinder, wall temperature was almost uniform in spite of the non-uniform heat transfer coefficient. Therefore, the effect of the non-uniformity in the heat transfer coefficient can be neglected for circular cylinders of copper and large diameter.

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The melting of a vertical ice cylinder into a homogeneous calcium chloride aqueous solution inside a cylindrical cavity is considered experimentally. The ice cylinder rotates with prescribed several speeds. The rotating speeds of the ice cylinder are 0, 35, 70 and 105 rpm. Melting experiments are performed on several different initial conditions of the solution. When a rotating speed is fast, melting front shows specific configuration similar to a “Bamboo node” due to the Taylor vortex flow. When the rotating speed is slow, a specific “screw” shape appears on the melting front. This specific configuration appears due to large buoyancy caused by large concentration difference and due to circumferential flow caused by rotation of ice cylinder. The melting mass fraction increases with the passage of melting time and with increasing of rotating speed. Transient melting mass fraction is correlated to Fourier and rotating Reynolds numbers and melting ability of the solution calculated from the equilibrium phase diagram.

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The objective of this study is to clarify performances of a method for heat transfer enhancement using porous material with high porosity by an experiment. The experiment has been performed using an apparatus which simulated the passage structure of the steam reformer to obtain characteristics of heat transfer and pressure drop. From the results obtained in this experiment, the heat transfer rate by this method showed a good performance in the laminar flow regime. It was also found that the method for heat transfer enhancement using porous material with high porosity is further improved under the high temperature condition as compared with the other methods for heat transfer enhancement. There is the possibility of the adoption of this method to the steam reformer of the hydrogen production system connected to a high temperature gas-cooled reactor.

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This paper describes the numerical simulation results of radiative heat transfer between the human body and an urban street canyon (building walls, pavement, and the sky) in the presence of participating non-gray gas mixtures consist of H₂O and CO₂. The ambient temperature of typical summer condition and the concentration of gas mixtures in summer Tokyo were assumed, and parallel infinite plane model and simple urban street canyon model were used. The results show that the participating gas significantly affects the infrared radiation field in urban street canyon. The radiation flux emitted by the participating gas is approximately 35% of the total incident radiation flux to the human body surface. This causes a homogenization of the infrared radiation field. Gas radiation plays an important role in the heat transfer between human and environment under hot and humid summer condition.

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Sub-millimeter-bubble injection is one of the most promising techniques for enhancing heat transfer for the natural convection of liquids. So far, we have investigated experimentally the heat transfer enhancement by sub-millimeter bubbles. However, the effects of the bubble diameter on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of bubble diameter on the heat transfer enhancement by sub-millimeter bubbles for the laminar natural convection of water along a vertical heated plate. We conduct temperature measurements using thermocouples and velocity measurements using a Particle Tracking Velocimetry (PTV) technique. We also carry out two-dimensional numerical simulations to comprehensively understand the effects of bubble injection on the flow near the heated wall. Temperature measurements show that the heat transfer coefficient increases with a decrease in the bubble diameter. This is due to a significant increase in the bubble advection effect.

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In this paper, we fabricated a Bi₂Te₃ thermoelectric micro-generator, and evaluated those performances. Bi₂Te₃ is one of popular thermoelectric materials with the highest thermoelectric properties at room temperature. The patterned thin film of Bi₂Te₃ was deposited on a free-standing Si₃N₄ thin film by using a flash evaporation method through shadow masks which were made by standard micro-fabrication processes. In the design of the micro-generators, we got the output voltages of the micro-generators by numerically calculating the temperature distribution of the freestanding thin film using ANSYS CFX. The calculated output voltages agreed well with experimental results. The output voltages of the fabricated micro-generators were measured while simply heating the bottom of the micro-device, and the maximum output voltage was 48 mV at a 13 K temperature difference.

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This study focuses on gasification technology of carbonaceous materials in molten carbonates since this gasifier can gasify those fuels catalytically and in-situ clean up the gasified gas at high temperature simultaneously. This gasification system has such advantages that alkali metal compounds show catalytic function for the gasification reactions, the molten alkali compounds can absorb sulfur compounds and the molten media can capture ash and unreacted particles produced. The molten carbonate employed in this study is an eutectic salt with the compositions of 43 mol% Na₂CO₃ and 57 mol% K₂CO₃. CO₂, is selected as a gasification agent. Before the gasification experiments, the optimum gasification and desulfurization temperature is evaluated by the chemical equilibrium calculations. Fundamental gasification and desulfurization experiments were conducted, by using an electrically heated reactor. As a result, the main compositions of the gasified gas are CO, H₂ and CH₄. H₂S and COS gases in the product can be absorbed almost completely by the molten alkali carbonates. These results suggest that this gasifier can gasify the carbonaceous materials and desulfurize even at high temperature inside the furnace simultaneously.

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It is very important to remove contaminant fully from waste PET bottles for bottle-to-bottle recycling. In this paper the mechanism to remove contaminant is proposed on the experimental degradation of waste PET bottles to the monomers by ethyleneglycol. It is made up of the separation of contaminant during the degradation reaction. This model is confirmed to be correct on the recycling of deliberately contaminated PET samples using a series of surrogates based on FDA protocol. We conclude that the contaminant on waste PET bottles is fully separated from PET bottles under the proper separating condition, such as the quantity of extract, separating temperature and time.

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We have analyzed the dependence of the concentration overpotentials on the properties of gas diffusion layers (GDLs) of a polymer electrolyte fuel cell (PEFC) using dual serpentine flow fields during a start-up operation. Moreover, we directly and separately analyze such dependence of the amount of the water accumulated at each component of a cell by measuring the weight of adherent water. As a result, the hydrophobic treatment with micro porous layer addition to a GDL substrate is found to be effective to improve the cell performance by suppressing the water accumulation at the electrode (catalyst layer) which increases the concentration overpotential. Suppressed water accumulation at the electrode also increases cumulative current that represents the power generation and calorific power important for warm-up. Besides, increase in the coarseness of the GDL substrate is not so effective for decreasing the concentration overpotential and increasing the cumulative current for the case of the serpentine flow field. Increase in the thickness of the GDL substrate increases the concentration overpotential and decreases the cumulative current. These results will offer proper design parameters of GDLs for improving the performance of PEFCs, in Particular during start-up.

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Homogeneous Charge Compression Ignition (HCCI) engines could offer low NO_x, PM emissions and high efficiency. However the operation region is limited because of knocking and misfire. Moreover the HCCI principal lacks direct combustion control and needs a system to control the combustion phasing with high accuracy. Cyclic dispersion is also a big problem in HCCI combustion. Today there exists various ways to control the HCCI combustion but these systems are heavy and complex. In this study, in order to develop a small and light HCCI engine, a simple HCCI combustion control system is proposed. DME (Di-methyl Ether) is used as a fuel to keep the structure small and light. This system uses throttles to change the mixing ratio of stoichiometric pre-mixture. hot EGR (Exhaust Gas Recirculation) gas and cold EGR gas. With this system, combustion control concept is evaluated and characteristics of cyclic dispersion are analyzed experimentally. Moreover, based on these results, reduction of cyclic dispersion is attempted by combustion control.

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The purpose of this study is to evaluate the potential of thermal and fuel stratification for reducing pressure rise rate in HCCI engines. The computational modeling work is conducted using a multi-zone code with detailed chemical kinetics, including the effects of thermal and fuel stratification charge on the onset of ignition, pressure rise rate and combustion efficiency.

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Effect of inhomogeneity of combustion chamber has been thought as one of the way to avoid dramatically generating heat in HCCI Combustion. The purpose of this research is to investigate the effect of inhomogeneity, especially thermal stratification, HCCI Combustion fueled with DME. Thermal stratification is made in combustion Chamber of Rapid Compression Machine with 3 Kind of pre-mixture has different temperature. The Pre mixture is adiabatic compressed and on that process, in cylinder gas pressure and two-dimensional chemiluminescence images are measured and analyzed.

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The purpose of this study was to gain a better understanding of the effect of fuel stratification by using chemiluminescence imaging. In order to investigate the fundamental aspects of fuel stratification, Di-methyl ether (DME) that has large heat release in LTR and n-Butane that has small heat release in LTR were used as test fuels. By using these fuels, investigations were conducted on five mixing conditions depending on DME or n-Butane and homogeneity or stratification as parameters. It is found that combustion phasing is changed by the condition of charging fuel, and maximum pressure rise rate is also changed by the condition of charging fuel. In addition, from chemiluminescence imaging, in the condition of charging fuel that achieves the lowest maximum pressure rise rate, chemiluminescence start timing is dispersed and its duration is longer.

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This paper presents basic combustion characteristics of a spark-ignition engine fuelled with three kinds of gaseous fuels; H₂, CO and CH₄. A single-cylinder engine was operated under WOT at 1 500 min^-1 condition. CO gas gives lower thermal efficiency than H₂ and CH₄, since the energy of the fuel can not be transferred to the pressure or the work, although it gives higher combustion temperature which makes the higher exhaust gas temperature and much higher NO_x emissions than those for CH₄. H₂ gives upper limit of flammability due to the occurrence of backfire and almost comparable thermal efficiency with that for CH₄ at its stoichiometric condition.

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DDM (Discrete Droplet Model) is widely used for the numerical analysis of a fuel spray. In order to achieve highly accurate calculations using DDM, many mathematical sub-models such as breakup, drag force and collision are employed with DDM. In the conventional DDM, an isolated droplet (parcel) is assumed and the influence of surrounding droplets is not directly considered. However, it is well known that the state of the wake flow of droplet or the vortex behind droplet changes by the distance between droplets, and the drag coefficient is influenced. Especially, this effect is important in a dense spray. In this study, a newly developed drag force model, containing the drag reduction effect with the droplet spacing as a parameter is adopted and also, the effect on the spray tip penetration and the spray volume is examined. As a result, the spray shape and Sauter mean diameter were found to depend on the mesh size that defines the droplet spacing. The drag force reduction by the droplet number density tends to increase the spray volume. The calculation of a diesel spray at the injection pressure of 133 and 55 MPa indicated better agreements with experiments compared to the result using a conventional model.

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A high-frequency (20 kHz) standing wave was applied to the unburned mixture upstream of the methane-air lifted jet flame using a bolt-clamped Langevin transducer (BLT) to improve stability. The flow field near the flame was visualized using acetone planar-laser-induced fluorescence (PLIF). The standing wave decreased the lifted flame height and increased the blow off limit. The upstream flow field of the center jet then bent. This phenomenon appeared when there was a density difference between the center jet and the surrounding secondary flow. When the density of the center jet was less than that of the co-flow, the center jet was redirected to the pressure anti-node side. Conversely, when the density of the center jet was greater than that of the co-flow, the center jet was redirected to the pressure node side. This redirection effect tended to stabilize the laminar lifted flame.

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The combustion processes of both gasoline and diesel engines are becoming similar, as a result of the application of direct fuel injection to the former and the reduction of the compression ratio of the latter. A novel time-scale interaction (TI) combustion model has been developed for simulating combustion phenomena with high accuracy, ranging from premixed charge combustion to diffusion combustion. This model is based on reasonable combustion modes, taking into account the characteristic time scales of the chemical reactions and turbulence eddy break-up. Comparisons of measured and calculated heat release rate patterns and cylinder pressure histories showed good agreement for various operating conditions. The diesel combustion mechanism was analyzed under several fuel injection timings and engine loads using the TI combustion model.

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Solidification characteristics of PME (palm methyl ester) and RME (rapeseed methyl ester) under high-pressure conditions up to 200 MPa were investigated. To improve low temperature fluidity of PME since it has high pour point, JIS No. 2 diesel fuel, ethanol and dimethyl ether (DME) were blended into PME. The influence of their blend ratio on cloud point and pour point were examined. Solidification characteristic of blended fuels under high-pressure conditions up to 200 MPa were also investigated. The result was that, solidification pressure of PME was less than 100 MPa, and RME did not solidify up to 180 MPa at room temperature. Pour point and cloud point lowering effect of blending DME are more significant than that of blending diesel fuel and ethanol. It is possible to use PME by blending DME in cold seasons and in regions where neat PME cannot be used. DME, diesel fuel and ethanol blend into PME made the solidification pressure at room temperature increase to 150 MPa or more. DME was more influential fuel on improvement of low temperature fluidity of PME than other fuels.

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Experimental study of soot formation in DME jet diffusion flame was performed to investigate the influence of the oxygen contained in the molecular structure of DME. The amount of soot in the flame was measured using the transmitted light attenuation method, and was compared with that of the partial premixing methane flame under the high temperature and various surrounding oxygen conditions. The results showed that the amount of soot in the DME diffusion flame is much less than that of methane flame in most conditions, and the partially premixied methane flame of φ=7 that is substantially equal in equivalent ratio with DME diffusion flame generated 3-10 times as much soot as DME. This result suggests that the suppression of soot formation in DME flame is not due to the decrease of substantial equivalent ratio with contained oxygen, but attributed to the molecular structure of DME. The volume of the methane that is generated by primary pyrolysis of DME might have considerable influence on the generated soot amount.

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Since Cellular Automata (CA) was proposed by von Neumann in the late 1940s, CA have been applied in a variety of scientific researches on complex system, including traffic models and biological fields. It is an idealization of a physical system in which space and time are all discrete. In this study, we have simulated evacuation dynamics in fire by Real-coded Cellular Automata (RCA) proposed as a new approach for pedestrian flow. To consider the flame spread in discrete time and space in calculation, a percolation model is used. We change initial number of people, evacuee velocity, exit width, and flame spread rate. We discuss the total evacuation time and number of fatalities involved in fire.

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In this study, we have examined co-flowing diffusion flames formed in a triple port burner. The coannual burner consists of three concentric tubes. Air flows in both inner (central) and outer tubes, and fuel flows in the annulus between these air tubes. These velocities are defined as U_1A, U_2F, and U_3A (or U_3N), respectively. The fuel is propane. Two diffusion flames are formed in the boundary of fuel and air. For comparison, nitrogen is ejected in the outer tube to examine the mutual effect of two flames. The luminous flame height was obtained by direct photographs. A laser induced incandescence (LII) technique was applied to examine instantaneous soot concentration. To discuss the mixing of fuel and air, a NO-PLIF technique was used, where NO is added in the fuel flow. Results show that, as the fuel velocity, U_2F, is increased, the flame height becomes larger. When nitrogen is ejected in the outer tube, the flame height is larger. However, the flame temperature for both cases is almost the same. The LII measurement shows that there are two soot regions in two luminous flame zones, which are emerged in the downstream. The soot concentration in the inner flame is higher than that in outer flame when U_1A< U_3A, but it is lower when U_1A> ^U_3A. The minimum soot concentration is achieved when U_1A and U_3A are the same.

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