The unsteady cavitation characteristics of flat plate cascade were analyzed by a singularity method based on closed cavity model allowing the cavity length change. Through the formulation of present analysis, it was found that the unsteady cavitation characteristics are dependent on the cavitation number/incidence ratio as well as the steady cavity length. It was also found that the unsteady cavitation characteristics of cascades with solidity larger than 0.75-1.0 are very close to those of semi-infinite cascade. The present analysis can evaluate the cavitation characteristics of flat plate cascades with various solidity, and can be easily extended to the analysis for cascades with blade thickness or camber.

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The active control of vortex shedding from a circular cylinder by rotary ocillations is studied experimentally using neural networks, which optimizes automatically the control parameters such as the phase lag and the feedback coefficient. This optimization procedure is applied to find out an optimum position of reference probe to attenuate the vortex shedding effectively. The attenuation effect of vortex shedding under this control is investigated by measuring the velocity fluctuations in the cylinder wake and the unsteady pressure distributions over the cylinder surface. It is found that the drag and lift forces acting on the cylinder are reduced under the optimum reference control in comparison with the control under other reference positions as well as those of the stationary cylinder.

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Mass and momentum transport phenomena in the process of vortex pairing in a spatially developing mixing layer is discussed based on the instantaneous velocity and scalar database obtained from the direct numerical simulation using 4-th order central difference scheme. It was pointed out that, as for the momentum transport, a gradient diffusion is dominant in the first half of pairing process and a counter-gradient diffusion occurs in the latter half process. On the other hand, a gradient diffusion is induced and pronounced for the mass transport in the whole process of vortex merging. A detail mechanism is discussed by analyzing the behavior of u′v′ and v′c′, which respectively represents the momentum and mass transport, in the vortex pairing process.

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A fully three-dimensional numerical procedure based on the two-fluid model is proposed for the prediction of developing turbulent two-phase bubbly flow in a rotating squre-sectioned duct. The effects of turbulence models on phase distributions are investigated by utilizing the standard k-ε model and Speziale's nonlinear k-ε model with or without additional source terms relating to Coriolis modification or phase-fraction fluctuations. By comparing with existing experimental results, it is found that the additional source terms related to phase-fraction fluctuations tend to underestimate the lateral phase distribution and that Reynolds stress anisotropy has more or less effect on the phase distribution but inconsiderable effect on the pressure, axial and secondary flow velocities.

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Discrete vortex method was employed for simulating a turbulent shear flow around a baffle plate, which was mounted on the downstream edge of a splitter plate. Two air streams were supplied from both sides of the splitter plate, and a mixing region was formed downstream of the baffle plate. Velocity ratio of two air streams was varied from 0.20 to 1.20, and the Reynolds number based on the plate height from 2390 to 9550. Present calculations suggest following results. 1) Separated flow around a baffle plate is well simulated by the discrete vortex method. The present calculated relationship between the Strouhal number and the velocity ratio is in qualitatively good agreement with the measured one. 2) Although the Strouhal number is insensitive to the velocity ratio between 0.5 and 1.2, the vortex structure significantly changes. 3) The baffle plate possesses a capability to decrease the initial frequency of velocity fluctuation, and movements of small particles produced by the vortex cluster appear in the near wake field of the baffle plate.

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A new Reynolds-stress model developed by the author is assessed for the computations of turbulent Couette flow and turbulent rotating channel flow. The turbulent Couette flow has two distinctive properties. In the wall layer the flow is a wall turbulence, but the flow is also a plane homogenous shear flow in the core region. The turbulent rotating channel flow is affected with Criolis forces associated with the rotation. There is no direct effect of rotation on the turbulence energy budget, but in the budget for the Reynolds-stress tensor, the rotational term appears explicitly. Thus, the two flows are suitable for the assessment of the Reynolds-stress model. The computational results are compared with the available experimental data, which shows that the performance of this Reynolds-stress model is good.

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This paper describes mechanisms of the breakup and the drop formation of a radially thinning liquid sheet, which is attributing directly to the transition from laminar to turbulent flow. A radial liquid film flow is generated by a water discharge from a thin cylindrical gap, which is constructed by the end of a circular pipe and the flat surface of a disk. The liquid film flows radially outward on the disk, detaching from the peripheral edge of the disk, and then the liquid flows outward as a sheet. Sudden laminar-turbulent transition occurs in the liquid sheet when the Reynolds number exceeds a critical value, resulting both in the perforation and the disintegration of the sheet under extremely high Reynolds number. The breakup process through perforation, ligament formation and drop formation is disclosed both by a zoom-in photography using a single pulse strobe and a steel camera and a high-speed photography using a multipulse laser and a drum streak camera. These photographs clearly show that droplets of a few tens micrometers are produced from the liquid sheet. Flow conditions for occurrence of atomization induced by the transition are also presented.

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An experimental study of developing turbulent flow in a distorted ellptical duct was carried out at Reynolds number 0.988×10⁵ by using laser-Doppler velocimeter. In a distorted elliptical duct, the configuration of cross section varies from elliptical to circular and from circular to elliptical along streamwise direction with a constant cross sectional area constant. Three components of velocity and the five of the five stress components were measured at seven different locations to clarify the development of turbulent structure. As a result of this experimental study, it was found that the distributions of streamwise velocity were influenced by the secondary flow and the averaged intensity of the secondary flow over cross section showed the maximum value at midway between inlet and outlet of a distorted duct. Adding to these points, experimental results displayed that the secondary flow of the second kind at inlet section transformed into that of the first kind induced by pressure gradient at a little distance from the inlet and that of the first kind again transformed that of the second kind at the outlet section. The location of the maximum intensity of streamwise normal stress moves gradually from near upper wall to near side wall as the flow develops. The two kinds of shear stress between streamwise fluctuating velocity and cross sectional fluctuating velocity shows distributions different from each other.

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The present study has carried out numerical analysis for turbulent flow developing in a sinuous duct with a square sectioned at Reynolds number of 4×10⁴. The sinuous duct was formed from three 180 degree bends with 80 mm hydraulic diameter and 160 mm mean radius of curvature. Straight ducts of 80 and 30 hydraulic diameter long are attached to the inlet and outlet planes of the sinuous duct, respectively. In calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulence precisely, and boundary-fitted coordinate system was introduced as the method of coordinate transformation. Calculated results were compared with the experimental data measured by hot-wire velocimeter. As a result of the comparison, it was found that the present method was able to reproduce the main features of streamwise mean-velocity and secondary flow although the agreement was certainly not perfect in all detail. As a great discrepancy, it is pointed out that the calculated intensity of the secondary flow near 90 degree of second and third bend shows greater value than the experimental data. Moreover, the pressure-driven, Reynolds stress-driven and centrifugal forces which generates the secondary flow, are evaluated quantitatively by using momentum transport equation. It is clarifyed that Reynolds stress-driven force also plays an important role near 90 degree of second and third sinuous duct.

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Numerical simulations by a finite-difference method have been made for a viscoelastic flow due to a rotating disc enclosed in a cylindrical casing with large axial clearance. The Giesekus model with a single relaxation time was applied as a constitutive equation. We could simulate some typical secondary flow patterns for viscoelastic fluids which were different from Newtonian fluids ; e.g., a secondary flow of which circulation direction at very low Reynolds number is reversed compared with that for a Newtonian fluid and a double-cell flow structure which Escudier et. al⁽2) observed at relatively high Reynolds number. We show that the double-cell flow structure relates to nonlinear terms of the constitutive equation. The secondary flow patterns are characterized by the elasticity number (=Weissenberg number/Reynolds number) from low to high Reynolds numbers.

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This report is the experimental study on drag reduction and mechanical degradation in turbulent pipe flow with dilute plant mucus solutions. Mucus samples were taken from vegetables such as taro, okura and onion. Then all of these dilute mucus solutions have shown the drag reduction (called Tom's phenomenon). Some of plant mucus were good drag reducing materials. But they also showed the remarkable mechanical degradation in a circulating pipe flow by a pump. Viscosity and first normal stress difference of the concentrated mucus solutions were measured by a cone-and-plate Weissenberg rheogoniometer. They, as well as synthetic polymer solutions, were found to show the shear-shinning and the first normal stress difference.

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A flow pattern of fine particles in a vertical vessel is visualized by tracer method when the flushing is occurred by a piston load on the particle surface, particles spouting out of a slit at the vessel bottom. It is found that when the piston load is applied the particle flow firstly starts near the slit, and disappears when the flushing ceases. The particle flow in the vessel is discussed classified into four regions.

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To control the flow around a square prism placed diamond in airstream, a rod was set upstream of the prism. The side length of prism, D, was 20 mm and the Reynolds number based D ranged from 5.1×10³ to 3.6×10⁴. The diameter of the control rod, d, ranged from 1 to 12 mm and the distance, L, between the axis of the prism and rod was 30 to 120 mm. Two flow patterns with and without vortex shedding from the rod were occurred. The flow pattern changes depending on the rod diameter, its position and the Reynolds number. For the case without vortex shedding from the rod, the shear layer from the rod reattaches on the front face of the prism. In this case, at d/D=0.6 and L/D=3.0 the average heat transfer increase by 23% compared with that of without rod, and the reduction of the total drag becomes to about 34%.

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We have investigated the oblique collision of two underwater shock waves in order to make an understanding of irregular reflection, espescially von Neumann reflection, of shock waves in condensed matter by both experimental and numerical techniques. The underwater shock waves used were generated by underwater explosion of high explosives in a simple assembly. Using a conventional Shadowgraph system, we took the streak and framing photographs of the collision of two underwater shock waves at different collision angles. We compared our experimental Mach-stem velocities with those obtained by Whitham's Shock-Shock theory. In the numerical technique, the Arbitary-Larangian-Eulerian method was employed for simulating the whole phenomena in detail. The simulation results demonstrated, at least qualitively, a well agreement with the experimental results. From the simulated Shadowgraphs, we can get a clearer knowledge of the conditions for the occurrence of von Neumann reflection as well as the basic characters of von Neumann reflection.

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Constant-temperature hot-wire anemometer is calibrated in a nozzle through which air is sucked from the atmosphere, and the heat transfer characteristic of the hot-wire at low Reynolds numbers is investigated from low subsonic to supersonic range. As a result, it is shown that the Nusselt number Nu which represents the heat transfer characteristic of the hot-wire is a function of both Mach number M and Reynolds number Re when M is in the range from about 0.3 to 1.1, although it depends only on Re in the cases of M<0.3 and M>1.1. It is also shown that Nu becomes maximum when M is about 0.6, which should be noted in measurement of mass flux by means of hot-wire anemometers.

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An impulsive pressure wave which is called a "micro-pressure wave" or a "tunnel sonic boom" radiating from a tunnel exit is one of the important environmental problems in high-speed railways. The strength of the impulsive wave depends on the waveform of the compression wave at the tunnel exit. In this study, the distortion of the compression wave during its propagation through the tunnel is investigated by field measurement and numerical analysis. The field measurement is conducted in the concrete slab (ballastless) track tunnel of the Shinkansen. The numerical analysis is also carried out on one-dimensional compressible flow using upwind TVD scheme. It takes account of steady and unsteady wall friction and of heat transfer to the tunnel wall. Our original numerical analysis method is based on Galilei transformation of the coordinate system moving with the compression wave. The results show that the agreement of the numerical analysis and the field measurement is good.

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Fluctuations of electric power demands in Japan are so heavy that development of electric sources for peak load generation is an important problem. Compressed air energy storage (CAES) system is one of the most promising candidates of energy storage system, and considered to follow pumping-up electric power plants. The CAES system stores compressed air in an underground reservoir using low-cost power from base load plants during off-peak periods. The stored air is used for gas-turbine power generation during peak periods. For successful design of the CAES system, accurate prediction of CAES champagne effect is required to avoid a loss of the stored air caused by blowout. In the present study, a computer program based on a one-dimensional two-fluid model including a simple gas release model was developed for prediction of the CAES champagne effect. This program was applied to simulation of experimental results of a high-solubility carbon dioxide/water laboratory model of the CAES system. The computer program developed was found to show good agreement with the experimental results if the mass transfer coefficient, that determines the gas release rate, was set to 0.4 mm/s.

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The acoustic characteristics of a new sound isolation panel, containing ventilation holes, was described in the first and second reports. The panel provides a considerable sound isolation effect in the required frequency band by controlling the acoustic anti-resonance frequency of the sound field inside the panel. However, when the panel is used under air flow field, acoustic normal modes inside the panel are excited by periodic vortex generation. As a result, the flow induced tone occasionally occurs with high sound pressure level. This paper describes a way to reduce the flow induced tone and the pressure loss coefficient with the help of flow visualization.

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In the former report, advantages of using a small duct for an air conditioning system were mentioned, and it was presented that the mixed flow multiblade fan, which was developed newly by authors, was adequate to a small duct fan. In this paper, the effects of parameters of the mixed flow multiblade fan on the fan performances were investigated experimentally. At first, the effects of a conical angle of the impeller and a vane setting angle on the performances were investigated. Then, two types of guide vanes were examined, and it was made clear that the guide vanes which overhang the impeller gave remarkable effects on the fan pressure and efficiency. At last, the experimental results regarding to effects of the inlet and outlet vane angles were presented.

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Pumping characteristics of the screw vacuum pump were investigated. The aim of this study is to establish a method of the performance prediction and a way to design the pump that satisfies requirements. The performance was analysed by the balance among geometrical pumping speed, net throughput and leaks. The leaks flow through clearances between a screw rotor and a stator, and clearances between two meshing rotors. These leaks were estimated with the results based on the linearized BGK model and the flows through ideal labyrinthes. Experiments were carried out by rotors of 120 mm diameter, and pumping speed and ultimate pressure were measured. The comparison between the measurements and the predicted values shows that the present method predicts the performance of the screw pump with a sufficient accuracy for practical applications.

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Pool boiling heat transfer results for a 10 mm×10 mm rectangular chip immersed in subcooled FC-72 were reported. Three kinds of surfaces were tested : an untreated silicon wafer surface, an etched surface of a thin SiO₂ film that was sputtered on a silicon wafer, and the same kind of SiO₂ surface with artificial cavities. The cavities were a re-entrant type with mouth diameters ranging from 0.7 to 1.4μm. These artificial cavities were effective in reducing the boiling incipience superheat. For degassed FC-72, the boiling incipience temperature agreed fairly well with the theoretical prediction of the heterogeneous nucleation theory. When the dissolved air content of the test liquid was sufficiently high, the chip temperatures at boiling incipience and at fully developed nucleate boiling were significantly decreased.

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The mutual diffusion coefficients of three global warming gases (CO₂, CH₄ and N₂O) into air and its component gases (N₂ and O₂) have been measured in the temperature range 0∼180°C and at atmospheric pressure by the use of the Taylor dispersion method. The mutual diffusion coefficients do not vary in practice on substituting pure N₂ or O₂ for air. The mutual diffusion cofficients for CO₂ and N₂O, which have almost the same molecular weight, agree with each other within the experimental uncertainty (±2%) and are smaller than that for CH₄. The present results can be reproduced well by the functional form D=AT^B, where D is the mutual diffusion coefficient at 1 atm (101 325 Pa) in m²/s and T is the absolute temperature in K. The constants A and B are as follows : CO₂-(air, N₂, O₂), A=5.75×10^-10, B=1.81 ; CH₄-(air, N₂, O₂), A=7.04×10^-10, B=1.83 ; N₂O-(air, N₂, O₂), A=5.34×10^-10, B=1.82.

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Water and heat transport in unsaturated packed beds due to supplying hot water have been investigated experimentally and theoretically. Using various sizes of glass beads, capillary pressure and permeability in packed beds were measured in unsaturated beds. The distributions in water saturation and temperature were predicted for one dimensional packed bed, based on a model assuming local thermal equilibrium among water, gas and particles at any specific space. The predicted temperature distributions were compared with the experimental results obtained using various glass sizes. In layered packed beds, water saturation becomes discontinuous at the interface of two layers because of the difference of the water characteristics between two beds. Water penetrates faster in coarse-over fine-textured profile compared with in fine-over coarse-textured profile. Similarly, the temperature rises faster in former profile under the same supplied heat quantity.

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Velocities of entrained droplet cluster were experimentally determined for vertical upward gasliquid annular mist flow. The velocities were measured using a set of optical sensers. In this study, system pressure in the closed-loop system was varied substantially from 5 to 15 MPa at constant fluid temperature. It was clarified that mean velocities of entrained droplet cluster draw near gas velocities under high pressure conditions. The correlation to predict the entrained droplet cluster velocity was presented. The correlation was applied to high pressure data and the droplet velocity, the entrainment holdup and the slip ratio of droplet were presented. The maximum value of entrainment holdup in gas core was 0.3.

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Time-spatial measurements of liquid holdup distribution along the tube axis were carried out over the length of 1325 mm in upward two-phase flow. In order to clarify the characteristics in behaviors of ephemeral waves, a method for determining sub-wave-veins, which were the traces of ephemeral waves on the time-spatial behavior charts of interface, was developed. This method was applied to the flow conditions in two regimes of huge wave flow and annular flow, and the sub-wave-veins in these flow regimes were successfully determined. Time-spatial behavior charts of interface with the determined sub-wave-vein were systematically presented and the characteristics of sub-wave-veins were discussed. Close inspection of the behaviors of sub-wave-veins reveals that there are two-types of ephemeral waves ; namely one has a shorter life span and the other has a longer life span during which causing absorption and discharge of small ephemeral waves.

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Some kinds of surfactants are useful to reduce flow drag in a turbulent pipe flow by Toms effect. However, it needs a lot of cost to make these surfactant harmless material to the environment. On the other hand, the fibrous substance such as pulp fibers and cellulose are harmless additives to the environment. This paper has dealt with the flow drag reduction and heat transfer characteristics of the water suspension flow mixed with fine fibers in a straight pipe. Measurements of velocity and temperature profile in a circular pipe flow were made in order to examine the flow drag and heat transfer characteristics of the turbulent and laminar flow. The nondimensional equations of pipe flow resistance and heat transfer were derived in terms of various nondimensional parameters.

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The effects of sea water on the CO₂ transfer across the air-water interface were experimentally investigated in both an oscillating-grid tank and a wind-wave tank. The results show that the CO₂ transfer velocities across non-breaking air-water interfaces for 3.5wt% salt, natural sea and artificial sea waters are damped to 50% of those for pure and tap waters. The reduction is caused not by surface contaminants characteristic of natural sea water but by the presence of very tiny surface-active impurities common to all the sea and fresh waters. The surface-active impurities reduce the molecular diffusivity of CO₂ at common interfaces to 7% of the molecular diffusivity at the really clean interface. The reduction amplifies the weak effect of electrolytes on the small difference of the molecular diffusivity between sea and fresh waters and it results in the large diffence of the CO₂ transfer velocity. Furthermore the ratio of the transfer velocity of sea water to that of fresh water increases from 0.50 to 0.97 as the interface is broken. Especially the differece between the transfer velocities becomes very small for intensively broken interface. This is attributed to that the effect of surface-active impurites on the mass transfer is weaken by the replacement of the interface by the fresh bulk-fluid.

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Flow and temperature distributions in silicon melt during the floating zone (FZ) crystal growth process are investigated numerically and experimentally. The main purpose of the study is to clarify the effect of radio frequency (RF) heating, which is widely used in industry, on the flow and temperature flelds in the melt. On the numerical study, we have made a model of RF heating and calculated not only the experimental situation but also the radiative heating case and compared each other. On the experimental study, we have visualized a flow field by using a RF-FZ furnace with real silicon and a X-ray radiography system. The result reveals that the RF induced convection becomes dominant and the direction is opposite with Marangoni convection. Further, the magnitude of the convection becomes one order high. On the other hand, strong timewise fluctuation of flow and temperature fields are obtained. This fluctuation seems to cause a strong striation in the crystal.

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In order to investigate the structure and the dynamics of zeolite-NaA including Na⁺ ions, molecular dynamics simulation was performed using a flexible framework and a central force potential model. The radial distribution functions, mean-square displacements of zeolite atoms and the Si-O-Al bond angles were obtained from the MD simulation, and were found to agree well with the available zeolite-NaA structure data. In addition, the dynamic behavior of water molecules in the flexible zeolite framework, especially adsorption and diffusion, was simulated using two types of central force potential models of water molecules ; that is, a pair potential model and a 3-body potential model. Although the sites of water adsorption coincided with the X-ray diffraction experiments in both models, only the 3-body potential model could simulate the diffusion of water molecules in the zeolite.

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An osmotic heat pipe is a top heat mode heat pipe driven by an osmotic force. Therefore, a concentration and a solution flow rate in a membrane module of the osmotic heat pipe are especially of great importance for the heat transport. Thus, the flow in the membrane module is investigated in detail. As a result, with a ratio of a concentration on the membrane wall to a mixed mean concentration derived semi-theoretically, correlations for the mixed mean concentration, the concentration on the wall and the solution flow rate along the channel in the membrane module were proposed, which can correlate the experimental data from reference (2) within±20% errors. In addition, a method of increasing in the osmotic pumping rate and heat transport rate was proposed.

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This study is attempt to burn pulverized Refuse-Derived Fuel (RDF) made from municipal solid waste (MSW) for thermally recycling of waste resources. RDF has a large content of volatile matter in weight in proximate analysis, which under devolatilization contributes significantly to the combustion behavior of RDF. The devolatilization properties of both RDF and its constituent materials such as plastics (polypropylene, polystyrene), fiber (nylon) and paper (newspaper) were observed by the thermogravimetry and differential thermal analysis (TG/DTA) to obtain fundamental data of RDF combustion. The thermogravimetric (TG/DTA) analyzer was used to measure weight loss and temperature difference of the selected sample components. The data of TG/DTA were obtained by changing the heating rates under the atmospheric condition of both nitrogen gas and air. It was observed that the weight of plastics and fiber decreased monotonously, however, the weight of RDF decreased under two or three stages with endothermic reaction during pyrolysis of RDF, and with exothermic reaction during combustion of RDF. This results indicate that the paper included in the RDF burns first at a lower temperature and then the constituent materials such as plastics and fibers burn at a higher temperature. The TG data obtained at some heating rates have been arranged in terms of Arrhenius plots versus 1/T for each sample in order to obtain the empirical activation energy and the frequency factor. The calculated weight loss using their empirical values have showed good agreement with the experimental results.

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Flame modes and blow-off limits at a high-intensity swirl burner are systematically studied by changing various parameters such as swirl intensity, fuel-flow rate, nozzle structure, combustion tube length and combustor pressure. Results show that higher-intensity swirl well stabilizes the flame above a critical swirl number S=0.6. In the case of fuel injection perpendicular to the burner axis under atmospheric pressure, the flame of premixed pattern appears and an extremely low NO_x concentration is realised at a lean combustion with long combustion tube. On the other hand, in the coaxial fuel injection along the burner axis, the flame of diffusion pattern appears and NO_x concentration becomes almost equal to that of premixed-pattern flame near the stoichiometric fuel-air ratio. As combustor pressure is elevated under a constant air-mass flow rate, NO_x concentration is increased even at a lean combustion due to less local misfiring.

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Effects of DC electric fields on burning velocity of methane-air premixed flame were investigated with a cylindrical flame burner with a earthed porous cylinder. The center electrode was mounted on the centerline of the porous cylinder, and the porous cylinder itself was used as the other electrode. The cylindrical flame was formed inside the porous cylinder, and the flame never deformed when electric fields were applied. Increase in flame radius was detected when the center electrode was over+7000V, and no change of the flame was detected when the center electrode was less than+7000V. When the center electrode was negative, no change of the flame was detected up to 9000V. Increase in flame radius with electric fields is considered to show increase in burning velocity because the flame radius at a fixed ejection velocity without electric field increases when the burning velocity of the premixed gas increases.

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Experimental studies are made of H₂/N₂-air laminar counterflow diffusion flames strained by impinging micro fuel or air jet from fuel or air side. Direct observation and two-dimensional temperature measurements by laser Rayleigh scattering method reveal the following phenomena. (1) The flame strained by the micro fuel jet from the fuel side is easily quenched locally, but the flame strained from the air side hardly extinguishes and the flame temperature tends to increase. (2) The flame is extinguished by higher strain rate even in the case of impinging micro air jet. (3) Relighting is observed at the place far from the initial flat flame. Phenomenological discussions with respect to preferential diffusion and flame curvature effects are included.

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The "integrated coal gasification combined cycle system" (IGCC) requires the development of a high temperature, gas turbine combustor using coal-derived, low-Btu gaseous fuel, which has high thermal efficiency and low NO_x emission. The authors of this paper have developed a 150 MW, 1500°C-class gas turbine combustor which adopts an advanced two-staged combustion technology designed mainly for achieving low NO_x emissions and stable combustion. Under high-pressurized conditions, we have successfully reduced NO_x emissions when fuel contains ammonia of about 1000 ppm, and have maintained flame stability. Moreover, we have optimized many design guidelines by clarifying the effect of pressure on combustion characteristics. This paper describes in detail the effects of pressure on the characteristics of the advanced, two-staged combustion technology for use in a gas turbine combustor in IGCC.

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An numerical simulation of hydrogen-oxygen reaction over platinum catalytic surface was carried out and the effect of surface diffusion velocity on catalytic reaction was studied. In this simulation, no convection is assumed to simplify the analysis. The numerical model is as follows ; A spherical platinum of 0.75 mm in radius is surrounded with the mixture. Three based partial differential equations, which govern mass, energy and species concentrations, are stated in one-dimensional polar coordinates. Axial symmetry, zero azimuthal velocity, and no gradient along the axis are assumed. Because of low Mach numbers, constant pressure is assumed, and therefore, momentum equation is not used. Langmuir-Hinshelwood mechanism was used for the catalytic reaction model. The adsorbed species are H, O, OH and H₂O and 3 elementary surface reactions are used. As the results, a steady state is observed. The surface temperatures at the steady state do not depend on surface diffusion velocities but on adsorption rates and desorption rates. The catalytic ignition temperatures increase as H (S) surface diffusion velocity decrease. They are independent on surface diffusion velocities of O (S) and OH (S).

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Effects of supercharging on a engine performance and exhaust emissions in a spark-assisted direct injection methanol engine were investigated under heavy load conditions. The test results indicated that the supercharging has the effects of improving thermal efficiency, CO and NO_x emissions. The combustion analyses showed that the supercharging suppress a rapid combustion of stratified mixture which include fuel spray drop, and makes contributions to promote premixture with rapid fuel spray evaporating and fuel-air mixing. As a result, supercharging increased heat release during the premixed combustion. In addition, increasing of premixed combustion with the supercharging reduced the deterioration of brake thermal efficiency during the EGR under heavy load conditions. The supercharging with EGR can significantly reduce the NO_x emissions while keeping the high thermal efficiency as direct injection diesel engines.

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Instantaneous measurement of density distribution as cross section of jet, in particular is very effective to understand direct factors, eq. scale or uniformity of mixture, which affect combustion performance. Using laser induced fluorescence, mixture spreading process of intermittent unsteady jet flow was measured, and transformed into visual image of instantaneous concentration distribution of jet at its cross section. Quantitative measuring method of density distribution in jet was thus established. In thus study, the following effects and problems of the concentration process to get concentration image from fluorescence image, such as : linearity between concentration and fluorescence emission, temperature and the kind of ambient gas effects on fluorescence, induced laser absorption and fluorescence extinction by fluorescence gas, are discussed.

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ATAC is "bulk-like" and/or "non-propagating" combustion process caused by compression autoignition of premixture, and it is stable in lean combustion region. And ATAC engine is expected to be an engine using alternative fuels which are difficult to apply to usual engines because of their generally low cetane number. In this study, a two-stroke ATAC engine test was carried out to evaluate an adaptability of alternative fuels for lean burn. Methanol, ethanol, dimethyl ether (DME), methane and propane were used as the test fuels. Engine speed, BMEP and equivalence ratio were considered parameters. The influence of fuel characteristics on autoignition timing, combustion duration and autoignition gas temperature were investigated. Using oxygenated fuels, the lean limit of ATAC operating region shifts to lean side. ATAC autoignition temperature of each alternative fuel, except methane and propane, ranges from 950K to 1150 K regardless of equivalence ratio, delivery ratio and engine speed, and it rises with increasing cetane number of fuel.

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Planar Laser-Induced-Fluorescence technique was applied to measure the NO fluorescence distribution in a spark ignition engine. The fluorescence intensity had high value near the flame front, and gradually decreased from the flame front to the postflame gas. The fluorescence was distributed in the broad flame zone as compared with the case of the constant-volume combustion chamber. The effect of equivalence ratio on the NO fluorescence intensity were investigated. At the flame-development duration, the total NO fluorescence intensity was high as the equivalence ratio became rich. However, at the rapid-burning duration, the total NO fluorescence intensity of a slightly lean condition had a maximum value. As the equivalence ratio became lean, the peak intensity of the radial NO fluorescence distribution increased and the width of the high intensity zone in radial distance broadened. The peak intensity and the width of the radial distribution reached the maximum value at a slightly lean condition.

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A pilot flame ignition system, which has superior characteristics in the high ignition energy and the large flame contact area to a conventional spark ignition system, is experimentally examined by the indicated pressure analysis and the high speed direct photography. A model combustion chamber, which simulates a Wankel-type direct injection stratified charge rotary engine, was employed to test the ignition performance of both the pilot flame ignition and spark ignition systems. As a result, it was found that the pilot flame system successfully ignites the very lean charge stratified mixture which the spark system fails to ignite and that the combustion characteristic difference using different ignition systems becomes small as the overall equivalence ratio is increased.

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An experimental study was made on a natural gas fueled spark ignition engine to improve its thermal efficiency and exhaust emissions by the lean burn operation. A multi-cylinder engine was used to obtain the data for practical application. Investigated were the effects of the throat area of the orifice which separated a prechamber from a main chamber, the position of ignition spark in the prechamber and the compression ratio on the thermal efficiency, the exhaust emissions and the lean limit of stable operation. The results showed that a small throat area resulted in low emissions of NO_x, low thermal efficiency and narrow lean limit. The spark ignition at the center of prechamber or near the throat was preferable to the top of prechamber in terms of the thermal efficiency. Higher compression ratio resulted in shorter combustion duration, higher thermal efficiency and extended lean limit.

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Effects of the intake air oxygen enrichment (IOE) on unburned hydrocarbon emissions during the warm-up period in a spark ignition engine were investigated. Hydrocarbon species from C1 to C6, as well as total hydrocarbon concentrations, were determined by gas-chromatography. As a result, the warm-up period of IOE operation was reduced to one third, and hydrocarbon emissions, such as ethylene and benzene, reduced by 90% compared with normal air operation. It was also found that the effect of the decrease in quenching area with IOE on the reduction in hydrocarbon emissions was relatively small.

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Many papers have been published on measuring in-cylinder flow of an engine, such as using hot wire anemometer or laser doppler velocimeter. Also the technique of flow visualization becomes more and more precise because of using high performance computers and development of softwares to analyze the imeges, and technique of flow visualization can be usually adapted to two dimensional flow measurement. The method proposed in this paper, using color layers, is to measure the two dimentional velocity from the length of tracer image as usual analysis, and velocity perpendicular to the image plane can be derived from the color, that is the location of tracer and the time of exposure to take the image. A fundamental measuring system was developed and examined the principle of color layers for measuring three dimensional position. It was confirmed that the developed measuring system and the measuring principle was valid to measure the three dimensional location.

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A partial ZrO₂/Ni functionally graded materials (FGM) chamber coated with the pure ZrO₂ layer and the ZrO₂/Ni FGM layer was cyclically tested using the bipropellant of nitrogen tetroxide (NTO)/monomethyl hydrazine (MMH) at a nominal chamber pressure of 1.0 MPa to show the effect of the coating on life. These thermal barrier coating were coated using a process that employed the electro-formed method. The ηC^* for the durability tests of the partial ZrO₂/Ni FGM chamber was 97% at P_c=0.9 MPa and MR=1.65. At cylindrical section of the chamber, the thermal barrier coating composed of a pure ZrO₂ layer remained partially intact. However, the inner surface coating of the chamber throat section occurred prematurely the delamination. In the cycle durability tests, the damage of the coating was inspected by using the Reprica method. After the total of 260 firing tests, the profile of the coating damage was evaluated by using the computer aided micro-analyzer (CMA) system.

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A small gamma-type Stirling engine was developed as a prime mover of a portable generator set. The engine target performance is 100W output power and 20% net thermal efficiency at 1000 rpm. Special bayonet-type heat exchangers whose inner tubes move inside of the outer tubes, were applied for the engine's heater and cooler. An annular regenerator was located in a displacer piston. The displacer piston had both of the heating and cooling inner tubes for the working gas which flows to and from outer tubes. The outer tubes for heating were located at the top of the expansion cylinder and the outer tubes for cooling were located in the middle of the cylinder. For a piston drive mechanism, a Scotch-yoke mechanism which was useful to realize the small-size engine without any lubricating device, was adopted. In this paper, the design methed using an adiabatic model which can treat several thermal and hydraulic losses, and a nodal model, SETMA, are introduced. The analysis results are compared with the experimental data to show the availability of the arranged design method. Also, the performance of the compact bayonet-type heat exchangers are briefly discussed.

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A 100W Stirling engine was developed as a prime mover of a portable generator set. Special bayonet-type heat exchangers whose inner tubes move inside of the outer tubes, were applied for the engine's heater and cooler. An annular regenerator was located in a displacer piston. The engine had already achieved the target performance. To improve the engine performance efficiently, a simulation model for the prototype engine was developed. The pressure in the working space was analyzed by an isothermal analysis which takes into account a gas leakage between the buffer space and working space, and a pressure losses in the heat exchangers. For the pressure loss in the regenerator, the model can treat the effects by the velocity distribution in the regenerator matrix. To estimate the engine output, the model calculates the mechanical loss and the buffer loss which is caused by a pressure change in the buffer space. The buffer loss was calculated with three models, an isothermal, an adiabatic and a simple heat transfer model to determine a suitable model for the buffer space. The analysis results were compared with the experimental deta carefully.

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