Experimental investigations on the unsteady cavity flow around an elliptic cylinder of axis ratio 1 : 3 in severe vibration region were carried out. The cavity flow around the cylinder was observed using high-speed camera. The fluid forces and the pressure fluctuations were measured to clarify the correlation between cavity behaviors and fluid dynamic characteristics. It was found that the cavity flow characteristics are strongly correlated with the severe variation of cavity configulation.

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Detailed flow structure of bubbly flows observed in a bubble plume is investigated by numerical simulation using the Lagrangian tracking method which can treat the bubble movement with high accuracy. Governing equations are formulated with emphasis on the translational motion of bubble in non uniform unsteady liquid flow. Numerical results reveal the dependency of bubble size distribution on the flow behavior and show good agreements with experimental results. In this 1st report, two-dimensional bubble plumes are chosen for analysis of detailed flow structure in bubbly flow.

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A numerical analysis using the Lagrangian tracking method for bubbly flow was carried out to elucidate the three-dimensional detailed flow structure and the turbulence mechanism of a bubble plume, which has various interaction between gas and liquid phases. The results revealed that the bubble plume exhibits several kinds of three-dimensional structures with spiral and sinuous behav-iors, depending on bubble size and void fraction. This macroscopic structure shows good agreement with experimental observation. Also, the bubble plume has a turbulence component, called pseudo turbulence with high frequency which is caused by the migration of large bubbles with large slip velocity inside the bubble plume.

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Transient shock wave phenomena in a liquid containing non-condensable gas bubbles are studied experimentally and numerically. In order to obtain a uniform spatial distribution of bubbles experimentally, an upwardly directed bubbly flow, whose initial gas volume fraction is 0.2%, is generated in a shock tube. The liquid used is silicone oil. Nitrogen, argon, and SF6 gas bubbles are tested to show the thermal effects of the bubble interior. The transient pressure profiles determined in the experiments for the upwardly bubbly flow agree well quantitatively with those obtained by numerical calculation using a uniform spatial distribution of bubbles. Since the thermal diffusivity of SF6 is much lower than that of nitrogen and argon, the damping on the radial oscillation of the SF6 bubble is mainly due to the compressibility of the liquid. Thus, the radial motion of the bubble should be estimated by solving an equation in which the liquid compressibility is taken into account.

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Bubble behavior in a swirling flow is discussed with the aim of developing a bubble rejection technology for flowing liquids. We show that bubbles in a swirling flow combine in the center of the bubble rejection device, that bubble volume has the maximum value, and that this maximum volume increases with an increase in swirling velocity. However, the maximum bubble volume decreases with excessive swirl velocity because of separation due to the strong swirl flow. It was found that bubbles combined at a lower flow rate under a microgravity condition than under a normal gravity condition, due to the smaller buoyancy force in the microgravity condition.

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A 3-D FEM/FDM composite scheme for viscous, incompressible flow problems is presented. It combines the finite element method, which is best suited to analyzed flow in any arbitrarily shaped flow geometry, with the finite difference method, which is advantageous in terms of both computing time and memory requirement. The combination of both methods enables large-scale viscous flow to be analyzed, which is crucial both for detailed analysis of 3-D flows and for solving flow problems around moving bodies. A modified ABMAC method is used as the basic algorithm, to which a sophisticated time integration scheme, proposed by the present authors, has been applied. In this paper, flow around a sphere is analyzed both as a static problem and as a moving body problem and numerical results show good agreement with experimental results.

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A spectral finite difference method with domain decomposition is used to solve the NavierStokes equation for incompressible fluids. In the domain decomposition method, some subgrids consisting of multiple orthogonal curvilinear coordinate systems and of overlapping region ( S ) are adopted, and one-dimensional interpolation is applied to the overlapping region in the case of twodimensional analysis to obtain neighboring values corresponding to a virtual boundary. Mass conservation on a virtual boundary is assured using a mass imbalance correction. Present numerical analyses for two-dimensional, internal, doubly-connected or triply-connected flow fields consisting of cylindric and elliptic boundaries show good consistency, accuracy and efficiency.

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To determine the quantities affecting electroviscous effects, we investigated the change of the effects due to electric field, shear stress, volume concentration of powder, and kind of aluminum powder and turbine oil in the previous study. In this study we examined the change of the effects by using various kinds of liquid with different dielectric constants. The same results were obtained for the various kinds of liquid. That is, the electroviscous effects were controlled by a nondimensional parameter expressed as the ratio of force acting on a conductor per unit area in the electric field to shear stress when no electric field was applied. Furthermore, by adding terms of the apparent dielectric constant of suspension and volume concentration to the nondimensional parameter, almost all the experimental data points were rearranged to lie approximately on one straight line in a plot with the new nondimensional parameter as abscissa and the effect as ordinate.

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The thermal effect on a liquid film of uniform thickness on a rotating disk is investigated. When the disk temperature Td remains constant and equal to neither the temperature T0 of the surrounding gas nor that of the initial liquid film, three parameters, namely the Prandtl number Pr, the Nusselt number Nu, and the dimensionless viscosity rate of change ε≡-μ0-1∂μ0/∂T(Td-T0)(Where μ is viscosity and μ0 is initial viscosity), govern the flow field thermally. The Navier-Stokes equations, the equation of continuity and the thermal diffusion equation in self-similar form are solved analyti-cally. In the last stage, it was found that the time dependences of the film thickness through these three parameters are Pr;t-3/2, Nu;t-1 and ε;t-1/2. Further, it was found that the last one is the same as that for the film thickness due to the centrifugal effect. From this, it can be concluded that the thermal effect on flow through ε is quite large and ε can be assumed to be another parameter,besides rotating speed, that controls the spin-coating process.

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A real fluid does not slip at the surface of a solid body. Most experimental results of a Newtonian fluid satisfy this condition. If a real fluid can slip freely over the surface of a solid body, how can we deduce the slip velocity? Although slip is a basic, interesting problem in fluid mechanics, fundamental data are lacking. The purpose of this study is to clarify fluid slip experimentally. Velocity profiles of tap water and 20 wt% glycerin solution flowing in a square duct with a highly water-repellent wall were measured by means of a hot-film anemometer. Consequently, slip of Newtonian fluids at the solid wall was revealed and explained by Navier's theory.

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This paper describes the flow visualization around the anterior communicating artery and the dynamic pressure at the apex along the medial wall. The anterior communicating artery composing the circle of Willis is one of the predilection sites where cerebral aneurysm occurs frequently. The flow field around the anterior communicating artery is simulated by two confluent tubes joined at on angle of 60 degrees, two parallel bifurcating tubes, and a junctional tube, bypass, connecting the four tubes. The flow field around the apex where cerebral aneurysm is apt to occur is vsivalized using a laser sheet. In particular the dynamic pressure to the apex at one confluent tube with a high flow rate is estimated, and the relationship between the dynamic pressure and the generation of aneurysm is discussed physiologically.

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In order to investigate the effect of gap size on the spanwise turbulence properties of a boundary layer flow through a gap in an isolated wall-mounted roughness element, the turbulence quantities and secondary velocity components have been measured. All measurements were made at a Reynolds number of 3 300, based on obstacle height and free-stream velocity. The three components of turbulence intensity, the Reynolds shear stress and the magnitudes of transverse and spanwise velocity components near the central region reach higher maximum values for smaller gaps. However, the present turbulence field can also be divided in the same way as mentioned in our previous paper. From the off-centerline turbulent quantities, the classification of the gap size proposed by Osaka et al., is definitely reasonable. Further downstream from the gap, it is shown that turbulent structures for 4 gap sizes flows are different from that of the undisturbed flow respectively but are identical to that of a two-dimensional fence flow. The downstream change of the spanwise averaged turbulent kinetic energy flux has been investigated for all gap sizes.

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An interaction between underwater shock waves and expansion waves occurred by the expansion of a product gas is investigated by both experimentally and by numerical simulation. Cylindrical high explosives are used in the experiments. Streak photographs and framing photographs are taken by a high-speed camera using a conventional shadowgraph system. When the cylindrical high explosive detonates in the water, an underwater shock wave is occurred and the product gas expands as the detonation wave propagates. Due to the expansion of the product gas, an expansion wave occurs and interacts with the underwater shock wave. The strength of the underwater shock wave is strongly effected by the expansion waves which changes its configuration. The attenuation process of the underwater shock wave is investigated theoretically using a method of characteristics. Using this theoretical work, it is possible to obtain the parameters of the Jones-Wilkins-Lee (JWL) equation of state for the product gas. The numerical results obtained by using the JWL parameters are compared with the experimental results. Good agreement between them is confirmed in the case of the underwater explosion of cylindrical high explosives.

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The Savonius turbine, which works at low rotatory speeds and gives a high degree of torque, has been used for a wind turbines. In order to examine the feasibility of applying the turbine as a wave energy conversion system, a Savonius rotor was installed in a casing and its performance was studied experimentally to examine the various geometrical configurations of the rotor and casing. When optimally cnfigured, the turbine exhibits higher efficiency than a wind turbine without a casing during steady flow conditions.

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The hydraulic performance of a 3-element automotive torque converter is analyzed by making flow measurements with 5-hole pitot tubes between these elements. The performance of each element, such as head, loss of head and efficiency, is evaluated. The results show that the pump is the major source of head loss in the range of speed ratio where vehicles are most frequently operated in daily driving. The loss coefficients for the three elements are also evaluated using a one-dimen-sional flow model. For the turbine, the coefficient of friction loss is nearly constant over the entire range of the tested speed ratio, whereas the coefficient for the pump and the stator varies consider-ably according to the operating speed ratio. The mechanism of loss generation in the pump and the stator is investigated using flow visualization in the vicinity of the passage walls. This procedure is useful not only for improving the accuracy of the performance prediction, but also for determining the direction of the improved design.

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A device for sweeping volcanic ash on lawn was designed and its capability has been tested. This lawn sweeper was installed above a conveyor belt on which artificial lawn was pasted. The ash was uniformly scattered on the lawn using a hopper, conveyed at a constant velocity to the lawn sweeper and swept by it. The lawn sweeper is composed of small air jets and an air flow in a channel above the lawn. The former lift up the volcanic ash from the lawn and the latter conveys it to the dust collector. In these experiments, the lawn velocity, i. e., scavenging speed, the velocity of air flow in the channel, the air jet velocity and the arrangement of the blow tubes are altered, and the rates of collection are examined. The effect of these conditions on the rates of collection, and the optimal conditions for a high rate of collection and uniform scavenging are clarified.

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To predict the performance of centrifugal pumps under gas-liquid two-phase flow conditions, a consistent one-dimensional, two-fluid model with fluid viscosity and gas-phase compressibility in a rotating impeller is proposed by considering the energy transformation of the flow discharged from the rotating impeller to the stationary spiral casing. The two-fluid model is numerically solved for the case of a radial-flow pump after various constitutive equations are applied. The head and shaft power predicted are found to agree well with the measured values within ±20% of the normal capacity.

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There are many advantages to using a duct of small diameter (0100) and a duct fan of small scale in an air conditioning system. In this study, the performances of five kinds of fan impeller, that is, axial flow fan, mixed flow fan, centrifugal multiblade fan impellers and mixed flow multiblade fan impeller were examined experimentally to determine the optimum type of duct fan impeller. The centrifugal fan and multiblade fan were scroll-less, because fans were built completely in a duct in order to make air flow in and out in an axial direction. A mixed flow multiblade fan impeller with overhanged guide vanes gave the highest pressure, and an axial flow fan impeller the highest efficiency at the specified point.

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Noise problems caused by two-phase flows in tubes connected to air-cooled heat exchangers have become more serious, since the level of air conditioner fan noise has decreased. In particular, when a slug flow occurs, the noise level greatly increases. In this study, an air-water two-phase flow was used to create a slug flow through a capillary tube in order to investigate the mechanism of the noise. We also investigated the relationship between the gas bubble state and the pressure pulsation by changing the void fraction. The results show that the pressure pulsation level, which is proportional to the noise level, is determined by the magnitude and the density of the impact pressure pulsation caused by the expansion of the gas at the end of the capillary tube.

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he formation mechanism of Fullerene, a new type of carbon molecule with a hollow caged structure, was studied using the molecular dynamics method with the empirical potential function. The clustering process starting from isolated carbon atoms was simulated under the controlled temperature condition, where the translational, rotational and vibrational temperature of each cluster was controlled to be nearly equilibrium. The structure of the cluster obtained after sufficient calculation time depended on the controlled temperature Tc ; yielding to graphitic sheet for Tc ≤ 2 600 K, fullerene-like caged structure for 2 600 K ≤ Tc ≤ 3 500 K, and chaotic 3-dimensional structure for Tc ≥3 500 K. Through the detailed trace of precursors, it was revealed that the key feature of the formation of the caged structure was the chaotic 3-dimensional cluster of 40 to 50 atoms which had large vibrational energy. On the other hand, when the precursors were kept under lower vibrational energy, the successive growth of a 2-dimensional graphitic structure was observed.

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The formation of a fullerene was simulated using the molecular dynamics method. The clustering process starting from 500 isolated carbon atoms was simulated under nearly equilibrium conditions at Tc=3 000 K with a density of 30 times lower than that in our previous study for investigation of the effect of annealing during collisions. The small clusters appeared in this simulation were simpler than those in the previous case ; they were grown with a simple chain or ring structure for Cn≤20, a 3-dimensional chaotic structure for around C20≤n≤40, and a fullerene-like caged structure for Cn ≥40. Since the density of carbon atoms in the simulation was still high due to the computational limitation, these clusters are expected to have a much longer collision-free time in practice. For further evaluation of the effect of annealing, a C60 structure obtained from the simulation was annealed without collision at Tc=2 500 K. Through successive organized network transformations known as Stone-Wales rearrangement, a perfect fullerene-structured C60 was finally formed in about 50 ns. From the viewpoint of the Arrehenius type reaction rate of rearrangement, the high temperature of 2 500 K and the time-scale of 50 ns for annealing were comparable to experimental conditions.

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The rapid solidification in a single roller process has been used to produce an amorphous ribbon. The thermal and fluid flow in that process is accompanied by free surfaces and a phase change. Since the cooling process is carried out over a very short time period, it is difficult to measure transient temperature distribution or cooling rates directly from the experiment. The present paper proposes a numerical method which is capable of simultaneously solving the thermal and fluid flow in molten metal and surrounding air and transient heat conduction in a cooling roller. The method, based on the VOF (Volume of Fluid) method, is improved to enable simulation of a transient two-dimen-sional thermal and fluid flow with a liquid-solid phase change and free surface. We simulated the cooling process of aluminum alloy amorphous ribbon. The shape of the amorphous ribbon, flow, temperature field and cooling rate were numerically obtained using parameters of the roll velocity, the nozzle slot breadth and the gap between nozzle and roller.

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An experimental study has verified the dynamic equation of state which is derived from a thermodynamic model representing simultaneous heat and mass transfer from the water supply front to the solid-liquid interface in a liquid saturated porous medium. Measurement of pore liquid pressure at the solid-liquid interface fixed on the top surface of an Ohya-tuff specimen (the porous medium) enables us to show experimentally the relationship between temperature, pore liquid pressure and solid pressure at the interface, and liquid supply pressure. This experimental method was established by reverifying the so-called Clausius-Clapeyron equation (GCCE), the static equation for a porous medium without liquid flow. This study also clarifies the relationship between the dynamic equation of state and the GCCE on the pore liquid pressure-liquid supply pressure plane.

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A method to estimate the heat transfer coefficient between fluid gas and solid materials of a porous medium is proposed. At first, local Nusselt numbers on the heated wall of a fluid passage with a porous medium are numerically obtained for the parameter Ha, including the volumetric heat transfer coefficient, hv, between the fluid and the solid material of a porous medium in advance. Then, experimental Nusselt numbers on the wall are obtained by measuring wall temperatures and heat flux. The volumetric heat transfer coefficient, hv, is estimated by corresponding experimental Nusselt numbers to numerical ones. This method gives the longitudinal characteristics of heat transfer in the porous medium.

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The condensation heat transfer coefficients of pure refrigerants in horizontal micro-fin tubes were predicted by solving the modeled equations. In the model, film condensation on the inner fins was estimated from the total unwetted area, while the forced convection condensation heat transfer coefficient of the liquid film was set to be equal to that of the smooth tube. The predicted results showed good agreement with the experimental results, and it was shown that effects of the parameters that characterize the micro-fin tube, i. e., pipe diameter, fin height, fin pitch and fin tip angle, were well predicted. Furthermore, the high heat transfer coefficient was reproduced in the high-quality range using the present model, which assumes that the liquid phase is distributed in the valley between the grooves in this region.

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In the present study, effective thermal conductivities of wet clothing material were numerically analyzed based on a proposed heat transfer model. The following simplifications are made. The clothing material is woven with a single yarn, there is no air movement among yarns, and also mass transfer is neglected. Numerical calculations were made based on the finite difference equations of steady three-dimensional heat conduction equations for several composite materials representing wet clothing materials. The following results are obtained. The effective thermal conductivity increases with increasing thermal conductivity of yarn and of water content. It is found that the present numerical results are in good agreement with the previously measured ones. The effective thermal conductivity of wet layered materials depends on the distribution of water, and attains a maximum in the wet layer.

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We present a new theory on the scattering of radiation by real fibers in engineering systems. The theory covers the scattering by fibers consistently over an entire range of fiber sizes, from smaller than to larger than the wavelength of radiation. A geometrical technique is presented for modelling a fiber with a rough surface of 3D-selfsimilar microstructure. Scattering characteristics of the fiber are described based on an electromagnetic wave theory of diffraction, in order to investigate the relationship among three main factors of scattering:wavelength of radiation,fiber diameter and microstructure of the fiber. It is clarified that with an increase in fiber diameter and a corresponding increase in rough fiber surface microstructure, the scattering changes from a particle scattering-type to a surface scattering-type. The transition occurs in the size parameter range of P=100-300.

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Several models to estimate the effective thermal conductivity of fibrous layers for radiative heat transfer are compared with these calculated using the Monte Carlo method. The models assuming isotropic scattering are shown to underestimate the effective thermal conductivity, and the model based on the two-flux model assuming the Milne-Eddington approximation is demonstrated to agree very well with the results obtained using the Monte Carlo method. When the incident radiation to the glass-fiber layers has spectral variation, the estimated thermal conductivity obtained assuming that the incident radiation is monochromatic with the peak wave-length differs from the one obtained considering all the incident spectral variation. For nickel-fiber layers, the difference is shown to be 15% or less.

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Infrared thermography is applied to measurement of turbulent heat transfer in order to investigate its applicability under near-ambient conditions. Natural convection along a vertical smooth flat plate and forced convection along a smooth flat plate are realized in a large darkroom, where individual heat transfer coefficients are quantitatively measured using infrared thermography in the laminar, transition and turbulent regions. The measurement error is then estimated using ANSI/ ASME PTC 19.1-1985 measurement uncertainty to confirm the accuracy. It is obvious from a series of application experiments and error analyses that the present technique is useful for estimating turbulent heat transfer quantitatively and dynamically. Infrared thermography is an appropriate measurement procedure for engineering applications because it can be applied to diagnose a twodimensional and dynamical temperature field instantaneously and nondestructively.

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We describe the investigation of the optical characteristics of four thermosensitive liquid crystals. Spectral characteristics are measured using a spectrometer, and their optical properties are evaluated using a CIE 1931 standard calorimetric system, XYZ. The peak position of the spectrum moves from the long-wavelength side to the short-wavelength side with temperature increase. The wavelength of maximum intensity does not show hysteresis for the temperature increase and decrease. The wavelength of maximum intensity and the hue value are well correlated with temperature. The spectrum distribution moves to the short-wavelength side with increase of the measuring angle. The wave change is not dependent on temperature.

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The present study describes the development of a thermometer to rapidly determine temperature from the color of thermosensitive liquid crystal using photodiodes. The output of photodiodes was calculated from the spectral characteristics of liquid crystal and the spectral sensitivity of photodiodes. In the experiment, reflected light on liquid crystal was measured in the steady state by two kinds(DC-50 kHz and DC-100 kHz)of avalanche photodiodes (APD) which have different spectral sensitivity. The ratio of each APD output was correlated with temperature. The speeding up of temperature measurement was realized by connecting this system to an oscillograph.

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This paper describes the use of our previous study's prediction procedures for thermal resistance and pressure drop in the optimization of heat sink geometries for impingement air-cooling of LSI packages. Two types of heat sink are considered : those having longitudinal fins and those with pin fins. We optimized the heat sink geometries by evaluating sixteen parameters simultaneously, including fin thickness, spacing and height. For the longitudinal fins, the optimal thickness was found to be 0.12-0.15 mm, depending on which of the four types of fans were used. For pin fins, optimal pin diameters were 0.39-0.40 mm. Under the conditions of constant pumping power, the optimal thermal resistance of the longitudinal fins was about 60% of that of the pin fins. For both types of heat sinks, the optimal thermal resistance by four off-the-shelf fans was only slightly (max. about 1%) higher than the theoretical optimum for the same pumping power. When manufacturing (cost-performance) is considered, the economically best fin thickness and diameter become about 5 to 10 times higher than the optimal values calculated without respect for manufacturing costs. Those values almost correspond to the actual limits of the extrusion and press heat-sink manufacturing processes.

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We investigate the heat storage characteristics of a cylindrical heat storage vessel packed with hollow spheres including paraffin wax as a solid-liquid phase change material. Aqueous ethylene glycol solution as a working fluid is introduced into the cylindrical heat storage vessel at a constant temperature and flow rate during the heat storage process. It is found that an increase in the temperature of the incoming working fluid prolongs the completion time of the heat storage process in the case of working fluid flowing at low velocity. Increasing the velocity of the working fluid results in a reduction of the completion time of the heat storage process. A nondimensional correlation equation of Fourier number expressing the completion time of the heat storage process is derived in terms of modified Stefan number, modified Reynolds number and Prandtl number.

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Predominant resonance can occur in flow-induced noise from an expansion-cavity-type muffler for particular combinations of muffler configuration and flow velocity. This phenomenon is caused by self-excited oscillation based on the feedback response from acoustic resonances of the muffler to shear flow. Usually, the sound pressure level is much higher when predominance of tail pipe resonance rather than cavity resonance occurs. The predominance of tail pipe resonance is shown to be strongly influenced by both the frequency characteristics of acoustic amplification of the tail pipe and the frequency of velocity fluctuation with a certain phase criterion. The predominance phenomena can be generalized using a new dimensionless independent variable, (L/l')(1/M), where L, l' and M are cavity length, acoustically equivalent tail pipe length and Mach number in the tail pipe, respectively.

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A simulation model for predicting air quality along urban main roads is being studied. The objective of the model is to predict the effects on air quality of various road-related parameters such as configurations of roads and surrounding buildings as well as traffic flow, chemical reaction, and other related phenomena. In this paper, the development of an atmospheric diffusion model, which will be the platform of the whole simulation model, is reported. A new concentration diffusion coefficient model is proposed, in which the effect of vehicle wind is taken into account. By comparing with field experiments in which the diffusing tracer gas concentration was measured in a real street canyon, the validity of the simulation model is verified. Also the new diffusion coefficient model is found to be capable of improving predictive accuracy of air quality around the street canyon.

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The effects of DC or AC (14 kHz) corona discharges, formed between the apexes of opposed needle electrodes, on the soot emission of a propane turbulent diffusion flame were investigated experimentally. The coronas were applied across the lower part of the flame, where soot inception occurs, or across the middle part of the flame where both agglomeration and oxidation of carbon particles proceed. On application at the lower part, with a gap width as the electrode apexes are located outside the reaction zone, a marked reduction in soot emission was observed in cases of both DC and AC corona discharges, suggesting that this reduction is not caused by entrainment or corona wind alone. The charged particles, added to the flame, are mostly produced in the vicinity of the apexes of electrodes where maximum field strength exists. As for the mechanisms of the soot reduction, the increased charged-particle density observed in the middle and upper part of the flame seems to play a role.

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This study describes a novel technique for obtaining transient measurements of a chemical species in combustion fields by applying the infrared absorption method. Thus, it is expected that the actual chemical species and fuel vapor concentrations in the flame should be detected in situ inside the combustion engines as well as in gas turbine engines. In general, the absorption spectrum of the chemical species depends on the pressure, concentration, temperature, and optical path length. As a first step, the absorption spectrum of the chemical species (CH4, CH2, CO) was measured with calibra-tion cell by means of the FTIR (Fourier Transform Infrared Spectroscopy) method. The temperature ranged from 300 K to 800 K under constant pressure and constant gas concentration. The tempera-ture dependence of the absorption spectrum was applied to the measurement of the chemical species in a CH4-Air premixed steady-state burner flame at the atmosphere state. The validity of this measurement method was investigated.

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Exergy regenerating combustion is aimed at direct extraction of high-quality energy, such as electric power, light, mechanical work from combustion. In an isothermal expansion process, all energy released by combustion is converted to external work. If the internal heating is utilized in the compression process, we can obtain a higher pressure ratio as well as high temperatures at the same compression ratio. A new gas turbine cycle based on isothermal expansion combustion and polytropic compression are proposed. Different from conventional views, the feature of this cycle indicates that the target of gas turbine is a high pressure ratio rather than a higher peaking temperature. In comparison to the case of a conventional gas turbine, higher efficiency is expected due to the high pressure ratio. Inasmuch as the temperature of exhaust gas is identical with maximum, it is plausible for combined cycle. In addition, related combustion schemes are briefly discussed.

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The hot surface ignition of methane-air mixtures in microgravity has been studied experimen-tally and numerically. Experiments on the ignition of the mixtures with electrically heated nickel wire and platinum wire in microgravity have been performed. Numerical calculations, including the catalytic reaction rate for platinum, have been performed to understand the experimental results obtained in microgravity. The ignition delays and ignition temperatures for a wide range of equivalence ratios were investigated. Experimental results show that the ignition temperatures with platinum wire have a maximum near the stoichiometric mixture ratio, while those with nickel wire increase as the equivalence ratio increases. Ignition temperatures with platinum wire are higher than those with nickel wire. Numerical results show that reactants next to platinum wire are consumed by the catalytic reaction. Therefore, a higher temperature is required to ignite mixtures with platinum wire. The catalytic inhibition of hot surface ignition is simulated successfully by the numerical model.

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In this study, we investigated the relationship of indicated mean effective pressure (IMEP) for a spark ignition engine under lean combustion with the cyclic variation of mass fraction burned by measuring the energy release from the spark plug, inteasity of the light emission from the flame and the cylinder oressure at the same time. In orde _o minimized an error in the initial and late combustion s ages of the mass fraction burned to be obtained by cylinder pressure, spark plug energy and intensity of light emission were measured. As a result, it was found that there are three main causes of cyclic variation of IMEP. These consist of the burning speed during the initial stage of combustion, variation in the total mass fraction burned, and variation of the late burning during the late expansion stroke. Thus, we determined that there is a favorable interrelationship between the IMEPs and the corrected mass fraction burned.

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In order to elucidate the pyrolysis process, in which droplets of cerium nitrate solution are altered upon denigration into cerium dioxide particles, the effects of the temperature of the surround-ing air, and the initial cerium concentration and normality, upon the droplet temperature, shape, composition, internal and external shape of produced particle and rate of reaction were examined. The pyrolysis process of the cerium nitrate droplet was categorized into four phases : evaporation, foaming, formation of the solid phase and pyrolysis. Correspondence between the time series of the droplet temperature, shape and composition was well recognized. Therefore, it might be possible to understand the dynamics of the pyrolysis process through measurement of the droplet temperature. Furthermore, with increase of the initial cerium concentration, the heating rate of droplet tempera-ture showed sharp, the foaming period and the formation solid-phase period became shorter, and the produced particle was composed mostly of cerium dioxide when the air temperature was above about 600K, resulting in well-crystallized particles. Under about the air temperature, the reactions were moderate, the reaction rate was low and the particle composition included water and nitrate.

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Three-dimensional numerical analysis of fuel liquid and mixture behavior in a port-injection gasoline engine is assessed by comparing calculations with measurements. The fuel mass distributed in the intake port and cylinder is measured using an engine with hydraulic valves and gas sampling system. The experimental results show that about half of the fuel mass per injection enters the cylinder, and the rest stays in the port. The difference in the mass fraction of injected fuel directly entering the cylinder is small between the cases of single pulse injection and serial injection. Therefore, using three-dimensional calculation presupposing single pulse injection is difficult for predicting the in-cylinder mixture formation process, although it can be used to analyze the amount of fuel wetting the port wall. The calculations are performed for a port-injection engine, and the differences in fuel behavior with respect to swirl control valve opening and wall temperature are discussed.

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The realization of a rich mixture combustion in the prechamber, the reduction of flame tempera-ture and the promotion of diffused combustion are of the utmost importance in improving the particulate and NOx emission from an indirect injection (IDI) diesel engine. The author studied a simple estimated method of particulate and a new combustion system in a four cylinder diesel engine with a 94 mm bore and a 120 mm stroke. The simple estimated method of particulate, which is calculated by smoke and HC concentration, was proven to be effective. The new combustion system, which features a refined jet passage and utilization of the interference of the jet passage and the piston top surface, was proven to reduce the particulate and NOx emission.

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Cycle-to-cycle changes in diesel exhaust gas emissions were investigated under two transient operation patterns. One is"interval step increasing load", where the fuel amount is rapidly decreased from high to low load, and after an interval, Δtint, the fuel amount is abruptly returned to the initial level. The other is "ramp increasing load", where the fuel amount is increased gradually. With the exception of immediately after a step increase in the fuel amount, THC concentration was almost completely determined by the piston wall temperature and the fuel amount. THC concentration immediately after a step increase in the fuel amount was much higher than that of the corresponding steady state operation with the same piston wall temperature. This overshoot concentration, ΔTHC,was almost constant when the interval,Δtint, was changed and can be suppressed by using ramp increasing load. The concentration of the other emissions were mainly determined by the fuel amounts while NOx increased slightly with increases in piston wall temperature.

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The shaft work calculated using the Schmidt model and the mechanism efficiency determined applying SENFT theory have been used to obtain by an analytical method the optimal values, at which shaft work becomes maximum, of engine compression ratio and average pressure of a low-temperature-difference Stirling engine. As a result, it was found that a low-temperature-difference Stirling engine must have a lower compression ratio than a high-temperature-difference Stirling engine to a drive the same mechanism efficiency.

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In this study, the friction force and slap motion of a piston in a gasoline engine were measured to determine the friction characteristics at the piston skirt. It was found that the increased friction force of the piston during the first half of the expansion stroke is caused by metal-to-metal contact at the upper part of the piston skirt. It was demonstrated that the friction force at the expansion stroke increases as the skirt width decreases. In addition, reducing the roughness of the skirt and coating it with resin effectively reduced the friction.

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Vol. 63 (1997) No. 609 p. 1805
修正箇所：右側
修正内容：
（誤） … 山下博士…9月掲載予定.
（正） … 山下博史…3502-3509.

抄録全体を表示