To clarify the effect of velocity ratio on the control of large-scale structures in mixing layers, two-dimensional spatially developing mixing layers perturbed periodically were studied using direct numerical simulation. The perturbation consists of fundamental and subharmonic modes of the most unstable wave based on linear stability theory. The results show that it is possible to control the development of large-scale structures by controlling the initial phase difference between two modes, and that there exists a certain initial phase difference which suppresses vortex pairing. This initial phase difference varies with the velocity ratio. The downstream variations of the phase difference between fundamental and subharmonic modes of streamwise velocity fluctuation were also investigated. In the linear growth region, the local phase difference increases at a constant rate which varies with the velocity ratio. This linear increase of phase difference is explained by the dependence of phase velocity on the velocity ratio, which is derived from the linear stability theory. Because of this linear increase of phase difference, the initial phase difference which suppresses the pairing varies with the velocity ratio.

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The simple mechanism of the vortex formation behind a circular cylinder is visualized using two LDVs and FFT-spectrum method. The present method can more easily eliminate the FM-AM modulations of the fluctuating velocities than the phase-average method. These distribution based on the mean and fluctuating velocity components clearly indicate a simple mechanism of vortex formation in a cycle. Namely, in the mean flow, the stationary symmetric twin vortices exist in the dead water region as well as in the stationary thin vortex layers along the upper and the lower separated shear layers. In the periodically fluctuating flow, however, an unsteady vortex whose center is on the x-axis is generated just behind the cylinder and moves within the wake. Therefore, a large vortex forms asymmetrically in the dead water region, as the stationary thin vortex layers and the unsteady vortex interact, affecting one another's vorticity and kinetic energy.

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This paper deals with an experimental study on the flow visualization of cavitation for steady and unsteady flows in cylindrical chokes of oil hydraulics. Experiments for the unsteady flow are carried out under a condition in which the inlet pressure p₁ in the cylindrical choke takes a trapezoided form with time, while keeping the outlet pressure p₂ constant. The behavior of the cavitation bubbles is clarified with an ultrahigh-speed camera under two geometric parameters: the diameter and the chamfered length of the choke. Also, a method for suppressing the occurrence of cavitation is studied. It becomes clear that a bubble which appears in the earliest stage of cavitation "grows, collapses, disappears and reappears repeatedly" at intervals of about 1.0x10^-4 seconds.

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The bronchi in the respiratory system are composed of many bifurcations. Gas mixing is expected to be induced by the asymmetry of axial flow during respiration and secondary flow through the bronchi. In the present study, the axial and transverse velocities through a symmetrical bifurcation simulating the bronchi in lung are measured by two-dimensional LDV in the sinusoidal oscillating flow. In the model, both daughter tubes bifurcate at 35 degrees symmetrically. The area ratio of both daughter tubes to the mother tube is 1.125. Consequently, it has been clarified that the axial flow is asymmetrical during the oscillation and the secondary mixing is enhanced around the flow divider of the bifurcation.

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The purpose of this experimental study is to investigate the effect of liquid viscosity on the flow patterns of upward air-liquid two-phase flow in a vertical tube 19.2mm in inner diameter and about 5.4m in length. Three different liquids, including water and aqueous glycerol solutions, were employed. Kinematic viscosity of these liquids varied from 1.0×10^-6 to 14.7×10^-6m²/s. The flow patterns were observed using a video recorder and still photography. The time-spatial characteristic maps of gas-liquid interfaces which were drawn using the mean liquid holdup signals detected by 70 pairs of holdup sensors arranged with the axial spacing of 15mm over the length of 1.035m were also used. In this report, we first defined the flow pattern of each flow. Next, the effects of liquid viscosity on the overall flow pattern and interfacial structures or the interfacial waves were discussed. Finally, based on those results we proposed flow pattern maps for each liquid viscosity. It is found that the flow pattern transitions strongly depend on the liquid viscosity.

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A numerical method for analyzing the 3-D unsteady incompressible viscous flow with complicated boundaries or irregular shaped grids is proposed. In this method, the unsteady Navier-Stokes equations in terms of the primitive variables are solved using a time-splitting method and the convective-difference scheme which is stabilized by means of the TVD conception. Poisson's equation for pressure is integrated using Gaussian Integration in order to remove the spurious errors, and solved by the iteration scheme. For irregular grids the finite-difference operators derived by the least squares polynomial approximation are used. As a numerical example, a complex recirculating flow in a three-dimensional cavity was calculated.

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We present a study on the effects of passive control on interaction of an oblique shock wave with a turbulent boundary layer. The experiments were carried out in a 10×8cm² supersonic wind tunnel at a free stream Mach number of 1.97. The incident oblique shock wave impinging on the porous wall of the floor of the test section was generated by a wedge mounted at the center of the test section. The effects of the passive control were studied by varying the porosity of the porous wall from 0% (solid) to 20% at various shock wave angles. Surface static pressure measurements and Schlieren observations as well as measurements of the blowing/suction velocity at the porous wall were made. It was found that for strong shock the reflected shock moves to the starting point of the porous region and the surface pressure increases linearly from this point. Furthermore, for a 5% porous wall the normal velocity was of the Darcy type and was about 30% of the main flow velocity.

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Fundamental characteristics of underwater shock waves generated by underwater explosion of high explosives are investigated by both experimentally and by numerical simulation. The attenuation process of the underwater shock wave is also investigated theoretically using a method of characteristics. Slab explosives are used in the experiments. Streak photographs are taken by a high speed camera using a conventional shadowgraph system. When the detonation wave propagates into the explosive, the underwater shock wave is generated at the boundary between the slab explosives and the water. The incident angle of the underwater shock wave is the same as that obtained by the impedance matching method between the explosives and water. The angle then changes due to the effects of interaction with the expansion wave occurring due to the expanded product gas. The attenuation process of the underwater shock wave is well explained by the method of characteristics.

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The mean velocity and turbulent field in a three-dimensional turbulent boundary layer on a thin cylinder rotating in a uniform stream are examined experimentally. Measurements of mean velocity and all Reynolds stresses are made by means of a single rotatable hot-wire method. Mean velocity distribution is well represented in the relative main flow direction with respect to the rotating cylinder by a logarithmic law deduced in an earlier study. Johnston's logarithmic law for 3-D turbulent boundary layers also accurately describes the present flow. Although turbulent intensities and Reynolds stresses all increased with rotation speed of the cylinder, their distributions are well represented by non-dimensionalization using the resultant velocity of the main flow and the peripheral velocity of the cylinder. Both eddy viscosities and mixing lengths increase with the rotation speed, and there is no evidence of isotropic eddy viscosity.

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The drawbacks of the dynamic sub-grid scale eddy viscosity model proposed by Germano et al. in 1991 are that homogeneous direction of turbulence is required to eliminate numerical instability due to negative eddy viscosity and that the model is unable to predict sub-grid scale turbulent energy backscattering from sub-grid scale to grid scale. In the present study, the localized dynamic sub-grid scale model proposed by Meneveau et al. in 1994 was utilized with the mixed sub-grid scale model proposed by Vreman et al. in 1994 to eliminate these shortcomings. A newly developed eddy viscosity type sub-grid scale model was used instead of Smagorinsky's model which does not require the local equilibrium state of SGS energy. The proposed model was tested by simulating turbulent channel flow at Re=180 normalized by channel-half width and friction velocity. The results showed good agreement with direct numerical simulation data obtained by Kim et al. Relationships between the turbulent coherent structures and the Grid scale turbulent energy dissipation by the SGS model were also investigated. Some advantages of using the scale similarity model to simulate turbulent coherent structures were pointed out.

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To develop a better understanding of gas and particle motion in a turbulent fluidized bed we have numerically solved the locally averaged three dimensional Navier-Stokes equations and the Lagrangian equations of particle motions taking into account the collisions between particles and the mutual interactions between gas and particles. Finite difference methods were used. In this simulation locally averaged variables such as gas velocities were obtained by averaging point variables over a very small region which is one computational cell. Small stress terms caused by the fluctuations from the locally averaged values are considered in terms of the subgrid scale (S. G. S) model. To calculate collisions, particles were treated as hard spheres of which the collision time is zero, that is, a collision occurs between only two particles. The calculated results well describe large-scale unstable gas and particle flows induced in turbulent fluidized beds. Also the results are in fairly good agreement with the measured turbulent characteristics in a coarse particle turbulent fluidized bed in which the particle concentrations are relatively dilute. Therefore the simulation can be used to quantitatively predict the gas and particle motions in a coarse particle turbulent fluidized bed.

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Numerical analysis is used to investigate three-dimensional turbulent structure and fluid flow behavior in a circular-to-rectangular transition duct. Turbulent flow through a circular-to-rectangular duct is characterized by streamwise curvature and streamwise vorticity embedded in the boundary layer. In the calculation, an algebraic Reynolds stress model together with a boundary-fitted coordinate system is applied to to a circular-to rectangular duct in order to solve anisotropic turbulent flow precisely. The calculated results are compared with the experimental results to examine the validity of the present method. As a result of this calculation, it is found that the present method predicts well a secondary flow pattern which develops into a discrete vortex pair along the duct sidewalls. This secondary flow arises as a result of lateral skewing of the near-wall flow in the vicinity of the sidewall induced by transverse pressure gradients associated with wall curvature. Moreover, the calculated contours of six Reynolds stress components are shown for comparison with the experiment. The distortion of Reynolds stresses by the vortex pair is clearly observed as well as the primary flow. Although agreement is not perfect, the main features are reproduced by the present method using the algebraic Reynolds stress model.

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The compression wave discharged from the open end of a tube causes positive impulsive noise. Active noise cancellation, which is cancelling of noise by the addition of an inverse wave, is a useful technique for reducing impulsive noise. We present a design for a negative impulsive wave generator utilizing unsteady mass influx. The generator consists of a vacuum chamber and a movale valve. In order to increase the strength of the negative impulsive wave, the effect of value geometry on the impulsive wave has been clarified, and a suitable choice of design factors has been suggested.

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This paper describes acceleration of the numerical simulation for chemical vapor deposition (CVD) step coverage problems. The CVD process is used to deposit thin films during LSI production. The thin film deposition process is generally simulated using a combination of the direct simulation Monte Carlo (DSMC) method and trench profile evolution, but much time is required to compute a trench filling shape when sticking probability is small. In the present work, reduction of the computation time was achieved by parallel processing using an engineering workstation (EWS) network system and stick-at-all-the-reflection-points (SARP) method which was newly developed. In the former case, more than 85% parallel efficiency on a 20-EWS system was achieved. In the latter case, computation was more than 780000 times faster than by the conventional method when an experimental poly-Si deposition process was considered.

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Laminar drag reduction for Newtonian fluids in highly water-repellent ducts has been reported. Measurements were carried out to investigate pressure losses in square and rectangular horizontal ducts with highly water-repellent walls and with wetted walls, with aspect ratios of 1.0 and 0.5, respectively. Tested fluids were tap water and aqueous solutions of glycerin at concentrations of 10 and 20 wt%. The maximum drag reduction ratio of tap water was about 22% for ε=1.0. The friction factors in highly water-repellent wal ducts in laminar flow region sifts parallel to the exact solution curve, which was obtained by assuming no slip conditions. These results suggest that the principal cause of drag reduction is fluid slip on the wall.

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The three dimensional motion of all particles in a rotating mixer with two baffles was calculated using a discrete particle simulation. The effects of the baffles on the motion of the particles and on particle mixing were studied. It was found that the mixing curve, which shows the relationship between the degree of mixing and time, agreed well with previous experimental results, qualitatively. The present simulation predicts that there is an optimal baffle length for particle mixing and that deformation pattern of the particle bed is affected by the baffles.

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In-pipe mobile micromachines have many applications including micro-maintenance robots for nuclear reactors and are expected to be realized in the near future. To realize practical in-pipe mobile micromachines, microactuators with sufficiently high output power are necessary and we have proposed the bellows microactuator which utilizes fluid power. In this study, an inchworm in-pipe mobile micromachine which can traverse branched pipes is fabricated using the bellows microactuators and its performance is examined. First, the performance of displacement magnification mechanisms useful in micromachines is theoretically investigated and the effectiveness of a pulley mechanism is proved. Secondly, the structure of the in-pipe mobile micromechanism is investigated. A bending and propelling mechanism using pulley mechanisms with 1 bending DOF is proposed and the structures of the front and rear supporting mechanisms are devised. Also the traveling sequence in branched pipes is theoretically investigated. Finally, an in-pipe mobile mechanism 25mm in diameter is fabricated and traveling experiments in straight and Y-shaped pipes are conducted. It is clarified that the traveling velocity in a straight pipe is increased from the output velocity of an actuator and the fabricated mechanism is able to traverse a Y-shaped pipe.

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Optical observation using a polarizing microscope was performed for flows of liquid crystalline polymers through rectangular channels containing a cylinder. Test fluids used were 50 and 60 wt% aqueous solutions of hydroxypropylcellulose. Highly birefringent areas were observed around the cylinder. Long black lines which seemed to correspond to streamlines, and cyclic black arcs which were produced in the diverging flow region, were observed. The disturbance of orientation was caused by the diverging flow just behind the cylinder, and remained far downstream. The highly birefringent line was present behind the cylinder along the centerline, and after the cessation of the flow, band texture was observed on this line.

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A water turbine through which fish can pass is studied in optimum-load operation. In order to examine the effects of the pressure and flow velocity on fish passing through the runner, four casings are used: one straight, two diffusers and one draft tube. A single stage axial runner is used. From the results of the measurement of the velocity and pressure distributions inside the turbine casing, the negative pressure and the flow velocity in which fish can swim are investigated. The kinds of fish tested are amago salmon and rainbow trout. Photographs of fish passing through the rotating runner are taken and analyzed.

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Experimental studies were performed with the objective of developing a jet pump to be used in new nuclear reactors in which the flow ratio (driven to driving flow rates) is relatively high compared to that of conventional jet pumps. Three series of experiments under atmospheric pressure and room temperature conditions were carried out for jet pumps having five nozzles, seven nozzles, and seven nozzles with swirling. The swirling flow was produced in the throat by inclining the six nozzle tips toward the circumferential direction of the pitch circle. It was shown that the maximum efficiencies of these three jet pumps were between 27 and 30 percent. Test results for jet pump having seven nozzles with swirling show slightly higher efficiencies than that without swirling. Measurements were made on pressure distributions and two-phase flow characteristics under the cavitation condition. Comparisons are also discussed between the measured and calculated efficiencies, considering the mixing effect in the bellmouth of the jet pump throat inlet.

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In this paper, we report the dynamic behavior of gases and projectiles in a single-stage gas gun. Although the one-dimensional model for single-stage gas guns gives fairly good agreement between calculated and experimental results, it can not be used to analyze the effect of an abrupt change in the cross sectional area of real guns. Here, a two-dimensional model is proposed and numerical analyses are carried out to determine the variations in flow velocity, temperature, and pressure as well as the projectile velocities by applying the finite difference method to the two-dimensional Euler equations. The numerical results were compared with the experimental results and those obtained using the one-dimensional analysis.

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A quantitative analysis of critical heat flux (CHF) under high mass flux with high subcooling at atmospheric pressure was successfully carried out by applying a new transition region model for a macro-water-sublayer on heated walls to the existing model of a vapor blanket over the macro-water-sublayer. The CHF correlation proposed in this study could predict well the existing experimental data obtained for water mass flux of 940 to 20 300kg/m²s using circular tubes of 2 to 4mm in diameter and 30 to 100mm in length with inlet subcooling of 30 to 90°C and rectangular channels heated from one side with gap of 3 to 20mm, length of 50 to 305mm and inlet subcooling of 30 to 77°C and revealed a unique feature of CHF that the effects of wall friction of subcooled boiling flow and the velocity of the steam blanket above the macro-water-sublayer at atmospheric pressure become the dominant factors while those were not dominant at higher pressures.

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Local heat transfer and pressure drop measurements were made during condensation of CFC 11 in microfin tubes. A smooth tube and two microfin tubes with different fin dimensions were used. Flow observation study with use of an industrial bore-scope revealed that the condensate swirled along the grooves, and a thick condensate film covered fins in the lower part of the tube in the low quality region. Static pressure gradients in the microfin tubes were up to 70 percent larger than that in a smooth tube. A correlation equation for the local frictional pressure gradient was derived, in which the effect of refrigerant mass velocity was introduced on the basis of the flow regime consideration. The measured frictional pressure gradient data were found by the present method to have a mean absolute deviation of 8.3 percent.

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Evaporation heat transfer coefficients depend on the mass flux and quality. When a non-azeo-tropic mixture is used as a working fluid, this dependence is significant due to the suppression of nucleate boiling. It is possible to improve the heat transfer performance if the channel cross-sectional area is enlarged at the latter part of the evaporator, namely, the mass flux is reduced in the high-quality region where the pressure drop is large. This work involves an analytical investigation on the enhancement effect by varying the channel cross section. It was assumed that the working fluid was a mixture of refrigerants R 123 and R 134 a, and that the tubes used were smooth or spirally grooved. As a result, the heat transfer area and the channel volume were reduced by more than 20% when the pressure drop is permissible enough.

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The transmission property of water and sodium chloride-water solutions with various salinity concentrations was clarified using spectra. This paper deals with the measurement of the spectral transmittance and the calculation of the total transmittance for water and NaCl-water solutions. The spectral transmittance of the NaCl-water solution over the infrared and nearby regions increased with increasing salinity concentration for constant specimen thickness and air mass. It was found that the spectral transmittance was useful for precisely calculating of the thermal performance of a solar pond, and by using an effective absorption coefficient, a 5-partition method dividing wavelength into five bands by which the total transmittance up to a water depth of 3m could be calculated, was found to be important practical example of solar pond technology.

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The device considered in this paper is a porous stud having microchannels running in three orthogonal directions, and was designed to enhance boiling heat transfer for liquid-cooled electronic components. The characteristics of boiling incipience at the microstructures on the porous stud were investigated. Experiments were performed to determine the temperature hysteresis during stepwise input of heater power Q to a simplified two-dimensional structure composed of parallel microchannels (cross section=0.3mm×0.5mm or 0.3mm×1.5mm). It was shown that wall superheating at incipience of boiling is almost independent of Q and channel cross section, remaining at a level of 10∼14K. Therefore, with increasing Q, temperature overshoot decreases. We also gave an analytical explanation, based on a transient heat conduction equation, for the mechanism of the incipience of boiling in the microchannels. Finally, using these results, the boiling incipience at the porous stud was explained.

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Flow visualization of the behavior of a large particle in a fluidized bed was conducted using neutron radiography. The large particle moved according to the bed materials, especially in the wake of a bubble. When the density of the large particle was high, the particle moved with a velocity different from that of bubble, and in some cases the particle moved downward through a bubble. When the density was low enough, the particle moved on the surface of the bubble wake. The drag force of the large particle immersed in the fluidized bed was measured. The drag force increased with increase in the volumetric gas flux as well as with increase in the particle diameter. The drag coefficient was derived and was well correlated on the basis of a two-phase model and experimentally determined effective viscosity of the bed materials.

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It is important that SiO₂ isolation film around aluminum connection lines has a flat surface in order to realize high-density devices. In this study, the transient change in liquid-SOG (spin-on-glass) film thickness distribution on a two-dimensional micro-grooved substrate during shrinkage was analyzed. Surface tension flow of the film was calculated. As the film was thin, boundary layer approximation was applied, and fourth-order equations of the film thickness were solved by an iteration method. The viscosity and the shrinkage rate were assumed to be functions of the concentration of the solvent in the film. When the value of [(surface tension)/{(shrinking speed)/(viscosity)}] is large and the width of projections is small, final surface undulations of the film are small. The effect of centrifugal force was also analyzed.

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Three-dimensional numerical calculations have been performed to simulate the viscous and porous inertia effects on the pressure drop in a non-Newtonian fluid flow through a porous medium. Cubes placed in an infinite space have been proposed as a three-dimensional model of microscopic porous structure. A full set of three-dimensional momentum equations is solved along with the continuity equation at a pore scale, so as to simulate a flow through an infinite number of obstacles arranged in a regular pattern. The microscopic numerical results, thus obtained, are processed to extract the macroscopic relationship between the pressure gradient-mass flow rate. Comparing the results based on the two- and three-dimensional models, it has been found that only the three-dimensional model can capture the porous inertia effects on the pressure drop correctly.

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The instantaneous heat transfer coefficient, particle volume fraction and particle velocity around a tube immersed in a fluidized bed were simultaneously measured, using glass beads with average diameter of 0.42mm and 1mm as fluidized particles. The measured results were analyzed by the conditional averaging method, distinguishing particle contact from no particle contact. The relationship between the local average heat transfer coefficient and the particle volume fraction during particle contact, on the lower side surface of the tube for the 0.42mm particles and on the entire tube surface for the 1mm particles, is consistent with Kunii's large particle model.

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Three-dimensional simulations of an unsteady separated and reattached flow and the heat transfer over a blunt flat plate are presented. The Reynolds number used is 5000. The vortices shed from the reattachment flow region have a hairpin-like structure. These large-scale vortex structures greatly influence the heat transfer in the reattachment region. The present results are compared with the previous three-dimensional calculations at a low Reynolds number and there is no essential difference between the two results with respect to flow structure. The reattachment length is about five plate thicknesses, which is the same as that observed in previous experiments. The velocity distributions and turbulent intensities are in good agreement with the experimental data. However, the Nusselt number and temperature distributions are different from the measured ones.

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We present numerical calculations of the generation, the growth and the impingement of a thermal plume in a two-dimensional buoyancy induced flow. Numerical values are obtained for aspect ratios H/W=1/4, 3/8, 1/2, Grashof numbers Gr=10⁴, 10⁵ and Prandtl number Pr=170. Impingement heat transfer on the upper wall is evaluated for various times. Numerical results show that before a thermal plume impinges on the upper heated wall, the thermal conduction layer near the upper wall becomes thinner and local heat transfer takes peaks. Local Nusselt number approaches steady situation after the impingement of a thermal plume. The stream function takes the symmetrical form of two ellipses under the present conditions.

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This paper describes the thermal analysis of a notebook personal computer (PC). A numerical analysis was carried out for the whole domain of the PC, excluding the display. The numerical model includes Si chips, packages, printed circuit boards (PCBs), casing, etc. Thus the model includes almost all the parts of the computer. To reduce computational load, the thermal analysis was divided into two stages. The calculation was performed on an EWS. Measured and calculated temperature rise of the electronic parts showed good agreement. This led to the conclusion that the present thermal analysis method can be a useful tool in the design of notebook PCs.

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Time-series information on both the cross-sectional mean liquid holdup along the tube axis and the gas-liquid phase distribution along a tube diameter was obtained by means of supermultiple-cross-sectional holdup probes (S-CHP) and semi-supermultiple-point-electrode probes (SS-PEP) for vertical downward gas-liquid two-phase flow. Typical time-spatial maps of wave behavior and gas-liquid interfacial profiles are presented. Close inspection of these results reveals that huge waves and disturbance waves appear in downward two-phase flow as well as upward flow. It was clarified that huge wave flow region covers a wide range of superficial gas velocity. Wave velocity, wave width and maximum liquid holdup of individual waves were examined by means of a wave-vein analysis. Probability distributions of these flow parameters were also investigated. It was found that there exist distinct differences in wave width and maximum liquid holdup between huge waves and disturbance waves.

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Wave velocities and wave widths were determined using the wave-vein analysis for a wide range of air and water flow rates. Clustering analysis by K-means algorithm was applied to distinguish between huge waves and disturbance waves for the present experimental conditions. Individual waves distinguished by clustering analysis correspond reasonably to those recognized from the relation between wave velocities and wave widths. Flow conditions for the appearance of liquid slugs, huge waves and disturbance waves were clarified. The characteristics of wave velocities, wave widths and maximum liquid holdups for huge waves and disturbance waves were discussed. Comparison between liquid slugs, huge waves and disturbance waves in terms of these flow parameters reveals that there exist distinct differences in wave widths of these waves.

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Gas-liquid interfacial porfiles in plug flow for both upward and downward flows were obtained using semi-supermultiple-point-electrode probes, comprising 67 sensing tips arranged on a tube diameter. Typical interfacial profiles are demonstrated for both flows. Close inspection reveals that four zones exist in a pair of gas and liquid slugs for the upward plug flow region and the high slip velocity region in downward plug flow. Lengths of the swelling liquid front zone and the wake zone were determined. The length of the wake zone strongly depends on the relative velocity between the liquid film around gas slug and the liquid phase in liquid slug. Characteristic distributions of bubbles within liquid slugs were found, i. e., three types of radial distributions of void fraction, namely saddle-shaped, trapezoidal and bullet-shaped distribution, exist for upward flow, while the two types except the saddle-shaped distribution exist for downward flow.

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Combustion behaviors of pulverized coal clouds suspended in a laminar upward flow were examined by heating them with a single pulsed YAG laser. Observation with a high-speed video camera revealed that only a few particles heated by the pulsed laser preceded the increase of the burning particles and the pulverized coal flame propagation. The lower limit of flame propagation of pulverized coals was determined from the relationship between suspended cloud concentration and flame propagation probability. Flame propagation velocity was also analyzed by processing of flame images. Near-the lower limit of flame propagation, propagation velocity increased with concentration and revealed its maximum depending on coal varieties and oxygen concentration in the flow. Coal containing less volatile matter showed lower maximum propagation velocity.

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An experimental study was made of the burning behavior of an emulsified fuel droplet under high pressure conditions. Fuel in water emulsions were employed, which consisted of a hydrocarbon fuel and water doped with the surfactant. The water content of emulsions was varied from 0% to 40%. Experiments were carried out at ambient pressures from 0.1MPa to 3.0MPa. The results showed that a pressure beyond which microexplosion does not take place exists, and that its value depends on the water content of the emulsified fuel. As the ambient pressure increases, the waiting time for the onset of microexplosion decreases and the intensity with which the microexplosion occurs decreases. The distribution of the waiting time is correlated with the wear out type of Weibull distribution at high pressures.

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Instantaneous and simultaneous measurements of two-dimensional temperature and velocity profiles using Rayleigh scattering images were demonstrated in a turbulent nitrogen-diluted hydrogen (H₂ 30%+N₂ 70%) diffusion flame. A Nd: YAG laser produced two pulses separated by 20μs to yield a pair of instantaneous temperature profiles. The velocity profile was derived from the Rayleigh scattering images by the cross correlation technique (RIV: Rayleigh scattering Image Velocimetry). Strain rate and thermal dissipation rate were estimated from the temperature and velocity profiles. Local temperature depression in the flamelet near the shear layer tends to occur when the flamelet inclines toward the centerline and the strain rate becomes positive and high. The thin flamelet with high strain rate is sandwiched closely between two layers with high thermal dissipation rate, inducing temperature depression and local quenching. On the other hand, a flamelet which has a broad high temperature profile tends not to have positive and high strain rate and is surrounded by layers with relatively low thermal dissipation rate.

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A numerical analysis was performed on the time dependent behavior of a premixed flame due to a concentration spot placed in front of a steadily propagating one-dimensional flame. As the flame passes through the spot, the burning velocity increases temporarily. In the one-dimensional flow field, the resulting time-dependent flame behavior disappears when sufficient time has elapsed, and the flame propagates steadily again. In a two-dimensional flow field, the induced interaction between flow field and flame configuration produces deformation of the flame configuration, which develops with time.

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The effect of oxygenated agent addition to diesel fuel on diesel combustion and emissions was investigated. Oxygenated agent addition to diesel fuel resulted in a slight change in NO_x a decrease in CO and THC, and a significant reduction in smoke and TPM specially in the higher load range. The reduction in smoke and TPM was explained reasonably by an increase in oxygen content in fuels which was almost independent of the type of oxygenated agent used. Oxygenated agent addition resulted in a slight increase in BSFC [g/(kW·h)], but did not result in a change in BSEC [MJ/(kW·h)]. Thus the thermal efficiency remained unchanged on addition of oxygenated agents into diesel fuel.

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Exhaust gas emissions and piston wall temperatures under decelerating operation when fuel amounts abruptly decreased in a small DI diesel engine were investigated and the results were compared with those in steady state and accelerating operation. Whole exhaust gas emitted during two consecutive cycles was sampled from the start of deceleration to about 3000 cycles after the start of deceleration using a newly developed gas sampling system. The results indicated that all kinds of emissions examined showed transient behavior after the start of deceleration before reaching a steady state condition corresponding to the change in the piston wall temperature, a simple exponential function of the cycle number. In particular, the THC emission during the deceleration increased gradually with decreasing the piston wall temperature before reaching a steady state concentration. The THC emissions at both acceleration and deceleration could be predicted by the concentrations at the steady state operation with the same fuel amount and piston wall temperature except immediately after the start of acceleration. The NO_x emission increased with a decrease in the piston wall temperature during decelerating operation in the same manner as in steady state operation.

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In order to reduce NO_x emission and increase the brake thermal efficiency of a stationary diesel engine, a new prechamber, which is placed at the center of a cylinder head and has a smaller volume than conventional prechamber, was installed in a single cylinder diesel engine with a 170mm bore and 180mm stroke, and it was tested to investigate its potential. The high injection pressure, and improvement of prechamber and main chamber promoted combustion and improved the brake thermal efficiency and smoke emission. The combustion temperature and thus the NO_x emission were reduced by realizing the enlargement of jet passage area. A NO_x concentration of 184ppm (13% excess O₂) at the brake thermal efficiency of 37% was obtained with this new prechamber combustion system.

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