The purpose of this study is to propose a computer simulation method using particle method to analyze the formation and collapse of primary thrombus due to platelet aggregation in the blood flow. In the employed particle method, the blood region was discretized by particles that were assumed to have the characteristics of plasma and platelet. The MPS method that was developed for incompressible viscous flow was applied to the plasma flow. It was assumed that the platelets stochastically aggregate to the injured wall, and that the probability is expressed by hypothetic attractive force. In addition, spring force was introduced to express the deformation of the aggregated thrombus as a solid-like material. Two-dimensional simulations revealed that the proposed method reproduced initial thrombogenesis, growth of the thrombus, and its destruction. The blood flow rate influenced not only the amount of the aggregated platelets, but also the speed of the formation of a thrombus and the duration until a thrombus collapsed. These results demonstrated that the proposed method is useful to investigate the process of primary thrombogenesis which is regulated under the influence of fluid mechanical factors.

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The Taylor-Dean flow through a curved duct of rectangular cross-section is investigated numerically by use of the spectral method. The calculation covers a wide range of the pressure gradient (Dean number) and the rotational speed (Taylor number) of the duct. In the present calculation, two types of aspect ratio, γ=2 and 3 are considered. Steady flow patterns of the induced secondary flow are obtained. Especially, multiple solutions appear in some ranges of the Taylor number when the secondary flows show very complicated behavior. In the case of γ=2, there appear four-vortex or six-vortex secondary flow patterns. For γ=3, flows having many secondary vortices, such as eight vortices or asymmetric flows appear. Finally, time evolution calculations of the solutions are performed. It is found that an unstable solution approaches a stable solution if it exists, while the flow oscillates periodically if there exists no stable steady solution.

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The flow through an abrupt expansion pipe has a large annular vortex region after the expansion. The negative pressure in this region causes a magnificent flow resistance. In this study, the reduction of the flow resistance by mounting a small ring shaped obstacle on the downstream pipe wall is newly shown and examined. Backward flow in the vortex region was reduced by mounting an obstacle. As a result, it was made clear that the obstacle of height 0.8H (H : step height) makes flow resistance smaller, and optimal distance of the obstacle from expansion is about 2H. In this case, the flow resistance is reduced by 26%. This new simple method is very useful for for a relatively large pipe and duct system.

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A gas-liquid two-phase flow through vertical sudden contraction pipe is an area that still little is known, although its application can be seen in many industrial and hydraulic components. In this study, the mean and fluctuating flow characteristics of a vertical upward gas-liquid two-phase flow through sudden contraction pipe is studied experimentally and visually, while a new simple method of controlling the flow in order to reduce the flow fluctuation is shown. The bubbly flow upstream the contraction changes to an intermittent and fluctuating flow downstream the contraction, depending on a formation of thick and thin bubble swarms. When mounting a ring-shaped obstacle before the contraction, the vortex generation at the contraction area is reduced. That is, the flow is suggested by mounting a ring-shaped small step before the contraction to lead to flow control where the fluctuating amplitude can also be suppressed. The effects of Reynolds number, void fraction and ring position are examined.

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The effect of drag reducing surfactant (C₁₄TABr) additives on the transition in pipe flow has been investigated through pressure drop measurement, LDV measurement and flow visualization. The experiment was carried out using the glass tube of diameter D=5.02 mm and D=2.61 mm. Two types of flow were experimented upon : the flow that decreased background -turbulences as much as possible and the flow that was disturbed by a ring-shaped roughness element. In the flow of the former, the following was understood : within the range from Re=3 000 to 4 500, a temporary rapid increase in the friction factor appeared although the flow was quasi-laminar. In a concentration that exceeds 400 ppm, a turbulent transition happened gradually and vaguely, not drastically as Re increased. In the flow of the latter, the following was understood : although in the case of water a turbulent patch generated in the initial stage of the transition in Re>2450 was a turbulent slug, the present study suggests that in 260 ppm, the turbulent puff was generated in the initial stage of the transition in Re=3 500. Furthermore, turbulent patches were not generated in the concentration above 400 ppm.

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The numerical simulation of the behavior of a single bubble passing through a circular pipe with the change of cross-section has been carried out by the C-CUP method coupled with CSF model and Level-set method. This method can deal with both incompressible and compressible two-phase flows including surface tension effect. The present calculation succeeds in satisfying the mass-conservation law for the compressible flow in a bubble in remarkably good accuracy. The results present how the shape of a bubble is deformed and the pressure changes when it passes in the parts of a sudden expansion and a throal of a pipe flow at different values of Re and We numbers. It is also shown that some vortex-rings are formed in a wake of a bubble through a sudden expansion part of a pipe at the high Reynolds number of 500.

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The mechanism responsible for the high pressures generated in gas phase during the shock wave interaction with granular layer on a wall was studied experimentally and numerically. The granular layer used in experiments was composed of spheres fixed to each other and to the wall of shock tube. The pressure under the spheres was measured, and the shock wave propagation in the gas phase between the spheres was visualized by shadowgraphy. Furthermore, numerical simulations of shock wave interaction with the sphere were conducted in order to observe the shock wave propagation in a narrow space between the sphere and the end wall, and pressure distributions on the end wall of the shock tube in a qualitative manner. The correlation between the shock wave propagation along the end wall and the first peaks in the pressure traces obtained under the spheres was revealed.

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The mean velocity field of turbulent jet issuing from rectangular nozzle (Aspect Ratio=12.5) with a rectangular notch at the midspan, has been investigated experimentally. Four aspect ratios of rectangular notch (NAR) were 2.5, 7.5, 12.5 and 165. The Reynolds number based on the nozzle width d and the exit mean velocity U_e, was kept constant 30000 (NAR=2.5 and 7.5), 15 000 (NAR=12.5) and 13 000 (NAR=165), respectively. In this experiment, the variation of the potential core length and the changing rate of both the velocity and the length scales in the characteristic decay region were examined, and the present study suggested the possibility of the engineering applications. From the relationship between these results and the inward secondary flow producing both on the rectangular jet axis and the rectangular notch axis, effects of the rectangular notch on the development of the rectangular jet were clarified. Furthermore, the difference of the NAR value changes both the magnitude and the direction of the secondary flow. Finally, it is revealed that the potential core length takes the maximum value in the case of NAR=12.5, and the half velocity width b_z/d on the rectangular jet axis shows the minimum value in the case of NAR=165.

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Mean flow quantities have been investigated for the equilibrium boundary layer developing over the rough surface with roughness height proportional to streamwise distance. The wall shear stress was measured by direct measurement with a floating element device of zero displacement mechanism. Local skin friction coefficient is independent of two parameters both streamwise coordinate and Reynolds number based on momentum thickness and has a value of 0.0826. The boundary layer thickness is proportional to the streamwise distance. Then, the relative roughness height keeps a constant value. The log-law profile has same slope of that for the smooth wall turbulent boundary layer in the logarithmic linear part. The value of the roughness function increases in the streamwise direction. The wake parameter approaches to the constant value of about 0.7. Also, the value is consistent with the result deduced from the analytical method used both the momentum integral equation and Coles's wake law. Then, the wake parameter decreases with increasing the friction parameter.

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The Reynolds number influence on turbulent blocking effects by a rigid plane boundary is studied using direct numerical simulation (DNS). A new forcing method proposed in the second report using Townsend's “simple model eddies” for DNS was extended to generate axisymmetric anisotropic turbulence. A force field is obtained in real space by sprinkling many space-filling “simple model eddies” whose centers are randomly but uniformly distributed in space. The axes of rotation are controlled in this study to generate axisymmetric anisotropic turbulence. The method is applied to a shear-free turbulent boundary layer over a rigid plane boundary and the blocking effects for anisotropic turbulence are investigated. The results show that stationary axisymmetric anisotropic turbulence is generated using the present method. Turbulence intensities near the wall showed good agreements with the rapid distortion theory (RDT) for small t (t<<T_L), where T_L is the eddy turnover time. The splat effect (i. e. turbulence intensities of the components parallel to the surface are amplified) occurs near the boundary and the viscous effect attenuates the splat effect at the quasi steady state at low Reynolds number as for isotropic turbulence. Prandtl's secondary flow of the second kind does not occur for low Reynolds number flows, which qualitatively agrees with previous observetion in a mixing-box.

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The pressure losses for three kinds of fur surfaces (those of ribbon, spotted and harp seals) were measured in a rectangular water channel flow using the water and a glycerol-water mixture. The data were compared with those of smooth and riblet surfaces. The drag reduction could be obtained for all kinds of seal fur surfaces the maximum reductions were estimated to be about 12% on ribbon seal, 8.5% on spotted seal and 3.5% on harp seal for glycerol-water. Compared to the riblet surface, the range of Reynolds number where the drag reduction ratio was almost the maximum was wider for ribbon and spotted seal fur surfaces with hydrophilic property, while it was not for harp seal fur surface with hydrophobic property. It was found that for the ribbon seal, unlike the riblet, a drag increase due to the effect of surface roughness did not appear even at the highest Roynolds number tested. The measurements of seal fur surfaces using a 3D laser microscope revealed that the roughness of three kinds of seal fur surfaces was comprised of various wavelengths.

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Accurate measurements of annular flow parameters such as local liquid film thickness, one-dimensional interfacial area concentration of liquid film, and local interfacial area concentration profile of liquid film were performed by a laser focus displacement meter at 21 axial locations in vertical upward annular two-phase flow using a 3-m-long and 11-mm-diameter pipe. The axial distances from the inlet (z) normalized by the pipe diameter (D) varied over z/D=50 to 250. Data were collected for preset gas and liquid flow conditions and for Reynolds numbers ranging from Re_g =31 800 to 98 300 for the gas phase and Re_f=-1 050 to 9 430 for the liquid phase. Axial development of the one-dimensional interfacial area concentration and the local interfacial area concentration profile of liquid film were discussed with the data obtained in the experiment. Total interfacial area concentration including liquid film and droplets was also discussed with regarding to the exinting drift-flux model, entrainment correlation, and droplet size correlation.

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This paper describes the flow past two perforated plates placed on a ground plane. The experiment was carried out in the 20 cm × 20 cm circuit-type wind-tunnel having the working section of 2 m length at Reynolds number of 1.32 × 10⁴. The time mean velocity in the flow field around the two perforated plates was measured by use of laser Doppler velocimeter. The streamline and recircuration region around the two plates were obtained. The results were discussed for the various values of porosity and spacing between the two plates in comparison with the result for the case of a single perforated plate. The flow pattern and vortices were observed by flow-visualization. Consequently, it was found that the windbreak is effective for the perforated plate of porosity ratio λ=0.238 for L/H=12.

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Numerical simulation of a coupled air-water flow and associated interfacial mass transfer is carried out. It is found that the concentration field near the interface responses to the surface divergence quickly even at high Schmidt numbers up to 100. High interfacial scalar flux regious are characterized by spotty structures, which are caused by impingement of the bulk liquid on the interface due to streamwise vortices. In order to clarify quantitative relationship between the local scalar flux and the surface divergence, a one-dimensional advection-diffusion equation is analysed. By introducing two time scales, i. e., renewal and transient time scales, we show that the surface divergence contributes to the mass transfer only when the renewal time scale is larger than the transient time scale and the local scalar flux is analytically calculated from the surface divergence by appling the Chan and Scriven's stagnation flow model. We demonstrate that the above mass transfer model holds fairly well at a wind-driven turbulent interface. This would be a primary reason why a total gas transfer rate is well correlated with the intensity of the surface divergence under a wide variety of flow conditions.

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This paper describes the characteristic of Plasma Synthetic Jet Actuator (PSJA). PSJA is flow control device using the EHD effect of the glow-discharge. Though the flow control around an airfoil with PSJA is mainly studied, its characteristics have not been clarified. The flow channel which is easy to measure the pressure change was used to compare the flow condition with and without PSJA. The experimental results show that the effect of PSJA had varied with various main current velocities and various width of electrodes.

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A new experimental method to generate single small gas bubbles from a submerged orifice using pulsed ultrasound wave in a liquid is presented. Pulsed ultrasound wave having frequency of 15 kHz and maximum pressure amplitude of about 10 kPa is irradiated to a bubble growing from an orifice. Single air bubbles ranging from about 0.05 to 0.2 mm in radius are obtainable in silicone oil (kinematic viscosity : 1 mm²/s) using two orifices (0.02 and 0.04 mm in diameter), and by varying the timing to apply the pulse. Bubble deformation and detaching process was visualized and analyzed using both high-speed photography and direct numerical simulation. Consequently, it is revealed that bubbles are forced to elongate upward due to the oscillatory flow of gas through an orifice with high velocity, and the elongation causes the bubble to detach from an orifice. The sizes of bubbles at detachment can be well estimated with a common spherical bubble formation model.

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This paper describes the investigations on the aerodynamic characteristics of a U-shaped and V-shaped wing in ground effect. The lift, drag, side force, and rolling moment were measured in a low turbulance wind tunnel, using a 6-component balance. The flow over the upper surface was visualized by the tuft method. The results obtained were as follows : The U-shaped and V-shaped wing had an almost equivalent lift-to-drag ratio compared to a planar wing. This was due to the dihedral angle of U-shaped and V-shaped wing, resulting in a decrease of the induced drag. While separation only occurred on the V-shaped wing at an attack angle of 6 degree, a higher lift-to-drag ratio of the U-shaped wing was obtaind at attack angle of 4 and 6 degree. With both wings, an almost equal restoring force and an even higher restoring moment were obtained than with a conventional box shaped wing. Thus, the U-shaped and V-shaped wing offer a more suitable wing configuration for the Aero-Train than a conventional wing does.

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The paper presents the instantaneous flow velocity measurements of a wind turbine with a brimmed diffuser by particle image velocimetry (PIV). The PIV is used to show the velocity vectors of the inner and downstream flow fields of the model at Reynolds number, 1 × 10⁵ for turbine blades rotating (3 700 rpm) and no turbine blades. Furthermore the flow fields between with and without the turbine blades are compared. If the turbine blades are rotating, the flow disturbances in a brimmed diffuser are suppressed. And there are two large vortices at downstream region of the diffuser. One vortex after Brim acts as suck in wind to the diffuser and raise the inlet flow velocity. Another large unsteady vortex appears at downstream. Consequently the wind turbine with a brimmed diffuser can be operated stably while the turbine blades are rotating.

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This paper presents about an investigation of unsteady three-dimensional flows in an overexpanded rocket nozzle during the shutdown transient. The experimental and numerical investigations are performed. It has been known that, in some case, an asymmetric flow induces the serious lateral force called “side load” during transient operation. The focus of the present paper is the clarification of the characteristics of asymmetric flow patterns during shutdown transient. Each result obtained by measurements and computation shows qualitative agreement. The flow pattern becomes asymmetric during the transition of the separation pattern from restricted shock separation (RSS) to free shock separation (FSS) and result in a large and impulsive side load. Additionally, during the transition, a three-dimensional vortex structure is formed on the nozzle wall in the separation bubble.

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The liquid flow perfused from the four types of cannula into an aortic arch glass model was visualized by using the PIV method. In the case of end-hole and Dispersion cannulae, the liquid jet from a cannula impinges on the inner wall of an aorta near a first bood vessel branch and flows toward a descending aorta along the outer wall of curvature of the aortic arch. The rms value of the velocity and the magnitude of the strain rate tensor have their large values on the outer wall of curvature. In the case of Soft-Flow cannula, the liquid jet from the cannula impinges on the top of the inner wall of curvature of the aortic arch, and flows toward the third branch. The rms value shows its large values in the whole area of the aortic arch. The magnitude shows its large values on the outer wall of curvature near third branch and the top of the inner wall of curvature. In the case of the SELECT 3D cannula, the liquid flow from a cannula impinges on the top of the inner wall of curvature, and then flows toward the descending aorta along the inner wall of curvature. The rms value and the magnitude have their large values on the descending aorta side of the inner wall of curvature.

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The flow of a high-speed unsteady jet is analyzed by using computational fluid dynamics for incompressible flow with the k-ε turbulence model. The pseudo-nozzle concept is applied to the inlet condition with a large pressure gradient. The results show that the time history of the jet development agrees with experimental data for methane and hydrogen fuels. In addition, the effect of the injection condition on the development of the jet tip is well described with this model. Furthermore, the effects of inlet conditions of the turbulence intensity and scale on the flow are investigated.

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A producing process of unburned hydrocarbons in the cylinder of a natural gas engine with prechamber was investigated. Distribution of unburned hydrocarbons (UHC) was measured by the planer laser induced fluorescence (PLIF) and acetone was selected as a tracer in fuel, after investigating of characteristic of acetone. The effects of acetone concentration in fuel and ambient pressure on laminar burning velocity were investigated. Furthermore, the effects of laser energy, ambient pressure and equivalence ratio on fluorescence were conducted. A single cylinder gas engine with 170 mm bore was used and the UHC was visualized by attaching a cylinder made of quartz on the top of the liner. The result obtained from the PLIF measurement showed that the UHC from the prechamber was little despite of rich mixture in the prechamber. In the main chamber, the UHC from the crevice of top land between the piston and the cylinder liner during expansion stroke was confirmed. And a little amount of UHC was observed in the burned gas at the end of combustion. This was also confirmed by the images with a high-speed video camera.

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Flow behaviors in a porous system employing multi-hole channels with or without surface ceramics layer, which is commonly used for filtering process in industrial applications, are investigated by using Magnetic Resonance Imaging (MRI) for measuring axial velocity distribution inside the channels and numerical calculation for pressure distribution inside the porous filter. It is revealed that flow in the filter without surface ceramics layer shows non-uniform axial velocity distribution where channels nearest to the outside annulus only shows large axial velocity. On the other hand, in the case with surface ceramics layer, uniform axial velocity distribution is observed, because a ratio of flow resistance of surface layer to that of porous base dominates flow uniformity.

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The turbulent thermal plume developing in stably stratified air above the square heated plate on a broad and horizontal surface is computed by DNS, and is elucidated. (1) At the weakly stratified ambient, turbulence is enhanced near the plate center due to both the high speed in the flow near the plate surface toward the heated plate center and the violent oscillation in the temperature plume bottom. (2) Whether turbulence exists or not near the plate center leads to different mechanisms of the turbulence suppression. (a) At the weakly and ordinarily stratified ambient, turbulence exists near the plate center, and is suppressed, i.e. the reverse transition and relaminarization, due to the flow energy consuming by both the upward flow and the brake effect in the negative buoyant region. (b) At the strongly stratified ambient, turbulence does not exist near the plate center, and is suppressed due to laminarization in the whole region of the plume. (3) The reverse transition and relaminarization occur in the unstable region with the negative buoyancy, where the large scale fluctuation occurs, and the velocity and temperature time-records have large fluctuations, and differ each other.

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A theoretical and experimental study was conducted to investigate the critical condition at which a liquid drop slides down on an inclined plate. When the drop starts to slide down, it is suggested that the advancing and receding contact angle may appear on the circumference of the contact area of drop on the plate. The critical condition can be obtained from the force balance in the same way as the classical theory. In order to verify the validity of the condition, the occurrence of the sliding down is investigated when the plate on which a drop is set is tilted gradually from the horizon. The critical inclination angle of the plate φ_c is theoretically calculated by use of the drop profile obtained from the Laplace equation. In the experiment, φ_c was measured for each combination between 3 kinds of test liquids and test plates. The results agree well with calculated ones within the accuracy of the measurements.

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A concept of finless heat exchanger, which is composed of micro tubes, is proposed and assessed for achieving higher performance and better compactness. In reality, however, the precise assembly of numerous micro tubes leads to high manufacturing cost, and even small deviation of assembled tubes may cause considerable deterioration in heat exchanger performance. To resolve these issues, the micro tubes are placed in contact each other in the streamwise direction, so that the manufacturability and quality of the micro finless heat exchanger could be drastically improved. In the present study, the basic characteristics of two kinds of new tube arrangements, i.e., side-contacted and wavy extruded tubes, have been invistigated through numerical simulation and experiment. As a result, it is found that the pressure loss for given volume and heat exchange rate is always smaller when the tubes are side-contacted in the streamwise direction. For these tube banks, empirical correlations of heat transfer coefficient and pressure drop are proposed. The correlation equations obtained agree well with the CFD data. The measured pressure drop is by 8% larger than the prediction because of imprecise tube arrangement, while predicted heat exchange rate shows satisfactory agreement with the experimental data.

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Although pressure drops decrease due to formation of rod-like micelles in surfactant solution flow, heat transfer coefficients also decrease. As a result, the larger heat transfer area will be needed in heat exchangers. The objective of this investigation is to examine heat transfer enhancement effects by injecting air into drag reduction flow like surfactant solution one. Flow and heat transfer characteristics of surfactant solution-air two-phase flow inside a horizontal tube are examined experimentally. The test tube is 5 mm in inner diameter, and consists of the flow developing and heating sections. They are 2000 mm and 900 mm in length, respectively. TTAB+NaSal is used as surfactant additives, and the concentrations are 500 and 1000 ppm. Friction factors and heat transfer coefficients were measured in the heating section. Heat transfer enhancement by injecting air was larger for surfactant solution flow than that for water flow. This indicates that air injection has not only the effects of mixing flow, but also of breaking micelle structure for surfactant solution flow.

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In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. To attain this purpose, heat transfer tubes used for a heat exchanger for recovering exhaust heat from gas turbine in combined-cycle type power generation must exhibit high heat transfer and low pressure drop. A spiral finned tube with an extended fin has recently been used for this purpose. This paper described that the effects of flow around fin on the heat transfer and pressure drop characteristics of the spiral finned tube banks used for the heat exchanger in the thermal power generation were clarified by measuring 3-dimensional velocity and turbulence intensity, temperature, and static pressure in the spiral finned tubes banks with different fin height.

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In recent years the requirment for reduction of energy consumption has been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. To attain this purpose, heat transfer tubes used for a heat exchanger for recovering exhaust heat from gas turbine in combined-cycle type power generation must exhibit high heat transfer and low pressure drop. A serrated finned tube with segmented fins to improve heat transfer performance has recently been used for this purpose. This paper described that the effects of flow around fin on the heat transfer and pressure drop characteristics of the serrated finned tube banks used for the heat exchanger in the thermal power generation were clarified by measuring 3-dimensional velocity and turbulence intensity, temperature, and static pressure in the serrated finned tubes banks with different fin height.

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Ocean Thermal Energy Conversion (OTEC) usually uses plate type heat exchangers. For the improvements of OTEC efficiency, it is important to improve the heat exchanger efficiency. There are some methods for improving of plate type heat exchanger. As a typical method, there are the method of arranging grooves to a channel, and the method of giving the forced oscillation to a flow. By the former method, since a self-sustained oscillatory flow is generated in high Reynolds number, heat transfer enhancement is expectable. By the later method, since the resonance phenomenon appears between self and forced oscillations in the high Reynolds number flow, heat transfer is improved. However, few investigations were carried out for heat transfer enhancement on the low Reynolds number flow. Therefore, we carried out numerical calculations in grooved channel flow with forced oscillation at the low Reynolds number, and evaluated the influence of heat transfer enhancement and pressure drop. In addition, we carried out visualization experiments in the same model, and compared with the numerical solutions.

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It is necessary to use the low temperature thermal energy around 100 degress C from a viewpoint of global warming prevention. Even if a shape memory alloy is bent in normal temperature, when it is heated, it has the character which returns to the original straight form. Using this character of a shape memory alloy, unused thermal energy will be able to transform into rotation energy. A shape memory alloy belt is hung on a high temperature wheel and a low-temperature wheel. On this simple pulley type shape memory alloy engine, a shape memory alloy belt is heated with a high temperature wheel, it occurs a moment when returning to the original straight form, the moment kicks a high temperature wheel by the principle of action reaction, and torque is generated. We solved this torque generating mechanism. We proposed the theory which can design the output power of the simple pulley type shape memory alloy engine. Furthermore, the validity of this theory was verified by experiment.

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The mechanism of cell injury during slow freezing of cell suspension was examined by conducting two different kinds of experiments with PC-3 human prostate adenocarcinoma cells. One was a freezing experiment and the other was a pseudo-freezing experiment that exposed cells to a change in NaCl concentration with a synchronized change in the temperature, which mimicked the change in the environment of cells during freezing process. The results indicated that the mechanical stress from extracellular ice crystals played an important role in damaging cells during freezing at relatively higher freezing temperatures, while the solution effect that indicates the effect of increase in the solute concentration became more significant at lower freezing temperatures. A non-monotonous effect of temperature on cell injury due to the solution effect was also found, suggesting that the experimental results at the temperatures above 0°C could not be extrapolated to predict cell survival at sub-zero temperatures.

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To investigate the instantaneous structure of the local reaction zone of the HiCOT (High Temperature Air Combustion Technology) flames, the characteristics of ion current obtained from the non-premixed flames of propane with highly preheated low-oxygen air have been closely examined. Luminous region is seen in the non-premixed flames of propane with highly preheated regular air and in the downstream part of the non-premixed flames of propane with highly preheated low-oxygen air. On the other hand, non-luminous region is seen only in the upstream part of the non-premixed flames of propane with highly preheated low-oxygen air. The ion current fluctuations, obtained from the non-luminous region of the HiCOT flames, look quite similar with those obtained from turbulent premixed flames in the reaction sheet regime. It has been clearly shown from the ion current that homogeneous combustion does not occur but the local reaction zone exists separately from burnt and unburnt gases. The thickness of the local reaction zone in the non-luminous region of HiCOT flames is not broadened but is similar to that of the laminar premixed flames. Thickness of the local reaction zone in the non-premixed flames of propane with highly preheated regular air is estimated approximately twice as much as that in the non-luminous region of the HiCOT flames.

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A numerical study was performed to examine the vortical structures for combusting flow from a two-dimensional bluff-body slot burner in the transitional recirculating flow. The numerical results support the flow visualization results for C₃H₈ combustion by Chin & Tankin. We identify the fuel effect on the dynamic vortical structures inside the flame for C₃H₈ and CH₄, fuels. The Reynolds number for the inner slot fuel flow is varied from 10 to 250 at a fixed Reynolds number of 400 for the outer slot air flow. The flame sheet model of infinite chemical reaction and the unity Lewis number are assumed in the simulation. As a result of the study on a two-dimensional bluff-body burner, it was possible to reproduce the dynamic motions of vortical structures obtained by Chin et al. visualization experiment. In the low Reynolds number region, vortex structures in the recirculating region gives large effect in the flame form. In addition, it was confirmed that independently of the fuel variety, the flow at the bluff-body aft comes into three shape varieties : pre-penetration, penetration-transition and penetration regime.

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An experimental study has been made of the evaporation of a droplet of miscible binary component fuel on a hot surface in high pressure gaseous environments. Photographic observation is made to elucidate how a fuel droplet or film behaves on a hot surface and to obtain the characteristic lifetime curve at various surface temperatures. Primary attention is toward the effect of ambient pressure on the evaporation of a binary component fuel droplet as distinguished from the phenomena of a droplet of single component fuel. The results show that a maximum in the film evaporation region of the lifetime curve appears as well as a Leidenfrost point. The increase in the ambient pressure causes the lifetime curve shifted toward higher surface temperature, and the decrease in the lifetime at these points which finally tend to disappear. The increase in the initial concentration of the highly volatile base fuel results in the maximum shifted toward higher surface temperature and the Leidenfrost point toward lower surface temperature. The lifetime curve shifts toward the higher surface temperature with a decrease in the volatility of low volatile base fuel.

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Diesel engines are inherently high thermal efficiency. However, regardless of the ability to mitigate the greenhouse effect, the major challenge of NO_x and PM emission control to achieve future emission standards has not been completed. Thus, the authors proposed a novel combustion control method by using the physical and chemical properties of mixed fuel. Although some potential exits in this approach because spray and combustion phenomena are initiated by fuel, few studies similar to this research have been conducted. Consequently, we have studied fundamental phenomena with regard to mixed fuel. In this paper, the ignition characteristics of mixed fuel were investigated through a constant volume vessel and analysis of results shows the physical and chemical effect of each component consisted in mixed fuel on ignition processes.

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Ignition and combustion characteristics of diesel spray impinging on a wall were experimentally investigated. Ignition position and appearance position of the luminous flame kernel were stereoscopically observed using a two-way fiber optical system. Flat impingement wall was fixed in a high temperature, high pressure combustion chamber. Inclined angle of the flat wall was set at 30 degees or normal against the center axis of the injection spray. Distance from nozzle tip to the impingement point on the wall was set at 50 mm. Effects of injection pressure and fuel quantity on ignition position were investigated. As the result, ignition positions were observed near the spray periphery. And the radial position of ignition was shifted to the larger radial position when the injection pressure increased. Luminous flame appeared near the wall surface in the both cases of 30 degrees and normal impingements. And the region of luminous flame appearance was not changed significantly with an increase of injection pressure.

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