The effects of dispersed droplets on mass transfer across the air-water interface with breaking waves were experimentally and numerically investigated. The diameter, velocity and horizontal flux of droplets were measured using a phase Doppler anemometer. The results show that the horizontal flux of droplets has an unversal size distribution independent of wind speed and height, and that the horizontal flux of droplets increases in proportion to the 8th power of friction velocity. In addition, the mass transfer across the air-water interface of a single droplet was estimated by means of a direct numerical simulation (DNS). The DNS shows that the contribution of dispersed droplets to the total mass transfer across air-water interface with breaking wave is about 0.3%.

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Momentum and mass transfer in developing liquid plane mixing layers was experimentally investigated and compared with that in a developed mixing layer. It is found that, in the developing mixing layers, the momentum and mass at relatively small scales (smaller than the roll-up frequency) can be transferred in the negative direction (counter-gradient flux) to those in the developed mixing layer. In regard to the mass transfer in the streamwise direction, the mass at large scales can also contribute to the negative production in the developing mixing layer. We also explained why the Reynolds shear stress in the laminar mixing layer was smaller than that in the tripped mixing layer, whereas our measurements were in reverse order in measurements by Bell & Mehta.

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For realistic turbulent flow simulation, quantitative representation of turbulent flow dynamics is desired. In the present study, two-dimensional homogeneous isotropic turbulence is simulated by using grid-free vortex method to focus on the viscous dissipation process. The results are compared with those of spectral DNS. Two viscous diffusion models, i.e., core spreading model and Moving Particle Semi-implicit (MPS) Laplacian model, are compared. For the former model, marge and addition process are incorporated to ensure uniform distribution of vortex elements. It is shown that the MPS Laplacian model is superior to the conventional core spreading model in terms of the decay rate of enstrophy and energy spectra. Computational time is remarkably reduced by using Fast Multipole Method (FMM) while retaining accuracy.

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Experiments have been performed on turbulent channel flow with injection through an inclined slit. The inclined angle is fixed to 30 degrees at the main stream velocity 10 m/s. The dimensionless injection flow ratio is varied eight steps in ranging 0.067-0.467. The cooling effectiveness, wall static pressure, wall shear stress, velocity profile and turbulent intensity are measured behind the slit. In addition, the temperature distribution is measured. The cooling effectiveness and pressure loss increases with increasing the injection flow ratio. When the injection flow ratio is 0.433, the highest cooling effectiveness is obtained. Turbulent intensity and Reynolds shear stress near the slit show the high peak in the near-wall region. However, this peak rapidly decays in the downstream direction. This phenomenon relates to improvement in the cooling effectiveness.

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A study was conducted to obtain fundamental flow characteristics for a practical spool valve whose inlet and outlet port position was set at 90°angle. Particularly in the present investigation two different geometric configurations of spool were examined. One spool has rectangular notches and another spool has no notch. Experiments were carried out to obtain basic flow and pressure relationship. By examining experimental data with numerical results, it was found that numerical results predicted the flow and pressure relationship very well, modeling approximate edge configuration on the spool and body. Various flow characteristics also were verified based on flow parameters of the spool valves.

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The turbulence structure of flow field including microbubbles in a horizontal channel is experimentally investigated using an image processing technique in order to clarify the mechanism for drag reduction caused by microbubbles. A new system for the simultaneous measurement of liquid and dispersed gas phases is proposed, which is based on the combination of Particle Tracking Velocimetry, Laser Induced Fluorescence and Shadow Image Technique (PTV/LIF/SIT). To accurately detect the velocity vectors of the liquid phase in the two coexistent phases, the tracer particles overlapped with bubble shadow images are almost entirely eliminated in the post-processing stage. Finally, turbulence characteristics of the objective flow field are presented with the measurements for both phases obtained by the proposed system. The local interaction between bubbles and surrounding liquid is clarified.

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Using laser-induced thermal acoustics, we demonstrate to measure non-invasively and remotely the speed of sound and temperature ranging from 278 K to 341 K in water at atmospheric pressure. The accuracy of measured the speed of sound and temperature is formed to be 3% and 4%, respectively. Single-shot precisions based on three standard deviation of 20 samples were within 4% for the speed of sound and the temperature. The time resolution for each measurement was 300 ns.

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Interaction between a vortex ring and shear layer vortices was simulated by the three-dimensional vortex blob method. The purpose of this research is clarifying interaction between a vortex ring and shear layer vortices, and is also the basic research of active control of the shear layer by introducing the self-propelling vortex ring from outside of the shear layer. Interaction of the vortex ring is effective in enhancing the local growth of the shear layer. Numerical simulation was performed in order to clarify the circulation ratio between the vortex ring and the shear layer vortex tube which promote the interaction between a vortex ring and shear layer vortices most. In the case of circulation ratio Γ_R/Γ_F of 1.0, shear layer vortices and the vortex ring interact strongly. Large vortices were generated by amalgamation between the shear layer vortices and the vortex ring. The vorticity thickness attains a maximum when circulation ratio Γ_R/Γ_F is 1.0. However, enhancement of the growth of the shear layer saturated when the ratio exceeds about 1.5. This is because the vortex ring which has large circulation passes through the shear layer.

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It is well known that a backflow occurs in the upstream of an impeller at low flow rate. Such backflow often accompanies a vortex structure. It is considered that the vortex structure is caused by the roll-up of the shear layer between the swirling backflow and an axial main flow. In order to verify this, a simple model test was carried out in which the effect of impeller was represented by an axisymmetric swirling backflow. In the present paper, the flow field of the simplified model test is simulated by using the LES to investigate detailed flow pattern. The computed results are compared with experimental results.

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The nonuniformity flow in the meridional section of a multi-blade sirocco fan has been represented as two domains. In the one domain, the air accompanied with the wake flows out to outside of impeller, and the vortex flow exists in another domain. In this study, the slip factor and the four pressure losses have been estimated. A pressure loss arose at the upstream side rather than the measurement point, and other losses were produced by the expansion of the scroll casing, mixing of the wake and the mixing of the vortex flow. As a result of analysis of the internal flow of the fan, it became clear that aerodynamic characteristics of the fan are influenced of the pressure loss produced in the process in which substantial channel reduced by the vortex flow carries out sudden expansion. When the effect on the mixing losses proposed in this study was applied to the estimate of the total pressure coefficient of the fan, the coefficient was able to be estimated within 6% errors.

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This paper describes the characteristics of the fluctuating lift forces when a circular cylinder vibrates in the cross-flow direction. The response characteristics on elastically supported the circular cylinder was first examined by a free-vibration test. Next, flow-induced vibrations obtained by the free-vibration test were reproduced by a forced-vibration test, and then the characteristics of the fluctuating lift forces, the work done by the fluctuating lift, the behavior of the rolling-up of the separated shear layers were investigated on the basis of the basis of the visualized flow patterns. The main findings were that (i) the fluctuating lift forces become considerably large than those of a stationary circular cylinder, (ii) negative pressure generates on the surface of the circular cylinder when the rolling-up of separated shear layer begins, (iii) the phase between the fluctuating lift force and the cylinder displacement changes abruptly as the reduced velocity Ur increases, and (iv) whether the generating cross-flow vibration becomes divergent or convergent can be described based on the work done by the fluctuating lift forces, Furthermore, it was found that the generation of cross-flow vibration can be perfectly suppressed when the small tripping rods are installed on the surface of the circular cylinder.

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The flow-induced in-line oscillation of a tapered circular cylinder which was supported by a plate spring was experimentally studied through free-oscillation tests in a water tunnel. The response displacement amplitude at a cylinder tip was measured at roduced velocity Vr from 1.0 to 4.0. The taper ratio was varied from 0% to 20% to investigate its effect on the response displacement. The tip diameter of each cylinder was 20 mm and the root diameter was varied. It was found that cylinders with taper ratios of 2.5% to 10% had two excitation regions, while cylinders with taper ratios less than 1% had one excitation region. The taper ratio, therefore, affects the amplitude of the second excitation region. The reference diameter of the tapered cylinder was defined by the diameter at 1/3 length from tip in consideration of the results of oscillation characteristics of tested cylinders. The cylinder with any taper ratio did not oscillated at Vr <1.0. The amplitude of the cylinder with any taper ratio was suppressed at less mass-damping parameter Cn than 2.5, which is the suppression criteria for in-line oscillation of 2-dimensional cylinder. The guideline JEME S 012 of the Japan Society of Mechanical Engineers is valid for tapered circular cylinders, since it is established in consideration of 2-dimensional cylinder.

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In this report we present the results of the 3-dimensional numerical analysis for the selection of the final modes on the Taylor vortex flow with a small aspect ratio. Some kinds of modes of the Taylor vortex flow are depended by a history of the increment of the Reynolds number even though the final Reynolds number and the aspect ratio were same value. In this numerical computation, 6 kinds of final Reynolds numbers and 6 kinds of accelerations of the Reynolds number were used at an aspect ratio 4.0 on the symmetric system. The mode formation processes in the numerical analysis were qualitatively consistent with the results in the experiment. And the final modes on the 36 sets of the histories of the increment of the Reynolds number were 75% accuracy consistent with the final modes in the equivalent experiment. The time development of the energy and the enstrophy in radial, axial and azimuthal directions of the Couette-Taylor flow were investigated. The energy and the enstrophy in the radial direction affected to the final mode.

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It is known that an oscillating airfoil can produce a driving force through the generation of a reversed Karman vortex street, and this can be expected to be a new highly effective propulsion system. A heaving airfoil model was made and it was operated within a water channel at low Reynolds number. The dynamic thrust and lift acting on heaving airfoil were measured simultaneously using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as heaving frequency and amplitude in NACA 0010 profile. The results showed that thrust coefficient increased with reduced frequency. We also presented the experimental results on the unsteady fluid forces of heaving airfoil at various parameters.

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In this paper, a novel passive mixer for μTAS, which has relatively complex shaped channel, is fabricated by use of MEMS technology. Furthermore, we make a numerical study to investigate the suitable flow conditions for μTAS and the diffusion characteristics of passive mixer by means of curvilinear coordinate transformation techniques. The experimental observation of liquids flow in micromixer is carried out using flow visualization technique. The experimental results of diffusion agree well with the numerical ones. It is revealed that the passive mixer developed here has reasonable performance and that the mixing process can be predicted by the use of technique in computational fluid dynamics.

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For interface-tracking simulation of incompressible two-phase fluids with a high density ratio, a numerical method based on the combination of a phase field model, Navier-Stokes equation, and a van-der-Waals Cahn-Hilliard (C-H) free energy was proposed in this study. The method was applied to several two-phase flow problems, by which it was confirmed that (1) the volume flux caused by a local chemical potential gradient in the C-H equation plays an important role in (a) volume conservation, (b) automatic reconstruction of gas-liquid interface, and (c) reduction of numerical diffusion and oscillation, (2) the proposed method gives good predictions of pressure increase inside a bubble caused by the surface tension force, and (3) a single liquid drop falling through a stagnant gas and merging into a stagnant liquid film was simulated well.

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Separation of particles or decreasing the particle concentration in a solid-liquid two-phase flow is desired. Utilization of ultrasound has been considered as an alternative technique for the separation of particles. It is known that particles are aggregated by the radiation pressure of ultrasound. However, the effect of ultrasound with cavitation on particle behavior is not well known. Thus, water with aluminum particles having a density of 2720 kg/m³ and diameters of 50 to 150μm or smaller aluminum powder in a rectangular vessel was horizontally irradiated by ultrasound with frequencies of 23 kHz or 100 kHz, and a standing wave was formed. The following results were obtained. For ultrasound with 100 kHz, the aluminum powder aggregated in vertical lines. For ultrasound with 23 kHz and acoustic cavitation, we noticed that the aluminum particles were gathered at points near antinodes of the sound pressure profile because of flow induced by acoustic cavitation. When the particles were provided continuously with relatively high concentration, particle clumps formed and remained. Then, the particle clumps became larger and suddenly fell faster than the surrounding small particles. Such phenomena repeated. For relatively low concentration, particle clumps did not become large, and remained at the same positions.

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It is well known that the suction performance of turbopumps in cryogenic fluids is much better than that in cold water because of thermodynamic effect of cavitation. In the present study, an analytical method to simulate partial cavitating flow with the thermodynamic effect in a cascade is proposed : heat transfer between the cavity and the ambient fluid is modeled by one-dimensional unsteady heat conduction model under the slender body approximation and is coupled with flow analysis using a singularity method. In this report, the steady analysis is performed and the results are compared with those of experiments to validate the model of the present analysis. This analysis can be easily extended into unsteady stability analysis for cavitation instabilities such as rotating cavitation and cavitation surge.

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A design concept of two-phase flow centrifugal impeller is described with experimental results. The short bladed forward impeller with high outlet blade angle is recommended to keep theoretical head higher even in two-phase flow condition and to disperse the air accumulating region on the suction blade surface by the water jet flow coming along the pressure blade surface. Furthermore, tandem arrangement of outer and inner rotating cascades with the same blade numbers was adopted to suppress the rotating stall phenomena appearing in the case of a single stage of outer cascade. Then how to evaluate the impossibility of pumping due to two-phase flow is shown from a relation between the two-phase flow head characteristic curve and the resistance curve of piping system.

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In order to improve the efficiency of a jet pump used in Boiling Water Reactors, the effects of nozzle and throat shapes on the mixing process between driving flow and induced flow in the throat and the pump efficiency were examined experimentally. The velocity profile and local skin-friction coefficient distribution in the throat were also obtained experimentally. Three kinds of nozzles, conventional throat and throat having a very gentle gradient were used. The following results were obtained. The circular nozzle with eight notches shified the efficiency to a bit high flow rate ratio region by reduced jet size. The flower-shaped nozzle decreased the efficiency by increasing skin-friction loss caused by enhanced mixing. The throat having a very gentle gradient reduced the skin-friction loss and enhanced the efficiency.

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The precise prediction of the performance of a wind turbine largely depends on the accurate knowledge of the flow around the rotor as it is subject to the induced velocity caused by the spiral vortex wake and the unsteady aerodynamic loads caused by the rapid change of wind direction. In this paper the flow around a horizontal axis wind turbine (HAWT) rotor in a yawed flow condition is analyzed by a panel method with a free wake model and the cyclic fluctuations of the aerodynamic load due to the asymmetric inflow condition are obtained. To include the viscous effects in the calculated results, the local angle of attack is investigated and is found to be defined well by the angle of incidence at a quarter chord point in the non-yawed condition. In the yawed condition the effects of highly skewed vortex wake on angle of attack are also discussed.

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Measurement results of the wake velocity profile behind 0.6 m-diameter wind turbine in wind tunnel and 10 m-diameter wind turbine in the field are shown. The development of wind turbine wake was observed with the use of particle image velocimetry for wind tunnel measurement. From the results of wind tunnel measurement, the wake was expanded from the position where the tip vortex was almost dissipated. The wake velocity behind field wind turbine was recovered in shorter distance than those for the turbine in wind tunnel measurement. The wake area was sifted toward radial direction related to wind turbine rotational direction. The wake velocity at lower half area below rotor axis was not much recovered by the effect of tower compared to those at upper half area above rotor axis.

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This paper describes the measurement of the flow field around rotor blade. Three-bladed upwind rotor was tested in an open jet type wind tunnel. The rotor has a diameter of 2.4 m. Flow field around rotor blade was measured with the use of two-dimensional LDV. The flow field was measured in x-y plane and z-y plane. The circulation around the blade sections were calculated by flow vectors around the rotor blade. The velocity vectors at optimum operation show a smooth flow around the blade and the bound vortex around blade cross-section seems to be persistent. On the other hand, the velocity vectors at stall condition demonstrate significant fluctuations in the near wake and separation on the blade suction side was observed. The circulation around blade span-wise section was calculated at the certain control volume. By the observation of flow field and calculated results of circulation, it seems that the flow is separated at the blade from middle-span region to tip region at stall condition. No separation was observed at the blade root region.

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The purpose of this research is to investigate the physical mechanisms associated with the tip vortex noise caused by rotating wind turbines. The present work describes the first part of the research, the direct noise simulation in the near field of a blade. The flow around a NACA0012 blade section at a Reynolds number of 2.87×10⁶ is calculated using compressible LES. The simulated blade surface pressure distribution and pressure spectra peak agreed quantitatively with experimental measurements. The Earth Simulator allows simulations with up to 300 million grid points. As a result very small eddy scales are captured, leading to reduced SGS dependency and improved predictions of the noise spectra in the high frequency domain. The flow field and aerodynamic noise caused by a NACA0012 blade with a tip in an incident flow is simulated. Quantitative agreement is observed between the noise level of the acoustic field caused by the complex tip vortex structures and experimental measurements. The noise generation process associated with the tip vortex formation is simulated with high accuracy due to the fine grid employed. In the next step the simulation method will be applied to wind turbines operating at similarly high Reynolds numbers.

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The purpose of this research is to investigate the physical mechanisms associated with tip vortex noise caused by rotating wind turbines. The flow and acoustic field around the WINDMEL III wind turbine is simulated using compressible Large-Eddy simulation (LES), with emphasis on the blade tip region. The acoustic near field is simulated directly by LES whereas the far field is modeled using acoustic analogy. Due to the fine grid employed, smallest eddy scales near the blade surface are resolved. Aerodynamic performance and acoustic emissions are predicted for the actual tip shape and an ogee type tip shape. A decrease of the sound pressure level in the high frequency domain is observed for the ogee type tip shape, corresponding to field test measurements. The simulation results will contribute towards designing new wind turbine blades for reduced noise emission.

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Active control of a lifted flame was achieved using a coaxial nozzle with micro magnetic flap actuators arranged on the inner periphery of the annular nozzle. The spatio-temporal structure of the flame was studied by using a laser-induced fluorescence method and a particle image velocimeter, while the exhaust gas was examined with an FT-IR gas analyzer. Near-field vortical structures in the coaxial jet are manipulated by introducing disturbances directly to the initial shear layer. They were generated by the flap actuators driven with square-or saw-wave signals. The lifted flame modified by the square-wave signal disturbances are stabilized at the downstream of the inner potential core, because the early breakdown of the coherent structures into turbulence is promoted. Mixing enhancement upstream of the flame base shortens the flame length and the emission of nitrogen oxides is decreased. On the other hand, the lifted flame controlled by the saw-wave signal disturbances can be anchored near the nozzle exit by the effect of shedding of large-scale vortices synchronized with the flapping motion. These vortices periodically supply premixture blobs to the flame base in such a way that Damkohler number, which is defined as the ratio between the supply and consumption time spans of the blobs, becomes approximately unity.

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In the present study, bubble nucleation in liquid oxygen where impurities (nitrogen molecules or helium ones) are dissolved is investigated using molecular dynamics simulation. When the mole fraction of impurities is 0.05, bubble nucleation mechanism is fundamentally different ; vaporization in homogeneous bulk makes a bubble in the case of nitrogen-dissolved liquid while phase separation of impurities makes a nucleus in the case of helium-dissolved liquid. The effect of fluctuation to bring a local void, which can grow to be a bubble, is stronger in the case of helium-dissolved liquid under the lower mole fraction (0.01) than in the case of nitrogen-dissolved liquid under the higher mole fraction (0.05). From these results, we found that helium molecules have much stronger action to raise bubble formation pressure compared with nitrogen. In this paper, the kinetically-defined critical nucleus, which is very important factor to evaluate the nucleation mechanism qualitatively, is also estimated through the calculation of size change rate of each nucleus.

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For the air cooling of electronic equipment, the pressure drop and heat transfer performance of the equipment are important factors. Recently, the authors carried out experimental studies on the pressure loss of a rectangular block on the wall of prarallel channel having height B. The effects of the opening ratio β=1-H/B and the side/height ratio of the cylinder C/H on the pressure loss coefficient ζ were clarified. In the present paper, the effect of the opening ratio β on the pressure drop and heat transfer of a rectangular block is investigated. The optimum opening ratio β for the performance of the heat transfer is examined at constant pumpimg power for the basic geometry of a rectangular block. The maximum heat transfer is obtained at the opening ratio β=0.32.

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In HVAC (Heating, Ventilating, Air Conditioning) unit used in an automobile air-conditioning system, hot air heated by a heater core and cold air cooled by an evaporator is mixed to control the air temperature blown into the compartment. In simulating numerically the temperature control characteristics of the HVAC, the modeling of turbulent mixing process of hot and cold air is a key issue for improving the performance of the simulation. Detailed knowledge on the turbulent air mixing in HVAC unit is, however, quite scarce. Hence, as the first step to make clear the air mixing process in HVAC, we have made an experimental study on trubulent thermal mixing in a simple planar shear layer. In particular, the distributions of turbulent heat fluxes and turbulent Prandtl number over the mixing layer have been measured for two velocity ratios, and based on the experimental data, the production mechanism of the turbulent heat fluxes has been examined in detail.

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Effect of fin on heat transfer around a tube in an aligned-arranged tube bundle was investigated experimentally, and the obtained results were compared with other arrangements, i.e. single tube, single tube row and staggered arrangement. It was clarified from the experiment, that the effect of fin begins to appear with larger fin spacing than the staggered arrangement, and the degradation in local heat transfer coefficient due to fin can be recognized not only in the downstream side of the tube, as observed in other arrangements, but also in the upstream side. As a result of this phenomenon, the degradation in average heat transfer coefficient becomes larger than the other three arrangements with the same fin spacing.

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A solid oxide fuel cell (SOFC) is one of the promising candidates for the distributed energy systems because of its high electric power generation efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be utilized for the fuel reforming because the operating temperature is very high. In the indirect internal reforming SOFC, the optimum heat exchange is achieved by coupling the endothermic reforming reaction to the exothermic electrode reaction. In this study, the internal processes of the tubular type internal reforming SOFC are analyzed taking into account the heat and mass transfer, electrode reaction and transport of electron and oxygen ion. The temperature distributions in cell components affected by the catalyst density of reformer are investigated. The effects of current density and anode gas recirculation on the cell performance are also studied. It is noted that the large temperature difference in the cell components is prevented by decreasing the catalyst density. The thermal efficiency is improved by decreasing the current density and promoting the anode gas recirculation.

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The hydrogen and oxygen fuel pipes, electric power line and exhaust heat output line of fuel cell co-generations for individual houses are connected, and cooperation operation is carried out. The energy demand pattern of the individual house in Tokyo was introduced, and the analysis method aiming at minimization of the operation cost by the genetic algorithm was described. The fuel cell network system of an analysis example assumed connecting the fuel cell co-generation of five houses. Compared with the energy supply method of the conventional system, the amount curtailment of consumption of 9% of city gas estimated at the maximum by the energy supply of the fuel cell network system from the result of analysis. 2% of this is an effect when introducing water electrolysis operation by fuel cells, and using the method corresponding to partial load operation of fuel cell co-generation.

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Real time analysis on impedance spectroscopy in PEFC (Polymer Electrolyte Fuel Cell) is tried using FFT (Fast Fourier Transform) method. It is proved this method can analyze the Cole·Cole plots of PEFC with high speed and high accuracy compared to conventional FRA (Frequency Response Analyzer). PEFC is simulated to equivalent circuit model with four resistances and three capacitances, and effects of running condition on those are analyzed by experiment. Results show this method has capability of on-board diagnosis and fuel cell system control.

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This study has been performed to investigate the heat extraction characteristics from shallow geothermal resources using a coaxial heat exchanger. First, the computer simulation program for a coaxial heat exchanger has been checked by laboratory experiments. After inspecting the effectiveness of the present computer program, a numerical simulation for a real scale model has been conducted under the condition that the heat transfer mechanism in the stratum is heat conduction. Unsteady heat extraction characteristics are presented, and the effects of the tube material, inner diameter, and circulation modes on the heat extraction rate are discussed. From the computed results it was found that the heat extraction performance using a coaxial heat exchanger greatly depended on the factors mentioned above in the range of the parameters covered in this study.

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The structure and numerically predicted results of a new Stirling engine with a circular disk heat exchanger consisting of pin-fin arrays are presented. Pin-fin arrays are carved into the circular heat exchanger disk's face. An annular cover plate is attached to these tips. A cooler of similar shape is located. So-called “α”, “β” and “γ” configurations are capable in present engine. Numerical prediction of power employing second-order approximation method is carried out in so-called “β” configuration engine case. The fluid resistances of many parts are regarded and some mechanical friction losses are regarded. The predicted engine output becomes 1 kW with the temperature of 773 and 298 [K] on the heating side and cooling side, respectively. In conclusion, the Stirling engine described here is suitable for biomass and solar use because its heater shape is circular and has unique feature that it doesn't need any heat exchanger pipe.

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A new distributed gasification system for solid fuels is proposed, which is named as MEET (the Multi-staged Enthalpy Extraction Technology) system. In order to realize this system, a demonstration plant of commercial scale, MEET-II, was constructed. The capacity of the MEET-II is 200 kg/ h. MEET-II facility consists of a pebble bed slagging-gasifier, a gas clean-up system, a high temperature air generator and a gas engine. The pebble bed slagging-gasifier contains a fixed ceramic ball bed under an entrained flow section. High temperature air of about 1000°C is used as a gasification medium in order to obtain higher calorific value syngas. Gasification and power generation tests at MEET-II facility were conducted using powdered wood biomass as a fuel. These tests demonstrated technical feasibility of MEET-II facility.

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Comprehension of the turbulent burning velocity for lean hydrogen mixtures is inevitable in the improved design of hydrogen engines. The present study is performed to examine experimentally the turbulent burning velocity of lean hydrogen mixtures whose laminar burning velocity S_L0 and equivalence ratio φ are varied extensively from 15 to 35 cm/s and approximately 0.9 to 0.3, respectively. The measured turbulent burning velocities at the same turbulence intensity show to increase as φ decreases until about 0.5. Those, however, does not show such increase when φ becomes lower than about 0.5, regardless of S_L0. This phenomenon is discussed by the observation of turbulent flame structure and the estimation of Markstein number. The estimation of the mean local burning velocity of the turbulent flame is made also taking account of the preferential diffusion. It is found that their tendencies with φ is changed when φ becomes about 0.5.

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A rotating tubular flame has received considerable attention in combustion research because it experiences flame curvature and flame stretch simultaneously. It is also interesting to note that the rotating tubular flame is very stable, and hence, addition of small amount of hydrogen enables lean combustion of heavy hydrocarbon fuels with this flame. In our previous report, it has been found that hydrogen addition of 3% by volume enables lean combustion up to the effective equivalence ratio of 0.1 for methane, and up to the ratio of 0.2 for propane flame. In this experiment, probing of the burned gas temperature and the burned gas composition were made. The results show that in the cases when hydrogen is added by 1, 2, and 3% by volume to methane/air mixture, and by 3% by volume to propane/air mixture, the burned gas temperature exceeds the temperature obtained by chemical equilibrium calculation (CEC) in some low fuel concentration ranges. In these ranges, the oxygen concentration in the burned gas becomes lower than that of CEC, while the water concentration exceeds that of CEC. These facts substantiate the validity of the previously postulated mechanism for extension of lean combustion that due to the effects of flame curvature and flame stretch, hydrogen preferentially diffuses across stream tube from the upstream, unburned gas side into the reaction zone, resulting in an increase of gas temperature and also of water concentration ; then lean combustion is achieved.

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This work investigates the soot formation process in a diesel jet flame using a detailed kinetic soot model implemented into the KIVA-3 V multidimensional CFD code. The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver. The detailed soot model used is based on the method of moments, which begins with fuel pyrolysis, followed by the formation of polycyclic aromatic hydrocarbons, their growth and coagulation into spherical particles, and finally, surface growth and oxidation of the particles. The model can describe the spatial and temporal characteristics of soot formation processes such as soot precursors distributions, nucleation rate and surface reaction rate. The calculation results show that the soot particles are formed to surround the soot precursor formation region and to extend downstream. It is also found that the dominant soot growth process differs by the region in the fuel jet. The particle inception is fast around the central region of the jet, and C₂H₂ surface reaction rate becomes higher toward the periphery of the jet.

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In HCCI Engine, inhomogeneity of fuel distribution and temperature in pre-mixture microscopically exists and has possibility to affect the ignition and combustion process. In this study, the effect of charge inhomogeneity of fuel distribution on the HCCI combustion process was investigated. Pressure profiles were measured and two dimensional chemiluminescence images were captured by using a framing camera with a 4-stroke optical access engine. DME was used as the test fuel. Changing the way of mixing air and fuel in the intake manifold, inhomogeneity of fuel distribution in the pre-mixture was varied. The result showed that luminescence started and stopped at the same instant in whole the combustion chamber on the homogeneous condition. On the other hand, on the inhomogeneous condition luminescence started with a spatial variation in the combustion chamber. However local luminescence duration was almost the same on both conditions. It is clarified that a time lag appears spatially in combustion in the chamber on the inhomogeneous condition.

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The combination of burner and combustion chamber is one of important factors controlling flame characteristics, which has never been to our knowledge investigated systematically. In the present study, coaxial jet diffusion flames in cylindrical combustion chambers have been studied in terms of inner diameter of the combustion chamber, global equivalence ratio and turbulence in air flow. A fuel nozzle is composed of a stainless steel tube of an inner diameter of 2mm with a coaxial pilot burner of 3.19mm i.d., surrounded by two air coaxial tubes of 12mm i.d. and 30 mm i.d. The inner and outer air tubes are for higher and lower air flows, respectively, and the turbulence in air flow is changed by the velocity difference. The main fuel is propane. Hydrogen is used for the pilot flame, with a volumetric fuel ratio of 0.3. The wall of combustion chamber is made of heat-resistant glass to visualize the flames and the inner diameter is changed in a range between 95 mm and 182 mm to investigate the effect of size of furnace on flame characteristics. It has been found that the increase in the diameter of combustion chamber enhances the exhaust gas self-recirculation, as the result decreases the NO_x emission. The increase in turbulence in air flow strengthens the entrainment of the exhaust gas transported by the recirculation vortex to the flame. The increase in the global equivalence ratio from 0.2 to 0.8 in the present study decreases the oxygen concentration of the exhaust gas and leads to the diluted combustion through the exhaust gas self-recirculation. It has been found that a proper combination of these factors can yield the low NO_x combustion.

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In general, it is difficult for the low NO_x combustion to occur in non-premixed flames. It was assumed that the premixing combustion by the spouting of fuel and air brought about the remarkable NO_x reduction in non-premixed flames. In the present study, experiments on non-premixed, lift-off jet flames in a high-temperature air stream were carried out. The premixing occurs in the lift-off region. The air temperature was 1073 K, and the mixture of ethylene and nitrogen were used for fuels. With the lift-off height changed, the effect of the premixing on NO_x formation was examined. It was shown that the increase of the lift-off height reduces NO_x emission. The results suggest that the premixing after the process of the injection of fuel becomes a very effective method for NO_x reduction in non-premixed combustion.

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Lean-burn spark ignition engines have the attribute of minimizing the emission of NO_x and, concomitantly, maximizing fuel economy. For combustion in lean fuel-air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special devices. The most effective among them is the injection of active radicals by means of the Pulsed Flame Jet (PFJ) ignition system. Presented here is an experimental proof of the action of OH radical produced by such an ignition system in a swirl flow with varying the spark discharge mode in the cavity of the PFJ igniter. The measuring apparatus used for this purpose was based on the Planar Laser-Induced Fluorescence (PLIF) method, and the effects of the spark discharge mode in the cavity of the PFJ igniter on the variation of OH fluerencence area in the jet and its intensity were revealed quantitatively.

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The CFD analysis showed that lower distillation temperature fuels improved evaporation of the fuel spray just after injection, resisted adhesion to the cylinder wall, and improved mixture homogeneity, probably due to its higher volatility. Analysis of components in the used lubricant oil indicated that a remarkable quantity of diesel fuel, corresponding to 7% of the total energy supply, was diluted to the lubricant oil when the fuel spray was allowed to impinge directly onto the cylinder wall. Lower distillation temperature fuel actually reduced fuel adhesion on the cylinder wall and prevents fuel dilution into the lubricant oil even with early injection when the fuel was allowed to impinge directly onto the cylinder wall. The deterioration in thermal efficiency that occured with advanced injection timing with ordinary diesel fuel was eliminated with the lower distillation temperature fuel without significantly altering the THC and CO emissions.

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Thermocouples are widely used to measure gas temperature due to its accuracy and convenience. However, it is difficult to employ thermocouples in a transient phenomena such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification is required. Secondly, a correction term was added to the basic equation, which was validated by experiments using RCEM. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber comparing to the estimated temperature using measured pressure data and assumptions such as chemical equilibrium to see the adaptability of this technique.

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The purpose of this paper is to investigate the combustion properties of CH₄/O₂ mixtures diluted by CO₂ compared to those of CH₄/O₂/N₂ mixtures to study the feasibility of the new combustion method, which is expected to be effective in the NO_x reduction and the improvement of combustion. Both experimental and numerical studies were conducted to scrutinize the effects of flame stretch on the burning velocity and the effects of flame instability which may play an important role in combustion performance not only for laminar flames but also for turbulent flames. In this study, experiments were conducted by using spherical combustion bomb for applications to internal combustion engines. First the effect of flame stretch was investigated experimentally and numerically and quantitative discussion was made in terms of Markstein number which means not-dimensional sensitivity of the burning velocity to flame stretch. As a result it has been found that Markstein numbers for both methane mixtures decrease with decreasing equivalence ratio. In addition CH₄/O₂/ CO₂ mixtures have the low values of Markstein number compared with CH₄/O₂/N₂ mixtures over the whole equivalence ratio.

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Partially premixed sprays have not been studied systematically although they are of practical importance. In the present study, burning behaviors of partially premixed sprays were experimentally studied with a newly developed spray burner. A fuel spray and oxidizer diluted with nitrogen was injected into air. The overall equivalence ratio of the spray jet was set quite larger than unity to establish partially premixed spray combustion. In the present burner, the mean droplet diameter of the atomized liquid fuel could be varied without varying the overall equivalence ratio of the spray jet. Two combustion modes with an internal flame and without it were observed. As the mean droplet diameter was increased or the overall equivalence ratio of the spray jet was decreased, the transition from spray combustion only with an external group flame to that with the internal premixed flame occurred. The results also suggested that the internal flame was a premixed flame supported by flammable mixture through the vaporization of fine droplets and the passage of droplet clusters deformed the internal flame and caused internal flame oscillation.

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The color of propane/air coflow laminar partially premixed flame was quantitatively determined by chromaticity coordinates defined by CIE 1931 standard colorimetric system. Equivalence ratio of the mixture was varied from 2.0 to 8.0. The differences in flame color attributed to burning conditions such as equivalence ratio, fuel flow rate and surrounding air velocity were examined with a colorimeter. Spectroscopic measurements were also taken to clarify the determining factors of the flame color. The contributions of the visible lights emitted from reaction zone, recombination zone and soot zone to the flame color were evaluated by introducing the concept of additive mixture of color stimuli.

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