In order to improve the reliability of butterfly valves, it is absolutely imperative to prevent fatal cavitation erosion and to control the flow rates precisely. In our previous studies, the erosive vortex cavitation, which takes place within the limited part of high-shear region, was found to play an important role in the erosion. This fact suggests to us a useful method for overcoming erosion. To date, many types of modified valves have been proposed, in which very singular shaped buffers are attached to the orifice- and the nozzle-side of the valve disc, although data on the results of their practical use are unavailable. In this paper, therefore, the erosive shock-pressure distributions on the inner pipe-wall surface downstream from the valve disc and the corresponding cavitation-flow pattern are precisely measured in the typical bounded flow around butterfly valves by means of pressure-sensitive films and high-speed photography. It is found that the erosive pulses and the range of their occurrence in the shear regions can be significantly attenuated by introducing simple buffers.

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The vortex wake of two parallel circular cylinders in tandem arrangement is investigated by visualization experiments using a towing a water tank. The cylinder spacing parameter L/d L being the distance between the two centers and d the cylinder diameter) is varied between 2 and 20 and the Reynolds number between 40 and 120. The flow visualition is orealized by the use of fine particles in suspension and/or white dye concentration dissolved into water, producing, respectively, streamline and streakline profiles of the relevant flow. In general, the flow analysis is carried out from direct observation of the visualization images but, in some cases, is complemented by image processing results pertaining to estimated values of stream function, vorticity and wake frequency.

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In the present paper, the evolution process of the mixing layer manipulated by a vortex ring was studied using a novel experimental technique. Mixing layers were generated downstream from a splitter plate towed in a straight long channel. The vortex ring was made to collided with the mixing layer large-scale structures in the transitional region. The interactions between the mixing layer and the vortex ring were investigated by means of the flow visualization and the flying hot-wire technique associated with the collision. The topology of the vortices effective for pairings of the mixing layer is presented in this paper. The experimental results reveal that the vortex ring deforms the mixing layer vortices and causes the deformed vortices to merge sooner than they do in the case forced by the subharmonic instability modes.

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The purpose of this paper is to clarify the features of the pressure fluctuation in the swirling flow through a conical diffuser in relationship to the diffuser performance of static pressure recovery. The results of both measurements of the wall pressure fluctuation and the velocity fluctuation revealed them to role the large part of the loss of the total pressure of the flow. In addition, the cause of the fluctuation of flow was showed to be the flow separation at the inlet of diffuser at low intensity of swirl but to be instability of the swirling flow at high intensity of swirl.

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The first part of this series of papers reported an interesting transportation mechanism of fluids using the progressive wavy motions of two elastic plane membranes sustained by two magnetic fluid layers which were driven by the magnetic field in the form of sinusoidal waves propagating along the series of magnetic coils. The present paper reports on improved digital electronic devices for driving and controlling magnetic coils more efficiently. By using newly constructed devices, experiments were performed on flow velocity and pressure induced dynamically, and the fundamental characteristics of the fluid transportation systems were examined on the basis of FFT frequency analyses.

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In order to clarify effects of the divergent angle θ upon the hydraulic losses ξ_m in heterogeneous sand-water two-phase flows through divergent pipes, systematic experiments on ξ_m and the corresponding flow patterns are carried out for several θ, sand concentrations C_v and average downsream velocities V_m2. Here, we discover the interesting fact that for θ≤=60°, the ratio (ξ_m)^^^- of ξ_m to the water flow counterparts ξ_w is fairly close to one, while ξ_m decrease a little for θ≥90°. The behavior of losses is also discussed.

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Knowledge of two-phase flow in a capillary tube is important to understand flow phenomena in narrow passages, for example, in a compact heat exchanger. The present authors have previously reported the characteristics of flow parameters such as pressure drop, and void fraction as well as flow pattern in an air-water two-phase flow in a horizontal capillary tube. In the present paper, we discuss the effect of flow direction on void fraction and flow patterns in two-phase flow in a vertical capillary tube. Two correlations relating bubble velocity with total volume flux and time-averaged void fraction with gas volume flow quality were proposed.

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A new technique for an active attenuator for pressure pulsation in liquid piping systems, which detects the progressive wave component of fluid-borne vibration and then controls the second source feed-forwardly by this detected signal so as to eliminate the progressive wave in its downstream pipe completely by producing cancelling fluid vibration, has been presented, together with experimental results. In this report, emphasis is placed on the design of a signal processing circuit for the controller applicable to the wide-band random fluid vibration. The desired (target) characteristics for the controller could be realized through a newly devised signal processing circuit combining the finite-impulse-response (FIR) digital filter and analog compensating circuit. The pressure pulsation, including many harmonic components over the wide frequency range, was produced by a rotary-type spool valve. It could be confirmed by the test in a model experimental pipeline that, when the present control system was operated, the pressure pulsation in a downstream pipe of the second source was reduced to around 1/10 (-20dB) of that in the case where the control system was off for almost all harmonics of 15 to 400Hz.

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The laminar flow in the radial liquid-film flow on a rotating disk has velocity profiles with a kind of three-dimensional boundary layer. The linear stability of the flow was analyzed, with the effects of Coriolis force and streamline curvature taken into account. In the experiment, the frequency of disturbance was detected through wall pressure and the direction of propagation of the spiral vortices was obtained by measuring the angle of distortion of the disturbance waves on the liquid surface. The results of the stability analysis showed that the instability of the flow changes, with an increase in the effect of disk rotation on the flow, from a viscous to an inflectional type : the weak three-dimensionality of the velocity profile causes a decrease in the amplification factor of disturbance, suppressing the transition accordingly, whereas the strong three-dimensionality promotes the transition because of the inflectional instability. The results of the stability analysis were in reasonably good agreement with the experimental results.

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Computational studies of the reflection process of a planar shock wave on an axisymmetrical parabolic wall were performed. The effects of the incident shock strength and depth of the reflector on the reflection process and on the maximum pressure and temperature were discussed in comparison with two-dimensional cases. The results are as follows. 1) The shape of reflected shock waves varies from a crossed pattern to an uncrossed one with an increase in the incident shock strength. 2) The pressure amplitude has a very large value near a sound wave, but shows a rapid decrease and has a minimum value with the incident shock strength. Then it increases slightly and levels off for incident shock Mach numbers stronger than 4 in a monoatomic gas. 3) After the shock focusing is achieved, clear discontinuities in density and temperature are formed in the region behind the reflected shock wave.

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Helicity, which is defined by the inner product of the velocity and vorticity, is an important indicator for large-scale vortical structures in turbulent flows. In order to incorporate these structures into a turbulence model, the effect of helicity on the Reynolds stress is taken into account and a three-equation model is proposed, whereby a model transport eqation for the turbulent helicity is added to the k-ε model. This model is applied to a swirling flow in a straight pipe. As a result, this model can recover some important properties of a swirling flow such as the slow-down of the axial velocity near the center and the decay rate of the strength of swirling.

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The purpose of this paper is to consider the relationship between the fractal aspect of iso-velocity sets and bursting phenomena in the wall region of a turbulent boundary layer. Burstings are detected by means of the VITA technique and quadrant analysis. With conditional averaging methods, we make it clear that the fractal features of iso-velocity sets depend only on the burstings that are detected by quadrant analysis but are independent of ones detected by the VITA technique. We also investigate the detective functions of bursting defined by each method. They have quite different statistical properties, and that of the quadrant technique has fractal structure. If detective function expressed the distribution of burstings, self similarity would remain in that distribution. This result suggests that burstings should be studied from the dynamical point of view.

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Turbulence structure of a backward-facing step flow in a separating region is investigated using the numerical flow field which is computed by a large eddy simulation (LES). The Reynolds number based on step height and main flow is 46000. The reliability of this value has already been confirmed by comparisons between experimental and numerical data. The profiles of mean velocities, Reynolds stresses, triple products and the budget of Reynolds stresses are indicated. We conclude that the turbulence structure of a separating region in backward-facing step flow is classified into four regions depending on the budget of Reynolds stresses.

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An experimental study is reported on the turbulence structure of a two-dimensional (2-D) two-phase gas-liquid flow. A test cannel, in which a nearly 2-D, uniform two-phase air-water flow occurs, was used. This channel was a vertical, narrow gap space made up of two large concentric pipes. Measurements of turbulent diffusivity of the liquid phase were made for bubbly flows and churn flows in this channel. Namely, a solution of dye stuff was introduced at a constant rate from a fixed line source into a fully developed uniform two-phase flow in the channel. Flow at the downstream locations was recorded by a video camera, and roughly one thousand pictures of the flow were analyzed to obtain the distribution of dye stuff concentration using image processing. From this distribution, the turbulent diffusivity was determined. As for bubbly flow, a model for the turbulent diffusivity is proposed and examined.

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In the analysis of rarefied gas flows, much uncertainty exists regarding the boundary condition on the solid surface. This is mainly due to a lack of understanding of the micro scale dynamics of gas-surface interaction under various conditions, such as mass ratio, incident angle and wall temperature. In this paper, the behavior of a Xe gas molecule which collides with the clean Pt(111) surface of very thin film is computed by the molecular dynamics method. A clean surface of Pt(111) is formed in the thermal equilibrium state and then a Xe molecule starts to approach it. The calculated initial-trapping probabilities agree with the experimental data. The calculated results reveal that the average normal momentum of the gas molecule after the first collision has a good correlation with the incident normal momentum.

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The optimum radial distribution for the circulation of the blade element of the annular rotor cascade in concentric cylinder is treated analytically in potential flow and examined by numerical examples. The main contents are as follows : (1) The exact solution is derived for the velocity potential of the helically trailing vortex sheets in concentric cylinders and then treated by asymptotic expansions. (2) An approximate solution is also proposed by the conformal mapping for two-dimensional flow within straight passage with an infinite series of vortex sheets perpendicular to the hub. (3) The radial distribution of circulation, translational axial velocity and kinetic energy of the trailing vortex sheets are clarified in optimum conditions through some numerical examples and in particular, the hub and tip clearance effects are discussed concretely. Furthermore the accuracy of the approximate solution is considered from comparisons with the exact one.

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The purpose of this work is to predict analytically the unsteady loading on vibrating blades of a supersonic through-flow fan and investigate the aerodynamic instability. In order to deal with this problem, a linearized unsteady lifting surface theory on the basis of the finite radial eigenfunction series approxmation is developed. It is assumed that each blade operates with zero mean loading, and vibrates with a small displacement amplitude. Numerical results for pure bending, pure torsional and combined bending and torsional vibrations are presented to demonstrate influences of interblade phase angle, location of torsion axis, axial Mach number and reduced frequency on the flutter boundary.

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Clearance between male and female rotors and that between the rotors and casing of an oil-free screw compressor in operation are calculated. Surface displacement vectors of both rotors due to, for example, thermal deformation, profile errors, and deviation of the center distance, are converted to such that the clearance between the rotors changes assuming that the rotor surface is approximated by a plane in the vicinity of the calculating point and that the normal line of the plane does not change direction before or after the displacements. The calculation is applied to a computer simulation for predicting air compressor performance. Change in volumetric efficiency related to suction air temperature was calculated and the results agreed well with experimental ones.

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A numerical simulation of unsteady flow behavior in linear cascades of a compressor rotor and stator system is conducted by applying a TVD finite difference scheme. Two-dimensional compressible N-S equations are solved iteratively in a rotor-fixed moving frame and in a stator-fixed stationary frame in order to match data along the sliding boundary, and the flow induced by the motion of the initially stationary rotor is analyzed. In addition to accelerating and final-state flow patterns, a stall pattern is obtained by throttling a resistance specified at the discharge boundary. Configurations of vortices detached from the blade during the flow acceleration, formation and convection of the rotor wake, and growth of the stall separation are satisfactorily demonstrated. The stage performance and the rotor wake profile in the final state at the blade Mach number of 0.18 show very similar features with compressor test data. However, partly due to a rather coarse mesh along the blade, the performance involving the stall margin is lower than the test result.

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Fuzzy control was applied to speed up the convergence of a Poisson equation solver for the numerical calculations of incompressible fluid. The optimizations of the control rule were carried out by means of a hybrid method of the conjugate gradient method and the improved random walk method. The residual of the equation and the relaxation parameter are employed as input for the controller. It is found that this method is effective in obtaining fast convergence. Moreover, it is clarified that this control does not affect the bifurcation characteristics of the solution. The changes in optimized relaxation parameter are similar to Bang-Bang control.

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A series of experiments was carried out to investigate the possibility of active surge suppression control in an actual size machine for industrial use. The diameter of the impeller used in experiments was 250mm. A closed-loop compressor system and an open-loop compressor system with a control valve at the suction pipe were used, which are different from the Epstein model. Active surge suppression control was possible in the actual size machine for industrial use, as well as in these compressor systems. The action of the control valve was observed to suppress flow fluctuations from dynamically unstable equilibrium point at every instant.

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Effects of control of the wings and the adjustment of the channel shape were studied experimentally, concerning the performance of a rotary pump using the Weis-Fogh mechanism. The opening angle was controlled by a rubber, but it had little effect on the performance. The reason for this was clarified by comparison with the reciprocal type, considering the results of the previously reported numerical simulation. On the other hand, the adjustment of the channel shape was very effective in improving the performance, and the reason for this was considered in terms of flow patterns obtained from flow visualizations.

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A detailed understanding of critical heat flux (CHF) for vertical rectangular channels is required for the thermohydraulic design and safety analysis of research nuclear reactors in which flat-plate-type fuel is employed. In this study differences in CHF between upflow and downflow were investigated, focussing especially on channel outlet subcooling, because differences in CHF between upflow and downflow under the subcooled condition at the channel exit had not been fully clarified systematically. With the investigation of the existing CHF data, it was elucidated that there was a systematic tendency in CHF between upflow and downflow under the subcooled condition at the channel exit with demensionless subcooling and coolant mass flux, and a new CHF correlation was proposed for the vertical rectangular channels based on investigation results. The condition that CHF differs between downflow and upflow was also made clear within the range investigated in this study with pressure of less than 4MPa and dimensionless mass flux of less than 2200.

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Experiments were performed to determine the melting heat-transfer characteristics along a bundle of horizontal tubes immersed in liquid ice. The mixture of fine ice particles and ethylene-glycol aqueous solution was the working liquid ice. Eleven staggered horizontal electrically heated tubes of 20mm in diameter were utilized. Measurements were carried out for the range of the fixed liquid-ice bed to the fluidized liquid-ice bed. The parameters investigated were air-flow rate, heat flux, and initial concentration of aqueous binary solution. The measurements revealed that the heat-transfer coefficient for the fluidized bed might be more than twenty-five times as large as that for the fixed one.

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Exothermic boundary layers were observed for a flat plate exposed to a diffusion or premixed methane-air flame using the Laser-Schlieren technique. Wall temperatures tested ranged from 600K to 1000K. The Schlieren photographs were analyzed with a film scanner and the data provided the surface heat fluxes and heat transfer coefficients. The results showed that the heat transfer coefficient increases with increasing wall temperature in the reacting region in contrast to the well-known heat transfer characteristics within nonreactive thermal boundary layers where heat transfer coefficients are almost independent of wall temperature. This behavior provides a possible explanation for the problem of whether heat fluxes increase or decrease during combustion at higher wall temperatures with the use of ceramics for engine combustion chamber walls.

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In wall turbulence, the well-ordered motions determine the essential features of turbulent transport phenomena. In the present study, we have refined a previously developed detection algorithm for well-ordered motions (i.e., trajectory analysis method based on the (u, v)-quadrant splitting technique) and have investigated the relationship between well-ordered motions and heat transfer from structural points of view, i.e., trajectory analysis of the VITA heat transfer events, extraction of basic flow modules and the relevant heat transport, and the simulation of temperature fluctuations by means of an autoregressive (AR) model. As a result, it is shown that phase relationship of fluctuating velocity components dominates the essential characteristics of the transport processes of heat and momentum in wall turbulence and there exist the distinct differences in individual correspondence between well-ordered motions and heat transport processes which cannot be revealed by the widely used VITA technique.

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This work is one of the fundamental steps in the study of thermal radiation characteristics of metallic materials in actual industrial or natural environments. A new algorithm is presented for modelling the micro-structure of a rough surface. A super-imposition tehnique is introduced to realize an idea of three-dimensional continuous self-similar micro-geometry. Scattering of radiation at the surface is described on the basis of an electromagnetic theory of diffraction. The proposed method is examined through a numerical calculation and through a laser-use bi-directional reflectance measurement.

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The enthalpy method for a solidification simulation is originally based on the explicit scheme. To enhance implicitness, we attempt to reformulate the thermal diffusion term into a linear function of enthalpy. In the proposed method, heat flux is expressed not by the temperature gradient, but by the enthalpy gradient. A transient phase change problem of a square cavity is stably demonstrated. Numerical diffusion of a transition region between liquid and solid phases is also surveyed at steady state.

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Measurements have been made to investigate the mechanism of turbulent heat transport in the thermal entrance region of a pipe. To capture the interface between hot and ambient cold fluids, we have developed new detector functions based on the the time-derivative of temperature fluctuations. The instantaneous position of the interface fluctuates widely around the time-averaged position in conformity to a Gaussian probability distribution function. As a result, ambient cold fluids penetrate deeply into the near-wall hot region. From the analysis of both the developing processes and the energy budgets of temperature variance and radial turbulent heat flux, it is shown that peak values of the productions of these quantities become gradually larger as the thermal boundary layer develops, whereas their diffusive transports near the wall reach a fully developed state very rapidly. The distributions of the turbulent Prandtl number show no similarity throughout the entrance region ; furthermore, they are not constant within the thermal boundary layer. This means that the analogy between turbulent heat and momentum transfer, which is often assumed in conventional heat transfer analyses, does not hold in the thermal entrance region of a wall turbulent shear flow.

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This study focusses on a new type of latent heat storage material (hydrate sodium acetate, CH₃ COONa·3H₂O, normal melting point of 58°), which stably maintains the supercooling condition with the aid of some additions. This phase-change material can store latent heat (liquid-solid phase) under the supercooling condition from -10°to 58°without the help of thermal insulation for a long time. This article discusses measured results of physical properties of this phase-change material, i. e., thermal conductivity, spcific heat, latent heat, density, kinematic viscosity and crystal growth speed under various temperatures (solid and liquid phases), including the supercooling condition.

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The replacement of working fluid of the alkali metal themoelectric converter (AMTEC) is eminently suitable for achieving higher performance under lower operating temperatures. Potassium is a reasonable condidate because it has lower latent heat of vaporization and higher vapor pressure than sodium over the AMTEC operating conditions. The performance of the AMTEC cycle with potassium as the working fluid has been evaluated and discussed based on the recently reported ionic conductivity data of potassium-β"-alumina solid electrolyte. The calculated results show that the replacement of working fluid increases the peak efficiency from 28% to 31% at 1100K with 1mm thick β"-alumina solid electrolyte. If the thinner solid electrolyte is practically developed, the improvement of the performance can obviously be recognized because of the decrease of ionic conductivity.

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An experimental study has been performed to investigate the freezing behavior on the convex wall of a return bend with a rectangular cross section. The experiments were carried out for the duct heights of 17mm and 30mm with a duct width of 300mm and a radius of curvature of 159mm. The convex wall temperature was uniformly maintained below the freezing temperature of water, while the concave wall was insulated. It was found that step wise ice formation was observed on the convex wall of the return bend and that the step position at the steady-state condition was closely dependent on both the water-flow velocity and the cooling-temperature ratio.

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Monochromatic radiative properties of anisotropically scattering fly-ash polydispersions in combustion gas, such as the extinction coefficient, scattering coefficient, scattering albedo and Ledendre expansion coefficients for phase function, are calculated by the Mie scattering computer code with the monochromatic complex refractive index measured and arranged in the wavelength region of 0.7∼13μm and with measured on estimated bimodal particle distributions of fly ash. The extinction and absorption coefficients calculated for fly-ash polydispersions almost agree with the results obtained by small particle (x«1) approximations when the Sauter diameter D₃₂ for polydispersions is much smaller than the corresponding wavelength (x₃₂<0.1), and they also agree with the complex refractive index near 1 (|m-1|«1) approximations when D₃₂ is much larger than the wavelength (x₃₂>10), but in the intermediate region (0.1<x₃₂<10), exact numerical calculations of Mie scattering are required.

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Effects of heat loss and flame stretch on the lean-limit extinction of laminar premixed flames in a stagnation point flow have been studied experimentally. The bulk stretch rate was varied from 40s^-1 to 420s^-1, while the Lewis number (Le) was varied from 0.85 to 1.8. The extinction of the lean propane/air flame (Le>1) is mainly caused by the flame stretch. On the other hand, the extinction of lean methane/air and lean methane/CO₂-O₂ flames (Le<1) is caused not only by flame stretch but also by heat loss, since the flame is intensified by the Lewis number effect. Therefore, heat loss is predominant in the case of the lean methane/CO₂-O₂ flame whose Lewis number is smaller than that of the lean methane/air flame.

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High-intensity premixed combustion [0.71-1.12×10⁹kJ/(m³·h)] was achieved using an opposed jet burner. The NO_x emission was measured by an NO/NO_x chemiluminescence analyzer. Maximum NO_x formation measured was extremely low and varied from 20 to 40ppm, depending on the combustion intensity. Such a low NO_x formation is attributed to the short residence time and the structure of the distributed reaction zone. The contribution of the Zeldovich mechanism is suppressed and the NO_x originating from prompt NO is predominant in the distributed reaction zone. The equivalence ratio at which NO_x maximizes was found to be 1.3. The temperature dependence of NO_x concentration can be given empirically by an Arrhenius expression.

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Research and development of an integrated coal gasification combined cycle (IGCC) have made steady progress. Low fuel-NO_x combustion technology presents great potential for improving IGCC combustors. The authors have developed an advanced rich-lean combustor designed mainly for achieving low-NO_x combustion and flame stability. Under pressurized conditions, we have success-fully reduced the NO_x emissions (to 60ppm corrected at 16 percent O₂) when ammonia concentration was 1000ppm. We have also optimized many design guidelines by clarifying the effects of pressure on combustor performance. This paper describes in detail the characteristics of the advanced rich-lean combustor for use in IGCC.

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Recently, experimental studies on closed cycle MHD power generation are being carried out as a promising topper generating cycle for gas turbine combined cycles. In closed cycle MHD, a working gas (argon or helium) should be heated up to about 2000°C by combustion gas. Therefore, development of a 2000°C class high temperature heat exchanger is required. A pebble bed regenerative heat exchanger was installed in the FUJI-1 test facility at Tokyo Institute of Technology, inhere maximum operating temperature has been limited to about 1850°C due to use of Al₂O₃ pebbles. This paper describes the reconstruction work on this heat exchanger aiming at increasing its operative temperature up to about 2000°C. New brick and pebble materials, made of Y₂O₃ stabilized ZrO₂ have been developed for this reconstruction work. The reconstructed heat exchanger is successfully operated at a maximum temperature of about 2100°C.

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The purpose of this study is to collect basic data required for the development of mercury heat pipes operating in the temperature range of 350°C to 600°C, which will be used in the industrial field. For this purpose, three kinds of mercury heat pipes were made of stainless steel tubing (SUS 316L) having 25mm in diameter and 1000mm in length. As a result of these tests, it was concluded that the mercury heat pipe exhibits good performance except during start-up, but the material compatibility of the stainless steel tubing and mercury is not very good.

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In order to obtain a general aspect of the spontaneous ignition in a fuel spray injected in compressed air at high temperature, which takes place usually in diesel and pulse jet engines, an experimental method using a shock tube is developed. A shock wave driven by high-pressure He gas propagates in the air in the low-pressure tube and reflects at a shock tube end. Through application of the pressure of the shock wave at reflection, n-octane fuel is injected into the air behind reflected shock waves in the shock tube. The fuel injection space is optically separated into 5 regions in the vertical direction, and the induction period of spontaneous ignition in each region is separately observed. As the induction period fluctuates markedly, the measured results are treated statistically and analyzed on the basis of the stochastic ignition theory.

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This paper discuses the atomization mechanism of a spray injected into a low-pressure field, as the focus of an injection system in a suction manifold of gasoline engines. Pure liquid fuel, which is n-Pentane or n-Hexame, is injected into a quiescent gaseous atmosphere at room temperature and low pressure through a pintle-type gasoline injector. Fuel sprays are observed through photographs with varying the back presure, and the changes in spray characteristics with the back pressure below atmospheric pressure are examined in detail. In particular, in the case of back pressure below the saturated vapor pressure of fuel, atomization mechanism is discussed from the viewpoint of the flash boiling phenomenon. Spray characteristics can be obtained with the pressure difference between the back pressure and the vapor pressure, corresponding to the intensity of the flash boiling, for various fuels.

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Spark ignition properties of combustible mixtures under high turbulence intensity conditions were studied using an ignition device which was able to vary the energy of capacitance and subsequent sparks independently. High-intensity turbulence was generated by mutual collision of injected mixtures at the center of a cylindrical combustion chamber. From schlieren photographs of flame kernel development, it was observed that turbulence had little effect on the flame kernel shape in the incipient stage. The experimental results showed that addition of the subsequent spark to the capacitance one improved ignition ability especially under high turbulence intensity conditions and that high ignition ability was obtained by an increase in the ratio of the subsequent spark energy to the total spark energy.

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The effect of the dimensions of the prechamber was researched using a medium-sized single cylinder engine. The air fuel ratio, A/F in the prechamber changed quickly, when only gas was supplied to the prechamber. The amount of gas supplied, ignition timing, and A/F in the main chamber were affected by the A/F in the prechamber at ignition timing. The larger volume ratio of the prechamber results in a higher level of NO_x and lower level of SFC. However, the dimensions of the hole result in improvement in the SFC level while maintaining the same level of NO_x. Suitable A/F in the prechamber allows the engine to the function, but this is also the source of NO_x. The volume of the prechamber must be small and the dimensions of the hole must be optimized.

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A three-dimensional turbulent jet discharging from a round nozzle along a flat plate has been studied experimentally. Measurements of the three components of mean and fluctuating velocities and the wall shear stress were obtained with a hot wire in various cross-stream planes. The estimation of the Reynolds stress balance was made with the help of the experimental results, and the role of the Reynolds stress to the jet diffusion was discussed. These results suggest that the jet behavior is explained well with the Reynolds stress distribution and that the pressure-strain correlation in the Reynolds stress balance is fairly approximated by the LRR's turbulence model.

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