The results of finite-difference solutions and experiments on low Reynolds number flows in axisymmetric circular tubes with abrupt enlargements and contractions are reported. Stream-lines and vorticity contours by the solutions with slip boundary conditions for rarefied gas are presented as functions of Reynolds numbers, Knudsen numbers, and momentum accommodation coefficients. Liquid flow visualizations using an aluminium dust method are in accordance with the stream-lines of the numerical solutions with non-slip boundary conditions. Measured pressure distributions of slightly rarefied-flows at the inner walls of the tubes are compared with the numerical solutions with slip boundary conditions.

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This paper describes experimental and theoretical bulk speeds in a circular pipe for some periodically oscillating air flows produced by two pistons with arbitrary phase differences including 180°. The following facts are found for the experimental conditions having a Reynolds number R_e= 1.32×10⁴-5.94×10⁴ and a reduced frequency √(ω')=10.9∼18.8. (1) The results of numerical simulation fairly well coincide with those of experiments. Therefore, the method of characteristics can predict, with good accuracy, the bulk speed of oscillating flows produced by two pistons. (2) The flows are almost axisymmetric. (3) When the piston phase difference is equal to 180°, the compressibility has no effect on the flow. But that effect becomes more remarkable as the phase difference becomes smaller from 180° to 90°. (4) If the effect of compressibility is comparatively small. the bulk speed is controlled by the time-averaged piston speed.

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A pressure control system using high speed on-off solenoid valves is treated in this paper. In the treated system, solenoid valves are connected to a cylinder. Such a system is commonly used in the anti-skid system for automobile use. The pressure transient behavior in such a system is calculated numerically using a characteristics method. The numerical results coincided with the experimental results. This method, however, is inconvenient for the purpose of system design, because there are many governing parameters. Therefore a simple design method using approximate analyses is proposed in this paper. The approximate method can only predict parts of pressure transient behavior in the system, but is very effective for determining the values of governing paramters on the occasion of system design. Newly desinged high speed on-off solenoid valves with 1 ms response time were used in the experimental work of this study.

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A new approach is proposed to investigate the frequency response of fluid in piping systems which include elements of complex geometry, A panel method was applied to the complex element and its adjacent parts, to make three-dimensional calculations. At both ends of the region in consideration, the assumption of a plane wave was employed. If the boundary condition is assigned at one end, the condition at the other end is determined from the law of mass conservation over the whole region in consideration. The employment of this condition, which has not been considered in the literature, is the feature of the present method. Numerical examples are shown for a divergent-convergent pipe element and for a strongly curved S-shaped bend.

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Quadrant analysis has been used to investigate the events contributing to Reynolds shear stress in the turbulent boundary layer over a d-type rough surface at a low-Reynolds number. By partitioning the stress into ejections, sweeps, and inwards and outward interactions, it was shown that the second quadrant, namely the ejection phase was the dominant event contributing to the stress through most of the boundary layer. Compared with the turbulent boundary layer over both a k-type rough surface and a smooth wall, the ratio of the fractional contributions of the second quadrant phase to the stress to that of the fourth quadrant one, and the ratio of the mean periods of those occurrences evaluated for a present wall flow were found to differ significantly. There existed a little correspondence between VITA events and the second and fourth quadrant type of events detected with the uv quadrant method.

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The phenomenon, that the flow rate of a loop with a cross pipe switches nonperiodically between a high level and a low level under certain flow conditions was found and experimentally investigated by using air and water. The flow behaves as if a bistable flow state exists like a flow in fluidics. It is observed by a flow visualization technique (spark tracing method and air injection method) that the switching synchronizes with the generation and the collapse of a swirl flow through opposing laterals of the cross pipe. The pressure loss coefficient of branching at the low flow rate level is about twice as much as that at the high flow rate level.

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The response of aerodynamic forces on a vehicle model passing in a wake behind a model of a main tower of a big suspension bridge has been investigated in a wind tunnel. A splitter plate placed behind a tower model prevents the vortex street from shedding in the wake and the effect of surviving velocity gradients is examined. We have prepared two kinds of vehicle models: a cylindrical model with a rectangular section and a box model. The results of the present study may be summarized as follows: (1) When a cylindrical model passes through the wake of a tower model with a splitter plate, the aerodynamic forces are influenced by the effects of an apparent angle of attack, the interference between the flows around a tower and a vehicle, and the effects of transient characteristics of flow. In the case of a box model, the aerodynamic forces are governed by the effects of the angle of attack (2) The fluctuation in a side force exerted on a cylindrical or a box model corresponds to the fluctuation in wind due to a wake vortex street behind a tower model, and its amplitude remarkably increases when a vehicle model gets out of the wake. (3) The aerodynamic forces on a box model respond more rapidly to the change in wind velocity than ones on a cylindrical model.

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Numerical solutions of the Navier-Stokes equations for a Poiseuille flow past an infinitely long square cylinder between two parallel walls are presented in the range of intermediate Reynolds numbers. The main object is placed on selecting the best way to make difference equation for the vorticity at corners. In the case that a position of a body is unsymmetry, the stream function on the surface is decided by a condition that the pressure is single-value. This way has been first proposed by Matida et al. treating the same flow model. Our results for some properties are investigated in more detail with finer one than their mesh length. Especially, the extrapolation from each value obtained in the mesh length of 0.1, 0.05 and 0.025 are given for drag, Iift and moment, respectively. Lastly, the flow patterns of interest are given at R_e=20, 40.

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The equation derived by Falkner and Skan has similar solutions for two-dimensional laminar boundary layer. It has received considerable attention and the existence and uniqueness of its solution have been investigated numerically and analytically. In this paper, similar solutions of the boundary layer which develops on stationary axisymmetric bodies of revolution in swirling axial streams are investigated. The meridional equation is the same as the Falkner-Skan equation except for the term representing the component of centrifugal force. The effect of rotation largely influences the solutions for equations. The existence of solution and branches similar to those in the Falkner-Skan equation are shown.

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The conditions of occurrence and characteristic frequencies (frequency of travelling azimuthal waves, and their frequency of modulation in the laboratory or rotating frames) of modulated wavy -Taylor-vortex flow (MWVF) between two concentric spheres with the inner sphere rotating are investigated by flow visualization (aluminum-flake method) and spectral measurements by means of light scattered by suspended aluminum flakes. Also, a modal analysis of MWVF is made, and the relations between these characteristic frequencies are considered. Quantitative data concerning the conditions for the occurrence of MWVF and dependence of these characteristic frequencies on Reynolds number are obtained. The relations between these characteristic frequencies of the spherical Couette flow system are found to be different from those in a circular Couette flow system.

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A discrete-vortex simulation has demonstrated that a flat plate being rotated 180° impulsively from its initial state, which is parallel to a uniform main flow, can produce isolated vortical structures. The rotation is around the mid chord, the trailing or the leading edge of the initial configuration. The vortical structures produced by the plate rotated in these modes are presented and discussed for a few typical values of the spin parameter. Especially the rotation around the trailing edge gives rise to a vortex pair travelling downstream. Paths of the vortical structures and their circulation as functions of the spin parameter for each mode of the rotation are also presented.

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The biconjugate-gradient method is applied to the finite element analyses of the Navier-Stokes equations. The minimum storage requirement is realized by use of the hybrid mesh which is com-posed of the usual irregular elements and the regular elements. since the matrices emanating from the regular meshes have a regular structure and need not be stored entirely. The convergence of the iterative procedures is accelerated by the multi-level meshes which consist of several meshes of different mesh size. The flow in a driven cavity and the channel flow past a valve are computed to show the practicability of the proposed methology.

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In order to make the simplest flow field of opposed jets, two circular pipes having the same geometrical dimensions were employed. Factors influencing the position of the impinging surface were experimentally studied by means of a rotary hot-wire anemometer. As a result, it was found that the position of the impinging surface was mainly decided by the pressure-diffusion term of the well known turbulent energy equation ; and a peculiar phenomenon on the center line velocity field was found.

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Experimental studies have been made on a three-dimensional separation zone at the segmented leading of a long blunt plate with right-angled corners. The leading edge is periodically segmented into a isosceles triangle with the apex angle e being changed from 180° to 60° with an interval of 30°. Surface flow patterns are presented and interpreted by nodes and saddles of the skin-friction vector field and by reattachment and separation lines. Distributions of time-mean and root-mean-square pressures on the surface are also discussed in terms of these singularities and the characteristic lines. The longitudinal extent of the separation zone defined as the distance between an apex and the most downstream reattachment saddle is less than that of the two-dimensional separation zone (θ=180°). The separation zone is dominated by spanwise large-scale vortices when e is more than a critical value θ_c(≒100°) and by longitudinal vortices when θ<θ_c Finally, the frequency at which the large-scale vortices are shed from the separation zone is found to increase with decreasing apex angle.

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The present method is based on the fringe shifts of interferograms from different ray directions around the temperature field. The contour of the temperature field is obtained from the envelopes drawn at the boundary of each fringe shift. The temperature are evaluated by solving the simultaneous equations of the first degree for the unknown refractive indices at the grid points in the contour of the temperature field. The method has been applied to the temperature fields of natural convection caused by heated plates as well as to those of heated-air jets with rectangular exit. The results have been compared with the temperatures measured by a thermocouple. It is found that the present method may be useful in evaluating temperatures and/or densities in some complex fields.

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The unsteady motion of a two-dimensional incompressible shear layer and its mass transfer process were numerically simulated by using the Discrete Vortex Method combined with the third-order Upwind Finite Difference Method. The visualized distribution of mass concentration showed that the occurrence of entrainment corresponded to the large eddy motion. The distribution profiles of the average concentration and the fluctuation intensity showed similarities. The distribution profile of the average concentration had a stepwise shape and that of the fluctuation had two peaks. The entrainment of the fluid of the high speed side proved to be larger than that of the low speed side.

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In this paper, prediction of the shaft power is studied. The slip factor and the leakage flow factor used for the performance calculation are obtained experimentaly. The method of prediction of the shaft power is based on the angular momentum theory, and it is derived from measurement of the slip factor, blockage factor and leakage flow. The slip factor is strongly related to the blade angle β₂, the number of blades Z and the capacity coefficient φ, and it is smaller than 0.35 at 170 degree of β₂, which is much smaller than that for the backward blades. The difference between the calculated values and the experimental results on the shaft power is 5 % for the range of φ less than 0.3 and is 11 % for φ= 0.45.

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In this report, the bending moment in the root of a rotating blade was directly measured by strain gages, and these experimental values were compared with the theoretical values estimated by annular momentum theory. In the experiment, a middle scale horizontal axis wind turbine having a diameter of 6 mφ was used. The maximum power of the turbine was 10 kVA. The number of blades was two. As a result, the following facts were found ; (1) Both values (theoretical and experimental) agree well. (2) The mean values of lapwise moment in the blade root were about three times larger than those of the chordwise moment. (3) The chordwise moment caused by the dead weight of the blade was very large compared with the chordwise moment caused by the fluid force. (4) The instantaneous moments in the blade root were about two times larger than those of the mean values per about I minute.

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In order to distinguish the impulsive pressures of a liquid microjet and a shock wave, a local pressure sensor was manufactured for trial. The local pressure sensor was composed of four local pressure sensor elements, whose sensitive area was made as small as possible. Each pressure sensor element was made of a tip which was cut out of a barium titanate pressure transducer by a string saw to be 0.45 mm in width and 5 mm in length. The gap of each sensor element was filled with soft-type silicon resin to prevent their interaction of outer pressure action. By the local pressure sensor an impulsive pressure generated by the collapse of a spark-induced cavitation bubble was detected and the pressure of a water microjet was distinguished from that of a shock wave. The result was ascertained by high-speed photographs, which indicated water microjet generation in the collapsing cavitation bubble.

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Variable area cage, contoureed plug and multi-hole cage valves are tested over a range of pressure reduction from 0.1 to 5 MPa. The valve size is almost 100 in Cv value. Acceleration data at the wall are analyzed in the frequency range over 100 kHz, introducing the following representations: ( a ) Rice frequency as a center frequency to find the incipience, and ( b ) spectrum amplification to determine the critical stage. The choking is determined by the data of pressure fluctuations in the pipe. The three limits show a power law correlation between the cavitation number and the discharge coefficient. Cavitation pictures taken at a low pressure condition are also presented for the clarification of the bubble configurations.

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When a valve opens rapidly in a hot water emergency dump line or in a closed piping system where the steam side is separated from the cold water side by a valve, pressure oscillation is induced. The oscillation mechanism and influential parameters of this phenomenon were investigated experimentally. It was found that the oscillation in the hot water emergency system was induced by transient two-phase flow due to self-flashing of hot water downstream of the valve, and that in the closed piping system it was induced by transient two-phase flow due to steam condensation caused by the contact between steam and cold water In order to prevent this phenomenon, it is most important to decrease the thermal non-equilibrium in the piping system.

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Statistical characteristics of pressure drop fluctuations have been investigated experimentally in order to obtain fundamental data for flow pattern identification of two-phase flow in a horizontal pipe. The experimental results show that the horizontal flow of nitrogen gas (or air) -water mixtures exhibits peculiar features of statistical properties (PDF, PSD), that its flow patterns can be classified by using the statistical features, and that the pressure drop fluctuations measured at a short interval of pipe have high sensitivity to flow change. The results suggest that it is possible to identify the flow patterns of horizontal two-phase flow on the basis of the features of statistical parameters (standard deviation and coefficients of skewness and excess).

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A cold-air study of an air cooled radial turbine was carried out to find out the effect on the aerodynamic performance of the coolant-air ejection from the pressure surface of the nozzle blades. The testing of the investigation was conducted at pressure rations of 1.5, 2.0 and 2.5 and over a range of coolant-air to primary-air mass flow percentages from zero to six percentages. The rations of coolant-air to primary-air temperature were from 0.7 to 0.8. Two calculation methods of the performance of the air-cooled radial turbine were proposed. One of them needs data of a noncooled radial turbine performanse ; the other does not need them. Both calculations are able to predict well the performance.

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Compressors in small gas turbines are usually composed of single stage centrifugal compressors, and their high efficiency and wide operation range are very important for the gas turbines. Although much research on fundamental technique have been reported by many researchers, there are questions to solve by practice in designing high pressure ratio machines. In this paper the authors relate the aerodynamic design and the experimental result of the advanced high pressure ratio centrifugal compressor for gas turbines.

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Front and rear spoilers have been in use as aerodynamic aids for automobile drag and lift reduction. However, the flow field effects which produce these improvements have not been well understood. Wind tunnel tests were perfomed under the boundary layer control using a suction box and a moving ground plane. A body similar to a ground vehicle such as a bus is proportioned. The model is tested with wheels, a front spoiler, a rear spoiler and proximity to the moving ground plane. Results are presented from an experimental study of the lift, drag, pitching moment and flow field of the near wake of the body. These spoilers reduce the aerodynamic lift and pitching moment for improved high speed stability and handling. The rotation of wheels is found to give significantly different lift and drag for small ground clearances characteristic of actual road vehicles.

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An analytical and experimental study has been performed to investigate the heat transfer characteristics of the unsteady natural convection of heat generating fluid in a horizontal cylinder. Experiments were carried out with dilute electrolyte which was heated by passing alternating current through. The rate of heat generation was constant and uniform, but changed stepwise with time. The temperature profiles and the heat transfer coefficients were determined with an interferometer. The governing differential equations were solved numerically to simulate the velocity and temperature distributions. From these results, the maximum temperature, and the maximum stream function and overall Nusselt number were correlated in terms of the Rayleigh number and Fourier number. The transient period, which is the time interval needed to get to a steady state, was also correlated to the Rayleigh number.

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The purpose of this paper is to obtain fundamental information concerning the heat transfer process and breakup behavior characteristics of individual small droplets impinging upon a hot surface. A uniform sized water droplet array at room temperature under atmospheric pressure was produced by the vibratory method to impinge upon a heated flat copper surface. And then, heat transfer from a surface to the droplets is assessed by a transient technique. Further, the deformation and the breakup behavior owing to the impingement of the droplet is observed by means of a drum camera recording high-speed microscopic photographs. Heat transfer effectiveness in a low temperature range of less than 125°C decreases as droplet impingement frequency increases because of interference between the impinging droplet and the remaining liquid film on a surface. It is possible that heat transfer per droplet is transfermed into a heat transfer coefficient by use of droplet residence time and film contact area on a surface. And Variations in the heat transfor coefficient for a droplet array with surface temperature are measured by difference calculus of the one dimensional unsteady heat conduction equation.

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An experimental study has been made on the forced convection boiling heat transfer in a narrow space The heated surface diameter was 20.0mm. The distance between the nozzle plate and the heated surface was changed within a range from 0.3 mm to 0.6 mm and the nozzle diameter was 2.2 mm. Saturated water was impinged on the center of the heated surface and flowed radially on it. In this report the nozzle plate had a flat bottom which was parallel to the heated surface. It is clarified in the present study that heat transfer characteristics varied with the change of space and mass flow-rate of the impinging jet, especially in the region of transition boiling. The quantity of maximum heat flux increased as the space decreased.

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Boiling heat transfer to an impinging jet which then flowed radially in a narrow space was studied experimentally. The space was confined with a circular heated copper surface of 20 mm in diameter facing upward and a nozzle plate of the same diameter parallel to the heated surface. In this report the nozzle plate had a brim of small height at its edge and a part of the radial flow was stemmed there. The aspects of boiling and fluid flow in the space were largely changed with this brim and the maximum heat flux was improved by about 45% compared with those in the 1st report, where the space was not limited at the end. The scale deposited on the heated surface was much reduced with this type of nozzle plate.

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The purpose of this paper is to investigate the fundamental features of R-113 pool flashing under rapid depressurization. Blowdown flashing of R-113 is initiated by the electro-magnetic valve opening and outflow of vapor from a pyrex glass vessel through the top orifice of designated diameter From the experimental results, it is remarked that the measured pressure variation in the vessel is characterized by a rapid decrease from the initial conditions to a level corresponding to the inception of flashing far below the saturation pressure and sevemal types of recovery by flashing. A two phase mixture yielded by its boiling spreads down from the vicinity of the free surface to the bottom of vessel. Furthermore, superheat limit of liquid R-113 under depressurization depends mainly on the depressurization rate in the present experiments. This limit of superheat corresponds to Gibbs number ; G_b&cong;22, according to the results of application of heterogeneous nucleation theory to our measured data.

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Critical heat flux (CHF) in a coexistence of saturated pool boiling with a liquid level below H=8 mm and forced convective boiling on an open heated disk being supplied with a saturated liquid through a small jet impinging at the center of the disk is studied experimentally employing Refrigerant 113 at atmospheric pressure. The characteristics of CHF in the coexisting boiling are categorized into three groups whose boundaries are dealt with depending on the liquid level and the jet velocity The experimental data of CHF for the liquid level of H=1 mm are predicted by the generalized correlation predicting the CHF for forced convective boiling with an impinging jet.

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Experiments were performed to obtain data for the heat transfer characteristics of latent thermal energy storage capsules. The arrangement of the capsules was in alignment with the flow direction. During the melting of the phase change material (n-Octadecane), there is less difference in the phase change rate of each capsule than for the solidification case because of the effect of natural convection in the liquid phase on heat transfer. It was also shown that the non-dimensional time required to complete the solidification of each capsule can be arranged without distinction of the rows in the flow direction.

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Analytical considerations were presented for the solidification process of latent thermal energy storage capsules. The arrangement of the capsules was in alignment with the flow direction. It was shown that good agreement between the predicted and the experimental results can be obtained by application of the quasisteady assumption on the solidification process. Numerical calculations for fifty rows of capsules showed that there is a certain location in the rows where the heat transfer rate between the capsules and the flow shows a maximum value, and the location moves to the down-stream rows as time proceeds.

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The enhancement effect of radiation heat transfer based on the multibands feature of radiative gas is analysed theoretically for the system of laminar-channel flow of high temperature C02 gas between two parallel heat absorbing surfaces. An integro-differential equation of energy conservation, which takes into account the multi-bands feature of the radiative gas is solved numerically, and the enhancement effect of heat transfer by installing a solid plate in radiative gas is calculated. From these calculations, it is shown that the enhancement of local heat flux by as much as 80% is obtained and that this enhancement effect is caused by the very high radiative heat flux from the solid surface to the heat absorbing surface, notwithstanding the slight decrease in the radiative heat flux from the gas by installing a solid plate. It is also made clear that the analysis using the conventional gray gas assumption overestimates the decrease in the radiative heat flux from the gas, and thus estimates a too small enhancement effect.

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Vapor explosion after the collapse of vapor film around a single drop and plural drops of hot LiNO₃ submerged in tapped ethanol, whose degree of subcooling is widely changed, are studied by photographic observation and pressure measurement. At small degree of subcooling the vapor bubble region expands rather gradually and the pressure curve has only a small peak which is correspond to the vapor film collapse. At large degree of subcooling the curve has three typical peaks, and the third peak is generally the maximum. The propagation phenomenon is photographed by plural drops experiments. Since the pressure curve of plural drops is similar with that of a single drop, the coherence of the phenomenon during the whole process is confirmed. A model for vapor explosion mechanism is proposed and discussed. The maximum pressure peak is considered to be depend on the same mechanism with that of the cavitation which generates at the collapse and reexpansion of cavitation bubbles.

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Experimental measurements on ablation properties of fine ceramics SiC and Si₃N₄ are performed in an atmospheric high-temperature argon plasma free jet The heat of ablation is measured for the heat flux of 1.2∼2.6×10⁴ kW/m². It is about 2×10⁴ kJ/kg for Si₃N₄ and 5-8×10⁴ kJ/kg for SiC. In addition, features of the ablated surface of the materials are observed with the aid of an electron microscope, and the mechanism of the ablation is discussed on the basis of it.

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An experimental study of the absorption process of water vapor into a lithium bromide solution film was performed. The lithium bromide solution is circulated between the absorber and the generator vessel. The absorber is a chrome-plated brass tube of 84 mm outer diameter and 400 mm length. The solution is fed from the annular slit at the top of the pipe. After absorbing water vapor, the weak solution is fed to the genetor for the recovery of concentration. The generated vapor is provided to the absorber vessel, and the enriched solution is then returned to the absorber. The absorbed water, which is measured as the vapor flow rate by a rotameter is plotted against cooling water temperature while keeping film thickness, inlet temperature and concentration constant. They are compared with the theoretical results by the method proposed previously. Although the experimental values are somewhat lower at 5 Torr, they showed good agreement with the theoretical ones.

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Some choresteric liquid crystals can be used as a thermometer because of their color changes with varying temperatures. However, it is impossible to employ human color sensation for precise quantitative evaluation of temperature from their color. Therefore, a new method of liquid crystal thermometry is developed using narrow band optical filters and an image processor to exclude the employment of human color sensation. Relations between filter wavelength and temperature were determined by calibration tests. Two dimensional temperature distributions on a heated plate were successfully measured by the present method.

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Two types of systems for measuring local humidity with optical fibers using infrared absorptimetry of water-vapor are proposed and the calibration results are presented. One uses a PbS infrared detector and a beam through 1.86μm narrow band pass filter (NBPF) and another uses a Ge detector and a beam through 1.37μm NBPF. Moist air with known dew-points of 10°C, 15°C, 20°C. 25°C and 30°C, and with 11 cm, 17 cm, 23 cm and 31 cm optical paths, respectively are used in the calibration test. Apparent absorption coefficients obtained, based on Beer's law, are 0.042 (kPa·m) ^-1 (the former system) and 0.035 (kPa·m)^-1 (the latter system), for different path lengths and the accuracy of the present measurements are estimated to be±1.1 g/m³ (the former system) and ±0.7 g/m³ (the latter system) for a 31 cm optical path. These results show that the latter system is more accurate at the present state and that the NBPF system is nearing a practical application.

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Catalytic combustion is controlled not only by surface reactions but also by gas phase reactions. When propane is used as fuel, contribution of gas phase reaction becomes significant, and fundamental information about gas phase reactions becomes important. From this point of view, experimental and theoretical studies were carried out for the catalytic combustion of propane on a platinum catalyst with a gas phase reaction. The platinum catalyst was placed near the stagnation point of a circular cylinder. Temperature and concentration profiles near the catalytic surface were measured These profiles were compared with the result of numerical calculations based on the three-step surface and gas phase reactions. Kinetic schemes proposed by Bracco et al. and by Bruno et al. have problems concerning their overall rate constants. So, new rate constants were proposed, and it was shown that calculated results based on new rate constants well predict the experimental results.

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The authors investigated the combustion characteristics and gas compositions of combustion with a closed vessel using hydrogen, methane, etc. which are attractive in view of the serious air pollution situation, and possible alternative fuels. As a result, it is possible to decrease the rate of pressure rise and the reduction of NO_x concentration by lowering the oxygen concentration in hydrogen-air mixture without deteriorating combustion characteristics such as combustion efficiency, maximum combustion pressure etc. And by using a blended fuel of hydrogen and methane, it was found that the reduction of the rate of pressure rise and NO_x concentration were obtained, in comparison with the use of hydrogen only ; and at the same time, the combustion efficiency and HC concentration were improved remarkably in comparison with the use of methane only.

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Sound-reducing and a flow-accelerating effect due to the attachment of a porous tube to an underexpanded nozzle was experimentally investigated and the most suitable length of the porous tube as a noise suppressor was examined. In the present experiment, the porous tube had the same diameter as the standard nozzle to which it was attached and also the porous pattern was fixed. The measurement of mean flow and turbulence of the jets from the porous surface of the tube was carried out as well as the measurement of sound and exit Mach number. The ratio of the jet pressure ratio to the atmosphere was mainly 3 and 4.5. It was demonstrated by the present experiment that the flow at the exit of the porous tube changes from underexpansion to correct or over expansion by its elongation and that there exists a kind of optimal length to suppress the jet screech according to its pressure ratio.

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The ignition delay of a diesel fuel was studied using a rapid compression machine that was developed in a previous study. By applying the hot motered technique proposed by Yu and others, the delay from the ignition start to the oneset of exothermic reaction and the delay required to pressure recovery were measured. The sum of the two delays was assumed to be the net ignition delay. Tests were performed for a range of air temperatures, pressures and fuel quantities. The results obtained are as follows : The temperature dependence of the initial delay is low at high temperatures due to physical effects such as heating up and vaporisation. The pressure recovery delay is largely affected by a fuel-air mixing rate below 750 K. Based on data obtained, an empirical formula of net ignition delay was proposed.

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When fuel is injected into the duct of a co-axial burner and a strong swirl is given to the outer air, two modes of flame, turbulent flame and flat flame, appear on the burner under some conditions If the exit is divergent, a stable flat flame may be realized, which features a compact and a high-density combustion. In the present study, the condition of forming such a flat flame mode was studied by measuring temperature, fuel mass concentration, and gas velocity at the burner exit. As a result, it has been suggested that the flat flame mode is formed if the centripetal force of the high-temperature combustion gases toward the burner rim exceeds that toward the burner axis.

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The scavenging efficiency of a two-stroke-cycle internal combustion engine is considered applying the numerical analysis technique developed by the authors. In this method liner ports are opened and closed by the reciprocating piston and so the unsteady scavenging flow in a cylinder can be simulated reasonably. Also, the scavenging efficiency can be estimated by analyzing residual gas concentration in a cylinder. The relation between liner port swirl angles and scavenging flow characteristics, especially the scavenging efficiency in a uniflow scavenging engine is obtained. An idea of liner port arrangement to improve the scavenging efficiency is proposed.

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A theoretical analysis was made of the transient fuel supply characteristics in a carburetor with secondary slow air bleed under decelerating drive conditions. Time-dependent one-dimensional equations of continuity and motion were derived for describing transient flow of fuel and air in the slow system of a carburetor, being solved by the finite difference method. Experimental work was also performed to verify the validity of the theoretical results. A carburetor under full-throttle operation was suddenly decelerated and the first appearance of fuel discharged from the outlet of idle port was detected by a set of phototransistor and LED. The results showed that the present analysis was successful in giving results consistent with experimental data. The secondary slow air bleed was found to be useful for improving the transient response of a carburetor. Delay time was mostly due to the period of time elapsed for fuel to arrive at emulsion holes of secondary slow air bleed.

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In this study, a thermal barrier (air gap) piston was used to improve the vaporization of methanol in the combustion chamber. The engine operating condition was fixed at 25 rps (1500 rpm) and wide open throttle. The experimental results are follows, (I) the degree of constant volume was improved about 2 % as compared to that of operation without the thermal barrier piston. (2) The indicated thermal efficiency was the same as that of operation with a fully vaporized methanol and air mixure. (3) The variation in maximum pressure and the rate of pressure rise were half that of operation with a liquid methanol and air mixture.

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Unburned hydrocarbon of Wankel type rotary piston engine is mainly emitted at the trailing portion of the combustion chamger. And, gas leakage, large surface to volume ratio of combustion chamber, and crevice volume and also caused by unburned hydrocarbon emission.

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The main causes of unburned hydrocarbon, or HC, emissions from Wankel type rotary piston engines were given in the first report. Test results of HC emissions from Wankel engines and the subsequent analysis and evaluation is shown in this second report. The characteristics of the unburned HC emissions have been reduced by after buring at the trailing side of the combustion chamber. Then, as a result of this study, a newly designed combustion chamber has been developed to reduce the HC emissions. Additionally, a change in HC, CO and NO_x emissions was observed when knoking occured.

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