To elucidate the influence of cavitation type upon cavity-breakdowns under violent vibrations on a cavitating hydrofoil, the lift-and the drag-fluctuations, the accelerations, and the corresponding cavitation aspects were carefully investigated in the water flow around an Eppler hydrofoil for various angles of attack, in which several types of cavitation, i.e., attached cavity-, traveling bubble-and mixed-type take place. It is found that a large difference in the lift fluctuation emerges between them. The lift fluctuation for the attached cavity reaches about 20 percent of the mean value and is larger than that of the mixed type, followed by that of the traveling bubble type.

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The cavitation process with a double peak in cavitation-events curve is examined in detail using circular cylinders of a large confinement ratio. Double-peak-type cavitation process means that cavitation bubbles redevelop to create the second peak of cavitation events after the first peak where cavitation bubbles occur and then become weak and/or disappear. At the time when the first peak transits to the second peak, the base pressure coefficient of a circular cylinder rises to a large extent and the alternate occurrence of vortex cavitation bubbles from both directions of the shoulders on a circular cylinder breaks down and is suppressed. Finally, it is made clear in the present investigation that the occurrence of cavitation bubbles can cause the transition of flow regime, especially the critical flow regime from subcritical flow towards supercritical flow.

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The structure of the separation vortices shed from a square plate standing vertically on a flat ground wall where a laminar boundary layer was developing was examined by means of a visualization technique. The following results were obtained. The structure of the shedding vortex could be classified into four patterns in terms of both the Reynolds number Re_h and the ratio of plate height to boundary layer thickness h/δ. The four patterns were : a horseshoe-like trailing vortex, a pair of ordinary trailing vortices, a row of symmetrical hairpin vortices and a row of asymmetrical hairpin vortices. It seems that the vortex pattern is mainly affected by the location of a stagnation point on the front surface of the square plate.

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This paper presents an experimental study on the flow around tapered and stepped circular cylinders and the structure of the shedding vortices. The surface pressure distributions on the cylinder and the spectra of the wakes were measured for them. The main results are as follows. (1) In the case of the tapered circular cylinder, the shedding vortices are connected within some spanwise width. The break points of the cell appear in a spanwise surface pressure distribution before the separation point. (2) In the case of the stepped circular cylinder, the Strouhal number is larger than that of the straight circular cylinder in the region where the pressure balances spanwise in the wake. (3) In the case of the stepped circular cylinder, the shedding vortices from small and big cylinders are connected with each other for a diameter ratio of more than 0.64 and are broken for a diameter ratio of less than 0.56.

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To facilitate improvement of the reliability of hydraulic machinery, detailed behavior of the violent vibrations is systematically observed by means of high-speed stereophotography for the Eppler hydrofoil. We can clearly observe the following three types of violent vibrations : (i) those resulting on a single attached cavity at a larger incidence α_i, (ii) those resulting on large travelling bubbles at a small α_i, (iii) the mixed type.

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This paper describes air-entraining vortices generated when water is drained from a vessel. The liquid used in this experiment is a mixture of water and bentonite. By changing the mixing ratio, the coefficients of kinematic viscosity of the liquid were changed to six values ranging from 0.015 to 0.0625 cm²/s. Air-core vortices and vortices without air core are not generated in liquid deeper than a certain depth. In the scope of this experiment, this depth increased with the increase of flow quantity. Also, it was found that vortices were not generated at the value of the radial Reynolds number Rr derived from the equation of motion lower than a certain value. For example, in liquids having the coefficients of kinematic viscosity, υ=0.0105 and 0.0652 cm²/s, air-entrained vortices are not generated at Rr < 3000 for the former and Rr < 800 for the latter. Although the inner diameters of effluent pipes were 2.03, 3.23, and 5.15 cm, effects of the difference were hardly found. However, it was found that the values of Rr in this limit were reduced as the viscosity of liquids increased.

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In order to improve the reliability of butterfly valves, it is absolutely imperative to prevent fatal cavitation erosion. In our previous studies, we developed a new butterfly valve with a tunnel-type buffer, and showed that it was effective in suppressing cavitation erosion on a specific valve opening when the erosive vortex cavitation occurred predominantly on a typical valve. Practically speaking, when the valve is operated near valve closure, erosion is an especially big problem. In this paper, therefore, the cavitation shock pressures and the highly erosive vortex cavitation arising around the butterfly valve with the tunnel-type buffer are compared with a typical valve counterpart by means of pressure-sensitive films and high-speed photography. It is found that the tunnel-type buffer is also useful in preventing erosion near valve closure.

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In order to clarify the mechanism of water-jet erosion, we systematically investigate the erosion-standoff-distance curves, the erosion-time curves, and detailed aspects of the eroded surface for two typical types of nozzles, i.e., conical and cylindrical nozzles. Clearly, the erosion-time curves are markedly different at the 1st peak, at the valley and at the 2nd peak. Hence, the mechanism of erosion is significantly changed with an increase in the standoff distance χ.

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The motion of a spherical particle in oscillatory flows is analyzed numerically. The so-called B.B.O. equation is used as the basic equation at low Reynolds numbers below 0.1. A new method of numerical analysis of the B.B.O. equation is proposed. The oscillatory flows considered here are sinusoidally time-dependent flows. The amplitude ratio of the fluid and the particle, the differences in the velocity between the fluid and the particle, and the dependence of the Basset history term on the velocity are obtained numerically. The numerical results quantify the deviation of the particle from the fluid itself. It is established that the differences in the dimensionless velocity between the fluid and the particle are much larger than the differences in the amplitude ratio of the fluid and the particle, and the Basset history term of the B.B.O. equation can be neglected at low dimensionless frequencies below 0.01.

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The leading-edge separation bubble of a blunt circular cylinder of diameter d was forced by sinusoidal disturbances with single frequency components at Reynolds numbers of the order of l0⁵. The disturbance was introduced by a woofer installed inside the cylinder through a thin slit along the separation edge. The level of forcing was defined in terms of the rms value of the velocity fluctuation of the forcing frequency at a position immediately upstream of the separation edge q'_f, being in a range of q'_f/U_∞=0.005-0.1, where U_∞ is the main-flow velocity. The reattachment length plotted against the forcing frequency attained a minimum for low and high forcing levels, and two minima for intermediate forcing levels, at frequencies in the range of (1.6- 2.1) U_∞/d. The minimum value decreases with increasing Reynolds number. A maximum of the reattachment length, which was greater than that without forcing, appeared at a forcing frequency of approximately one-half of the frequency of the Kelvin-Helmholtz instability immediately downstream of the separation edge. The reattachment length was independent of the forcing frequencies if they were greater than twice the Kelvin-Helmholtz frequency.

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A vortical structure within a turbulent boundary layer and spanwise variation of turbulent flowfields have been investigated for further understanding of the development of turbulent boundary layer interacting with the spanwise periodic longitudinal vortex arrays which is artificially generated in a free stream. One of the parameters, spanwise periodicity of longitudinal vortices L/S (L denotes the spanwise distance between neighboring airfoils, S airfoil span), rules both magnitude and streamwise path of secondary vortices caused within the turbulent boundary layer. As a result, whether the turbulent quantities show linear or nonlinear interaction is significantly dependent on the value of L/S. Therefore, in the case of L/S< 1, although the spanwise distortion of turbulent quantities in the outer region is not remarkable, those spanwise periods change in the streamwise direction due to the rapid vortex diffusion following corotating vortex amalgamation. However, in the case of L/S >1, turbulent quantities show a noticeable spanwise periodic variation corresponding to the arrangement of airfoil elements, and those spanwise periods are strictly maintained. Comparing the spanwise variations of turbulent flowfield and those of mean flowfield, mechanisms of spanwise variation of turbulent boundary layer are discussed.

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In this study, compressibility effects on turbulence were analized by performing Direct Numerical Simulations (DNS) of compressible isotropic turbulence. In compressible turbulence, there are two dilatational terms ; dilatation dissipation (ε_d) and pressure-dilatation correlation (PD), and one solenoidal term ; solenoidal dissipation (ε_s). These terms influence the decay rate of turbulent kinetic energy. Dilatation dissipation is inherent in compressible turbulence and is affected only by the dilatational velocity field. 0n the other hand, solenoidal dissipation is determined by the solenoidal field. Using the Helmholtz decomposition of the velocity field into solenoidal and dilatational components, turbulent kinetic energy was divided into two parts : a solenoidal part (q²_I) and a dilatational part (q²_c). The relationship among q²_I, q²_c, ε_s and ε_d was introduced by using the energy spectrum, and DNS results were shown to be in good agreement with this relationship. The role of PD and the asymptotic values of the dilatational part of turbulent kinetic energy or pressure fluctuation variance were also analized. Finally, a new model for turbulent kinetic energy and pressure fluctuation in compressible isotropic turbulence was proposed.

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With the aid of direct simulation data (DNS), we have constructed near-wall modeling of the dissipation-rate equation for a κ-ε turbulence model. All the budget terms in the exact ε-equation are incorporated in the modeled ε-equation, and both term-to-term and overall comparisons of model predictions with the DNS data are performed. It is found that the wall region should be partitioned into at least two regions so as to reflect different mechanism of generation processes in the dissipation of turbulent kinetic energy. Pressure diffusions in the κ-and ε-equations are found to be equally important and thus be modeled. Comparisons of the resultant κ-ε model with the DNS data of channel and flat-plate boundary layer flows show close agreement of various turbulent quantities. In particular, near-wall behavior of ε is accurately reproduced with the present model.

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When a fluid flows through a curved pipe, there exists a secondary flow. and the frictional resistance increases considerably compared to that of a straight pipe. The friction factors of curved pipes have been studied by many investigators theoretically and experimentally, but literature on three-dimensional coiled pipes is seldom found and there still remains an unexplored domain. The purpose of this paper is to present results of measurements of the hydraulic losses for flow through such tubular coils wound continously in a figure 8. Consequently, it is confirmed that the friction factors in coils λ_n decrease with the increase of the number of turns of coils n, and the flow in coils comes to a saturated state in the first seven turns of the coils.

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Polystyrene, polyethylene and polyvinyl pellets with mean diameters of 1. 7, 3. 1 mm and 4. 3 mm, respectively, were transported as test particles in a swirling flow pneumatic conveying system consisting of a horizontal pipeline of 13 m length and 80 mm inner diameter. The initial swirl number was varied from 0. 58 to 1. 12, the mean air velocity from 9 m/s to 24 m/s and the solid mass flow rate from 0. 43 kg/s to 1. 17 kg/s. It is found that the critical and minimum air velocities of swirling flow pneumatic conveying are lower than those of axial flow pneumatic conveying, the maximum reduction rates being 13% and 17%, respectively. In the lower air velocity range, the power consumption and additional pressure drop are decreased by the swirling flow pneumatic conveying system.

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The pressure losses are experimentally studied for the case of airflow in a channel consisting of a periodically serrated wall and a plane one. The profile of the serrated wall is a right triangle. There exists a difference in the pressure losses due to the directions of the main flow, that is, the direction in which the width of the channel gradually diverges and suddenly converges is called diverging flow, and the direction in which it suddenly diverges and gradually converges is called converging flow. This difference is examined by taking as parameters the following three dimensionless numbers : the Reynolds number based on the minimum clearance, the aspect ratio (the ratio of the minimum clearance to the length of one tooth in the serrated wall) and the angle of inclination of the serrated wall. In the range of Reynolds number of about l00 and under, the coefficient of the pressure loss increases as the angle of inclination decreases. It goes without saying that the pressure loss in diverging flow is larger compared with that in converging flow. However, it is experimentally found that, in the cases of a small angle of inclination or/and small clearance, the pressure loss in diverging flow is smaller compared with that in the converging flow. These experimental results are visually clarified by using a visualizing technique undertaken in waterflow with a free surface.

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Liquid films are encountered in many industrial applications such as chemical process equipment and exchangers. Most of the previous experimental studies on the hydrodynamics of liquid films have been performed with liquid film flow on a vertical surface or an inclined upward-facing surface. This study concerns flow behavior of thin water with or without surfactant films on an inclined downward-facing plate. Here, the dependence of behavior such as flow (10<Re<500) on experimental parameters (surface roughness, inclination angle of surface, surface tension of liquid, initial film thickness) was investigated through flow visualization by a tracer injection method. Several wave patterns which appeared at the free surface of flowing film were observed under certain flow conditions. Adding surfactant has the effect of damping of waves. As a result of demensional analysis for l_F, the flow-distance until flowing film detouches a smooth plate, l_F is in proportion to the product of Re^1/2 and Fr^1/3. Under the experimental conditions here, surface roughness has more effect on the film flow behavior than surface tension.

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An experimental study was made for torque characteristics of a slitted rotating disk enclosed in a cylindrical housing. Measurements were carried out when the disk was positioned at and off the center of the housing clearance, and comparison was made between a slitted and a non slitted disk. The slits in the disk had little effect on the performance for a Reynolds number less than l000 except for a slight decrease in torque. At larger Reynolds numbers, however, slits act as impeller passages of a centrifugal pump, and this enables more torque to be transmitted. The torque for a disk which is set at off the center of clearance depends only on the ratio of upper and lower clearances for Reynolds numbers below 1000, but for larger Reynolds numbers it depends on the sum of the clearances irrespective of the difference between upper and lower clearance.

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Three-dimensional incompressible turbulent flow within a linear turbine cascade with tip clearance is analyzed numerically. The governing equations involving the standard κ-ε model are solved in the physical component tensor form with a boundary-fitted coordinate system using coarse grids. In the analysis, the blade tip geometry is treated accurately in order to predict the detailed flow phenomena through the tip clearance in case of the blade with large thickness. The results are also compared with the experimental data. Although the number of grids employed in the present study is rather coarse, the computed results show good agreement with the measured ones. Moreover, the results exhibit the locus of minimum pressure at the rear part of the pressure side at the blade tip.

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This paper describes measurements of pressure distribution around a semicone body with a wing traveling at the hypersonic speed of Mach number l0. The semiapex angles of the delta wing and semicone are 30°and 15°, respectively. The measurements are carried out under the condition that the angles of attack are 0°, 10° and 20°. In this study, the pressure distribution measuring method using magnetic tape has been improved to be suitable for measuring pressure distribution around hypersonic vehicles. The pressure distributions are measured by utilizing the improved method.

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An experimental investigation was made to clarify the effects of tube diameter on the velocity, frequency, wavelength and wave height of liquid lumps in vertical upward gas-liquid two-phase flow in capillary tubes. The capillary tubes were of six different diameters ranging from 6.0 to 0.5 mm. The results of the statistical quantities of the liquid lumps reveal that the waves in the capillary tubes are roughly divided into two groups ; i. e., one has relatively high velocity with long wavelength and high wave height, and the other has low velocity with short wavelength and low wave height. The former is dominant in the tubes of diameters larger than 4.0 mm and the latter is dominant in the tubes of diameters less than 0.9 mm. Both waves coexist in the tubes of diameters between 2.0 and 1.45 mm.

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An experimental investigation was made into the mechanism of discrete frequency noise ( DFN )generation from a NACA 0012 blade placed in a uniform oncoming flow. It was clarified that DFN was generated when the boundary layer on the blade surface was laminar and separated at the location upstream of the trailing edge. A dead air region was formed just after the trailing edge of the blade. Therefore a Karman vortex street occurred. Meanwhile we could not observe a close relationship between the existence of a separation bubble and the generation of DFN. That is, DFN was generated even when the attack angle of the flow was nearly zero and no separation bubble was observed. When a separation bubble existed, the boundary layer became turbulent and the flow did not separate up to the trailing edge, so a dead air region was not formed behind the blade, which resulted in the disappearance of DFN. The prediction of the sound pressure level of DFN generated from this stream lined blade by Fukano's theory for a flat plate model agreed well with the measured value.

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An experimental study of a three-dimensional free jet of air issuing from a cruciform nozzle with finite axis length is performed in order to clarify how the inward secondary flow on the y axis in the upstream region affects statistical properties of the present flowfield. Reynolds number is kept at 15000. The velocity measurements are made using an X-type hot-wire probe and two constant-temperature anemometers. It is found that the streamwise variation of integral scale along the x axis takes a minimum value in the upstream region owing to the inward secondary flow on both the y and z axes. Skewness and flatness factors on the x axis in the upstream region take maximum and minimum values due to turbulent diffusion transport, respectively. The turbulent kinetic energy and Reynolds shear stress on both the y and z axes are transported toward the jet center region by turbulent diffusion transport. The inward secondary flow on both the y and z axes in the upstream region promotes the inward turbulent advection transport.

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The evolution of a round turbulent jet issuing from a nozzle with a collar is simulated by using a discrete vortex method under the constraint of axial symmetry. The vortex sheets shed from the orifice and the edge of the collar are represented by vortex ring elements. The collar is represented by vortex rings of appropriate strengths to satisfy the no-through-flow condition. The effect of the collar on the development of the jet shear layer is investigated with and without harmonic excitation. When harmonic excitation in the range of St = 0. 3 to 0. 7 is applied to the model jet issuing from a nozzle without a collar, large-eddy structures corresponding to the frequency of the excitation are formed. When St ≥ 0. 5, these eddies coalesce immediately and are converted into eddies of St/2. The evolution of the jet shear layer is greatly affected by the collar. The preferred frequency varies with the dimension of the collar.

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This paper prenents some waveform analyses on the recorded pressure fluctuation in a waterhammer by collapse of a cooling cavity and the estimated collision velocity of the liquid column to the blind end of a pipe. Real damping and peak period shortening, whose effects are alike in appearance on a graph of the change with passage of time, are separated by means of graphs of the change with passage of cycle number. The discussion on the damping is generalized using logarithmic decrements. The obtained results are that the air in the cavity strengthens the damping, its strengthening is larger early in the waterhammer, and the peak period shortening takes place rapidly not later than between the 2nd and the 3rd peaks in the case where the initial air concentration is over 30% and is almost finished by the peak periods. In addition, taking note of the ripple of bottom pressure, the physical mechanisms of those damping and peak period shortening are discussed.

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In order to enhance numerical stability of a transportation equation, we attempt to reformulate a coefficient matrix to a diagonal dominant one. The method is based on a transformation of a source term into a linear form with a negative gradient. So far, the linearization has been derived by an analytical procedure. Here, a numerical linearization is proposed, which is theoretically based on the relaxation method through inertia. A flow simulation of the viscoelastic fluid passing over a backward facing step and an example of the total pressure prescription method of multiple exit boundaries of a manifold are also presented.

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In our previous papers, the Modified Galerkin Method (MGM) was proposed for the one-dimensional and the two-dimensional convection-diffusion equations as one of the most efficient methods using the error analysis technique. In this paper, this approach was applied for two explicit finite element methods and eight explicit finite difference methods. The corresponding correction coefficients were obtained for these methods in order to improve their numerical accuracies. All of these newly formulated schemes were evaluated from the standpoints of phase error and dissipation error. From the error analysis results, we confirmed the higher accuracy of our proposed finite difference method for a convection dominated problem and our proposed finite element method for a diffusion dominated problem. Through numerical experiments using the explicit finite element schemes, we confirmed the effectiveness of our proposed method and the general correspondence between the error analysis and the numerical simulation.

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Two-phase flow dynamics plays an important role in understanding the kinetics of a nuclear reactor and boilers. The difficulty has been reported in obtaining the numerical solution of the two-phase flow by the two-fluid model which was described as ill-posed. Few papers have studied the difficulty under the ill-posed condition. The present paper aims at practical discussion of the property of the numerical solution of the well-defined heat-conduction equation under the above condition, comparing these solutions with the exact solution as functions of the round-off error, the mesh size and the difference scheme. The present paper can serve as an alternative in understanding the ill-posedness of the two-fluid model.

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A numerical analysis is developed for sound radiation from cyrindrical ducts. The structure of the radiated field is numerically obtained for unflanged, flanged, and horned type ducts, including the effect of mean flow field. The governing equation for acoustic disturbances is a linearized unsteady Euler equation about a steady compressible mean flow. The numerical simulation is conducted by a fourth-order accurate finite difference scheme. The present result for the reflection coefficient shows good agreement with the experiment and available theory. The results also show that a nonuniform mean flow reduces the sound pressure level, although this is not valid for a uniform mean flow.

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Design constants for impeller outlet dimensions, psi and phi, were examined and derived based on loss analysis for the impeller and volute which was originally developed for performance and efficiency conversion. The design constants were calculated using outlet dimensions of the impellers which were designed for the requirement of the same flow rate and speed of rotation but with various pump heads and outlet angles giving minimum hydraulic and disc friction losses. The investigated design constants coincide relatively well with the conventional values given, for example, by Stepanoff in the range of blade outlet angle of about 20°. Furthermore, the results provide good suggestions for the values of psi and phi to be chosen for the outlet angles larger than 20°.

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A new technique for visualizing the vapor concentration in an evaporating spray, called silicone-particle scattering imaging (S. S. I. ), was proposed. When the fuel mixture containing silicone oil as 1% mass fraction was injected into a nitrogen environment at a temperature of 640 K, the volatile base fuel in the droplets vaporized rapidly leaving behind small droplets of silicone oil suspended in the vapor-gas mixture. The residual silicone oil droplets were illuminated by a thin laser sheet, and scattered light was imaged by a still camera. A simultaneous comparison between the scattering image and the fluorescence image in a cross section of an evaporating spray showed that the residual silicone oil droplets in an evaporating spray approximately represent the fuel vapor concentration. Using the S. S. I. method, the difference between the inhomogeneous structures of evaporating and nonevaporating sprays was investigated.

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Gas entrainment processes of intermittent low-speed gas jets were quantitatively analyzed with the laser-induced fluorescence of ambient gas ( LIFA ) technique. The results showed that mean injectant concentrations decreased with decreased nozzle diameter (D), shorter nozzle hole length, higher kinematic viscosity of jet, and elapsed time after injection (t). Also, the mean injectant concentration could be approximately related with ReD/Ut, where Re is the discharge Reynolds number, and U is the discharge velocity of the jet. When two jets were injected in series, the mean injectant concentration showed a minimum at the end of the first injection. The injectant concentration distribution of intermittent gas jets was similar to that of steady gas jets, except in the umbrella region at the top of the jet.

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This paper describes a new injection system that uses a hydraulic acceleration of moving bodies consisting of a spool and a plunger. Acceleration is initiated electromagnetically and jerks the fuel into the pipeline. The fuel extraction at the end of injection is performed by the reverse motion of the moving bodies due to the induced pressure acting on the plunger. Computer simulations showed that such an injection system is promising for attaining high-pressure injection. A prototype system was designed based on the simulation work. Bench tests using the devised system indicated the practical feasibility.

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A new type of pilot injector for low emission combustion in DI diesel engine has been developed by applying the authors' creative conception which are an active control of the time-dependent spray penetration and an appropriate radial distribution of local Sauter Mean Diameter during the ignition lag. The concept was realized in the new-type pilot injector where the opening pressure of the second stage (main injection) was higher than that of the first stage (pilot injection). In this paper, the new spray concept and the relationship between the design factors of the Dodge Plunger set in the injector and the fundamental injection characteristics were made clear.

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Soot concentration is very high in the periphery near the head of an unsteady spray flame which is achieved in a quiescent atmosphere in a rapid compression machine. To reduce soot concentration in this region and enhance combustion, it was intended to improve fuel- air mixing in the flame head by letting the flame impinge on a turbulence-generating plate. Two types of turbulence-generating plates, one of the donut type and the other of the cross type, were tested. Soot concentration in the flame was imaged using the laser shadow technique. The overall soot concentration was remarkably reduced in the case in which the flame impinged on the cross type plate at 333 nozzle diameters from the nozzle exit.

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The pilot injection pattern was optimized and some effects of pilot injection on combustion and exhaust emissions were investigated using a single-cylinder DI diesel engine. (1) In order to avoid the increase of smoke, both a small-hole nozzle and very accurate control of pilot injection quantity and pilot-main interval are essential. These improve the atomization of the pilot fuel and the air entrainment into the main spray. (2) With pilot injection. NO_x is not reduced at injection timing of TDC but is gradually reduced at more retarded injection timing. This is because the main combustion is accelerated at early injection timing but is decelerated at retarded injection timing, due to the promotion of ignition. (3) With pilot injection, the effect of NO_x reduction is generally small but the prevention of HC increase is obtained only under light-load, injection- timing retard conditions.

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A basic study on white smoke has been carried out on an optically accessible DI diesel engine. The purpose of this study is first to clarify the flame characteristics under the condition that white smoke occurs, and second to investigate the relationship between flame characteristics and both white smoke and HC. The results showed that, (1) for a smaller quantity of injected fuel and longer ignition delay, most of the flame within the combustion chamber became non-luminous, and (2) both the white smoke and the HC emissions were strongly related to flame characteristics such as the maximum flame area, and the propagation speed of flame.

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Time series analyses of diesel exhaust gas emissions under transient operation were carried out using a gas sampling system to efficiently collect all exhaust gas over several cycles. The effects of fuel properties and other operating parameters on the exhaust emissions under transient runs were analyzed. The results showed that THC increased abruptly to 2-6 times the steady-state concentration immediately after the start of acceleration and then decreased to the steady-state values after 70-200 cycles. At acceleration, NO_x increased abruptly to about 80% of the steady-state value, and then increased gradually to reach the steady-state values after 60-500 cycles. The behaviors of THC and NO_x during transient operation can be described by the exponential functions of the elapsed cycle numbers and the final emission concentrations. The concentrations of CO, CO₂, O₂, and smoke changed abruptly to the steady-state values at the start of acceleration. One of the dominant factors affecting the gas emissions during transient operations is the deposition of fuel on the combustion chamber wall.

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The paper presents results of experimental verification of a theory which predicted the possibility of combustion similarity in differently sized diesel engines. Combustion similarity means that the flow, pattern and flame distribution develop similarly in differently sized engines. In the experiment, observations were made of the similarity in fuel jet distribution in a model apparatus, and comparisons of thermal efficiency, heat release rate, and emissions were made for engines varying from 260 to 400 mm in bore size. Comparisons were also made of combustion patterns of differently sized engines by a three-dimensional computer simulation. All of the results showed good agreement with the theoretical prediction. The establishment of the theory of size effects can provide model experiments and a method to correlate the vast amount of independent data that are available, and offer significant opportunities for diesel engine research and design.

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The paper presents a theory and its experimental validation on optimum conditions of fuel injection systems and swirl flow, which gives the maximum thermal efficiency and minimum smoke emission. The theory predicts air entrainment change into fuel sprays for a variety of swirl speeds, number of nozzle holes, nozzle diameters, engine speeds, injection speeds and fuel densities. Experiments were conducted to verify the theoretical prediction. The results showed good agreement with the theory : maximum combustion rate arranged on theoretically predicted lines for number of nozzle holes and swirl speeds. The study provides opportunity for engine designers and researchers for understanding diesel combustion characteristics for injection systems and swirl flows.

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An experimental study was made of the planar measurements of fuel vapor concentration in the combustion chamber of a spark ignition (SI)engine with laser-sheet-induced Rayleigh scattering. The conventional engine was modified to introduce YAG laser sheet light into the combustion chamber. The scattered light from the measuring plane was allowed to transmit an optical glass window installed on the extended piston and captured with a CCD camera fitted with a gated doublemicrochannel-plate image intensifier by lens coupling. The time histories of fuel vapor concentration distribution and the effect of injection methods on them were investigated thoroughly. It was found that the fuel vapor concentration was highly heterogeneous during the intake stroke, and the inhomogeneity decreased in the compression stroke. However, even at the end of the compression stroke, small lumps of unhomogeneous mixture still existed randomly inside the engine combustion chamber.

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Pulsating flow characteristics of hot-wire air flow meters for gasoline fuelinjection systems were investigated to analyze simple methods of measuring data processing. It was clarified that backward flow components due to pulsation are detected as forward flow by the probe in the conventional meters, increasing errors. The errors due to pulsation can be reduced by using a meter with a hot-wire probe located in a bypass passage, compensating aerodynamically forward and backward flow components.

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A thick Burning zone including unburned and burned gas is observed in the turbulent premixed flames. In this study, the burning rate and the ion-current in the burning zone were investigated in propane-air turbulent flames in a spark-ignition engine cylinder and a constant volume combustion chamber. The main results are as follows : (1) In propagating turbulent flame, the rate of mass burned is not equal to the rate of mass entrainment to the flame front. (2) The ratio of the combustion rate per unit area of turbulent flame front to that of laminar flame, Z=(M_bT/A_r)/(M_bL/A_L), is a reasonable expression of the effect of turbulence on the combustion of propagating flame. (3) The ion-current signal has multiple peaks in the turbulent flame. The average number of ion-current peaks increases with the enlargement of burning zone and the value of Z.

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Compression-ignition processes of hydrocarbon/oxidizer mixtures are visualized using a combination of an image intensifier and a high-speed camera in wide range of temperatures. Onset images of cool-, blue- and final hot-flames are identified. Three typical regions of low-temperature ignition are classified and characterized. The cool flame onset followed by its degeneration is relatively homogeneous. Spatially nonuniform ignition is emphasized, though it does not always appear first in the vicinity of the cylinder wall as hitherto mentioned. Ignition in the blue flame dominant region, the highest temperature region of the low-temperature ignition, does not come under the category of the high-temperature thermal ignition usually obtained in shock tubes.

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Large-eddy simulation of a turbulent premixed flame in an engine is performed in a wide range of operating conditions such as engine speed, airfuel ratio, and ignition timing. A numerical method for estimating supergrid fluctuations of physical quantities and the space-averaged quantities accurately is proposed. As the subgrid estimations, the Yakhot-Orszag turbulence model based on the renormalization group theory and a flamesheet model are employed. For some variations of the operating conditions, obtained computational data agree well with experimental data on turbulence intensity and pressure history. It is also shown that the developed numerical model has the potential of calculating the cyclic variations of flow and combustion. An important understanding on the physical situation in conventional 4-valve engines, is obtained from the present study, which is that laminar regions may exist at the low engine speeds.

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A three-dimensional numerical analysis was applied to the prediction of the fuel vapor concentration profile in the cylinder of a typical four -cycle reciprocating spark ignition engine with an off center valve. The conservation equations of mass, momentum and energy were solved on the basis of the finite volume method. The ordinary two-equation model was employed as the turbulence model. It was assumed that the fuel injected in the intake port flows into the cylinder as a vapor. Calculation was done from the TDC of the intake stroke to the TDC of the compression stroke every 10 degrees of the crank angle. The temporal variations of velocity and fuel mass fraction profiles were predicted during both intake and compression strokes. The results showed that the fuel mass fraction distribution was not uniform at the last stage of the compression stroke. The effect of the inflow velocity distribution on the mixture formation process was discussed.

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The diffusion process of intake mixture (homogeneous mixture of air and gaseous fuel) in the cylinders of dual-intake valve S. I. engines has been analyzed numerically using the GTT and CIP methods and the κ-ε turbulence model. The following have been found : In one engine in which a tumbling vortex is generated. the mixture is localized mainly in half of the combustion chamber : namely, it is stratified when the fuel is supplied into only, one intake port. In another engine in which a swirl is generated by holding one intake valve closed, a relatively homogeneous mixture or an axially-stratified mixture is generated in the chamber depending on early or late fuel supply.

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In a four-valve spark-ignition engine, the turbulence produced by tumbling gas motion plays an important role in promoting the combustion. In this study, the tumbling flow and its turbulence in cylinder were measured with LDV under the condition of no firing in changing with the parameters of piston stroke, compression ratio, configuration of the intake port and engine speed. Furthermore, the oil spot method was applied to observe the flow pattern on the piston surface near the top dead center (TDC) of the compression stroke. The main results are as follows : (1) The tumbling air motion is converted into several smaller eddies before the TDC, and this phenomenon contributes to the increase in the intensity and the degree of isotropy of turbulence near the TDC. (2) The experiments in changing the engine speed and stroke express clearly that the turbulence intensity increases linearly with increasing mean piston speed.

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The velocity variations in an exhaust pipe of small two-stroke engines have been measured using the FLDV technique. The relationship between the velocity variation and the pressure wave propagation of the burnt gas was investigated. The measured results show that large velocity gradient and spiky velocity peaks were formed due to the burnt gas pressure propagation after EO, and the velocity peak positions could be estimated from the exhaust pipe pressure. The flow profiles indicate pulsative pipe flow. The measured data could be used to understand fresh air short circuit.

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In order to utilize exhaust gas energy effectively, various engine systems equipped with the exhaust gas turbine have been proposed. Since their performances depend greatly on the matching technique, the authors have been developing a method of optimizing these systems on the basis of mathematical treatments. The purpose of this paper is to describe a mathematical optimization procedure and to show its application to a Turbocharged diesel engine. This procedure consists of three steps : (1) choice of parameters representative of turbine and compressor characteristics, (2) efficient estimation of turbine and compressor behavior, (3) parameter optimization. The application showed that the method proposed has the capability of optimizing the engine system efficiently.

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