In this paper, the attenuation and the nonuniformity regarding the strength and the shape of the shock wave front propagating through a double elbow were explored by numerical simulation. Computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by using the total variation diminishing (TVD) scheme. Computations were performed for six types of elbow and two incident shock Mach numbers (M_s=1.3, 2.0). The flow field were numerically visualized by the pressure and vorticity contours, pressure distributions on the walls and time histories of the pressure contours on the walls. The attenuating process of the shock front and the generating and diminishing process of the nonuniformity of the shock front were clarified.

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A new algorithm for simulating homogeneous decaying turbulence in an incompressible fluid subjected to uniform system rotation has been proposed. The complex helical waves decomposition is introduced to diagonalize the Coriolis term of the Navier Stokes equations in the Fourier space. The integral factor technique has been extended to the Coriolis term. Since the Coriolis term is integrated analytically in the algorithm, time increment is not restricted by the system rotation. It is proved that the new algorithm is effective at high rotation rate. The effect of system rotation is observed clearly in high rotation cases. It is also indicated that the energy spectrum depends on the modulus of wave vector κ and cos θ, where θ is the angle between the rotation vector Ω and the wave vector κ.

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A subgrid-scale model for the filtered reaction term is presented to develope the large eddy simulation (LES) of nonpremixed, turbulent reacting flows. The subgrid-scale model is based on the subgrid-scale probability density function (PDF) and subgrid-scale conditional expectation. The subgrid-scale PDF is assumed to follow the beta distribution and the subgrid-scale conditional expectation is given using the filtered data obtained from the direct numerical simulation of an air mixing layer downstream of turbulence generating grids with a second-order chemical reaction. Further, the subgrid-scale model for the filtered reaction term is evaluated by comparing with the DNS. The results show that the subgrid-scale model can accurately estimate the filtered reaction term and it is applicable to the LES of turbulent reacting flows.

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For the problem where two phase flow is expected to change very slowly in time or not to change, it may be possible to obtain adequate information from an approximate solution based on very large time step. This would be advantageous if a reliable and efficient means could be found for solving difference equations treating all terms by backward differences. This paper describes a fully implicit numerical method and numerical examples for two dimensional incompressible two-phase flow with two-fluid model. The method is an extension of SIMPLEST scheme which is widely used to analyze various single-phase thermal hydraulic problems. Further extension of the method to tree-dimensional analysis and/or compressible two phase flows is also straightforward.

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The behavior of gas suddenly injected from a nozzle into a stationary liquid in a horizontal circular pipe is studied regarding the case where the inner diameter of the pipe is much greater than the limiting bubble thickness. If the ratio of the nozzle diameter to the inner diameter of the pipe is greater than 0.3, the front of the gas-liquid interface acceleratedly advances. If the ratio is less than 0.25, the front advances almost at a constant velocity due to the gravity current. A thin liquid film is left on the wall after the interface front passes. At high gas flow rates, the film thickness is almost uniform everywhere on the wall. At low gas flow rates, it depends on the surface tension and the viscosity of the liquid alone. At lower gas flow rates, it is almost constant regardless of the gas flow rate.

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A numerical analysis has been performed for turbulent flow developing in longitudinally finned tubes. Three tube geometries were calculated : two 8-finned tubes (fin hight to radius ratios of 0.333 and 0.167) and one 16-finned tube (fin height to radius ratio of 0.167). In calculations, an algebraic Reynolds stress model was adopted in order to predict precisely the secondary flow of the second kind induced by anisotropic turbulence and boundary-fitted coordinate system was introduced as the method of coordinate transformation. Mean velocities in axial, radial and circumferencial directions, pressure drop in tubues and primary shear stress distribution are compared with the experimental data. As a result of this analysis, it was found that the present method could predict well the streamwise mean-velocity. In the case of 8-finned tube of tin height-to-radius ratio 0.333, two secondary flow cells which were measured in experiment, were reproduced by the present turublent model although a small intensity of secondary flow were observed compared with the experiment. Moreover, numerical results suggest that these two secondary flow cells disapper in 8-finned tube of tin height-to-radius ratio 0.167 and the secondary flow has a influence on the wall shear stress distribution. The calculated results also show that the turbulence in the interfin region is greatly reduced as well as the experiment.

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In the flow around a circular cylinder, the sudden decrease in the drag force occurs at around Reynolds number Re=3×10⁵, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In this paper, in order to make clear the flow characteristics for grooves' depth of a circular cylinder with grooves, the unsteady flow was analysed by applying the RNG (Renormalization Group) κ-ε turbulent model to a flow around a circular cylinder with grooves each of whose section shapes being as same as that of a dimple on a golf ball, with changing grooves' depth and Reynolds number. This result made clear the characteristics of lift and drag, Strouhal number, flow pattern behind the circular cylinder, pressure distribution and separation points. Moreover, the time averages of these values almost agreed with the experimental values.

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The effects of tangential blowing on the performance of subsonic diffuser for supersonic air intakes are numerically investigated in order to develop a high performance subsonic diffuser with short length. Using a κ-ε turbulence model, numerical simulation is performed on five types of diffuser configurations with and without tangential blowing. The results show that our calculation reproduces the qualitative features of the flow, and remarkable improvement of diffuser performance can be achieved by tangential blowing into the separation region. Moreover, it is suggested that tuning a model constant has possibility to predict the flow more reasonably.

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To improve the performance of disk MHD generators, it is suggested to install inlet swirl vanes to introduce azimuthal velocity component in the supersonic inert working gas flow at the inlet of the generator channel. But, currently used swirl vanes employing symmetric nozzles has a problem that flow field non-uniformity in azimuthal direction grows due to incompleteness of the nozzle design. For solving this problem, some swirl vane design methods using asymmetric nozzles are proposed. Technical validity of these design methods from the viewpoint of flow field uniformity is evaluated by numerical simulation of two dimensional turbulent flow. Finally, design optimization of the nozzles is discussed for introduction to disk MHD generator.

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Oscillation of the circular pseudo shock in the radial and spiral supersonic flow between two parallel discs was investigated both numerically and experimentally. In the simulation, 2 nd-order accurate, Harten-Yee's upwind TVD scheme was used for high resolution and numerical stability, and Baldwin-Lomax's algebraic model was used as the turbulence model. To simulate shock wave oscillation, the back pressure was fluctuated at the outlet boundary. The X-type pseudo shock, which appears at higher Mach number, is more stable than the A type one, which appears at lower Mach number. Oscillation of mode 0 is predominant when the swirl is absent, while it becomes weaker and higher modes appear with the increase in the swirl.

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The pressure effect on diffusion flames was investigated in magnetic field at low flow rates of propane gas by using of a rectangular and a circular nozzle. The flame deformation has been studied by the former burner, and the numerical analysis to the inclination of flame axis has been studied by the latter burner. The deformation of the flame was independent of the direction of the magnetic field and was proportional to the two powers of the strength of magnetic field (=H²). The force acted on the boundary between the flame and the air by the magnetic field was induced by the difference of the volumetric susceptibility of combustion gas, propane gas and air. The numerical analysis to the turn of the flame axis was made at the inflection point of the flame by the use of the relation between the buoyancy force and the force induced by magnetic field. The angle between the direction of the buoyancy force and the flame axis was independent of the momentum of the stream in the axial direction at the point of the flame. The analytical results to the angle of turn at the point showed good agreement with the experimental results.

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The mean flowfield of a turbulent air jet issuing from a quasi two-dimensional nozzle with a rectangular notch at the midspan has been measured using linearized constant temperature anemometers. The aim of this study is to examine the effects of the rectangular notch on velocity and length scales of the two-dimensional jet, and to clarify an asymptotic process of the present jet to the two-dimensional jet. In all experiments, Reynolds number based on the nozzle width and the exit mean velocity, was kept constant 13000. Using the experimental results, an interactive region affected by the rectangular notch in each constant section of x/d was defined and an empirical equation of interactive region affected by the rectangular notch in the z direction, was obtained. Furthermore, it was revealed that the streamwise mean velocity U_ox on the x axis approached to U₂ and the half width by on the y axis to b₂ of the quasi two-dimensional region, so it was derived that the present flowfield became a two dimensional jet in the far downstream section.

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Results of the transition to turbulence in three dimensional low Reynolds number slit nozzle free jet (Re=800) are presented. A direct numerical simulation (MAC method) is used, based on the fourth order central difference scheme for convection terms and the second order Runge-Kutta method for time developing terms. Computational cells are smaller than Kolmogorov's micro-scale. Calculated results are verified by experimental turbulent characteristics. We examine the transition to turbulence by calculated results. We show various velocity wave profiles with time in the jet. The time-spatial characteristic maps of velocities, convection terms and vorticities show the processes of merging vortices which cause mainly the transition to turbulence and also show non linear convective effects.

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Behavior of spray-to spray impingement, where two spray jets were formed EFI (Electronic Fuel Injection) nozzles and impinged each other, was studied experimentally. This system was named MISS EFI. Spray penetration and the Sauter mean diameter of the spray were measured to investigate the effect of spray-to-spray impingement. When the impingement location was set at the vicinity of the nozzles, impingement phenomena became to be jet to jet impingement of the liquid column. In this condition, the penetration became shorter than that of the individual penetration. However, the penetration did not changed after spray-to-spray impingement. From the photographs of jet-to-jet impingement, it was confirmed that the liquid film was formed by the impingement, and then this liquid film disintegrated to small droplets. In the spray-to-spray impingement, on the other hand, the relatively large droplets still existed in the impinged spray, because the two sprays crossed each other without disintegration of the droplets. The photograph of the spray-to-spray impingement showed that the droplet-to-droplet impingement in the spray was rarely observed. Further, the chance of coagulation of the droplets was less observed than the disintegration of the dropled. These behavior of the spray-to-spray impingement agreed with the reduction of the Sauter mean diameter of the impinged spray.

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This research deals with the oscillation mechanism of a flip flop jet nozzle based on the measurements of both pressure and velocity in a connecting tube. The traces of pressure difference between the ends of the connecting tube are modeled simply, and velocities in the connecting tube are calculated by the method of characteristics. The authors assume that a jet switches when the integral of momentum J^* reaches a certain value, where J^* is the accumulated value of the momentum flow which enters through the connecting tube into the low pressure bubble on a reattaching wall. Strouhal number calculated on this assumption agrees well with experimental ones.

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The authors proposed the method of performance improvement by blowing moist air for a water jet ship. The authors investigated on the performance of the water jet ship by blowing air into the nozzle in former papers but there was the limit by blowing only air. In this study, the method of moist air blowing was investigated to obtain more thrust. Steam blown into the nozzle condenses just after the outlet and the average density of fluid increases. By the increase of density, the fluid in downstream can be easily accelerated by expanding bubbles of air. The experiment on this method was performed in a towing tank and the result showed that the thrust increased about 20% in comparison with the conventional method. There are many sources for supplying moist air like exhaust engines and boilers in actual ships. Our propulsion method is promising for practical use.

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This paper reports about experimental investigations of rotordynamic fluid force moments on an open type centrifugal impeller in precessing motion. The results show, at design flow rate, that the fluid force moment becomes destabilizing in the region of negative precession frequency ratio: -0.3<Ω/ω<0. With a decrease in flow, rate, the range of the destabilizing fluid force moment appears at small positive precessing frequency ratio: 0.2<Ω/ω<0.4. To identify the cause of the fluid force moment, the fluid force moments directly measured with 4-axis sensor are compared with the fluid force moments estimated from the unsteady pressure measured on the front and back casing walls, and those estimated from the pressure difference across the blades.

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A method for measuring propagation of disturbance in a high-speed flow has been developed by using a laser induced fluorescence (LIF) technique. A cross correlation function between the time-dependent LIF signal and a pressure sensor signal at a reference point enables to measure a propagation speed of disturbance. Through a bandpass filter, the speed of disturbance with a particular frequency can he obtained. A feature of disturbance propagation can be grasped by drawing maps for the cross-correlation coefficients on a space at successive delay-times and making an animation. The method was applied to a supersonic flow over a rectangular cavity with length to depth ratio of 2, to elucidate feedback mechanisms of self sustaining flow oscillation with several dominant frequencies.

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A radial cylinder pump of which variable displacement is controlled by a pulse flow servomechanism has been applied to a diesel-fuel flow control system. This pump converts mechanical moment to hydraulic output by a fluid-force couple mechanism instead of conventional sliding cams or pistons, which reduces not only mechanical friction force and flow resistance of inlet / outlet ports, but controlling force of variable displacement mechanism. This paper describes steady state and dynamic characteristics of the pump by making a prototype of maximum displacement of D_p=48 cm³/rev controlled by 3-port PWM switching valves. The pump delivers flow rate of 30 L/min at a rotational speed of N_t=1500 rpm and pressure of 14 MPa with mechanical efficiency of η<pt>=95% and volumetric of η<pv>=90%, and changes flow rates within 50 ms for 20% step response of variable displacement

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The rubber isolation bearing, which consists of thin rubber sheet and steel plate, is used to protect buildings from earthquake damage. In the manufacture of the bearing, the time required for the laminated rubber to be heated for valcanization is a serious problem, causing low productivity. Conventionally, the laminated rubber is heated using a hot plate press. However, with such an external heating method, it takes a long time for the internal rubber to heat up, because rubber has low thermal conductivity. Therefore, this paper proposed a new heating method. This method is focused on the steel laminated structure, whereby the confined steel plates are heated by induction heating. The possibility of using inductive heating for a laminated steel plate is discussed using the results from a small scale test and a simulation. As a result, it is demonstrated that this new heating method is available to pre-heating of the laminated rubber.

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The laminated rubber bearing is confined within the mold during the vulcanization process in order to be pressed. The mold suitable for inductive heating was discussed by using the simulation. As a result, a SUS mold with a slit, which breaks the inductive current circuit in the mold, was found to effectively heat up laminated steel plates. The SUS mold with a slit for the Φ500 laminated rubber was manufactured and it was verified that the measured heat rate from induction heating is considerably larger than the conventional rate. Consequently, it was proved that Φ500 laminated rubber by using induction heating has similar dynamic characteristics to a conventional rubber bearing from the result of the load tests.

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Transient heat release characteristics of a latent heat storage vessel packed with surface cross-linked form stabilized high-density polyethylene pellets as a phase change material (PCM) have been investigated numerically and experimentally. The obtained results revealed the effects of the inlet velocity, the inlet temperature of ethylene glycol/water solution as a heat transfer medium, and the amount of the PCM on the heat release characteristics. As a result, the nondimensional correlation equation of the completion time of the heat release process was derived as a function of some nondimensional parameters.

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The numerical simulations have been conducted to clarify the effects of the turbulence in the liquid on the onset of protrusions on liquid jet surface. The turbulences in the liquid jet were simulated by the Rankin vortices. The liquid jet surface was tracked numerically by the VOF method. By the numerical simulations, the protrusions on the liquid jet surface are induced by the vortices in the liquid of which the rotation direction is that decelerates the jet surface. Instead of the distance between vortices, the displacement of the liquid jet surface increases linearly in time at almost the same growth rate. In the initial region where the displacement of the liquid jet surface is amplified, as the major semiaxis-to-minor semiaxis ratio of the ellipsoidal vortex increases the growth rate of the displacement increases. The initial growth rate of the wave on a liquid jet surface is almost proportional to the vortex intensity.

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Abrupt Change of wake oscillation and surface character and effects of fluid type on it are elucidated by numerical calculation on suppression of the Karman vortex street due to positive buoyancy from a heated elliptic cylinder submerged ill upward mainstream of mercury, air or water. Abrupt change in the buoyant wake from an elliptic cylinder occurs at two different Richardson numbers, i.e. one is the first critical Richardson number, Ri_tr, and the other the second one, Ri_c(>Ri_ir). At Ri_tr, the mean coefficient of the shear stress and the mean Nusselt number decrease abruptly for mercury and air, but increase abruptly for water. At Ri_c, the Strouhal number decreases abruptly for mercury and air, but begins to decrease continuously for water. The above characters for water differ qualitatively from those for mercury and air.

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Measurements of time-varying spatial liquid holdup distributions and interfacial profiles were carried out for the transition flow region between plug and annular flows using the liquid with three types of liquid viscosity ν_ι=1, 10 and 20 cSt. Time-spatial maps of interfacial behavior were drawn and close inspection revealed that two types of waves appeared for each liquid viscosity, namely one is disturbance wave with small height, width and velocity. The other is huge wave with large height, width and velocity. Furthermore, it was clarified that no wave continuing in the measuring section appears in higher gas velocity and lower liquid velocity conditions for ν_ι=10 and 20 cSt and the interface was covered with ripple waves. To clarify the differences between huge wave and disturbance wave definitely, a wave vein analysis was carried out. Probability distributions of these flow parameters were determined. The characteristics in these probability distributions revealed that two types of distributions existed for both of wave width and velocity and these distributions corresponded to those of huge wave and disturbance wave, respectively.

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Turbulent transport computations of a scalar quantity for fully developed turbulent pipe flow with uniform surface heat flux were carried out by means of a direct numerical simulation (DNS) procedure. The number of computational grids used in this paper is 256×128×128. Prandtl number of the working fluid is 0.71. The Nusselt number is in good agreement with the empirical correlation. The scalar variance and scalar flux obtained by the present DNS are in very good agreement with the previous experimental data. The present DNS results can be used as a reference data base.

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Fluid flow and heat transfer of natural convection around large horizontal cylinders were investigated experimentally. The main concerns were the turbulent transition and its influence on the local heat transfer. The experiments were performed in the range of modified Rayleigh numbers from 1.0×10⁸ to 5.5×10¹¹. The test fluid was air. The flows over cylinders were visualized with smoke. The results show that three dimensional separation occurs over the surface when the Rayleigh numbers exceed 3.5×10⁹. The separation becomes a trigger to the turbulent transition, and transitional and turbulent flows appear downstream the separation. The local heat transfer coefficients were also measured. The results show that the coefficients are increased significantly in the transitional and turbulent regions.

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The shell side heat transfer and pressure drop to water flowing counter were experimentally investigated on the basis of the overall heat transfer coefficient. The investigation was intended to identify ways to get higher performance for the cooler in a BWR nuclear power plant. The following three conclusions were reached in the study. (1) From estimated performance of the heat exchanger using the overall heat transfer coefficient based on the outside area of the tube K₀, performance of this heat exchanger was enhanced 92% as compared with the measured performance of the conventional segmental heat exchanger. Assuming that the fouling factor is R_f=8.6×10^-2 m²K/kW, the former was enhanced about 23%. (2) The tube side pressure drop ΔP_t=20 kPa and the shell side pressure drop ΔP_s=70 kPa were obtained, and they were within the allowable value ΔP_a=80 kPa. The shell side pressure drop of the standard spacer could be decreased 20% as compared with that of the low pressure drop spacer. (3) The enhancement constant of heat transfer of the low pressure drop spacer with thin plate type supports was about 1.2 times as large as that of the standard spacer. The heat exchanger with the low pressure drop spacer was about 1.6 times more compact than that using the standard spacer.

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Enhancement of heat transfer in evaporation of falling film was studied on horizontal tubes with triangular grooves on the tube circumference. An analysis of laminar film in a vertical triangular groove revealed that grooves are effective in enhancing evaporation heat transfer. To verify the enhancement associated with grooved tubes, an experiment was performed in the range of film Reynolds number 100 to 1000 with saturated refrigerant R11 (CCl₃F) at a pressure of 0.2 MPa used as the working fluid. Three grooved tubes were tested and enhanced heat transfer coefficient well beyond the geometrical surface increase, yielding larger enhancement than expected from the analytical prediction and about 4 to 8 times higher heat transfer coefficient than that for plain tube. The observed enhancement is probably attributable to an extension of falling film in the valley of the groove as predicted in the analysis. Moreover an intermittent wetting of the crest portion of grooves caused by wavy falling film and subsequent evaporation of thinner film left behind is contributed largely to the enhancement.

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Heat transfer measurement and flow visualization test were performed to investigate heat transfer enhancement mechanism of angled ribs mounted on two opposite walls of a rectangular duct with turbulent flow. Seven rib configurations were studied: 90 deft, rib, 60 deg oblique rib, 60 deg V-shaped rib, 60 deft, A-shaped rib, and their discrete ribs. It was found that the rotational direction of secondary flow induced by ribs plays a dominant role in determining the heat transfer performance. If the rotational direction of the secondary flow is to convey fluid from central core region of a duct directly to the heat transfer wall, the heat transfer performance of the wall is augmented appreciably. This is attributed to (1) transportation of colder fluid from the core region to the heat transfer wall, and (2) suppression of separated region behind a rib through the introduction of higher momentum fluid from the core region of the duct. The mechanism clearly accounted for the heat transfer characteristics of each rib, for example, heat transfer superiority of V-shaped rib over A-shaped rib.

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This paper describes the effect of turbine blade surface roughness on the heat transfer rate and metal temperature in gas turbine long term field operations. The metal temperature of Ni based super-alloys can be estimated from changes in microstructure due to the aging. Applying this technology to the rotating blades used in gas turbine field operations, long term operational metal temperature were higher than during short term operation. Also, it was observed that the surface roughness of rotating blades increased during long term operations compared to new blades, which corresponds to the increase in metal temperature. The increased heat transfer rate on the rough surface of the rotating blades was predicted analytically. From these results, the relationship of the rotating turbine blade surface roughness and the increase in the metal temperature in gas turbine field operations can be estimated.

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Experiments on pool boiling of water were performed under decompression. Temperature fluctuation measured with 3 thermocouples which were equipped on copper block surface by plating. Rapid temperature drops in this fluctuation arise at same times. This shows the existence of evaporation of microlayer under bubbles. The evaluation of this evaporation of the microlayer and rapid temperature drops showed the existence of a new evaporation factor in obedience to the liquid surface overheating. Temperature drops have two types at decompression. One is rapid drop due to the cavity existence and the other is slow drop due to the generation in the superheated bulk liquid on the mirror surface. This rapid temperature drop have gradual drop at first stage. For verification of gradual drops, we introduced a equation concerned micro film thickness under the bubble on the basis of the viscosity and the preservation of momentum. This equation has exponential factor about microfilms. Numerical calculations showed a good agreement with the experimental data.

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Microbubble emission boiling (MEB) which appears in transition boiling region of subcooled liquid provides extremely high heat flux. That accompanies violent emission of many microbubbles and a large sound. An overview of many available data about MEB classified this phenomenon into three different types, i.e., stormy microbubble emission boiling I and II (S-MEB I and II), and calm microbubble emission boiling (C-MEB). In this experiment, observations of the bubble behavior with a high speed video camera and measurements of the pressure fluctuation with a pressure transducer were performed in each regime of boiling of subcooled water flowing vertically upward along the surface, to try to make clear their characteristic feature. Much higher peak pressure was observed in MEB I and II than in C MEB or film boiling. This peak in fluctuating pressure corresponds to the collapse or growth of each coalescent bubble, and the frequency of this peak is equal to the cycle of the bubble motion.

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We investigated the gas exchange process of a spherical bubble rising in water. We developed an experimental system that use a CCD camera coupled with a microscope to follow the rising bubble. By measuring the bubble size and the rising speed from the bubble motion data recorded with a personal computer, we could precisely estimate the gas exchange rate across the bubble-liquid interface. We also calculated the gas exchange process by estimating the drag coefficients and Sherwood number. The measured and calculated change of bubble radius agree well when the bubble is strongly affected by contaminants. The results also show that when the concentration of carbon dioxide in water is small, the normalized equilibrium radius can be estimated by the initial partial pressures in the bubble and by the pressure of dissolved gas in the water.

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Absorption refrigerator is getting attention with a view point of environmental protection and energy savings because it can be driven by waste heat. As absorption refrigerator has a lot of solution which is so expensive, this makes it difficult to reduce the initial cost and improve the response speed in start up and shut down. Hence, it is expected to reduce the charging quantity of solution. But if it is decreased too much, disturbance such as the charge of the waste heat affects the characteristics of the absorption refrigerator greatly. To investigate these problems, it is necessary to clarify the dynamic characteristics of the absorption refrigerator. In the elements of the absorption refrigerator, the generator has the largest amount of solution and is affected directly by the change of the waste heat Therefore this research aims to clarify the dynamic characteristics of the generator in detail by simulation and experiment. As the generator for the absorption refrigerator, a pool boiling type and falling film type generator have been used. In this paper as the first report, the dynamic characteristics of the pool boiling type are investigated with simulation and experiment. As a result, detailed dynamic characteristics were clarified, and the validity of the dynamic model of the generator was confirmed.

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Overhead valve mechanism (OHV) is a widespread mechanism for internal combustion engine, but in this type of valve train, a serious problem known as valve jump is likely to occur at high speed. A rig test is arranged in such a way as to enable the measurement of the push rod force representing the vibration state of valve mechanism under different engine speed. By means of FFT analysis, the engine speed at which the first jump occurs can accurateiy be determined. Accurate detection of the part responsible for the jump can be achieved by isolating electrically all the parts constituting the valve train and measuring the different forces under different rpm's. It is clarified that valve jump is the phenomenon which separates between can and tappet, those which constitute valve mechanism.

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Combustion and exhaust gas emissions characteristics of natural gas injected into the cylinder of a four-stroke-cycle diesel engine and ignited by pilot injection of liquid diesel fuel have been investigated numerically and experimentally. A 3D-CFD simulation has been conducted to examine the effect of natural gas injection timing on the behavior of natural gas mixture. As a result, the optimum injection timing of natural gas was examined for an engine operating condition, which led to improved THC emissions and thermal efficiency. This can be explained by the fact that the distribution of natural gas at ignition plays an important role in combustion and exhaust gas emissions.

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A fully three dimensional numerical model for the combustion process in a spark-ignition engine was established using the combustion submodel described of the flame area evolution. Computations carried out the process of premixed combustion and they were compared with the results using the combustion submodel of the eddy break-up. The combustion in a disc chamber of constant volume was simulated. The results show that the course of flame propagation is well predicted. The calculations for different conditions in a natural-gas engine are performed. It is shown that the effects of fuel-air equivalence ratio and swirl intensity on flame propagation are described. The cylinder pressure histories are agreed with measured one, and the distributions of velocity vectors and temperature in a cylinder are revealed.

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The No_x emissions exhausted from diesel engines can be reduced significantly by extremely advancing the injection timing of fuel, because of homogenizing the mixture of fuel vapor and air. In this study, as fundamental research of combustion phenomena in a homogeneous charge compression ignition engine, the ignition delay of light oil spray was investigated under various conditions of cylinder charge. A direct injection diesel engine with a bore of 92mm and a stroke of 96mm was used for the experiment. The degree of homogeneity of mixture was varied by changing fuel injection timing and mixing gaseous fuel (propane and methane) in intake air. Consequently, it was recognized that the ignition delay of light oil injected early was predicted by Livengood-Wu concept for ignition.

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The in-chamber and exhaust gases from a premixed lean compression ignition engine were evaluated with high-speed direct gas sampling and gas chromatography. The results showed that in a premixed lean CI engine the in-chamber concentrations of THC and CO were always much higher than in conventional diesel combustion and remained nearly constant after the main part of the heat release was finished. The THC near the piston cavity wall was much higher than the the center of the combustion chamber and near the cylinder head. Deposition of fuel on the piston face was proved to be the main reason for higher THC emissions from premixed lean CI engine. The experiments with the model fuels showed that during combustion amounts of unburnt hydrocarbon components with lower boiling points decreased more than higher boiling point components, while there was little difference in the relative fractional amounts based on component ignitability.

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Extinction and structure of ultra lean premixed flame formed in opposite flow has been studied experimentally. Two different concentration mixtures, extremely lean premixed gas and lean premixed gas, impinged on each other. The bulk stretch rate were varied from 80^-s to 270^-s, and the Lewis number (Le) were varied from 0.99 to 1.85. The local stretch rate due to flow divergence and the stagnation point were estimated by measuring the centerline velocity profile with LDV and the reaction zone was identified by OH profiles using PLIF (Planar Laser-Induced Fiuorescence). The extinction behavior depends on the mixture property and the flow strain rate. For small strain rate and Le>1, the extinction limit is nearly constant regardless of super lean premixed gas condition. On the other hand, for Le<1 and the strain rate large, ultra lean premixed gas interacts with lean premixed gas and the stable region extends to the lower fuel concentration zone.

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An experimental study has been made of the ignition process of fuel droplet array subjected to a laminar fiat flame propagating through a lean homogeneous propane-air mixture at constant pressure. A combustion chamber made of a transparent duct was installed with spark electrodes, a pair of fine quartz fibers to suspend fuel droplets and a shutter to allow the burned gas to flow out. A high speed video camera was provided for the photographic observation of the droplets ignited by the propagating flame and for the determination of the ignition delay. The results showed that the ignition delay increased with a decrease in the volatility of liquid fuel and an increase in the initial droplet diameter. A part of the propagating flame behind the droplet was deformed to be convex toward the unburned gas as it passed by the highly volatile fuel droplet. Also evident was that the ignition delay of the second droplet showed a minimum as a function of droplet spacing.

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An experimental study has been made of the evaporation, autoignition and combustion of a single fuel droplet in supercritical gaseous environments under microgravity during the parabolic flight of airplane. A video camera was provided to observe the behavior of the fuel droplet. The fuel tested was octadecanol which solidifies at 331 K, and critical conditions of which are 1.4 MPa and 747 K. The experiments were done in the quiescent gaseous environments at low oxygen concentration to reduce the soot yield in the flame and to make it possible to observe the backlighted image of the droplet. The ignition delay and the burning time showed minirag at the ambient pressure approximately equal to the critical pressure of the fuel. The burning rate constant determined from the time histories of the droplet diameter showed a peak at ambient pressure 1.4 times as high as critical pressure of the fuel.

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The characteristics of combustion process in internal combustion engines are affected by mixing process between the injected fuel and the ambient gas. Therefore, it is necessary to understand the flow field in diesel fuel sprays. In this study, a single spray was injected into a quiescent atmosphere with room temperature at high pressure through a single hole nozzle for simplification. To discuss the flow field in diesel sprays, structure of the spray was visualized by laser light sheet method. And, it was revealed that the vortex structure inside the spray affects the classification of droplet particles by taking microscopic photographs of the droplets with high resolution film. And applying PIV method into the spray photography, both the formation of meandering structure of the spray mainstream and the ambient gas entrainment process are clarified.

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The combustion process in internal combustion engine is dominated by turbulent mixing the injected fuel with the ambient air. Therefore, in order to realize the high efficiency and clean combustion, it is necessary to understand in detail phenomena concerning these turbulent mixing process. Then, as a fundamental work elucidating the mechanism of mixture formation in the turbulent flow field, the gas velocity inside the transient gas jet was measured by PIV method, the concentration distribution of the entrained air was measured by LIF method. In addition, with two fluorescence tracer method proposed in this study, it is possible to measure simultaneous characteristics of fuel and surrounding air flow and concentration distribution. As the result, there is the stronger inverse proportional relation between the change in the ambient concentration and that in the axial turbulence intensity against that in the radial turbulence intensity. The change in the radial turbulence intensity is larger than that in the axial turbulence intensity, as a consequence that in the concentration is larger.

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The present report is concerned with NO formation characteristics in a DI diesel engine operated with dimethyl ether (DME). Chemical equilibrium calculations were made to understand the basic NO formation properties of DME. An experimental study was also conducted with a small DI diesel engine, and the results were compared with the results of calculations using the three zone model. It was found that DME has the adiabatic flame temperature and equilibrium NO concentration which are both higher than alcohols but comparable to diesel fuel. In addition, it was suggested that the air mixing rate for DME spray is lower than that for diesel fuel and this is the cause of the relatively high NO emission when DME was used in the diesel engine.

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Due to the increasing interest in the CO₂ problem, the request for alternative fuels from regenerated vegetable energy sources is increasing. The present work describes the results of experiments using rapeseed oil, emulsified rapeseed oil, rapeseed oil methyl ester, and gas oil in a swirl-chamber diesel engine. The results show that the viscosity of rapeseed oil methyl ester is a little higher than that of gas oil and that the smoke concentration of rapeseed oil methyl ester is about 50% lower than that of gas Oil. Furthermore, NO_x and smoke concentrations of emulsified rapeseed oil are lower than those of gas oil and energy consumption is similar to that in the case of operation with gas oil and rapeseed oil methyl ester.

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Ignition delay of diesel fuel sprays is investigated experimentally using a rapid compression expansion machine at operating conditions which are common in modern diesel engines. A comparison of experimental result with published data shows that higher injection pressure and smaller orifice diameter can shorten ignition delay respectively. In an attempt to make the physical ignition delay as short as possible, an experiment is conducted using injection nozzles with tiny orifices processed by a laser drilling. The result shows that ignition delay becomes short as the orifice diameter decreases, but it remains unchanged if the orifice diameter is smaller than 0.05 mm. It is also worth noting that there exists a temperature range around 790 K in which ignition delay remains almost constant being independent of the temperature. This trend is similar to that observed in shock tube studies concerning homogeneous mixture autoignition, implying that the ignition delay obtained with those nozzles is governed mainly by chemical ignition delay.

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The requirements of meeting increasingly stringent emission regulations dictate increasing complexities in diesel engines and new thinking in the engine design. In this respect investigation of the diesel spray and mixture formation within the combustion chamber have attracted much attention. The diesel spray behavior has usually been investigated photographically in a pressurized vessel at ambient temperature. This paper presents the results of the fuel spray behavior for a modified direct injection diesel engine with a square piston of different combustion chambers. It was found that a strong squish affects the top side of spray significantly at early injection timings, higher engine speeds and narrow head clearances. The round lip in a reentrant type combustion chamber contributes to a better confinement of fuel and concave shape of the bottom surface helps the spray to reach to the air rich zone of the combustion chamber and mixture formation improves.

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