Recently, high pressure injection systems have been used in many direct injection diesel engines. These systems are effective in improving fuel consumption, exhaust performance and so on. But cavitation erosion in the fuel injection tube is a problem in these systems. Measurement of negative pressure is important to prevent occurrence of cavitation phenomena and erosion in the fuel injection tube. Therefor we trial manufactured a device to measure negative pressure exactly and a measured negative pressure as the same time cavitation bubbles using a system to observe bubbles and a negative pressure sensor. In this work we also determine which retraction volume of the delivery valve does not influence cause of negative pressure and cavitation bubbles. Moreover, we confirmed that when using a low retraction volume delivery valve, growth remarkable negative pressure to such a degree that -1 (atg) below.

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Drag coefficients of a spherical rising gas bubble were estimated experimentally and numerically. We developed an experimental apparatus in which a CCD camera with a microscope follows the rising bubble and used it to precisely estimate the drag coefficients of the bubble below Reynolds number of 100 by measurement of the bubble size and the terminal velocity. We also estimated numerically drag coefficients of a gas bubble in an infinite liquid by directly solving a Navier-Stokes equation. The experimental results agree well with the numerical results. Moreover, we compared the experimental results with several proposed equations for estimating drag coefficients and determined the region of applicability of each equation. Finally, we proposed an equation for estimation of drag coefficient by correlating with experimental results.

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This work is part of a continuing research program aimed at clarification and control of the flow structure in an asymmetric expansion channel with local changed channel geometry. Laminar separated flow in two-dimensional symmetric and asymmetric sudden-expansion channels has been investigated numerically. The results of calculation are consistent with flow visualization results. For the asymmetric expansion channel, backward-facing steps of both the upper and lower walls in the channel were placed a distance L_P a part in the streamwise direction. A Navier-Stokes equation was solved by the finite difference method using a pseudo-unsteady technique. The calculations were performed for the cases of eight different distances L_P and of eight different channel expansion ratios a for the range of Reynolds numbers Re≤1600. In this report, the degrees of similarity of separated vortexes and the relation between the flow pattern and the dynamical behavior were examined from the viewpoint of engineering applications.

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We describe an experimental study on the process involved in the disappearance of arch vortices shed from a circular cylinder of finite length, and the accompanying changes in the turbulent near wake, as a function of the aspect ratio of a circular cylinder. The experiment was carried out in a circuit-type wind tunnel having a 200 mm×200 mm working section of 2000 mm length at the Reynolds number Re of 9200. The time-mean velocity and turbulence intensities were measured by use of a laser Doppler velocimeter. Vortex formation was observed by flow visualization in a water channel at Re=4600. Consequently. details of the flow pattern in the turbulent near wake behind a circular cylinder were revealed, including information on shedding arch vortices.

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A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition of a moderate Womersley number a=10, which is a physiologically interesting nondimensional frequency. and a Dean number D=300. The secondary flow motion was rendered visible by means of a tracer method using nylon particles, and photographs were taken at four phases in one cycle and at axial locations from the upper stream tangent to the downstream in the curved pipe. The instantaneous velocity vectors and profiles of the secondary flow and its intensity were obtained from the photographs. We discuss the secondary flow characteristics in the entrance region of the curved pipe. Development of the secondary velocity field can be quite well explained from the axial flow field. The secondary flow pattern changes with the phase at the inlet region are complicated, especially at Ω=20∼50°around the curved turn. The intensity of the secondary flow is high during the inflow term of one cycle in the curved pipe, and is high during the outflow term in the upper stream tangent. The inlet length according to the information regarding the secondary flow agrees with the length evaluated from the amplitude of the axial flow velocity in our previous work given by the reference (7).

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The torsional flutter margins of a pitching hydrofoil in the subcavitation region under various flow and vibrational parameters, i.e, the angle of attack, the cavitation number, the reduced frequency and the torsional axis, were expermentally investigated. The cavitation aspects of the hydrofoil are shown using high-speed photographs. The unsteady lift and moment were measured using a torsional vibration-apparatus with load cells which can eliminate the mechanical inertia force and moment of the pitching hydrofoil. The type and intensity of the separation on the hydrofoil have a large influence on the cavitation aspect, the unsteady fluid force and the flutter margin in the subcavitation region. In the case of nonseparation. an unstable range of the flutter exists neither in the noncavitation region nor in the subcavitation region. In the case of separation in the noncavitation region, the flutter margin expands to the higher reduced frequency side as the angle of attack increases, and in the subcavitation region, these flutter margins remain until the cavity length reaches the mid-chord. However, the flutter margin slides toward the higher reduced frequency side maintaining the same width as the cavity length extends from the mid-chord to the full chord.

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Following the study of drag reduction by machining a V-groove along the surface of a cylinder, the drag reduction of an airfoil was experimentally investigated. The airfoil used in this research was NACA 6508 (10) with a 200 mm chord length. First, experiments were done using the airfoil without grooves. The airfoil was placed in the test section of a cryogenic wind tunnel. The Reynolds number was varied from 3×10⁵ to 4×10⁷, and the angle of attack from -6°to 12°. Pressure distributions along the surface were measured, and velocity and pressure distributions were also calculated. The effects of the V-grooves on the pressure distributions and form drag and lift were obtained. The form drag coefficient of the suction surface was reduced by 0.025 in an angle of attack range from 1°to 4°. The reduction occures because of the decrease in pressure on the front part of the airfoil suction surface. The lift coefficient is also increased by this reduction in pressure. In the case of a cylinder, there were two reasons for reduction : one is that the laminar boundary layers remain on the surface longer, so the pressure drops in the front part, and the other is that the retardation in flow separation and pressure rise occurs on the back part. In our experiments the reduction of drag of an airfoil was achieved as a result of the front reason.

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The three dimensionalization process of a boundary layer transition is investigated by wind tunnel experiments. Attempts to generate velocity fluctuations similar to those which appear in the later stages of transition are carried out using a vibrating wire. The wire, with a diameter of about 30% of the displacement thickness, is attached to the surface wall in the spanwise direction, and is forced to vibrate back and forth in the streamwise direction. It is shown that this method is capable of generating a Tollmien-Schlichting wave (T-S wave) and an oblique wave in a flat-plate boundary layer.

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In the 1st report, we showed that the renormalization group (RNG) theory for turbulence developed by Yakhot and Orszag (1986) and reformulated by Yakhot and Smith (1992) is not related to Wilson's theory. Also it was pointed out that the Kolmogorov constant was evaluated by setting ∈-0 and ∈=4 in the same equations and that the constants in the K^^-@ε^^- model are invalid because of the same problem. In this study, we have used an iterative averaging method which does not require the ∈-expansion technique, and applied it to derivation of eddy viscosity. Using the exact governing equations for turbulent shear flows, we have obtained the eddy viscosity more consistently than with the previous RNG method ; the present form is equivalent to Boussinesq's postulate, and the model constant C_μ is determined from the value of the Kolmogorov constant.

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A full turbulent transition process is created on a yawed flat plate using a displacement body system in a wind tunnel. It was found that high frequency secondary instability drives the crossflow dominant boundary layer into a full turbulent state. Taking into account such transition structures, effective control of the flow field to delay the transition is possible. That is, by placing grooving line suction holes along each streamwise crossflow vortex, and as is causing selective suction in the low momentum flow, the appearance of the secondary instability is successfully delayed turbulent transition. This suction system also has an advantage over a uniform system in that the amount of suction air volume required to control the flow field is much less than in uniform suction. Thus, a great deal of energy needed for flow control is saved. We also attempted to determine the most appropriate condition for selective suctioning.

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Thermal and nuclear power plants have many T-tubes where a hot fluid and a cold fluid flow into each other and mix. An optimally designed T-tube can be used to shorten mixing time which can lead to more compact plants. We have experimentally investigated the mixing characteristics of hot and cold fluid flows into a T-tube. This paper shows the mixing distance, an analogy between thermal and mass diffusion, and the optimum condition for rapid mixing. We propose a T-junction arrangement using a downstream bent tube as a mixing promoter. The experiments so far clarify that the bent tube can best enhance mixing when the branch tube in the T comes from the opposite direction to the bend. For example, at the velocity ratio u/U=1. the bent tube can reduce the mixing distance from 35D to 8D and still achieve sufficient mixing.

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The log-law of a zero pressure gradient turbulent boundary layer is obtained by analyzing the similarity of the probability density functions of the streamwise velocity fluctuation. The slope of the log law is found to be constant, independent of the Reynolds number. We used the Kullback Leibler divergence of probability density function to identify the log-law region in experimental data. The outer edge of logarithmic region does not indicate the constant value when normalized by the boundary layer thickness. Rather, it is a function of the Reynolds number, and when the Reynolds number is suffucuently high, this value approaches to 0.2.

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Up to now there has not been any universally accepted model that describes the basic char acteristics of electrorheological (ER) fluid. In order to find a model applicable to the prediction of rheological properties of ER fluids, experimental studies of laminar channel flow are performed for two types of ER fluids. The experimental setup is designed to provide reasonable estimates of ER fluid response to steady electric fields. Obtained data are adequately modeled using a well-established constitutive equation of Bingham plastic fluids, which is thought to be one of the most likely candidates for predicting the behavior of ER fluids. Calculations of frictional factors as functions of the proposed apparent Reynolds number are also found to be possible using the measured data. In the experiment, both the apparent viscosity and the yield stress are found to be highly dependent on electric field intensities. In addition, the analysis presented in this study predicts, with high accuracy, the dependence of the stress response in steady shear flows on electric field intensities.

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The subject of analysis in this study is a human brain exhibiting edema. The cells of an edematous brain contain an overabundance of cerebrospinal fluid (CSF). Brain edema appears as a white region in magnetic resonance images of the brain. However, such images show only that an excess of CSF is present in the cells ; they give us no information on the direction or quantity of CSF flux. Therefore, we studied the flow of CSF in brain through computer simulation. First, we constructed a two-dimensional model of a brain using FEM based on Poisson's equation and a diffusion equation and simulated the CSF flow in the brain tissue in order to determine the quantity of CSF present. Second, we simulated a case in which colored-albumin is poured into the brain tissue at the site of edema and compared the distribution of CSF in this case with that in a CT image which exhibits edema. The results on CSF flow obtained in the simulation are similar to those obtained by pathological observation. Moreover, we believe that these simulations help us to develop new medical treatments for brain disease such as edema.

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In this study, the compression characteristics of wet vapor refrigerant are investigated theoretically and experimentally. In the theoretical analysis, vapor and liquid phases, and the heat transfer between them are modeled in three different ways, i.e., homogeneous model, slug model and droplet model. The influence of the parameters, such as quality of wet vapor and cylinder wall heat transfer, on pressure as well as on temperature are investigated. On the other hand, two different types of experiment have been conducted to check the validity of the models. One is the refrigeration cycle experiment which was conducted using a reciprocating compressor under liquid suctioning. The results agree with the model in which the vapor-liquid mixture is considered homogeneous. The other is a model experiment which was conducted using the components of the reciprocating compressor without connection to the refrigeration cycle. The liquid refrigerant is injected into the compressor cylinder and different qualities of vapor and liquid slug are created inside the cylinder prior to compressor start. The results agree with the model in which the vapor and liquid slug are assumed to be separated with constant liquid slug temperature. Furthermore, the results of both experiments are investigated with the help of a droplet model with different droplet sizes.

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Plasma fluctuations in a flow field with a steep increase in static pressure in a closed cycle disk magnetohydrodynamic (MHD) generator, caused by varying the pressure at the channel exit, were examined by means of a quasi-one-dimensional numerical simulation. In order to compute the plasma properties at the exit boundary for subsonic flow, the characteristic theory where the effects of the MHD interaction are taken into account was developed. The computational results indicated that the fluctuations of the gas dynamic and electrical properties propagated upstream at a speed of sound relative to the local plasma flow velocity. The time variation of the output Hall voltage due to the application of pressure pulse decreased with time and, finally, the Hall voltage reached almost the same level as that for the steady-state.

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We have investigated the behavior of clusters of ferromagnetic particles in a colloidal dispersion subjected to a simple shear flow. To do so, the Stokesian dynamics method has been used under the assumption that the effect of Brownian motions are negligible. For the case of no shear flow, the aggregate structures obtained by the Stokesian dynamics simulations agree well with Monte Carlo results qualitatively. We can, therefore, conclude that the Stokesian dynamics simulations can capture thick chainlike clusters without introducing a specific clustering algorithm, which is indispensable for Monte Carlo simulations. The behavior of the thick chainlike clusters in a simple shear flow is summarized as follows. The thick chainlike clusters decline in the shear flow direction as time advances. Since longer clusters experience larger shear forces, long clusters are difficult to survive in such a situation. The thick chainlike clusters dissociate into some short clusters. Such clusters are relatively stable in a shear flow, so that they do not dissociate significantly any more. The viscosities have a strong relationship with the internal structures of the aggregates. The instantaneous viscosities, therefore, fluctuate significantly for the case of the thick chainlike clusters.

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Investigations of both noise and aerodynamic characteristics of a centrifugal fan without scroll casing were performed with respect to the effects of three parameters : (1) the distance between the leading edge of the blades and the inner wall of the mouthpiece, (2) the gap between the outer wall of the bellmouth and the inner wall of the mouthpiece and (3) the geometry at the outlet of the bellmouth. A formula was determined to predict the sound pressure level of turbulent noise from a centrifugal fan without scroll casing. It was shown that the total pressure and efficiency of the fan was reduced as the distance between the leading edge of the blades and the wall of the mouthpiece increased. If the geometry at the outlet of the bellmouth was straight, the sound pressure level appeared in the neighbourhood of 1.5 kHz and specific noise level was reduced as the gap between the outer wall of the bellmouth and the inner wall of the mouthpiece decreased. The agreement between the measured values and the predicted values of the sound pressure level of the turbulent noise was satisfactory.

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In the present study, a prediction model for condensation of binary refrigerant mixtures inside a horizontal smooth tube is proposed. In this model it is assumed that the phase equilibrium is only established at the vapor liquid interface, while the bulk vapor and the bulk liquid are in a nonequilibrium state. The predicted results are compared with the experimental ones for the condensation of IIFC134a/HCFC123 mixtures ; in the experiment, the bulk mass fraction of HFC134a ranged from 0.35 to 0.85 kg/kg, and the mass velocity of 120 to 300 kg/(m²s). Since the mass transfer characteristics in the vapor core are assumed to be expressed as Sh_v=0.046 Re^0.8_vSc^0.3_v, the predicted heat flux distribution along the tube axis is in good agreement with that of the experiment. The mass transfer characteristics during the condensation, determined by the prediction calculation, are also presented.

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This paper describes thermal and aqua-reserve characteristics of a super-absorbent polymer gel which absorbs an aqueous solution of calcium chloride as a heat absorbent in a firewall during fire. Only gels which absorbed 10 to 40 mass% of the solutions were tested. The absorbency of the polymer and latent heat of the gel were measured using a thermal analyzer of TG/DTA. To obtain the aqua-reserve characteristics, changes in weight of the gel which was left in a room under controlled temperature was measured. Also, an equilibrium concentration of the calcium chloride solution in the gel was obtained.

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Heat transfer during boiling and its relationship to the boiling configuration on a small platinum film heater immersed in subcooled ethyl alcohol at atmospheric pressure and heated so rapidly so as to realize the fluctuation nucleation on it are studied. The rate of temperature rise of the heater examined ranged from 5.7×10⁵ K/s to 20×10⁶ K/s. Concurrent generation of a large number of tiny bubbles, the behavior of which is well predicted by the theory of homogeneous nucleation, was observed at a higher rate. The tiny bubbles coalesced with each other to form a large bubble on the heater slightly after the boiling incipience and immediately before the transition to film boiling, which was identified by a sudden rise in the temperature time curve. At a high rate, no appreciable increase in the heat transfer rate after the boiling incipience was observed, whereas at a low rate, the increase rate of the wall temperature decreased due to a sudden increase in the heat transfer rate before the boiling transition. After the boiling transition, the heat flux decreased markedly to about 50% of the value before the boiling incipience. The coalesced bubble grew once and then contracted as a reaction of the excess growth due to inertia. The heat flux increased markedly when the bubble collapsed. The results for water are, in general, the same as those for ethyl alcohol.

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The possibility of methanol conversion from a methane and water vapor gas mixture was investigated for a new and highly efficient energy conversion system. Reforming process of methanol to hydrogen cas be used for a low-temperature thermal energy utilization. Direct methanol production from methane and wetar-vapor mixture by spark or glowlike discharges has been achieved experimentally. High methanol production rate of 0.5% has been obtained by both discharges. The effects of reaction time, total pressure and ratio of gas mixture on the conversion efficiency have been clarified experimentally. The electric energy consumption for the methanol production by the spark discharge is 0.01 times smaller than that by the glow discharge. The methanol conversion process has also been analyzed theoretically by considering 104 elementary reactions. The result suggests that a very short period energy input such as a spark discharge can effectively produce methanol.

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Linear stability analysis is applied to the absorption of water vapor into lithium bromide aqueous solution film when a small amount of surfactant is added to the solution. The condition under which an instability occurs and the role of the surfactant are investigated. The analysis shows that the film becomes unstable at a positive Marangoni number when the heat transfer is more determining than mass transfer. In contrast, when the mass-transfer is more determining, the film becomes unstable at a negative Marangoni number. As for LiBr aqueous solution, mass transfer is more ratedetermining than heat transfer, so the instability is promoted and maintained when the Marangoni number is negative. In the case of film flow absorption, the analysis shows that the disturbance of the film flow becomes more unstable in the transverse direction than in the longitudinal direction as the Reynolds number increases.

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In a previous paper, we proposed an improved renormalization group (RNG) theory based on iterative averaging for turbulent shear flows to obtain an eddy-viscosity-type turbulence model. In the present paper, we have applied this theory to the governing equation for a thermal field, and derived a thermal eddy diffusivity representation relevant to the turbulent heat flux. We have also obtained an RNG-based equation for the turbulent Prandtl number Pr_t, with a high Reynolds number limit as Pr_t=0.79.

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A discrete particle model for simulating an accurate temperature field for a toner particle packed bed during fusing has been proposed. Several toner particle arrays consisted of one to three particles are separately built on a paper surface. Particle-particle and particle-paper are thermally connected via contact resistance. Thermal contact conditions are theoretically examined for obtaining the contact resistance. In the examination, a contact area is derived from electrostatic force acting to the particle and Hertz's equation. The calculations of the temperature field have been carried out by a finite difference method. The calculated result, under a condition that the contact resistance decreases during fusing, indicates excellent agreement with experimental result. It is revealed that the contact resistance and its decrease during fusing play an important role for the heat conduction in the toner packed bed, which has been less considered in the current analysis.

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We have developed a three-dimensional, clothed human thermal model for prediction of physiological response and micro-climate within clothing to thermal environments. The model is a coupled simulation system of the human thermal model and the clothing thermal model. It can simulate heat and mass transfer processes including moisture sorption of fabric. The performance of the model was experimentally verified. The following results were obtained : (1) The model predicted skin temperature distributions, and the micro-climate within clothing basically agreed with the experimental data. (2) Both model prediction and experimental data for the same thermal conditions showed that the skin temperature of the clothed body parts was higher than that of the corresponding body parts in nude condition, as well as the skin temperature of both the hands and the feet.

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A Fredholm-type boundary integral expression for evaluation of the forced convection heat transfer from an object with arbitrary surface temperature distributions is proposed. The Fredholm kernel function for a heated circular cylinder was calculated by numerical simulation of the forced convection fields, and then generalized heat transfer coefficients for arbitrary surface temperature distributions were defined. By use of the generalized heat transfer coefficients, it is shown that the difference in local heat transfer characteristics between the case of an isothermal cylinder and that of a uniform heat flux one can be explained only as the difference of the surface temperature distributions. Moreover, the mechanism of the effect of the surface temperature distribution on the characteristics of forced convection heat transfer from a cylinder is clarified in detail through the generalized heat transfer coefficients.

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An experimental study was conducted to investigate the characteristics of wall heat transfer and momentum loss for a turbulent duct flow disturbed by insertion of a complicated body composed of a LEBU (Large Eddy Break-Up) plate and winglet-type vortex generators. It was found that the LEBU plate reduces the wall heat transfer in the region downstream of the insertion position and that this suppression of heat transfer could be recovered by attaching vortex generators to the LEBU plate, i.e., conspicuous heat transfer enhancement was achieved over a large streamwise distance. The obtained spatial distribution of heat transfer coefficient shows the same features as that observed in the previous study of a flat plate turbulent boundary layer. Therefore, the flow and thermal field structure of the turbulent duct flow downstream of the inserted body should be basically the same as those in the same region of the turbulent boundary layer. The effect of a notch, open in the LEBU plate behind the vortex generator, on heat transfer and pressure drop was also examined. The notch simulates the hole of the LEBU plate to be produced in practical application, when a vortex generator is produced by punching from the original plain LEBU plate. A vortex generator having an open notch was found to work best not only in augmentation of the wall heat transfer but also in suppression of the increase of momentum loss.

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The cross-flow between two subchannels in a BWR fuel assembly has typically been analyzed using three types of mixing models, namely, pressure difference, turbulent mixing and void drift, which are expressed by time-averaged flow parameters. However, in our previous paper, we expressed the above cross flow phenomenon simply by a fluctuating pressure model and confirmed its validity experimentally. In this study, we examine the relationship between the fluctuating pressure difference and the cross-flow rate more precisely by using a short mixing zone with no steady pressure difference. Results show that the experimental cross flow data agree well with the calculations applied to the model. Furthermore, we tried to express the fluctuating pressure difference by using a sinusoidal wave as a new cross-flow model. It was shown that the model has no dependence on frequency. We verified that the cross flow could be analyzed using only the pressure difference amplitude.

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In this study, a numerical simulation for analyzing the temperature and velocity distributions within the polymer melt was performed for an innovative injection molding process. The most important characteristic of this process is that infrared radiation energy is applied in order to control the temperature distributions within the molten polymer during the filling stage. The model used in the present study assumes that molten polymer flows at constant mean velocity between two parallel mold walls. One mold is made from metal and the other from material that is transparent to the radiation. The governing equations were solved by a finite-difference method using the control volume approach under realistic molding conditions, and the effects of radiation heating on the temperature profiles were investigated. The results clearly showed that the radiation heating prevented the usual temperature drop in the vicinity of the molded polymer surface, and decreased the shear rate within the flow passage. It was also shows that the efect on the process time (decrease in productivity). caused by this process, was much smaller than that caused by the conventional process which utilizes conduction heating.

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Medium-Btu coal gasified fuel, the higher heating value of which is about 4.2 to 12.7 MJ/m³, is composed of CO and H₂, as its main combustible components. Moreover, it contains small amounts of NH₃ and CH₄. NH₃ will be converted to NO_x in the combustion process. In this study, the basic combustion characteristics of the coal gasified fuel were examined by combustion experiments using a laboratory scale combustor. The main results are as folows : (1) The amount of thermal-NO_x production increases rapidly as the amount of fuel calorific value of coal gas increases. (2) When the two stage combustion method is used, the optimum equivalence ratio of the primary combustion zone by which the NO_x conversion rate is made minimum exists. This optimum equivalence ratio become higher when the fuel calorific value is high. (3) The NO_x conversion rate rises as CH₄ concentration increases. When the two stage combustion method is used, the optimum primary equivalence ratio which makes the NO_x conversion rate minimum rises as CH₄ concentration decreases.

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Numerical simulations were performed to predict fluid motions induced by interactions between density and pressure gradients. The presence of a vortex string situated in a deviated position from the jet flame axis generates two pairs of vortices near the flame front where a significant density change exists. It is predicted that the deformation and stretching of the flame front take place once the vorticity production becomes stronger than the dissipation due to viscosity. Vorticity production is caused by the baroclinic effect in the upstream position, but the generation due to gas expansion supersedes that of the baroclinic effect in the downstream position. When the pressure gradient is greater than a certain critical value, the vorticity production proceeds at a higher rate, which promotes the deformation of the flame front and accelerates the heat release.

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Optical observations of ignition and burning processes in a two-dimensional valveless pulse combustor are carried out : to examine the phases of termination and initiation of fresh inflows. The acoustic effects of the fresh inflow supply lines on the combustion characteristics, as well as the relationship between the heat release rate and the combustion chamber pressure are clarified. Measurements of mean velocities of air and fuel inflows in three typical phase durations are also attempted using the Schlieren optical system. It is found that the air flow terminates almost simultaneously with the fuel inflow, while the former initiates earlier than the latter by about a 1/4 period, suggesting a dominant acoustic effect of the upstream supply lines on the pulse combustion mechanism. The velocity of fresh inflow at the point just downstream of the baffle plate, which reaches up to 17 m/s, is high enough to enhance mixing and burning within a pair of large eddies. The fluctuation of the overall heat release rate is advanced in phase by about a 1/4 period ahead of the pressure fluctuation. Therefore, it is understood that a relatively small amount of energy is added to the present pulse combustion system to maintain stable pulsation.

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It has been identified that the strong turbulence in the nozzle hole caused by cavitation phenomena, contributes to the atomization of the liquid jet. On the basis of this result, experiments were performed under atmospheric conditions using nozzles of various length to diameter ratios, L/D, of the nozzle hole, and setting a wire netting over the inlet and installing a gap at the nozzle hole in order to promote atomization by cavitation. It was clarified that when a large disturbance is applied to the liquid flow, the atomization of the liquid jet is increased. When the disturbance, which is caused by the collapse of cavities, exists near the exit of the nozzle hole, the atomization of the liquid jet is considerably increased.

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Active thermo-atmosphere combustion (ATAC) is "bulk-like" and/or "non-propagating" combustion caused by compression autoignition. and it is stable in a lean combustion region. We carried out an ATAC engine test to elucidate the effect of fuel properties on the engine performance in a lean combustion region. Several combustion characteristics, i.e., the ATAC operation region, brakespecific fuel consumption, exhaust emissions, the cyclic variation of maximum cylinder pressure, rate of heat release, autoignition timing, combustion duration, autoignition cylinder pressure and autoignition gas temperature were demonstrated for gasoline, methanol and methane. From the results of these tests, the influences of the equivarence ratio and the compression speed on the autoignition and combustion period were clarified, and we evaluated the adaptability of various fuels to lean burn in an ATAC engine. With use of methanol, the ATAC operation region could be widened in the lean region and the amount of brake specific fuel consumption was decreased. With use of methane, ATAC operation was impossible. The autoignition temperature of methanol in an ATAC engine is lower than that of gasoline by about 140K. We can say that methanol is most suitable for lean burn in an ATAC engine.

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The effects of pilot injection and reduced initial fuel injection rate on combustion and pollutantand noise-emissions were experimentally studied on a high-speed direct injection diesel engine using an injection system which gives different injection rate waveforms. The results show that the exhaust NO_x concentration at middle load is lowered at a reduced rate of initial injection. For the pilot injection, the pilot fuel amount and the interval between pilot and main injections significantly influence the engine performance and exhaust emissions. At middle load, the pilot injection with a smaller amount and a longer interval may reduce NO_x and engine noise. At high load, a reduced rate of initial injection lowers the exhaust NO_x concentration and noise emission and increases the concentration of smoke. However, the smoke can be significantly reduced by increasing the average injection rate. This characteristic is marked at lower engine speeds and shows little dependency on the nozzle orifice diameter. For this reason, it is concluded that the most favorable situation is high-pressure injection with low-pressure pilot injection.

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This paper describes the application of a i.e. fuel water-fuel injection system for diesel engines. This system makes it possible to inject water during fuel injection from the same nozzle hole without mixing the liquids. First, it was confirmed that NO_x reduction and improvement of thermal efficiency and smoke density could be achieved using this system. The reason for such improvement of combustion with water was investigated in detail using a special test engine with which burning flames could be visualized by taking high-speed photos. Moreover, the distribution of the water vapor in the fuel spray was estimated through calculations using the "KIVA" code. Using these studies, this system may soon be put to practical use.

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This study investigates the atomization mechanism of fuel spray dissolved in noncondensable gas, such as N₂, CO₂. The fuel spray was injected at room temperature and in an atmospheric pressure field through a diesel-hole-type nozzle. In this paper, N₂ gas was dissolved into diesel fuel, n-tridecane, under several pressurized conditions using a gas bubbling method in a constant volume vessel. This fuel, with high gas solubility, was injected under several injection pressures using an accumulated injection system designed by the authors. It was found that the dissolved gas separated into gas bubbles like gas cavitation phenomena under the atmospheric field. The change in spray patterns caused by the gas solubility is discussed using photographs of the patterns.

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In this paper, propose a new fuel injection system using diesel fuel dissolved in liquefied CO₂. The system has the capability of reducing both NO_x and soot simultaneously. This concept strives to improve the atomization of fuel spray by flash boiling liquefied CO₂ gas. Moreover, it is possible to control the combustion system, for instance, and internal EGR effect is produced by the separated CO₂ gas. In this paper, the characteristics of diesel spray of the fuel dissolved with liquefied CO₂ were investigated using several optical measurements and the variance of CO₂ molar fraction, ambient pressure and ambient density under room-temperature conditions. The spray characteristics were revealed using analysis in chemical thermodynamics. The atomization and dispersion of a free spray composed of fuel dissolved in liquefied CO₂ are much better than those of normal diesel fuel oil, due to the flash boiling process in the relatively low pressure field.

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Experimental investigations are being conducted on a single-cylinder direct-injection diesel engine to examine the transient heat transfer characteristics. Transient temperature data from stationary locations in the piston and cylinder head were used as the basis for determining the transient heat flux rates. Transient surface temperature was measured using the thin film thermocouples. At first, the transient heat flux rates calulated from the analysis method used in this paper were compared with the results from FEM. The results showed good agreement. Using this analysis method, the transient heat flux rates were calulated. The tests were performed at 1200 rpm with constant air flow. The parameters that were varied included the fuel rate and injection timing. Based on these results, the present paper discusses the mechanism of heat rejection in a direct injection diesel engine.

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Experimental investigations are being conducted on a single-cylinder direct-injection diesel engine to examine the effects of combustion chamber specifications and swirl ratios on the heat release and transient heat transfer characteristics. Heat rejection was examined on the basis of heat release calculations using cylinder pressure time histories. Transient surface temperature data obtained from stationary locations in the piston and cylinder head were used as the basis for determining the transient heat flux rates. The results showed good agreement with the heat rejection calculated from cylinder pressure data and that transient heat flux in a piston cavity was reduced with the larger cavity diameter and a higher swirl ratio. On the other hand, a transient heat flux in a piston head was not changed by the cavity diameter and swirl ratio.

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