To elucidate clear the behavior of ambient-and inflow-cavitation-nuclei distributions associated with high-speed submerged water-jet tests, we systematically measured the distributions, and the change in them with time by means of a Coulter counter. These distributions are one of the most dominant parameters in all ambient and inflow types of cavitation. It was shown that our test facility is very suitable for high-speed submerged-water-jet tests, and it was also noted that the distributions varied in the test water with high-pressure treatment applied by a plunger pump.

抄録全体を表示

The leading-edge separation bubble of a blunt circular cylinder was excited by sinuous disturbances with single-frequency components at Reynolds numbers of the order of 10⁵. The disturbance was introduced by a woofer installed inside the cylinder through a thin slit along the separation edge. The level of the disturbances was defined by (i) the positive peak value of the sinuous velocity fluctuation at the middle of the slit without the main flow, and (ii) the r. m. s. value of the velocity fluctuation at a position immediately upstream of the separation edge with the main flow. Method (ii) was found to be more appropriate than method (i) although the latter was employed by previous investigators. In both methods the reattachment length was less than that for the unexcited separation bubble, attaining a minimum at a particular excitation frequency. This frequency for (ii) was approximately 5 times the frequency of shedding of large-scale vortices from the reattachment region. The vortex-shedding frequency was interpreted in terms of a feedback mechanism in which a disturbance produced by a large-scale vortex impinging on the surface propagates upstream to be accepted at the separation edge to modify the rolling-up of the separated shear layer.

抄録全体を表示

The most important issue for the flow field of an angled annular impinging jet is whether or not the first critical distance exists. With decreasing distance between the angled annular nozzle and the impinged flat plate, the forward stagnation point formed on the impinged flat plate is abruptly changed to the reverse stagnation point at the first critical distance. Existence of the first critical distance also separates the flow field of the angled annular impinging jet from that of recirculating flow formed by the Coanda effect. This paper deals with the relationship between the first critical distance and the geometrical dimensions of the angled annular nozzle. As a result, the existence of a critical opening angle was established and fundamental characteristics of the flow field were elucidated.

抄録全体を表示

The distribution of wall shear stress in the developing process occlusion in an arterial wall has been experimentally studied using an electrochemical method in laminar pulsating flow. The configuration of the flow model is axisymmetric stenosis expressed by the cosine curve. The wall shear stress around the narrowest section of stenosis changes more steeply at period of increasing flow rate. The wall shear stress just downstream of the narrowest section suddenly decreases and has a negative value, and the flow separates there. Around the separation point just downstream of the stenosis, the oscillation shear index has a finite value ; the flow direction periodically changes. Furthermore, the gradient of wall shear stress with respect to the tube axis is very high. Therefore, the change in wall shear stress and its direction of action periodically changes at the region where vascular disease would be anticipated.

抄録全体を表示

In this paper, an experimental study is presented for the squeeze film problem between rigid and compliant surfaces with a central air source. The lower squeezing plate is a compliant one and is fixed to an electric vibrator. The upper squeezing plate is a rigid floating body supported by squeeze air film. The weight of the floating upper plate is 1.75 N to 3.75 N and the range of frequency of vibration is 0.5kHz to 1.8kHz. The effects of volumetric flow rate, exciting frequency and amplitude of the squeezing plate on the characteristics of squeeze air film are investigated. Numerical analysis is also conducted for a simplified model. It is found that the combined effects of static pressure of the central air source and squeeze effects improve the load carrying capacity and stability of the floating mass.

抄録全体を表示

The unsteady flow of a viscoelastic fluid which is derived from wall motion parallel to the fluid movement, is calculated numerically using the integral constitutive model (WJFLMB model). Two cases of the wall movement pattern are considered : (a) steplike movement and (b) sinusoidal movement. The calculations are performed by converting the integral form to the finite difference form. The present calculation results show that the constant of a in the WJFLMB model has a strong effect on the calculation results and that the increse in a increases the difference between the Newtonian fluids and the viscoelastic fluids.

抄録全体を表示

The steady flow characteristics of emulsions through a pipe are studied experimentally in the transitional flow region. Butyl benzonate, a mixture of butyl benzonate and castor oil, and a mixture of liquid paraffin and carbon tetrachloride are used as the dispersed phase. In addition, water is used as the dispersion medium. The experimental results are summarized as follows. 1) These emulsions have the effect of decreasing the critical Reynolds number. 2) In the case of emulsions with a large diameter for the dispersed phase (about 10μm), a decrease in the apparent viscosity coefficient in a high laminar flow region can be observed. 3) These results conform well to the existing experimental results for blood.

抄録全体を表示

Outflow boundary conditions have been examined for the finite element analysis of internal viscous flow problems. As a test problem, the combination of Poiseuille flow and Benard-Rayleigh convection in a two-dimensional duct has been chosen. Using the test problem, two types of conditions are tested : (A) vanishing of a normal gradient of a quantity and (B) vanishing of a linearized convective derivative. Condition (A) is often used in the finite element analysis of internal fluid flows. In the present test case, it has been found that condition (B) yields better results, showing little reflection of outgoing waves back into the computational domain. In the last part of the paper, a generalized method for including the outflow boundary condition of type (B) into the finite element formulation of Navier-Stokes equations is shown.

抄録全体を表示

A numerical analysis has been performed for three-dimensional developing turbulent flow in an elliptical duct by a modified Reynolds stress equation model. Governing equations are transformed from the physical plane to the calculation plane by boundary-fitted coordinate systems. The calculated results are compared with the experimental data available. The predicted results of mean velocity along the axes and friction factor agree relatively well with the experimental data. The results of this analysis enable the prediction of the secondary flow of the second kind which characterizes noncircular duct flow. At the same time, a clear statement of the distribution of the various Reynolds stresses is made, showing their characteristic aspects. The secondary flow of the second kind reaches maximum intensity in the midst of development. This is a result of shear layer interaction effects as the boundary layer developing along the wall of the elliptical duct begin to merge.

抄録全体を表示

We propose a new turbulence model which is modified from the low-Reynolds-number k-ε model developed by Nagano and Tagawa. The main improvement is made by the introduction of the Kolmogorov velocity scale, u_ε≡(νε)^1/4, instead of the friction velocity uτ, to account for the nearwall and low-Reynolds-number effects. We have also reevaluated the model constants in the transport equations of the turbulent energy and its dissipation rate. With these modifications, it is shown that the present model predicts quite successfully a diffuser flow with a strong adverse pressure gradient and the separating and reattaching flows downstream of a backward-facing step.

抄録全体を表示

It is very important to investigate a shock wave / turbulent-boundary-layer interaction for the prediction of compressible flows. For this problem numerical procedures have been making rapid progress, for example TVD scheme, but turbulence models have not. This is partly because there is scarecely available data of compressible flows with a shock wave. However, recently a direct numerical simulation can be done and the results will be used to modify compressible turbulence models. I studied a compressible k-ε model. The propriety of k equation was investigated for the 1-dimensional turbulent flow passing through a normal shock wave. I found that the mean pressure gradient / velocity fluctuation correlation term in k equation plays the most important role in the behaviour of turbulence.

抄録全体を表示

This paper presents an experimental study of passive control of shock wave/turbulent boundarylayer interaction induced by a step placed on the floor of a wind tunnel. The experiments were carried out in a 8×10cm² supersonic wind tunnel, at a free-stream Mach number of 1.98. The basic model was equipped with an interchangeable insert in the shock region to allow measurements with varying geometrical parameters. The following factors influencing the passive control of shock-boundary layer interaction (PCSB) were studied : 1) area of the porous region, 2) porosity, and 3) type of porous surface. Surface static pressure measurements as well as Schlieren observations of the flow field were obtained. It was found that the mean cavity pressure is equal to the mean surface pressure and the effect of the porosity is much larger than the effect of the hole diameter. Furthermore, the forward-facing inclined holes is more effective than the backward-facing inclined holes.

抄録全体を表示

A new stochastic mixing model has been developed for chemically reacting turbulent flows. The Lagrangian particle tracing technique is used to represent turbulent diffusions. Concentrations of passive scalars are numerically estimated by the "fast mixing model", which proposes if two fluid particles approach each other within a certain prescribed distance as a result of stochastic processes, mixing occurs instantaneously and the concentrations become the average of the initial two values. The results obtained using this model were in good agreement with analytical solutions and gave an accurate diffusion coefficient.

抄録全体を表示

Shock wave focusing in a log-spiral duct is numerically studied by a finite volume method. A MUSCL TVD scheme with flux-vector splitting is applied to the Euler equations. Results show that an initially planar shock wave accelerates along the log-spiral wall and deforms in shape, but no reflected shock wave appears during implosion. With further increasing distance, the pressure gradient along the shock wave becomes stronger, and eventually a second shock wave forms behind the incident shock wave ; a triple point and a shear layer appear. After focusing, the reflected shock wave moves outward. An interaction between the reflected shock wave and the second shock wave produces a triple point. As a result, a second shear layer appears. At the same time, another interaction between the reflected shock wave and the original shear layer which formed during implosion also produces a shear layer. These two interactions are coupled to produce a strong vortex behind the reflected shock wave.

抄録全体を表示

In this paper, flow pattern and aerodynamic performance of vortex blowers with 3-dimensional blade form are studied. It is shown that the velocity within the casing increases with decreasing blade angle. Pressure and power coefficients are about two times as large as those of the 2-dimensional vortex blower. Results indicate that the peripheral direction velocity values at the blade inlet and blade outlet in the vortex blower are large, and the flow revolues passes several times between the inlet and outlet of the casing. The pressure and power coefficients are strongly related to the outlet blade angle the inlet blade angle, the number of blades and the ratio of the inlet diameter to the outlet diameter. The pressure coefficient is increased three fold as the outlet blade angle is decreased from 90 degrees (2-dimensional) to 70 degrees (3-dimensional), and is also increased by 20% as the inlet blade angle is decreased from 70 degrees to 40 degrees.

抄録全体を表示

Starting characteristics of a supersonic flow are investigated experimentally in the low Reynolds number range of interest for supersonic flow chemical oxygen-iodine lasers. It is shown that the supersonic flow cannot be started in the test section of constant cross-sectional area at low Reynolds number due to the unacceptale pressure loss, even though a second throat is not utilized. The supersonic flow can be stared at higher Reynolds number with a reasonable pressure ratio which is predicted by the normal shock theory. However, the Mach number in the test section decreases rapidly along the flow due to the presence of thick boundary layers. The use of the diverging test section resuls in a lower critical Reynolds number for starting the supersonic flow and lowers the temperature, although a considerably high pressure ratio is required.

抄録全体を表示

The rotors and stators of turbomachinery operate in partially cavitating condition in the case of high speed hydraulic machinery, and further they operate in various types of shear flows such as boundary layers, jets and wakes. This paper aims firstly to apply the existing theory for the two-dimensional supercavitating hydrofoil in exponential shear flow to partial cavitation and secondly to make it possible to clarify the effects of shear parameter on both cavitation and force characteristics of hydrofoil in the shear flow.

抄録全体を表示

Three-dimensional boundary-layer transition experiments are currently being conducted on a 45° swept wing in the Arizona State University Unsteady Wind Tunnel. Crossflow-dominated transition is produced via a model with contoured end liners to simulate infinite swept-wing flow. Fixed-wavelength, stationary and traveling crossflow vortices are observed. The frequencies of the most amplified traveling waves are in agreement with linear-stability theory; however, traveling waves at frequencies an order of magnitude higher than predicted are also observed near transition. Boundary-layer profiles measured at several spanwise locations show streamwise disturbance profiles characteristic of the crossflow instability. Near the transition location, severe distortions of the steady boundary-layer profiles are observed in the form of multiple inflection points. This distorted boundary layer is due to the stationary crossflow vortex and is subject to a Rayleigh-type instability in the stream direction. As a result, a high-frequency secondary instability is detected in the transition region, and spatial relations of the process are well documented by the coupled use of flow visualization and hot-wire measuremests. In all cases, we observe a transition due to this high-frequency Rayleigh instability induced by the stationary crossflow vortex.

抄録全体を表示

Equations for evaluating the longitudinal stability in steady motion of high-speed wing-in ground-effect craft were formulated. The craft may consist of an arbitrary number of wings within, or out of, the ground effect. Small perturbations superposed on steady forward motion of the craft were assumed and were linearized in comparison with steady forward motion. The procedure has yielded a fifth-order equation with respect to the characteristic roots. It was applied to special conditions for trend analysis and to an experimental WIG craft. A parametric study on the effect of size and location of the horizontal tails of the craft on the stability has given reasonable figures and tendencies.

抄録全体を表示

Experiments were carried out to study the feasibility of active stabilization of vaneless diffuser rotating stalls. Pressure fluctuation at the diffuser inlet was monitored and used to control the rotating stall. A. C. controll flow, which is produced by a loud speaker, was introduced into the diffuser at the diffuser inlet. It is shown that the rotating stall can be suppresed when the phase of the control flow has certain relation with the phase of the rotating stall. By considering the energy flux due to the A. C. control flow, it is shown that the rotating stall is suppressed when the control flow is in the phase such that the energy is subtracted out from the diffuser flow. Discussions are made on the relations between the energy flux and the amplitude of the pressure fluctuation due to rotating stall.

抄録全体を表示

The purpose of this paper is to investigate the relationship between static pressure recovery and turbulent characteristic values of the velocity field, in the case where a swirling flow streams into a conical diffuser. We introduce a turbulent characteristic value which is obtained by intergrating the turblent energy over the sectional area of the diffuser. Results of our experiments show that the static pressure recovery depends strongly on the magnitude of the turbulent energy in the diffuser, and that this magnitude of the turbulent energy varies as the intensity of swirl at the diffuser inlet.

抄録全体を表示

This paper firstly summarizes the features of surge and rotating stall in a multistage axial compressor on the basis of test results, showing various patterns of their occurrence, and describes subjects for numerical study of surge and rotating stall. Secondly, some numerical results obtained from the previous fundamental numerical model, which can deal with both surge and rotating stall, are described, including the relationship between compressor parameters and unsteady behavior modes, and the effect of inlet distortion on inception points of surge and rotating.

抄録全体を表示

A three-dimensional Lagrangian stochastic process model of a particle pair has been suggested for prediction of concentration fluctuations by a point-source plume in a low Reynolds number grid turbulence. The velocity correlation function between two particles at a given instant has been taken as the Eulerian velocity correlation, which obeys the continuity conditions. Moreover, the model explicitly contains the effect of molecular diffusivity. Simulation of two types of source (a plain Gaussian source and a uniform concentration circular plain source) has been made and compared with the experimental data. The main results are as follows : (1) the radial profiles of the mean concentration, rms value and intermittency coefficient by simulation are in good agreement with the experimental profiles in both the sources ; (2) the simulated downstream variation of the rms value in the case of the plain Gaussian source agrees well with the data. However, the mean concentration shows a slightly faster downstream decay than the experiments.

抄録全体を表示

This solution is based on a discrete singularity method in two-dimensional potential theory. For computational examples, the following bodies were chosen : groups of circular cylinders and elliptic cylinders in an infinite flow field, and a group of circular cylinders in a cylindrical container. Their added-mass coefficients were then calculated. As a result, it was clarified that this approximate method of solution is effective for calculation of the added-mass coefficients of two-dimensional bodies of any form, and that it is better than the imaginary method in view of its generality.

抄録全体を表示

A new scheme of cold and hot wire thermo-anemometer was developed. Effects of the change in flow conditions upon the gain of the cold wire due to the heat capacity of its prong was instantaneously compensated by a newly designed phase compensator for a low-frequency range. Errors caused by a spatial difference between the two wires were automatically compensated by a digital delay circuit transforming the spatial difference to a time difference on the frozen pattern hypothesis. The present system's reliability was checked in the wake of a heated cylinder and was capable of providing precise wave traces of instantaneous temperature and velocity signals for the frequency range from DC to about 5kHz.

抄録全体を表示

Among noises emitted from an automobile radiator cooling system, discrete-frequency noise is found to be largely related to the uneven velocity distribution of the flow to the fan. When the inflow is asymmetric with respect to the axis, each blade undergoes a change of velocity in every rotation, which generates cyclic pressure change in the suction side of the blade. By using an aerofoil with 6 percent camber, the decrease in the pressure fluctuation and discrete-frequency noise is obtained without any deterioration in the fan performance.

抄録全体を表示

Air flows near the leading edge of the axial fan blades in an automobile radiator cooling system were studied by flow visualization and surface pressure measurements in order to reduce the noise emitted from the fan. In the region where the flow separated from the blade surface, fluctuations of the static pressure were largely increased, resulting in the generation of a higher noise level. Using two-dimensional aerofoils of different cambers, effects of the camber on the pressure fluctuations were examined, and an aerofoil with a camber of 4 percent was found to exhibit the minimum pressure fluctuation at the same value of a lift coefficient C_L=0.6.

抄録全体を表示

In order to pursue the enhancement of condensation heat transfer of binary vapors of immiscible liquids, detailed experiments have been conducted with regard to the condensation of an azeotropic mixture of carbon tetrachloride and water on vertical flat plates with enhanced fins. The condensation mechanism of this kind of vapor on finned surfaces was clarified through measurements of the droplets departure frequency and heat transfer rates. The experimental results indicate that finned surfaces are more effective in the enhancement of condensation heat transfer of binary vapors of immiscible liquids, and that an optimum configuration and dimensions of fins exist.

抄録全体を表示

Experimental study has been carried out to clarify the characteristics of the liquid film thickness of air-water two-phase flow in helically coiled tubes of 500 and 1000mm coil diameters and 25mm tube diameter. The wave of liquid film on the outer side of a coil differs from that on the inner side in not only the wave height but also the wave shape. The liquid flow rate does not affect the film thickness at the inner side, whereas at the bottom and the outer side, it makes the film thicker. The center of gravity of liquid film is in the region about 45 degrees inward from the top or the bottom of the tube. The coil diameter has little effect on the characteristics of the liquid film.

抄録全体を表示

Rapid quenching of thin horizontal platinum wires (0.3 and 0.5mm in diameter) was studied experimentally using CaCl₂ solutions as quenching liquids. The boiling curve was obtained in the ranges of CaCl₂ mass fraction of 0 to 40%, solution temperature of -20 to 50°C, falling velocity of the wire of 0.1 to 1.5m/s, and initial wire temperature of 600 to 1400°C. The maximum heat flux and the degree of superheat at the minimum heat flux point increased considerably with increasing mass fraction. The average heat flux 2.4 times as high as the pure water value was obtained using a 30% solution in the wire temperature range of 950 to 500°C.

抄録全体を表示

To predict the effect of anisotropic surface roughness on the contact conductance of the interstitial gas layer between nominally flat surfaces, the applicability of the Gaussian surface theory that was developed for isotropic surfaces is theoretically extended to surfaces with surface slope anisotropy. It is proven that the effect of local gap variation due to the anisotropic surface roughness can be predicted using the same equation that was previously obtained for the case of isotropic surfaces. Also, the experimental data for actual conductors are examined, using the present theory. It is found that, in the range corresponding to the contact between the component and the conductor, the local gap effect is negligibly small. From this result, the adequacy of the simple approximation based upon the mean gap is confirmed

抄録全体を表示

A numerical study was carried out to examine the local heat transfer and flow situation around a square rod in a parallel plate duct as a spacer. Momentum and energy equations were solved by means of the pressure correction and the CONDIF methods. Effects of the space between the end of the rod and the opposite insulated wall were simultaneously estimated in the three-dimensional system. Three horseshoe vortexes were generated around the end of the rod at Re=1700. The characteristics of the local heat transfer and the flow behind the rod were elucidated.

抄録全体を表示

Heat transfer in natural-convection film boiling with a wavy interface is investigated analytically. The vapor-film-unit model proposed in the first report for saturated film boiling is extended to subcooled film boiling with a wavy interface. In this extended model, based on the mean vapor velocity and the vapor film thickness under a subcooled condition, the vapor-film-unit length along an inclined flat plate is determined for subcooled film boiling as a function of the inclination angle. Using this result and accounting for movement of the vapor-film units, vapor-film units are arranged along the vertical surface and the periphery of the horizontal cylinder. The time-averaged local heat transfer coefficient is determined by integrating the time-dependent local heat transfer coefficient. The heat transfer coefficient averaged over the surface is determined by integrating the distribution of the time-averaged local values. The predictions of the model agree well with experimental data for film boiling along long vertical surfaces and around horizontal cylinders of large diameter. It is concluded, thus, that the extended vapor-film-unit model can correctly describe the effects of fluid properties, liquid subcooling, surface superheating and surface dimensions on film-boiling heat transfer with a wavy interface.

抄録全体を表示

This paper presents heat transfer correlation for natural-convection film boiling with a wavy interface. Natural-convection film boiling of this type includes film boiling on horizontal flat plates facing upward, long inclined flat plates, long vertical surfaces, and horizontal cylinders of large diameter. First, it is shown that saturated film boiling along vertical surfaces can be correlated to the capillary length, and the physical meaning of this feature is made clear by focussing attention on the vapor-film-unit length in the author's vapor-film-unit model. Next, using the unit length, a heat transfer correlation for saturated film boiling along long vertical surfaces is developed, and it is shown that this correlating equation is valid for other film boiling systems with a wavy interface if the unit length is given correctly. Finally, a heat transfer correlation for subcooled film boiling with a wavy interface is developed using the heat transfer correlation for subcooled film boiling with a smooth interface and the unit length.

抄録全体を表示

There are some analytical methods for the steam absorption process, but they do not achieve overall mass balance perfectly. In this paper, the model proposed in the previous paper is modified to include the velocities normal to the film and the change of film thickness. The basic equations are rewritten in the body-fitted coordinate system and solved by the control volume method. The numerical results for a stagnant film show good agreement with the analytical results. Falling film cases for the range of 20-1000 in Re used in absorption refrigeration are calculated by the proposed method. For Re=20, the flow rate and the film thickness increase by 10% and 3% respectively after flowing down 1m. For Re=1000, the increase of flow rate and film thickness are small but the velocities normal to the film are not negligible relative to the effect of diffusion.

抄録全体を表示

Numerical simulation was conducted to study the thermal history of Czochralski growth of large silicon single crystals. The computations were performed for various crystal diameters and emissivities of the crucible inner wall. The analysis gives the change of temperature distribution in the crystal and the shape of the solid-melt interface. The computed results show the importance of the effects of radiation from the crucible inner wall and the melt free surface on crystal growth. Also, increasing crystal diameter decreases the pull speed and increases the concavity of the solid-melt interface into the crystal. The result of this analysis is in good agreement with measurement of the pull rate on production apparatus, and the shape of the crystal-melt interface showed a tendency to qualitatively agree with the observations of X-ray diffraction.

抄録全体を表示

Formation behavior of polycyclic aromatic hydrocarbons such as benzene and naphthalene, and C₂ in laminar one-dimensional premixed acetylene-air flame is numerically studied by considering 47 species with 168 elementary reactions. Although benzene and naphthalene are mainly formed in the visible flame region, they are also generated in the downstream region with decreasing burned gas temperature. Although the peak height of benzene concentration at φ=2.5 is lower than that at φ=1.0, the concentration of intermediate species for growing into polycyclic aromatic hydrocarbons at φ=2.5 is higher than that at φ=1. C₂ is formed in the downstream region of high temperature at φ=2.5, while at φ=1, it is formed in the narrow region behind the visible flame region having the concentration peak at about 2000K. Even in the flame at φ=2.5, the formation of C₂ decreases with decreasing burned gas temperature.

抄録全体を表示

In order to minimize the cell-temperature gradient in an indirect internal reforming molten carbonate fuel cell (IIR-MCFC), three directions of fuel (CH₄) flow in the reforming unit have been investigated. Temperature distribution in each type of stack was analyzed, and experiments were also conducted. As a result of the analysis, it was suggested that the temperature gradinent was minimized when the fuel in the reforming unit flowed perpendicular to the flow direction of the reformed gas in the anode gas channel while the cathode gas flowed in a diagonal direction to that of the reformed gas. The analytical results were compared with the experimental results, and reasonable agreement was obtained. As a consequence, it was found that the analytical method was useful for stack designing.

抄録全体を表示

An experimental study of detonation was carried out for mixtures of blended fuels (H₂/CH₄ or H₂/C₃H₈) and air. The detonation tube length is 7m and its inner diameter is 10mm. Fast deflagration and detonation speeds were measured by means of photodiodes, which are fitted with the tube by a special technique and detect light emitted from the reaction zone. The effects of mixing ratio of fuels on the behavior of deflagration to detonation, detonation speed and detonability limits were investigated. There exists a deflagration speed at the exit of the spiral that establishes detonation, and a reproducible pulsating deflagration speed can be seen near the limit of detonation. Detonation velocity increases monotonically with equivalence ratio or the ratio of hydrogen in blended fuels.

抄録全体を表示

The mixture formation processes of unsteady gas jets were visualized and quantified with an adaptation of the LIF technique (LIFA). The mixture strength was quantified by the fluorescence intensity of iodine in the ambient gas which was excited by the sheet light of a Nd : YAG laser. At the optimum setting of the initial iodine concentration in the ambient gas, a better than 95% accuracy was obtained with this method for the air entrainment ratio, and better than 75% was obtained for equivalence ratios over 2.5 with methane fuel jets. The result showed that a considerable amount of air was entrained just under the umbrella profile at the top of the jet.

抄録全体を表示

Experimental studies have been carried out to investigate some problems in the development and practical use of a catalytic combustor using a methanol mixture. For the suppression of undesirable exhaust emission, the possibility of using a catalyst with a higher amount of noble metal than the usual level as a component of the entire catalyst layer is examined. The combustion characteristics of the catalytic combustor with water-containing methanol and with aged catalysts are also investigated. From the results, it was found that undesirable exhaust emission during the startup period was suppressed by use of the higher noble metal loaded catalyst as a component of the catalysts. Formaldehyde emission was increased as the contained water was increased in the range of zero to 15wt%. The reaction region moved downward with the use of the aged catalyst, and the catalyst temperature profile was decreased. This indicates that the emission characteristic on unburned species is degraded.

抄録全体を表示

Effects of heat insulation of combustion chamber walls on particulate emissions were investigated using a single-cylinder direct-injection diesel engine. Two types of coated pistons which had thin PSZ layers on different portions of their surfaces were prepared to examine the effects of insulation on emissions of particulates, especially on soluble organic fractions (SOF). Results show that the weak insulation, which has little effect on the gas temperature and combustion process on a large scale in the combustion chamber, can change SOF and THC emissions. The piston with an entirely coated upper surface promotes SOF emission at medium equivalence ratios. A difference of locations of insulated surfaces gives different trends for SOF and THC.

抄録全体を表示

In a two-stroke-cycle engine, the scavenging flow plays a very important role in the combustion performance. In this type of engine, the loop-flow scavenging system is superior with regard to maintenance because the engine with this scavenging system has no exhaust valve and so has a simple structure. On the other hand, in this engine, the distance between a scavenging port and an exhaust port is shorter and the short pass flow of fresh air to the exhaust port occurs frequently, hence, the scavenging efficiency is generally inferior to that of a uniflow scavenging type of engine. Many experimental and numerical analyses of the scavenging characteristics of loop-flow type two-stroke-cycle engines have been conducted, but the authors believe that the development of a simulation technique for scavenging flow of this type of engine has not yet been completed. The authors have developed a numerical method for this type of engine. In this report, we present an examination of our numerical method comparing our findings with experimental results.

抄録全体を表示