This report describes the behavior of wave packets trailing an isolated turbulent spot produced in the laminar region of a radial liquid film flow. The liquid film flow was formed by a water discharge to the atmosphere from a thin cylindrical gap between a pipe end and a disk surface. The turbulent spot was produced by a pulse-like jet injection into the laminar flow through a small hole in the disk, and was observed by high-speed photography. Furthermore, the evolution of a pulse-like disturbance, which was added to the basic flow, was analyzed by the finite difference method with VOF method. It was found that the strong turbulence of the spot results in the generation of a pair of oblique wave packets on both sides of the spot and the amplified wave packets break down to new turbulent patches. It was also found that the group velocity of the wave packet is 1.4 times as large as the phase velocity of oblique disturbance wave which is equal to the ordinary disturbance wave.

View full abstract

To consider the non-reflection property of the turbulence subjected to system rotation, a new method was proposed to introduce turbulence helicity into an isotropic turbulent flow field for direct numerical simulation (DNS). The effects of the helicity and the rotation on turbulence statistics and vortical structure were investigated by theoretical analysis and DNS of the homogeneous decaying turbulence. The DNS results show that both the rotation and the helicity inhibit the energy decaying. The theoretical analysis shows very different mechanisms for the rotation and the helicity to produce this effect, i.e. the helicity directly decreases the energy transfer while the rotation suppresses the energy transfer due to the so called scrambling effect. The rotation elongates the vortical structure along the rotation axis, and it a appears to weaken this tendency with the presence of the helicity.

View full abstract

Cross-correlation PIV is repetitively applied to obtain the time-change of instantaneous velocity vectors, which enables us to analyze turbulence kinetics. Each term in the balance equation of turbulence energy is evaluated, based on the ensembles of fluctuating velocities and instantaneous velocity-gradients, thereby finding primary factors of production and dissipation of turbulence energy. It is shown that turbulence production rate is high in the shear layer because of a large Reynolds stress, and viscous dissipation of turbulence energy occurs mainly near the jet axis. Furthermore, typical turbulence eddies in the shear layer are sampled to discuss the effect of instantaneous vortex-motions and fluctuating flows on turbulence production. It is observed that the pair of counter-rotating vortices appears and accelerates the flow in between, resulting in an increase in quantities of instantaneous Reynolds stress at a particular direction.

View full abstract

Interaction process between a turbulent plane wall jet and a pair of streamwise vortex was investigated experimentally. Two kinds of vortex pair, i.e., common-flow up and common-flow down generated with half-delta wings mounted on the wall, were introduced into a self-preserving stronger wall jet. Measurements on the mean velocity and mean streamwise vorticity were made to examine deformation and relaxation process of the mean flow field as well as evolution of the streamwise vortex. As a strategy in the present experiment, the vortex center goes into the outer layer in the case of common-flow up and stays in the inner layer in the case of common-flow down. Consequently, streamwise vortex pair interacts strongly with the large-scale eddy governing the entire wall jet. The following remarks were recognized for the common-flow up in comparison with results of both cases ; 1) growth of vortex radius and decay of streamwise vorticity are greater, 2) recovery of the mean velocity field is much slower. The evaluation of streamwise momentum flux confirms that it is possible to manage turbulent wall jet with streamwise vortex.

View full abstract

The phase-averaged characteristic of a single pulsed vortex generator jet which is injected periodically into a turbulent boundary layer is described. Detailed measurements of the three components of the velocity in the jet made by a hot-wire anemometer with the X-type probe show evolution of the longitudinal vortex in the jet. The pulsed vortex generator jet in the stable period has a similar longitudinal vortex structure to that in the steady one. Down-wash motion of the longitudinal vortex in the jet introduces high wall shear stress.

View full abstract

As a part of the laboratory experiment on a microburst, the circumferential instability and the associated instantaneous velocity field of a vortex ring impinging onto a normal wall have been investigated. Vortex rings have been generated at the circular orifice by the impulsive motion of the speaker corn and have been visualized by filling ethylene glycol smoke. The instantaneous velocity fields induced by a vortex ring were measured by employing the PIV in which the cross correlation method was used. The wave number of the circumferential instability increases with an increase of the initial Reynolds number. The wave number at the same initial Reynolds number decreases as the distance from the orifice increases. It was shown that the development of induced secondary vortex ring influences the change of velocity vector fields.

View full abstract

The effect of the introduction of swirling motion into turbulent flow in a curved pipe is studied experimentally. The friction of the flow in a straight pipe is known to increase as the introduced swirling motion intensifies. In the present study, it is found that the friction in a curved pipe is reduced when weak swirling motion is provided. In order to investigate this drag reduction, velocity distributions are measured at some cross sections in the curved pipe by use of the rotating probe technique with an inclined hot-wire. Detailed measurements of the velocity field reveal that interesting swingback phenomena appear as the vortical flow structure develops from the entrance of the pipe, which may cause the drag reduction in case of weak swirls.

View full abstract

In this study, flow around an in-line forced oscillating circular cylinder was investigated by two-and three-dimensional calculations at the Reynolds number Re=1.0×10³, at the amplitude ratio of cylinder oscillation a/D=0.14, in the range of the non-dimensional frequency St_b=0.0∼0.48. It was simulated that the three-dimensional vortex structure appeared for St_b=0.0∼2.5 and disappeared for St_b=0.30∼0.48, and that the vortex shedding changed from asymmetrical vortex shedding to symmetrical one at St_b=0.48. It was found that three dimensional vortex structure was not observed in the process of the change from asymmetrical vortex shedding to symmetrical one, unlike an experimental result.

View full abstract

In this study, a numerical method has been developed in order to solve fluid-structure interaction problems, and vortex-induced vibration for incompressible viscous flow past an elastically supported circular cylinder is simulated by two-and three-dimensional calculations. In the results of the three-dimensional calculation the lock-in region, the drastic change of the phase angle between lift force and cylinder displacement, and response amplitude of a cylinder in transverse direction show good agreement with experimental values. Furthermore, the hysteresis loop of the response amplitude can be simulated in the lock-in region, and it is pointed out that the hysteresis depends on the change of three-dimensional vortex structure. Because of such a mechanism hysteresis loop and lock-in phenomenon cannot be simulated with sufficient accuracy in the results of a two-dimensional solver.

View full abstract

This paper presents a method for the velocity and the pressure distribution around the car in three dimensional flows using the source panel method and the discrete vortex method. The discrete vortex method has been applied to simulation of unsteady separated flow at a high Reynolds number. We distend in three dimensional flows a simple method, which is proposed by Akamatsu in two dimensional flows on the boundary element method to calculat the pressure distribution. The calculation results are in good agreement with the experiment one. It shows effectiveness of the boundary-layer control by setting rotating cylinders and Fin. They are valid. When the lean angle between uniform flow and the car has α=45°, separation bubble and wake becomes conical and their bottom aspects are connected.

View full abstract

Anomalous flow phenomena in an axial compressor rotor at near-stall conditions have been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulation show that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists ant turns violently with time, thus interacting with the pressure surface of the adjacent blade. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the tip leakage flow field at the near-stall conditions : no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the blade pressure surface. As the flow rate is decreased from the near-stall conditions, the movement of the tip leakage vortex due to the vortex breakdown becomes so large that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction gives rise to the three-dimensional separation of the suction surface boundary layer.

View full abstract

Pressure fluctuations on the casing wall of an axial flow fan were measured. These measurements were used to investigate the inception of rotating stall at different rotor-blade stagger angles. Near the peak of the pressure rise, stall cells formed around blades with the design stagger angle as well as around blades with a larger stagger angle. When flow rate was decreased, the stall cells were developed in the case of the design stagger angle, but not developed in the case of the larger stagger angle. Rotating stall was not observed in the case of a smaller stagger angle untill the flow rate was much lower than that at the peak pressure rise. It was confirmed that the formation and development of stall cells were affected by the throat length of the rotor blade passage and the pressure fluctuation magunitude.

View full abstract

In the nemurical fluid analysis, high accuracy and upwinding are necessary for the convection term of the Navier-stokes equation because this term is non-linear. In general, bilinear element is used in FEM (Finite Element Method) and the discretization by this method corresponds to the 2nd-order center difference. As a result, we can't obtain adequate accuracy for high Reynolds number flow. Although many upwind methods have been proposed, we use CIP (Cubic Interpolated Pseudoparticle)-FEM in the present work, and analyze natural convection in a square cavity. This problem has been analyzed by many investigators. However, it is difficulut to analyze this flow at high Rayleigh numbers Ra≥10⁹ because numerical divergences and vibrations occur in energy equation. We analyze natural convection from 10³≤Ra≤10⁹ and show that the present scheme analyze this flow stably and is effective by comparing with other numerical results.

View full abstract

To investigate natural convection in a square-section cavity with sinusoidal gravity modulation, we computed it by the finite difference method. The full Navier-Stokes equation in 2D coordinates are simplified with the Boussinesq approximation. The Rayleigh number Ra and the Prandtl number Pr are equal to 1.5×10⁴ and 7.1, respectively. While gravity-acceleration amplitude η is fixed at 0.1, non-dimensional angular frequency ω is varied from 10⁰ to 10⁴. The temperature's amplitude, as well as the velocity's one, can have a maximum value at a certain angular frequency ω_max both locally and globally. More specifically, although ω_max varies depending on the location or on the quantity in concern, ω_max is equal to 100 for the most part. Being compared with our previous study on cylindrical cavity, the results suggest that the present convective mode is rather stable.

View full abstract

In this study, we propose a novel method to specify the added-mass coefficients of arbitrary two-dimensional bodies in an incompressible viscous fluid. This method is based on a discrete singularity method in which a fundamental solution of the Brinkman's equation is employed as a singularity. For computational examples, the following bodies are chosen : a circular cylinder in an infinite flow field and in cylindrical containers, an elliptic cylinder in an infinite flow field and a square-section cylinder in an infinite flow field. As a result, the effectivity of this method is confirmed.

View full abstract

Te vortex structure within a separated flow region changes when the disturbance is introduced in a mean-flow. This change was investigated by numerical simulation. The periodic velocity fluctuation introduced into the mean-flow at the upstream of separation shear layer, and its amplitude is 30% of the mean-flow velocity. By this periodic fluctuation, the shear layer is flapped to make vortices be shed with the frequency of fluctuation. For making the separation region narrow, it is found that the most effective frequency is about twice of the frequency which is dominant in the separation flow without fluctuation. Furthermore, first sub and super harmonics of that frequency make the flow be periodic. These resonance are explained by using the wave number which is equivalent to the vortex scale.

View full abstract

The influence of the multi-dispersed particles on the turbulence of air flow was examined by the use of a P.D.V. (Phase Doppler Anemometry) in a horizontal pipeline with inside diameter of 80mm. The mean diameters of glass beads are 54.6μm and 468.0μm, respectively and both densities are 2590kg/m³. It was found that the presence of fine particles suppressed the turbulence of air flow and it was predicted that the most effective mass flow rate ratio for that suppression existed. It is noteworthy that the turbulence of air flow in the case that a little of coarse particles mixed into the fine particles is more promotive than that in the case of coarse particles alone. Furthermore, it was found that the accelerative pressure loss in that case was larger than that in the case of the monodispersed particles.

View full abstract

In order to clarify the draft-tube-performance of cross-flow-turbines or the submerged-water-jet-performance, in the same two-dimensional aerated-bubbly-flow within a narrow duct reported previously, we experimentally systematically investigate the characteristic behavior of the mean-and the local-void fraction, of the vortical flow and of the bubble distribution, when the jet is vertically injected. It is shown that the mean-void fraction is a control parameter of the hydraulic losses, when the jet velocity is low. The intermediate vortical flow containing huge number of very fine bubbles often results in circulating string bubbles and fluctuates periodically at about 0.6s in period. Owing to the Daily's effects, the bubbles in the up-flow and in the down-flow are considerably concentrated into the intermediate vortical flow.

View full abstract

Drag reduction on highly water-repellent solid surfaces, characterized by its low surface energy and ultra small-scale concave-convex structure, has been investigated. The torque between brass cone and tested plain surface where water is confined was measured in the experiment. PTFE (polytetrafluoroethylene) membrane filter, which has water-repellence and porous structure with micrometer-order pores, was one of the surfaces that exhibited the drag reduction. 0.8 μm pore-size filter showed the reduction by maximally 8% at Reynolds number around 60000. Also tested was the ultra small-scale concave-convex surface made on 4inches silicon wafer by lithography and RIE (Reactive Ion Etching). The surface with high contact angle of 150 degrees for water droplet of 1.4 mm diameter showed the drag reduction by maximally 10% at Reynolds number around 65000.

View full abstract

The Piston effect means the uniform airflows are caused by the motion of trains in a tunnel. Interactions between a moving train and the air are discussed theoretically to clarify behaviors of the uniform airflows. The two fluids model are used as the basis of the theory. A variable to describe the interaction is presented in terms of fluctuations of density and velocity of airflows in the region between the train and the tunnel wall. This is utilized to derive a set of self-consistent equations which govern the behavior of uniform airflows. Justifications of the theory are made by the comparison between field tests and numerical calculations based on the equations.

View full abstract

Predicting the transient thickness of liquid film on a rotating substrate is one of great practical importance. The effect of surface wettability on liquid film has been examined, despite it's an important factor in practical processes. We examine the effect of surface wettability here. Surface wettability is generally defined by the contact angle between the liquid and the substrate. The transient thickness of liquid film was measured for three substrates that have different contact angles. The thinning rate of the liquid film increases when the contact angle increases. We propose a modified Emslie's equation to account for the effect of surface wettability. The transient thickness of liquid film predicted by the proposed equation agrees well with the measured transient thickness.

View full abstract

The active utilization of the pressure rise phenomenon of an oil hammer and a new type of hydraulic pressure intensifier using an oil hammer are proposed. In this paper, application of this intensifier to the hydraulic motor is studied through experimentation and simulation. The influence of the volume at the hydraulic motor entrance on the rotation angle and the pressure change is tested. The rotation angle of the hydraulic motor is made to follow up the desired value using a technique similar to that of PWM control. The relation between the rotation angle of the hydraulic motor and the pulse width for opening and shutting the solenoid-operated valve to generate an oil hammer is measured. Using the result, the rotation angle of the hydraulic motor is controlled to follow up the desired value. The influence of the load torque on te follow-up control and the efficiency is examined.

View full abstract

The purpose of this study is to clarify hydrodynamic characteristics of a human hand model. Three different models of an adult mene's right hand (Model A, thumb only opened ; Model B, all fingers spread ; Model C, all fingers closed) were made with polyester resin. The magnitudes of pressure acting on holes which were located at the hand model surface, were measured for various pitch angles using a wind tunnel test device. Moreover, the flow visualization of air around the model was conducted using the laser beam. By means of these pressure data, the magnitudes of fluid force were calculated. The experimental results reveal that the way in which the fingers are opened has a large influence on the fluid force over the entire hand. When the thumb side became a leadng edge, the Model A, thumb only opened seems to be advantageous for generating lift force. When the little finger leads, the Model C, all fingers closed can produce more lift force than other models.

View full abstract

We have developed a new cooling system for the engine of construction machinery. This system produces two different air flow routes by a double suction type centrifugal fan with backward blades. We first measured aerodynamic performance and sound level of the double suction type fan, which consists of two single suction type fans of different design, and compared these measurements to those of single suction type fans. Next, we installed the fan in a scale model of the new cooling system. The performance of this double suction type fan was different to that of a single suction type. It is considered that the effect of interaction of the exit flows from the two different fans caused this performance change. The test model installed in an engine compartment showed that this cooling system reduced the area of air inlets and outlets around the engine and did not cause re-circulation of cooling air.

View full abstract

It is reported recently that the pump head deterioration near the best efficiency point, from single-phase flow to the choke due to air entrainment became less in a screw-type centrifugal pump than in a general centrifugal pump. Moreover, at a narrow tip clearance, the pump head became partially higher in two-phase flow than that in single-phase flow. However, the internal pressure fluctuations on this pump due to air entrainment have not been studied yet. For that reason, we have examined the influences of void fraction, flow coefficient and impeller tip clearance on pressure fluctuations in the casing. At narrow tip clearance, the pump head increment in two-phase flow mainly depends on the pressure increasing in the volute casing. And the void fraction became larger, the influence of tip clearance on pressure distribution became less. Moreover, we have observed the internal flow patterns by using a stroboscope and a halogen sheet light. Then, we have investigated the influences of flow coefficient on air-water two-phase pump performance.

View full abstract

Pump efficiency drops rapidly with a decrease in specific speed n_s in the very low n_s range. In order to improve a pump efficiency and to establish the optimum design method of a volute pump of very low specific speed around n_s=60∼70[m, m³/min, rpm], several combinations of centrifugal impeller and volute casing were tested. The results showed that the maximum efficiency is largely influenced by the volute design parameters, such as a volute tongue, a volute width and a gap between the impeller exit and the volute tongue, while the maximum efficiency differs little by the design of impeller. The BEP of a very low n_s pump agrees well with the designed discharge of a volute and is far form that of an impeller. With a decrease in the space between an impeller and a volute-tongue, the pump efficiency increases, and the pressure fluctuation due to interference does not increase, which is quite different from usual n_s pumps.

View full abstract

This paper proposes the counter-rotating type machine for water power generation which is composed of the two-stage runners and the double rotors in the generator, and discusses the performances and internal flow conditions based on the experiments for the trial model. The maximum output power is obtained at the same counter-rotational speeds as designed, but such speeds differ from the maximum efficiency point. In the individual runner, the maximum output power of the rear runner is slightly less than that of the front runner, but the efficiency is overall good though the inlet flow condition of the rear runner is disturbed by the front runner. The flow conditions around the runners suggest the further improvement points for the runner profiles.

View full abstract

In this paper we clarify directional characteristics of thermal radiation reflection on rough metal surfaces and establish a technique for determining the parameters for heat transfer computation of radiation energy exchange among surfaces. Directional distribution of bidirectional reflectance ρ of surfaces of root-mean-square roughness Σ=0.1∼1μm to te irradiation of a visible laser of wavelength λ=0.6328μm and to that of an infrared laser of λ=3.39μm is investigated experimentally. The optical roughness (Σ/λ) ranges from 0.028 to 1.27. A measure of an order of specular reflection is presented. A model for describing the ρ-distribution is presented, and the experimental results of the ρ-distribution are analyzed quantitatively and systematically to determine the values of the specular reflection component R_s and the perfect-diffuse reflection component R_d of the hemispherical reflectance R_H, which are input parameters for radaiation heat transfer computation.

View full abstract

In this study, direct contact melting of porous material as the PCM is investigated experimentally and analytically. The PCM is made of fine ice particles, the particle diameter of which is changed as an experimental parameter. In the experiment, cylindrical porous materials are melted on the heating plate, and the time dependency of the height of the PCM and the temperature of the heating surface are measured. In the analysis, the melting process that the melted liquid permeates into the solid is calculated as a direct contact melting phenomenon. As the result, it was found that the melting rate increases in the initial stage of the melting process, because the melted liquid permeates into the solid rapidly due to capillary effect and the liquid film becomes thinner. The phenomenon was found to be more significant for smaller particle size. Moreover, the experimental and analytical results coincide with each other in case of the small particle.

View full abstract

Heat transfer through the inner and outer rings of an Angular ball bearing was investigated experimentally and heat transport by the ball rotation was analyzed theoretically. The bearing used was lubricated by oil film and was rotated in the range from 600-4000r/min. Considering heat generation by the friction, the net heat flow between the rings could be evaluated. The results show that the heat transfer based on the ball rotation is dominant and its conductance depends on the rotational speed and the axial force. The other route of heat transfer is considered mainly due to the convection of air and its heat flow rate depends on the rotational speed.

View full abstract

A conjugate numerical model proposed by Nakayama et al. for the problem of cooling a fluid flowing through aspiral coil, has been successfully extended to investigate the processes of heat storage and recovery associated with a packed bed saturated with a molten salt. An axi-symmetric numerical procedure is described for determining the temperature development in the heat storage process. For the heat recovery process, a one-dimensional heat balance equation for the two-phase flow within a coil is introduced to update the wall surface temperatures, which are needed to calculate the temperature field in the packed bed. The numerical results for both storage and recovery processes agree very well with the corresponding temperature data obtained from the experiment.

View full abstract

One of the circular cylinders with several diameters was elastically suspended with springs in the jet impingement region between a jet slot and a heat transfer target plate. The slot-to-plate distance H was kept constant to be 3 or 5 times of the slot width, h=15mm. The Reynolds number was fixed at 10000, being exceptionally 5000 in the case of flow visualization. Periodical swinging motion of the cylinder across the jet was observed because of the cylinder vibration self-induced with the jet flwo. It was found that this vibration has direct effects on the characteristics of the flow and heat transfer around the stagnation region. The ensemble-averaged values of velocity and its fluctuation depend on the cylinder diameter and the impinging distance. The local Nusselt number in the case of H/h=3 with the vibrating cylinder of the smallest diameter D=4mm was increased up to 1.15 times of the Nusselt number without the cylinder. The interesting patterns of intermittency function defined together with threshold levels of turbulence intensity were observed in the above case.

View full abstract

It is expected that pure and high performance materials could be manufactured in space under the micro-gravity environment. However, if bubbles are initially trapped in the molten material, they cannot escape from the material under the micro-gravity condition and could adversely affect the product quality. in the present study, an ultrasonic acoustic standing wave field is adopted to control the bubble motion under the micro-gravity environment. At first, the experiment with a single ultrasonic transmitter in a fluid with a free surface was conducted to design and develop new horn. It was experimentally confirmed that the bubble can be held stable and stationary in the ultrasonic wave field with new horn. Next, the bubble control experiment was conducted by using dual ultrasonic vibrators. The ultrasonic acoustic standing wave field was moved by shifting the phase difference between the dual ultrasonic transmitters. It was experimentally confirmed that the present technique is applicable to control the bubble position in liquid. Finally, the experimental results were also confirmed by numerically solving the Rayleigh-Plesset equation and bubble motion equation in the translational direction.

View full abstract

This paper presents a slug-churn flow model for predicting turbulent mixing rates of both gas and liquid phases between adjacent subchannels in a BWR fuel rod bundle. In the model, the mixing rate of the liquid phase is calculated as the sum of the three components, i.e., turbulent diffusion, convective transfer and pressure difference fluctuations between the subchannels. The components of turbulent diffusion and convective transfer are calculated from Sadatomi et al.'s (1996) method, applicable to single-phase turbulent mixing, by considering the effect of the increment of liquid velocity due to the presence of gas phase. The component of the pressure difference fluctuations is evaluated from a newly developed correlation. The mixing rate of the gas phase, on the other side, is calculated from a simple relation of mixing rate between gas and liquid phases. The validity of the proposed model has been confirmed with the turbulent mixing rates data of Rudzinski et al. as well as the present authors.

View full abstract

The program for a 200T/D entrained flow coal gasification pilot plant was initiated in fiscal year 1986 and successfully finished fiscal year 1996. In this program, a two stage pressurized air-blown entrained flow coal gasifier was adopted, which CRIEPI and Mitsubishi Heavy Industry, Ltd, have developed jointly using a 2T/D bench scale P.D.U.. In the 200T/D pilot plant, domestic Taiheiyo coal, and Australian Moura, Warkworth coal were used for test runs. On the other hand, the commissioned tests of these 3 types of coals by NEDO/IGC Association have been carried out in CRIEPI's 2T/D coal gasifier, prior to the pilot plant operation. The research results obtained by the 2T/D gasifier were reflected in the operation of the pilot plant. From gasification test results with 2T/D and 200 T/D gasifiers, the gasification characteristics such as carbon conversion efficiency, cold gas efficiency and heat absorption rate to gasifier wall were evaluated.

View full abstract

The combustion characteristics of pulverized Refuse-Derived Fuel (RDF) in a vertical type cyclone combustor were investigated. Experiments were carried out by evaluating performance at excess air ratios of 1.2 to 1.6, and combustion loads of 0.35 to 0.61 MW. It was found that pulverized RDF is a viable fuel and that its combustion characteristics can be effectively controlled and evaluated by the classical parameters used in current oil and coal combustors, under various conditions. The NO and CO emissions were examined to show the combustion characteristics and combustor performance under various excess air ratios and combustion loads. It was found that concurrent NO and CO reductions could not be achieved. CO reductions are achieved by changing the excess air ratio, which causes an increase in NO_χ levels. A stable combustion operating range can be determined by changing the excess air ratio and combustion load in terms of NO-O₂, CO-O₂ relationships. Further CO reduction can be demonstrated by changing the combustor exit nozzle diameter, which can contribute to stable combustion, but also increases NO emissions. The emissions of dioxins (PCDDs, PCDFs) were evaluated during start up and stable combustion. Very low dioxins levels of 0.019ng-TEQ/Nm³ were achieved with the cyclone combustor.

View full abstract

Effects of acoustic disturbance on supersonic combustion were investigated experimentally for a practical interest in a control of a scram jet engine combustor. Subsonic hydrogen was injected parallel to the main supersonic airflow. Acoustic disturbance, which was generated by a cavity mounted on the wall of a test section, impinged on the initial supersonic double shear layer. Combustion efficiency at the exit of the test section was increased with the acoustic disturbance.

View full abstract

Recently A lean-rich combustion is drawing attention as a way to decrease the level of NO_χ. But the lean-rich combustion burner has a problem that an aldehyde is generated in the ignition process. Numerical unsteady-state analysis was performed in order to make clear the aldehyde formation process in ignition of the methane-air lean-rich combustion flame. In the lean-rich flames, the lean and the rich slit burners were set side by side in the combustor. A two-dimensional numerical analysis was performed based on Skeletal Chemistry proposed by Smooke M.D. which includes 35 elementary reactions with 16 chemical species. We compared the 2 ignition cases. One case was that the combustion chamber was filled with air, the other case was that the combustion chamber was filled with mixture of fuel and air. So we found that the aldehyde was generated when the combustion chamber was filled with mixture of fuel and air.

View full abstract

Hydrogen has higher combustion velocity and smaller quenching distance compared with hydrocarbon fuels, and is supposed to have special characteristics in combustion process of internal combustion engines. In this research, influencing factors to thermal efficiency in a hydrogen premixed spark ignition engine were analyzed and compared with methane combustion. Results showed that hydrogen combustion had higher cooling loss to combustion chamber wall than methane combustion, and thermal efficiency of hydrogen combustion was mainly dominated by both cooling loss to combustion chamber wall and degree of constant volume. It was also cleared that characteristics of cooling loss can be qualitatively analyzed with indicator diagram.

View full abstract

Split Injection has a potential to reduce simulataneously both NO_x and soot emissions from a D.I. Diesel engine. But the mechanisms of simultaneous reduction of both NO_x and soot emissions have not been clarified. To figure out the mechanism of change in emissions characteristics of the D.I. Diesel engine with the Split injection, an experimental study was conducted by using electrically controlled common rail injection system and a high pressure bomb. One of the sprays from a multi hole nozzle was injected into a two-dimensional model combustion chamber. The spray was observed by schliren photography with a high-speed video camera. In this report, effects of an injection mass ratio between the 1st and 2nd injection stages are described. The spray for the 2nd injection has larger tip penetration thanthose of the 1st or single injection spray. Especially, when the injection mass ratio is 50-50% and the injection interval is the shortest, the 2nd spray gains the largest spray tip velocity.

View full abstract

Cyclic variation analysis was demonstrated to grasp scavenging flow fluctuation in a practical small two-stroke engine in terms of pressure, velocity and HC emission. Simultaneous measurements of velocity, pressure and HC emission were carried out in an exhaust pipe with high time resolution over thousand cycles. The results show typical variation characteristics of scavenging flow and gas exchange in the cylinder, which can be estimated by pressures at the crankcase and the exhaust pipe. The HC emission variation was examined with time-series IMEP.

View full abstract

In this study a neural network prediction method that can be used in predicting engine behavior is proposed. Using data from a series of characteristic experiments, this method eliminates the need for complicated mathematical calculations used in prediction models. To test this method exhaust emissions and engine performance data from intake gas composition variation experiments were taken and compared with the predicted data from this network. The method has been tested and found effective in predicting engine exhaust emissions and engine performance. This technique can be a valuable tool in engine research.

View full abstract

It is important to shorten the computation time of radiative heat transfer when doing a conjugate numerical heat transfer analysis. The relation between the computation time and the total number of surface elements is shown for an analysis of radiative heat transfer. A method that shorten the computation time by reducing element number has been developed. The method merges elements of low radiative heat flux using the results of a rough calculation. It seems promising for reducing the computation time without increasing errors. The distribution of radiative heat flux on a wafer in a lamp heating apparatus was calculated using the method. The results show that the distribution of the heat flux can be reduced by using a diffusive reflector.

View full abstract