The reverse transition of accelerated turbulent flow is investigated using a direct numerical simulation (DNS). The tendency of the results is consistent with those of the previous experiments. Our major finding is that the response of streaks and quasistreamwise vortices to the acceleration does not coincide qualitatively. The streamwise component of turbulence intensity near the wall is maintained, even in the accelerated flow field. However, the other components of turbulence intensities and the streamwise vorticity are reduced in the whole region of the accelerated flow field because of the termination of the energy redistribution. Furthermore, it is found that the stretching of main flow reduces the regeneration of quasi-streamwise vortices through the decrease in distortion.

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It is well known that the turbulence energy is overpredicted by the k-ε model at the stagnation point. This problem causes inadequate predictions of flow field. In particular, since the wind-power energy is proportional to wind velocity cubed, it is crucial to predict a correct profile of wind in selecting the best site for a wind-power plant. The effects of the ground are often neglected owing to the very large length scale of the real environment. However, the complex terrain affects a profile of wind near the ground. Therefore, we have to consider the ground effects to obtain an exact profile of wind near the ground. In this study, to evaluate the performance of a low-Reynolds-number type turbulence model for flows on a complex terrain, we carried out a simulation of a flow around various complex terrain. From evaluation, we have improved the model introducing the time scale based on the velocity gradient parameter. The proposed model is evaluated in four complex turbulent flows, i.e., forward-facing step, two-dimensional block, two-dimensional hill and three-dimensional block flows. The proposed model indicates good agreement with the experimental data.

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The objectives of this study are to investigate the structures and characteristics of flows and heat transfer for plane turbulent impinging jets in a confined space, where a wall-jet type of flow is influenced by both lower (impingement) and upper walls, and to obtain turbulent statistics for the construction of a turbulent heat-transfer model. For these purposes, we have performed direct numerical simulations (DNS) of impinging flows with heat transfer. To obtain the effects of an impingement distance on heat transfer, the value of H is chasged in calculations, where H is the distance between the impingement wall and the upper wall. It is found from the present DNS that the Nusselt number increases with a decrease in the distance H similar to the experimental results. In addition, the Nusselt number of the case with the longest distance decreases monotonously in the wall-jet development direction, while the second peak of the Nusselt number is clearly observed away from the stagnation point in shorter distance cases, due to the increase in wall-normal turbulence intensities in the region away from the stagnation point.

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Transport coefficients of the Statistical Inelastic Cross-Section (SICS) model for continuous rotational energy with Parker's rotational energy gain function are examined by simulation of molecular diffusion in a homogeneous heat bath gas and channel flow between parallel flat plates. This study reveals that the transport coefficients of SICS model are inconsistest with the Chapman-Enskog (CE) theory, Euken correction (EC), and recommended data because of overestimation of effective collision frequency. The scattering law of the SICS model is modified by introducing the reduced impact parameter. Transport coefficients of the modified SICS (MSICS) model are in reasonable agreement with those of CE, EC solutions, and recommended data, except for the low-temperature range.

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The spatial structure of large scale streaks in core region of turbulent Couette flow has been studied by using data from hot-wire and smoke-wire visualization. To extract the large scale streaks, two-dimensional discrete wavelet energy spectrum and spanwise correlation of streamwise velocity u'₁ were considered. The spanwise size of the extracted large scale streaks is of the order of the channel hight (2h) and the streamwise length of (10-40) × 2h. The streak has partly a zig-zag pattern along streamwise direction and partly straight. The zig-zag pattern has (20-25) × 2h streamwise wavelength. From the visualization of cross section (x₂, x₃) there exist a large scale motion related to the streamwise vortex in core region. Some near-wall ejection motions are connected to the large scale motions.

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This paper presents development of numerical model of plasma synthetic jet actuator (PSJA) used to active flow control. Proposed Eulerian-Lagrangian model, named pseudo-viscosity particle model computing effect of PSJA is applied to 3-dimensional flow around a NACA 0012 airfoil with single PSJA and is compared its result with another numerical model, namely, synthetic jet model and experimental data. Using our model, PSJA have an influence on apparent viscosity, that is, it reduce turbulent eddy viscosity calculated by Large Eddy Simulation (LES) and is traced by Lagrangian particles. For the case of angle of attack are 0 and 7 degress, results using our model agreed with experimental profile on wake qualitatively but synthetic jet model didn't.

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Using SPH method a new formulaion is introduced for incompressible viscous flow analysis. The method uses SMAC algorithm well known in finite difference scheme to solve time integral of Lagrangian form Navier-Stokes equation which is expressed by particle systems. The results show more excellent incompressibility than earlier approaches of SPH (PSPH and WSPH) within Reynolds number of 1.0 to about 1000. For low Re number (Re below 1.0) the results show good accordance with theoretical values. Moreover the method successfully introduced stress tensors to the viscous term of Navier-Stokes equation instead of using artificial viscosity treatment used in earlier approaches, which enables to solve incompressible viscous flow phenomena more realistic and exactly. The large deformation of free surface flow (typically in wave problem) can be analyzed with sufficient smoothness and naturalness.

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A three-dimensional vortex method for gas-particle two-phase compound round jet is proposed. The method simultaneously calculates the behavior of the vortex elements, discretizing the gas flow field, and the particle motion through the Lagrangian approach. The two-way coupling is based on that for the two-dimensional vortex method presented by one of the authors in a prior paper. To discuss the validity and applicability of the method, an air-particle two-phase jet issuing into the co-flowing air is simulated. It is confirmed that the change in the air turbulent features due to the loaded particles is parallel with the existing measured and simulated results.

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We measured the velocity and number density of powder jet falling from a hopper by using a phase Doppler anemometer and obtained the following results. The center line velocity of powder jet near the hopper exit is close to the free falling velocity of a single particle in disregared of the fluid drag, which is independent of the diameter, density and mass flow rate of particle, and far from the exit tends to approach the terminal settling velocity of a single particle. When the particle diameter is small and the mass flow rate is increased, the ratio of the center line velocity to the terminal velocity increases. The axial fluctuation velocity profile of powder jet takes a minimum at the jet axis and after taking a maximum decrases toward the outer edge. The profile becomes flat when the mass flow rate is small and the falling distance is increased. The number density profile takes a maximum near the jet axis and rapidly decreases toward the outer edge. The center line number density of the small particle is larger than that of the large particle. Itis inferred that the dimensionless mass flow rate of the entrained air is increased with increasing the falling distance, being independent of particle size and density.

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The purpose of this study is to clarify the structure of pseudo-shock waves in under-expanded jet issuing from asymmetric nozzle with an oblique outlet. In particular, the steady characteristics of a single jet flow were studied. The flow was visualized by the shadowgraph method and the mean pitot pressures were measured. It was clarified that the asymmetric under-expanded jet was deflected by the stagnation pressure. As a result, it was found that the structure of pseudo-shock wave was affected considerably by the stagnation pressure in an air chamber and the outlet angle of nozzle, and consequently the structure of the pseudo-shock waves were different from the axisymmetric under-expanded jet.

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A steam control valve causes vibration of the piping when the opening is in the middle condition. For the rationalization of maintenance and management in the plant, the valve should he improved, but it is difficult to understand the flow characteristics in detail by experiment, because the flow around the valve is complex 3D structure and becomes supersonic (M>1). To clarify this phenomenon, as the first step, we introduce an small scale air experiment to investigate the region of the pressure fluctuation. At only the middle opening condition, a circumferentially propagating spike-type pressure fluctuation can he seen. The occuring region of this fluctuation depends on mass flow rate and valve structure.

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A steam control valve causes vibration of the piping when the opening is in the middle condition. For the rationalization of maintenance and management in the plant, the valve should he improved, but it is difficult to understand the flow characteristics in detail by experiment because the flow around the valve is complex 3D stlacture and becomes supersonic (M>1). In this report, a high-precision 3D CFD code for compressible flow is developed. After validating the code by comparing with experiments, the detailed flow characteristics around the valve are studied. At only the middle opening condition, a circumferentially propagating spike-type pressure fluctuation caused by asymmetric flow around valve can be seen. As this fluctuation causes cyclic side load on the valve body, it is thought to be the cause of vibration.

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The characteristics of a pressure wave propagating against two parallel subsonic streams in a constant-area straight duct have been investigated experimentally and numerically. Optical observations by the schlieren method as well as wall pressure measurements have been performed to clarify both the structure and the propagation velocity of the pressure wave. Computations have been carried out by two-dimensional Euler equations using the Chakravarthy-Osher-type TVD scheme. The effects of the static pressure ratio across the pressure wave on the propagation velocity are shown and discussed.

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The aerodynamic performance of subsonic diffusers has been investigated numerically in order to obtain the knowledge for the optimal design of subsonic diffusers. The area distribution, which is one of the parameters of the diffuser configuration, strongly affects on the aerodynamic performance because it is associated with the boundary layer development. It is found that the inflection point of the area distribution can correlate the pressure loss and there exists the optimal location of the inflection point of the area distribution. The optimal location of the inflection point was turned out to be shifted downstream in the case of subsonic diffusers with thick incoming boundary layer. In the case of diffusers of which the offset is enough large possibly to occur the boundary layer separation, the centerline configuration becomes an important design parameter to suppress the boundary layer separation.

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Feedback control system for velocity profile employing three parallel planar jets was established. Velocity distribution was measured by an array of three hot-wire probes and jets exit velocity were manipulated by PI controller and conditioner in order to suppress fluctuation of the peak position of mean velocity distribution. Time constants of blowers output and fluid movement were investigated and performance of control was evaluated in various time scales. Suppression of the peak position fluctuation was realized compared to that without control, and the system became robust against the cross-flow disturbance.

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In order to establish the active control system by using the vortex generator jets (VGJs), it is necessary to understand the detailed suppression mechanism of the separated flow in the diffuser. An opening angle of the diffuser can be changed from 8 to 15 deg corresponding to three flow regimes, “Unstalled”, “Appreciable Stall” and “Transitory Stall”. A micro wall flow sensor was used for measurement of forward flow fraction. It is found that VGJ makes the local forward flow fraction increase and prevents the flow detachment. Although the effect of separation control is obtained resulting from the higher jet velocity ratio, excessive jet velocity ratio introduces lower diffuser effectiveness due to the mixing loss.

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In the present study, the flow over a swept backward-facing step, at a Reynolds number (based on the step height and the free stream velocity) of 8 000 for the swept angle of 30 degrees, was investigated experimentally. Measurements were made for the mean flow field such as the surface flow direction, forward flow fraction, and mean velocity components. The flow field was examined in the regions of separation, reattachment, and following recovery to the two-dimensional flow. Lateral flows induced by the swept step significantly contribute to the variation of mean velocity profiles in the separated region. Reattachment distance of the flow over the swept step becomes about 10% shorter than that of the two-dimensional one. The mean velocity profiles collapse reasonably well on the Johnston's triangular model in the recovery region, and the profiles near the wall also collapse on the three-dimensional logarithmic law proposed by Johnston.

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This paper describes the wind assessment of high layer for siting the wind turbine on the complex terrain, which is based on the data measured by the use of Doppler SODAR. Although a rough estimation of the wind assessment using standard meteorological anemometers at low layer are cost effective and easy to be installed, it is necessary to measure the wind condition at hub height for accurate assessment. Comparison between measured data by Doppler SODAR and the data predicted from observation of the wind condition at low layer is performed. Large difference is seen in the measured wind profile and calculated power law plots of the wind. Estimation of generation power of wind turbine due to SODAR measurement agrees well with the actual turbine generation power. In the complex terrain, it can be said that observation of the low layers does not suffice to assess accurately the wind, while Doppler SODAR measurement is useful.

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The time-averaged and fluctuating fluid forces of two identical circular cylinders in staggered configurations were investigated experimentally at a Reynolds number of 5.5 × 10⁴. Measurements were performed for stagger angles α=10°, 25°, 45°, 60° and 75°, and the spacing between two cylinders T/D=0.1-5.0, where α is the angle between the free-stream flow and the line connecting the centers of the cylinders, T is the gap width between the cylinders, and D is the diameter of the cylinders. The new findings for characteristics of the fluid forces of two cylinders are as follows. (i) Bistable nature of flow at a series of spacing ratio T/D is found for the setting angle α of two staged circular cylinders. Also, these are responsible for large difference in magnitudes of fluid forces acting on the two cylinders. (ii) In case of bistable flow at small spacing of two cylinders, a turbulent reattachment and detachment of gap flow between two cylinders cause flow patterns in which lift forces acting on those have greater difference. (iii) Another kind of bistable flow almost is similar to that at the critical spacing of two tandem cylinders for α=10° and 25°.

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In view of the practical importance of the drift-flux model for two-phase flow analyses at microgravity conditions, the constitutive equations for distribution parameter and drift velocity have been developed for various two-phase flow regimes at microgravity conditions. A comparison of the model with various experimental data over various flow regimes and a wide range of flow parameters taken at microgravity conditions shows a satisfactory agreement. The newly developed drift-flux model has been applied to reduced gravity conditions such as 1.62 and 3.71 cm/s², which correspond to the Lunar and Martian surface gravities, respectively, and the effect of the gravity on the void fraction in two-phase flow systems has been discussed.

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The arterial branch from abdominal aorta to renal artery is one of the predilection sites of atherosclerosis. In the present study, we have experimentally studied the velocity profile and the wall shear stress at laminar steady flow in a flow model simulated the renal arterial branch where the side branch asymmetrically bifurcates from the trunk at right angle with a round upstream corner. The wall shear stress is estimated from the velocity gradient on the basis of the velocity. The flow situation from the abdominal aorta to the renal artery is characterized by the distribution of wall shear stress around the entrance of side branch. The wall shear stress along the upstream corner of side branch varies with large amplitude of several times more than the wall shear stress of the Poiseuille flow in the upstream trunk. The large gradient of wall shear stress along the upstream corner is closely associated with the initiation of atherosclerosis.

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In order to reveal the nature of turbulence in a lung, the measurements of turbulence in the oscillatory flow in a model of bronchial bifurcation were made by a two-colour laser-Doppler velocimeter. Experiments were performed for the Reyonolds number from 1 100 to 10 000, and for the frequency parameter from 3 to 10. The spatial and temporal variation of turbulence were strongly dependent on the secondary flow structure generated by the branch. It was also found that as the frequency parameter became larger, the transition Reynolds number became smaller compared with that for the straight tube.

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A complete set of the basic equations for magnetic fluids with internal rotation is proposed in this paper. The basic equations and constitutive equations are derived by the thermodynamical method in which free energy and dissipation function are used on basis of the conservation laws. The balance equations are derived from the conservation laws of mass, momentum, angular momentum and energy. The constitutive equations such as the stress tensor, the coupled stress tensor, the magnetization are determined by the principle of maximal dissipation rate and the principle of material frame indifference. The constitutive equation of magnetization which includes Shliomis's relaxation equation is proposed.

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We have developed a purification separator that combines high gradient magnetic separation using a newly developed continuously rotating single magnetic filter with a superconducting magnet. In a purification experiment, we used the purification separator to remove ferromagnetic floc, which we generated by adding ferromagnetic powder and coagulant to influent water. The experiment showed that the continuous rotary magnetic filter can be practically used in the developed purification separator and that when the separator operates at a high speed (i.e. about 100 times faster than normal speed), it achieves a good (90% inproved) performance.

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High-pressure water jet is used as an instantaneously mixing and emulsifying two kinds of liquids which do not dissolve mutually. In this method, two liquids which mixed beforehand are pressurized and are injected from the small nozzle at high speed. In general, high speed and high shear force of water jet are effective for emulsification. One side, the cavitation bubble which occurred by high speed jet makes the emulsification liquid become cloudy. In this approach, we exhaust the back pressure after injecting from the nozzle, and we showed the relation to the emulsification characteristic by the situation of cavitation bubble. As a result, it was confirmed that the back pressure was effective to the emulsification performance from particle size distribution. In addition, by the fluctuating pressure and visualization in the dispersion chamber under the back pressure, we clarified the break and constrain of the cavitation bubble by the back pressure.

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Thermal striping tests in mixing tees with same pipe diameters were conducted in order to construct databases for entablishment of an evaluation method for high-cycle thermal fatigue of piping systems. Hot and cold water with a terperature difference of 40 degrees Kelvin were supplied to the mixing tee. In order to clarify characteristics of fluid temperature fluctuations and its heat transfer, temperature fluctuations of the fluid and pipe wall were measured as the velocity ratio of the flow in the branch pipe to that in the main pipe was varied from 0.1 to 5. Characteristics of flow patterns and fluid temperature fluctuations were reported in our previous paper. In this paper, heat transfer coefficients were evaluated by using the power spectrum method. The ratios of the measured heat transfer coefficient to that evaluated by Dittus-Boelter's empirical equation were independent of the velocity ratio and Reynolds number, and they were within 1.6.

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Effect of a difference in the thermal boundary condition is examined for the turbulent channel flow. DNS was carried out for constant wall temperature difference condition for Re_τ =180, 395 with Pr =0.71 to obtain statistical cross-correlation coefficients, turbulent Prandtl number, skewness factor and flatness factor. The obtained results are compared with those of an existing DNS for the uniform heat flux heating. A large difference was obtained in the skewness and flatness factors of the temperature variance for the two thermal boundary conditions.

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Natural air-cooling needs neither a fan nor a blower. However, cooling capability of natural air-cooling is low, so the improvement of its capability is indispensable. In this paper are presented the results of the experimental casings on the chimney effect in natural air-cooled electronic equipment. The system box is inclined for the purpose to raise the capability of natural air-cooling. Experiments have been carried out using three models of thin laptop PC that have two kinds of heat sources. It has inlet and outlet vents on the front and rear walls of the casing. The box was inclined 0 to 90 degrees up from the horizontal plane. The influence by the box inclination, the box dimensions, and the heating element size was investigated. The result shows that the temperature inside casing and heater surface temperature are gently diminished by the effect of inclination, and the increase in natural circulation flux in the box is quantitatively proven by experiments. But, a substantial benefit of casing inclination is only at angles lower than about 40 degree. In the other hand, the experimental data were reduced to a Nusselt number-Rayleigh number correlation by using modified the reference length we supposed that does not include explicitly the box dimensions, the heat source size, and the inclination angle. The experimental data almost fall on a straight line which gives a correlation Nu^* =0.0038 Ra^*0.6, and are collapsed in a narrow band.

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A Weavless Aluminum Fiber Layer (WAFL) is an aluminum fiber collection (wool) with its diameter of about 120 μm. In the previous study, the effective thermal conductivity λ_ey of WAFL, placed horizontally on the measurement equipment, i.e., heat transfers across the WAFL thickness, indicated a relatively low value as a insulation material. However, the effective thermal conductivity λ_ex of WAFL, placed vertically placed on the equipment, i.e., heat transfers parallel to the WAFL surface, indicated significantly larger value compared with the λ_ey. As the results, it is found that the effective thermal conductivity of the WAFL indicates larger anisotropic characteristics, and also is largely affected by its density or porosity.

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Heat transfer on tube bundles embedded in a liquid-fluidized bed was investigated experimentally. In the experiment, 5 kinds of staggered tube bundles of equilateral triangular pitch, including single tube, were used. Tested particles were of glass and ceramics, and their diameter was from 2.1 to 6.0 mm. It was found, that the distribution of the local heat transfer coefficients around a tube depends on the tube pitch, and does not depend on the kind of particles, when a good fluidization is maintained. Based on the experimental data, a correlation was derived to predict average heat transfer coefficient, which could be applied for the tube bundles having a tube pitch to diameter ratio of 1.2 to infinity (single tube).

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The current spacecraft trend toward high density packing of the payload electronics and increased waste heat flux will require the development of lightweight high thermal conductive materials and innovative thermal control techniques. Additionally, new challenging missions will require the new techniques to adapt a variety of environmental conditions. In this study, a new passive thermal control device-a Reversible Thermal Panel (RTP) based on high thermal conductive graphite sheets and shape memory alloy was proposed. The RTP changes its function reversibly from radiator to solar absorber by deploying/stowing the reversible fin. The thermal analyses were conducted to predict the fundamental thermal performances of the RTP. A prototype model of the RTP based on the graphite sheets and aluminum alloys was fabricated, and the thermal vacuum test was conducted with the reversible fin deployed and stowed. The variability of thermal performances of the RTP by deploying/stowing the reversible fin was demonstrated. Comparison of the predicted results with test results indicated a good agreement

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An innovative heat storage system with metal hydride (MH) applied to air conditioning of buildings is investigated. The characteristics that metal hydride generates heat at absorption process and absorbs heat at desorption process is useful for new air conditioning system without chlorofluorocarbon (CFC). The trial system is composed of two heat storage vessels of a “shell and tube type” heat exchanger with heat transfer fins and filled with MH and a compressor equipped for hydrogen transfer. The system proposed in this paper is simple because the heat storage vessel has two functions of heat source and heat storage, and suitable for environment because of no usage of CFC. The purpose of heat storage is to decrease the difference of the electric power demand at daytime and that at night. That is to say, the effective heat storage system consumes electric power at night and requires no power at daytime. In the innovative heat storage system with metal hydride, the hydrogen is transferred using electric power at night and transferred in reverse only by the pressure difference between two heat storage vessels at daytime. The trial system was operated at actual loading condition, and the performance of the MH heat storage system was evaluated. As the experimental result, heat storage finishes in a limited time, and heat storage quantity was 13.5 MJ, which was sufficient for the heat capacity to cool the 10 m² room for 3 hours. And, the storaged heat per unit MH volume is 305 MJ/m³, which is sufficiently high compared with the conventional system using water or equivalent ice. In addition, the coefficient of performance of the system is 2.44.

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The fundamental characteristics of the two-dimensional gas-liquid two-phase flow of liquid helium through a vertical converging-diverging duct near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the gas-liquid two-phase flow of liquid helium though vertical converging-diverging nozzle is shown in detail, and it is also found that the geneation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid-to vapor-phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.

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The partial flow dilution tunnel system is one of the most typical systems to measure the particulate matter emission from diesel engines. This system requires to lead the exhaust gas to the tunnel at a constant split ratio, and to confirm the uniformity of the split ratio during test. Due to lack of real time measurement procedure of exhaust gas flow in transient condition, partial flow dilution system is currently applied only to steady-state engine operating conditions. This paper describes a vortex exhaust gas flow meter with resonator developed to realize the direct flow rate measurement in transient engine operating conditions. Results of the several scheduled driving tests defined for emission test lead that the developed gas flow meter system has enough accuracy in measuring the exhaust gas flow rate in transient conditions.

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The partial flow dilution system is one of the typical measurement systems for particulate matter emission from diesel engines. In this system, exhaust gas at a transient flow rate should be transferred to a dilution tunnel at a constant split ratio of exhaust gas. The current partial flow dilution system is used under steady-state engine operating conditions in lieu of direct flow rate measurement of exhaust gas. Therefore development of an exhaust gas flowmeter is indispensable in the partial flow dilution system for transient engine operating conditions. An ultrasonic exhaust gas flowmeter had been developed. As for the developed ultrasonic exhaust gas flowmeter, the transient characteristics measuring exactly and instantaneously temperature, pressure and velocity that are the components of the exhaust gas mass flow rate, has not been perfectly verified. We have inspected the transient characteristics of the developed ultrasonic exhaust gas flowmeter by using a laser Doppler velocimeter and numerical calculation. Consequently, an ultrasonic exhaust gas flowmeter has been confirmed to be capable of measuring the exhaust gas flow rate with sufficient transient characteristics.

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This paper describes multiple hollow-cone spray formation behavior by using newly developed plate-type multi-hole nozzle. The nozzle consists of multi-hole nozzle plate, flat tip needle, and thin screens located between the nozzle plate and the needle. One of the remarkable features of the nozzle is better atomization with relatively low fuel pressure. Flow pattern was observed in detail and the atomization characteristics were examined experimentally. It was found that hollow-cone shaped liquid film was injected from each nozzle hole. The shape of each liquid film was similar to that from swirl atomizer. Breakup length of the liquid film was much shorter than that from conventional plate-type nozzle. Mean droplet size was also much smaller than that of the conventional nozzle. Liquid flow in the nozzles was simulated numerically and the mechanism of hollow-cone liquid film formation was discussed. The results showed that the liquid flew into each nozzle hole with circumvolution. Owing to the circumvolution, hollow-cone liquid film was injected from each nozzle hole.

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Reduction of CO₂ is urgently required and we are attracted by H2 fuel alternative to hydrocarbon energy sources. In the present study, we introduced CO₂ emission index to estimate the greenhouse effect of the hydrocarbon fuels. The combustion characteristics of H₂-Air-N₂ were investigated using a counterflow burner. Also, effects of turbulence were examined. Results show that the critical stretch rate appears on the leaner side than the equivalence ratio of the maximum burning velocity. Critical stretch rates decrease with the oxygen concentration. For Le <1, the double flame stands closely and extinguishes by incomplete combustion. Contrarily, for Le> 1, the distance between the double flame increases and extinction occurs by the flame stretch. The Karlovitz number Ka at extinction of the H₂ flames is the same as that of hydrocarbons. Additional stretch induced by turbulence is represented by the inverse of the Kolmogorov time scale. Sum of the stretch rates by mean flow and turbulence is found to coincide with the critical stretch rate of the laminar flame.

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The stabilizing and lifting mechanisms of a jet diffusion flame developing in a coaxial-flow burner were investigated experimentally, using propane as fuel. Measurements of stability limits, and visualization of flame and fuel jets have been performed using the Mie scattering technique, instantaneous schlieren, and particle tracer methods. As a result, it is found that the flame stability limits increases as the rim thickness (δ=0.2-4mm) is increased, and the increase leads to changes of the velocity and size in the recirculation. Four types of flame stabilizing mechanism were clarified i.e., Type 1 lifted off of the attached flame due to local extinction, Type 2 blew-off of the attached flame due to flame stretch, Type 3 blew-off due to thermal quenching, and Type 4 blew-off due to changes of the flow in the recirculation for a greater rim thickness. For Type 1, it is very familiar with the local extinction of the flame zone near the transition point. Furthermore, for Type 2 and 3, it was found that the displacement rate based on the concept of flame stretch theory agrees with the critical stretch rate at which the laminar counterflow diffusion flame extinguishes. It was suggested that the stabilizing mechanism of jet diffusion flame is similar to the extinction problem of the laminar counterflow diffusion flame.

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Laser induced fluorescence (LIF) method was applied to the measurement of PAHs (Polycyclic Aromatic Hydrocarbons) in a propane diffusion flame. Various PAHs were excited by a KrF excimer laser and a dye-laser pumped by the XeF excimer laser. By measuring the enission spectra of various PAHs vapors, it was found that the peak wavelength in the emission spectrom of LIF shifted to the longer wavelength side with an increase of PAHs carbon numbers. The carbon numbers of PAHs in a diffusion flame was presumed from the data of peak wavelength of emission spectrum. It was confirmed that the carbon numbers of PAHs in the diffusion flame increased as approaching to the flame surface. The maximum carbon number was about 26 at the layer close to the flame surface.

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The flame propagating into the lean region of the stratified mixture below the lower flammability limit was supported by the burned gas behind it. In this study, the effects of the flame stretch on this supported flame was investigated numerically. The supported flame and the burned gas behind it were linked to the counterflow flame configuration of the lean mixture and the hot nitrogen. The results show that the flame stretch deteriorates the reaction of the supported flame. The production of CO and unburned hydrocarbons increases with increasing the flame stretch rate. Moreover, the self-sustaining flame in the flammable range turns into the supported flame by the intense stretch.

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Outwardly propagating spherical laminar flames in the constant volume bomb were studied. Markstein length was employed to quantify the effects of the flame stretch on the burning velocity. The effects of the pressure on the unstretched laminar burning velocity and the Markstein length were investigated using methane and propane-air mixtures at the equivalence ratios from 0.8 to 1.4 varying the initial pressure from 0.10 to 0.50 MPa. The Markstein length increased for the methane mixture and decreased for the propane mixture with increasing the equivalence ratio. The Markstein length decreased with increasing the initial pressure at all the equivalence ratios irrespective of fuel. It was negative for the lean methane and the rich propane mixtures at high pressures. Flame was unstable and covered with cells in such cases.

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Dimethyl ether has been studied as a fuel for homogeneous-charge compression-ignition combustion (HCCI) engine by many researchers. However, there is a difficulty to control the ignition timing in accordance with the engine load. This research newly proposes a DME fueled HCCI combustion engine system with an ignition control by DME-reformed gas (DRG). Authors claim that the DRG that contains hydrogen and carbon monoxide with high anti-knock properties can control the auto-ignition of DME. In the system, the DRG is to be produced by an on board DME-reformer utilizing exhaust heat from the engine. This paper analyzes characteristics of HCCI combustion of DME and two types of DME-reformed gases. One type is by partial oxidation, and the other is by steam reforming. The experiments are conducted by varying the proportion of the fuels and equivalence ratio. The overall thermal efficiency based on DME is also analyzed for ideal reforming conditions.

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Original KIVA code cannot take account for the spray and combustion processes of multicomponent fuels. Therefore, it is necessary to produce the sub-models for multicomponent fuel using KIVA code. In this study, the modeling of detailed physical properties and evaporation process for multicomponent fuel was conducted. In addition, the effects of fuel composition in multicomponent fuel on vapor distribution, spray tip penetration, vapor mass and evaporation rate, and sauter mean diameter were numerically investigated by using KIVA 3 V code with this multicomponent fuel spray model. From the numerical results, the spray characteristics of multicomponent fuel varied with a change in mixing fraction in multicomponent fuel. Especially, the evaporation of multicomponent fuel was not necessarily improved, even if much amount of high volatility fuel was mixed in the multicomponent fuel.

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The effect of molecular structure on pyrolysis products has been investigated for paraffin fuels and oxygenated fules. Reaction producs from the pyrolysis of various fuels were analyzed with gas chromatography. Results show that paraffin fuel with higher carbon numbers, produces much more poly-aromatic hydrocarbons (PAHs). Furthermore, the experiments using normal-octane, iso-octane revealed that PAH formation becomes high in order of cyclo-octane, iso-octane and normal-octane. For exygenated fuels, the characteristics of PAH formation depends on C-O/C-C ratio in molecular structure of fuel. These results indicate that ether fuels have more effective PAHs suppression effect than ester fuels.

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The reciprocating engine has the maximum pressure and temperature in the cylinder, higher than that of the conventional gas turbines. When the gas engine is integrated with gas turbine instead of turbocharger, ETCS (the engine-turbo compound system) is composed. This paper defines the compound system with ERGT (the Engine Reheat Gas Turbine) and optimizes the engine operating condition. Natural gas firing steam/gas turbine combined cycle is selected as the standard system of thermal power plant. The higher TIT (Turbine Inlet Temperature) of gas turbine usually enables the higher power generation efficiency. This paper shows the effect of engine exhaust temperature on the cycle performance with no change of TIT and that the exhaust of 900°C increases the system power generation efficiency from 46 to 50% LHV (TIT 1 150°C) and 54 to 57% LHV (TIT 1 350°C), respectively.

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