Nonlinear responses of surface waves in a square tank, subjected to horizontal excitation with an oblique angle, are investigated. In the theoretical analysis, the modal equations of motion for the seven sloshing modes are derived. Then, van der Pol's method is used to determine the frequency response curves. In the numerical calculations, as the direction of excitation increases from 0° to 45°, the shapes of the response curves become complicated due to the nonlinear coupling of (1,0) and (0,1) sloshing modes. In the experiments, the validity of the numerical results was confirmed.

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This paper deals with an active control to suppress a flow-induced web flutter by multi-point and non-contact control devices using pressure wave. A flexible web, as a controlled object, is supported at one end and subjected to fluid flow in the passage. The flutter occurs to the web due to the fluid flow with a self-excited feedback mechanism resulting from fluid-structure interaction. The web flutter is suppressed by the active control using the pressure wave from loudspeakers. The loudspeakers are driven with changing a controller gain and phase-shift between the displacement of the web and the pressure. As a result, it is shown that the web flutter is effectively suppressed by the proposed method of multi-point non-contact control.

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The chief sources of aerodynamic noise generated by rapid trains are cavities on their surfaces, e.g. bogies under the trains.The shear flow separated from the upstream edge of a cavity impinges on the downstream edge, and frequently alternates flowing into the cavity with flowing out from it.This fluid motion induces noise in low frequency range. A ' scoop deflector ' attached at a downstream edge has been found to be effective to reduce the noise. In this study, in order to determine the most effective dimensions of the scoop deflectors, the noise reduction by scoop deflectors was experimentally investigated by use of a scale model of a two dimensional cavity in a wind tunnel. Considering a train to travel in two directions (i.e. back and forth) along the tracks, a double scoop deflector, a set of scoop deflectors at both upstream and downstream edges, was dealt with. The optimum dimensions of the deflector were obtained; the ratio of the depth to the opening and the ratio of the length to the opening were 0.06 and 0.1, respectively.

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The fluid-acoustic interactions in a flow over a cavity in a turbulent boundary layer are investigated by directly solving the compressible Navier-Stokes equations. Phase-averaged flow fields reveal the mechanism for the acoustic radiation. Large-scale vortices form in the shear layer that separates from the upstream edge of the cavity. When a large-scale vortex collides with the downstream wall, the low-pressure fluid in the vortex spreads along the downstream wall. As a result, a local downward velocity is induced by the local pressure gradient, causing the upstream fluid to expand. Finally, an expansion wave propagates to the outside of the cavity. The computations for backward-facing step flows with an artificial acoustic source clarify that convective disturbances in the shear layer are induced by the acoustic waves and the disturbances grow into the large-scale vortices due to the Kelvin-Helmholtz instability.

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An aeroacoustic noise generated from a rectangular cavity can be suppressed by placing a square rod at a proper location on the bottom surface of the cavity. The present paper focuses on the relation between the fluid motions inside the cavity and the generation of cavity noise. The results of flow measurement and the wavelet analysis of sound signal imply that the rod causes the formation of the feedback loop system take place intermittently and occasionally, suppressing the cavity noise.

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Perforated plates are often placed inside the muffler to reduce noise and enhance the strength of the muffler. However, the flow passing through the perforated plate would impinge on another inner plate and generate flow-induced noise. This study experimentally researched characteristics of the flow-induced noise generated by air flow passing through perforated plates and impinging on a flat plate. The perforated plate was installed at the end of the pipe through which steady air flow was supplied from a blower. The air flow passing through the perforated plate impinged on the flat plate. We examined effects of the hole diameter, dimensionless hole spacing, and distance between the perforated plate and the flat plate with constant total hole area and constant flow velocity at the hole. The results show that the flow-induced noise decreased with the increase in the distance between the perforated plate and the flat plate at frequencies higher than 100 Hz but increased at lower than 100 Hz.

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The numbers and diameter of the holes on the side of the resonance tube immersed under the water on sound quality to develop the downsized water musical instrument have been studied. A hole having a large diameter doesn't influence the change in the level of water surface, and then by setting the hole of a larger diameter the resonant frequency we hope to gained. Based on these results, water musical instrument is manufactured.

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The influence of water depth on the impact sound of water drops on the water surface has been studied. When water depth becomes shallow, not only the bubble diameter becomes smaller, but also the time of generation of bubble vibration is delayed.

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In order to clarify the relation between the discrete frequency noise of the propeller fan and the circular flow formed in the wake, the characteristics of the propeller fans were analyzed by the measurement of the flow and the CFD. The absolute velocity in the main flow domain of the meridional plane in the wake of the propeller fan became 30 m/s while the velocity in the inclined plane was decreased to 25 m/s. The velocity fluctuations on the vertical plane in the wake were weakened at the diagonal line by the velocity deformation formed to the circumferential direction around the impeller. Then the circular wake formed in the propeller fan was broken by the velocity deformation. It is considered that the discrete frequency noise of the propeller fan in the second harmonics became large since the fourteen dynamic rotors and the pseudo four stators made by the broken circular wake resonated.

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This paper presents the measuring result that the turbulent flow around the wing tip and the aerodynamic sound of NACA0012. Reynolds number based on the chord length of the airfoil and the uniform velocity is 3×1O^5. The airfoil is the lifting condition when the angle of attack is 15 degrees. The results of the velocity fluctuation and the pressure fluctuation showed that the formed vortex at the suction side near the wing tip called secondary vortex is comparatively high fluctuation level. In addition, the secondary vortex doesn't seem to contribute to Strouhal number of 4 to 10.

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Sibilant /s/, one of unvoiced fricative sounds or consonants, is believed to be produced by turbulence of a jet created in a sibilant groove. In addition to turbulence, we hypothesize that the impingement of a jet to the anterior teeth induces vibration of anterior teeth, whereby contributing to the production of sibilant /s/. The present study is designed to investigate the possibility that the vibration of teeth contributes to the production of sibilant /s/. A morphologically simplified model of an oral cavity is fabricated. An air is steadily delivered at 45 L/min to the model to produce aeroacoustic sounds. Sound and vibration of teeth (obstacle wall) are measured simultaneously with a microphone and the Michelson interferometer. The spectrum analysis showed two peaks in the sound at 1275 and 3525 Hz, and one peak in the wall vibration at 3525 Hz. An association of the peak at 3525 Hz between the sound and wall vibration suggested that this sound is produced as a result of wall vibration. These results demonstrated potential of the proposed method for exploring the production mechanism of sibilant /s/ and possibility of the contribution of teeth vibration to the production of sibilant /s/.

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The optical microphone picks up the integrated line sound on the laser beam. An application of CT (Computed Tomography) technology to the data measured with the optical microphone could be converted into the point sound. In this research, a reconstructed image of the sound field radiated from speaker and jet is made.

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In order to control the aerodynamic tonal noise from rearview mirrors, an active flow control techniques were tested in a wind tunnel experiment. Since the aerodynamic tonal noise of rearview mirror was generated by a small perturbation caused by a small step on a surface of backward-facing step or rearview mirrors, synthetic jet was introduced to break it. The experimental results showed that the noise reduction level depended on the frequency and intensity of the synthetic jet. The noise reduction level was about 6dB at synthetic jet frequency was almost the half of the frequency of the tonal noise. The amplitude of the jet velocity was only 0.2 m/s, it was quite small compare to the uniform velocity. It revealed that the synthetic jets effectively reduced aerodynamic tonal noise with small amount of energy.

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Photoresist stripping process in photo lithography plays an important role in manufacturing large-scale integration. In the present study, experimental information is obtained to establish high concentrated ozone water technology, in stead of chemicals such as sulfuric acid or hydrochloric acid. We examine flow structure between a stationary and a rotating disk for the sake of improving removal rate of photoresist using flow structure between the disks. Three-components velocities which are a radial, rotational and z directional flow velocity in a plane are obtained with stereo micro PTV measurement of a flow in the narrow gap. It is confirmed that z directional flow exits near the edge of the disk.

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The purpose of this study is to elucidate a relationship between acoustic cavitation and sonoluminescence. We focused on the spatial distributions and behavior of Multi-bubble Sonoluminescence (MBSL). We obtained the MBSL distributions in purified water by using an intensified-CCD camera. We changed the exposure time in order to characterize the MBSL distribution. The MBSL obtained in each case was distributed in a circular ring. The onset of MBSL is not simultaneous. We found out two types of sonoluminescence; the one is spotlight-like sonoluminescence, the other one is filament-like sonoluminescence. The former one was tended to emit at the same point. The later one was not observed in the short exposure time.

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Ultrasound velocity profiling obtains 1-D 1-C flow velocity distribution from a single ultrasound transducer, and is suitable for monitoring one-component dominant flow field such as in pipes. Instead, two-dimensional flow structure such as vortex cannot be directly observed. This note reports several trials done by the author in terms of two-dimensional flow field reconstruction that is classified into three flow confifurations; transverse, rotational, and outward measurements.

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This paper described about a flow structure on a bubble jet flow. Bubbles and seeding particle are simultaneously visualized by the single high-speed camera. The obtained images are separated to bubble and particle images by image processing. These liquid phase velocities are calculated by PTV (Particle Tracking Velocimetry) and rearrangement method. These time-series velocity data are analyzed by POD in order to decompose temporal and spatial flow structures.

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An optical measurement system was used to investigate the effect of microchannel length on adiabatic gas-liquid two-phase flow characteristics. Experiments were conducted with 1,676 mm long, circular microchannel with the diameter of 100 μm. Two-phase flow patterns, void fraction, gas and liquid slug lengths and their velocities were measured at the location of any distance from gas-liquid mixer to channel exit. The mean void fraction and the mean velocity of liquid slug showed the values by the homogeneous model up to about channel exit when the mass flow rate of the liquid was constant and that of the gas was lower. In case of higher mass velocity of the gas the transition of the flow patterns from slug flow to ring film flow occurred at a location of downward section of the channel.

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Experiments were done to clarify the mean void fraction, the mean holdup, the velocities of gas and liquid slugs and the flow patterns of air-water two-phase flow in horizontal flat rectangular microchannels with the dimensions of the narrow width and depths of 1.0x0.1 mm and 1.0x0.2 mm. The remarkable flow characteristics of rivulet flow and the flow with dry patch were observed in slug flow and annular flow regions in a channel with the depth of 0.1 mm.

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The migration of Light Non-Aqueous Phase Liquid (LNAPL) in dry/wet sandy soils was visualized by the model tests in plane strain condition and using X-ray Computed Tomography (CT) method. To evaluate the saturation degree of water or LNAPL in the sandy soil, new method to decide the threshold value in X-ray CT image was proposed in this report. It was concluded that saturation degree of sandy soil changed the migration mechanism of LNAPL.

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It is difficult to apply optical techniques to the velocity measurement of the fluid-particle flows, especially when the volume fraction of particles becomes high, hi the present paper, the MRI (Magnetic Resonance Imaging) measurement is applied to dense liquid-particle flows. The velocity distribution of the liquid-particle flow is measured non-invasively by the phase method.

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Development of marine heat recovery system is considered as one of the useful device to improve the energy efficiency, and motion prediction of the catalyst in system to the motion of a marine wave is an important element. Then, in this research, the visualization in waving circulating fluidized bed was performed using the capacitance CT. Capacitance CT is the system that measures a dielectric constant between electrode pairs attached to the circumference of a pipeline and calculates the particle concentration distribution in a pipe from the value. This result shows change for different flow state and waving situation. In this experiment, the particle concentration in the pipe became (in the case of a wave state) lower compared with the upright state.

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Temperatures play a vital role in almost all industries. This paper introduces the applicability of Electrical Capacitance Tomography (ECT) as a new and non destructive technique in tracking the temperature distribution on a polycarbonate (PC) material for injection molding application. 20 ml polycarbonate resins have been placed inside the 30 ml. 12-Electrodes connected from the ECT are attached circumferentially inside the beaker to measure the capacitance of PC while the heat is continuously applied until the given time of 1Omin elapsed. The measured capacitance values pass through the ECT data acquisition system and fed into computer to display the inner process and by using a non-iterative algorithm; the cross-sectional image has been reconstructed. ECT is not only suitably excellent in measuring electrical parameters of a certain material but also in determining one of the thermodynamic parameters that contributes phase change such as temperature.

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The control of state of the abrasive water jet spouting out is very important for the improvement of the accuracy on the processing by the abrasive water jet. However, it is too difficult to know how the jet state is because of the differences of the phenomena caused by the differences on the apparatus, e.g., the nozzle shape, the abrasive supply method, the water flow in the tube. Especially, mixing particles have big influences on the state of the jet flow diffusion and velocity distribution. Therefore, the knowledge of the mixing state of the jet will be necessary. In this study, the transparent mixing nozzle made of acrylic acid resin was used to visualize the mixing state of the jet in it, and the instantaneous photographs of the jet flow in the mixing nozzle were taken in stereo by using two digital cameras and two stroboscopes. After image processing, the 3-D distribution of the particles in the mixing nozzle was obtained.

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In this study, the fundamental three dimensional particles manipulation properties with a dielectrophoresis (DEP) are investigated by a particle tracking method and a deconvolution technique between planar parallel electrodes in a minichannel. These properties are important to develop three-dimensional particle separation and classification systems for medical and industrial applications. As results, three dimensional particles behavior with a DEP force near planer electrode are observed and the effect of the electric field intensity and frequency on the particle velocities are clarified.

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We have developed a human interface to support learners in acquiring the motions in sports and dances. At first, we assumed that a dance consists of each position of the body parts at each time. Therefore we measured the motions of the reference person's dance by using a motion capture device and developed a system which instructs the learners how to dance by showing a target position with a head-mounted stereo-display on virtual space. We carried out two kinds of motion-instructing experiments: one motion is to put subject's hand on a target position, i.e. a virtual wall, and the other is to move both hands of the subject while keeping a relative position of the both hands.

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This paper describes a method of estimating the angle of inclination and length of the flat plates by Ground Penetrating Radar (GPR) where the flat plates is assumed to be buried tilted in the scanning direction of the GPR. In the estimation, we use two information of both the propagation time and the intensity of the first peak of the reflected wave. Especially, to estimate the angle of inclination, we compare the propagation time derived from a model of the geometric position and that from the scanned data. Then, we estimate the length of the plates based on the intensity of the scanned data. Since the intensity is strongly influenced reflection by the scattering cross section, it is difficult to make an analytical model with the absolute intensities. Therefore, we made a model of relative intensity at both ends of the buried plates to those at the center of the plates.

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Abstract So far, in. pervious virtual reality systems, haptic presentation devices have been developed and their usages have been discussed However, combination effects of tactile and haptic sensations have not been investigated in spite of their possibilities on virtual reality systems. In this study, we developed a mouse capable of presenting pressure distribution and slippage force to discuss the combination effects on virtual reality. The mouse was equipped with bimorph piezoelectric actuators and electro-magnetic linear motors to present pressure and slippage force respectively. In order to evaluate the presentation accuracy of the mouse, we performed a series of edge tracing oriented to several directions. In the present experiments using real step-height specimen, the smallest standard deviation is obtained from horizontal edge while the largest constant error is obtained from horizontal edge. Although human subject judges horizontal edge direction with high discrimination accuracy, recognized orientation is deviated from horizontal datum line.

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There are motor point maps as index of stimulation points to move each muscle for functional electrical stimulation (FES). However we'll usually have to search detailed motor points by trial and error when arranging electrodes since individual differences are large. In this research, we developed a system aids searching motor points of fingers and wrist muscles. It contains 12 × 10 electrodes which cover a forearm and sensors which catch movement of each finger and wrist. It chooses a pair of electrodes in order and stimulates a subject. When the response was measured, it records the response movement and the position of electrode pair. As a result, we obtained the generated motor point map.

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This paper describes task support in upper-limb exoskeleton power-assist robot with perception-assist. If the robot has not found any problems in the user's motion, then the ordinal power-assist is carried out by the robot. On the other hand, if the robot has found some problems in the user's motion during the task, the robot tries to modify the user's motion to perform the task properly. In the perception assist by using exoskeleton robot, it is important to recognize objects which user has, because robot assists the task based on them. In this paper, the method which uses task estimation by the motion of user's arm in combination with image processing is proposed. To estimate the motion of user's arm, the feature quantity which is calculated by hand vector is used. The effectiveness of the proposed method was evaluated by the experiments.

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In this paper, we describe the construction of a VR system for the transmission of lathe operation skills, and brain activity analysis of the effect on the trainee of using the VR system as compared with training on an actual general-purpose lathe, based on near-infrared spectroscopy (NIRS) measurements of brain activity during lathe operation with the VR system and with an actual lathe. Brain activation responses at various NIRS measurement positions during the performance of three basic movements showed that the positions of change in oxyHb were clearly influenced by direction of movement and body posture at the time of the movements, and that the degree of change was largely governed by the level of force which was applied. The results, taken together, show that brain activation response during the performance of lathe operation in the VR environment is very close to that which occurs during operation in the actual environment, and thus indicate that training in such a VR environment will be effective and useful.

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In the velvet hand illusion (VHI), a person rubs his/her hands together on either side of wires strung through a frame, producing the sensation of rubbing a very smooth and soft surface like velvet. We investigate the VHI mechanism to obtain an effective hint for a new tactile display because such tactile illusions play a good role in deceiving the brain so that operators believe that a virtual sensation is real. To elucidate the VHI mechanism, we propose two approaches: one uses psychophysics to obtain human mental models; the other is a finite element method (FEM) to evaluate the tactile stimulus that causes VHI. In FEM analysis, a mesh model of fingertips is produced to mimic an actual finger to evaluate the strain energy density (SED) because one mechanoreceptive unit is a slowly adaptive mechanoreceptive type I unit (SAI) that well responds to SED. There is a considerable difference between the SEDs of the one-finger case and the two-finger case (VHI case): the peak SED value for the VHI case is around half of that for the one-finger case. The VHI mechanism is assumed as follows: although the area bounded by two wires moves relative to the hands, tangential force does not occur on the hand surface except for the wire-passing portion, causing operators to experience the illusion of touching a smooth virtual film with a zero coefficient of friction. Since VHI decreases with a decrease of wire spacing and an increase of the peak value of SED, excessive temporal stimulus generated by wire prevents VHI from increasing.

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This pare proposes the new framework of the driver assistant system that will be useful for attention guidance to hazards in driving situation. The system consists of two important technologies that are the detection of hazard factors in driving envi- ronments and the driver-vehicle interface to inform drivers of hazardous factors without nuisance. We focus on both neural network to predict hazard factors and subliminal visual cue. The system configuration and performance are introduced

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This paper presents a primitive study on operating performance of driving games under the influence of ultrasound from a subliminal information point of view. The lap time of driving game that is equivalent to the performance of the driving operation with / without ultrasound is measured for each subject Results show us the operational characteristics of subjects are changed by ultra sound environments

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It is essential to increase compression ratio to improve thermal efficiency in gasoline engines. The direct-injection system is necessary to avoid knock at high compression ratios together with lowering hydrocarbons and soot emissions. A fundamental study was conducted on a lift-off gasoline stray combustion system devised to achieve combustion free from knock and soot and HC emissions at high compression rations. Gasoline was directly injected into high pressure and temperature air in a constant volume chamber. Test results showed that combustion is controlled by mixing with air and the relative location spark plug. A CFD model, KIVA-3V could reproduce such lift-off combustion phenomena in the combustion chamber.

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The purpose of this study is to realize high-efficient dual fuel combustion with natural gas and diesel fuel. Diesel fuel was injected directly into combustion chamber of a single cylinder diesel engine. And diesel fuel was injected through micro-hole nozzle with a common rail system. The natural gas was injected at an intake port as premixed gas. In order to distribute diesel fuel spray in combustion chamber, one diesel injection event was split into twice ones, where diesel fuel was injected earlier than usual and around TDC. In this study exhaust emissions and heat release characteristics were investigated. The result show that a timing and an amount of 1^<st> injection significantly influence on unburned emissions and thermal efficiency. And it seems that precise control of diesel fuel distribution has a great importance to combustion performance of natural gas with diesel fuel.

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This study aims to explore effects of fuel property and injection conditions on ignition delay for various combustion methods using a constant-volume vessel. Ignition delays of binary-component fuels which have same ignition delay under a specified ambient condition and a specified injection condition were measured under several ambient conditions. The results show that ignition delay depends on the boiling point of high-ignitability component when the ambient pressure and temperatures are reduced and on the fuel properties when the injection conditions are changed.

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In this research, problems of exhaust emission when using SVO (Straight Vegetable Oil) into DI Diesel Engine was studied in terms of sprays characteristics. In particular, influence of sac volume and injection pressure on SVO spray was examined. SVO and GO (Gas oil) spray images were taken using optical system. Later, the spray characteristics were compared with each other. From observation, SVO spray development was delayed compared to GO spray, particularly very short penetration and narrow spray angle soon after the start of injection. In addition, high fuel injection pressure at end of injection produced large size of droplets thus affects exhaust emission.

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This paper investigates the performance, emissions, and combustion characteristics of a dual fuel diesel engine fueled by CNG (Compressed Natural Gas) as the main fuel. The experiments used two fuels for the ignition: one is OME (Oleate Methyl Ester), a major component of biodiesel, and the other is ordinary gas oil. The results show that the conditions where operation with CNG/OME is possible are very similar to those of CNG/gas oil. When the CNG supply rate was raised to 75%, the brake thermal efficiency was similar to that of ordinary diesel operation at BMEP=0.65MPa. When the CNG supply rate was higher than 75% ignition became very unstable and the brake thermal efficiency decreased significantly as well as the HC and NOx emissions increased sharply.

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An objective of this study is to realize high efficient dual fuel combustion with natural gas and diesel fuel. Natural gas was injected from an intake port and diesel fuel was injected directly into combustion chamber of a single cylinder test engine. In this report, we focused on a low NOx dual fuel combustion by diesel early injection. In order to understand this combustion mechanism, observing combustion behavior in an optical engine with high speed camera coupled with image intensifier was conducted. And numerical analysis of diesel fuel spray was also conducted. Result showed that combustion area of natural gas correlated with distribution of diesel fuel spray.

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The effect of a disturbance on a piston compression ignition of a stoichiometric n-butane/oxygen/argon mixture was observed using a rapid compression machine with a stepped piston crown in a wide temperature range. When a stepped or a dished piston crown was used for the mixture compression, the polytropic index was smaller than usual. The cool-flame onset retarded and the blue-flame delay was not changed in the cool-flame dominant temperature regime. In the blue-flame dominant temperature regime, the total ignition delay was elongated. The onset position of the hot-flame in the high temperature side of "negative-temperature-coefficient regime" was fixed near the stepped piston head. These have suggested that the stepped piston generates a disturbance have the capability of promoting a compression ignition.

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Recently, environmental problems such as global warming and acid rain have become more serious. Therefore, a decrease of exhaust gas is demanded with the internal combustion engine. The EGR (Exhaust Gas Recirculation) is one of the methods for decreasing it. But it is ignitability and the stability of the flame decrease by using extremely lean mixtures. This experiment has been carried out to determine the influence of CO_2 concentrations and initial temperature of mixtures on combustion characteristics of hydrocarbon-air mixtures by using an opposed rapid compression machine. The combustion behavior, such as pressure history, heat release rate and flame speed is observed by measuring the pressure and the travel time of flame front in the combustion chamber.

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A flame propagation in a small diameter tube has been experimentally investigated with use of a small diameter tube and a swirl injector for methane and propane/air mixtures Results show that, in a 3.6 mm tube, a flame can propagate rapidly along the tube axis due to vortex bursting. The propagation range in equivalence ratio is on the relatively fuel lean side, between 0.75 and 1.1 for methane, whereas on the very fuel rich side between 1.1 and 2.2 for propane. The Lewis number of a deficient species and the heat loss to the cold wall strongly affect the occurrence of vortex bursting in a small diameter tube. Further experiments have shown the flame speed is lowered down near the stoichiometric methane mixture, notwithstanding the large flame/core diameter ratio. This retardation of the flame speed seems to be resulted from an increase in the burned gas density due to cooling by the cold wall.

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Biomass, a renewable and carbon-neutral energy source, is widely recognized as an alternative to fossil fuels. But, because of the supply instability, it is hard to use Biomass as a single fuel in Engine. In this study, the combustion characteristics of a HCCI Engine using Mixture of City gas 13A and Biomass gas are investigated. As a result, it is noted that the ignition timing advances and the combustion duration becomes longer, when the ratio of 13A decrease and/or the intake gas temperature becomes higher. Moreover, it is suggested that the effect of H_2 on the ignition timing is more significant than other combustible components.

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The aim of this study is to establish the control method of natural-gas HCCI combustion by re-breathing nitrogen oxides, which can enhance auto-ignition and combustion. The exhaust gas was re-circulated into the intake gas through an oxidation catalyst, in order to reduce carbon monoxide which suppresses HCCI combustion. Experimental results are, however, go against our prediction. In the case of a low intake gas temperature, by reducing the CO concentration in the intake air, HCCI combustion is suppressed rather than improved. If the intake gas has a high temperature and a high NOx concentration, the combustion characteristics are not affected by CO concentration in the intake gas.

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The objective of this study is to investigate the effect of injection conditions on exhaust emissions and engine performances in a natural-gas-fueled dual fuel engine. An experimental study was performed using a single-cylinder test engine with a common rail injection system, varying fuel injection quantity and injection timing. The results show that problems of high CO and THC emissions at low load range can be mitigated by adjusting fuel injection timing. Furthermore, it was possible to decrease NOx emission without an increase in CO and THC emissions by using two-stage injection.

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Improvement of thermal efficiency in a spark ignition gas engine with longer strokes was investigated with two engines with stroke / bore ratios of 1.0 and 1.5 and the similar stroke volumes. The indicated thermal efficiency improved significantly with longer strokes mainly due to reductions in cooling loss over wide operation ranges while the degree of improvements decreased slightly in comparison with another longer stroke case under the same bore with increasing stroke volumes reported previously. The degree of improvement in thermal efficiency with longer strokes was more significant under the lean range than the stoichiometric range but the combustion stability deteriorated when the excess air ratio exceeded 1.5 and the lean limit was richer. The indicated thermal efficiency improved over the wide range of the indicated mean effective pressures with longer strokes due to reductions in cooling loss.

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In this study, combustion mechanisms and effects of flame stretch on the local burning velocity of two-component fuel mixtures of DME, hydrogen and methane were investigated by chemical kinetics computations. Lean and rich mixtures having nearly the same laminar burning velocity were prepared by adding nitrogen to mixtures where the fuel mixing rate δ is varied from 0 to 1 at equivalence ratios of 0.4-2.0. As a result, it is elucidated that Markstein numbers of lean two-component fuel mixtures changed monotonically with increasing 8 depending on the effective Lewis number, however, those of rich flames showed a complicated trend with change in the equivalence ratio and δ. These characteristics of response to flame stretch were discussed in light of the chemical reaction mechanisms.

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The homogeneous charge compression ignition (HCCI) combustion has attracted much interest because it can simultaneously achieve high efficiency and low emissions. However, it is difficult to control the ignition timing with this type of combustion. The HCCI combustion process also has the problem that combustion proceeds too rapidly under high load operation. Supercharging the intake air is one of the effective methods for increase the operating load of HCCI combustion. In our previous studies, the heat release rate of hot flame can be moderated by using supercharged HCCI combustion. In the present study, a blended fuel of dimethyl ether (DME) and methane, with each component having different ignition characteristics, a supercharged HCCI combustion were used to investigate the effects of the mixing fuel ratio and injected heat value on the heat release characteristics of the hot flame.

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Homogeneous Charge Compression Ignition (HCCI) combustion has attracted considerable interest as a new combustion concept for internal combustion engines. HCCI combustion process has three issues to be resolved: ignition timing control, slower combustion, expanding stable operation region. In an earlier study, the ignition timing can be controlled and the rapidity of combustion can be lessened by using a fuel having two components with different ignition characteristics. In this study, ignition and combustion in an HCCI engine processes were investigated in detail by using spectroscopic measurements.

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