Ichiyanagi Mitsuhisa

<p>Internal combustion engines have been required to improve the thermal efficiency and reduce the pollutant emission, and the previous studies were developed by controlling the air-to-fuel ratio and reducing the pressure fluctuations. For further improvement of the thermal efficiency, it is expected to model the heat transfer phenomena at the intake system and predict the air mass flow rate into the cylinder, which causes to keep the stoichiometric air-to-fuel ratio and improve the fuel consumption. The present study experimentally developed the empirical equation of the heat transfer at the intake system. This was based on Colburn's equation considering the development of the thermal boundary layer and the unsteady heat transfer phenomena, which was expressed by using the Reynolds, Graetz and Strouhal numbers. Compared with the experimental data and the present empirical equation, the maximum and average errors were estimated within 10.5% and 3.1%, respectively.</p>

<p>This study presents an experimental optimization of the thermal efficiency of a short-stroke small engine with a supercharger, which has the advantage of high engine power and the shortcoming of increased loss of cooling from the combustion chamber walls. This shortcoming is responsible for the reduction of the net thermal efficiency. For improving the thermal efficiency, the present study considered using the lean mixture combustion, and optimized the valve lift, the valve overlap angle, the air-fuel ratio (A/F), the ignition timing, the boost pressure, and the surface treatment. Firstly, the valve lift and the valve overlap angle were changed, which lead to the reduction of the blowby and the blow-back gas. We investigated the effects of the A/F and the ignition timing on the engine torque and the brake specific fuel consumption rate (BSFC), and these results showed that it was possible to improve the BSFC, although the engine torque decreased along the overall engine speed range. Secondly, for the improvement of both the engine torque and the BSFC, we optimized the relationship between the boost pressure and the A/F and adapted the surface treatment, which lead to the reduction of the pumping and the friction losses. From the above optimizations, the averaged engine torque, the averaged BSFC and the maximum net thermal efficiency were improved by 6.3%, 10.9% and 38.8%, respectively.</p>

For further development of the thermal efficiency of SI engines, the robust control of the air-fuel ratio (A/F) fluctuation is one of the most important technologies, because the A/F is maintained at the theoretical constant value, which causes the increase of the catalytic conversion efficiency and the reduction of pollutant emission. We developed the robust controller of the A/F, which is the method to change the fuel injection rate by using the feed-forward (FF) controller considering the heat transfer at the intake system. The FF controller was verified under transient driving conditions for a single cylinder, and the A/F fluctuations were reduced at approximately 84%.

The present paper summarizes our recent research in combined laser-based measurement techniques for investigating micro- and nanoscale transport phenomena. Micrometer-resolution particle image velocimetry has been combined with the laser-induced fluorescence (LIF) technique in order to simultaneously analyze velocity and scalar fields. The measurement system is based on confocal microscopy to realize a depth resolution of approximately 2 mu m, and we have applied this technique to liquid-liquid mixing flows, gas-liquid two-phase flows, gas permeation phenomena through membranes, and surface-modified microchannel flow. Furthermore, in order to evaluate the electrostatic potential at a solid-liquid interface (i.e., zeta potential), the LIF technique was extended by evanescent wave illumination, and only the fluorescent dye within approximately 100nm of the microchannel wall was irradiated. The extended LIF technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. The proposed techniques will contribute to novel applications related to microscale multiphase flows or electrokinetics.

A molecular tagging technique using the spark tracing method has been applied to measure velocity distributions in sub-millimeter-scale gas flows, formed as air jet flows through a sub-millimeter channel. Spark lines are generated by air ionization when applying high voltage due to the electrical discharge phenomena. The velocities measured using the displacement of spark lines were 10-30% smaller than those using the theoretical equation in a rectangular channel. In order to identify the cause of the measurement error, the relationship between the ionized air regions and the gas flow velocities was investigated by numerical simulation. The simulation revealed that a spark line goes through the pathway with the minimum electric resistance, and that the velocities from the theoretical equation agreed with the spark line velocities when the spark line width is assumed to be zero. Using this result, we propose a new velocity correction technique using the relationship between the spark line width and the measured velocity. The velocities from the experiments with the suggested correction agreed well with those from the theoretical equation. Furthermore, the corrected spark tracing method was applied to a mixing air jet flow field with different temperatures through two channels.

Ultra high-speed micron-resolution particle tracking velocimetry (UH-μPTV) technique has been developed to advance the novel method to generate microbubbles using a T-shaped microchannel. The method can produce microbubbles with 10-μm order diameter by applying the gas pressure of several tens of kilopascal and injecting the deionized water with the speed of a few meters per second. The conventional μPTV was restricted to the velocity measurement of the order of millimeter per second due to a few kilohertz frame rate CMOS camera. On the other hand, the present UH-μPTV technique achieves to measure the liquid velocity of the order of meter per second by combining the bright-field microscopy and the ultra high-speed camera with 1 MHz frame rate. For improving the spatial resolution, the phase sampling method has been introduced and results in 10 velocity vectors in 20 μm × 20 μm area. The validation of the velocity measurement using UH-μPTV has been conducted through the comparison with the theoretical solution, and it has been shown that the proposed technique can capture the velocity vector field higher than 1 m/s. Furthermore, from the 1-μs time-series imaging, the microbubble generation process has been classified into two stages: the intruding stage and the growing stage. It has been shown that the bubble diameter becomes smaller by increasing the liquid velocity with reducing the period of the growing stage. In addition, from the velocity-vector maps, the normal components of velocities to the gas-liquid interface in the intruding stage are compared with those in the growing stage, and it has been observed that the velocity amplitudes in the growing stage are much larger than those in the intruding stage. This fact suggests that the high-speed liquid flow normal to the gas-liquid interface plays an important role in microbubble generation process.

A molecular tagging technique using the spark tracing method has been applied to measure velocity distributions in sub-millimeter-scale gas flows, which were formed as air jet flows through a sub-millimeter channel. Spark lines were generated by applying a high voltage, based on the air ionization via the discharge phenomena. The velocities using displacements of spark lines were smaller from 10% to 30% than those using the theoretical equation in a rectangular channel. In order to identify the cause of measurement errors, the relationship between the ionized air regions and the gas flow velocities was investigated by the numerical simulation. The simulation reveals that an actual spark line goes through a pathway with a minimum electric resistance, and the velocities from the theoretical equation are agreed with the velocities when the spark line width is limited to zero. The results suggest us to propose the new correction technique which estimates velocity distributions by varying the spark line widths. The velocities from the experiments with the correction were agreed well with those from the theoretical equation. Furthermore, the spark tracing method with the correction technique was applied to a mixing air flow through two channels, and the effect of the gas temperature on the velocity detection was examined.

The three-dimensional CO2 dissolution process through a gas-liquid interface in microfluidic devices was investigated experimentally, for the precise control of CO2 dissolution. The gas dissolution was evaluated by using confocal micron-resolution particle image velocimetry (micro-Ply) combined with laser induced fluorescence (LIF), which has the ability to measure the velocity and dissolved CO2 concentration distribution in a liquid flow field. The measurement system is based on the confocal microscope, which has excellent depth resolution and enables visualization of the three-dimensional distributions of velocity and dissolved CO2 concentration by rendering two-dimensional data. The device is comprised of a polydimethylsiloxane chip, whose microchannels were fabricated by using a cryogenic micromachining system. The width and depth of the liquid flow channel are larger than those of the gas flow channel. This is due to the need for decreasing the width of the gas-liquid interface and increasing the hydraulic diameter of the liquid channel, whose conditions generate a static gas-liquid interface. The experiments were performed for three different liquid flow conditions corresponding to Reynolds numbers of 1.0 x 10(-2), 1.2 x 10(-2) and 1.7 x 10(-2), and the gas flow rate was set to be constant at 150 mu L/min. The LIF measurements indicate that an increase in the Reynolds number yields a decrease in dissolved gas in the spanwise directions. Furthermore, molar fluxes by convection and diffusion were evaluated from the experimental data. The molar fluxes in the streamwise direction were at least 20 times as large as those in the spanwise and depthwise directions. This reveals that an increase in momentum transport in the spanwise and depthwise directions is an important factor for enhancing mass transfer in the gas-liquid microchannel flow.

The evaluation technique of gas permeable characterization has been developed for an increased efficiency of gasliquid chemical reactions and high accuracy of environmental diagnosis. This technique enables us to measure spatial distributions of velocity and dissolved gas concentration by utilizing confocal micron-resolution particle image velocimetry combined with a laser-induced fluorescence technique. Microfluidic devices with gas permeability through polymer membranes are composed of a cover glass and a polydimethylsiloxane (PDMS) chip with the ability to permeate various gases, since PDMS is an elastomeric material. In the chip, microchannels are manufactured using a cryogenic micromachining system. The gas permeation is dominated by several factors, such as the gas and liquid flow rates, the membrane thickness between the gas and liquid flow, and the surface area of the membranes. The advantage of the present device is to realize the control of gas permeability by changing the surface roughness of PDMS, because the cryogenic micromachining enables us to control the surface roughness of microchannels and an increase in roughness yields an increase in the surface area of membranes. The experiments were performed under several conditions with a change in the gas flow rate, the PDMS membrane thickness and the surface roughness, which affect the gas permeation phenomena. The spatial distributions of velocity and dissolved gas concentration were measured in the liquid flow fields. The results indicate that the velocity-vector distributions have similar patterns under all experimental conditions, while the dissolved gas concentration distributions have different patterns. It was observed that the gas permeability through PDMS membranes increased with an increase in gas flow rates and surface roughness and with a decrease in membrane thicknesses, which is in qualitative agreement with membrane theory. The important conclusion is that the proposed technique is suggested to have the possibility of evaluating the characterization of gas permeable microfluidic device through membranes.

A molecular tagging technique utilizing evanescent wave illumination was developed to investigate the motion of a caged fluorescent dye in the vicinity of the microchannel wall surface in electroosmotic and pressure-driven flows. A line pattern in a buffer solution was written by a pulsed UV laser and the uncaged dye was excited by the evanescent wave with total internal reflection inside the glass wall using an objective lens. The velocities calculated by the measured displacement of the near-wall tagged region were compared with the results of molecular tagging using volume illumination, which represents the bulk flow information. Concerning electroosmotic flow, the micro-PIV technique using a confocal microscope system was applied to the microchannel rinsed by the caged fluorescein beforehand in comparison with a pure glass-PDMS microchannel to examine the effect of dye adsorption to the wall on the electroosmotic mobility. The electroosmotic mobility obtained by evanescent wave molecular tagging (EWMT) showed close to the micro-PIV measurement result near the glass wall for the rinsed case and the uncaged dye at the almost constant velocity remained in the depthwise illumination region. On the other hand, the dye velocity in pressure-driven flow by EWMT increased rapidly with respect to time. The uncaged dye convected to the streamwise direction dispersed toward the wall due to the concentration gradient of the dye, which was confirmed by the numerical simulations.

Effects of surface modification patterning on flow characteristics were investigated experimentally by measuring electroosmotic flow velocities, which were obtained by micron-resolution particle image velocimetry using a confocal microscope. The depth-wise velocity was evaluated by using the continuity equation and the velocity data. The microchannel was composed of a poly(dimethylsiloxane) chip and a borosilicate cover-glass plate. Surface modification patterns were fabricated by modifying octadecyltrichlorosilane (OTS) on the glass surface. OTS can decrease the electroosmotic flow velocity compared to the velocity in the glass microchannel. For the surface charge varying parallel to the electric field, the depth-wise velocity was generated at the boundary area between OTS and the glass surfaces. For the surface charge varying perpendicular to the electric field, the depth-wise velocity did not form because the surface charge did not vary in the stream-wise direction. The surface charge pattern with the oblique stripes yielded a three-dimensional flow in a microchannel. Furthermore, the oblique patterning was applied to a mixing flow field in a T-shaped microchannel, and mixing efficiencies were evaluated from heterogeneity degree of fluorescent dye intensity, which was obtained by laser-induced fluorescence. It was found that the angle of the oblique stripes is an important factor to promote the span-wise and depth-wise momentum transport and contributes to the mixing flow in a microchannel.

A non-intrusive and continuous separation technique for suspended particles in a microchannel has been developed by utilizing acoustic radiation force with two ultrasonic transducers. The technique has two major advantages that the acoustic radiation force acts on particles in proportion to particle diameter, and collects particles to the nodal positions of the standing wave field perpendicular to the flow direction. Thus the large size particles have shorter time of transfer to the nodal positions than the small size particles. Particle velocities toward the nodal position within the sound field were measured by particle tracking velocimetry, and both the migration times of particle transfer to the nodal positions and the acoustic radiation force were evaluated from the particle images and velocity data in order to separate particles in the flow field. The ultrasonic transducers with 5 and 2.5 MHz were equipped parallel to the flow direction. Both large and small particles in the aqueous solution were trapped at the nodes of the upstream in 5 MHz sound field, and 2.5 MHz transducer was radiated to move only large particles toward a nodal position of its sound field. The exposure time of 2.5 MHz transducer was determined from the migration times of large and small particles transfer to the nodal positions. It is confirmed that the continuous and selective separation based on particle diameter was accomplished by the present technique.

A simultaneous measurement technique for the velocity and pH distribution was developed by using a confocal microscope and a 3CCD color camera for investigations of a chemical reacting flow field in a microchannel. Micron-resolution particle image velocimetry and laser induced fluorescence were utilized for the velocity and pH measurement, respectively. The present study employed fluorescent particles with 1 mu m diameter and Fluorescein sodium salt whose fluorescent intensity increases with an increase in pH value over the range of pH 5.0-9.0. The advantages of the present system are to separate the fluorescence of particles from that of dye by using the 3CCD color camera and to provide the depth resolution of 5.0 mu m by the confocal microscope. The measurement uncertainties of the velocity and pH measurements were estimated to be 5.5 mu m/s and pH 0.23, respectively. Two aqueous solutions at different pH values were introduced into a T-shaped microchannel. The mixing process in the junction area was investigated by the present technique, and the effect of the chemical reaction on the pH gradient was discussed by a comparison between the proton concentration profiles obtained from the experimental pH distribution and those calculated from the measured velocity data. For the chemical reacting flow with the buffering action, the profiles from the numerical simulation showed smaller gradients compared with those from the experiments, because the production or extinction of protons was yielded by the chemical reaction. Furthermore, the convection of protons was evaluated from the velocity and pH distribution and compared with the diffusion. It is found that the ratio between the diffusion and convection is an important factor to investigate the mixing process in the microfluidic device with chemical reactions.