一柳 満久

ディーゼル機関の過渡性能向上にはオンボード・モデルベースト制御による着火時期の予測が重要である．著者らは，筒内ガス温度をサイクルごとに予測するため，低計算負荷の圧縮ポリトロープ指数予測モデルを開発した．過渡運転条件に適用し，１Ｄ数値計算と比較した結果，構築したモデルの有用性が認められたので報告する．

本論文は，実機エンジンの吸気管にて温度測定を行い，吸気システムでの伝熱現象を検討した．その際，流れの非定常性および温度境界層の発達を考慮し，Nu数をRe数，Gz数，St数で表した実験式を導出した．また，熱力学モデルに基づきシリンダに吸入される空気温度を推定したところ，5.6%の誤差で推定可能であることがわかった．

The present study conducted the derivation of the empirical equation in terms of the heat transfer phenomena at the intake manifold of internal combustion engines and the implementation of its equation to 1-D engine simulation. The derived equation allows to calculate the Nusselt number at the intake system, which causes to predict the mass flow rate of intake air into the cylinder accurately, ultimately improving the fuel consumption by controlling the auto-ignition timing. The empirical equation was developed based on the Colburn equation, taking into consideration of the effects of the thermal boundary layer development and the intermittent air flow induced by the opening and closing of intake valves. Compared with the experimental data, the average errors of the Colburn equation and the empirical equation were estimated to be 91.1% and 2.7%, which gives to improve the prediction accuracy of the Nusselt number by deriving the empirical equation. The equation was then implemented in 1-D engine simulation and compared to the results of the Colburn equation, revealing the maximum and average intake air temperature differences of 11.4 K and 2.7 K, respectively.

<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>

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.

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.

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.