• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.3
• /
• pp.58-64
• /
• 2003

Dimethyl Ether(DME) has been considered as one of the most attractive alternative fuels for compression ignition engine. Its main advantage in diesel engine application is high efficiency of diesel cycle with soot free combustion though conventional fuel injection system has to be modified due to the physical properties of DME. Experimental study of DME and conventional diesel spray employing a common-rail type fuel injection system with a 5-hole sac type injector was performed in a constant volume vessel pressurized by nitrogen gas. Spray cone angles and penetrations of the DME spray were characterized and compared with those of diesel. For evaluation of the evaporating characteristics of the DME, shadowgraphy technique employing an Ar-ion laser and an ICCD camera was adopted. Tip of the DME spray was formed in mushroom-like shape at atmospheric chamber pressure, which disappeared in higher chamber pressure. Spray tip penetration and spray cone angle of the DME became similar to those of diesel under 3MPa of chamber pressure. Higher injection pressure provided wider vapor phase area while it decreased with higher chamber pressure condition.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.5
• /
• pp.1222-1233
• /
• 1990

The formation and oxidation processes of soot particles in a diesel flame were investigated with a rapid compression machine. A cloud of soot particles was successfully visualized by means of the instantaneous laser shadow photographs technique and the equivalence ratio of the soot formation zone was estimated from a measured fuel concentration distribution in a nonevaporating spray. The temporal and spatial variation of soot concentration in the flame was also correlated with the rate of heat release. Soot particles appears first in a region near the flame tip when diffusion combustion period starts, and its concentration is a maximum at about the end of injection, then decreases due to oxidation. The reason for soot being formed in a fuel lean region near the flame tip is the evaporated fuel requires time to be pyrolized as it travels through the burning fuel rich zone towards the flame tip.

• Journal of ILASS-Korea
• /
• v.23 no.1
• /
• pp.22-29
• /
• 2018

The purpose of this study is to investigate the macroscopic spray characteristics and spray pattern of a gasoline direct injection (GDI) injector according to the increase of injection pressure. The macroscopic spray characteristics, such as a spray tip penetration and spray angle, were measured and analyzed from the frozen spray images, which are obtained from the spray visualization system including the high-speed camera, light-source, long-distance microscope (LDM). The spray pattern was analyzed through the deviation of the center of the spray plum and images were acquired using Nd: YAG Laser and ICCD(Intensified charge coupled device) camera. From the experiment and analysis, it revealed that the injection pressure have a significant influence on the spray tip penetration and spray pattern. However, the injection pressure have little influence on the spray angle. The increase of injection pressure induced the reduction of a closing delay. In addition, the deviation of spray center increase with the increase of injection pressure and the distance from a nozzle tip.

• Journal of the Korean Vacuum Society
• /
• v.8 no.4B
• /
• pp.530-535
• /
• 1999

W made a near-field optical microscope(NSOM) apparatus and evaluated it. To control the distance between a tip and a sample, we used a piezoelectric translator and a He-Ne laser, and consequently obtained the spatial resolution better than 100nm. For the semiconductor spectroscopic applications, we performed photoluminescence and photocurrent experiments on the GaAs/AlGaAs MQWs samples. In the case of PL experiment, we obtained the low signal to nose ration due to the extremely small power of a light source passing through the nanometric optical fiber tip. However photocurrent experiment shows a hundred times better signal to noise than that of PL experiment. This suggests that photocurrent experiment using NSOM have the possibility to provide the spatial resolution better than 10nm.

• Journal of ILASS-Korea
• /
• v.12 no.2
• /
• pp.101-107
• /
• 2007

The purpose of this study is to analyze spray and evaporation characteristics of DME fuel at the high pressure and temperature. For the numerical analysis of dimethyl ether(DME) fuel spray characteristics, hybrid breakup model was applied to the DME spray and its breakup process. In order to obtain experimental results for comparison with the predicted ones, the visualization of the spray evolution process was executed by using a Nd:YAG laser. Also, the numerical investigation was conducted by the two hybrid models for primary and secondary breakup of the DME spray. The primary breakup model was used the Kelvin-Helmholtz(KH) breakup model. In the secondary breakup process, Rayleigh-Taylor(RT) and Drop Deformation Breakup(DDB) model was applied. The results of this study provide the macroscopic characteristics of the spray such as spray tip penetration and cone angle, and prediction accuracy of the two hybrid model.

• Journal of ILASS-Korea
• /
• v.9 no.1
• /
• pp.1-7
• /
• 2004

This paper describes the characteristics of injection rate and macroscopic behavior of fuel spray injected from common-rail type diesel injectors with different nozzle geometries. The injection rates according to the nozzle geometries were measured at different energizing duration of the injector solenoid and injection pressure by using the Bosch's injection rate meter based on the pressure variation in the tube. The spray behaviors injected from the different nozzles were visualized using the spray visualization system composed of an Ar-ion laser, an ICCD camera, and a synchronization system at various injection and ambient pressures. It is revealed that VCO nozzle has higher spray tip velocity at the early stage of injection duration and wider spray cone angle than the mini-sac nozzles. Also the spray cone angle is increased with the increase of nozzle diameter.

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.214-214
• /
• 2000

This paper deals with the non contact optical sensor to measure the shape of transparent plates such as glass panel of LCD(Liquid Crystal Display). The conventional methods to obtain the shape or thickness of a transparent plates are contact type sensor such as LVOT(Linear Variable Differential Transformer). Due to the contact between the tip of the sensor and the surface of objects, the tip is abraded. In addition, the high temperature glass casting makes the size of sensor body changed. These reasons makes the sensor degraded. In this paper, to overcome these problem, we proposed a low cost noncontact optical sensor this is composed of the Hologram laser unit of a CD-Pickup and a plastic lens. To evaluate the performance of the proposed optical sensor, a series of experiments were performed for various measurement condition. Based upon observation of the experimental result, the developed sensor shows good result for measuring the shape of transparent plates.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.4
• /
• pp.136-146
• /
• 1992

This paper provides the end-point positioning of a single-link flexible robot arm by inverse dynamics. The system is composed of a flexible arm, the mobile ballscrew stage as an arm base, a DC servomotor as an actuator, and a computer. Actuator voltages required for the model of a flexible arm to follow a given tip trajectory are formulated on the basis of the Bermoullie-Euler beam theory and solved by applying the Laplace transform method, and computed by the numerical inversion method proposed by Weeks. The mobile stage as the arm base is shifted so that the end-point follows the desired trajectories. Then the trajectory of end-point is measured by the laser displacement sensor. Here, two kinds of functions are chosen for the given tip trajectories. One is what is called the bang-bang acceleration profile and the other is the Gaussian velocity profile.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.3
• /
• pp.99-106
• /
• 1998

Recently, scientists introduced a new type of microscope capable of investigating nonconducting surfaces in an atomic scale, which is called AFM (Atomic Force Microscope). It was an innovative attempt to overcome the limitation of STM (Scanning Tunnelling Microscope) which has been able to obtain the image of conducting surfaces. Surfaces of samples are imaged with atomic resolution. The AFM is an imaging tool or a profiler with unprecedented 3-D resolution for various surface types. The AFM technology, however, leaves a lot of room for improvement due to its delicate and fragile probing mechanism. One of the room for improvements is gap control between probe tip and sample surface. Distance between probe tip and sample surface must be kept in below one Angtrom in order to measure the sample surface in Angstrom resolution. In this paper, AFM system modeling, experimental system identification and control scheme based on system identification are performed and finally sample surface is measured by home-built AFM with such a control scheme.

• Journal of Magnetics
• /
• v.10 no.2
• /
• pp.58-62
• /
• 2005

Periodic magnetic nanodot arrays were successfully produced on glass substrates by interference laser lithography and electron beam lithography methods. Magnetic force microscopy (MFM) observation was carried out on fabricated nanodot arrays. MFM tip induced magnetization effects were clearly observed in ferromagnetic elliptical nanodots varying in material and aspect ratio. Fe-Cr dots with a high aspect ratio show reversible switching of the single domain magnetization state. At the same time, Co nanomagnets with a low aspect ratio exhibit tip induced transitions between the single domain and the vortex state of magnetization. The simple nanolithography is potentially an efficient method for fabrication of patterned magnetic arrays.