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박상재(Sangjae Park),김성제(Sungjei Kim),최윤식(Yoonsik Choe) 대한전기학회 2009 정보 및 제어 심포지엄 논문집 Vol.2009 No.10
웨이블렛 변환은 영상압축에 효율적인 방법으로 알려져 있으며 구현하는 방법으로는 Lifting scheme이 널리 사용되고 있다. Lifting scheme을 구현하는 방식에는 예측-갱신(predict-update) 방식과 갱신-예측 (update-predict)방식이 있는데 갱신-예측 방식을 사용하면 적응적 예측과 정에서 방향선택에 관한 추가 정보를 보낼 필요가 없다는 장점이 있다. 본 논문에서는 갱신-예측 방식을 사용하여 부호화기 내에 복호화기를 포함한 구조에서 템플릿 매칭을 사용해서 효율적인 적응적 예측을 하고자 하는 알고리즘을 제시 하였다. 영상의 기울기 값을 이용한 Gerek 과 Cetin의 방법에 비해서 최대 약 0.10㏈정도의 성능 향상이 있었다.
박상재 ( Sangjae Park ),이상욱 ( Sanguk Lee ),배충식 ( Choongsik Bae ) 한국액체미립화학회 2018 한국액체미립화학회 학술강연회 논문집 Vol.2018 No.-
With high pressure gasoline direct injection, the Lean stratified combustion is a realizable solution to reduce loss in air exchange process of reciprocating internal combustion engine. However, due to the particle generation from the combustion process, the application of lean stratified combustion has been limited at commercialized vehicles. More gradient of stratification makes the combustion stable, but generates more locally rich mixture which could promote the soot generation. In other words, to accomplish stable combustion and low particle emission in stratified combustion, quite certain stratification between fuel cloud and surrounding air and well distributed fuel inside the cloud are required simultaneously. Therefore, in this study, by analyzing the spray and flame propagation of stratified combustion, the direction of injection strategies are suggested for cleaner gasoline stratified combustion. For the fuel injection process, an outwardly opening injector was applied to make hollow cone spray. The experiment was conducted under constant volume combustion chamber with elevated ambient pressure and temperature conditions. Higher ambient pressure make the atomization of spray enhanced, but the total area of spray was contracted. In addition, with higher temperature of surrounding air, the larger recirculation zones at inner and outer side of hollow cone, at relative upstream than lower case. The faster atomization and momentum dissipation was surly better to generate more homogeneous mixture. However, by overlapping of inner side recirculation zone, highly rich mixture was generated with elevated ambient temperature and pressure conditions. The locally rich mixture was observed as luminous flame in combustion process, with stationary position inside the hollow cone. On the other hand, low ambient pressure and temperature make the spray area larger, with retained momentum of spray. So that, the recirculation zone was smaller and more consistent than that of elevated temperature and pressure conditions. In combustion process, this consistent vortex generated locally rich mixture, and the larger area make the gradient of fuel ratio higher. As results of those, highly luminous flame was generated in the lower pressure and temperature condition, accompanying faster quenching of flame propagation. By summarizing these results, elevated pressure and temperature of surrounding air was better to reduce combustion loss and particle emission, but the overlapping of recirculation zone should be reduced to avoid the highly rich area inside the hollow cone. For engine application, more retarded injection would be better to reduce particulate emission and loss from combustion process.
박상재 ( Sangjae Park ),정진영 ( Jinyoung Jung ),배충식 ( And Choongsik Bae ) 한국액체미립화학회 2016 한국액체미립화학회 학술강연회 논문집 Vol.2016 No.-
In spark ignition engine, mixture formation process is critical issue to reduce emission from combustion, such as particulate matter. Smaller liquid droplet, higher homogeneity, and higher vaporization are pursued as target of direct injection technologies. But, due to limitation of plume direction and high vapor pressure of fuels, especially in wall-guided system, spray structure collapse under flashboiling conditions are rising as a supreme question to be avoided. Flashboiling is a spray expansion with drastic pressure drop of ambient across the vapor pressure. In spark ignition engine, cone-like-shaped spray were developed to achieve wallguided mixture formation, so that the injector nozzles have been optimized to the representative fuel; gasoline. By following the gasoline engine technologies, Liquefied Petroleum Gas (LPG) spray were also developed, but the spray shapes are significantly different due to higher vapor pressure and boiling characteristics. Typical conical sprays under flashboiling circumstances show a contracted shape with expanding shape after nozzle outlet, accompanying large penetration and recirculation vortex. But, the LPG, primarily composed with propane and n-butane, have quite different from gasoline spray, because it has different physical characteristics and it would be continuously exposed to boiling ambient condition. Each plume of LPG fuel spray was wider compare to gasoline spray, due to higher volatility and larger vapor pressure, so that the interaction between plumes was severe compare to typical liquid fuels. Accordingly, optimization processes of nozzle designs were necessary to achieve better mixture characteristics. In this paper, single-, double-, tripleand 6-hole nozzle were examined, and the influences of counter-bore on n-butane spray structure were identified. Under flashboiling conditions, the number of nozzles had impact on inter-plume interactions, more severe spray collapse with higher numbers. In addition to the number effects, counter-bore also make the spray structure sensitive to flashboiling, which could deteriorate mixing processes. But, in an aspect of penetration of the sprays, due to large momentum exchange of fuel droplet with evaporating n-butane, higher vaporizing rate under flashboiling could reduce spray penetration with less nozzle injectors. In case of 6 nozzle injector, the tendency followed that of liquid fuel spray, but with less number of nozzle than 3 the flaring tendency of penetrations was not observed. This transition was originated from high volatility of nbutane, which causes not only expansion of bubble in liquid core, also in each droplet to evaporate faster. To establish certain model for n-butane spray, the models in preceding researches are not sufficient, so that it is necessary to evaluate the evaporating character of the fuel in ambient and the design of injector nozzles in terms of spray structures.
미립화 및 분무장치 1 : 노즐 홀 출구 형상과 감압비등 현상이 직분식 다공 가솔린 인젝터의 노즐 출구 적심에 미치는 영향
박찬수 ( Chansoo Park ),박상재 ( Sangjae Park ),오희창 ( Heechang Oh ),이주헌 ( Juhun Lee ),배충식 ( Choongsik Bae ) 한국액체미립화학회 2015 한국액체미립화학회 학술강연회 논문집 Vol.2015 No.-
Nowadays, direct fuel injection into the engine cylinder technologies are becoming standard fuel injection regime in spark ignition engines. Unlike conventional port fuel injection (PFI) engines, Particulate matter (PM) emission from the direct injection spark ignition (DISI) engines is an important issue in the automotive industry due to stringent emission regulations. Fuel wetting on the surface of the injector nozzle tip has been pointed out as a major source of PM emission and injector tip fouling in the DISI engines. In the present study, the degree of gasoline fuel wetting on the surface of nozzle tip was evaluated, and the mechanism of injector tip wetting was explored. To measure the quantity of the wetted fuel, laser induced fluorescence (LIF) imaging technique was used. Fourth harmonic wavelength (266 nm) high intensity laser light from Nd:Yag laser was used as an excitation source. Emitted light from the wetted fuel was filtered by a bandpass filter (300-430 nm) and captured by intensified charge coupled device (ICCD) with a long distance microscope. Ambient conditions are adjusted to gasoline fuel injection timing of real engine operating conditions under different engine load, and experiment was performed in a constant volume chamber. From the result, a conventional step-hole shaped nozzle showed less fuel wetting than that of diverging shaped nozzle hole, and fuel wetting reduction potential of converging shaped concept can be expected even though it was hard to compare the results of the converging concept to the other concept. Fuel wetting under flash boiling conditions were higher than that under non-flash boiling conditions. In order to explore the mechanism of fuel wetting on the surface of the injection nozzle tip, back light illuminated spray imaging technique was utilized. The fuel wetting mechanism could be analyze through the transient fuel injection phenomenon including opening and closing events. Especially, it is thought that fuel wetting of wide near nozzle spray angle at the start of injection (SOI), transient spray angle fluctuation during the injection and low momentum liquid ligaments as well as droplets are main reasons of injector nozzle tip wetting.