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염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The effects of density change in ambient gas on mixture formation process have been investigated in high temperature and pressure field. To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Ambient gas density was selected as experimental parameter. The ambient gas density was changed from ㎩=5.0㎏/㎥ to ㎩=12.3㎏/㎥ with a high pressure injection system(ECD-U2). For visualization of the experiment phenomenon, a CVC(Constant Volume Chamber) was used in this study. The ambient temperature and injection pressure are kept as 700K and 72㎫, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas.
염정국(Jeongkuk Yeom),박종상(Jongsang Park),김시범(Sipom Kim),정성식(Sungsik Chung),하종률(Jongyul Ha) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.7
The characteristics of combustion process in an internal combustion engine are affected by the mixing process between injected fuel and ambient gas. Therefore, it is necessary to understand the mixture formation process of diesel spray. In this study, the spray structure was visualized by the exciplex fluorescence method, which can provide the simultaneous 2-D images of vapor and liquid phase in inner spray. For accurate investigation, the liquid-phase images were recorded with a 35mm still camera and CCD camera. Consequentially, it could be confirmed that the high-concentration vapor phase is formed in the region of spray tip and the edge of the liquid phase where droplets exist in the evaporating diesel spray, and the formed vapor is spread by diffusion. Also, the distribution of vapor is determined by the motion of droplets that exist in the edge of the liquid phase and the spray-tip region.
상변화를 동반하는 디젤분무의 혼합기형성과정에 대한 고찰
염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.10
In this study, the effects of change in ambient gas viscosity on spray structure have been investigated on the high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Also emissions of diesel engines can be controlled by the analyzed results. Therefore, this study examines the evaporating spray structure in the a constant volume chamber. The viscosity of ambient gas was selected as the experimental parameter, is changed from 21.7 μPaㆍs 32.1 μPaㆍs by change in ambient gas temperature. In order to obtain images of the liquid and vapor-phase of injected spray, exciplex fluorescence method was used in this study. The liquid and vapor-phase images were respectively taken with 35mm still camera and CCD camera. Consequentially, it could be confirmed that the distribution of vapor concentration is more uniform in the case of the ambient gas with high viscosity than in that of the ambient gas with low viscosity.
염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.6
In this study the penetration distance of liquid phase fuel(i. e. liquid phsae length) was investigated in evaporative field. An exciplex fluorescence method was applied to the evaporative fuel spray to measure and investigate both the liquid and the vapor phase of the injected spray. For accurate investigation, images of the liquid and vapor phase regions were recorded using a 35㎜ still camera and CCD camera, respectively. Liquid fuel was injected from a single-hole nozzle (l/d=1.0㎜/0.2㎜) into a constant-volume chamber under high pressure and temperature in order to visualize the spray phenomena. Experimental results indicate that the liquid phase length decreased down to a certain constant value in accordance with increase in the ambient gas density and temperature. The constant value, about 40㎜ in this study the, is reached when the ambient density and temperature of the used fuel exceed critical condition.
하동흔(Dongheun Ha),김민철(Mincheol Kim),박종상(Jongsang Park),염정국(Jungkuk Yeum),하종률(Jongyul Ha),정성식(Sungsik Chung) 한국자동차공학회 2008 한국자동차공학회 지부 학술대회 논문집 Vol.2008 No.11
This study was carried out to investigate the availability of using CNG fuel in a commercial two-cylinder gasoline engine and to derive the optimum performance of the engine. The results of this study is used to determine the optimized injection quantity at the time of dual injection and to improve the engine efficiency through comparing and investigating the performance of a PFI(Port Fuel Injection) and a sub-chamber DI(Direct Injection) type engine in order to establish the base of using PFI and sub-chamber DI type together in a multi-cylinder engine. A gasoline engine was adapted for this study, and air excess ratio was controlled using Lambda sensor and handle accelerator, and spark timing and injection timing were controlled using the ECU that was made personally. Combustion characteristics in accordance with air excess ratio and injection timing were investigated by multi-point injection using CNG fuel. On the basis of PFI type, the standard of fuel injection duration is obtained and it is applied to DI type. According to the air excess ratio, in-cylinder pressure, rate of heat release, IME(Indicated Mean Effective pressure), mass fraction burned, COVimep(Coefficient Of Variation), and so on are derived. As a result, the engine operation in PFI type is the safest at stoichiometric ratio and the engine operation in sub-chamber DI type is the safest at lean mixture ratio. This result is applied to the next study in order to obtain the optimized injection quantity and to improve the efficiency.
직분식 CNG 엔진에서 연료공급 조건이 연소와 출력 특성에 미치는 영향
강정호(Jeongho Kang),염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_1
A CNG fuel is one of the most promising alternative fuels because of lower exhaust emissions and lower CO₂ emission with high thermal efficiency. However, the brake horse power is reduced because a CNG fuel has a low volumetric efficiency due to the gaseous charge and increase in time losses with lower burning speed as compared with gasoline fuel. To solve these problems, the DI Diesel Engine was modified to the DI CNG engine which a spark plug was mounted on the engine cylinder head. The purpose of this study is to investigate the effect of different injection conditions (early injection mode, late injection mode) on combustion and performance in the DI CNG engine. The combustion characteristics of the DI CNG engine such as in-cylinder pressure, cycle variation, combustion duration and emissions were investigated in this study. The results show that late injection timing during the compression stroke significantly extended lean limit in the low load. Consequently, it could be verified that the overall combustion duration and lean limit were improved by using the variation of injection timing and the stratification was controlled by injection timing in the DI CNG engine.
직접분사식 CNG 엔진에서 연료공급 조건이 연소에 미치는 영향
강정호(Jeongho Kang),염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 한국자동차공학회 2005 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-
CNG fuel is one of the most promising alternative fuels because of lower exhaust emissions and lower CO2 emission with high thermal efficiency. However, the brake horse power is reduced because a CNG fuel has a low volumetric efficiency due to the gaseous charge and increase in time loss with lower burning speed as compared with gasoline fuel. To solve these problems, the DI Diesel Engine was modified to the DI CNG Engine which directly supplies natural gas into the engine cylinder. The combustion characteristics of the Dl CNG engine such as cylinder pressure, cycle variation, combustion duration and emissions were investigated in this study. Consequently, it could be verified that the volumetric efficiency, overall combustion duration and lean limit were improved by using DI technique in the CNG Engine.
강정호(Jeongho Kang),염정국(Jeongkuk Yeom),정성식(Sungsik Chung),하종률(Jongyul Ha) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
A CNG fuel is one of the most promising alternative fuels because of lower exhaust emissions and lower CO2 emission with high thermal efficiency. However, the brake horse power is reduced because a CNG fuel has a low volumetric efficiency due to the gaseous charge and increase in time loss with lower burning speed as compared with gasoline fuel. To solve these problems, the DI Diesel Engine was modified to the DI CNG Engine which directly supplies natural gas into the engine cylinder. The combustion characteristics of the DI CNG engine such as cylinder pressure, cycle variation, combustion duration and emissions were investigated in this study. Consequently, it could be verified that the volumetric efficiency, overall combustion duration and lean limit were improved by using DI technique in the CNG Engine.