An experimental study on the effects of impingement-walls on the spray and combustion characteristics of SIDI CNG

염정국,정성식,Liu Yu 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.8

Compressed natural gas (CNG) is regarded as one of the most promising alternative fuels, and maybe the cleanest fuel for the sparkignition (SI) engine. In the SI engine, direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need of throttle valve. During low load and speed conditions, DI allows engine operation with the stratified charge, and the use of extremely lean fuel-air mixture enables relatively higher combustion efficiency. In this study, a combustion chamber with a visualization system is designed. The spray development and combustion propagation processes SIDI CNG were digital recorded. It was found that high injection pressure reduced the ignition probability significantly because of quenching of flame kernel. To improve the ignition probability, three kinds of impingement-walls were designed to help the mixture preparation. It was found that the CNG-air mixture can be easily formed after spray-wall impingement and the ignition probability was also improved. The results of this study can contribute important data for the design and optimization of spark-ignition direct injection (SIDI) CNG engine.

증발디젤분무의 발달 과정에 관한 연구

염정국,박종상,정성식,하종률,김시범,Yeom, Jeong-Kuk,Park, Jong-Sang,Chung, Sung-Sik,Ha, Jong-Yul,Kim, Si-Pom 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.3

In this study, the effects of change in ambient gas viscosity on spray structure have been investigated in the high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Emissions of diesel engines can be reduced by the control of the mixture formation process. Therefore, this study examines the evaporating spray structure in the constant volume chamber. The viscosity of ambient gas was selected as the experimental parameter, is changed from 21.7 mPa s to 32.1 mPa s by changing 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 taken with 35mm still camera and CCD camera, respectively. 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.

증발디젤분무의 혼합기 형성과정에 대한 열역학적 접근

염정국 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.03

The focus of this work is placed on the analysis of the mixture formation process under the evaporative diesel-free spray conditions. In order to examine homogeneity of mixture within the vapor phase region of the injected spray, image analysis was carried out based on the entropy of statistical thermodynamics. As an experimental parameter, the injection pressure and ambient gas density were selected, and effects of the injection pressure and density variation of ambient gas on the mixture formation process in the evaporative diesel spray were investigated. In the case of application of the thermodynamic entropy analysis to evaporative diesel spray, the value of the dimensionless entropy always increases with increase in time from injection start. Consequently, the dimensionless entropy in the case of the higher injection pressure is higher than that of lower injection pressure during initial injection period.

Diagnosis of the behavior characteristics of the evaporative diesel spray by using images analysis

염정국 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.9

In this study, the effects of change in injection pressure 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 a constant volume chamber. The injection pressure is selected as the experimental parameter, is changed from 72 MPa to 112 MPa with a high pressure injection system (ECD-U2). The PIV (Particle Image Velocimetry) technique was used to capture behavior variation of the evaporative diesel spray. Analysis of the mixture formation process of diesel spray was executed by the results of flow analysis in this study. Consequentially the large-scale vortex flow could be found in downstream spray and the formed vortex governs the mixture formation process in diesel spray.

Diagnosis of the behavior characteristics of natural gas jet

염정국 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.1

We analyzed natural gas fuel (Methane, CH4) jet at STP (standard temperature and pressure) using a commercial program, ANSYSCFX release 11.0, and compared the results with experimental ones obtained by using shadowgraph method. The combined MCM(multicomponentmodel) and k-ε turbulence model is used in the simulation. Injection pressure is selected as a main parameter in both experimentaland numerical study. In the analysis, longer jet tip penetration was measured each time after start of injection for high injectionpressure. Also, the process of mixture formation before combustion was examined by comparing the experimental and the numericalresults on the behavior of jet and ambient gas flow. It was found that the experimental and the numerical results are consistent with eachother. Further, the use commercial CFX program for the analysis of the macro jet behavior characteristics such as jet tip penetration, andflow of ambient gas can be recommended. In particular, in the analysis of the jet development process it is important to investigate themixture formation by the interaction between the injected fuel and ambient gas.

A Proposal of Quantitative Analysis Method of Emission Characteristics of Biodiesel Fuel in Diesel Engine

염정국,윤정환 한국정밀공학회 2015 International Journal of Precision Engineering and Vol.16 No.7

In this study, the exhaust characteristics of the diesel engine for the change of the mixing ratio of biodiesel fuel were quantitatively analyzed by using the numerical analysis method. As the fuel in the experiment, the diesel and biodiesel (waste cooking oil, soybean oil), mixture BD2 (diesel only), BD3, BD5, BD20, BD50 and BD100 were used. The injection pressure (pinj) was set at 400 bar, 600 bar, 800 bar, 1000 bar and 1200 bar as the experimental variables. The concept of the standard deviation, Pearson’s correlation coefficient and Spearman rank-order correlation coefficient based on the statistics were introduced in order to analyze the exhaust characteristics of the quantitative NOx and Soot according to the injection pressure and the mixing ratio of biodiesel blended fuel. The regression method was introduced in order to obtain the increasing and decreasing aspects of NOx and Soot that can not be known from the correlation coefficients alone. From the study it is inferred that, for the waste cooking oil, NOx and Soot can be simultaneously reduced through control of the mixing ratio in the region of pinj=400 bar and pinj=600 bar, and the Soot can be reduced without affecting the emission of NOx for pinj more than 800 bar. For the soybean oil, NOx and Soot can be simultaneously reduced at pinj=400 bar and the Soot can be reduced without affecting the emission of NOx at pinj=600 bar.

연료의 임계조건을 고려한 디젤 액상분무거동에 관한 연구

염정국,박종상,김시범,정성식,하종률 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.5

Effect of Fuel Injector-type Spark Plug on Combustion Characteristics

염정국,정성식 한국분무공학회 2009 한국액체미립화학회지 Vol.14 No.4

This study proposes a new stratified charge system for low emission and ultra lean burn. In order to examine combustion characteristics of the new system, sparkplug with a hole at positive pole and a common CNG injector for injecting fuel were used in this study as injector-type spark plug. The new stratified charge system injects fuel of extremely small quantities and ignites mixture around sparkplug gap. Also, the system was fitted in a visualized constant volume chamber. Then, for analysis of the combustion characteristics, we examined combustion pressure, lean inflammable limit, and visualized combustion flame according to equivalence ratio by comparison with homogeneous charge (HC) method and the new stratified charge (SC) method. As results of this study, in the case of using this system, the propagation speed of initial flame was increased and total combustion period was reduced in the ultra lean burn in the same equivalence ratio. These phenomena occurred clearly under the conditions of lean equivalence ratio. Furthermore, the lean inflammable limit of mixture was extended by using the injector-type spark plug.

디젤-과산화수소 에멀젼연료의 증발거동특성에 관한 연구

염정국(Jeong Kuk Yeom) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.12

본 연구는 디젤-과산화수소 에멀젼연료의 과산화수소 혼합비가 증발특성에 미치는 영향을 분석하였다. 실험에 사용한 에멀젼연료의 디젤과 과산화수소를 혼합하기 위해 계면활성제를 전체 체적의 3%로 고정하여 혼합하였고 과산화수소의 혼합비가 다른 5종류(EF2, EF12, EF22, EF32 및 EF42)의 에멀젼연료를 사용하여 실험을 실시하였다. 실험은 가열판을 이용하여 에멀젼연료 액적 한 방울의 증발을 관찰하였고, 증기의 가시화를 위해 쉴리렌방법을 이용하였다. 또한 실험결과를 토대로 상용프로그램을 사용하여 수치해석을 실시하였다. 본 연구의 결과로서 에멀젼연료 내 과산화수소의 증발로 인해 발생하는 미세폭발현상을 관찰할 수 있었고, 혼합비가 증가할수록 증발이 활발해지는 것을 확인하였다. 또한 수치해석으로 과산화수소 체적분율 계산을 통하여 미세폭발현상의 모사 방법을 제안하였고, 그 결과를 실험해석으로 구한 결과와 비교 · 검토하여 사용한 수치해석 방법의 유효성을 확인하였다. In this study, the effects of the mixing ratio of hydrogen peroxide in diesel-hydrogen peroxide emulsified fuels were analyzed using evaporative characteristics. A surfactant with 3 of total volume was added to create an emulsified fuel of diesel and hydrogen peroxide. An experimental study was conducted on mixing ratios in five diesel and hydrogen peroxide fuels (EF2, EF12, EF22, EF32, and EF42). In this experiment, one droplet of emulsified fuel was evaporated using a heat plate, and the Schlieren method was used to visualize the vapor. Furthermore, a numerical analysis was conducted based on the experimental results using a commercially available program (ANSYS CFX). These results showed that a micro-explosion was caused by the evaporation of the hydrogen peroxide in the emulsified fuel, and as the mixing ratio increased, the evaporation became active. Additionally, a simulation of the micro-explosion was proposed via calculation of the volume fraction of hydrogen peroxide.

선박엔진용 릴리프 밸브에 관한 연구

염정국(Jeong Kuk Yeom) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.12

본 연구에서는 크랭크케이스의 급격한 압력상승 방지와 함께 화염을 차단할 수 있는 선박용 대형엔진을 위한 크랭크케이스 릴리프 밸브(Crankcase relief valve) 설계를 위해 열․구조 해석을 수행하였다. 수치해석은 범용유한요소해석 프로그램인 ANSYS를 이용하였고, 크랭크케이스에서의 시간에 따른 압력변화를 적용하여 해석을 진행하였다. 또한 고압 하에서 부품의 정상작동을 보장하기 위하여 5가지 형상의 플레임 트랩에 대하여 열 · 구조해석을 수행하여 최대응력 및 온도가 최소로 되는 형상을 결정하였다. 다음의 수치해석 결과를 바탕으로 미로형 밸브 디스크를 제조하여 릴리프 밸브 장착 전후의 폭발현상을 비교하였다. 그 결과, 폭발 시의 초과압력을 외부로 배출하면서 화염의 외부배출을 차단하는 릴리프 밸브의 유효성을 확인하였다. In this study, thermal and structural analyses are carried out to design a crankcase relief valve for marine diesel engines that are capable of preventing the flame and sudden pressure rise of the crankcase. Numerical analyses are performed using a commercial program (ANSYS), and by applying the pressure change according to the time in the crankcase. In order to ensure the normal operation of the part under high pressure, thermal and structural analyses of five types of flame traps are performed to determine the shape using the maximum stress and minimum temperature. Based on the numerical analysis results, the maze-type valve disk was manufactured. The explosion phenomenon was compared before and after mounting the relief valve. As a result, the effectiveness of the relief valve was confirmed by the prevention of the external discharge of the flame while discharging the excess pressure during an explosion.