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.

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.

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.

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.

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.

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 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.

설계변수에 따른 디젤 인젝터 캐비테이팅 유동에 관한 연구

염정국(Jeongkuk Yeom),정우성(Woosung Jeong),이무연(Mooyeon Lee),김시범(Sipom Kim),정성식(Sungsik Chung),하형수(Hyeongsoo Ha) 한국자동차공학회 2013 한국자동차공학회 지부 학술대회 논문집 Vol.2013 No.4

In this study, the CFD simulation analysis(ANSYS 13.0 CFX) about inner flow of the multi-hole injector was conducted directly. Based on these processes, DOE was applied to obtain the effect of injector nozzle design parameters on cavitation. The design parameters that is judged affecting cavitating flow are defined to nozzle hole diameter, nozzle hole length, nozzle hole angle and K-factor of the nozzle hole for design sensitivity and S/N ratio analysis. Also the 16 experimental points were used to analyze the effect of each parameter. In order to reveal inner flow of nozzle, the numerical analysis program and analysis of S/N ratio are applied in this paper. Consequently, it was founded that effect of K-factor is larger than any other parameters (hole diameter and hole angle) on generating cavitation.

증발장에서 에멀젼연료의 거동특성에 관한 연구

염정국(Jeong Kuk Yeom),윤정환(Jeong Hwan Yoon) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.3

본 논문은 에멀젼연료(Diesel/H₂O₂)에 있어 과산화수소의 혼합비가 혼합연료 액적증발 및 분무거동 특성에 미치는 영향을 연구하였다. 연료혼합을 위한 계면활성제는 span 80, tween 80을 9:1로 혼합하여 에멀젼연료 총 부피의 3%로 고정 혼합하였다. 또한 과산화수소의 혼합비율은 계면활성제의 혼합비를 고려하여 EF (Emulsified Fuel)0, EF2, EF12, EF22, EF32 및 EF42로 설정하였다. 에멀젼연료 액적의 증발특성을 관찰하기 위해 가열판에 액적 방울을 투하시켜 액적이 증발하는 현상을 산란광 및 쉴리렌기법을 통하여 촬영하였다. 또한 혼합비 변화에 따른 혼합연료의 분무거동특성을 해석하기 위하여 혼합연료 EF0~EF22를 선택하여 150℃로 유지된 정적용기에서 증발자유분무 거동해석 실험을 실시하였다. 그 결과 과산화수소의 혼합비율이 EF0보다 높은 EF22 에멀젼연료의 자유분무성장이 연료 속에 혼합된 과산화수소의 증발촉진으로 인하여 보다 신속하였다. In this study, the effects of the mixing ratio of emulsified fuel on the droplet evaporation and spray behavior characteristics were analyzed. A surfactant comprising span 80 and tween 80 mixed at a 9:1 ratio was used for the emulsified fuel. The fuel and surfactant were mixed at a ratio of 3:1 for the emulsified fuel. In addition, considering the mixing ratio of the surfactant, the mixing ratio of H₂O₂ in the emulsified fuel was set as EF (emulsified fuel)0, EF2, EF12, EF22, EF32, and EF42. To observe the evaporation characteristics, droplets of the emulsified fuel were dropped on a heating plate and observed using scattered light and a Schlieren system. In addition, to analyze the effect of the H₂O₂ mixing ratio, the behavior characteristics of the evaporative free spray were investigated in the mixing ratio range of EF0 to EF22 using a constant volume chamber with heaters. Consequentially, it was found that in the case of EF22, the free spray development of the emulsified fuel was faster than that of EF0 (diesel only) because of the promotion of the evaporation due to the phase change in the peroxide contained in the emulsion fuel.