Ock Taeck Lim

Numerical study of the effects of exhaust gas recirculation stratification on reducing the rate of pressure rise in dimethyl ether homogeneous charge compression ignition combustion

This work investigates the potential of in-cylinder exhaust gas recirculation stratification for reducing the rate of pressure rise in dimethyl ether homogeneous charge compression ignition engines and its coupling with both thermal stratification and fuel stratification. Numerical analyses were performed using a five-zone version of the CHEMKIN-II kinetics rate code and the kinetic mechanics of dimethyl ether. The effects of inert components were used to represent the presence of exhaust gas recirculation in calculations. Three cases of exhaust gas recirculation stratification were tested in terms of both thermal stratification and fuel stratification at a fixed initial temperature, fixed initial pressure and fixed fuelling rate at bottom dead centre. In order to explore the appropriate stratification of exhaust gas recirculation, the exhaust gas recirculation width (defined as the difference between the exhaust gas recirculation ratios in zone 1 and zone 5 in the five-zone model) which we employed was from 0% to 30%. The case of exhaust gas recirculation homogeneity (called case 1), in which the exhaust gas recirculation width is 0%, was examined. In case 2, exhaust gas recirculation is located densely in a hot zone for combination with thermal stratification or in a fuel-rich zone for combination with fuel stratification. The last case (case 3) was the inverse of case 2. Ringing was reduced to an acceptable level in the case of fuel stratification with an appropriate exhaust gas recirculation distribution, which slowed the rapid burning during the compression stroke.

The Research about Free Piston Linear Engine fueled with Hydrogen using Numerical Analysis

This paper presents a research about free piston linear engine (FPLE) fueled with hydrogen, in which, numerical model was built to simulate the different processes that take place during the full stroke of engine. Dynamic model and thermodynamic model were used to predict piston speed, piston acceleration, in-cylinder pressure, indicated mean effective pressure (IMEP) and indicated efficiency. The compression ratio and bore were changed to provide information for the prediction. In this paper, the thermodynamic model was calculated based on an idealized Otto cycle, including compression, combustion and expansion. Simulation results show that velocity and acceleration increase when compression ratio and bore increase. Beside, by increasing compression ratio, IMEP and indicated efficiency also increase. On the contrary, by increasing bore, IMEP and indicated efficiency will decrease accordingly.

Study on Performance and Emission Characteristics of CNG/Diesel Dual-Fuel Engine

In a CNG/diesel dual-fuel engine, CNG is used as the main fuel and a small amount of diesel is injected into the cylinder to provide ignition priming. In this study, a remodeling of the existing diesel engine into a CNG/diesel dual-fuel engine is proposed. In this engine, diesel is injected at a high pressure by common rail direct injection (CRDI) and CNG is injected at the intake port for premixing. The CNG/diesel dual-fuel engine had an equally satisfactory coordinate torque and power as the conventional diesel engine. Moreover, the CNG alternation rate is over 89% throughout the operating range of the CNG/diesel dual-fuel engine. PM emission by the dual-fuel engine is 94% lower than that by the diesel engine; however, NOx emission by the dual-fuel engine is higher than that by the diesel engine.

Research on the Combustion and Emission Characteristics of the DME/Diesel Dual-fuel Engine

Abstract : This study investigates the potential of DME/Diesel dual fuel engine for reducing emissions with same power. Dual fuel engine controls the combustion using two different fuels, DME and diesel with different auto-ignition timings. In the previous work, the caracteristics of combustion and emissions under single cylinder engine and ignition is done by compression ignition. Pre-mixture is formed by injecting low-pressure DME into an intake manifold and high-pressure fuel (diesel or DME) is injected directly into the cylinder. Both direct diesel injection and port fuel injection reduced the significant amount of Smoke, CO and NOx in the homogeneous charge compression ignition engine due to present of oxygen in DME. In addition, when injecting DME directly in cylinder with port DME injection, there is no changes in emissions and energy consumption rate even operated by homogeneous charge compression ignition. Key words :Diesel(경유), Diffusion combustion(확산연소), DME(Di-Methyl-Ether, 디메틸 에테르), Direct Injection(직접분사), Emission (배출가스), Port injection(포트분사), Premixed combustion(예혼합연소)

Development of DME engines for light-duty trucks using a large EGR system

A light-duty truck diesel engine fueled with DME using a jerk-type in-line DME injection system which meets the JAPAN 2009 emissions regulation was developed. It includes lower exhaust emission technology such as a large exhaust gas recirculation (EGR) system with air-throttled and inter-cooled turbo-charging. The National Traffic Safety office, Environment Laboratory and BOSCH Corporation have demonstrated low-emission engines which reduce NOx emission levels to about 50% of the 2009 emissions regulation without a NOx reduction catalyst system.

The Investigation of Diesel Spray Combustion in DME HCCI Combustion

Abstract The purpose of the research is to investigate of diesel spray combustion for simultaneously reduction way of NOx and PM．The diesel injection were done into intermediates that are generated by very lean DME HCCI combustion using a RCM. The concentration of intermediate could not be directly measured, so we estimated it by CHEMKIN calculation. Two dimensional spontaneous luminescence images which are created by chemical species reaction at low temperature reaction (LTR) and high temperature reaction (HTR) are captured by using a framing streak camera. Also，combustion events were observed by high-speed direct photography. The ignition and combustion events were analyzed by pressure profiles and the KL values and flame temperatures were analyzed by the two-color method. 기호설명 HCCI : 예혼합압축자기착(Homogeneous Charge C ompression Ignition) HTR : 고온산화반응 (High Temperature Reaction) LTR : 저온산화반응 (Low Temperature Reaction) t LTR : 저온산화반응 시작시각 (ms) t HTR : 고온산화반응 시작시각 (ms) T LTR : 저온산화반응 시작온도 (K) T

An Experimental Study of Fuel Economy and Emission Characteristics for a Heavy-Duty DME Bus

*** 조상현 · **** 임옥택 · * 울산대학교 기계자동차공학부 한국에너지기술연구원 한국가스공사 연구개발원 * , ** , *** **** 전북자동차기술원 Abstract: The experimental test was conducted for a heavy-duty DME bus in JE-05 exhaust gas test mode using a chassis dynamometer, exhaust gas analyzers, and a PM measurement system. The heavy-duty DME bus was not equipped with after-treatment systems such as DOC or DPF. The dynamic behavior, emission characteristics, and fuel economy of the bus were investigated with an 8.0-liter, 6-cylinder conventional diesel engine. The results showed that the dynamic behavior in DME mode was almost the same as in diesel mode. However, there was little difference among the two operation modes for NOx and CO emissions. THC emissions were lower for DME mode than for diesel mode. Also, the amount of PM emissions was remarkably lower than for the diesel mode because DME contains a greater amount of oxygen than diesel. The data showed that CO2 emissions were almost similar in the two modes but fuel economy (calculated using heating value) was lower for DME mode than for diesel mode.

Numerical Analysis of Effect of Inhomogeneous Pre-mixture on Pressure Rise Rate in HCCI Engine by Using Multizone Chemical Kinetics

초록: HCCI 엔진은고효율, 저공해를실현할수있는차세대내연기관이다. 그러나HCCI 엔진이상용화되기위해서는몇가지문제점들이해결되어야한다. 그중에서가장큰문제점은과도한압력상승률이노킹을발생시키기때문에운전영역이제한되는것이다. 이번연구의목적은HCCI 엔진에서압력상승률저감을위하여온도성층화와농도성층화효과를조사하는것이다. 그리고 Multi-zone 모델을이용한화학반응수치해석을통하여연소및배기가스특성에미치는영향을알아보았다. 수치해석에서2 단계열발생을가지는DME와1단계열발생을가지는메탄을사용하였다.Abstract: The HCCI engine is a prospective internal combustion engine with which high diesel-like efficiencies and very lowNOx and particulate emissions can be achieved. However, several technical issues must be resolved before HCCI engines canbe used for different applications. One of the issues concerning the HCCI engine is that the operating range of this engine islimited by the rapid pressure rise caused by the release of excessive heat. This heat release is because of the self-acceleratedcombustion reaction occurring in the engine and the resulting engine knock in the high-load region. The purpose of this studyis to evaluate the role of thermal stratification and fuel stratification in reducing the pressure rise rate in an HCCI engine.The concentrations of NOx and CO in the exhaust gas are also evaluated to confirm combustion completeness and NOxemission. The computation is carried out with the help of a multizone code, by using the information on the detailedchemical kinetics and the effect of thermal and fuel stratification on the onset of ignition and rate of combustion. The engineis fueled with dimethyl ether (DME), which allows heat release to occur in two stages, as opposed to methane, which allowsfor heat release in a single stage.

The effects of inhomogeneity in DME-Air mixture in combustion chamber on homogeneous charge compression ignition combustion

In the HCCI Engine, the inhomogeneity exists in fuel distribution and temperature in the pre-mixture microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of the inhomogeneity in DME/n-Butane-Air mixture in the combustion chamber on the HCCl combustion was investigated by chemiluminescence method in order to understand the spatial distribution of the combustion. DME and n-Butane were used as a test fuel because those of combustion characteristics are different. First, in the 4-stroke optically accessible engine, after clarifying the relation between the heat release and the chemiluminescence from DME/n-Butane-Air mixture HCCl combustion, the effects of the inhomogeneity in fuel distribution in the pre-mixture on the heat release, flame structure and exhaust gas composition were evaluated. Next, HCCI combustion without the hot residual gas was realized in the 4-stroke engine and the rapid compression machine, and the effect of the inhomogeneity in temperature and gas composition due to the hot residual gas on the heat release and flame structure was evaluated.