• 한국자동차공학회논문집
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• 제25권3호
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• pp.326-335
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• 2017

It is known that diesel engines have the disadvantage of high emission levels of NOx and PM. Therefore, many combustion strategies have been developed to reduce these harmful NOx and PM emissions in a diesel engine. Among these strategies, HCCI(Homogeneous Charge Compression Ignition) and PCCI(Premixed Charge Compression Ignition) are the most popular as these can reduce NOx and PM simultaneously. However, when a single fuel like diesel is applied, it is difficult to control the combustion phase and this can lead to power reduction. In this study, premixed gasoline and pilot diesel were used to overcome the problems of controllability of the combustion phase and harmful emissions. We injected gasoline directly into the combustion chamber and the gasoline/air mixture was ignited with a pilot diesel fuel near the top dead center. The results showed that the combustion and emission characteristics of dual-fuel combustion were comparable to those of conventional diesel combustion. When we applied the dual-fuel PCCI combustion concept, more than 90 % of NOx and PM emission was reduced simultaneously without significant degradation of efficiency compared to conventional diesel combustion.

• 한국자동차공학회논문집
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• 제19권2호
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• pp.35-41
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• 2011

This work investigates the potential of in-cylinder thermal stratification and fuel stratification for extending the operating ranges in HCCI engines, and the coupling between thermal stratification and fuel stratification. Computational results areemployed. The computations were conducted using both a custom multi-zone version and the standard single-zone version of the Senkin application of the CHEMKINII kinetics rate code, and kinetic mechanism for di-methyl ether (DME). This study shows that the potential of thermal stratification and fuels stratification for extending the high-load operating limit by a staged combustion event with reduced pressure-rise rates is very large. It was also found that those stratification offers good potential to extend low-load limit by a same mechanism in high-load. However, a combination of thermal stratification and fuel stratification is not more effective than above stratification techniques for extending the operating ranges showing similar results of fuel stratification. Sufficient condition for combustion (enough temperature for) turns misfire in low-load limit to operate engines, which also leads to knock in high-load limit abruptly due to the too high temperature with high. DME shows a potential for maximizing effect of stratification to lower pressure-rise rate due to the characteristics of low-temperature heat release.

• 대한기계학회논문집B
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• 제35권9호
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• pp.869-874
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• 2011

CNG/diesel dual-fuel 엔진은 CNG 를 주 연료로 사용하고 소량의 디젤을 착화제로서 실린더 내에 분사한다. 본 연구에서는 기존의 디젤엔진을 커먼레일직접분사(CRDI)를 통하여 고압으로 디젤을 분사하고, 예혼합을 위하여 CNG 를 흡기포트에 분사하는 CNG/diesel dual-fuel 엔진으로 개조하였다. CNG/diesel dualfuel engine 은 기존의 디젤엔진과 동등한 수준의 토크 및 출력성능을 나타내었다. 또한, CNG 대체율은 CNG/diesel dual-fuel 엔진의 전체 운전영역에 대하여 89% 이상을 만족시켰다. Dual-fuel 엔진의 PM 배출농도는 디젤엔진보다 94% 더 낮게 나타났지만, NOx 배출농도는 더 높게 나타났다.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.80-86
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• 2008

Recently, controlled auto ignition(CAI) in gasoline engines are drawing more attentions due to its extremely low level of NOx emissions and potentials in lowering the fuel consumption rate. The one of the key techniques for realizing CAI combustion in engines is the control of valve system. Since the valve linkage system with higher complexity, or even earn-less valve systems, such as electro-hydraulic and electro-magnetic system, are adopted in CAI engines, it is not easy to estimate the valve lift profile from earn profiles. Therefore new measurement techniques for valve lift in CAI engines have been tried and tested. In this paper, hole type valve lift sensor was developed and tested to check the applicability in CAI engines. The valve lifts could be obtained from the sensor signal, which depends on the distance from the sensor to magnet attached to valve. Various engine speeds, ranging from 2,000 to 6,000 rpm, and valve lifts, maximum up to 9.7 mm, were tested. It was found that the sensor output for valve lift had accuracy of 98% in comparison with the basic specifications of valve lift through improvements of sensor driving circuit.

• 대한기계학회논문집B
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• 제34권5호
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• pp.449-456
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• 2010

HCCI 엔진은 고효율, 저공해를 실현할 수 있는 차세대 내연기관이다. 그러나 HCCI 엔진이 상용화되기 위해서는 몇 가지 문제점들이 해결되어야 한다. 그 중에서 가장 큰 문제점은 과도한 압력 상승률이 노킹을 발생시키기 때문에 운전영역이 제한되는 것이다. 이번 연구의 목적은 HCCI 엔진에서 압력상승률 저감을 위하여 온도 성층화와 농도 성층화 효과를 조사하는 것이다. 그리고 Multi-zone 모델을 이용한 화학반응 수치해석을 통하여 연소 및 배기가스 특성에 미치는 영향을 알아보았다. 수치해석에서 2 단계 열발생을 가지는 DME와 1단계 열발생을 가지는 메탄을 사용하였다.

• 한국분무공학회지
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• 제25권1호
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• pp.21-26
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• 2020

The objective of this work is to numerically reveal the effect of equivalence ratio change on the simultaneous reduction of NO_X and soot emissions from the simulated-EGR compression ignition engine containing CO₂. An experiment was conducted by using a single-cylinder common-rail injection system engine, an intake control system, and exhaust emissions analyzers. The numerical analysis results were validated under the same experimental conditions. To investigate the effect of equivalence ratio by simulated-EGR containing CO₂, the O₂, N₂, and CO₂ mole fraction were changed in the initial air conditions to the cylinder. The results were analyzed in terms of peak cylinder pressure, indicated mean effective pressure, indicated specific nitrogen oxide, and indicated specific soot. It was revealed that ignition delay characteristics and heat release rate (ROHR) characteristics were not significantly different according to the equivalence ratio. However, as the equivalence ratio increased from 0.68 to 0.83, the maximum combustion pressure and IMEP decreased by about 6.5% and 9.4%, respectively. In the case of ISFC, as is well known, the trend is opposite of IMEP. In the case of ISNO, as the equivalence ratio increased, less NO was generated, and as the equivalence ratio increased by 0.05, the ISSoot value of about 10% increased.

• 대한기계학회논문집B
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• 제34권10호
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• pp.941-946
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• 2010

1.7L 커먼레일 직접분사 디젤엔진에 대하여 바이오 디젤 연료가 conventional 연소(PM-NOx 트레이드오프 존재)와 저온 연소(low temperature combustion, LTC)에서 배기가스 배출에 미치는 영향을 분석하였다. LTC 연소는 conventional 연소 대비 다량의 EGR 과 연료분사 조건 최적화를 통하여 이루어졌다. 실험에 사용한 두 가지 연료는 초저유황 디젤연료(ultra low sulfur diesel fuel, ULSD), ULSD 에 대두유를 20%(vol. base)혼합한 바이오 디젤 연료(B20)이다. 사용된 연료에 관계없이 LTC 연소를 통하여 conventional 연소 대비 PM 및 NOx 의 동시 저감이 가능하였다. 동일한 엔진작동 조건에 대하여 conventional 연소의 경우 B20 는 ULSD 보다 PM은 적게 배출되나, NOx 는 많이 배출되었다. LTC 연소의 경우 B20 는 ULSD 보다 PM 및 NOx 생성이 많았다.

• 한국연소학회지
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• 제18권2호
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• pp.32-41
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• 2013

This study presents both experimental and numerical investigation of ignition delay time of n-heptane and n-butanol binary fuel. The $O_2$ concentration in the mixture was set to 9-10% to make high exhaust gas recirculation( EGR) rate condition which leads low NOx and soot emission. Experiments were performed using a rapid compression machine(RCM) at compressed pressure 20bar, several compressed temperature and three equivalence ratios(0.4, 1.0, 1.5). In addition, a numerical study on the ignition delay time was performed using CHEMKIN codes to validate experimental results and predict chemical species in the combustion process. The results showed that the ignition delay time increased with increasing the n-butanol fraction due to a decrease of oxidation of n-heptane at the low temperature. Moreover, all of the binary fuel mixtures showed the combustion characteristics of n-heptane such as cool flame mode at low temperature and negative-temperature-coefficient(NTC) behavior. Due to the effect of high EGR rate condition, the operating region is reduced at lean condition and the ignition delay time sharply increased compared with no EGR condition.

• 한국가스학회지
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• 제26권4호
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• pp.1-8
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• 2022

디젤엔진의 대체 연료로 연구되고 있는 청정연료인 DME는 디젤엔진의 중요한 문제 중 하나인 배기가스를 줄일 수 있으며, 세탄가와 산소함유량이 매우 높다. DME는 LPG와 유사한 특성을 가진 연료로 LPG 유통 인프라를 사용할 수 있다. 본 연구에서는 플런저식 고압펌프의 성능평가를 위해 토출된 질량유량에 대한 기초 데이터베이스 구축을 목표로 하였으며, 커먼레일 압력과 모터 회전속도를 변화시켜 플런저식 고압펌프의 질량유량을 분석하였다. 실험 조건은 커먼레일 압력을 300 bar, 400 bar, 500 bar 로 변경하였고, 모터 회전 속도를 300 rpm에서 1000 rpm 으로 증가시켰다. 실험 결과 두 경우 모두 질량유량이 증가하였다.

• 한국수소및신에너지학회논문집
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• 제34권1호
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• pp.59-68
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• 2023

In this study, the performance of high-pressure fuel pumps was compared to find a high-pressure pump suitable for dimethyl ether (DME) fuel, and to establish a database of basic data on flow rates. The use of DME in compression ignition engines can reduce pollutant emissions. The cetane value of DME is higher than that of diesel fuel. The physical properties of DME are similar to liquefied gasoline gas (LPG), and when pressurized at a pressure of 6 bar or more, it changes from gas to liquid. Two types of high pressure pumps used in this study were independent injection type pump and a wobble plate type pump. Two high-pressure pumps with different injection types were compared. By measuring and comparing the performance changes of the two high-pressure pumps, a pump suitable for DME was selected and performance improvement measures were proposed. The changed experimental conditions to measure the performance change of the high pressure pump were increased in the units of 100 to 1,000 rpm and 100 rpm, and the experiment was performed at common rail pressures 300 and 400 bar. it was confirmed that the DME inside the fuel supply system remained in a liquid state through temperature sensors, pressure sensors, and pressure gauges. As a result of the experiment, it was confirmed that the flow rate discharged from the high-pressure fuel pump increased as the motor rotational speed increased, and the flow rate of the high-pressure fuel pump