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디젤엔진 요소수 분사 SCR 시스템에서 촉매 내 암모니아 흡장량의 증가에 따른 NOx 저감효율 향상 특성에 관한 연구
김양화 ( Kim Yanghwa ),임옥택 ( Lim Ockteack ),김홍석 ( Kim Hongsuk ) 한국분무공학회 2020 한국액체미립화학회지 Vol.25 No.4
Nowadays, urea SCR technology is considered as the most effective NOx reduction technology of diesel engine. However, low NOx conversion efficiency under low temperature conditions is one of its problems to be solved. This is because injection of UWS (Urea Water Solution) is impossible under such a low temperature condition due to the problem of insufficient of urea decomposition and urea deposits. In several previous studies, it has been reported that appropriate control of the amount of ammonia adsorbed on SCR catalyst can improve the NOx conversion efficiency under low temperature conditions. In this study, we tried to find out how much the NOx conversion efficiency increases with respect to the amount of ammonia adsorbed on the catalyst, and what the temperature conditions that the ammonia slip occurs. This study shows the results of 8 times repeated WHTC test with a diesel engine, in which UWS was injected with NH<sub>3</sub>/NOx mole ratio of ‘1’. Through this study, it was found that 13% of the NOx conversion efficiency of WHTC increased while the θ (ammonia adsorption rate) increased from “0%” to “22%”. In addition, it is found that in cases of high θ value, the significant improvement of NOx conversion efficiency at low temperatures presented during the beginning period of WHTC and at high temperature and transient conditions presented during last part of WHTC test. The NH<sub>3</sub> slip occurring condition was 250℃ of catalyst temperature and 10% of θ, and the amount of NH3 slip increased as the temperature and θ are increased.
Multi-Zone 모델링을 통한 온도성층화와 농도성층화가 존재하는 DME HCCI 엔진의 운전영역 관한 수치해석연구
정동원(Dongwon Jeong),임옥택(Ockteack Lim) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
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 are employed. 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 Φ) 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 Φ. DME shows a potential for maximizing effect of stratification to lower pressure-rise rate due to the characteristics of low-temperature heat release.
디젤 엔진의 저온 NOx 저감특성 향상을 위한 Cu-SSZ-13 zeolite 촉매의 저온 산점 암모니아 흡탈착량 분석 연구
김양화(Yanghwa Kim),김홍석(Hongsuk Kim),임옥택(Ockteack Lim) 한국자동차공학회 2021 한국자동차공학회 부문종합 학술대회 Vol.2021 No.6
디젤 자동차에서 배출되는 NOx(질소산화물)은 대도시 대기오염의 주요 원인 중의 하나이다. 세계 여러 나라에서 NOx 규제를 지속적으로 강화하고 있으며, 보다 더 우수한 성능을 갖는 NOx 저감 기술개발이 계속되고 상황이다. SCR(Selective Catalytic Reaction, 선택적 환원 촉매) 기술은 디젤 엔진의 가장 효과적인 NOx 저감 기술로 손꼽히고 있으나 저온 조건에서의 낮은 NOx 저감효율은 개선이 필요하다. 이전의 여러 연구에서 SCR 촉매의 암모니아 흡장반응에 대해 다양한 연구를 진행하였다. 이로부터 이온교환된 지올라이트의 암모니아 흡장 및 탈착 특성에 대한 이해의 폭을 넓히게 되었으며, 암모니아 흡착량을 증가시키는 등 적절하게 제어하면 저온조건에서 NOx 전환 효율을 향상시킬 수 있다는 연구결과가 제시되기도 하였다. 그러나 저온 SCR 반응에 중요한 염기성의 암모니아가 결합되는 산점(acid sites)의 종류와 양, 그리고 암모니아와 산점 사이의 반응 메케니즘 등에 대한 연구가 부족하여 저온 SCR 반응을 이해하고, 제어하여 NOx 저감 효율을 개선하는데 어려움이 있어왔다. 본 연구에서는 열적 내구성이 우수하여 자동차용으로 주로 사용되는 Cu-SSZ-13 zeolite 촉매를 이용하여 암모니아흡장 특성에 대해서 연구하였다. 이와 같은 연구를 활용하여 향후 저온에서 NOx 저감효율을 높이고자 하는 것이 본 연구의 목적이다. 먼저, 본 연구에서는 저온 standard SCR 반응 메케니즘 중에서 암모니아의 acid sites 흡착과정이 NO 분자를 환원하는데 어떤 역할을 하는지 문헌연구를 통해 고찰하였다. 또한 저온에서 Cu-zeolite 촉매에 암모니아를 일정량 분사한 후, TPD(Temperature- programmed desorption) 방법으로 점차적으로 온도를 높이는 실험을 진행하였다. 이상의 연구를 통해서 Cu-zeolite의 acid sites를 구분/정의하였으며, acid sites에 암모니아가 흡착되는 순서와 흡착량을 정량화하였다. 이와 같은 연구결과는 향후 저온 조건에서의 SCR 효율 향상을 위해 암모니아 acid sites를 어떻게 제어해야 하는지에 대한 중요한 정보를 제공할 것으로 보인다.
수치해석을 이용한 DME HCCI 엔진의 열적성층화 효과에 대한 메커니즘 연구
오충환(Chunghwan Oh),나랑후 잠스란(Narankhuu Jamsran),임옥택(Ockteack Lim) 한국자동차공학회 2012 한국자동차공학회 지부 학술대회 논문집 Vol.2012 No.11
Homegeneous charge compression igrition(HCCI) engine has been attracted as the potential engine combustion process which has high efficiency and low-emission. However, there is one task to be solved. In the high-load range, the engine operating range is limited because of the knocking. To solve this problem, some studies to reduce the cause of rapid combustion have being progressed. In this study, some numerical analyses were conducted to analyze mechanisms on the thermal stratification effects. Under the condition of the I degree, the reaction timing of low-tempenture oxidation and high-temperature oxidation according to variation of initial temperature was considered. Also, when the width of thermal stratification was varied, it considered that the change of low-temperature oxidation and high-temperature oxidation.
수치해석을 이용한 DME HCCI 엔진의 열적성층화 효과에 대한 메커니즘 연구
오충환(Chunghwan Oh),나랑후 잠스란(Narankhuu Jamsran),임옥택(Ockteack Lim),정재훈(Jaehoon Jung) 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11
Homogeneous charge compression ignition(HCCI) engine has been attracted as the potential engine combustion process which has high efficiency and low-emission. However, there is one task to be solved. In the high-load range, the engine operating range is limited because of the knocking. To solve this problem, some studies to reduce the cause of rapid combustion have being progressed. In this study, some numerical analyses were conducted to analyze mechanisms on the thermal stratification effects. Under the condition of the 1 degree, the reaction timing of low-temperature oxidation and high-temperature oxidation according to variation of initial temperature was considered. Also, when the width of thermal stratification was varied, it considered that the change of lowtemperature oxidation and high-temperature oxidation.
예혼합기의 성층화 상태가 DME HCCI 연소에 미치는 영향에 관한 수치해석 연구
정동원(Dongwon Jeong),Soyol-Erdene,권오석(Oseock Kwon),임옥택(Ockteack Lim) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
It has been known from numerical analysis that HCCI combustion can be significantly affected by thermal and fuel stratification of the in-cylinder gas. With the same combustion timing (CA50), large thermal and fuel stratification tends to prolong the combustion duration and lower down the in-cylinder pressure-rise rate that make HCCI engines be operated at high load. Numerical analysis on pre-mixture having 40K thermal width with 0.15 fuelling width is presented for predicting the change of Pressure-rise rate and IMEP in four cases. Furthermore, comparing pressure traces of four cases with those of thermal stratification and fuel stratification. The fuel used, Di-Methyl-Ether (DME) which indicates two-stage auto-ignition has less cycle-to-cycle variation so that potentially can help effects of thermal and fuel stratification to expand operating range in DME HCCI engine.