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.

Multi-zone 모델링을 통한 온도성층화와 농도성층화가 존재하는 DME HCCI 엔진의 운전영역에 관한 수치해석연구

정동원(Dongwon Jeong),임옥택(Ocktaeck Lim) 한국자동차공학회 2011 한국 자동차공학회논문집 Vol.19 No.2

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.

온도 성층화를 갖는 예혼합압축자기착화엔진에서 부스터 효과에 관한 수칙해석

정동원(Dongwon Jeong),권오석(Oseok Kwon),임옥택(Ocktaeck Lim) 한국자동차공학회 2009 한국 자동차공학회논문집 Vol.17 No.6

The method of thermal stratificationin cylinder is known for reducing rate of pressure rise, but which has its limit to extend the higher-load operating region of HCCI engines, giving an output of insufficient IMEP. High fueling rate could be one way to get the enough IMEPbut it could be occurring engine knock. This work investigates the potential of in-cylinder thermal stratification for reducing the rate of pressure rise in DME HCCI engines, and the coupling between thermal stratification and booster effect to get reduced rate of pressure rise as well as high IMEP. The computations were conducted using Senkin application of the CHEMKINll kinetics rate code, and kinetic mechanism for Di-Methyl Ether (DME). DME has unique 2 stage reaction called Low Temperature Reaction (LTR) and High Temperature Reaction (HTR). Due to the heat release from LTR, the thermal stratificationof in-cylinder would be formed just before HTR with large temperature difference so the heat release from oxidation reaction dispersed through combustion process. Intensity of intake pressure is closely concerned in input calorie which means a higher IMEP would be appeared without high fueling rate. The study also shows that increasing the in-cylinder thermal width of the charge between each zone would allow the booster pressure to be raised from 0.1㎫ to 0.18㎫ to get the higher IMEP as well as high thermal efficiency with low emissions.

온도 성층화를 갖는 예혼합압축자기착화엔진에서 Booster 효과에 관한 수치해석

정동원(Dongwon Jeong),권오석(Oseock Kwon),임옥택(Ocktaeck Lim),박규열(Kyuyeol Park) 한국자동차공학회 2009 한국자동차공학회 부문종합 학술대회 Vol.2009 No.4

The method of thermal stratification in cylinder is known for reducing rate of pressure rise, but which has its limit to extend the higher-load operating region of HCCI engines, giving an output of insufficient IMEP. High fueling rate could be one way to get the enough IMEP but it could be occurring engine knock. This work investigates the potential of in-cylinder thermal stratification for reducing the rate of pressure rise in DME HCCI engines, and the coupling between thermal stratification and booster effect to get reduced rate of pressure rise as well as high IMEP. The computations were conducted using Senkin application of the CHEMKINll kinetics rate code, and kinetic mechanism for Di-Methyl Ether (DME). DME has unique 2 stage reaction called Low Temperature Reaction (LTR) and High Temperature Reaction (HTR). Due to the heat release from LTR, the thermal stratification of in-cylinder would be formed just before HTR with large temperature difference so the heat release from oxidation reaction dispersed through combustion process. Intensity of intake pressure is closely concerned in input calorie which means a higher IMEP would be appeared without high fueling rate. The study also shows that increasing the in-cylinder thermal width of the charge between each zone would allow the booster pressure to be raised from 0.1㎫ to 0.18㎫ to get the higher IMEP as well as high thermal efficiency with low emissions.

온도 성층화를 갖는 예혼합압축자기착화엔진에서 부스터 효과에 관한 수치해석

정동원(Dongwon Jeong),임옥택(Ocktaeck Lim),백영순(Youngsoon Baek) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The method of thermal stratification in cylinder is known for reducing rate of pressure rise, but which has its limit to extend the higher-load operating region of HCCI engines, giving an output of insufficient IMEP. High fueling rate could be one way to get the enough IMEP but it could be occurring engine knock. This work investigates the potential of in-cylinder thermal stratification for reducing the rate of pressure rise in DME HCCI engines, and the coupling between thermal stratification and booster effect to get reduced rate of pressure rise as well as high IMEP. The computations were conducted using Senkin application of the CHEMKINII kinetics rate code, and kinetic mechanism for Di-Methyl Ether (DME). DME has unique 2 stage reaction called Low Temperature Reaction (LTR) and High Temperature Reaction (HTR). Due to the heat release from LTR, the thermal stratification of in-cylinder would be formed just before HTR with large temperature difference so the heat release from oxidation reaction dispersed through combustion process. Intensity of intake pressure is closely concerned in input calorie which means a higher IMEP would be appeared without high fueling rate. The study also shows that increasing the in-cylinder thermal width of the charge between each zone would allow the booster pressure to be raised from 0.1 ㎫ to 0. 18㎫ to get the higher IMEP as well as high thermal efficiency with low emissions.

히트펌프를 이용한 급탕 탱크에서의 온도 성층화에 대한 실험적 연구

김진만,임태훈,하만영 대한설비공학회 2019 설비공학 논문집 Vol.31 No.11

The heat energy storage of the domestic hot water system is an energy management technology that efficiently stores and supplies heat energy when needed. One of these thermal energy storage technologies, the water heat storage method using sensible heat, is a method commonly used for heating water at residential facilities. According to the heat exchange method for accumulating heat, there are indirect heating methods using a heating coil in the tank and the direct heat exchange method from water circulating with the heat pump. In this study, the stratification performance and COP of the heat storage tank were reviewed through experiments. It can change the heat exchange method inside the hot water tank from hot water generated by the heat pump system as the result of the stratification experiment of the hot water tank. It is confirmed that the mixing state was formed in both experiments, and that there was no formation effect of the variable temperature layer. 본 연구에서는 가정용 히트펌프 시스템에서 생성된 온수를 급탕탱크 내에서 열교환하는 방식을 달리하여 축열 탱크 성층화 성능 및 COP를 실험을 통해 고찰하였다. 이를 통해 다음과 같은 결론을 도출하였다. (1) 초기 시작 온도 30℃에서 목표 온도인 50℃까지 도달 시간은 직접 열교환 방식이 간접 가열코일 방식 대비 10분 단축됨을 확인하였다. 이는 열교환 효율 차이에 의한 결과로 동일한 시간 기준 시 직접 열교환 방식의 열교환 효율이 상대적으로 높음을 알 수 있다. 목표 온도까지의 시스템 운전 시간을 줄일 수 있어 가정용 급탕 부하에 더 효과적으로 대응할 수 있음을 의미한다. (2) 탱크 내 성층화 측면에서는 두 가지 실험 모두에서 혼합 상태가 형성됨을 확인하였고, 변온층의 형성 효과는 없는 것으로 확인하였다. 직접 열교환 방식의 경우, 워터 펌프에 의해 만들어지는 강제 대류가 부력에 의해 생성되는 변온층 형성을 방해하기 때문이다. 간접 가열코일의 경우, 히트펌프에서 공급되는 온수가 나선형의 간접 가열코일을 순환하여 코일 상층부에 고온을 형성하기는 하나 급탕탱크 내에 접촉하는 표면적이 적어 탱크 성층화를 형성하기에는 부족함을 실험 결과를 통해 확인하였다. (3) 히트펌프 COP 측면에서는 직접 열교환 방식이 간접 코일 방식 대비 14% 정도 우수함을 확인하였다. 이는 간접 가열코일 사용 시 열교환 효율 저하 및 히트펌프의 고압 운전에 기인한다. 히트펌프를 이용한 급탕시스템 설계 시 고장에 의한 소비자의 피해 방지를 위해 간접 가열코일의 적용을 권장하고 있다. 따라서 간접 코일을 적용한 가정용 급탕시스템의 효율 향상을 위한 간접 코일의 형상 및 믹싱밸브를 적용한 온수 제어 기술에 대한 추가 연구가 필요하다.

온도 성층화를 갖는 예혼합압축자기착화엔진에서 초기압력변화에 관한 연구

권오석(O Seok Kwon),처거(G.Tsogtjargal),임옥택(Ock Taeck Lim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

HCCI engine is next generation engine, which has high efficiency and low emission. HCCI engine can be an alternative of SI engine and DI engine. However a pressure rise rate is a major cause of limitation of high load range and power reduction. Recently, we are able to reduce pressure rise rate by using thermal stratification. Nevertheless, it is not enough to get high power. In this study, we confirm that the reducing of a pressure rise rate by using thermal stratification and increased HCCI engine power by using boost pressure. We get those by using of CHEMKIN and modified SENKIN. Moreover, this study shows characteristic of the HCCI combustion by the effect of thermal stratification and booster pressure. Those are the result of thermal stratification condition. A CA50 and an IMEP were not affected by the thermal stratification. As a result, for thermal stratification condition, as initial average temperature increase and as thermal width is large, pressure rise rate become low. CA50 and IMEP were not affected by the thermal stratification. For increasing boost pressure, it is possible to get higher IMEP while the pressure rise rate increases little in HCCI with thermal stratification..

바닥공조시스템의 온도 성층화에 따른 에너지 성능 분석

손정은(Jeong-Eun Son),유병호(Byeong-Ho Yu),김홍욱(Hong-Wook Kim),이광호(Kwang Ho Lee) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6

Properly controlled UFAD systems under cooling operation produce thermal stratification exhausting the conditioned-air supplied from floor diffuser to the return plenum after removing the heat load of occupied zone. Thermal stratification is one of the important features of UFAD systems; it eliminates the necessity to consider heat from convection that occur in areas other than lower occupied zone. Hence, the system is more energy effective compared to conventional overhead systems that presume the entire space as an air conditioning space. Thus, enhancing the thermal stratification is necessary for the UFAD systems performance. In this study, we assess the UFAD energy performance by considering the thermal stratification as an input variable through the EnergyPlus simulation. As a result, enhancing thermal stratification improves the cooling energy saving potential by more than 15% as expected. On the other hand, the reduction of thermal stratification causes the increase in supply air volume so that air conditioning of occupied zone as well as upper mixed zone is needed.

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.

상부 코일히터를 갖춘 나선재킷형 태양열 축열조의 성능예측을 위한 CFD 해석모델 개발 및 검증

백승만(Seung Man Baek),종일명(Yiming Zhong),남진현(Jin Hyun Nam),정재동(Jae Dong Chung),홍희기(Hiki Hong) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.4

태양열 온수급탕 시스템에서는 태양열 에너지가 집열판에서 획득되고 열매체로 전달되어 최종적으로 온수의 형태로 축열조에 저장된다. 본 연구에서는 상부 코일히터를 갖춘 나선재킷형 축열조의 축열성능 특성을 정확하게 해석할 수 있는 전산유체역학 모델을 개발하였다. 본 연구에서 고려한 축열조는 벽면에 열매체의 나선유로가 형성된 맨틀형 축열조의 일종으로 시스템 설계 단순화, 저유량 운전, 성층화 촉진 등의 장점을 지닌다. 또한 축열조 내부에 추가적인 코일히터가 장착되어 축열성능과 성층화의 추가적인 향상을 도모할 수 있다. 본 연구에서 개발된 해석모델의 검증은 실제 태양열 온수급탕 시스템의 실증실험 결과와 비교를 통하여 수행되었으며, 온수의 온도변화, 열매체의 온도변화, 성층화 온도분포의 측면에서 잘 일치하는 결과를 얻었다. In a solar domestic hot water (SDHW) system, solar energy is collected using collector panels, transferred to a circulating heat transfer fluid (brine), and eventually stored in a thermal storage tank (TST) as hot water. In this study, a computational fluid dynamics (CFD) model was developed to predict the solar thermal energy storage in a hybridtype TST equipped with a helical jacket heater (mantle heat exchanger) and an immersed spiral coil heater. The helical jacket heater, which is the brine flow path attached to the side wall of a TST, has advantages including simple system design, low brine flow rate, and enhanced thermal stratification. In addition, the spiral coil heater further enhances the thermal performance and thermal stratification of the TST. The developed model was validated by the good agreement between the CFD results and the experimental results performed with the hybrid-type TST in SDHW settings.