디젤 가솔린 융합 연소에서 스월 컨트롤 밸브와 고압 배기 가스 재순환이 미치는 영향에 대한 연구

학위논문(석사) -- 서울대학교대학원 : 공과대학 기계공학부, 2021.8. 장요셉.As the emissions regulations become stricter, various studies have been conducted to reduce the emissions. Dual-fuel combustion, which uses two fuels with different reactivity, can reduce nitrogen oxides (NOx) and particle matter (PM) emissions by increasing air-fuel premixing ratio. It can also achieve higher thermal efficiency by compression ignition process. In contrast, dual-fuel combustion involves difficulty to ensure combustion stability at low load condition as low reactivity fuel leads to less auto-ignition tendency. In this study, the effect of swirl control valve (SCV) and high pressure exhaust gas recirculation (HP-EGR) have been investigated to find the optimal operating strategy which can improve the incomplete combustion and combustion stability at low load condition. Total Hydrocarbon (THC) and Carbon Monoxide (CO) emissions can be reduced by applying SCV and HP-EGR. It can be concluded that swirl flow motion and high intake temperature improved the incomplete combustion and combustion stability. However, fast combustion with high swirl ratio and intake temperature increased NOx emission and max pressure rise rate (mPRR). Based on experimental results, the optimization experiment can derive the optimal operating strategy of SCV and HP-EGR at the four operating conditions. At low load conditions, incomplete combustion and low combustion stability is major challenge of dual-fuel combustion. High swirl ratio and HP-EGR can improve combustion stability and thermal efficiency at low load conditions. At high load conditions, satisfying mPRR and NOx emission is important to optimize dual-fuel combustion. Low swirl ratio and LP-EGR to decrease mPRR and NOx emission can be considered at the high load conditions. The experimental results show that applying the SCV and HP-EGR can improve the incomplete combustion and combustion stability on dual-fuel combustion at the low load condition.강화되는 배기 규제에 대응하기 위하여 반응성이 다른 두 연료를 사용하는 융합 연소에 대한 연구가 진행되고 있다. 융합 연소는 저반응성 연료의 예혼합률을 높여 질소 산화물과 입자상 물질 배출량을 줄일 수 있으며 압축 점화 방식을 통하여 높을 열효율 또한 달성할 수 있다. 하지만 융합 연소는 저반응성 연료의 낮은 자발화 특성으로 인하여 저부하 운전영역에서 연소 안정성을 보장하는데 어려움이 있다. 본 연구에서는 융합 연소의 저부하 운전 영역에서 불안전 연소 및 연소 안정성을 개선할 수 있는 최적은 운전 전략을 찾기 위해 스월 컨트롤 밸브(SCV)와 고압 배기 가스 재순환(HP-EGR)의 영향에 대하여 확인하였다. 스월 컨트롤 밸브와 고압 배기 가스 재순환 시스템을 적용하여 미연탄화수소 및 일산화탄소 배출량을 줄일 수 있었다. 이는 강한 스월 유동과 높은 흡기온도를 통해 불완전 연소 및 연소 안정성의 개선 가능성을 확인하였다. 하지만 스월 비와 흡기 온도가 높은 빠른 연소는 질소 산화물 배출량과 최고 압력 상승률을 증가시키는 경향을 보였다. 위 실험 결과를 바탕으로 최적화 실험을 통하여 네 가지 운전 조건에서 스월 컨트롤 밸브와 고압 배기 가스 재순환의 최적 운전 전략을 도출할 수 있었다. 불완전 연소와 낮은 연소 안정성이 한계인 저부하 운전 조건에서는 강한 스월 유동과 고압 배기 가스 재순환을 통하여 연소 안정성과 열효율을 개선할 수 있는 최적의 운전 전략임을 확인하였다. 최고 압력 상승률과 질소 산화물 배출량을 만족시키는 것이 주요한 고부하 운전 조건에서는 최고 압력 상승률과 질소 산화물 배출량을 줄일 수 있는 약한 스월 유동이나 저압 배기 가스 재순환 운전 전략이 유리함을 알 수 있었다.Chapter 1. Introduction 1 1.1 Research Background 1 1.2 Previous Research 2 1.3 Research Objective 5 Chapter 2. Experimental Setup and Conditions 6 2.1 Experimental Setup 6 2.2 Swirl Control Valve and HP-EGR System 12 2.3 Experimental Condition 15 Chapter 3. Experimental Results and Discussion 18 3.1 Effect of Swirl Control Valve with Varying DIT 18 3.2 Effect of HP-EGR 23 3.3 Optimal Strategy of SCV and HP-EGR on Dual-fuel Combustion 28 Chapter 4. Conclusion 36 Chapter 5. Bibliography 38 국문초록 41석

Evaluation of Water Supply Stability for Upland Crop in Reservoir Irrigation Districts

As the agricultural land use shifts from paddy to upland, ensuring reservoir water supply stability for upland crop irrigation becomes essential. The objectives of this study were to estimate the irrigation water requirements considering the upland irrigation scenario and to evaluate the reliability of the water supply from the agricultural reservoir using resilience indexes. Two study sites, Sinheung and Hwajeong, were selected, and soybean and red peppers, the most water-intensive crops, were selected as study crops, respectively. For the irrigation scenario, two irrigation methods of traditional scheduling (which irrigates all sites at once) and rotational scheduling (which distributes irrigation by districts), along with the upland conversion rate, were considered. The net irrigation requirement was estimated through a water balance analysis. The stability of the reservoir was evaluated using resilience indexes based on the simulated 10-years reservoir water levels and drought criterion. Overall, the water supply of the reservoir was evaluated as stable during the simulated 10 years, except for the one year. Compared to the two irrigation methods, rotational scheduling resulted in lower irrigation water usage in both sites, with reductions of 1.6%, and 0.3%, respectively. As the upland conversion rate increases, the water deficit could be intensified in Hwajeong with a conversion rate exceeding 50%, showing the number of deficit(ND) over the one and a rapid increase in the deficit ratio(DR). It was confirmed that the reservoir operation criteria can be enhanced by incorporating resilience indicators along with crop growth information, thus, this will be a further study.N

Classification of Summer Paddy and Winter Cropping Fields Using Sentinel-2 Images

Up-to-date statistics of crop cultivation status is essential for farm land management planning and the advancement in remote sensing technology allowsfor rapid update of farming information. The objective of this study was to develop a classification model of rice paddy or winter crop fields basedon NDWI, NDVI, and HSV indices using Sentinel-2 satellite images. The 18 locations in central Korea were selected as target areas and photographedonce for each during summer and winter with a eBee drone to identify ground truth crop cultivation. The NDWI was used to classify summer paddyfields, while the NDVI and HSV were used and compared in identification of winter crop cultivation areas. The summer paddy field classification withthe criteria of –0.195<NDWI<0.15 was 90.9% accurate on average when compared with ground truth. Model performance for the winter crop fieldclassification was also excellent showing the accuracy greater than 98.2% on average for both models. However, cloud and greenhouses appeared todemonstrate optical similarity with paddy in the NDWI values, implying additional caution should be taken when removing cloud and greenhouseeffects. Overall the developed methods for paddy and winter crop classification performed reasonably well at the irrigation district level and furtherstudies are needed to investigate model performance at regional or national scales.N

Economic Analysis of Upland Crop Irrigation Between Individual and Collective Well Water Supply

밭은 논에 비해 수익성이 높고 경작면적도 증가 추세에 있어 적절한 용수공급의 중요성이 커지는데도, 밭 용수기반은 부족한 상황이다. 본 연구의 목적은 밭 재배지의 공간분포에 따른 개별관정과 집단관정에 의한 밭 용수공급의 경제성을 비교 평가하는데 있다. 노지 밭작물 중 고추, 배추, 사과, 콩 네 작물에 대해 충청권역에서 각 작물의 주요 생산지역인 청양군, 당진시, 예산군, 괴산군을 대상지역으로 선정하였다. 경제성 분석 결과, 고추, 배추, 사과 콩의 B/C ratio는 개별관정 시나리오에서 1.49, 1.36, 1.90, 0.71, 집단관정 시나리오에서 1.45, 1.20, 1.91, 0.65로 산정되어 콩을 제외한 고추, 배추, 사과는 밭 용수공급시설의 개발이 경제적 타당성이 있는 것으로 나타났다. 특히 작물의 가치가 큰 사과와 고추재배의 경우 밭용수 공급의 효과가 커서 작물가치가 관정개발의 중요한 인자로 나타났다. 작물 총수입에 대하여 민감도 분석을 수행한 결과 작물의 총수입이 낮은 작물일수록 가격변동이 경제성에 미치는 영향이 큰 것으로 나타났다. 집단관정 개발을 위한 필지 수에 따라 경제성 분석을 수행한 결과 고추와 배추의 경우 밭의 공간분포가 밀집되지 않아 집단관정 개발 시 규모의 경제 효과가 나타나지 않았으며, 사과와 콩의 경우 20개 이상의 필지를 집단화한 경우 규모의 경제의 효과가 나타났다. 결론적으로, 관정을 이용한 용수개발은 작물가치가 큰 사과나 고추 작물에 유리하고, 집단관정의 효과는 실제 작물 재배의 공간분포자료를 바탕으로 추가적인 분석이 요구된다. Profitability of upland crops is better than paddy crops and proportion of upland is increasing. However, there is a lack of infrastructures for upland irrigation. The object of this study were to develop water supply scenarios using individual and collective agricultural wells to evaluate economic feasibility to consider geographical analysis of upland farms and water supply facilities. Cheongyang, Dangjin, Yesan, and Goesan were selected as study areas where four different crops of red pepper, chinese cabbage, apple, and bean, respectively, were mainly produced in Chungcheong province. As a result, B/C ratio was estimated as 1.49, 1.36, 1.90, and 0.71 in using individual wells scenario, and 1.45, 1.20, 1.91, and 0.65 in using collective wells scenario for red pepper, chinese cabbage, apple, and bean. It turned out that change of price effected on economic feasibility a lot for crops with low production income. As a result of evaluating economic feasibility by number of plots for developing collective well, there was no effect of economy of scale for red pepper and chinese cabbage. In case of collectivizating more than 20 upland plots, effect of economy of scale appeared for apple and bean. In conclusion, development of water using high value crops including red pepper and apple, and effect of collective well requires additory analysis of .spatial distribution of farms.N