Journal of the Korean Institute of Gas (한국가스학회지)

The Korean Institute of GAS (한국가스학회)
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Effect of Varying Excessive Air Ratios on Nitrogen Oxides and Fuel Consumption Rate during Warm-up in a 2-L Hydrogen Direct Injection Spark Ignition Engine

2 L급 수소 직접분사 전기점화 엔진의 워밍업 시 공기과잉률에 따른 질소산화물 배출 및 연료 소모율에 대한 실험적 분석

  • Jun Ha (Dept. of Mechanical System Engineering, Jeonbuk National University) ;
  • Yongrae Kim (Dept. of Engine Research, Korea Institute of Machinery and Materials) ;
  • Cheolwoong Park (Dept. of Engine Research, Korea Institute of Machinery and Materials) ;
  • Young Choi (Dept. of Engine Research, Korea Institute of Machinery and Materials) ;
  • Jeongwoo Lee (Dept. of Autonomous Vehicle System Engineering, Chungnam National University)
  • 하준 (전북대학교 기계시스템공학과) ;
  • 김용래 (한국기계연구원 모빌리티동력연구실) ;
  • 박철웅 (한국기계연구원 모빌리티동력연구실) ;
  • 최영 (한국기계연구원 모빌리티동력연구실) ;
  • 이정우 (충남대학교 자율운항시스템공학과)
  • Received : 2023.06.22
  • Accepted : 2023.07.26
  • Published : 2023.09.30
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Abstract

With the increasing awareness of the importance of carbon neutrality in response to global climate change, the utilization of hydrogen as a carbon-free fuel source is also growing. Hydrogen is commonly used in fuel cells (FC), but it can also be utilized in internal combustion engines (ICE) that are based on combustion. Particularly, ICEs that already have established infrastructure for production and supply can greatly contribute to the expansion of hydrogen energy utilization when it becomes difficult to rely solely on fuel cells or expand their infrastructure. However, a disadvantage of utilizing hydrogen through combustion is the potential generation of nitrogen oxides (NOx), which are harmful emissions formed when nitrogen in the air reacts with oxygen at high temperatures. In particular, for the EURO-7 exhaust regulation, which includes cold start operation, efforts to reduce exhaust emissions during the warm-up process are required. Therefore, in this study, the characteristics of nitrogen oxides and fuel consumption were investigated during the warm-up process of cooling water from room temperature to 88℃ using a 2-liter direct injection spark ignition (SI) engine fueled with hydrogen. One advantage of hydrogen, compared to conventional fuels like gasoline, natural gas, and liquefied petroleum gas (LPG), is its wide flammable range, which allows for sparser control of the excessive air ratio. In this study, the excessive air ratio was varied as 1.6/1.8/2.0 during the warm-up process, and the results were analyzed. The experimental results show that as the excessive air ratio becomes sparser during warm-up, the emission of nitrogen oxides per unit time decreases, and the thermal efficiency relatively increases. However, as the time required to reach the final temperature becomes longer, the cumulative emissions and fuel consumption may worsen.

지구 기상이변에 대해 탄소중립의 중요성이 대두됨에 따라 무탄소 연료인 수소의 에너지원으로서의 활용도 역시 증대되고 있다. 일반적으로 수소는 연료전지(FC, Fuel Cell)에 활용되고 있으나, 이는 연소를 기반으로 하는 내연기관(ICE, Internal Combustion Engine)에도 활용될 수 있다. 특히 연료전지만으로 수소 활용 및 인프라 확장이 어려운 때에 이미 생산 측면이나 공급 측면에서 인프라가 기 구축되어 있는 내연기관은 수소 에너지 저변 확대에 큰 도움을 줄 수 있다. 다만 수소를 연소기반으로 활용할 경우 고온에서 공기 중 질소가 산소와 반응하여 유해배기물질인 질소산화물(NOx, Nitrogen Oxides)이 생성될 수 있는 단점은 존재한다. 특히 냉간 (Cold Start) 운전 영역시 포함될 EURO-7 배기규제의 경우 워밍업(Warm-up) 과정에서 발생하는 배기배출물의 저감을 위한 노력도 필요하다. 따라서 본 연구에서는 2 L급 수소 직접분사방식 전기점화 (SI, Spark Ignition) 엔진을 활용하여 냉각수를 상온에서 88 ℃로 워밍업하는 과정에서 질소산화물 및 연료소모율의 변화 특성을 살펴보았다. 특히 수소는 기존의 가솔린, 천연가스, 액화석유가스(LPG, Liquified Petroleum Gas)와 달리 가연범위(Flammable range)가 넓기 때문에 공기과잉률(Excessive air ratio)을 희박하게 조절할 수 있다는 장점이 있다. 이에 본 연구에서는 워밍업하는 과정에 있어서 공기과잉률을 1.6/1.8/2.0으로 변화하여 그 결과를 분석하였다. 본 실험의 결과는 워밍업 시 공기과잉률이 희박해질수록 시간당 질소산화물의 배출이 적고, 열효율도 상대적으로 높으나 최종 온도까지 도달 시간이 길어짐에 따라 누적 배출량 및 연료소모율은 악화될 수도 있음을 시사한다.

Keywords

Acknowledgement

본 연구는 한국기계연구원 주요사업 중 "수소 직분사 엔진 대상 평가 (IN8360)" 과제의 지원으로 수행되었으며, 한국연구재단 "수소 연료기반 초희박 SPCCI 엔진 운전 전략 및 하드웨어 개선 기술 개발 (NRF-2021R1G1A1004451)" 및 한국산업기술평가관리원 "무탄소 수소연료 기반 직접분사식 수소엔진 원천기술개발 (No. 20018473)의 지원을 통해 작성되어 이에 감사를 표합니다.

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