For the last four decades, engine combustion researchers have been researching about advanced combustion technologies which have great possibility to reduce particulate matter (PM) and nitrogen oxides (NOx) emissions simultaneously during the combustion process in the diesel compression ignition engine. However, any advanced combustion technology could not be an alternative combustion technology to replace the conventional diesel combustion (CDC). In this study, the single-fueled and dual-fueled advanced combustion technologies, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI), and dual-fuel premixed charge compression ignition (DF-PCCI), were implemented to reveal the obstacles as a pre-research in a heavy duty single-cylinder engine. The single fueled advanced combustion technologies have difficulty to control the combustion phase. Therefore a lot of previous studies adopted massive exhaust gas recirculation (EGR) and various injection strategies to improve the controllability of combustion phase and burn duration. However, massive-EGR could increase the incomplete combustion, and thus it can deteriorate the combustion efficiency and thermal efficiency. In contrast, DF-PCCI combustion, which utilizes two different reactivity fuels, could control the combustion phase and burn duration without EGR much easier than the single-fueled advanced combustion technologies. Therefore, DF-PCCI combustion could expand the operating range toward high load conditions, and it could improve high thermal efficiency by controlling the combustion phase and burn duration effectively. However, DF-PCCI have weakness point, which was deteriorated combustion efficiency due to the bulk quenching phenomena under the low load condition. In this study, the effects of global equivalence ratio and initial charge temperature were investigated to mitigate the bulk quenching phenomena under the low load conditions. The throttle, charge heating, and hot-EGR strategies were conducted to control the global equivalence ratio and initial charge temperature. The optimized mixture charge control strategy, which utilized throttle and hot-EGR, could reduce hydrocarbon (HC) and carbon monoxide (CO) emissions, and improve the combustion efficiency while maintaining under the EU-VI NOx and PM emission legislation. Moreover, DF-PCCI combustion could reduce dramatically carbon dioxide (CO2) emissions compared to CDC by utilizing the low carbon fuel such as compressed natural gas. Through this study, it has been confirmed that DF-PCCI combustion have great potential to become an alternative combustion technology to replace the CDC, however, the amounts of HC and CO emissions under low load conditions on DF-PCCI combustion were still higher than that of CDC. Therefore, DF-PCCI combustion need to additional researches which aim to reduce the THC and CO emissions under low load condition.
지난 40여년동안 내연기관 연소분야 연구자들은 디젤압축착화연소과정 중 PM과 NOx를 동시에 저감할수는 신연소기술에 대한 연구를 지속적으로 수행하였다. 다중연료 신연소기술(DF-PCCI)은 높은 연소상제어 성능으로 여러가지 신연소기술들 중 실용화 가능성이 가장 높은 연소기술로 인식되고 있다. 그러나 다중연료 신연소기술의 경우에도 저부하 운전이 제한되는 한계점을 가지고 있다. 본 연구에서는 다중연료 신연소기술에서 다양한 흡기제어 전략을 적용하여 저부하 영역에서 발생하는 연소불안정성을 해소하고 연소효율을 개선하여 저부하 영역으로 운전영역을 확장하고자 한다. 본 연구에서는 흡기제어 전략으로 연소실내의 전체당량비 및 혼합기 초기온도 변화에 따라 bulk quenching 현상의 경감 가능성에 대하여 연구하였다. 그 결과 흡기제어전략을 이용하여 EU-VI 배기규제 이하 수준으로 NOx와 PM을 동시 저감할 수 있었으며, 저부하 영역에서 다량 발생하던 미연탄화수소와 일산화탄소를 획기적으로 저감하여 연소효율을 개선할 수 있었다. 그리고 DF-PCCI 연소에서 저탄소연료인 천연가스를 채택한 결과 일반디젤연소에 비하여 이산화탄소 배출을 획기적으로 저감할 수 있는 가능성을 확인하였다. 본 연구를 통하여 DF-PCCI 연소기술이 일반디젤연소에서 문제시되는 NOx와 PM 배출 문제를 극복하기에 최적의 연소기술임을 확인 할 수 있었다.
