Effects of Hot and Cooled EGR for HC Reduction in a Dual-Fuel Premixed Charge Compression Ignition Engine

摘要

Most internal combustion engine makers have adopted after-treatment systems, such as selective catalytic reduction (SCR), diesel particulate filter (DPF), and diesel oxidation catalyst (DOC), to meet emission regulations. However, as the emission regulations become stricter, the size of the after-treatment systems become larger. This aggravates the price competitiveness of engine systems and causes fuel efficiency to deteriorate due to the increased exhaust pressure. Dual-fuel premixed charge compression ignition (DF-PCCI) combustion, which is one of the advanced combustion technologies, makes it possible to reduce nitrogen oxides (NO_x) and particulate matter (PM) during the combustion process, while keeping the combustion phase controllability as a conventional diesel combustion (CDC). However, DF-PCCI combustion produces high amounts of hydrocarbon (HC) and carbon monoxide (CO) emissions due to the bulk quenching phenomenon under low load conditions as a huddle of commercialization. In this study, the effects of exhaust gas recirculation (EGR) rate and EGR temperature were investigated to overcome the bulk quenching phenomenon under low load conditions in the DF-PCCI combustion. Natural gas (NG) and diesel were selected for low reactivity fuel (LRF) and high reactivity fuel (HRF) respectively. As experimental results, adopting the high temperature EGR could reduce the HC emission, and improve combustion efficiency (η_c) and fuel conversion efficiency (η_f), while maintaining the NO_x and PM emissions under the EU-VI emission regulations. The results suggest that controlling the global equivalence ratio (Φ_(global)) and increasing the initial charge temperature by hot-EGR are quite effective way to mitigate the bulk quenching phenomenon and incomplete combustion under low load conditions in the DF-PCCI combustion.