Combustion and Emission Characteristics of a HCCI Engine Fuelled with Different n-Butanol-Gasoline Blends

摘要

Biobutanol, i.e. n-butanol, as a second generation bio-derived alternative fuel of internal combustion engines, can facilitate the energy diversification in transportation and reduce carbon dioxide (CO_2) emissions from engines and vehicles. However, the majority of research was conducted on spark-ignition engines fuelled with n-butanol and its blend with gasoline. A few investigations were focused on the combustion and exhaust emission characteristics of homogeneous charge compression ignition (HCCI) engines fuelled with n-butanol-gasoline blends. In this study, experiments were conducted in a single cylinder four stroke port fuel injection HCCI engine with fully variable valve lift and timing mechanisms on both the intake and exhaust valves. HCCI combustion was achieved by employing the negative valve overlap (NVO) strategy while being fueled with gasoline (Bu0), n-butanol (Bu100) and their blends containing 30% n-butanol by volume (Bu30). The results indicate that, with the increase of n-butanol volume fraction in the blend, the autoignition timing advances and the combustion duration shortens, but indicated mean effective pressure (IMEP) decreases at the same conditions. The addition of n-butanol to gasoline can expand the low load boundary in HCCI combustion mode. But it decreases high load boundary in HCCI combustion mode. In addition, oxides of nitrogen (NO_x) emissions sharply decrease with advanced exhaust valve closing timing. The addition of n-butanol results in a reduction in NO_x emissions.