Combined Impact of n-Butanol Additive and Spark Timing on Combustion and Efficiency of a GDI Engine

Abstract

The influence of n-butanol additive and spark timing on the combustion process was studied in a gasoline direct injection (GDI) engine, as well as fuel efficiency and relevant performance indicators. Three concentrations of n-butanol blended fuels (i.e., Bu15, Bu30, and Bu50) were used as tested fuels and compared to regular gasoline at low and high loads. The results indicate that increasing the n-butanol concentration or advanced spark timing can increase the combustion pressure and temperature, improve the burning rate, and reduce combustion duration. Moreover, brake thermal efficiency (BTE) increases with rising n-butanol concentration, but its change with spark timing is affected by n-butanol concentration. At the low load, the highest BTE with regular gasoline and Bu15 occurs between varying spark timing with advanced spark timing, while BTE reduces persistently for Bu30 and Bu50. At the high load, furthermore, BTE increases for all the tested fuels with advanced spark timing. However, increasing n-butanol concentration or advanced spark timing may increase knock tendency. To summarize, varying spark timing or n-butanol concentration can affect the combustion process and fuel efficiency distinctly depending on fuel properties and engine loads. Spark timing should be adjusted to achieve better fuel efficiency for high concentration of n-butanol blended fuels.