Investigation of compression ratio and fuel effect on combustion and PM emissions in a DISI engine

Oxygenated fuel components such as the alcohols of 1-butanol and ethanol are well-known for their potential to improve engine combustion and PM emissions, and these particular fuels are receiving ever greater attention due to their renewable nature giving them great CO2 emission reduction potential. This paper investigates the effect of compression ratio and fuel properties on combustion, gaseous emissions and PM emissions of an experimental single-cylinder direct injection spark ignition (DISI) engine. The tests were carried out at an engine load of 8.5 bar, at various compression ratios between 10.7 and 11.5, with Bu20 (20%vol 1-butanol in gasoline) and E20 (20%vol ethanol in gasoline) fuel blends along with a reference fuel of gasoline. The results show that 1-butanol and ethanol addition to gasoline is effective to advance the MFB50 point and shorten the combustion duration. 1-butanol addition to gasoline is effective to reduce PM number emissions, while NOx reduction is the main benefit of ethanol addition. It is concluded that synergies between compression ratio and alcohol addition to gasoline enable to simultaneously control gaseous and particulate matter emissions while improving fuel economy with respect to standard gasoline combustion.