Premixed charge of n-butanol coupled with direct injection of biodiesel for an advantageous soot-NOx trade-off

In this study, a direct injection (DI) compression ignition engine fueled with biodiesel was supplemented with n-butanol port fuel injection (PFI) in order to simultaneously reduce in cylinder nitrogen oxides formation, decrease soot and favorable modify their trade-off. The combustion and emission characteristics were investigated for regimes of 1-5 bars IMEP at 1400 rpm. By applying this methodology, for the regimes in which the n-butanol PFI was applied, the premixed charge combustion has been split into two regions of high temperature heat release, an early one, BTDC, and a second stage ATDC, oxidizing the soot formed from biodiesel combustion and therefore modifying favorable the soot-NOx trade-off. With n-butanol injection, the soot emissions showed a significant decrease as much as 90%, concomitantly with a 50% NOx reduction at higher PFI rates. Non-regulated emissions measurements showed increases in acetaldehyde with n-butanol PFI. There was no significant loss in mechanical efficiency when implementing n-butanol PFI while the strategy was able to maintain the thermal efficiency comparable with biodiesel values. The results of this work indicate that n-butanol PFI may be an effective technique to concomitantly reducing NOx and soot emissions from a diesel engine for selected regions on the engine map.