Experimental Investigation On The Combustion And Emission Characteristics Of Partially Premixed Compression Ignition In A Diesel Engine Fueled With N-Butanol-diesel Blends

Partial Premixed Compression Ignition(PPCI) in diesel engine is a combustion mode between conventional diesel combustion and Homogeneous Charge Compression Ignition(HCCI) combustion, which has the potential to simultaneously reduce NOX and smoke emissions and also improve thermal efficiency. N-butanol as a kind of clean and renewable biofuel can effectively prolong ignition delay and enhance fuel/air mixing because of their low cetane number and high volatility fuel characteristics, which make it a better alternative fuel to achieve PPCI.In this paper, PPCI combustion in a four-cylinder common rail diesel engine fueled with n-butanol–diesel blends was achieved through early or late injection condition in which the whole amount of fuel was delivered before ignition. The exploration strategies were focused on the early or late injection timing, injection pressure and load rate to evaluate the effects of n-butanol fuel characteristics on PPCI combustion and emissions. Besides,the effects of injection timing and load rate on PM mass-size distribution have also been investigated by using a Low Pressure Impactor(LPI). Results show that both early and late injection have long premixed duration which is helpful to form more homogeneous mixtures, reducing the soot mass and shifting the peak mass size to the smaller side. With the increase of n-butanol blending ratio, ignition delay was prolonged and the smoke emission can be reduced by up to 70%, while NOX shows a slight increase when compared with pure diesel under the same condition. Moreover, n-butanol-diesel blends can effectively reduce the soot mass, but has little influence on the peak mass size. In addition, PPCI combustion can be achieved with reasonable injection timing, lower injection pressure, moderate EGR without penalties in fuel consumption when using high n-butanol blending ratios. However, as the load rate increases, the premixed combustion fraction decreases apparently due to the short ignition delay. And the diffusion combustion plays a dominant role in the combustion with high heat release peak and long duration for B00. While the premixed combustion fractions in the combustion of B30 are still much higher than B00, which indicates that n-butanol-diesel blends are more suitable for PPCI.Based on the single injection, we investigated the effects of post injection parameters on PPCI combustion and emissions. Results show that appropriate main-post injection interval and post injection quantity can further reduced the smoke and hydrocarbon emissions, while they have less effect on the BSFC.