Effect of butanol addition in diesel and biodiesel fuels on OC, EC, particulate PAH, and alkyl-PAH emissions from a common-rail diesel engine

Characteristics of carbonaceous particle substances, i.e., organic carbon (OC), elemental carbon (EC), particulate polycyclic aromatic hydrocarbon (PAH), and their derivatives, emitted from modern common-rail diesel engine fueled with high-chain alcohol are ambiguous. In this study, OC, EC, PAH, and alkyl-PAH emissions from a common-rail diesel engine fueled with diesel (D100), biodiesel (B100), 15% and 30% butanol addition in diesel (D85Bu15 and D70Bu30), and biodiesel (B85Bu15 and B70Bu30) at four engine loads were analyzed comprehensively. Compared with D100 samples, the reduction in EC emission for B100, B85Bu15, and B70Bu30 samples is approximately 90% due to their oxygenated compounds with OH that populate even locally fuel-rich zones, while the variation of OC emissions with butanol addition is related with the engine operation condition and the proportion of butanol in the blends. For D100 samples, similar PAH emission profiles at different engine loads and several 2-ring to 4-ring PAHs are the most abundant compounds. The abundant of two predominant alkyl-PAH compounds (1-methylphenanthrene and 2-methylfluoranthene) accounts for 10–20% fractions of total PAHs for D100 samples, while they sharply decrease to less than 5% for D85Bu15 and D70Bu30 samples. Butanol addition into diesel slightly affects PAH profile distribution characteristics, and Pyr, Flt, and Nap are the three most abundant PAH species in D100, D85Bu15, and D70Bu30 samples. The abundant of heavier compounds (from cyclopenta[cd]pyrene to coronene) significantly increases with butanol addition into diesel and biodiesel, especially for D70Bu30 and B70Bu30 samples, indicating the contribution of pyrogenic origination instead of fuel origination PAH for these samples derived from fuels with high proportion of butanol in the blends. Compared with D100 samples, total PAH emissions approximately decrease up to 60% for B70Bu30, while a slight reduction in PAH emissions for 30% pentanol addition in biodiesel and even sharp increase for the high blend ratios of diesel/n-butanol was observed by Yang et al. (Fuel 209: 132–140, 2017) and Yilmaz and Davis (Process Saf. Environ. 166: 430–439, 2022b). The discrepancy is probably associated with the different fuel and engine properties. On average of the four engine loads, the particulate toxicity decreases 50–80% for B100 and butanol content samples compared with D100 samples, which is ascribed to the low PAH emissions, although the relative abundance of high cyclic PAH (4–6 rings) with high toxicity dominates in these samples.