Effects of the variation in diesel fuel components on the particulate matter and unregulated gaseous emissions from a common rail diesel engine

Diesel fuel mainly contains n-alkanes, iso-alkanes, cycloalkanes and aromatics, and varies with the source of crude oil and refining process. Although satisfying the same emission regulation, the particulate matter (PM) emissions and unregulated gaseous emissions of diesel fuel maybe vary a lot due to different fuel components. A series of experiments was conducted on a single-cylinder diesel engine fueled with diesel respectively blending with 10% and 20% fuel components to study the aldehyde, olefins, methane emissions and particulate matter (PM) emissions under engine loads from indicated mean effective pressure (IMEP) 1 bar to 8 bar. In this study, ndodecane, iso-dodecane, tetralin and decalin were chosen to represent n-alkanes, iso-alkanes, aromatics and cycloalkanes, respectively. The results show that when IMEP less than 4 bar, the aldehydes emissions are relatively high even above 100 ppm. Blending fuel components in diesel causes the aldehydes emissions increasing except for n-alkanes. At low load from IMEP 1 to 3 bar, as blending ratio increase, aromatics and iso-alkanes noticeably worsen the hydrocarbon emissions especially. The hydrocarbon emissions of diesel/20% iso-dodecane and diesel/20% tetralin are respectively more than twice over those of diesel/10% iso-dodecane and diesel/10% tetralin. Aromatics and cycloalkanes have relatively high-level particle numbers which mainly distribute in nucleation mode with diameter ranging from 10 nm to 50 nm at IMEP 1 bar and 2 bar because of their lower H/C ratio leading to a tendency for precursor formation. At heavy load, the particle number presents a regular pattern that n-alkanes > cycloalkanes > iso-alkanes > aromatics and the peak value of particle size distribution moving towards to the right side due to prolonged combustion duration resulting in more time to polymerize.