Effect Of Fuel Identity On The Exhaust Particles From Diesel Engine

Particulate matter (PM) from diesel engines is one of the main sources of fineparticulate matter (PM2.5) in the atmosphere, and its formation mechanism and controltechnology have become research focuses. In the present study, the effects of dieselfuel identity and operating conditions of diesel engine on physic-chemical propertiesand oxidation reactivity of the diesel particles have been comprehensivelyinvestigated.Firstly, the present paper investigated the fuel properties and composition onregulated pollutants, the particulate number concentration and PAH emissions.Compared to conventional diesel fuel (DF), the biodiesel (BD) and coal-to-liquid(CTL) diesel fuel can significantly lower the emissions of regulated pollutants, theparticulate number concentration and the emissions of PAHs in both gaseous-andparticle-phases. Moreover, the physic-chemical properties of soot with different fuelswere compared. The agglomerates emitted from diesel engine exhibit irregular shape,which consisted of nearly spherical primary particles. The fractal dimensions ofagglomerates for these three fuels range from1.58to1.8, and are in the order at thesame engine operating mode: BD> DF> CTL. Besides, the mean diameter of primaryparticles falls within the scope of5-65nm with an order of DF> BD> CTL at thesame engine operating mode. Both the fractal dimension of agglomerates and meandiameter of primary particles increase with an increase in the engine load, and firstdecrease and then increase with an increase in the engine speed. At idling condition,the primary particles present larger mean particle diameters. As the engine loadincreases, the decreases in the mean separation distance and tortuosity and an increasein the fringe length are found within the nanostructure of primary particles. When theengine speed increases, the mean separation distance and tortuosity firstly decline andthen increase, while the fringe length simultaneously exhibits an opposite trend. Thedegrees of disorder have the sequence of BD> DF> CTL under the same operatingcondition. The amount of aliphatic C–H surface functional groups shows a decreasewith an increase in the engine load, while firstly increases and then decreases with anincrease in the engine speed. The equivalent ratios of C-H groups are in the range of0.11-0.5. The O/C ratio, amount of hydroxyl functional groups and sp3/sp2hybridization ratio of particles for these three fuels have similar trends as the variations of the amount of C-H groups with respect to engine load and speed,respectively. The values of these three parameters aforementioned present an order ofBD> DF> CTL under the same operating condition. The carbonyl surface functionalgroups not only exist with a small content, but also are do not show any perceivabletrends relating to the nature of fuel or engine operating mode. The light-off andburn-out temperatures for the soot particle generated from three fuels are in a rangeof394-622.5oC, and the apparent activation energies are138.1-172.5kJ/mol. Theoxidation reactivity shows a decrease with an increase in the engine load and adecrease after an initial increase with an increase in the engine speed. Under the sameoperating condition, the order of soot oxidation reactivity for the fuels is BD> DF>CTL. Finally, the analysis of partial least squares regressive indicates that the sootoxidation reactivity is affected by fuel identity, engine operating condition, andphysicochemical properties of soot particles. The nanostructure, especially for meanseparation distance and tortuosity, acts as a more important factor in governing thesoot oxidation reactivity than either of fuel composition and surface functionalgroups.The results obtained above not only have important theoretical significance tounderstand the nature as well as formation and evolution mechanism of PM, but alsothe potential to guide purification technology applications.