Particulate emissions by a small non-road diesel engine: Biodiesel and diesel characterization and mass measurements using the extended idealized aggregates theory

Particulate emissions from a 4.8-kW diesel generator running on ultra-low sulfur diesel and biodiesel fuels are characterized as a function of engine load. Number distributions measured by a scanning mobility particle sizer (SMPS) show that particle mobility diameters rise with increasing engine loads. The elemental carbon (EC) to organic carbon (OC) ratio, measured by thermo-optical transmission evolved gas analysis, with careful attention to avoid OC sampling artifacts, increases from about 0.5 at idle load to 3.8 at 100% load when using diesel fuel. Transmission electron microscopy (TEM) images of the particles showed that at idle, the particles were liquid droplets together with a few aggregates. When a load was applied, the droplets were replaced by chain aggregates, which had a mean primary particle size of 29±9 nm at 100% load. Fractal dimension averaged 1.63±0.13, consistent with much larger diesel engines emissions reported in the literature. The use of biofuel (B100) results in emissions of particles that are compact, irregular, and lack the clearly defined primary particles of diesel aggregates, and yet at maximum load they have similar EC and OC content as diesel particles. The accuracy of the idealized aggregate (IA) theory correction and its extension to the transition regime [Lall, A.A., Friedlander, S.K., 2006. On-line measurement of ultrafine aggregate surface area and volume distributions by electrical mobility analysis: 1. Theoretical analysis. Journal of Aerosol Science 37, 260–271] was tested as a method to obtain mass distributions for diesel aggregates using and SMPS. The total mass concentrations calculated from the SMPS measurements using the extended IA theory are in good agreement with the mass concentrations obtained from gravimetric and EC/OC measurements. The loss of aggregates in the TSI SMPS inlet impactor is also discussed.