Abstract
Particulate matter coming from the combustion of renewable diesel (RD), ultra-low sulfur diesel (ULSD) and a volumetric blend of 30% of RD with ULSD (RD30) were collected and physico-chemically characterized. Soot samples were generated in two flame burner types (non-premixed flame, NPF, and partially premixed flame, PPF) trying to simulate the diffusion and premix regimes found in diesel engines. The impact of both fuel nature and burner type was assessed on soot mass, particle size and morphology, particle nanostructure and surface functional groups. In general, although the results of HRTEM and SMPS suggested that the addition of RD reduced the average particle size and increased the concentration of ultra-fine particles, the mass emission of soot was drastically mitigated regardless of the burner used. The results also suggest that the changes in the chemical characteristics of the soot were slightly more sensitive than the changes in the internal nanostructure of the particles, since the graphitic character (as showed by Raman and infrared analysis) increased as the RD content increased, being stronger for the PPF system. Comparisons between engine soot and flame soot confirmed that the addition of RD into ULSD produced smaller and more carbonized particles. In fact, some engine results were located in between those obtained in PPF and NPF burners, suggesting that both combustion regimes are contributing to soot characteristics in engines. This consistency suggests that a first assessment of the impact of alternative fuels on the characteristics of particulate matter can be conducted through the basic approach offered by laboratory flames, thereby avoiding the costs associated with generating large quantities of fuel and the complexities of in-cylinder physical interactions and engine parameters.