Nanoparticle formation burning biofuels

Biofuels are gaining increased attention as alternative to fossil fuels. The main motivation is the mitigation of climate change and energy security objectives. Biofuels may produce less net carbon dioxide emissions than oil-based conventional fuels. Moreover, there is also a general idea about their ability to reduce exhaust emissions, particularly polycyclic aromatic hydrocarbons (PAHs) and particulate matter. In spite of this general belief, experimental re- sults performed in laboratory-scale experiments and in engines have shown that the e ect of biofuels on the formation of particulate matter is controversial. Biofuels produce pollutants similar to conventional hydrocarbon fuels and their formation can be promoted or reduced with respect to hydrocarbon molecules having the same number of C-atoms according to operative conditions. The role of ethanol, dimethyl ether, and furanic fuels, namely furan, methylfuran and 2,5 di- methylfuran, as substituent to ethylene, on the formation of particulate matter is investigated in di erent flame configurations by using in situ optical techniques and differential mobility particle sizer. Laser induced fluorescence and incandescence signals, correlated to small precursor nano- particles and large soot particles, respectively, have been measured in premixed and coun- terflow di usion flames of ethylene doped with di erent amounts of biofules. In premixed flames, the addition of biofuels to ethylene reduces nanoparticle and soot parti- cle formation. The e ect is stronger for the soot particles, that is, particles with sizes larger than 10 nm, and in flames operated close to the soot threshold limit. The addition of biofuels even reduces soot particle concentration below the detection limit, whereas nanoparticles are still formed in large amounts. These results are confirmed by the measurements of the parti- cle size distributions that show a dominance of sub-10nm particles in flames operated with increasing concentrations of biofuels. The counter-flow di usion flame configuration shows a di erent behavior. In the fuel side of the flame, typical of fuel-rich conditions in engines, a noticeable increase of both nanoparticle and soot particle concentrations is detected by adding biofuels. Conversely, in the oxidizer side of the flame, particulate matter is always reduced when biofuels are added to the fuel. The results show that the role of biofuels in the formation of nanoparticles and soot is not always in the sense of reduction, but it strongly depends on the combustion conditions. Moreover, if particulate matter concentration is reduced, the particle size distribution of the emitted particulate matter is dominated by sub-10nm particles.