In this work the presence of soot in laminar diffusion of diesel and blends diesel/biodiesel flames were investigated in the following proportions: 5, 10, 20 and 50% of biodiesel. The technique of laser-induced incandescence (LII) was used for the soot detection. Horizontal mapping were performed at two heights (80 and 260 mm above the burner) to investigate the distribution of soot along the studied flames. The experiment was performed with a pulsed Nd:YAG laser with the wavelength of 1064 nm. The results have shown that the soot emission decreases as the amount of biodiesel increases in the blends. Keywords: laser-induced incandescence, soot, biodiesel, combustion IntroductionDiesel engines are currently the largest source of power generation in the planet. They are widely used in quite different areas, as transportation and mining machinery. They are popular due to their high efficiency, low-cost and durability if compared with gasoline and other automotive fuels.1,2 Nevertheless, diesel engines also presents another remarkable feature: they are largely responsible by the emission of soot, one of most pollutants of environment. 3 Soot is basically formed by particles of impure carbon, with diameter from 10 to 50 nm. Due to its small size, soot particles can penetrate in the lung alveolus of human beings causing serious respiratory and cardiac diseases. 4 Besides health and ecological issues, soot also plays an inconvenient role in the energy generation from combustion processes. [5][6][7] In general, the presence of soot diminishes the overall efficiency of the combustion processes. Soot production is associated to the cracking reactions of hydrocarbon chains that generate carbon solid clusters. These reactions are carried out in gaseous phase and compete directly with the mechanism of oxidation of hydrocarbons that are responsible to the energy release. 8It means that soot is preferentially formed in fuel-rich and high temperature combustion flames, as diffusive flames. These flames are largely used as industrial energy sources. In diffusive flames, as the fuel is burned using only the oxygen available from surroundings, soot presence is higher than the other kind of flames, like premixed ones In some specific applications, like boiler devices, however, a moderate amount of soot is desirable, as its presence increases the heat transfer rate.7 Soot is also quite important in the production of carbon black, which is employed as active filler in rubber products and as component of printing paints.Among the strategies to reduce soot emission from diesel engines, recently a vegetable fuel, known as biodiesel, has been developed. 9 Biodiesel is a kind of biofuel made by alkyl esters from long-chain fatty acids derived from vegetable oils or animal fat. Biodiesel shows a better flammability if compared to other biofuels, and can replace the diesel oil, or diesel/biodiesel blends, in compression ignition engines without significant changes. 10It also presents the following advantages over pure diesel: there are no a...

Soot particles usually cause respiratory diseases and other problems to human health. To prevent or at least reduces soot emissions it is necessary to know its formation mechanism. Laser-Induced Incandescence (LII) has been used to detect soot and its precursors, known as polycyclic aromatic hydrocarbons (PAHs), in diffusion flames. In this work, several mixtures of diesel/biodiesel blends were investigated using two laser wavelengths, at 532 nm, which excites both soot and PAHs, and at 1064 nm, which excites only soot. Thus, the difference of intensity between both LII signals provides the proportion of soot/PAHs in the irradiated regions of flames, and it can be associated to the evolution of soot formation along the flame.