Laser-Induced Incandescence and Smoke Point Measurements to Characterize the Sooting Propensity of Biodiesel Diffusion Flame

Combustion of biodiesel is rapidly expanding around the world, mainly for its significant reduction of emissions such as soot particulates. The presence of carbonaceous soot emitted indicates a reduction in efficiency of practical combustion systems In addition, sub-micron soot particles can have substantial impact on the environment and human health. Common emission studies of neat and blends of biodiesel and diesel fuels have been investigated using compression ignition engines and capturing soot particles in the post-combustion zone. However, soot particles produced in the primary combustion zone can greatly influence the products in the post-combustion zone. To study soot formation in the primary combustion zone, laser diagnostic is performed on a laminar diffusion wick lamp. In this paper, the sooting propensity of various blends of soybean biodiesel and Ultra Low Sulfur Diesel (ULSD) fuels are investigated using both a traditional ASTM D-1322 standard smoke lamp and modern Laser-Induced Incandescence (LII) technique. Laser excitation is achieved using a pulsed Nd. YAG laser operating at 532nm wavelength. Although ultraviolet and infrared spectra can be used, the choice of an Nd. YAG laser operating at the second harmonic wavelength is preferred because interference from excitation of polycyclic aromatic hydrocarbons (PAHs) and the C-2 Swan band can be reduced. A fast-gate Intensified Charge Coupled Device (ICCD) camera and a 450nm narrow band-pass filter are used to detect the spatially resolved LII signal. The qualitative LII signal provides the soot profile of different volume mixtures of biodiesel and diesel diffusion flame. Many researches report show reduction in soot particles emitted in the exhaust when biodiesel is used as a blend in compression ignited engines. The contribution of this research is to investigate whether similar sooting characteristics can be seen in the primary combustion zone by making measurements in the proximity of the flame front. In general, the LII signals and smoke point measurements show a decrease in soot particles produced when blending ratios of 25% biodiesel - 75% diesel (by volume) are used. One limitation of using the ASTM standard wick lamp is flame instability at higher blending ratios due to the increases in carbon deposit on the wick, which reduces the fuel vaporization rate. Therefore, smoke point measurement for blending ratios above B25 is not accurate since the flame height is not stable; hence, future experiments rely on LII technique to characterize soot emission properties. In order to perform LII laser diagnostics using higher blending ratios, comparison between smoke point measurements and LII signals will be characterized in this report using lower blending ratios.