Effect of injection pressure on soot formation/oxidation characteristics using a two-color photometric method in a compression-ignition engine fueled with biodiesel blend (B20)

Biofuels are an alternative to petroleum fuels in transportation. Among various biofuels, biodiesel has been mixed with diesel fuel for use in compression ignition (CI) engines. Many countries legislate that standard diesel fuels contain a certain amount of biodiesel to reduce exhaust emissions. An increase in biodiesel content to a 20% volumetric ratio (B20) requires only minor modification to existing vehicle systems. Since discrepancies in fuel properties between B20 and conventional diesel fuel, much research has been performed on B20 combustion and emissions for the implementation of vehicles. The present study investigated spatial B20 combustion and soot emission processes in an optical CI engine under various injection pressure conditions. Volumetric 20% of soybean biodiesel added to diesel fuel and both blend fuel and conventional diesel fuel were used as test fuels. Apparent combustion and emissions were observed with respect to auto-ignition, brake power, and thermal efficiency. In addition, visualization system permitted a profound analysis of the spatial combustion flame and soot propagation. A two-color photometric method extracted quantitative soot density from the captured combustion images, which allowed to study the soot formation and oxidation processes. Although soot emissions decreased significantly out of the engine, the variations in the soot formation and oxidation processes in the combustion chamber were remarkable. Compared with neat diesel flame B20 fuel produced higher flame temperature over all injection pressure conditions. While B20 flame temperature was increased, soot emission of B20 fuel was exhausted with higher concentrations. Under a low load and high speed condition, B20 emissions revealed different results from those of general bio-blends with high thermal efficiency regardless of the injection pressure.