Behavior of a Diesel Injection System with Biodiesel Fuel

Biodiesel fuels are widely known to yield an increase in NOx emissions in many diesel engines. It has been suggested that the increase in NOx is due to injection timing differences caused by the low compressibility of biodiesel. In this work, comparisons of injection timing and duration were performed for diesel fuel and a range of biodiesel blends (B20 to B100). The fuel injector on a 4-stroke, single-cylinder, four horsepower, air-cooled, direct injection diesel engine was positioned in a spray chamber while the engine was motored and fuel was delivered to the injector by the fuel pump on the engine. Spray visualization and quantification of injection timing were performed in the spray chamber using an engine videoscope, light attenuation from a HeNe laser and fuel line pressure, and were synchronized to crank shaft position. Shifts in injection timing were observed between the fuel blends, amounting to a 1 crank angle (CA) degree difference between diesel fuel and pure biodiesel (B100). Combustion studies were also performed to see how the shift in injection timing affected the timing of the combustion process. There was an advance in ignition of up to 4 CA degrees with B100 which can be attributed, at least in part, to the advanced injection timing.