Experimental study on particulate and NOx emissions of a diesel engine fueled with ultra low sulfur diesel, RME-diesel blends and PME-diesel blends

Ultra low sulfur diesel and two different kinds of biodiesel fuels blended with baseline diesel fuel in 5% and 20% v/v were tested in a Cummins 4BTA direct injection diesel engine, with a turbocharger and an intercooler. Experiments were conducted under five engine loads at two steady speeds (1500 rpm and 2500 rpm). The study aims at investigating the engine performance, NO_x emission, smoke opacity, PM composition, PM size distribution and comparing the impacts of low sulfur content of biodiesel with ULSD on the particulate emission. The results indicate that, compared to base diesel fuel, the increase of biodiesel in blends could cause certain increase in both brake specific fuel consumption and brake thermal efficiency. Compared with baseline diesel fuel, the biodiesel blends bring about more NO_x emissions. With the proportion of biodiesel increase in blends, the smoke opacity decreases, while total particle number concentration increases. Meanwhile the ULSD gives lower NO_x emissions, smoke opacity and total number concentration than those of baseline diesel fuel. In addition, the percentages of SOF and sulfate in particulates increase with biodiesel in blends, while the dry soot friction decreases obviously. Compared with baseline diesel fuel, the biodiesel blends increase the total nucleation number concentration, while ULSD reduces the total nucleation number concentration effectively, although they all have lower sulfur content. It means that, for ULSD, the lower sulfur content is the dominant factor for suppressing nucleation particles formation, while for biodiesel blends, lower volatile, lower aromatic content and higher oxygen content of biodiesel are key factors for improving the nucleation particles formation. The results demonstrate that the higher NO_x emission and total nucleation number concentration are considered as the big obstacles of the application of biodiesel in diesel engine.