Combustion and emissions characteristics of Diesel and soybean biodiesel over wide ranges of intake pressure and oxygen concentration in a compression-ignition engine at a light-load condition

Thermal efficiency and carbon monoxide (CO) contour maps revealed two distinctive regions divided at an intake oxygen level of 8 vol% (or an equivalence ratio of 0.85). In the oxygen-sufficient region intake pressure exhibited dominant impacts on combustion duration, stability, and thermal efficiency. The NOx-soot contour map clarifies the location and size of the “soot barrier” in Diesel, which was not observed in B100. B100 achieved simultaneous NOx and soot reduction to 0.2 g/kW h and 0.1 filter smoke number (FSN), respectively, at 150 kPa intake pressure with 11 vol% intake oxygen concentration. Corresponding thermal efficiency was approximately 43%. Increased intake pressure over 150 kPa lowered thermal efficiency at the maximum brake torque (MBT) timing. The apparent net heat release rate traces indicated that most heat release event occurred before top dead center (TDC) and burn duration was elongated when intake pressure was above 150 kPa.