An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine was used to study the soot and combustion processes using European low sulfur diesel and biodiesel fuels with multiple injection strategies. Influences of injection timings and fuel type on soot and combustion characteristics were studied under similar loads (4 bar IMEP). In-cylinder pressure was measured for heat release analysis. High-speed combustion video was captured for all the studied cases. Transient late cycle soot was measured using a back-illumination light extinction method. NOx emissions were measured in the exhaust pipe. Different combustion modes including conventional diesel combustion and low-temperature combustion were observed from the heat release rates and the combustion images. Soot was found consistently lower for bio-diesel fuel than the European diesel fuel. However, for NOx emissions, under conventional combustion cases, it was found that biodiesel fuel leads to increased NOx emissions. But for low-temperature combustion modes, NOx emissions were lower for bio-diesel fuel than the diesel fuel. Under certain conditions, simultaneous reduction of NOx and soot was achieved for advanced lowtemperature combustion for both fuels.