Increasing attention has been devoted to the use of biodiesel fuel in internal combustion diesel engine due to its positive attributes as compared to the other types of fuel: e.g., being a renewable source, non-petroleum-based, with lower carbon monoxide, hydrocarbon, and particulate matter emissions. This work investigates the performance and the air emission of a small displacement engine fueled with blends of distilled biodiesel (from this point forward biodiesel only) and ultralow-sulfur diesel fuel up to 40% by volume. The considered engine plays a leading role in city cars and urban vehicles; the urban congestion and the antipollution regulations for urban vehicles make this kind of engine very attractive in the near future, especially if it will be fueled with biodiesel blends for their potential of reducing the pollutant emissions in urban areas. The first part of this work aims at comparing the results obtained with biodiesel blends and those determined using diesel fuel as a reference under various operating regimes without any modification to the injection process. The impact of biodiesel blend fuels on the engine's power, specific fuel consumption, and emissions is analyzed. The second part of this work aims at investigating the influence of a variation of the injection parameters on the performance and emissions of the engine using biodiesel blends (20% and 40%). Five engine operation modes are considered, in which the engine is tested with split injection (preinjection and main injection) and various preinjection and main injection timings and durations.