The use of biodiesel as alternative to fossil fuel for light duty CI engines to reduce greenhouse gas emissions was widely investigated. However, poor stability of biodiesel - diesel mixture limits the use of biodiesel to low volume concentrations. This paper presents the results concerning the use of a novel fuel additive package containing antioxidant (AS), pour-point depressant (D) and biocide (Bi) with the aim to increase the quality and amount of biodiesel in the diesel-biodiesel blends. Some of the goals are linked to the degradative effects due to free radicals oxidation, contamination by water and microorganisms. The interaction between two different additive packages and two biodiesel (soybean and rapeseed) - diesel blends at 20% in volume was investigated. Optical studies have been performed to characterize the spatial and temporal spray evolution both in a high pressure quiescent vessel and in an optically-accessible single-cylinder 2-stroke CI engine. Soot and NOx emissions were measured at the exhaust. Physicochemical tests showed that the stability of dieselbiodiesel blends was strongly influenced by the use of the two packages of additives. The mixture containing the biocide "P" (B20SMEASDP) was approximately 87.33% more stable than the same sample containing the biocide "C" (B20SMEASDC). Furthermore, no significant changes were observed in term of engine efficiency, fuel injection rate and spray penetration. Hence, it was demonstrated that use of additive package increased the durability of the blends without exhaust emission and performance penalties.