Oxidized biodiesel as a cetane improver for diesel–biodiesel–ethanol mixtures in a vehicle engine

Most work in literature claim that the addition of biodiesel into diesel usually increases NOx emissions of compression ignition engines. Ethanol can be added to diesel and biodiesel blends in order to reduce NOx and also to increase the renewable fraction of the mixture. In this work oxidized biodiesel (induction period of 0 h) was evaluated as a cetane improver for blends containing diesel, biodiesel and ethanol so that the negative effects from the high resistance to auto-ignition (low cetane number) of ethanol can be mitigated. 13 blends of diesel, biodiesel, oxidized biodiesel and ethanol as well as an additivated mixture using 2-ethyl hexyl nitrate (2-EHN) were tested in a vehicle equipped with a four cylinders, turbo charged, common rail, diesel engine. The volumetric percentage of ethanol in the mixtures of diesel, biodiesel and ethanol was 0, 2, 4 and 6%, while the biodiesel volumetric content was 0, 5 and 35%. The results have revealed no significant changes in the wheel power for small percentages of ethanol and biodiesel. The use of 20% of oxidized biodiesel has proved to be an interesting additive for cetane improvement enabling quicker responses in acceleration and higher wheel power in comparison to the commercial additive (2-EHN). Emission tests using a mixture containing 90% of conventional diesel, 4% ethanol, 5% biodiesel and 1% oxidized biodiesel have shown reduction in NOx and PM emissions in comparison to conventional diesel.