(289b) Deterioration of B20 Under Compression Ignition Engine Operation Conditions
Biodiesel has been widely accepted as an alternative for fossil-derived diesel fuel for use in compression ignition (CI) engines. Several properties, such as oxidative stability, cloud point, and pour point restrict the use of biodiesel beyond current B20 blend levels (20% biodiesel in 80% ULSD) for on-road vehicle applications. Maintaining the properties of B20 as specified by ASTM D 7476-08 is important because once out of spec, B20 will result injector coke formation, fuel filter plugging, increased exhaust emissions, and overall loss of engine performance. Although the properties of initial B20 are within the specifications, under engine operating and longer storage conditions, B20 could deteriorate. In a diesel engine, the fuel that goes to the injector and does not enter the cylinder is then recycled back to the fuel tank. The recycled fuel returns to the fuel tank at an elevate temperature, which can cause thermal oxidation. In this study the oxidative stability, cetane number, viscosity, cold flow properties, and acid number of a B20 fuel on a heavy duty CI engine with a 200 gallon fuel tank were measured as a function of engine run time. The oxidative stability decreased by 50% within 80 hours of engine run time. Also the viscosity, cetane number, and acid number were increased with time. The thermal degradation of B20 is due to several factors, such as high temperature, depletion of reactivity of antioxidants, and dissolution of metals from engine parts at high temperatures. These property changes are explained with the compositional changes. These results will help understand the methods of minimizing degradation of B20.