Pressure drop hysteresis effect on biodiesel filtration

Filter plugging is one of the main cold flow problems associated with the use of biodiesel blends in cold climates. We developed a new fuel screening test to analyze the cold flow properties of the biodiesel and its blends with ULSD based on pressure drop measurements across a test filter. The fuel is pumped through a test filter under controlled temperature and flow conditions and the pressure drop is measured. As temperature is reduced at a constant flow rate, the pressure drop increases and the rate of the pressure drop increase goes up sharply as a plugging condition is approached. Biodiesel blends in general exhibit higher pressure drops than ULSD and the pressure drop increases with the biodiesel fraction. When fuels are cooled to −30 °C and then reheated, the pressure drop at each temperature is higher than that measured when the fuels are being cooled. The difference between the cooling and heating curves decreases as the fuel isheated but is still present at 20 °C. Both ULSD and biodiesel blends exhibit this hysteresis effect, but the effect is much larger with biodiesel blends. This means that exposure of biodiesel blends to low temperatures predisposes them to filter plugging even if they are dispensed and used at higher temperatures. In addition, the pressure drop hysteresis will remain unless fuel properties return to their original state when reheated to 40 °C or higher.