For countries that possess cold weather climates such as Canada, the performance of biodiesel and biodiesel blends in lower temperatures is of great importance.  The cloud point of a fuel is defined as the temperature of a liquid specimen when the smallest observable cluster of hydrocarbon crystals first occurs upon cooling under prescribed conditions.  The formation of these “clouds” signify the beginning of the fuel to form a gel, leading to potential plugging of filter or other small orifices in an engine and an overall decrease in performance.  Cloud point values vary depending on the type of feedstock used, with animal fat generally having a higher cloud point temperature due to the presence of saturated (i.e. single bond) fatty acids.   A reduction in the cloud point can be achieved through the use of anti-gel additives

Significance

There are three standard test methods for quantifying the cloud point in biodiesel: ASTM D2500, D5773 and D7397.  For D2500, the cloud point is determined visually by subjecting a sample to decreasing temperatures in a cloud point/pour point bath and checking for crystals every 1-2 degrees Celsius.  Methods D5773 and D7397 are automated methods that determine the cloud point by a change in light level as measured by an optical sensor.