Cold Flow Properties

Pure biodiesel (B100) has poor cold-temperature properties as straight die­sel fuel. Biodiesel’s cloud point (CP) and cold filter plugging point (CFPP) are both high, thus making pure biodiesel (B100) unsuitable as a cold-climate fuel without blending or additives. When biodiesel is cooled below a certain temperature, some ingredient molecules of biodiesel start to aggregate and form crystals. This temperature varies depending on the biodiesel feedstock, but is consistently quite high. As the biodiesel is further cooled and the crys­tals become larger than one quarter of the wavelength of visible light, the fuel system starts to look cloudy. This point is known scientifically as the cloud point. The cloud point measurement follows the ASTM 2500. The low­est temperature at which biodiesel can pass through a 45-micron filter is called the cold filter plugging point. A high cold filter plugging point tends to clog up vehicle engines more easily. As biodiesel is further cooled below the CFPP, it will gel and eventually solidify. This point is called the gel point. Another important cold flow property is the pour point, which is defined as the lowest temperature where the fuel is observed to flow. As all these tem­peratures are generally higher for biodiesel (B100) than petrodiesel, biodiesel freezes faster than most petrodiesels. Commercial additives developed for diesel to improve its cold flow properties are mostly applicable to biodiesel and biodiesel blends [47].