Low-Temperature Operability

In many areas of the country, the cold flow properties of biodiesel are important. Unlike gasoline, petroleum diesel and biodiesel may freeze or gel at common winter temperatures; however, biodiesel’s cloud point (the temperature at which crystals begin to form) can be significantly higher than that of petroleum diesel. If the fuel begins to gel, it can clog filters and eventually become so thick that it cannot be pumped from the fuel tank to the engine. However, with proper blending and handling, B20 has been used successfully all year in the coldest U.S. climates.

Soy biodiesel, for example, has a cloud point of 0°C (32°F). In contrast, different petroleum diesels have a wide range of cloud points. Petroleum diesel cloud points can be as low as -45°C (-49°F) or can be higher, such as -7°C (19°F), depending on time of year and region of the country. Blending of biodiesel can raise the cloud point above that of the original diesel fuel, depending on the starting cloud point of the diesel fuel. For example, a recent study13 showed that when soy biodiesel was blended into a specially formulated cold weather diesel fuel (cloud point of -38°C [-36°F]) to make a B20 blend, the cloud point of that blend was -20°C (-4°F). In very cold climates, this cloud pointmay not be adequate for wintertime use. To accommodate biodiesel in cold climates, low-cloud point petroleum diesel or low-temperature flow additives, or both,are necessary. Another option is to reduce the percentage of biodiesel in the blend. Generally speaking,with the same biodiesel and diesel fuel, a B10 will havebetter cold weather operability properties than a B20.