Biodiesel Characteristics

Biodiesel is both biodegradable and nontoxic, and has significantly fewer emissions than petroleum-based diesel fuel. Tests have shown that the use of soybean B100 biodiesel fuel in urban transit buses reduces net carbon dioxide emissions by more than 75%. B100 fuel contains about 11% oxygen, which improves combustion, reducing most exhaust pollutants. Biodiesel users also note that the exhaust smells better than the exhaust from engines burning conventional diesel.

One of the most important characteristics of any diesel fuel is its ability to auto-ignite. The cetane number for biodiesel ranges from 46 to 57 for soybean oil, with an average of around 50. This means biodiesel fuel ignites more quickly than petroleum diesel, which normally has a cetane rating ranging from 40 to 52. As a result of the increased ignition quality, diesel engines run more quietly, smoothly, and cleanly than engines with standard diesel fuel.

Lubricity is a measure of a fuel’s lubricating properties. Fuel injectors and some types of fuel pumps rely on the fuel itself for lubrication. Sulfur is an important lubricating component of petroleum diesel fuel, but ultralow-sulfur petroleum diesel is limited to containing a maximum of 15 parts per million of sulfur by weight. The addition of a very low proportion of biodiesel, even a 1% or 2% volumetric blend with low-sulfur petroleum diesel, substantially improves the fuel’s lubricity.

Biodiesel is a better solvent than petroleum diesel, so it helps to clean the fuel system. However, it can break down and flush out residue deposits in vehicles that have been running on standard petroleum diesel fuel. As a result, it is important to clean the lines before changing over to biodiesel fuel. If this is not done, the solvent action of the fuel will quickly clog fuel filters by flushing out accumulated deposits in older and dirty fuel systems. Additionally, it would be wise to change the fuel filters more often until you are sure the fuel system is completely clean.

Although it has some performance advantages, biodiesel does have some disadvantages. Biodiesel fuels made from yellow grease, or recycled cooking oil, perform worse than soybean-based biodiesel. It is important to understand that recycled waste cooking oils are inherently an unknown product, whereas biodiesel products that are refined professionally have been tested to meet American Petroleum Institute (API) standards. The API sets the standards for all American petroleum products, including natural gas and biodiesel fuels.

As previously mentioned, at low temperatures, diesel fuel forms wax crystals, which can clog fuel lines and filters in a vehicle’s fuel system. The cloud point is the temperature at which a fuel starts to appear cloudy, indicating that wax crystals have begun to form. At even lower temperatures, diesel fuel becomes a gel that cannot be pumped at all. The pour point is the temperature below which the fuel will not flow. The cloud point and the pour point temperatures for biodiesel are both higher than those for petroleum diesel, so it performs less well at low temperatures.

The energy efficiency of a vehicle is the percentage of the fuel’s energy delivered as engine output. The energy content per unit of volume measure of biodiesel is around 11% lower than that of petroleum diesel, so biodiesel is less economical to use. Energy efficiency is usually expressed as miles traveled per gallon of fuel, or kilometers per liter of fuel; therefore, vehicles running on biodiesel are likely to achieve fewer distance units per volume units of fuel. This is calculated by multiplying the lower efficiency factor of biodiesel (11%) by the proportion of biodiesel in the fuel. In B20 fuel, the biodiesel component is 11% less efficient, but it only makes up 20% of the total fuel; thus, 11% times 20% equals 2.2% fewer miles or kilometers traveled.

Although more expensive to produce than petroleum diesel, biodiesel is becoming more and more common in many countries as an alternative to regular diesel fuels. Certainly, the biodiesel blends are already well established in the industry. At the very least, biodiesel fuels reduce our dependence on fossil fuels and support our local economy. These and the other advantages discussed indicate that biodiesel fuel is here to stay.