Drawbacks of Biodiesel Use

Drawbacks of Biodiesel Use
Biodiesel contains 8% less energy per gallon than typical No. 2 diesel in the United States; 12.5% less energy per pound. The difference between these two measurements is caused by the fact that biodiesel is slightly more dense than diesel fuel, so there are slightly more pounds in a gallon of fuel.

All biodiesel, regardless of its feedstock, provides about the same amount of energy.

The difference in energy content can be noticeable if you are using B100. If you are using B20, the difference in power, torque, and fuel economy should be between 1% and 2%, depending on the diesel with which you are blending.

Most users report little difference between B20 and No. 2 diesel fuel. As the biodiesel blend level is lowered, any differences in energy content become diminished and blends of B5 or less do not cause noticeable differences in performance compared to diesel No. 2.

A further drawback to biodiesel use is its less favorable cold flow properties compared to conventional diesel. The cold flow properties of biodiesel and conventional petrodiesel are extremely important. Unlike gasoline, petrodiesel and biodiesel can both start to freeze or gel as the temperature gets colder. If the fuel begins to gel, it can clog filters or eventually it can become thick enough that it cannot even be pumped from the fuel tank to the engine.

Biodiesel has been shown to increase nitrogen oxide (NOx) emissions in many engines on engine stand tests. Biodiesel does not contain nitrogen so the increasing NOx phenomenon is not related to fuel nitrogen content. NOx is created in the engine as the nitrogen in the intake air reacts with oxygen at the high in-cylinder combustion temperatures. The NOx increase observed for B20 is believed to occur primarily at low engine speed but high load (or torque) conditions. Testing of entire vehicles may be a better predictor of real-world emission impacts than engine stand tests. Ongoing testing of B20 in heavy-duty vehicles at the National Renewable Energy laboratory is showing that NOx emissions do not always increase for B20 and in some cases actually decrease.

Because of the conflicting results of engine stand and vehicle tests, the impact of B20 on NOx must be regarded as unknown at this time. As with petroleum based diesel fuel, the exact composition of the biodiesel can also influence NOx emissions. Data shows NOx variability between the various biodiesel meeting ASTM D6751 of around 15%, with soybean oil based biodiesel producing the highest NOx increase. This is similar to the variability observed for conventional diesel fuels spanning the range of the ASTM diesel fuel specifications (ASTM D975).