In the past, biodiesel conjured images of hippies concocting fuels from McDonald's waste cooking fat, an operation that could take place in the barn or perhaps a kitchen. The definition of biodiesel is a little hazy because the term can be applied to a number of 'homemade' fuels as well as those refined under more stringent guidelines. In describing biodiesel here, we will use ASTM standard D6751 and the US Department of Energy (DOE) research rather than referencing some of the cruder do-it-yourself technologies. This is not to take anything away from those who manufacture their own fuel you can bet that official recognition of biodiesel as a viable technology has probably been hastened by them. But fuels from homemade sources will not be used to power highway trucks. Biodiesel is fuel produced from farm products. Its base is vegetable oil and alcohol. And yes, the commercially sold vegetable oil can be sourced from recycled restaurant greases so it has great appeal to those who advocate renewable energy practices.

Combusting biodiesel

Biodiesel burns more cleanly than petroleum based diesel fuel. Most of the harmful emissions produced by combusting petroleum diesel fuel are reduced with the exception of oxides of Nitrogen. NOx emission is slightly increased over diesel fuel because biodiesel is an oxygenate fuel, that is, like alcohol there is an oxygen component in the fuel. Perhaps the biggest disadvantage of biodiesel is its inability to flow at colder temperatures. This means that its primary markets are going to be in warmer climates. Actually, these markets are already becoming established in the southern states. Biodiesel becomes a more versatile fuel when it is mixed at a 20% ratio with diesel fuel when it becomes known as B20. Biodiesel B20 is able to retain some of the advantages of biodiesel B100 (100% vegetable base) and is probably more practical as a commercial vehicle fuel in the near future. B20 and B100 are compared in with current diesel fuel in the table that follows.

Emission	B100	B20
Carbon monoxide	-43%	-12%
Hydrocarbons	-56%	-11%
Particulates	-55%	-18%
Nitrogen Oxides	+6%	+1.2%
Air Toxics	-80 to -90%	-20%

Biodiesel Costs and Availability

Biodiesel is new, expensive and limited to seasonal use in much of the United States and Canada. These factors have meant that the supply infrastructure has been slow to grow. Biodiesel sells at between $1.00 and $1.70 per gallon in 2002 prices. Add a further $.50 tax and it is expensive compared with current #2 diesel fuel though this is changing through the price increases we have seen through 2004. This means that consumers tend to opt for cheaper B20 than B100. However, the DOE is actively working with the biodiesel industry to reduce the cost of the product. Combine this with EPA efforts to make highway fuel cleaner (and more expensive!) reducing the cost differential, and the future for biodiesel may be bright. The DOE suggest that it is best to avoid any biodiesel that does not meet the ASTM D6751 standard.


Biodiesel: power and fuel economy

Using of B100 in place of diesel fuel will reduce power by about 10%: quite simply, there is less heat energy in biodiesel. This means that you will use more of it. For every gallon of diesel fuel consumed, approximately 1.1 gallons of B100 will have to be consumed. The difference is less noticeable when B20 is used, most data indicates that the reduction in power and fuel economy is around 2%. Finally, you should know that some OEMs do not approve of biodiesel use in their fuel systems. Using biodiesel can void warranty. If you are considering the use of either B100 or B20, consult the OEM and ensure that it is approved.


(adapted from Truck Engine, Fuel and Computerized Management Systems.)