Biodiesel Provides a High Energy Return and Displaces Imported Petroleum

Life-cycle analyses show that biodiesel contains 2.5 to 3.5 units of energy for every unit of fossil energy input in its production, and because very little petroleum is used in its production, its use displaces petroleum at nearly a 1-to-1 ratio on a life-cycle basis. This value includes energy used in diesel farm equipment and transportation equipment (trucks, locomotives); fossil fuels used to produce fertilizers, pesticides, steam, and electricity; and methanol used in the manufacturing process. Because biodiesel is an energy-efficient fuel, it can extend petroleum supplies.

Biodiesel Reduces Life-Cycle Greenhouse Gas Emissions

When biodiesel displaces petroleum, it significantly reduces greenhouse gas (GHG) emissions. By one estimate, GHG emissions (including carbon dioxide [CO2], methane, and nitrogen oxide [NOx]) are reduced by 41%, if biodiesel is produced from crops harvested from fields that were already in production. When plants such as soybeans grow, they take CO2 from the air to make the stems, roots, leaves, and seeds (soybeans). After the oil is extracted from the soybeans, it is converted into biodiesel. When the biodiesel is burned, CO2 and other emissions are released and return to the atmosphere. This cycle does not add to the net CO2 concentration in the air because the next soybean crop will reuse the CO2 as it grows. When fossil fuels such as coal or diesel fuel are burned, however, 100% of the CO2 released adds to the CO2 concentration levels in the air.

Biodiesel Reduces Tailpipe Emissions

Biodiesel reduces tailpipe PM, hydrocarbon (HC), and carbon monoxide (CO) emissions from most modern four-stroke CI or diesel engines. These benefits occur because biodiesel contains 11% oxygen by weight. The fuel oxygen allows the fuel to burn more completely, so fewer unburned fuel emissions result. This same phenomenon reduces air toxics, which are associated with the unburned or partially burned HC and PM emissions. Testing has shown that PM, HC, and CO reductions are independent of the biodiesel feedstock. The EPA reviewed 80 biodiesel emission tests on CI engines and has concluded that the benefits are real and predictable over a wide range of biodiesel blends (Figure 2). EPA’s review also indicated that B20 increased NOx by about 2% relative to petroleum diesel use. A more detailed analysis of the database examined by EPA, plus more recently published results, confirms the positive impact of B20 on emissions of HC, CO, and PM. However, examination of the NOx results shows that the effect of biodiesel can vary with engine design, calibration, and test cycle. At this time, the data are insufficient for users to conclude anything about the average effect of B20 on NOx, other than that it is likely very close to zero.

In contrast, when biodiesel is used in boilers or home heating oil applications, NOx tends to decrease because the combustion process is different (open flame for boilers, enclosed cylinder with high-pressure spray combustion for engines). The NOx reduction seen with biodiesel blends used in boilers appears to be independent of the type of biodiesel used. In blends with heating oil up to 20% biodiesel, NOx is reduced linearly with increasing biodiesel content. For every 1% biodiesel added, NOx decreases by 1%. A B20 heating oil fuel will reduce NOx by about 20%.10,11 Sulfur dioxide (SO2) emissions were also reduced when the two fuels were blended, because biodiesel contains much less sulfur than typical heating oil does. A 20% blend of biodiesel in heating oil will reduce SO2 by about 20%.

Heating oil and diesel fuel dyed red for off-road use (agriculture, power, boiler fuels, construction, forestry, and mining) can contain as much as 500 ppm sulfur. Blending biodiesel into off-road diesel fuel can significantly reduce SO2 emissions. Nonroad diesel will transition to 15 ppm sulfur beginning in 2010.

 Biodiesel and Human Health

Some PM and HC emissions from diesel fuel combustion are toxic or carcinogenic. Using B100 can eliminate as much as 90% of these air toxics. B20 reduces air toxics by 20% to 40%. The positive effects of biodiesel on air toxics have been shown in numerous studies.

Recently, the U.S. Department of Labor Mining Safety Health Administration (MSHA) has implemented rules for underground mines that limit workers’ exposure to diesel PM. MSHA found that switching from petroleum diesel fuels to high blend levels of biodiesel (B50 to B100) significantly reduced PM emissions from underground diesel vehicles and substantially reduced workers’ exposure. However, even low concentrations of biodiesel reduce PM emissions and provide significant health and compliance benefits wherever humans receive higher levels of exposure to diesel exhaust.

Biodiesel Improves Engine Operation

Even in very low concentrations, biodiesel improves fuel lubricity and raises the cetane number of the fuel. Diesel engines depend on the lubricity of the fuel to keep moving parts, especially fuel pumps, from wearing prematurely. One unintended side effect of the federal regulations, which have gradually reduced allowable fuel sulfur to only 15 ppm and lowered aromatics content, has been to reduce the lubricity of petroleum diesel. The hydrotreating processes used to reduce fuel sulfur and aromatics contents also reduces polar impurities such as nitrogen compounds, which provide lubricity. To address this, the ASTM D975 diesel fuel specification was modified to add a lubricity requirement (a maximum wear scar diameter on the high-frequency reciprocating rig [HFRR] test of 520 microns). Biodiesel can impart adequate lubricity to diesel fuels at blend levels as low as 1%.

Biodiesel Is Easy To Use

Finally, one of the biggest benefits to using biodiesel is that it is easy. Blends of B20 or lower are literally a “drop in” technology. No new equipment and no equipment modifications are necessary. B20 can be stored in diesel fuel tanks and pumped with diesel equipment. B20 does present a few unique handling and use precautions, but most users can expect a trouble-free B20 experience.

Article Source: Excerpt from the 2009 NREL Biodiesel Handing and Use Guide