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 NREL's renewable diesel research focuses on biodiesel, with limited work on ethanol and other oxygenates. Our Fischer-Tropsch diesel research is described on the Gas-to-Liquid Fuel page.
Renewable Diesel
Renewable fuels for diesel engines improve energy security by displacing petroleum. The primary renewable diesel fuel today is biodiesel, which consists of fatty acid methyl esters and is made from vegetable oil, animal fat, or waste grease. Biodiesel is typically used as a blend with conventional diesel. Ethanol can also be blended into diesel fuel, but this blend is not as safe as conventional diesel because of its low flashpoint. Fischer-Tropsch diesel is of interest because it can be produced from biomass. Finally, a number of different oxygenates might be produced from renewable resources and blended with diesel fuels.
Biodiesel R&D
 Biodiesel represents a significant energy resource and could someday supply 3% to 5% of the distillate fuel market. According to an NREL biodiesel life cycle analysis (PDF 671 KB) (Download Adobe Reader), roughly 81% of the well to wheel energy in biodiesel is renewable and displaces petroleum. Based on discussions with industry, several issues that currently prevent broader market penetration for biodiesel are being addressed by NREL researchers:
Ensuring Fuel Quality
Engine manufacturers and fuel consumers are concerned that biodiesel is not of adequate purity and quality for engine and fuel system component durability. NREL is performing nationwide surveys of biodiesel and biodiesel blend quality in order to reveal the extent of this problem, and to assist the biodiesel industry in addressing it.
Ensuring Fuel Stability
Engine and fuel injection equipment manufacturers are concerned that biodiesel may undergo oxidation during storage, handing, and use and form fuel system deposits. These deposits could cause plugging and damage engine fuel system components. NREL is examining biodiesel stability as part of the nationwide fuel quality surveys. Additionally, research to understand the fundamental chemistry of biodiesel oxidative degradation is being performed. This work is directed ultimately at developing a practical test for assessing the stability of a fuel, and should eventually lead to including an oxidation stability requirement in the standard specifications for biodiesel and biodiesel blends.
Ensuring Reliability
Even if a fuel is of adequate purity and stability, engine manufacturers and fuel consumers are concerned about the effect of biodiesel on the durability of engine and fuel system components. NREL is assessing the impact on reliability with fuel pump and fuel injector wear tests, along with materials compatibility tests.
Maximizing Environmental Benefits—Reducing NOx Emissions
Although the primary benefits of biodiesel use are petroleum displacement and carbon dioxide emission reductions, biodiesel also causes a reduction in the emissions of diesel particulate matter and toxic compounds. However, many studies have shown that NOx emissions can increase. NREL is measuring the extent of the NOx emissions increase in fully modern engines, and is working to develop fuel formulation, fuel additive, and engine operational strategies to eliminate it.
Demonstrating Performance—Fleet Case Histories and Demonstrations
The ultimate proof of the impact of biodiesel on engine durability is a long-term assessment of the effect of biodiesel use on vehicle maintenance and that operate costs. NREL is engaged in fleet evaluations of biodiesel where the renewable fuel is compared to carefully selected control vehicles operating on conventional diesel. These studies will reveal the impact of biodiesel on fuel economy and maintenance costs over many months of operation in a real world setting.
More Information
See our biodiesel publications for more information.
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