Diesel Vehicles Using Biodiesel
Biodiesel and conventional diesel vehicles are one in the same. Although light-, medium-, and heavy-duty diesel vehicles are not technically "alternative fuel" vehicles, many are capable of running on biodiesel. Biodiesel, which is most often used as a blend with regular diesel fuel, can be used in many diesel vehicles without any engine modification. The most common biodiesel blend is B20, which is 20% biodiesel and 80% conventional diesel. B5 (5% biodiesel, 95% diesel) is also commonly used in fleets.
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 from wearing prematurely. Federal regulations have gradually reduced allowable fuel sulfur to only 15 ppm and lowered aromatics content. The unintended side effect of these regulations has been the reduction in the lubricity of petroleum diesel. To address this, the ASTM D975 diesel fuel specification was modified to add a lubricity requirement. One advantage of biodiesel is that it can impart adequate lubricity to diesel fuels at blend levels as low as 1%.
Before using biodiesel, be sure to check your engine warranty to ensure that higher-level blends of this alternative fuel don't void or affect it. High-level biodiesel blends can have a solvency effect in engines and fuel systems that previously used petroleum diesel which may result in degraded seals and clogged fuel filters.
What is Clean Diesel?
Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million or lower sulfur content. ULSD combined with advanced emission control technologies is referred to as clean diesel. This type of diesel is now the only diesel fuel used in all on-road diesel vehicles as of 2010. The sulfur content of ULSD has been reduced by 97% compared to diesel fuel used in the past. The United States began its changeover to ULSD in June 2006, after the U.S. Environmental Protection Agency (EPA) mandated that 80% of highway diesel fuel produced or imported contain 15 ppm or less sulfur. Biodiesel is also considered a USLD because it does not intrinsically contain sulfur.
Petroleum-based ULSD is produced by removing sulfur during the oil refining process, often called hydrotreating. In this process, a heated mixture of petroleum feedstock and hydrogen passes through a reactor with catalysts—substances that facilitate chemical reactions without being consumed by the reaction—to separate sulfur from hydrocarbon molecules.