DETROIT — Biodiesel is going mainstream this week, as new standard definitions of the fuel have been issued.Until recently, biodiesel has been somewhat of a cult favorite among truckers, farmers and environmental activists. A few manufacturers certify their diesel engines to run on biodiesel, but only for light blends such as B5, which is 5 percent biodiesel. Now the American Society for Testing and Materials (ASTM) has released a completely new set of specifications that covers biodiesel blends between 6 (B6) and 20 (B20) percent biodiesel for on-road diesel engine use.Biodiesel is a domestically produced, renewable alternative to diesel fuel and can be made from plant oils, animal fats, recycled cooking oils or new sources such as algae. Biodiesel must be properly processed to meet the approved ASTM specifications regardless of the feedstock used to produce it.Prior to these standard definitions, everyday use of carbon-neutral biodiesel had been a practical impossibility for drivers who wanted to comply with the factory warranty on their diesel-powered vehicle.Now, manufacturers can gear up to test and certify their newest diesel products for use with the fuel, and diesel owners will be able to fuel with the appropriate mix of the renewable fuel without violating their warranty. Several more companies are expected to raise their approvals to B20 now that the final ASTM specifications for B6-B20 blends have been approved and published.Some companies, such as Chrysler, had stated that the need for that spec was the single greatest hurdle preventing full-scale acceptance of B20 in their diesel vehicles.Chrysler Safety and Regulatory spokesman Max Gates said, 'The publication of these new biodiesel blend standards by ASTM marks a major milestone in our nation's effort to expand the role of renewable fuels, including biodiesel, in addressing our energy, environmental and economic challenges. Chrysler LLC is committed to working with our partners in the transportation industry to build on this action and make biodiesel an alternative available to all of our customers.'So far, Audi, Dodge, Ford, GM, Mercedes, Mitsubishi, Nissan and VW are among the manufacturers who have announced plans to bring diesel-powered cars or trucks to the market within the next two years.Inside Line says: As new high-mileage diesel cars and trucks come on line, diesel owners will be able to burn a cleaner fuel that does not depend on imported oil. It's a small step, but one in the right direction. — John Stewart, Correspondent