Clean energy has become a holy grail of sorts for scientists. Dwindling fossil fuel reserves and rising concerns over global warming have pushed researchers to look for cleaner, renewable alternatives. So far, there are many contenders vying to be the fuel of the future, but no single clean energy technology has separated itself from the pack.Now, Audi has announced that they have successfully created diesel fuel from water and carbon dioxide via a carbon neutral process using only renewable energy. While the production process is only being carried out in a pilot program, if it can be scaled up to industrial levels, it could mark a major breakthrough.Audi is most well-known for its luxury cars, rather than hybrids. So far, Audi has lagged behind rivals , such as Toyota and Ford, in the hybrid and plugin race, but the company's process for creating diesel fuels could propel it to the front of the race.The fuel Audi has created through its pilot program has been nicknamed “blue crude”, owing to the blue hue of the final e-diesel product. The fuel is produced using a three step process that harnesses renewable energy and carbon dioxide from the atmosphere.First, energy is harvested using solar panels. Then using the harnessed energy, water molecules are split to create oxygen and pure hydrogen. Finally, the pure hydrogen is mixed with carbon monoxide, which was itself created from carbon dioxide captured from the atmosphere, to form the long-chain hydrocarbon compounds needed to produce diesel fuel. Diesel differs from gasoline in that the fuel is compressed to the point of combustion, rather than ignited by a spark plug. Diesel automobiles are very popular in Europe , though owing to the high levels of emissions created by older diesel motors, the fuel has largely been relegated to semi-trucks in the United States. Advances in diesel engines over the last few decades, however, mean that modern diesel engines are actually more efficient and produce less emissions than traditional gasoline-based cars.Audi claims its Dresden based pilot program is the only of its kind in the world. Audi is collaborating with the German clean energy firm Sunfire to produce the fuel.Not only is blue crude harvested using sustainable methods, but the fuel itself has actually shown signs of being able to outperform conventional diesel. The fuel offers superior combustion with an energy efficiency of 70 percent, meaning as the fuel is burned more of it is converted directly into energy. Researchers from Sunfire claim cars running on blue crude run quieter and produce fewer pollutants than cars running on traditional diesel.While only 160 liters of blue crude are currently being produced per day, researchers believe that the process can be scaled up, and that the fuel's final price point for consumers will fall between 1 and 1.5 euro. Given that fossil fuel diesel in Europe generally sales for more than 1.5 euro a liter, this could give blue crude a cost advantage.