Get the full story on Audi's legal battle TDI, and find out why an EU court refused Audi's trademark claim, inside.

A European Union court in Luxembourg has denied an Audi and Volkswagen attempt to trademark the term "TDI" for exclusive use on their engines, according to German newswire Deutsche Presse-Agentur (dpa). The judges presiding over the case said that the letters are an abbreviation that is not unique in the European Union.

Thus, they ruled that because the term has historically been used elsewhere, there was not enough evidence to rule that "TDI" should be owned by Audi. Under EU law, an abbreviation describing the attributes of a product, such as "Turbo Direct Injection" and "Turbo Diesel Injection", may not be trademarked, according to the dpa report.

Audi and Volkswagen will be required to pay all related court costs.

Gallery: EU to Audi: No TDI trademark for you