I think you are talking about the premium diesel fuel. I have been using this fuel in my A5 and the Q5. It gives you more mileage in the car. It is more expensive but good on the engine. I am using Shell V Power
Shell V-Power Diesel is an advanced performance fuel designed to help the latest diesel engines continously deliver more power.
Designed to keep your engine in top condition
Modern diesel engines use highly precise injection technology to help deliver great driving performance efficiently and with reduced emissions. Over time, deposits can build up in diesel fuel injection systems - reducing engine power. To sustain great performance, it is critical that these extremely precise and sophisticated parts of the engine are kept in top condition.
Shell V-Power Diesel, with its unique formulation, is designed to remove and prevent such deposits - enabling diesel engines to continuously deliver an improved driving experience
Modern high performance diesel engines are precision engineered, high performance machines designed to be quiet, responsive and highly fuel-efficient. Shell V-Power Diesel is specifically designed to help diesel engines achieve and sustain optimum performance.
High performance diesel engines require multiple fuel injections into the combustion chambers every second, delivered by sophisticated and precision engineered diesel injection equipment.
With some everyday diesel fuels, deposits can build up on the fuel injectors of new diesel engines. These deposits can impair the fuel spray and reduce fuel flow, so giving non-optimum combustion and power loss.
Hope this helps