Diesel fuel additives have two main functions. the first of diesel fuel additive is to maintain injector cleanliness. A clean injector will spray a perfect "fox tail" pattern mist of diesel fuel allowing for efficient combustion. Dirty injectors produce a fuel spray that is not a uniformly fine mist which will affect fuel mileage, power output, and idle quality, among other things.
Second is to prevent gelling in cold weather. Without the proper additive diesel engines just won't start when the temperature gets below a certain point. Even while running dow the highway a diesel fuel system can gell and stall the engine without the proper fuel formulation.
The best diesel fuel additives also include a cetane booster, which boosts power and provides many other performance benefits. It is recommended that a cetane booster additive be used as a form of insurance. Many fueling stations, advertising their fuel as "premium" might lead a consumer to assume that the fuel has a higher cetane rating than it does. So since your going to be using an additive anyway, buy one with cetane booster! You'll be glad you did.
Other diesel fuel additives include fuel stabilizers to protect the characteristics of diesel fuel when stored for long periods of time. There are lubrication benefits provided by most diesel fuel additives. Other benefits include addressing other diesel fuel issues such as low fuel filterability, microorganism infestation, insufficient detergency and water contamination. there are even new additives produced from blends of renewable agricultural products.
By law any current diesel fuel additives will comply with the current government specification regarding sulfur content. Some respected brand names include Stanadyne, Amsoil, Power Service, Racor, and Lucas. First decide what your needs are beyond the basics of injector cleaner and cold weather protection. If you don't leave in a northern climate, or its summer time, anti gelling won't be a concern. There are numerous online resurces to help a consumer make an informed choice!