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Quality improvement by the addition of additives, which has been a common practice with gasoline fuels for many years, has also become popular for diesel fuels. Depending on their purpose, diesel fuel additives can be grouped into four major categories:
The effects of different additives may be seen in different time frames. Some additives have an immediate effect (e.g., cetane improvers), others may bring an effect after a long period of operation (e.g., detergent additives). The overall concentration of additives is generally below 0.1%, so that the physical properties of the fuel, such as density, viscosity, and volatility are not changed.
Additives may be added to diesel fuel at three different stages: (1) at the refinery, (2) in the fuel distribution system, and (3) after the fuel has left the control of the producer. Additives of the latter group, when added by the end user or a reseller, are called aftermarket additives.
Refinery Additization. Fuel refiners must ensure that their products meet specifications and are suitable for the intended use. This can be achieved through such means as the choice of crude oil, refinery processing, blending, or the use of additives. The final choice of methods is driven by economics. Some refineries may rely on additives, while others may be able to provide high quality fuel with no additives. Since refiners do not publish such information, the exact extent of additive usage remains unclear.
Fuel manufacturers use multiple effect additive packages, rather than single additives. In the USA, common additives include pour point reducers and fuel stability additives . Cetane improvers are especially common in California, to achieve the emission reductions mandated for the CARB diesel. Cloud point is usually controlled by processing changes, rather than by additives. In Europe, on the other hand, low temperature operability is often enhanced through the use of CFPP improving additives. Antifoam additives are used in Europe and Asia to prevent spills when consumers fill their tanks. Foaming is a lesser problem in North America, due to the lower distillation point of diesel fuel and different design of tanks and fuel dispensing systems. Lubricity additives are used worldwide in fuels with ultra low sulfur content.
Distribution System Additization. Pipeline operators sometimes inject drag reducing additives (to increase the pipeline capacity) and/or corrosion inhibitors. Fuel properties may be also upgraded at the terminal or even at the retail pump—such as from a regular to a ‘premium diesel’ grade—by treating the fuel with additives. An example additive package may include a detergent/dispersant, stabilizing additives, a cetane number improver, a low temperature operability additive (flow improver or pour point reducer), and a biocide . Of course, the additive package must be always tailored to the fuel properties.
Aftermarket Additives. Some users use additives to further improve the fuel to meet their particular needs, for instance cold climate operation, or because they believe they need a higher quality fuel. A wide range of aftermarket additives are available from a number of suppliers. Some of these additives may have legitimate uses. For instance, the use of de-icers may be warranted under cold weather conditions and/or when problems with fuel system icing are encountered. In many cases, however, aftermarket additives packages consist of compounds such as detergents, lubricity improvers and cetane enhancers that would normally be added at the refinery or fuel terminal by the fuel marketer.
Users should be cautious when considering the use of any aftermarket additives. Some aftermarket additives are aggressively marketed, with performance claims that are often too good to be true. Yet, in most cases, they are not needed and should be avoided. Quality commercial fuels from reputable marketers contain all the additives that a fuel needs and have been extensively tested to minimize the possibility of adverse interactions between different additive and/or fuel components.
If the user still feels that additives are needed, they should be chosen based on careful research, and used in accordance with the recommendations of the supplier and the engine manufacturer. Inappropriate use of additives may have adverse effects on the engine, and may affect engine warranties (for example, some engine makers require that alcohol based de-icers not be used).