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Diesel fuel differentiation – the role of multifunctional additives

Innovation is an ongoing requirement to remain competitive in the fuel additives business, often driven by legislation that demands higher quality fuels. For example, diesel produced at South African refineries contains additives to meet certain essential specification property requirements of the SANS 342 diesel standard.


Today’s engines cannot perform optimally on yesterday’s fuel, which begs the need for innovation. For instance, reducing sulphur content in middle distillate fuels has led to the need to develop lubricity additives to protect diesel injector pumps and other metal components. Other essential properties that additives need to protect are cetane rating, cold weather performance, and stability. 

The quest for cleaner and more fuel-efficient engines is never-ending, and engine developments are advancing rapidly. Yet engine manufacturers also recognise that fuel additive development must accompany and support these technology improvements to maintain enhanced performance over an engine’s lifetime.   

The use of diesel additives reflects the impact of growing diesel demand and the changing technology of diesel engines. More than a century ago, during the early phases of diesel engine development, cold starting and ignition quality were the primary concerns. That’s why one of the first diesel additives developed was an ignition improver that is still being used today. The use of this additive, together with the diesel engine’s low fuel consumption, resulted in the extensive adoption of the diesel engine as the preferred power unit for heavy goods vehicles. 

Multifunctional additive packages

Petroleum companies can differentiate their fuel offering using performance or multifunctional additives in finished fuels. The additives often offer the benefit of both an antioxidant that helps to minimise corrosion within the engine and a combustion improvement agent to ease the stress on engine pistons.

Also referred to as marketing additives, multifunctional additives have at their core a carefully formulated blend of ingredients that may include some (or all) of the following:

  • Deposit control additives
  • Demulsifiers
  • Anti-foam and dilutant solvents
  • Antioxidants
  • Lubricity improvers 
  • Metal deactivators
  • Cetane and cold flow improvers
  • Anti-static and anti-corrosion agents

Multifunctional fuel additive packages often combine a deposit control additive with a corrosion inhibitor and demulsifier additive. Such additives are added to the fuel at the terminal loading rack as the fuel is loaded into bulk trucks. While the additives typically represent less than 0.1 percent volume of the finished fuel, they can make a significant impact. Concentrations vary but usually fall within the 200 ppm to 800 ppm range.

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The deposit control additive (DCA) part of the package is designed to keep fuel injectors clean. Clogged injectors affect injector flow rates, fuel atomisation and distribution, all of which can lead to a loss in power, reduced fuel economy, increased emissions and increased maintenance costs over a vehicle’s lifetime. Therefore, a DCA is probably the most critical ingredient in a multifunctional additive package and, if carefully formulated, can provide significant benefits to any vehicle, regardless of age.

Excessive exposure to water can lead to corrosion of the metal parts of the fuel delivery system. A corrosion inhibitor provides a protective layer on the surface of these parts to increase durability. Such an inhibitor can be applied at the refinery, petrol station, depot, or as part of a multifunctional additive package.

Diesel fuel tends to aerate and produce foam as the tank fills, often spilling from the tank before the pump trigger shuts off the fuel flow, almost like pouring a beer or fizzy drink too vigorously. After foaming occurs, it takes a while to settle fully, meaning that the fuel tank may not be full after a fill-up. 

This could add up quickly for commercial truck operators with multiple trucks on the road, resulting in unnecessary waste and collective downtime. In addition, it can stain the customer vehicle’s paintwork or spill onto the pump attendant. Including an anti-foam agent reduces the amount of foam produced and significantly shortens the foam’s collapse time. 


Avoid shortcuts

When it comes to additives, there are many risks associated with an aftermarket additive, which is why we recommend using a premium diesel with all the required additives already built in.

Caltex with Techron D contains all three aforementioned components as part of an industry-leading, multifunctional additive package. Proof of performance is demonstrated using several standards and verified industry-recognised engine and laboratory tests. A top-quality multifunctional diesel fuel, Techron D is exclusive to Caltex and specially formulated to keep an engine clean by minimising deposits, maintaining fuel injector cleanliness, and ensuring optimum performance around the clock.

In some instances, marketers may formulate multifunctional additive packages with additional components. These could include cetane improver to boost the cetane number of the diesel, the metric used for diesel fuel ignition quality. A high cetane number results in quieter engine operation and reduced smoking. Today, cetane improver additive is a widely used and cost-effective product in high-quality diesel fuels.

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Both diesel and petrol can attract water into fuel tanks through natural condensation or loose-fitting fuel caps, which can be highly detrimental to a vehicle. A demulsifying additive increases the ability of diesel to shed water that may be emulsified or held in suspension in the fuel by separating it from the fuel. 

As mentioned earlier, users should be cautious when considering the use of aftermarket additives. Through aggressive marketing, many make performance claims that are often too good to be true. Modern, high-technology diesel engines hardly – if ever – require any aftermarket additives. Instead, good quality fuel from reputable marketers already contains all the additives that a fuel needs.



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