The truth about marine fuel additives

Over the years, fuel additives have developed a questionable reputation in the shipping industry due to actions of a few unscrupulous suppliers. This perception unfortunate in the light of growing regulatory and performance demands being placed on marine diesel equipment today—areas where high quality fuel additives can make a difference in terms of lower operating costs and reduced emissions.

Modern marine engines are designed for fuel efficiency and reduced emissions. For an engine to operate at peak levels, it needs to burn fuel completely throughout the entire combustion cycle. Unburned or partially burnt fuel wastes energy and increases emissions. The right combination of fuel additives can deliver enhanced combustion, protect against wear and prevent deposit build-up. As a result, marine engines and hardware can work to their full potential, over longer periods, with reduced maintenance costs.

In certain areas, governmental regulations require the use of higher quality, low sulphur distillate fuels in near-shore areas. Although these fuels burn cleaner than their heavier, residual fluid counterparts, there is still room for significantly better performance with the use of fuel additives. Poor or incomplete combustion can lead to deposit build up, liner lacquering and bore polishing, all of which can have a negative impact on equipment performance and result in impaired fuel economy.

An optimum additive formulation can eliminate many of the difficulties associated with incomplete combustion. For instance, deposit control additives can clean fouled fuel injectors and prevent loss of fuel economy by inhibiting deposit build-up. Another area of concern is liner lacquering. In this case, the cross-hatch scoring on the cylinder liner, which is used to control oil consumption, fills in with lacquer and a smooth surface forms. As a result, more cylinder lubricant must be used, resulting in increased cost and decreased performance. A similar situation occurs when the cross-hatch scoring on the liner wears out, a condition known as bore polishing. In these instances, the right combination of cetane improvers, deposit control additives and combustion improvers have proven effective to prevent problems arising and improve performance.

In 2010, Lubrizol conducted a six-month field trial with test vessels on the Mississippi River. Results indicated the addition of a multi-functional diesel fuel additive delivered reduced emissions. The test also showed a statistically significant average fuel efficiency improvement of 2.33%. By improving fuel efficiency, ship operators can move cargo at a lower cost, an important consideration in today’s highly competitive market.

While cleaner distillate fuels may offer environmental benefits, reducing the sulphur levels can have a negative impact on equipment performance. For example, many fuelling systems were designed to be lubricated by the diesel fuel itself. The fuel contains trace amounts of polar compounds that provide protective lubrication. The hydro-treating process of removing sulphur from fuel also removes these compounds, leading to a loss of lubricity, which can mean reduced wear protection and potential equipment failure. As noted in a report from the International Fuel Quality Center, “Treatment with lubricity-improving additives is sometimes required for fuels which have been severely hydro-treated to produce ultra-low-sulphur diesel.”

Ultra-low-sulphur diesel fuel, together with recent fuel injection equipment design changes, has been identified as a potential reason for an increase in internal diesel injector deposits (IDID) that can cause injectors to seize and stop performing, a problem that can be alleviated with the use of certain injector cleanliness additives.

Fuel switching—the process of changing from residual to distillate fuel as a ship nears a designated special emission control area (SECA)—is not a new development, but it poses its own set of challenges. Distillate fuel stored onboard for long periods of time can degrade. The right additive can stabilise the fuel, making the change over from residual to distillate less problematic.  

Overall, in terms of distillate fuels, the right fuel additives have been proven to extend engine maintenance intervals and reduce engine downtime, resulting in savings in both time and costs.

When ships are at sea, where emissions regulations are less strict, many operators prefer to burn residual fuels because of their lower costs. These heavy fuels pose some significant challenges, particularly in regard to asphaltenes—complex organic materials present in crude oils or any fuel grade with some residual content. Asphaltenes have the potential to lose their solubility in fuel, leading to instability and dropout. When this happens, the resultant deposit can clog fuelling and distribution systems, leading to significant maintenance disruption.

Asphaltene dropout tends to occur in a low aromatic fuel environment and can be triggered when mixing fuels together. If asphaltenes are separated from the fuel and deposited into the sludge tank, valuable hydrocarbons are being wasted. Dispersant additives can be used to keep asphaltenes intermixed with the fuel allowing them to be burned, increasing fuel efficiency.

As is the case with distillate fuels, poor or incomplete combustion can be a serious issue with residual fuels. Again, the right additive formulation can improve fuel combustion, leading to better fuel economy, and in the case of soot build-up, improved safety. With incomplete combustion soot can build up in exhaust systems, sometimes all the way to the stack, presenting a fire hazard. Preventing soot build-up ensures the efficiency of exhaust track hardware, a safer operation, and reduced emissions into the environment.

Corrosion control is also an issue with residual fuels. Because residual fuels are very high in sulphur they produce a large amount of SO₃, which can be converted to sulphuric acid and that leads to post-combustion corrosion issues. Metal-based fuel additives can help by neutralising the acid and controlling corrosion.

It is always wise to be sceptical of unsubstantiated claims in the marine industry or anywhere else. Shipowners and operators should always ask to see proof of performance, which a legitimate additive supplier will be pleased to provide.