Changes lead to many flavors of diesel

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Due to mandated changes in exhaust emission standards diesel fuel is changing. The emissions-driven changes in diesel fuel are on the whole beneficial for both the environment and for our engines, although the new fuel contains about 1 percent less energy per pound.

At the same time, the desire to substitute renewable energy sources for petroleum has introduced blends of petroleum diesel and vegetable-sourced oils, some of which are claimed to be usable in place of 100-percent petroleum diesel. Some of the alternative, so-called biodiesel fuels may be acceptable for use in marine diesel engines, however, a prudent boat owner will inquire of the manufacturer of his engine before using any fuel other than normal petroleum diesel. The marine diesel engine’s reputation for efficiency, durability, reliability and safety depends in large measure on the qualities and characteristics of the diesel fuel.

Getting the sulfur out
The recent and ongoing emission-driven changes in the formulation of petrodiesel include limiting and in some applications banning the use of 5,000 ppm (0.5 percent) sulfur content high-sulfur diesel (HSD), requiring substitution of low-sulfur diesel (LSD) whose sulfur content may not exceed 500 ppm. The progressive elimination of sulfur from diesel fuel continues with the introduction of ultra-low-sulfur diesel (ULSD), which may contain no more than 15-ppm sulfur. In general the sulfur content changes from HSD to LSD have taken place without causing major disruptions in the distribution and use of the fuel, although some problems have occurred in boats’ fuel-delivery systems and in engines where the reduced sulfur content caused some elastomers to shrink, with resulting fuel leaks.
The most recent change in fuel specification, to ULSD, began in 2006 and initially applies to fuel used for “highway use,” limiting the production of LSD to not more than 20 percent of the amount of diesel fuel produced in each region of the U.S. HSD will no longer be available for marine use after June 1, 2007. LSD may continue to be used in marine engines until 2012, however, unless you fuel at a dock that serves large vessels you will likely be buying ULSD this year since the diesel fuel supplied to a typical marina is delivered by the same tank truck that supplies the local automobile fuel station. (California mandated the exclusive use of ULSD as of Jan. 1, 2007). Although few problems are anticipated from the switch to ULSD it will, as always, be worth taking a few extra minutes when you do your engine checks to look for any indication of a fuel weep at joints in the fuel lines at the tank, filters and on the engine.
If you are fastidious about tracking fuel consumption you might note a small increase (perhaps 1 percent) in fuel use when burning the ULSD. This is a consequence of the refining process used to eliminate the sulfur, which reduces the fuel’s aromatic content. As initially refined, the lubricity of ULSD fuel, its ability to lubricate and protect the engine’s injection system from wear, is less than that of LSD fuel. The reduction in lubricity is another consequence of the refining process used to remove the sulfur since it also removes some naturally occurring lubricity agents in the fuel. The required lubricity is restored with the additives so that the fuel will meet the standards of ASTM D975. (The sulfur content of the fuel does not add to its lubricity.)
The bottom line for both LSD and ULSD is that they are efficient, safe fuels for virtually any marine diesel engine.
A great deal of publicity has been accorded biodiesel, fuel created by mixing specially processed vegetable oils with petroleum diesel. The most common blend is usually identified as B-20, 20 percent vegetable-sourced oil and 80 percent normal diesel fuel. This fuel has been well supported by generous tax credits at many stages of its production and use and is widely praised by many environmental groups.
There have been numerous reports, largely positive (and sponsored by the promoters of biodiesel) about the use of biodiesel in marine engines. Since the diesel engines used in many boats and modest size yachts are little different from the engines in school buses that are running on B-20 it may be tempting to assume that the fuel can be used in similarly powered boats. However, this assumption may not be correct. Marine engine operating cycles can be very different from what a similar engine encounters in a vehicle. Marine engines are frequently operated for sustained periods of time at 70 to 75 percent of maximum power (an engine driving a fixed pitch prop at about 250 rpm less than maximum will be operating at about 75 percent power) while vehicle engine power demand may average substantially less than 30 percent.
Engine manufacturers have expressed concern about the use of fuels other than conventional petroleum diesel. Some of the engine manufacturers will allow the use of fuel that contains up to 5 percent vegetable-derived oil. Some, such as MAN, advise that the engine lubricating oil, oil filter and fuel filter change interval be halved if a 5-percent bio diesel fuel is used. MAN also specifically warns against the use of any biodiesel identified as containing FAME (fatty acid methyl ester) in their common rail engines. The most prudent course of action for a boat owner is to ask the manufacturer of your engine for a written statement specifying the extent to which the warranty will apply if anything other than petrodiesel is used.
Another formulation of diesel fuel, E-Diesel, a blend of petrodiesel and or biodiesel with between 7.7 and 15 percent ethanol is being investigated and will likely be promoted as a way to both reduce dependence on non-renewable petroleum and reduce exhaust emissions. At this time the fuel experiments are being carried out primarily in vehicles and farm equipment, and are primarily supported by the manufacturers of farm equipment and the farm state organizations that would benefit from additional demand for the farmed crops used to produce the ethanol. It is fortunate that the testing is being done in vehicles rather than in vessels since the addition of ethanol to diesel to create the E-Diesel fuel changes the flammability of the fuel from difficult to ignite to something more akin to gasoline. (The increased risk inherent in this fuel is clearly recognized and has led to programs for testing flame arrestors that would be necessary for the fill pipes of fuel tanks used to store the E-Diesel fuel.)
A number of E-Diesel test reports suggest that while the use of the fuel may not harm diesel engines the data have raised questions about the life of various engine components when using this fuel. Both Cummins and MAN have warned against the use of this fuel in their engines. At this time it appears likely that the use of diesel fuel containing ethanol would void engine warranties.
The bottom line for fuel for your diesel marine engine is quite simple: Buy clean, fresh fuel. Avoid fuel that has been stored in drums. Always add a biocide when fueling. Keep fuel tanks as full as possible to limit the amount of water that collects due to diurnal changes in temperature. Periodically sump the tank by drawing off and examining a fuel sample from a point lower than the bottom of the fuel pickup pipe. Install a water-separating fuel filter between the fuel tank and the on-engine fuel filter. Consider installing a magnetic fuel treatment device (I have used a DeBug unit for about 15 years and know that it works on my boat). And finally, use only those fuels approved by the manufacturer of your engine.
By Ocean Navigator