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.
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.
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.
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.