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Stanadyne White Paper on Diesel Fuel
Low-Sulfur Diesel Fuel Requires Additives to Preserve Fuel Lubricity
U.S. Environmental Protection Agency regulations requiring diesel fuel sold for highway use to be less than 500 parts per million (ppm) sulfur and with lowered aromatic content will go into effect on Oct. 1. 1993. The environmental benefits of the regulation - including a significant reduction in particulate emissions - are commendable. Reducing sulfur also decreases the acids formed in engine combustion chambers, offering the promise of extended engine life. However, fuel system manufacturers are concerned that the methods used to reduce sulfur content can also impact fuel lubricity and may cause accelerated fuel system component wear.
Today, the most cost-effective way for refiners to produce low-sulfur diesel fuel is through hydrotreating, a process that removes sulfur by treating it with hydrogen. Because hydrogen is a highly reactive element, it also reacts with other components in the fuel, reducing the content of desirable. lubricity - enhancing chemicals.
When the hydrotreating process compromises fuel lubricity, wear rates increase in many fuel injection systems, most of which are designed to benefit from the natural lubricating properties of traditional diesel fuel.
Lubricity wear problems associated with low-sulfur diesel fuels have already been observed in Canada, California, Texas, Arizona and some parts of the Northeast U.S. where fleets have elected to use low-sulfur fuels to reduce emissions.
Problems encountered have ranged from underrun / stalling annoyances to fuel pump failure requiring replacement.
Lubricity problems are not new. During the Vietnam War, a manufacturer of jet engines experienced similar difficulties. In order to extend the life of the jet fuel pumps, the military created a new fuel specification, called JP8, which greatly improved stability, lubricity and anti-corrosive properties. The additive technologies used then are available to the diesel fuel market today . Stanadyne Automotive Corp. is the leading diesel fuel injection equipment manufacturer in North America, and manufactures fuel injection pumps, nozzles, and filtration products, and as such is very concerned with wear problems resulting from low-sulfur fuel.
Addressing fuel problems
Current testing has shown that performance proven fuel additives do restore the lubricity of low-sulfur fuel. In developing its own line of fuel additives, Stanadyne has proven that additive technology exists today which can effectively restore the beneficial fuel properties lost during hydrotreating. Stanadyne strongly advocates the use of lubricity additives, and recommends they be inserted during the refining or fuel distribution stage so consumers will not be burdened with this task.
Stanadyne also recommends the use of lubricating fuel additives for off-road applications. Off-road vehicles are not subjected to the low-sulfur fuel regulations, however, several manufacturers have said they will only manufacture the low-sulfur grade dictated by the higher demand for the on-highway regulated fuel. That means off-road vehicle users are likely to be exposed to the low-sulfur fuels where they fill up.
Lowered aromatic content in diesel fuel also may have a negative impact on winter operability. Aromatics in the fuel help keep the fuel's paraffin's from solidifying; by removing aromatics, filter plugging resulting in loss of power or engine stalling may be experienced at higher temperatures than in the past. This problem is generally worse in winter weather.
In the U.S. it has been customary to "winterize" fuel to prevent filter plugging by blending #2 diesel fuel with a lighter fuel, such as jet fuel or #I diesel fuel. After enactment of the diesel regulation, low-sulfur DF#1, which has always been both rare and expensive, will be the only acceptable blending agent
An alternative practice to blending is to use well-proven wax modifiers as fuel additives. These chemicals greatly reduce the pour point of diesel fuel and offer a significant operating temperature improvement of up to 15 to 20 degrees Fahrenheit. A fuel heater placed in or near the fuel filter also can provide significant operating advantages in cold weather. The combined use of fuel additives and in-filter heaters should allow most operators to use economical #2 diesel at temperatures less than -15 degrees F.
A call for standards
These issues make it clear that diesel fuel lubricity standards are necessary. A barrier to the new specifications is agreement on a standard test for fuel lubricity.
One proposed test for the fuel lubricity is an enhanced version of the BOCLE (Ball On Cylinder Lubricity Evaluator). Engineers have used this test machine for years to evaluate the lubricity of lubricating oils. It may be able to be adapted for evaluating the lubricity of diesel fuels.
The BOCLE test involves pressing a ball bearing against a rotating ring partially immersed in the lubricating fluid; in this case, diesel fuel. Weight is applied on the ball bearing until the lubricating film fails, leaving a scuff mark on the rotating cylinder. An enhanced version of the BOCLE test is the BOCLE scuffing test, which is more definitive. Initial data has correlated well with actual fuel pump tests. but further refinements are needed.
Stanadyne is working with other manufacturers and industry organizations, including the Society of Automotive Engineers (SAE), the American Sociey for Testing and Materials (ASTM), and the International Standards Organization (ISO), to help define a diesel fuel lubricity standard and a test method that can be used to assess the properties of the proposed low- sulfur fuels.
Another possible alternative to the BOCLE is being developed in England by PCS Instruments, a company comprised of former researchers from the Tribology Department at Imperial College, London. It is called the high- frequency reciprocating rig (HFRR) test, and because it vibrates one piece of metal against a stationary one with the test fluid in between, it more closely models the action of reciprocating injection pump components.
Without a lubricity standard, neither consumers nor fuel distributors can be certain of the lubricity properties of American low-sulfur diesel. If problems arise, end users have no recourse because the fuel need not have lubricity to conform to the existing standards (ASTM-D975).
According to ongoing Stanadyne studies, early prototype low-sulfur diesel fuels exhibited adequate lubricity characteristics. However, actual production fuels obtained in recent months have exhibited significantly poorer lubricity capabilities. This loss of lubricity may be the difference between fuels from a controlled laboratory environment and a cost-conscious production environment.
However, even the best quality low-sulfur fuels offer varying degrees of lubricity, and testing indicates that virtually all diesel users will experience problems.
A history of potential problems
The U.S. has been closely observing low- sulfur fuel usage around the world. In Sweden, for instance, strict regulations require sulfur levels no higher than 100ppm and 10 percent aromatic fuel. In Canada, low-sulfur diesel fuels have been marketed for several years. Problems with increased wear have been encountered in both countries. Wholesale introduction of the low-sulfur fuel in Sweden had disastrous effects on diesel engine operation and resulted in a crisis situation for Swedish refiners and a European rotary fuel pump manufacturer. Swedish refiners are now using additives to prevent excessive wear in fuel injection systems and their problems are apparently under control. Certain major Canadian refining companies are adding lubricants before delivering fuels to the customer.
At this time, neither the ASTME, SAE nor ISO have set fuel-lubricity specifications for supplying or testing low-sulfur fuel. Because of added cost, refiners are unlikely to consider supplying a pre-additized fuel before a specification has been set.
Stanadyne and other fuel injection manufacturers are concerned that the problems experienced in Sweden could be repeated in the U.S. -- a regrettable situation since solutions to avoid the problems exist today.
Until the lubricity specification is written and followed, the responsibility rests with diesel equipment end-users to use fuel additives to maintain the reliability of their diesel engines. Consumers can ensure normal reliability and life-expectancy of their diesel fuel systems by individually treating their fuel tanks with additives proven by diesel equipment manufacturers.
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