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The Reality of the Single-Fuel Concept

To simplify fuel operations, the Department of Defense (DOD) has adopted a single-fuel concept (SFC) that requires U.S. forces to use only one fuel while deployed. Although the concept has merits, it also has shortcomings. The challenge is to develop a policy that will best meet all military fuel needs.

Evolution of the SFC


Waxing and fuel filterability problems with the North Atlantic Treaty Organization’s (NATO’s) standard diesel fuel, F54, during cold weather created severe problems for the engines of M1 Abrams main battle tanks and other gasoline turbine-powered equipment when they were introduced to U.S. forces in Germany in 1981. [Diesel fuel typically has a high paraffin hydrocarbon content, which prevents it from flowing at low temperatures. Waxing refers to this situation, in which the paraffin hydrocarbons in the fuel congeal and wax-like particles are formed that can either coat the surfaces they contact or plug fuel filters.]

The interim fix for these problems involved blending the F54 diesel fuel with aviation kerosene turbine fuel (either JP5 or JP8) to lower both the waxing tendency and the viscosity of the diesel fuel. This blended fuel, known as the “M1 fuel mix,” was used for all diesel-fueled equipment in forward areas from November through April annually. Other NATO countries soon adopted the blend (50 percent F54 and 50 percent JP8 or JP5), which subsequently was given the NATO code number F65. These fixes for the low-temperature operability problems more than likely served as the genesis for the SFC.

The subsequent requirement for blending of fuels created logistics problems that prompted the Army to adopt JP8 as an alternative to diesel fuel in 1986, circumventing the need to blend other fuels with diesel. DOD issued a directive on fuel standardization in March 1988 that specified JP8 as the primary fuel for air and land forces.

Testing and Field Trials

Users expressed concerns about using JP8 as a substitute for diesel fuel. These concerns included whether JP8 would burn hotter, if it would increase fuel consumption, and if it would be compatible with existing systems. As a result, the Army conducted many tests in the laboratory and on engine dynamometers, in addition to field and fleet tests, to validate using aviation kerosene turbine fuels in diesel engines and to dispel concerns. [Dynamometers measure mechanical power and assess engine durability and performance.]

Of the many successful fleet tests, one was particularly noteworthy. This 10,000-mile durability test was conducted with several commercial utility cargo vehicles (CUCVs) at the General Motors Desert Proving Ground in Mesa, Arizona, where they were exposed to round-the-clock operations in continuously hot climates. The test revealed no significant impacts on vehicle performance or fuel-injection pump wear, and no measured differences in engine operating temperatures were noted, which dispelled the fears of engines overheating because of supposedly hotter burning fuels.


One of the more significant and comprehensive tests of JP8 was a field de-monstration conducted at Fort Bliss, Texas, from October 1988 through July 1991. This field demonstration in-volved about 2,800 diesel-powered vehicles and pieces of equipment that consumed over 4.7 million gallons of JP8. The demonstration proved successful: no catastrophic failures were attributed to JP8. In fact, no major differences in procurement costs, fuel consumption, oil change intervals, or component replacements were identified when compared to historical data for the same fleet of vehicles and equipment using diesel fuel.

Implementation of the SFC Since 1990


When approved by the combatant commander, the primary fuel support for air and ground forces in overseas theaters will be a single, kerosene-based fuel. The SFC was first implemented in December 1989, when JP5 was used as the single fuel during Operation Just Cause in Panama.

In August 1990, DOD implemented the SFC by providing Jet A1 (JP8 without its three mandatory additives) for U.S. forces in Operations Desert Shield and Desert Storm. During those operations, some Air Force units were located on bases where only JP4, which could not be used in ground vehicles and equipment, was available. Some Army units requested diesel fuel instead of JP8 because JP8 did not make acceptable smoke in the M1 Abrams’ exhaust-system smoke generators. Further compounding the problems was the lack of training of ground units, which would have reduced their initial concerns about using aviation fuels in ground vehicles and equipment. Despite these problems, the SFC was considered a success.

The SFC was im-plemented next for combat operations in Somalia, Haiti, and the eastern Balkans with the same success that it had achieved duringOperations Desert Shield and Desert Storm.

Minor Problems

During Operations Desert Shield and Desert Storm, certain families of engines that used fuel-lubricated, rotary-distribution, fuel-injection pumps experienced some op-erational problems that resulted in hot-starting difficulty and gradual loss of power. (Hot starting refers to restarting a vehicle while its engine is still hot.) Usually, the engines that experienced the most problems were the General Motors 6.2-liter and 6.5-liter engines, which use the commercially manufactured Stanadyne fuel-injection pump. These engines power smaller tactical wheeled vehicles, such as CUCVs and high-mobility, multipurpose, wheeled vehicles (HMMWVs). The Stanadyne fuel-injection pump is used on a variety of other engine systems that provide power to combat support and combat service support equipment.

Causes of the problems with the engines included—
• Sustained operation during high temperatures.
• Failure to retrofit the Stanadyne fuel-injection pump with elastomer insert drive governor weight retainer assemblies.
• Improperly manufactured replacement parts.
• Corrosion.
• Unauthorized oils and fluids added to Jet A1 fuel.
• Use of Jet A1 that did not contain corrosion inhibitor and lubrication-enhancing additives.The viscosity of the Jet A1 fuel being supplied by Saudi Arabia under a host nation support agreement was very low, as was the sulfur content, which further compounded the hot-starting problems.

Ironically, none of these problems occurred during the extensive testing at Fort Bliss. In hindsight, the test at Fort Bliss used JP8, which has a higher viscosity than the Jet A1 fuel typically refined in the Middle East, and temperatures at Fort Bliss were at least 15 degrees Fahrenheit lower than those encountered in Southwest Asia.

Fuel-Injection Pump

Of the many types of fuel-injection pumps manufactured commercially, such as the single-cylinder pump, the inline pump, and the distributor pump, the rotary-distribution, fuel-injection pump is the most sensitive to the lubricating quality of the fuel. This pump is inexpensive and is used in a wide variety of commercial and military equipment typically powered by light-duty diesel engines. In these pumps, the fuel provides the needed lubrication to the internal moving components. When the lubricity (lubricating quality) of the fuel becomes marginal or insufficient, the pump components will wear.

If fuel viscosity is sufficiently high, the fuel will physically separate the injection system’s sliding components, preventing wear. With a lower viscosity, the potential for wear increases significantly because the surfaces of the sliding parts can begin to interact. However, certain additives to the fuel will generate surface films that provide the needed wear protection. The viscosity of fuel decreases as the fuel temperature increases, thus decreasing the fuel’s ability to lubricate the injection system and increasing users’ dependence on lubricious surface films to control component wear. American Society for Testing and Materials (ASTM) D 975, Standard Specification for Diesel Fuel Oils, sets the current industry standard for the minimum viscosity of grades 1–D and low sulfur 1–D diesel fuel at 1.3 square millimeters per second (mm2/s) at 40 degrees Celsius. While the viscosity of JP8 at 40 degrees Celsius is not identified in the JP8 specification (MIL–DTL–83133E), the observed range of viscosity varies from 1.0 to 1.7 mm2/s at 40 degrees Celsius. Obviously, using a fuel with viscosity lower than 1.3 mm2/s will accelerate the potential for component wear. Of the four major manufacturers of rotary-distribution, fuel-injection pumps, Stanadyne Automotive Corporation is the only one that provides factory retrofit kits for lessening the potential for wear and hot restart problems when using low viscosity fuel.

Another adverse effect resulting from using low-viscosity fuels in rotary-distribution, fuel-injection fuel pumps is the increased potential for internal leakage. A combination of low-viscosity fuel and increased clearances between surfaces due to wear (resulting from insufficient lubricity) can result in increased internal fuel leakage that reduces the amount of fuel delivered to the combustion chamber. More internal leakage in the pumping sections occurs at low engine speeds, causing hot-starting and hot-idle problems. Some of these problems surfaced during the latter stages of Operations Desert Shield and Desert Storm.

Major Problems Since 9/11

With the recent major combat operations in Afghanistan and Iraq, fuel-related problems have increased significantly as a result of using low-viscosity fuels as the single fuel. In Afghanistan, much of the aviation kerosene that initially was procured was Russian TS1 aviation kerosene because the neighboring refineries produce aviation kerosene as TS1 instead of Jet A1 or JP8. The Russian TS1 aviation kerosene is similar to Jet A1, but it is more volatile because it has a lower flash point and a lower viscosity.

The fuel being used in Iraq is JP8. However, in both Afghanistan and Iraq, the ground vehicles and equipment are being used much more extensively than they would be used in normal service. Considering this added use, the hot temperatures that typically prevail in the Middle East, and the increasing engine-power demands imposed by the increased weights of up-armor kits, it is no wonder that the ground vehicles and equipment that have rotary-distribution, fuel-injection pumps have had many fuel-related engine problems.

An article in the July 2004 issue of National Defense magazine, “Army Ponders New Diesel Engine for Humvee Trucks,” notes that maintenance nightmares have been experienced in Iraq because engines regularly break down and often must be replaced after only 1,000 to 2,000 miles of operation. Much of the blame for this is placed on the bolted-on armor protection that adds weight to the vehicles. However, the inability of the rotary-distribution, fuel-injection pumps to operate satisfactorily for sustained periods of heavy-duty operation is probably a contributing factor, especially when low-viscosity fuel is used in a hot environment. Interestingly, the fuel-injection pumps in many, if not all, of the HMMWVs operating in Southwest Asia have been retrofitted with Stanadyne’s Arctic Fuel Conversion Retrofit Kit. This kit apparently has done little to offset the significant increases in maintenance that have been experienced recently.

Rethinking the SFC


Combat operations that occur in higher temperature environments certainly will intensify the operational and maintenance problems of diesel-powered vehicles and equipment with fuel-lubricated fuel-injection pumps. Since almost half of the Army’s diesel vehicles and equipment have rotary-distribution, fuel-injection pumps, a solution is urgently needed.


Despite the maintenance and readiness problems it has created, the SFC has created many benefits. One fuel is considerably easier to manage than multiple fuels. The functions of fuel storage, transportation, and distribution can be tailored for maximum efficiency. Using a single fuel lessens the possibility of dispensing the wrong fuel. Using JP8 as the single fuel has enhanced long-term storage stability, improved cold weather vehicle operation, reduced engine combustion component wear, and reduced fuel system corrosion problems.

The most recent version of DOD Directive 4140.25, DOD Management Policy for Energy Commodities and Related Services, stipulates that “. . . it is imperative that combat support and combat service support vehicles and equipment be capable of receiving support (i.e., fittings, nozzles, etc.), achieving and sustaining acceptable operational performance using both kerosene-based turbine fuel and diesel fuels to the maximum extent practical.” Policy directives may not always match reality, which is the case with the large numbers of diesel-fuel-consuming vehicles and equipment with rotary-distribution, fuel-injection pumps.

Certainly, the significant increases in maintenance requirements that have been experienced in Afghanistan and Iraq strain an individual’s understanding of the phrase “sustaining acceptable operational performance.” This is not saying that the SFC doctrine is flawed, but some changes are urgently needed.

Ironically, a strategy research project completed in April 1996 at the Army War College identified some possible problems with the SFC and gave
several recommendations. Two of the more significant recommendations were—

• The fuel pumps on all new equipment must be compatible with JP8.
• All future military equipment must be designed to use JP8 as the primary fuel source.Both of these recommendations are as relevant today as they were in 1996.

DOD Directive 4140.25 requires that acceptable operational performance be achieved with both kerosene-based turbine fuels and diesel fuels. However, one fuel type must predominate over the other, and, since compression-ignition engines are essentially designed and manufactured for diesel fuel consumption, the predominant fuel naturally would be diesel. An engine’s fuel pump must be JP8 compatible in all types of operating conditions, not just in environments with cold to moderate temperatures.

Because of the large number of existing vehicles and equipment that use the fuel-lubricated, rotary-distribution, fuel-injection pumps, one approach would be to make the SFC doctrine more flexible by requiring use of diesel fuel when systems operate for sustained periods in a high-temperature environment. This change would least affect the Air Force because it typically operates from fixed sites that are removed from direct combat operations so that two fuel distribution and storage systems are easier to implement. The Army and Marine Corps would be affected more because they require one fuel distribution system for ground equipment and a second for helicopters and both systems require intense protection and support. This dual-system option is complicated further by doctrine calling for highly mobile, distributed, autonomous combat units.

Another, albeit more complicated, approach would be to require that the rotary-distribution, fuel-injection pumps be replaced with pumps that are less sensitive to fuel viscosity and lubricity, such as the common rail or pump-line nozzle systems.
Failure to recognize and act on the problems inherent in the use of kerosene-based fuel with rotary-distribution, fuel-injection pumps will only serve to decrease operational readiness and increase maintenance costs over time. ALOG

Maurice E. Le Pera is the president of Le Pera and Associates of Harrisonburg, Virginia. He is a graduate of the University of Delaware and had 36 years of Government service.

The author wishes to thank Emilio S. Alfaro of the Air Force Petroleum Office and Edwin C. Owens of the Southwest Research Institute for their assistance in developing this article.