Nobody disputes the need for a premium diesel fuel spec. How it's defined is another matter.

Signs promoting "premium" diesel fuel are popping up with increased regularity across America's asphalt landscape. The word "premium" conjures up images of enhanced performance - the perfect thirst quencher for today's more muscular powerplants. While that may be true down the road, current premium blends may carry little more than a premium price tag.

"There is no product specification for premium diesel fuel," explains Gary Pipenger of Amalgamated Coal and Petroleum Specialists. "Therefore, since there are no firm requirements to which the fuel industry must adhere, petroleum industry in-house guidelines dictate what this grade looks like when it is sold."

The National Conference of Weights and Measures (NCWM) is about to change that. Under the leadership of Roger L. Leisenring Jr., diesel fuel technologist for Texaco Additives International (TAI) and co-chairman of the premium diesel task force, the group has been toiling for the last year and a half to develop just such a premium diesel fuel specification.

"The need for a premium diesel fuel definition arose from concern about the misuse or vagueness of the term premium on the grade panel and the desire to provide some minimal level of consumer protection in the developing premium diesel fuel market," explains Leisenring, who also chairs the diesel section of the American Society of Testing and Measurements (ASTM) and the Society of Automotive Engineers (SAE).

The task force wants to ensure that a premium diesel classification delivers a benefit above the existing ASTM D975 diesel fuel standard. It understands that in order to be effective, any specification must give clear direction to refiners for building the premium grade, and to state enforcement agencies for making sure it lives up to its billing.

Although NCWM approved the new premium standard last month (effective January 1, 2000), the definition does not automatically become the law of the land. Instead, like the existing base diesel standard (ASTM D975), it would represent a voluntary guideline that each state would have to adopt on its own.

The NCWM committee started out by winnowing the list of fuel properties to those that represented objectives that could be achieved and measured. They settled on five: energy output, cetane number, detergency, thermal stability, and cold-weather operability. To wear the "premium" label, a fuel would have to meet two of the five performance characteristics. "We will set the minimum level and leave it to the marketplace to determine the others," Leisenring explains.

Energy output. Nobody disagrees that diesel with a higher energy content can provide higher power and improved fuel economy. Power is directly related to the heating value of the fuel, measured in British thermal units. The higher the Btu, the more power the fuel produces.

This is important during colder driving seasons because of the practice of blending kerosene, a lower gelling fuel, with No. 2 diesel. Such blending lowers the density of the diesel, thus lowering its Btu content. The extent to which fuel economy suffers depends on the amount of kerosene used in the winter blend. "It's possible for the fuel economy penalty to be as high as 8.7%," says Leisenring. "Power is also affected and a penalty of as much as 7.2% could be experienced."

Selecting the minimum Btu requirement was achieved by reviewing data on the gross heat of combustion of more than 100 randomly gathered field fuel samples. It varied from a minimum of 134,773 to a high of 140,819 Btu/gal. The top quartile value - 138,700 Btu/gal. - was selected to be the minimum energy content value.

Cetane. Cetane measures how fast the fuel ignites. The higher the number, the faster the ignition. This results in smoke and increased engine noise from fuel being burned after the piston reaches the top dead center of its travel. The problem is more pronounced in cold weather operations, where fuels with low cetane values have trouble firing and belch white smoke.

Current base fuel stocks are rated at a minimum cetane level of 40, although the industry average tends to float in at about 43. The new premium classification will boost that up to 47. Cetane also tends to promote better fuel economy because engine pressure rises faster, resulting in a more complete fuel burn.

Detergency. This refers to the natural cleansing property of the fuel, which helps keep injector nozzles clean and retains performance for better fuel economy. Some powerplants - generally older mechanical offerings - are more susceptible to fouled injectors.

Whether electronic or mechanical, "if engines are running the way they're supposed to," fleets are unlikely to experience some of the problems caused by over-fueling older engines, says David Fehling, director of technical education and services for the Association of Diesel Specialists, Kansas City, Mo.

"Injector problems caused by overfueling have been virtually eliminated," he says. "We still see older engines experiencing problems from excess fuel entering the combustion chamber. That either goes out the stack as black smoke or accumulates inside the combustion chamber in the form of soot and carbon buildup."

Thermal stability. This is the measurement of the ability of a fuel to maintain its chemical structure even in the face of extreme heat. Thermal stability is particularly important in today's operating environment, where fuel is being called on to help cool the engine. Plus, the increasing amount of fuel being recirculated returns the juice at higher temperatures. Hotter fuel attracts more water, which is soluble in the fuel, giving rise to large clumpy fuel compounds that don't break down.

These compounds clog filters and restrict fuel lines, leaving behind a black shiny film on the filter. This problem can go unnoticed because when the engine is shut down, it is not uncommon for the debris to fall back into the fuel, allowing a more complete fuel flow.

Cold weather operability. The prevalence of low-sulfur fuel has led to an increase in paraffin content, which compromises its ability to work in low temperature conditions. Traditionally, kerosene blending was used to improve fuel flow in colder climates. But since kerosene now has a lower sulfur content, it's not always available.

Cold weather operability is also compromised by the existence of water in the fuel, which can freeze. In addition to impeding the combustion process, these ice crystals do not atomize and can blow out today's high-pressure injector nozzles.

These five characteristics of fuel yield a total of 26 different combinations. That means the marketplace could experience some confusion as to what kind of premium the label reflects.

"Keep in mind that now there is no definition, so anything is an improvement," says TAI's Leisenring. "We're not saying that it's an end-all. It's a starting point that will change."

The Engine Manufacturers Assn. (EMA) sees things differently. "Controlling only two properties while leaving all other properties uncontrolled could actually result in a poorer performing fuel overall, EMA said in a June 8 letter to Leisenring's task force. "For example, today's premium gasoline has only an octane requirement, and it has been found in the marketplace that poor driveability can result in some vehicles as the result of reduced fuel volatility in premium gasoline."

Diesel engine characteristics range from small displacement high-speed engines to large displacement low-speed engines, the group added. Satisfying the different needs of this wide variety of engines requires a fuel meeting a broad spectrum of characteristics. A truly "premium" fuel definition is one that encourages fuel marketers to make the kind of improvements that would allow consumers to use a single premium fuel to address a broad range of problems.

The NCWM spec doesn't go far enough, according to EMA. "Specifications should not be set at a bare minimum above the national average," the group added. "Rather, a premium fuel specification should be well above the national average such that an end-user seeking a premium fuel will find noticeable improvements in all important areas."

For now, most fleet executives would agree. Most remain skeptical that any advantage would outweigh the increased cost of a premium product - initially pegged at a nickel a gallon. Fleets still buy diesel fuel strictly on price.

One such fleet is Old Dominion Freight Line, a regional less-than-truckload carrier based in High Point, N.C. "I don't have any desire to spend any more money on a product that has questionable benefits," says Rick Wilson, fuel administrator. "I don't see any advantage to us. The advantage would fall into the pockets of the oil companies."

Wilson relies on three strategies to fuel his 2,100-plus unit fleet. The first is bulk fuel consumption. Of the company's 90 terminals, 18 have bulk fueling, which meets 60% of the fleet's fueling needs. The rest is split between a negotiated nationwide pricing program through truck stops (25%) and mom-and-pop independent fueling facilities (15%).

Wilson hasn't encountered any fuel-related maintenance or performance issues. He credits his practice of dealing only with reputable oil companies and strong third-party vendors. He relies on his relationship with the fuel providers, plus a budding network of like-minded fuel czars at other trucking companies, to keep him out of hot water.

In addition, the fleet's scheduled equipment replacement strategy has helped introduce more efficient powerplants into the fleet, thus minimizing some of the performance issues associated with older engines.

Similarly, Andy Gilliland, fleet manager for Pemberton Truck Lines, has yet to experience any fuel-related downtime, despite buying all his fuel on the road. "The color may be different depending on the area of country, but we don't see any clogged filters and the Btu output is the same," he says.

It dissolves varnish, carbon, and gum deposits, resulting in increased combustion efficiency, smoother operation, faster starts, reduced misfire, and lower exhaust emissions."

So reads the label of a typical fuel additive. Fleets are bombarded with a wide variety of similar additive claims purporting to cure a wide variety of what ails diesel fuel. Additive suppliers claim their products can, by supplementing properties not included in the diesel fuel specifications, correct existing engine performance problems or protect the powerplant from excessive engine wear and operating deficiencies such as high oil consumption, excessive smoking, and the like.

Because of the competing claims, fleets are left to wonder whether fuel additives are needed in the first place, whether they will really work, whether they will cause side effects, and whether they will void manufacturers' warranties.

Adding to the confusion is the fact that there are no industry standards on additives. Fleets must rely on prior product knowledge, advertising, or word of mouth.

"Without industry standards such as those that have been developed and are in use for gasoline, diesel fuel, and engine oils, there is no easy and definitive way to assess the performance of these aftermarket additives or to discern any differences between the many brands," says Maurice E. LePera, a former U.S. Army official now with his own consulting business, LePera and Assoc., based in Woodbridge, Va.

During his 40-year military career, LePera was besieged by many proposals, requests, and congressional recommendations of aftermarket additives. That's because the Army was the lead agency in determining the fuels used by the Dept. of Defense for ground vehicles and equipment. LePera helped establish the Army's standard testing protocol for product evaluation, and to determine potential side effects.

What can fleets learn from LePera's experience to help guide them through the maze of additive claims?

* Analyze the contents of the additive. Request an MSDS list of the additive package and be wary of any product that contains 99% solvents.

* When performance claims are made (improved fuel economy, reduced engine wear, improved power and acceleration, etc.), ask for documented test data.

* "Information such as testimonials from past or current users is often supplied to support a product's claims," he adds. "These are generally inadequate for clearly answering the improvement questions, where standardized testing protocols and procedures are the rule."

* View with caution any reports based on non-standardized tests that have little correlation to an engine's environment or a fleet's operation.

* Oh, and don't forget the old admonition that if something appears to be too good to be true, it generally is.

Many believe that the problem is not the fuel spec, but what's been left out. In that vein, let's examine what the proposed spec does not cover.

Flash point. The flash point temperature of diesel is the minimum temperature at which the fuel ignites. The flash point varies inversely with the fuel's volatility. Minimum temperatures are required for proper safety and handling.

Water and sediment. Water and sediment can and will cause shortened filter life or plugged filters that can, in turn, lead to fuel starvation of the engine. In addition, water fosters microbial growth.

Distillation. This property provides a measure of the temperature range over which a fuel turns to vapor. Volatility is one of the primary factors that will distinguish No. 1 and No. 2 diesel. The highest temperature recorded during distillation is called the end point.

Viscosity. This affects injector lubrication and fuel atomization. Fuels with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps or plungers, resulting in leaks or increased wear. Fuel atomization is also affected by fuel viscosity. Diesels with high viscosity tend to form larger droplets on injection, causing poor combustion and increased smoke and emissions.

Ash. The ash content is the measure of the amount of metals contained in fuel. High concentrations can cause injector-tip plugging, combustion deposits, and injection system wear. Soluble metallic materials cause deposits while abrasive solids will lead to injection equipment wear and filter plugging.

Gravity. The gravity of diesel fuel affects engine power. There is a 3-5% decrease in the thermal energy content of fuel for every 10-deg. increase in API gravity. This has a corresponding decrease in engine power.

Lubricity. This describes the ability of a fluid to minimize friction between surfaces. Diesel fuel injection equipment relies on the lubricating properties of the fuel. Shortened life of engine components such as injection pumps and unit injectors can be traced to the lack of lubricity.

A strong economy, combined with low diesel fuel prices, continues to pump up the bottom lines of the nation's motor carriers. That's because, after labor, fuel is the highest expense item for the typical motor carrier. So the fact that diesel fuel prices have been doing the pricing version of the limbo has been an energizing bit of news for motor carriers.

Most market observers feel that we've wrung as much as we're going to out of the cost of a gallon of diesel. They point to projections of a 13% increase in the number of trucks on the road by the year 2003, as well as predictions that mileage will rise 28% over the same period, fueling increased demand.

Plus, trucking is likely to grow thirstier still if, as expected, diesel engine technology continues to displace gasoline engines in medium- and light-duty applications.

The upward pressure on pricing will hit truckload carriers first and hardest. This segment spends 20 cents of each revenue dollar on fuel, according to BT Alex. Brown. The companies that have higher percentages of owner-operators will insulate themselves from major price swings. Also, the longer the haul, the more susceptible a carrier's operation is to fuel price fluctuations. "Revenue per mile declines, and fuel as a percentage of revenue increases, as the length of haul increases," the investment broker concluded in a recent report.

Fuel is a much smaller component of the cost structure of LTL carriers, where 60 cents out of every revenue dollar is spent on labor and their terminal networks.