Keeping the fuel clean and contaminant-free is a major challenge, particularly when you have large equipment fleets spread over many jobsites.
Not all fuel is created equal. You need to understand what you are purchasing to maximize efficiency and uptime.
During cold weather, paraffin wax can clog fuel filters if the diesel fuel is not properly treated.
Although it's tempting to purchase the cheapest diesel fuel available, you really need to understand how it affects performance and operating costs. While No. 2 diesel fuel conforming to ASTM D-975 can have the appearance of a commodity, look more closely and you will discover important differences.
"The ASTM D-975 specification sets the requirements for a No. 2 diesel fuel," says Chad Pistulka, product manager, refined fuels, CHS, marketer of Cenex brand products. However, he notes that many OEMs and consumers would prefer to see even higher standards. "An operator can save money with a premium-type diesel fuel that provides higher cetane, better lubricity and contains a multipurpose detergent package."
Joe Fell, Ryan Central Inc., Janesville, WI, has actually given presentations on managing fuel costs at the Chevron Construction Symposium. Ryan Central ranks among the largest nationwide site work and mass excavation contractors.
According to Fell, much more goes into the fuel purchasing decision than price per gallon. "You have to look at your equipment rate right now," he advises. "Fuel continues to be a larger percentage of that rate."
On the surface, a cheaper fuel may appear to lower costs. But if it means more maintenance or less productivity, your overall costs may actually increase. "You have your people cost, your equipment cost and your fuel cost," Fell points out. "You have to weigh that balance."
Numerous factors can influence fuel quality. Doing a little homework can ensure you get the quality you need. "I try to stay up on all of the additives, different companies, different products," says Fell. "Know what products are available to you. Know what the options are - what they can and can't do. Then work with your fuel vendors to ultimately get it into the fuel that is going to be delivered to your machines."
Ryan Central evaluates fuel based on several criteria. "In our business, a big part of that is service," says Fell. The company wants the fuel supplied directly to equipment in the field, which keeps potential contamination from storage and handling to a minimum. It also looks at the energy content of the fuel.
"There can be a very wide variation in diesel fuels and their quality," says Dave Harvey, manager, fuels quality, technology & technical services, Citgo. He advises first consulting with the prospective suppliers to determine conformance to the ASTM standard. Next, take a look at the energy content of the fuel. "A higher British Thermal Unit (BTU) content of a diesel fuel translates directly into a higher energy delivery per gallon or pound of fuel." A key question is whether that energy is sufficiently high to deliver a noticeable improvement in work performed per gallon.
Cetane number, API gravity, cloud point and lubricity are just a few factors to consider when comparing fuels. "If a company is buying fuel from a supplier that has a good track record, they should ask the supplier to provide as much information as available regarding the additive package that they are supplying," says Roger Gault, Engine Manufacturers Association (EMA). "If alternate sources of supply are evaluated, the additive package can be compared in addition to price."
Likewise, when selecting winter blends or biodiesel, you need to compare options. "Biodiesel offers the same performance as regular diesel in blends of B20 and lower," says Amber Thurlo Pearson, National Biodiesel Board. "Biodiesel in its pure form, or B100, is said to have a 10% decrease in fuel economy. However, most biodiesel is sold to end users as a blend of B20 or lower, which has the same fuel economy."
Biodiesel is currently less regulated than regular diesel fuel. Ensure the fuel meets the biodiesel quality specifications addressed by ASTM D-6751. This can be accomplished by carefully selecting your supplier. "Request fuel from a BQ-9000 certified marketer, or from a BQ-9000 accredited producer," says Pearson.
Energy content of diesel fuel is measured in BTUs per gallon. The higher the energy content, the more power you can get out of your fuel. No. 2 diesel typically contains 130,000 BTU/gal.
Ryan Central has looked at the cost per BTU of its diesel fuel. "You look at all of your costs performance-wise," says Fell. "A lot of times, by using a higher BTU fuel content, you are going to come out ahead. Ultimately, you will have a lower cost per BTU."
One way to gauge how much BTU a fuel contains is by the API gravity measurement. "API gravity is a measure of fuel density, and affects the heating value (BTUs) of a fuel," says Bob Theisen, manager, technical services, CHS.
"It can also be used to predict the relative viscosity of a diesel fuel," Harvey adds. "As a rule of thumb, the lower the API gravity, the higher the energy density, viscosity and mass density of the fuel." For example, a diesel fuel with an API gravity of 30 will generally be higher in energy content, more viscous and heavier on a weight per gallon basis compared to a fuel with a 40 API gravity.
Blending diesel for winter conditions can impact the energy density. "Higher density fuels generally have higher energy content, meaning better fuel economy. But generally, these fuels are not viable for cold climates," says Gault. No. 1 fuel or fuel blends of No. 1 and No. 2 tend to be less dense, and therefore lower in energy content. "But they are required to prevent fuel flow problems in cold conditions."
Cetane number is an indication of how easy the fuel is ignited in your engine. The higher the cetane number, the shorter the ignition delay between the start of injection and combustion of the fuel. "The higher the cetane number the better, if all other aspects of the fuel are equal," says Gault.
Currently, No. 2 diesel fuel has cetane values that range from 40 to 55. "ASTM D-975 specifies a minimum cetane number of 40 for any diesel fuel," says Harvey. "Most owner manuals also require a minimum cetane number of 40." For winter fuel, you should look for a cetane level closer to 50.
"As the cetane number increases, you can expect better cold temperature starting, improved combustion and emissions, in addition to a quieter running engine," says Theisen. "We know that premium-type diesel fuels tend to have higher cetane numbers."
If the cetane number is too low, the engine will be more difficult to start, particularly in cold weather, and it may run rough. Oil sludge may accumulate more quickly, along with engine deposits. Yet, there is no benefit to running a cetane level higher than engine manufacturer specifications.
There is a tendency to misinterpret cetane level as an indication of the fuel's energy content. But a level that is higher than required will not enhance engine efficiency.
"Just because a fuel has a high cetane number does not mean it will provide optimum performance," says Harvey. "A high cetane number can - but not necessarily does - suggest a lower BTU/gal. if the No. 2 diesel fuel has been blended with kerosene to achieve the higher number."
Gault adds, "Generally the higher cetane number fuels are less dense, and therefore have lower fuel economy, so there are tradeoffs. EMA recommends a minimum cetane number of 47 for the best combination of performance and fuel economy."
Cold weather performance
Cloud point and pour point directly affect cold weather performance. "During the summer months, cloud and pour points do not carry the importance they will for winter months," says Harvey. "For winter operability, fuels exhibiting low cloud and pour points can generally provide a wider range of operability temperatures, especially at low ambient temperatures."
The cloud point is the temperature at which crystals of paraffin wax first appear. (This creates a cloudiness in the fuel.) These crystals collect and plug the fuel filter. The pour point refers to the temperature at which the diesel fuel will no longer pour; it becomes too thick.
A common practice has been to blend kerosene or No. 1 diesel fuel with No. 2 diesel to make the cloud and pour points acceptable for cold weather application. But not everyone likes this approach. "There are still a number of people who blend with a No. 1 in the wintertime," says Fell. "It is so expensive, and you can get the same benefits from using a No. 2 with an additive."
One of the biggest problems in cold weather is water in the fuel. "Through the combustion process over the entire year, you are going to inherently build up water within your system. And that water will freeze," Fell notes. "Winter fuel on top of that doesn't take the water out. The first thing you need to do is treat everything with a dehydrator to get all of the water out of your system. Typically by October 15th, we try to start making sure we have the appropriate winter additives flowing through our machines to give them enough time to actually treat it."
Fuel systems need adequate lubricity to ensure life. Since the EPA mandated dramatic cuts in fuel sulfur content, the severity of hydro treating at the refinery to remove sulfur from blend stocks used to produce diesel fuel has resulted in removal of natural lubricant hydrocarbons. Thus, the fuel's lubricating capabilities have been reduced. Diesel fuel suppliers have now turned to other additives to meet lubricity requirements.
"Lubricity is a specification requirement contained in ASTM D-975, but it is not necessarily produced at the refinery to meet that specification," says Harvey. "Therefore, most fuel marketers are injecting an additive at the bulk storage terminal just prior to delivery to the end user to ensure the lubricity standard is met."
Pistulka notes that most product data sheets show the typical value for lubricity. "All fuel in the U.S. must meet a certain lubricity maximum of 520 microns in the ASTM D-6371 test, which is part of the D-975 diesel fuel specification," he adds. "Premium-type diesel fuels may further enhance the lubricity performance."
EMA recommendations go beyond the minimum standard. "The current specification is a maximum High Frequency Reciprocating Rig (HFRR) rating of 520 microns. This number refers to the dimensions of a scar left behind after a 200g steel ball is rubbed on a steel disk submerged in the fuel over a 1mm stroke," Gault explains. The smaller the dimensions of the scar left behind, the better. "The specification sheet should include an HFRR rating. And while the maximum allowable is 520 microns, EMA recommends a maximum of 460 microns."
Biodiesel is a premium product that has an advantage in terms of lubricity. "Biodiesel can lead to increased longevity and less maintenance due to its added lubricity, which prevents premature engine wear and tear," says Pearson.
Housekeeping Impacts Quality
Cleanliness and housekeeping practices can have a major impact on fuel quality. "Fuel cleanliness cannot be emphasized enough," says Roger Gault, Engine Manufacturers Association. "Clean and dry fuel can significantly reduce fuel system problems and associated vehicle maintenance."
A critical part of ensuring quality is the housekeeping associated with the storage, distribution and sale of the fuel. "Maintaining a clean distribution system helps to ensure that a quality product can be produced in a factory, transported sometimes over a thousand miles and still delivered to the end user as a product that meets their needs," says Dave Harvey, Citgo. "A safe and reliable supply of quality fuel, as defined by ASTM D-975, is paramount to meeting the needs of the customers and their engines, and for providing satisfactory performance."
Over time, diesel fuel degrades. "If it is stored underground in a sealed tank, it will not significantly degrade over a period of a year," says Harvey. "This is provided that the tank does not contain water or sources for microbial infestation, which can degrade the fuel. Under conditions of wide temperature swings - such as in an above-ground tank that is vented to the atmosphere and not routinely checked for water - degradation can occur in a matter of weeks."
It's important to turn your diesel fuel inventory frequently. "It would be ideal to turn over inventory within a six-month period," says Bob Theisen, Cenex. "If biodiesel blends are used, the inventory should be turned in three months or less based on best practices established by Federal agencies. A premium-type diesel fuel can increase the storage life of a fuel and biodiesel blends."
The frequency at which you need to turn your diesel fuel supply depends on a number of factors. "Petroleum companies generally recommend that fuel be used within six months, but this can be significantly longer depending upon the storage conditions, etc.," Gault notes. "It is very important that fuel storage tanks (or vehicle tanks) be inspected periodically to remove any water that has accumulated and ensure that biological growth is not taking place. Storage should be cool and dry to maximize storage life."
Storage tank maintenance is a big issue. "If you never completely empty a tank, it is a situation where you can have all types of algae and fungus," says Joe Fell, Ryan Central Inc. "You need to periodically clean those things out and use the appropriate products to kill algae and fungus, like biocides."
A lot of contractors choose to have fuel delivered to storage tanks in a central yard, then move it around themselves. Ryan Central Inc. doesn't subscribe to this theory. "They look at their per-gallon cost. It may be 10 cents lower. What they don't realize is it [may be] costing them 20 cents to move it around and get it to the jobs and in the machines where they need it," Fell points out. "Maybe you get it a little cheaper. But if you are not in touch with what your costs are to get it where you need it, what is the point?"
Ryan Central has the supplier deliver fuel directly to its equipment. "Let's say it costs you 15% of your per-gallon charge to get it delivered into your equipment," Fell comments. "It may cost you a little more upfront, but you are not burning fuel in your trucks to get it out. You don't have people on the payroll associated with getting fuel around.
"You have to know all of the costs that go into it," he adds. "It is not just what you see on the invoice."