By Paul Nazzaro, President, Advanced Fuel Solutions, Inc.
It won’t be long before municipal fleets are out hauling salt spreaders to de-ice the roads. The general principle is this: salt lowers the freezing point of water; the more salt you add, the lower the freezing point; the colder the temperature, the more salt (or salt solution) it takes.
Those behind the wheel of the vehicle often assume that the same rule applies to the low temperature operability of their fuel—the colder the temperature, the more cold flow additive it takes to lower the cold weather operability of the fuel and eradicate fuel gelling. This misconception commonly leads to a phenomenon known as reversion, wherein the performance gains achieved by the proper dose of the additive are reversed due to an overdosing of the fuel.
While it’s true, in a sense, that salt is to water as cold flow additives are to fuel, the two chemical interactions are actually very different. While salt inhibits crystallization of water molecules, cold flow additives modify the size and shape of the wax crystals that precipitate in diesel fuel under cold conditions, enabling the fuel to flow freely through engine components without plugging filters.
Calibrate With Care
It’s important to recognize that cold flow additives are themselves waxy materials, meaning that they actually add more wax to the system. The dosage must therefore be carefully calibrated in order to achieve the optimal response. Raising the dosage above the recommended treat rate will offer little or no additional benefit, and, in extreme cases, will cause a reversion of low-temperature properties that can leave the fuel even worse off than its pre-treated state.
Fuel can generally be over-treated with any kind of additive, in any type of application. High levels of certain lubricity improvers can react with contaminants (sodium, calcium, etc.) to form materials that cause filter plugging. Going too high with a corrosion inhibitor in the presence of the same contaminants can cause internal injector deposits. In short, every category of additive has a treat rate that is too high. Overdosing—particularly in combination with common fuel contaminants—can result in a loss of engine performance and fuel efficiency, and, worse, may damage expensive engine components.
Overdosing can happen for any number of reasons, at any point in the supply chain—at the refinery, due to (or in response to) an ‘upset’; at the terminal, due to a control valve malfunction at the rack; or at the pump, where a driver adds a bottled product assuming that more is better, or accidentally treats fuel that has already been treated upstream.
Whether you’re that municipal fleet manager mentioned above or anyone in the business responsible for diesel equipment functionality in cold weather, it’s up to you to ensure your fuel’s performance, regardless of quality assurances proclaimed by your supplier.
Stay on Top of Things
While working with established fuel and additive suppliers is a good start, it does not eliminate the need for diligent oversight. If you’re working with suppliers that pre-blend your diesel at the rack, make it a point to understand their operability expectations and declarations. If you choose to buy and treat your own fuel, be sure to randomly and periodically have your product screened by an analytical laboratory so you can predict what the performance levels will be in the field. If you have high blood pressure and take medication, you likely have periodic screenings to determine if the medication is working at the prescribed dosage; why wouldn’t you do the same for your fuel?
Not all diesel fuels are created equal, nor are the additives used to enhance them. Diesel fuel comes with a wide range of cloud points and physical properties, some more suitable for cold weather treatment than others. Several years ago, you might have been able to source a single digit cloud point diesel fuel. Today, that would be like finding a needle in a haystack, not impossible but not the norm, unless of course an upstream participant modified the diesel cloud with kerosene, an expensive and unreliable option for managing a diesel fuel’s tolerance to cold weather. Likewise, cold flow enhancing additive packages can have very different properties, some more advanced than others. For instance, new technology is emerging with advanced polymers and synergists that suspend wax that would otherwise precipitate out of fuel during extended equipment shutdowns. These wax anti-settling agents keep the heavy paraffin in the fuel from settling to the bottom of the tank, preserving the flow rate of fuel after a vehicle has been sitting idle. A well-rounded cold flow package will also include a component to address moisture, the most common contaminant of all.
How Do You Really Know?
If you wish to adopt a theory that an effective cold flow-enhancing additive can deliver an 8ºF to 12ºF drop below the fuel’s base cloud point, then you would agree that winter operability temperatures would range between 0ºF and -10ºF. Additive providers can make misleading claims and exaggerate the performance of their products all day because the vast majority of diesel fuel buyers do not conduct their own oversight or analyze the performance of the additives they buy. With little if any knowledge of operability points and the variability associated with them, most diesel buyers can only hope that the seller has prepared them for the worst.
How these additives work is quite simple, they suspend wax that may precipitate out of the fuel during extended equipment shutdown. That municipal fleet manager we keep picking on buys a load on Thursday or Friday afternoon, heads home for the weekend, and the New England winter hits hard. Sustained single digit temperatures grip the region. The fuel now sits idle in an above ground storage tank with a fuel rated with a cloud point of +12 ºF while the weekend temperatures were +4 ºF or worse -4 ºF. Without a wax anti-settling agent, that wax in the diesel fuel becomes so prevalent that it drops to the bottom of the tank awaiting for the first truck to load Monday morning. The diesel operator begins fueling his truck at a much reduced flow rate because of the increased viscosity. What’s next? A plugged dispenser filter, then the call to the supplier ranting that the fuel… “well, you know the rest of this story.”
Additive components combine to provide a multifaceted prevent defense to ensure “go in the cold” performance. But remember, more is not always better. Start by working with reputable fuel and additive suppliers, know your recommended additive treat rates, and monitor your fuel—both in the field and through laboratory screenings—to ensure that proper additive levels are used. Like a well-rounded additive package, a well-rounded oversight process will help maximize “up time” for your fleet no matter how low the temperature drops.
Advanced Fuel Solutions, Inc (AFS), based in North Andover, MA, provides fuel quality consulting services and diesel additives designed to keep fleets on the road profitably.