Monday, August 15, 2011
Diesel fuel additives are simply chemicals that change the properties of untreated diesel fuel.
The biggest users of additives are refineries and distributors. Each batch of crude oil is different from the next, and each batch of refined diesel fuel is different from the next. Refineries and distributors use additives in bulk to make their diesel fuel more consistent before they sell it. This is called the “pipeline specification”.
More additives are used in “premium” grade diesel. In 1999, the NCWM (National Conference on Weights and Measures) defined five properties of diesel fuel and set standards for “premium” diesel. The refiners and distributors use additives in bulk to improve the fuel so it meets one or more “premium” standard.
IF THE REFINERS & DISTRIBUTORS USE ADDITIVES IN BULK, WHY DOES ANYBODY HAVE TO USE BOTTLED ADDITIVES?
1. You have to use bottled additives because there are additives that refiners & distributors don’t use.
The first and cheapest additive that a consumer wants is a water remover. Water enters fuel at refining, transport, storage, and engine operation. ASTM has specs for maximum amounts of water in diesel fuel. Suspended water in diesel fuel hurts combustion, lowers energy content, fouls injectors, wears out pumps, abrades injector tip needles, and causes gum and varnish. In cold weather, waters ices up and blocks fuel lines. Water can separate into oxygen and hydrogen, and combine with fuel to create sulfuric acid. You’ll never see a water remover as an additive in standard fuel or premium fuel because ppm (parts per million) of water changes daily. The only way to get a water remover is a bottled additive.
2. You have to use bottled additives because refiners & distributors don’t use enough quantity.
The refiners and distributors treat their regular grade fuels enough to make them consistent from batch to batch, or at least pretty consistent. But “consistent” doesn’t mean “good”. Impartial national organizations like ASTM (American Society for Testing and Materials), NCWM, TMC (The Maintenance Council of the American Trucking Associations) and EMA (diesel Engine Manufacturers’ Association) all have specifications for “good” fuel that go above and beyond regular grade fuel.
3.You have to use bottled additives because refiners & distributors don’t use enough kinds of additives.
I mentioned above that NCWM defined four properties of diesel fuel and set standards for calling it “premium”. The four properties are cetane number, low-temperature operability, thermal stability, and fuel-injector cleanliness.
Diesel fuels identified on retail dispensers, bills of lading, invoices, shipping papers, or other documentation with terms such as premium, super, supreme, plus, or premier, must conform to the following requirements:
– Cetane Number – A minimum Cetane number of 47.0 as determined by ASTM Standard Test Method D613
– Thermal Stability – A minimum reflectance measurement of 80% per ASTM D6468
– Low Temperature Operability – A cold flow performance measurement which meets the ASTM D975 tenth percentile minimum
– Lubricity – A maximum wear scar diameter of 520 microns per ASTM D6079. If a single test of more than 560 microns is determined, a second test shall be conducted. If the average of the two tests is more than 560 microns, the sample does not conform to the requirement.
Does a consumer get good cetane number, low-temperature operability in certain months, thermal stability, and fuel-injector cleanliness if he buys a “premium” fuel? Not necessarily. A refiner or distributor can call it “premium” fuel if the fuel meets all four standards. Low-temperature operability does not apply in most months and in many locales, so a “premium” fuel assures a consumer of only three standards.
For instance, the NCWM standard for cetane in “premium” is 47. A study found one “premium” grade fuel with a cetane of only 35, which is actually below the federal minimum standard of 40 for regular grade diesel. A consumer hoping for a certain cetane number from this “premium” fuel would be badly disappointed. This situation is not rare. The most recent Premium Diesel Fuel Survey from Hart’s Diesel Fuel News shows that 26 major refiners/distributors make 34 brands of premium diesel fuel. Only one of the 34 brands of premium fuel claims to meet all four NCWM properties. Thirty-three of 34 admit to falling short on one, two, three, or four properties. Another study of 64 “premium” fuels showed none meeting all four standards.
WHAT CAN ADDITIVES DO ABOUT “HIGH CETANE NUMBER”?
“High cetane number” improves cold temperature starting and idling for all engines, and is required by some engines. If it doesn’t come out of the pump, there are additives that increase cetane number.
WHAT CAN ADDITIVES DO ABOUT “LOW-TEMPERATURE OPERABILITY”?
“Low-temperature operability” means the fuel won’t gel up and clog the fuel lines or fuel filter. Most fuels from the pump are treated in bulk with additives or kerosene. Some meet a specification, some do not. If they don’t meet a spec, or if the weather becomes colder than the spec, or if the fuel is headed to a colder area … then gelling is a risk. The consumer first wants a water removing additive, because ice forms faster than wax gels. Next there are preventative anti-gel additives to give more protection than the fuel from the pump. There are also remedial additives which un-gel fuel that has clogged the fuel lines or fuel filter.
WHAT CAN ADDITIVES DO ABOUT “THERMAL STABILITY”?
“Thermal stability” means the fuel’s ability to resist particle formation as it circulates from the tank to the engine and back again. Such particles clog filters and injectors. Consumers using high pressure injector systems with fuel as a re-circulating coolant can easily assure thermal stability with a bottled additive.
WHAT CAN ADDITIVES DO ABOUT “FUEL INJECTOR CLEANLINESS”?
“Fuel-injector cleanliness” means the fuel has a detergent that keeps clean injectors clean. Injector tips are precision instruments. Even a little dirt or varnish will damage proper spray pattern and combustion, waste fuel, rob power, and reduce mileage. Dirt is caused by thermally unstable fuel. Dirt is caused by worn needles and over-rich fuel feed; needle wear is caused by water abrasion. Varnish is caused by suspended water in the fuel. You can stop the causes of dirty and varnished injectors with regular use of water removing and thermal stabilizing additives. You can clean larger accumulations of dirt with an additive that contains a high concentration of detergent. Cummins L-10 is the accepted specification for detergency. You can keep clean injectors clean with a fuel that contains detergent.
WHAT CAN ADDITIVES DO ABOUT “LUBRICITY”?
The joint definition of “premium” grade by TMC and EMA uses the same properties as NCWM. TMC and EMA standards are a little tougher. For instance, their minimum standard for cetane is 50 compared to 47 for NCWM. TMC and EMA definition adds lubricity as another property. (In fact, lubricity was discussed by NCWM as a sixth property, but they couldn’t agree on how to measure it, and they are still working on it.)
“Lubricity” means the lubricating value of fuel. Low sulfur fuel has less lubricity. Low sulfur fuel also absorbs water more readily, and water is an abrasive. Untreated fuel often causes excessive wear on fuel pumps and injector tips. Many additives have a lubricity improver, by itself or in combination with other chemicals.
ARE BOTTLED ADDITIVES A GOOD DEAL?
Generally yes. Premium diesel is 5¢ to 15¢ per gallon higher than standard. You are assured of good quality in one to five important properties of diesel fuel. Additives cost 2¢ to 4¢ per gallon to assure good quality in one important property of diesel fuel: to remove water, to clean injectors, to lower pour point, to boost cetane three numbers, or to add lubricity. Combination additives assure good quality in several important properties of diesel fuel, and cost 5¢ to 10¢ per gallon. In most cases – but not all — you’ll get more benefit for less money by using bottled additives.