Chemical additives are part of every drop of oil and diesel fuel that your consumes. Engine oils have evolved significantly over the years to survive the increased stresses of the engine components and EPA compliance, especially in the newer Tier 3 and Tier 4 engines. Unlike diesel fuel, oil is constantly improved to stay current with SAE regulated standards. Diesel fuel standards on the other hand, have not changed since 2004 and the introduction of ULSD and Biodiesel have not been a benefit the the engine life or performance
In the USA, over 100,000 miles of pipeline carry refined petroleum products to terminals across the country. Most of this product is “fungible” (co-mingled) and the standard for diesel traveling this expansive network is the same D975 which has not changed despite the improvements in injectors and fuel systems. There is very little incentive for producers to produce anything better than would just meet these standards. Although refiners and pipeline companies are always using, lubricity improvers, conductivity improvers, drag reducers and possibly flow improvers in cold weather climates, no further action is required to improve a fuels fundamental specifications. A few exceptions occur where crude slates are very good quality and refining practices and dedicated pipelines, result in a higher quality fuel. Terminal operators and fuel marketeers are the last option where additional chemistry can be added to improve a fuels quality and performance. Additional lubricity, antioxidants, cetane improvers and cold weather chemistry are among the main components of terminal operators and marketeers will add to call their fuel “Premium”. Unfortunately, there are no standards to be able to make this claim with respect to diesel fuel and it is often very abused.
From the refinery, down the pipeline and to the terminal operators and fuel marketeers, additives are used in various amounts to meet specifications or to upgrade the fuel to a premium or branded level.
There are a number of commercial diesel fuel additives that the petroleum industry may use to meet and maintain diesel fuel properties. It is appropriate to make a few distinctions with regard to commercial diesel fuel additives. Additives and fuel components are not the same. Components add volume to the fuel and fall into hydrocarbon classes such as naphthenes, isoparaffins and aromatics. Additives, on the other hand, are added at very low levels, usually at the parts-per-million level, and do not add significant volume to the fuel. Also, commercially available additives are generally added only when the need to do so has been determined by the fuel manufacturer. This is as opposed to over-the-counter (OTC) additives, which are added without knowing if there is really a need. While there are always exceptions, OTC additives are of limited use, since the additives are already in the fuel if there is a need for them.
There are numerous additives available that are designed to be used in diesel fuel. The US EPA maintains a list of approved additives.
- Cetane improvers – Improves ignition quality by raising cetane number, better starts, reduces white smoke
- Lubricity improvers – better lubrication in fuel pumps and injectors.
- Detergents and dispersants – prevent fuel injector deposits and clean dirty injectors, which promotes better spray patterns.
- Anti-oxidants – Reduce formation of gum and precipitates. This extends the storage life of the fuel.
- stabilizers – Inhibit oxidation & extend storage life
- metal deactivators – Deactivate copper compounds in fuel, thereby promoting longer storage life.
- Biocides – Inhibit bacterial & fungi growth, help prevent fuel filter plugging.
- Pour point depressants – to improve cold flow properties.
- Cloud point depressants – reduce the temperature at which paraffins (waxes) solidify, thereby lowering the cloud point.
- De-icers – prevent fuel line or filter freezing.
- Smoke suppressants – Promote more complete combustion, reduce exhaust smoke
- Anti-foaming agents – Reduce fuel foaming during fill-ups.
- Rust preventors – Reduce rust formation in fuel systems and in storage tanks.
- Emulsifiers and dehazes – Used to increase the rate of water separation from the fuel.
- Dyes – To identify grades of diesel for regulatory compliance purposes.
Other additives used in the pipeline:
- anti-drag additives – used to improve pipeline flow rates
- conductivity improvers – improve the dissipation of static charge
Note: The use of low temperature operability additives, such as pour point depressants and cloud point depressants, provides an advantageous alternative to blending with No. 1 diesel. In years past, winterized diesel was recommended for subzero temperatures. This was accomplished by blending No. 1 diesel into No. 2 diesel, which would lower the temperature at which the fuel would start to gel, because of the blend’s lower cloud point. Unfortunately, No. 1 diesel has a lower heating value (lower btu content per gallon) than No. 2 diesel, so this approach results in a fuel economy penalty and power loss. As an example, a 50/50 blend of No. 1 and No. 2 diesel may reduce fuel economy by nearly 5 percent and result in a power loss of up to 4 percent compared to No. 2 diesel. Cloud point depressant additives can be used to change the size and shape of wax crystals that form at low temperatures. These alterations allow fuel to more readily pass through the wax that may accumulate in the fuel filter without the reduction in power and fuel economy described above for fuel blending.
Premium Diesel Fuel
The growing population of late-model, high technology diesel vehicles has led to some companies offering a premium diesel fuel.
The ASTM specifications do not specify what constitutes a premium diesel fuel. Premium gasoline is defined primarily by a higher octane number. Many engine manufacturers and state regulators believe a premium diesel fuel requires more than just a higher cetane number. The National Conference on Weights and Measures (NCWM) has adopted standards for premium diesel fuel. These requirements are set forth in the National Institute of Standards and Technology (NIST) Handbook 130, Engine Fuels, Petroleum Products and Automotive Lubricants Regulation. The requirements of the NIST Handbook 130 are model regulations, not federal requirements. However, many states adopt the requirements of the NIST Handbook 130, or use them as guidance in developing their own regulations. Their requirements represent input from fuel manufacturers, engine manufacturers and state regulators.
The portion of the regulation applying to premium diesel specifies that any diesel fuel designated as premium, super, supreme, plus or premier conform to the following:
Cetane Number:
Minimum 47
Low Temperature Operability:
A cold flow performance measurement which meets the ASTM D 975 tenth percentile minimum ambient air temperature chart and maps by either the Cloud Point Test or the Low Temperature Flow Test. These requirements apply October 31st through March 31st.
Thermal Stability:
A minimum reflectance measurement of 80 percent as determined by ASTM Test Method D 6468 (180 minutes, 150ºC).
Lubricity:
A maximum wear scar diameter of 520 microns (by ASTM Test Method D 6079 – certain enforcement retesting may be applicable).
The combination of these is meant to ensure that premium diesel provides superior ignition quality and improved low temperature operability characteristics. In addition, the potential for fuel degradation in storage is reduced, and a specific level of lubrication is required. This standard was last amended in 2003. As with ASTM Standards, the NCWM and NIST constantly review their requirements to determine if updates are necessary. In many states that do not specifically regulate what properties premium diesel should possess, the fuel may only meet one or two of the NIST requirements. These fuels are often sold as “Premium” yet add very little value to the customer.