Basic Additive Groups, Functions And Performance Tests

Fuel additives are the last chance an equipment user or fleet manager has for improving performance and/or solving fuel-related problems. The success of a diesel fuel additive package can vary upon geographic location, fuel marketer, and equipment user. Listed below are the basic additive groups that may comprise a diesel fuel package. The equipment user and/or the fuel marketer have the flexibility of deciding on the package components/performance requirements based upon operational requirements. On-road diesel fuel additives should be registered with the EPA in accordance with the regulations set forth in the code of federal regulations (40CFR79). In addition, diesel fuel additives should have only non-metallic components as part of the package.

The proof of the additive performance is defined by laboratory and/or field test data. However, fuel additives can be fuel specific and may react differently in different batches of fuel. Always use a reputable supplier who runs "actual tests" when selecting fuel additives, or when blending No.2 diesel and No.1 diesel.

Many additive categories are listed below. Because some components have far greater significance to the trucking industry than others, equipment users and fuel marketers should address only those most relevant to their operation.

Anti-foam Agents
Functions:

These are used to reduce the rate of foaming while filling a fuel tank. This component may be especially useful during rapid filling such as at a vehicle refueling station.

Categories:

Anti-foamers (non-metallic)

Performance Tests:

NF M 07-075, Determination of the Foaming Tendency of Diesel Fuels .

Possible Side Effects:

These compounds should be tested for compatibility with other fuel additives. The additive supplier should be able to produce no-harm support data.
Biocides
Functions:

These are used to kill or inhibit microorganism growth and avoid the effects of microbiological growth. Serious problems that can arise from microbiological proliferation are:
- Sludge formation
- Acid and surfactant formation with subsequent water entrainment
- Fuel storage/dispensing system corrosion
- Premature fuel filter, screen, and line plugging
Categories:

Water phase

Fuel phase

Dual phase

Performance Tests:

Measure effectiveness of biocides in both fuel and water phases using appropriate incubation of treated and untreated samples and using relevant microbiological strains. A common non-ASTM test used in the field is the Humbug Test. (Hammonds, Inc., Houston, Texas).

Possible Side Effects:

Interaction with other additive components. Fuel filter plugging due to bio-mass deterioration.
Cetane Improvers
Cetane number is the most universally accepted measure of ignition quality of diesel fuels. Proper ignition during the combustion cycle is essential for optimum operation, economics, and durability.

Possible Benefits:
- Faster cold starts
- Less white smoke
Categories:

2 ethyl-hexyl nitrate (most common)

Di Tert Butyl Peroxides

Other alkyl nitrates

Performance Tests:

Cetane Number-Engine test ASTM D613. The Cetane number is based on running the fuel in a test engine. Federal test method 791 is another test method used for cetane number. The change in ignition quality of a cetane improver can be determined using this test.

Cetane Index-Cetane Index is calculated from distillation points and density (ASTM D976 and D4737). It is used to approximate the actual cetane number of the fuel. Cetane improvers and any subsequent improvement are not accounted for in the calculation.

Possible Side Effects:

Excessive levels of cetane improver can impact the oxidation stability of the fuel.
Cold Flow Improvers
Functions:

Cold flow improvers (CFI) are designed to depress the cold temperature operability limit of diesel fuels. The economic advantage of CFIs is the ability to use a denser fuel at a lower cost per gallon when compared to reaching the same operability limits with No. 1 diesel.

Categories:

There are numerous names and chemical families involved in cold flow additives. The following is a list of the more common terms found within the industry. These components can be used individually or in combination. This list should not be considered complete.
- Cold filter plugging point (CFPP) additives
- Pour point depressants
- CFI additives (generally a CFPP and pour point additive combination)
- Low temperature flow test (LTFT) additives
- Nucleators
- Wax modifiers
- Wax dispersants/wax suspension agents (WASAs)
- Cloud point depressants
Performance Tests:

Cloud Point (CP)- ASTM D2500

This test indicates the temperature when wax becomes visible in the fuel. This temperature is usually above the operability limit of the vehicle especially if the fuel has been treated with an effective CFI. ASTM D2500 is recognized by ASTM D975 diesel fuel specifications.

ASTM D2500 is recognized by ASTM D975 for diesel fuel specifications, however other ASTM Cloud Point methods may be relevant, such as ASTM D5773, Standard Test Method for Cloud Point of Petrole um Products and Liquid Fuels (Constant Cooling Rate Method).

Pour Point (PP) - ASTM D97

This test predicts the gel point at which fuel no longer flows in the fuel system. The operability limit is always higher than the pour point. ASTM D97 is recognized by ASTM D975 for diesel fuel specifications Other pour point test methods may include ASTM D5949, Standard Test Method for Pour Point of Petroleum Products (Automatic Pressure Pulsing Method).

CFPP-IP 309 CEN 116

This test was developed to find the lowest temperature at which that a diesel fueled vehicle could start and operate. This is the industry standard in Europe and is commonly used in the USA as well. IP 309 CEN 116 is recognized by ASTM D975 diesel fuel specification, however other CFPP testing is applicable such as ASTM D6371, Standard Test Method for Cold Filter Plugging Point of Diesel and Heating Fuels .

LTFT-ASTM D 4539

LTFT is a more time consuming and more expensive test to run than CFPP, as it attempts to simulate the effects of slower fuel cooling. LTFT can take an additional day to run. LTFT is generally a more conservative measure of operability and is normally less responsive to CFI additives or No.1 diesel blending.

Wax Anti-settling Tests

There are several bench, rig, and tractor tests used by additive suppliers to find the value of holding wax in suspension in the fuel. For example a CFPP test can be run on a fuel bottoms sample after the fuel has been slowly cooled and stored at 5-10°F below the cloud point. These tests are applicable where diesel fuel may be stored for periods of time at or near the fuel's cloud point.

Possible Side Effects:

Adding too much CFI can reduce CFPP response. Refiners and terminals often add low levels of CFI, and to a lesser extent cloud point suppressants. This can reduce the chance to reach CFPP performance targets with additional CFI. CFI must be added above the cloud point of the fuel (similar to the state of fuel in underground storage tanks) or the fuel must be warmed to above the cloud point. CFI should be added based on recommended treat rates from the supplier; however, not all fuels respond equally to CFI. Some fuels are "hard to treat", meaning the recommeded treat rates might have varying degrees of success depending on the fuel being treated.
Combustion Improvers
Functions :

Designed to increase fuel economy via improved combustion efficiency and/or reduce/suppress diesel exhaust emissions and smoke. Special caution should be taken to ensure the supplier has valid field testing or controlled engine testing to validate any claims of fuel economy and/or emissions reduction. Before using these products, proof that no-harm testing has been completed is essential to ensure there are no negative effects.

Categories :

Cetane improvers

Organometallics (generally not available to US On-Highway market)

Organic combustion improvers

Performance Tests:

Fuel mileage testing -

TMC/SAE Type II/III/IV, etc.

Dynamometer testing

Emissions testing

Possible Side Effects

Caution must be observed when metallic compounds are present. Interaction between other additive components, deposit forming tendencies, and toxicity issues should be addressed.
Corrosion Inhibitors
Functions:

Prevents oxidation (rust) on metallic surfaces due to moisture and acids. Different corrosion inhibitors can protect against two of the following three corrosion types.
- Typical oxidation on metallic surfaces due to moisture
- Internal corrosion of injectors and other injection system parts
- Microbial induced corrosion (may not be addressed by typical corrosion inhibitors)
Categories:
- Anti-rust
- Anti-erosion
Performance Tests:
- ASTM D130, Detection of Copper Corrosion from Petroleum Products by the Copper Strip Tarnish Test
- ASTM D665, Standard Test Method for Rust Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
- NACE TM0172 - 2001, Determining Corrosive Properties of Cargoes in Petroleum Product Pipelines
Possible Side Effects:

Some corrosion inhibitors can react with other fuel and lubricant additives or metal contaminants to form gums, sludge and soap deposits especially if used at higher dose levels. Additive suppliers should be able to demonstrate no-harm performance when these additives or components come into contact with other fuel additives and/or lubricants. Lubricant contact can occur in certain types of fuel injection equipment or through the practice of mixing/burning used lubricants with the fuel as a disposal method.
Dehazers/Demulsifiers
Functions:

Fuel can become hazy and impact operability when fine drops of water become dispersed or emulsified within the fuel. Demulsifiers/dehazers allow water to coalesce and subsequently settle out. They are often in detergent/dispersant packages to avoid "pick-up" of water from the bottoms of fuel storage tanks and vehicle fuel tanks.

Categories:

Demulsifiers

Performance Tests:
- ASTM D1094, Water Reaction of Aviation Fuels
- ASTM D7451, Water Reaction
Possible Side Effects:

Incorrect treatment can lead to haze stabilization which can lead to increased fuel filter icing, bacterial infestation, large amounts of water in the water separator, and fuel system corrosion.
Deicers (anti-icers)
All efforts should be made to remove water out of diesel fuel before use.

Functions:

Deicers are intended to reduce the freeze point of water that may separate from the fuel or to disperse the water in such small droplets that ice crystal formation is precluded or inhibited.

Categories:
- Glycol ethers
- Glycols
- Alcohols
- Demulsifiers
Performance Tests:
- Measurement of fuel system icing inhibitors in aviation fuels ASTM D5006 (Limited to ether types; EGME DiEGME)
- Freeze Depression Test: Proprietary tests are used to measure the performance of complete additive systems assuming reasonable amounts of dissolved and free water in the fuel. This is a research tool used to optimize the deicer chemistry and dosage.
Possible Side Effects:

Deicers should be added as far downstream of the refinery as practical which allows for as much water to separate from the fuel before treatment. Methanol is difficult to solublize in the fuel except by using additive injection. Methanol droplets can cause severe injector damage. Isopropyl alcohol can separate out of the fuel with the water phase, causing excessive fuel pump corrosion and wear. Both isopropyl alcohol and methanol have low flash points which can lower the fuel flash point below ASTM D975 diesel fuel specification. Water and alcohol mixtures also have very low lubricity which can cause problems in diesel fuel injection systems. Original equipment manufacturers (OEMs) are mainly concerned with overtreatment of deicers which can cause more water to be drawn into the fuel. Some glycol ethers also have significant safety warnings on their material safety data sheet (MSDS).
Deposit Control Additives (Detergents)
Functions:

These additives can prevent deposit formation or remove deposits in the combustion chamber and on injector parts. Users may see benefits in:
- recovered fuel economy.
- increased engine, fuel system and fuel filter life.
- some products may deliver increased fuel filter life
- National Council on Weight Measurement (NCWM) Premium Diesel supports these requirements if proven by ASTM D2068, Standard Test Method for Determining Filter Blocking Tendency, following Procedure B.
- reduced exhaust emissions and smoke.
ASTM D975 for ULSD No. 2 and ASTM D7467 for biodiesel blends from B6 to B20 do not require deposit control additives. With continued use of unadditized ULSD No. 2 and biodiesel blends, users could experience sustained deposit formations. The proper use of quality no-harms data backed deposit control additives should remedy these issues. In comparison, NCWM Premium Diesel specification does require any fuel providers at retail dispensers using the following language: Premium, Premier, Supreme, & Super, to have their fuels contain deposit control additives and meet CEC F-98-08 DW-10 Injector Coking Test performance parameters. Top Tier™ Diesel requires use of deposit control additives

Categories :
- Keep Clean (at prescribed treat rates)
- Clean up (at prescribed treat rates)
Performance Tests:
- CEC F-98-08 DW-10 Injector Coking Test
- CEC F-23-01 XUD-9 Injector Coking Test
- TMC Fuel Consumption Test Procedures-Type II (RP 1102A), Type III (RP1103A), Type IV (RP 1109B)
Possible Side Effects:

Proper housekeeping of fuel systems before initial use of detergents/dispersants may reduce fuel filter plugging as old deposits and tank sludges are removed from fuel systems that have not been well maintained. Extra care should be paid to housekeeping to minimize the effects of this fuel system clean-up during initial use of detergent additives.
Dyes/Markers
Functions:

Dyes and markers serve to identify fuels for taxation and tracking purposes. Currently all non-taxed diesel fuels must be dyed red to meet federal standards. Some fuel marketers use dyes and/or invisible, covert marker systems to track fuel movements through their distribution systems.

Categories:
- Azo compounds
- Furfural
- Diphenylamine
Performance Tests:
- Dyes-visual inspection for detectable color
- Markers-each supplier has a proprietary testing protocol
Possible Side Effects:

These compounds should be tested for compatibility with other fuel additives. The additive supplier should be able to produce no-harm support data.
Lubricity Agents
Functions:

Lubricity additives protect against wear of the engine fuel system (e.g. injection pump, injectors, etc.) by forming a protective layer on the metal surfaces.

Categories:
- Mono-Acidic
- Neutral
Performance Tests:
- ASTM D6079, High Frequency Reciprocating Rig (HFRR);
- Rotary Injection Pump Rig Tests
Possible Side Effects:

Additive suppliers should present no-harm data demonstrating compatibility with other fuel additives and lubricants as described in the Corrosion Inhibitors section.
Metal deactivators
Functions:

Reduce oxidation catalysts due to the presence of fuel soluble compounds of metals such as copper and zinc. They can also be useful in preventing side reactions of various detergent/dispersant compounds with fuel soluble metals. These byproducts can form soap-type compounds which can negatively impact engine operation.

Categories
- N, N'-disalicylidene-1, 2-propanediamine (most common)
Performance Tests:
- Modification of Mil-S-53021
Possible Side Effects:

Periodic monitoring of fuel stability is recommended if these additives are being used.
Solvents
Functions:

These are not active components but are usually required to maintain product fluidity at normal handling temperatures and hold all the active components in solution. Solvents can impact the flash point. Lower flash point products should be handled appropriately.

Possible Side Effects:

Engine damage due to the use of improper solvents, such as gasoline, should be avoided.
Stability Improvers
Functions:

Stability improvers are designed to prevent fuel degradation by precluding various reactions andsuppressing free radical propagation of peroxy or alkyl radicals.

Categories:
- Antioxidants
- Stabilizers
- Metal deactivators
Performance Tests:
- ASTM D6468, Accelerated Thermal Stability (Octel F21 test 1.5 or 3 hour)
- ASTM D2274, Oxidation Stability of Fuel Oils Accelerated Method
- ASTM D4625, Distillate 13-week Fuel Storage Stability (43°C)
- ASTM D7545, Standard Test Method for Oxidation Stability of Middle Distillate Fuels-Rapid Small Scale Oxidation Test (RSSOT) , also known as "PetroOXY"
- EN15751, (Rancimat IP Method) Oxidation Stability Test
Possible Side Effects:

Periodic monitoring of fuel stability is recommended if these additives are being used.