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Lubricity and Performance Testing

Updated: May 20, 2023

Importance of Engine Lubricity ...

What is lubricity in fuel and why is it important?

Lubricity is best described as the ability of a fluid or lubricant to minimize

the friction and damage between surfaces in relative motion under load. In

a diesel engine the fuel is part of the lubrication process but with current

regulations continuously enforcing stricter emission standards on diesel

fuels, the importance of fuel lubricity has become a major concern to both

engine manufacturers and users. We know that without lube oil in an engine

all of the metal parts in the engine will rub against each other causing

catastrophic wear and damage, we can safely say the same about the fuel

components thus making fuel testing a critical element to determine or

measure the lubricity. Due to the fine tolerances of the components within

the fuel-injection system, some of which are measured in ten-thousandths

of an inch. If the fuel’s lubricity is too low, improper lubrication will shorten

the service life of fuel injectors and high-pressure pumps. They will

essentially grind themselves to death. Insidiously, this failure typically

doesn’t display any outward symptoms; the engine runs just fine, there’s no

smoke or knocking, and fuel economy remains normal until the engine

becomes difficult to start or the injection pump fails, by which time the

damage is done.

As diesel fuel is further refined to remove the polluting sulfur, it is

inadvertently stripped of its lubricating properties. This vital lubrication is a

necessary component of diesel fuel as it prevents wear in the fuel delivery

system. Specifically, it lubricates pumps, high pressure pumps and injectors.

Traditional Low sulfur diesel fuel typically contained enough lubricating

ability to suffice the needs of these vital components. ULSD fuel, on the

other hand, is considered to be very “dry” and incapable of lubricating vital

fuel delivery components. As a result, these components are at risk of

premature and even catastrophic failure when ULSD fuel is introduced to the

system. According to multiple diesel studies and engineers there is a

common belief that All ULSD fuel purchased at retail fuel stations

SHOULD be adequately treated with additives to replace this lost

lubricity. The potential result of using inadequately treated fuel, as

indicated above, can be catastrophic.

There have been many documented cases of randomly tested samples of

diesel fuel. These tests prove that often the fuel we purchase is not

adequately treated and may therefore contribute to accelerated wear of our

fuel delivery systems. For this reason, it’s important to use DF5 to ENSURE

adequate lubrication of the fuel delivery system. Additionally, DF5 offers the

added benefits of a Cetane improver, that eliminates the need for a separate

anti-gel in the winter.

In today’s advanced, high-pressure diesel systems, both the pump and

injector rely solely on fuel for their lubrication. This sets the stage for

prevention of diesel lubricity problems.

Since the switch to ULSD (Ultra Low Sulfur Diesel), fleet owners and regular

diesel users alike have complained about the following:

• Lower energy content (BTUs) compared to low sulfur diesel (LSD),

resulting in lower fuel economy.

BTU is the unit used to measure heat energy and is also known as

British Thermal Units. Larger BTU readings and output mean that

your fuel is stronger and produces more power per stroke. Pretty

similar to the logic behind the octane levels for gasoline. Prior to

2006, LSD fuels ruled the day. Now ULSD fuels are the standard and

requirement since changes were made by the EPA to reduce

emissions. Sulfur is the keyword here, as it’s the lubricant for the

fuel and affects all system components related to combustion.

Lower energy content means the engine needs to burn more fuel to

create the same output of power as a fuel with higher energy

content, resulting in less fuel economy.

• ULSD is a hygroscopic fuel, meaning that it absorbs moisture from

the air or atmosphere.

This is an important point. Water wreaks havoc in diesel fuel

systems causing corrosion and failure of metal components, such as

fuel tanks, pumps and injectors. Absorbing moisture from the air

can also make your fuel go bad much faster. Fuel going bad will

result in lower energy content (BTUs) and overall lower

performance. The moisture absorbed from the air can also lead to

formation of rust inside the fuel tank. The presence of rust not only

affects the fuel but can also clog up filters or worse, injectors and

pumps. In the wintertime, the presence of moisture leads to “diesel

gelling”. Diesel fuel changes it’s liquid state into solid, clogging

everything and making your truck or other diesel burning vehicle


• Reduced levels of lubricity

Since diesel systems rely on the lubricity of the fuel to function

correctly, a reduced level of sulfur will increase wear and the

possibility of other complications appearing throughout.

Above mentioned are the elements discovered by users at first glance.

However, fuel systems can develop ULSD related problems in the long run.

Most commonly, these issues are:

• Rust and corrosion form in lines as well as fuel tanks. This happens

due to the aggressive chemicals within the fuel and because of its

hygroscopic nature.

• Low fuel lubricity causes wear or scarring in pumps and injectors.

Lack of lubrication affects especially expensive and accurate

components that work with very small tolerances.

• Sludge can build up inside tanks and result in plugged filters. Sludge

or diesel fuel algae is a microbial biomass formation that appears due

to the ULSD’s moisture attracting nature. It forms a jelly, slimy

contaminant that will work to clog up filters or injectors and pumps as

previously mentioned.

Independent Laboratory Testing...

DF5 was tested using two different third-party independent laboratories,

which is preferred by manufacturers and is industry standard. Quality of

diesel related to its lubricity is determined using the high frequency

reciprocating rig (HFRR), it is a wear test method that was developed by

Infineum and Imperial College in London. The design, test method and

results from HFRR are well described in standards like ASTM D6079 and ISO

12156. HFRR is a powerful tool in lubrication, as it is become a key enabler of

pollution control. HFRR test method is recognized by several regulatory

bodies that control the quality of diesel and its emission of pollutants ( see

attached SWRI Lab Test).The results of the independent testing showed a

16% increase in lubricity after adding DF5 to the fuel (see attached SPL

Laboratory Test).

2023 01 13 Lubricity and Performance Testing
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