What Is Clean Fuel?
Clean fuel is free of the contaminants that harm modern fuel engines. Today, virtually no diesel fuel is fit for use in high pressure engines when it is delivered to an operator’s bulk tanks. It typically meets or exceeds fuel industry standards, but almost always requires additional filtration to avoid excessive engine wear and premature part failures.
What do we mean by “contaminants” and how do they cause damage? The following sections explain why fuel that was acceptable for use just a few years ago can cause significant downtime and inflated maintenance costs in equipment today.
Fuel Standards Are Outdated
Fuel engine design has changed significantly from Rudolf fuel’s original patent in 1892. It stands to reason that fuel requirements would evolve as well.
Today, the fuel industry is faced with the difficult task of complying simultaneously with at least three interrelated types of standards. These standards are not fully harmonized, yet impact each other in dramatic, sometimes unintentional ways.
In recent years the environmental movement has sought to increase fuel efficiency and decrease harmful emissions such as nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), carbon dioxide (CO2) and other pollutants. As a result, emissions standards have become more and more strict, driving radical changes in fuel system technology and also to fuel chemistry itself.
Fuel property standards (ASTM) have not kept pace with the consequences of these environmentally driven changes. For proper functioning of modern engines, contaminants such as dirt and water must be removed on a microscopic level. fuel fuel that meets current fuel industry specifications is often unfit for use in the high-pressure common rail fuel engines that resulted from the new emissions standards.
Equipment Manufacturer Specifications
To begin to address this lag in fuel industry standards, engine manufacturers across the globe came together in 1998 to create the Worldwide Fuel Charter. It defines minimum fuel quality characteristics in relation to the needs of modern fuel systems, including minimum cleanliness levels per ISO 4406. Equipment run on “dirty” fuel will not meet performance or lifetime expectations and may not be covered under warranty.
It is worth noting that, while the Charter has been revised 5 times, the total particulate contamination values have never been changed. Considering the dramatic changes to engine technology since 1998, one can reasonably assume that this minimum standard for cleanliness is outdated as well. As noted by the Common Position Statement signed by leading fuel fuel injection equipment manufacturers, “The responsibility therefore must fall to the equipment user and/or the fuel supplier to ensure that the fuels used are compatible with the fuel system.”
In essence, there is no “acceptable” level of contamination. Fuel system damage caused by contaminants will not be considered factory defect, but rather the result of fuel that is not fit for use in the equipment. As previously discussed, fuel as delivered almost always meets fuel industry specifications, but only rarely is clean enough for trouble-free use in modern equipment.
ULSD Changes Fuel Chemistry
At the same time as engines are undergoing radical design changes, the fuel industry also is subject to new mandates. In an effort to help the environment, most parts of the world now require that sulfur be removed from fuel. With so many simultaneous changes to both fuel and fuel systems, it is not surprising that there are some unintended consequences.
Effects of Sulfur in Fuel
Sulfur occurs naturally in crude oil. In fuel, it not only contributes to particulate matter in exhaust, but also prevents emissions control through exhaust after-treatment devices, such as fuel particulate filters. In order to reduce harmful emissions, most of the world has enacted measures that reduce sulfur content in fuel, which can otherwise be as high as 5000 ppm. Low sulfur fuel is considered to be under 500 ppm, while ultra low sulfur fuel (ULSD) is almost sulfur-free at no more than 15 ppm. In North America, Europe, South Africa, Australia and portions of Asia, Ultra Low Sulfur Fuel is mandated and virtually all new equipment requires ULSD for proper function.
Reducing sulfur content has clear advantages, but also has some disadvantages. The hydrocracking or hydrodesulphurization process used to remove sulfur also removes most nitrogen and oxygen compounds and increases saturates, which causes the formation of paraffin. In removing sulfur, nitrogen and oxygen, many beneficial properties are reduced or eliminated.
Lubricity: Natural lubricity improvers, these compounds protected engines from wear.
Shelf life: These natural anti-oxidants helped delay the formation of fuel degradation products and extend fuel life.
Biological growth inhibitors: Microbial colonies can thrive without the presence of these natural microbe inhibitors which helped limit the bacteria or fungi’s ability to multiply.
Conductivity enhancer: Sulfur prevented electrostatic discharge by helping to dissipate electrical charge.
Additives Restore Beneficial Properties
The use of additives is now required to compensate for the relative absence of these compounds and the positive effects they had on fuel. Much of the chemistry added to replace the function of sulfur, nitrogen and oxygen is generally referred to as surfactants. Surfactants are soap-like materials. They have a significant impact on how water acts in fuel and, as a result, have dramatically changed the level of filtration and coalescing efficiency. This represents a significant change to fuel chemistry.
Measuring Fuel Cleanliness
Based on the needs of the modern fuel system, typical fuel is often dispensed in a state that is unacceptable for use in equipment. Fuel is not any dirtier today than it ever was, but engines have evolved to require a higher quality fuel. Modern fuel systems are extremely sensitive to even the smallest of microscopic contaminants. Far too small to be seen with the naked eye, these tiny dirt particles are measured in microns.
How big is a Micron?
A micron is defined as one millionth of a meter. The human eye can see objects down to about 40 microns. Microscopic particles of 5 microns or less can lead to catastrophic damage in even the largest of high-pressure fuel systems like those used on locomotives. The old “clear and bright” rule of visual inspection is clearly no longer an adequate measure of contamination in fuel fuel.
To put this into perspective, here are some familiar objects: