Diesel Engine Standards

A higher injection pressure is a key factor in reducing an engine's untreated emissions... The greater the injection pressure, the more finely both the injector and injection nozzle can be constructed. This improves atomization and results in a better air-fuel mixture, meaning that optimum combustion is achieved and no soot can form."
Pressure in diesel engines
11 November, 2013 
Diesel Standards are Outdated 

Diesel engine design has changed significantly from Rudolf Diesel's original patent in 1892. It stands to reason that fuel requirements would evolve as well. 

Today, the diesel 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.

      • Diesel property standards 
      • Emissions standards 
      • Equipment manufacturer specifications 

The American Society for Testing and Materials (ASTM) is a major source of diesel specifications and test standards worldwide. What is often misunderstood is that this is a voluntary association of fuel industry professionals, each with a unique point of view. New specifications proposed by ASTM must obtain 100% consensus of all voting members, a practice that makes change a slow and deliberate process. 

The meticulousness of this process is partly intentional. The consequences of a change can be so significant 
and far-reaching that a good deal of empirical evidence must prove that there will be an improvement for all those who use diesel. A new specification passed by ASTM applies to all diesel and covers every circumstance. ASTM D975 is intended as a fungible minimum standard, not specific to any one diesel engine type or fuel system. A diesel characteristic that is essential for some might be unnecessary or even undesirable for others. If so, this property will not be included in the ASTM standard. Instead, it might be included in the series of non-mandatory appendices to the standards that address more specific circumstances. 

A good example of this is cold-weather operability standards. Certain diesel specifications allow for diesel to operate in warm climates without a problem. However if those same specifications are applied to diesel used in a cold climate, it may cause trouble for operators. A good fuel distributor will provide diesel that is appropriate for the region, but since the specifications don’t require this practice, it is up to the vigilant consumer to demand diesel that is fit for application (using ASTM annexes as a guide).

ASTM and its members work diligently to improve the experience of diesel users. Current projects include the development of a broader definition of “contamination” that includes more than just hard particulate, and improvement of test methods for cold-weather operability and for injector deposit formation and treatment. 

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 diesel fuel chemistry itself.

Diesel 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. Diesel fuel that meets current fuel industry specifications is often unfit for use in the high-pressure common rail diesel engines that resulted from the new emissions standards. 

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 diesel quality characteristics in relation to the needs of modern fuel systems, including minimum cleanliness levels per ISO 4406. Equipment run on "dirty" diesel 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 diesel 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, diesel as delivered almost always meets fuel industry specifications, but only rarely is clean enough for trouble-free use in modern equipment.