The distribution of particle sizes within diesel fuel is vastly different from other hydrocarbons seen in the industry. Lubrication oils, engine oils, and hydraulic oils typically have a wide distribution of particle sizes within a given sample. A typical sample of diesel fuel, however, comprises of approximately 80-97% of particles at or below 4μm in size. With such a high percentage of particles in the fuel, at the same size that causes the greatest damage in a HPCR injection system, filter companies have responded by reducing the filtration rating on engine fuel filters to below 4μm. This transition to a lower micron rated filter has resulted in additional pressure on the life of the filter element. Correspondingly, most fuel filters have not increased in physical size to combat the additional load.
In many industries, engine fuel filters are typically changed on a time based planned maintenance (PM) strategy measured in hours worked. The OEM of each engine, or asset, typically advises the PM event timing, along with additional information being provided by industry specialists. Most engine manufacturers in most locations around the world typically schedule engine fuel filter changes at 500 hours. As filter micron ratings have reduced to target contaminants below 4μm, we are now starting to see some engine manufacturers advising their customers to once again reduce the fuel filter PM intervals from their current 500 hour intervals to 250 hours on new equipment fitted with HPCR injection systems. This new requirement is starting to place additional pressure on existing maintenance strategies as additional PM intervals must also be refined or considered to ensure engines or assets are not being taken out of service just for a fuel filter change.
Reducing the PM interval of an engine fuel filter from 500 to 250 hours is a direct response by filter manufacturers to ensure that the engine fuel filter will not completely block during its time in service due to reduced micron rating. It is, however, a false economy and not required should the asset fuel tank be delivered with a fuel cleanliness that does not overload the engine fuel filter in the first place.
Engine fuel filters do not employ a bypass valve, which would enable fuel to bypass the filter in the event that it becomes blocked with contaminants. Rather, the engine management system constantly monitors engine fuel filter differential pressure and will regulate the fuel flow to the engine based on the condition of the filter. If the engine management system indicates that a fuel filter has a high differential pressure, the fuel flow is automatically reduced causing a loss of power, and possible machine speed.
The situation again circles back to the specification of fuel cleanliness levels being delivered to the machine at refueling. While the filter micron rating has reduced to a level where the majority of contaminants in the fuel are being targeted, what has not occurred is a reduction in the specified fuel cleanliness level being filled into the asset fuel tank; it remains at ISO18/16/13. The answer employed by the OEM is to simply change out the engine fuel filter sooner. What should change is the cleanliness of the fuel entering the fuel tank in the first place.
Filters are not intelligent devices; they remove contaminants within the fuel as they are presented to the filter media. Reducing or maintaining the level of contaminants being presented to the engine filter each hour will increase its service life; this is an undeniable fact. It is, therefore, difficult to understand why engine OEM’s are not advising their customers of this.