Understanding The Problem

Because many people assume they’re buying quality fuel that meets the required specifications, diesel fuel cleanliness is seldom questioned.

But higher fuel system operating pressures, lower system tolerances, tighter filtration and the EPA’s ultra low sulfur requirements have pushed fuel cleanliness into the maintenance spotlight.

Engine manufacturers are realizing that diesel fuel cleanliness can have great impact on overall engine performance. In fact, many are now recommending that diesel fuel that does not meet an ISO Cleanliness Code of 18/16/13 should be filtered before introduction to the fuel system.

Engine fuel systems made in the 1960’s operated at around 400 – 500bar, had tolerances of around 50µm (microns) and filtration systems with a micron rating of around 25µm. The fuel systems of the 1990’s ran at pressures of around 1300 – 1500bar, tolerances of 35µm and filtration micron ratings of 15µm. But today, operating pressures have increased to as much as 1800bar, tolerances of 2µm and filtration micron ratings of only about 3µm. This means that with control valve operating clearances of only 1-3 µm, today’s injectors are a lot less tolerant to particulates than they once were – particulates that are now moving through the system at over four times the pressure.

Fuel system pumps and injectors are most susceptible to contamination from water, micro-organisms, wax, asphaltines, dirt, sediment and rust.

Water, not only contaminates the fuel, it also provides a breeding ground for micro-organisms that feed on the fuel’s hydrocarbons.

The formation of wax crystals is the result of exposure to low temperatures while asphaltines are the result of exposure to high temperatures.

Dirt, sediment and rust are typical of poor maintenance practices.

Fuel Tank Cleaning
Multi-Stage Filtration
Advanced Fuel Chemistry

It explains the importance of fuel cleanliness to the successful operation of Cummins® Engines.
Modern fuel systems have been developed to reduce emissions and fuel consumption, and improve engine performance. These high pressure systems operate at pressures approaching 2100 bar [30,500 psi] and with component match clearances typically from 2 to 5 microns for injectors. At these pressures, very small, hard particles are potential sources of fuel system malfunction.
Excessive contamination of diesel fuel can cause premature clogging of diesel fuel filters and/or premature wear of critical fuel injection system parts. Depending on the size and nature of the particles, this can lead to:

Reduced component life
Component malfunction
Fuel system and/or engine failure
Increased exhaust emissions.

Determining fuel cleanliness requires measuring both the size and number of particles per size class in the fuel, i.e. the particle size distribution. The International Standards Organization (ISO) has developed a protocol for expressing the level of contamination by coding the size distribution called ISO 4406.

ISO 4406 cleanliness codes are expressed as a series of three numbers (e.g. 18/16/13), which correspond respectively to the number of particles greater than 4, 6, and 14 microns. For example, the numbers in the ISO 4406 rating of 18/16/13 translate to:
18 – Up to 2,500 particles larger than 4μm (per mL of fuel)
16 – Up to 640 particles larger than 6μm (per mL of fuel)
13 – Up to 80 particles larger than 14μm (per mL of fuel)

Engine builders and fuel injection equipment manufacturers have found that the particles greater than 4 microns and greater than 6 microns are particularly critical to the durability of the fuel injection system. They also recognize that the fuel systems must be robust to hard particles smaller than 4 microns that are difficult to filter out, even with the finest filtration. To maximize the efficiency and effectiveness of filtration, Cummins Inc. has adopted the recommendation of the World Wide Fuel Charter that fuel supplied to engines meet the ISO 4406 code of 18/16/13 maximum for respectively 4, 6, and 14 micron particle sizes.
Cummins Inc. recommends that if the fuel does not meet the ISO cleanliness code of 18/16/13 in bulk storage, additional filtration be applied before the fuel is delivered to the equipment’s fuel tank.