How Clean Is Your Fuel?

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, usually due to condensation, 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.

These particulates will quickly clog fuel filters, erode injectors and cause valves to stick and damage or clog injector spray nozzles causing irregular spray patterns that can lead to over-fueling, inefficient combustion and piston crown wear. Performing an ISO Particle Count can extend fuel filter life and maximize injector performance by identifying both the size and concentration of contaminant particles present. See Table 1.

Table 1: Reference Chart for Establishing ISO Cleanliness Codes

A small amount of fuel is passed through an optical laser counter. Any particles are counted and reported by the number of particles present in each of eight micron ranges, typically up to 100 microns. An ISO Cleanliness Code is then assigned based on the number of particles present at the 4, 6, and 14 micron levels.

ISO Particle Count Data for a #2 Ultra-Low Sulfur Diesel Fuel
Source: POLARIS Laboratories Statistical Analysis*

*This analysis is based on test results for 162 #2 ultra-low diesel fuel samples processed by POLARIS Laboratories.

The above median ISO Cleanliness Code of 18/15/10 illustrates that 50% of the samples in this analysis are at or below 18/15/10. That means that about 50% of the samples tested do not meet the OEM ISO Cleanliness Code recommendation of 18/16/13. By these numbers, half of the fuel you will purchase should be pre-filtered. And the only way to know for sure, is to have it tested.

So, how clean is your fuel?

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