In an effort to reduce particulate and nitrogen- oxide emissions of diesel engines, the EPA has a set of emission rules currently in place. These rules are referred to as “Tier 4” rules. In response, diesel engine manufacturers have designed equipment that complies with those rules, known as “Tier 4 engines.” It seems like everything should work out just fine, until you realize that the Tier 4 engines have very tight tolerances concerning fuel cleanliness.
Figure 1
There are many ways to report the particulate contamination of petroleum products, with the most common being a method called ISO 4406. Commonly, laser-light extinction is used to measure the size of individual particles, and they are put into three different categories: 1. Those that are greater than 4μ, 2. greater than 6μ and 3. greater than 14μ (where μ represents a “micron” and is equal to one-millionth of a meter). Each category is inclusive, meaning that if a particle is greater than 6μ, then it is also greater than 4μ and counts in both bins. Particles greater than 14μ count in all three bins. The results are reported as X4/ X6/X14, where the bins represent the number of particles larger than 4μ, 6μ and 14μ, respectively. The chart in Figure 1 is used to calculate the results.
In this example, a result of 16/14/12 would indicate there are between 320 and 640 particles sized 4 microns or larger per milliliter of sample.
The problem: Recent studies from the Southwest Research Institute and Donaldson Filtration Solutions have indicated that the most damaging particles in a Tier 4 engine are between 2 and 3 microns in size. That is smaller than the smallest particle that the ISO 4406 method begins to count. To put this in perspective, if there are 300 particles between 4 and 6 microns, you can expect about 9,500 particles less than 4 microns per milliliter of sample.
To address the problem, OEMs have recommended that final diesel fuel filters have a first-pass efficiency of 99.9 percent in the 2-3 micron range. Tighter filters mean more frequent filter plugging and shorter service intervals. You can’t really blame the filters for plugging too frequently. They are just doing their job. The key to prolonging fuel filter life is in the prevention of particle ingression in the first place. I recently had an opportunity to look at a used diesel filter under a microscope, seen in Figure 2. From there, I was able to see that the largest quantity of particles seemed to be dirt. Regardless of whether a tank is for storage, transportation or fueling equipment, every time 150 gallons is removed, it is displaced with 20 cubic feet of air, and air contains dirt. Vent filters can help reduce air and should be installed and maintained on every tank.
Figure 2
Moreover, this happens any time fuel is pumped out of a tank, all along the supply chain. Other particles such as rust and microbiological growth can form inside the tanks themselves. This type of contamination usually happens in the presence of water. For this reason, it is important to keep your Tier 4 diesel fuel clean and dry from the refinery all the way to your jobsite, and filter for particulates every time the fuel is transferred. Cleaner fuel means longer service intervals and less downtime.
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