The first signs of poor fuel delivery could be a loss of power, or in extreme cases an engine failing to start. Early signs of fuel contamination will be increasingly regular replacement of filters, or more seriously, damage to expensive fuel injection components. However, while new filters may tackle the symptom at the time, they do little to solve the problem at its source.
Contaminated fuel concerns
Common contaminants in today’s diesel fuels include water, waxes, hard particles, debris and microorganisms. Water occurs in diesel storage mainly through condensation. This is particularly prevalent with more recent common-rail diesel engines, where hot fuel is returned from the engine, heating the tank and causing condensation as it cools.
Hard particles and debris will usually have been added to the fuel tank unintentionally during refilling. Any opening to the tank, whether that is the filling port, faulty caps or gaskets, ventilation points, or areas of the tank that have been damaged, provides an easy entry for contaminants into the fuel.
Waxes tend to come from the fuel itself, from additives that are used to lubricate the injection system during operation. A fuel’s cloud point is the temperature where wax begins to drop out of fuel, creating a translucent appearance. The wax forms crystals – 50 to 200 microns in size – that can quickly plug the fuel filter.
Microbial organisms, also known as the ‘diesel bug’, are harder to track down. Diesel fuel will always have some level of microorganisms present within the tank. These are sometimes incorrectly called algae, but algae require light to exist, which is seldom found in a closed tank. Microbial bacteria or fungi live in the water that is commonly found in diesel storage and they feed off the hydrocarbons in the fuel.
A report by filter manufacturer Donaldson, said that microbial colonies can proliferate in any fuel tank. When there is free water in the tank, the microbes have everything that they need to grow, though warm weather and the presence of biofuels will accelerate this process. Donaldson claims that a microbial colony can consume up to 1% of your fuel investment, while destroying the rest.
Changes to fuel composition
According to fuel testing specialist Conidia Bioscience, there have been two major changes to the composition of diesel fuel over recent years, both of which could increase the risk of diesel fuel contamination. Increasing levels of biodiesel and the reduction of sulphur in fuels, have both been adopted primarily to help the environment, yet either one could promote an increase in contamination.
Biodiesels, known as FAME (Fatty Acids Methyl Esters) can increase the growth of microorganisms, as they absorb more water from the atmosphere, adding to the risk of contamination. Almost all red diesel sold today has a biodiesel blend, of up to 7-20% FAME.
The adoption of ultra-low sulphur diesels could also be a factor in the increasing risk of diesel contamination, though the scientific community has differing opinions on this. Regardless of that, low sulphur diesel is more expensive to produce, making diesel maintenance even more important.
Recognising the diesel bug problem
In the early stages, a small build-up of microorganisms may be invisible to the naked eye. However, Conidia Bioscience says that diesel contamination can appear as a shiny film layer called biofilm, which builds up as some species of microorganisms live off the by-products of others. Microbial cells stick together and to nearby surfaces, becoming embedded in a slimy extracellular matrix, that is composed of extracellular polymeric substances (EPS).
There may also be a thick, slimy material, called biomass. This can reduce the effectiveness of fuel injection components, or stop the engine completely. One of the most common microorganisms is a fungus called Hormonconis resinae (H.res). This also causes bulky biomass and blockages in fuel systems and filters.
A paper from Dow Chemicals, called Microbial Contamination of Diesel Fuel: Impact, Causes and Prevention, states that as biomass turns over, and as metabolic waste and dead cells accumulate, they settle as sludge on tank bottoms. It is therefore vital that fuel pick-up pipes do not take diesel from the bottom of the fuel tank.
Diesel contamination can also result in the creation of dangerous acids in the fuel. Over time, these can destroy plastic, rubber and even metal components within the fuel system.
Despite the evidence of microbial contamination in diesel fuel and gas turbine engine operations, very few operators actually treat their fuel with antimicrobials. This is partly due to the subtle nature of microbial contamination, which often goes undetected until a catastrophic failure takes place. However, by that time, fuel performance, system integrity, filter life and even engine life can have been degraded significantly.
It is recommended that at least every six months, operators should test bulk fuel supply tanks for contaminants. This can be carried out in-house or a professional service provider can perform the test. A small amount of water can be removed, but if significant amounts of water or sludge are found, you will need to drain and clean the entire tank. To help monitor your supply tank, keep a preventive maintenance log, that includes maintenance history, filter changes and particle counts.
It is essential that companies make sure any fuel entering a bulk storage tank passes through a dispensing filter, to boost the effectiveness of the machine’s fuel filter and help prevent contaminants from entering. Additionally, fuel tank filters should be capped and the tank vent must be filtered. Tank filters typically have a 10-micron-or-fewer fuel filter to help remove moisture as fuel is dispensed through the vent.
Diesel fuel, especially in common-rail systems, can reach high temperatures during the workday. As the machine cools, condensation can form in air gaps. If possible, make sure that every machine is filled with diesel fluid at the end of the day, to help reduce condensation and save on maintenance costs.
If contamination is found, it may be possible to employ fuel polishing in storage tanks. Fuel polishing is a fuel filtration technique that improves and maintains the quality of fuels in storage facilities. It can be carried out on site, by mobile fuel polishing systems.
Ensure that fuel is not picked-up from the bottom of a tank, where sludge and microbial biomass can accumulate. FuelActive’s fuel pickup unit is the most efficient way to prevent water, dirt and other contaminants from entering the fuel injection system. The patented FuelActive fuel pickup helps to preserve operating efficiency and performance, avoiding costly downtime and reducing harmful emissions.