SubscribeMatt Fielder, Hydrocarbon/Aviation Market Manager at Parker Hannifin’s Filter Division Europe, discusses the issue of contamination in jet fuels, and introduces the latest technology available to detect and eliminate the problem, maintaining optimum performance levels and reducing operating costs.
Fuel contamination is a major problem across a diverse range of applications, resulting in escalated maintenance costs and downtime; however, the need to monitor dispersed contamination in aviation fuels is especially critical, with safety a major concern for airlines. As soon as any hydrocarbon fuel leaves the refinery, it is susceptible to contamination, as it flows through pipes, is transferred into bulk storage tanks, shipped as marine cargo and brought into contact with other already contaminated distribution systems.
Although jet fuel does have a better chance of staying free from solid particulate when compared to other types of fuel, as in most cases it is moved in dedicated systems that only transport jet fuel, water contamination remains a problem. Jet fuels and other hydrocarbon fuels are susceptible as they have a marginal solubility for water, and one that is very temperature dependent, potentially resulting in water forming at the bottom of the tank and or pipelines in cold conditions.
Poorly maintained storage and transportation systems that allow water to accumulate will quickly encourage microbiological growths. Depending on the extent and species composition of the infestation, rapid corrosion and erosion of tank coatings and vessel floors and walls can occur to such an extent that in very rare cases a breech may happen. If, as with many pipelines, the system is uncoated, any free water by way of hydrogen embrittlement will very quickly start to attack the steel, producing a never ending supply of solid particulate in the form of rust.
Although filtration systems have been developed and installed in order to remove solids, water and other contaminates, with fuels on average being filtered up to 14 times before being burnt, it is essential that contamination be measured accurately to ensure the safety of the engine systems in which it is being used. Current methods used in the aviation industry to measure contamination have been in place for many years.
The first is the "Clear & Bright" (C&B) test, or the "White Bucket" test, which involves an operator taking a sample of fuel and observing it. If any particles of solid are seen, or, in the case of the C&B test, when holding the sample up to the light the fuel is hazy, it fails the test.
This method is extremely subjective and open to manual error. Furthermore, the human eye is capable of seeing 30-40 microns or larger; under normal circumstances, these relatively large particles will drop out of suspension and even if they are carried along with the flow of fuel, the filtration systems installed are more than capable of catching these particles.
Another method, which is more scientific in its nature, is also flawed to the degree that repeatability and reproducibility are questionable. The Gravimetric test method requires an operator to draw a sample of fuel through a filter cell containing 2 x 0.8mµ membranes; the first is the working membrane which captures the dirt and the second is a control membrane which is used as a datum when measuring the solids loading. This filter cell is then taken to a laboratory where it is dried and the two membranes separated.
Again, there are important limitations with this type of testing. The time taken to analyse the sample can be between 24 and 48 hours, making it impossible to prevent an aircraft taking off if problems are found. Furthermore, manual error is again a problem with this type of testing; results can be misinterpreted if the amount of sample taken is not the correct volume, the sample membranes are not matched weight, or if there is a leaky path within the membrane cell.
The latest generation of Automatic Particle Counters (APCs), such as those developed by the Filter Division Europe of Parker Hannifin, have been designed in response to these problems. Particle counting is based on the principle of light obscuration, otherwise known as light blockage or light extinction; all of these terms relate to an object passing in front of a light source creating a shadow. In the APCs, the shadow of a particle suspended in a fluid passing through a light source is measured by way of a voltage drop across a light sensitive diode.
The signal generated as a result of the shadow is dependent on the size of the particle and the speed at which it passes through the light. There are other types of particle counting but the light obscuration technique is a more common and accurate method and is well regulated through ISO standards and practices.
Particle counting is well suited for use on fuels, specifically the Aviation industry, as it provides accurate results immediately. This enable more frequent, real time testing of fuels to be undertaken, ensuring the safety of aircraft and minimising costs as no laboratory consumables are required. Particle sizes and numbers can be effectively measures, eliminating subjectivity.
The technology is also well governed & regulated by ISO standards (ISO11171). The latest generation of particle counters are building on technology that has already proven time and again that fast, reliable, repeatable and reproducible data, previously only available in the laboratory, is possible on-line. Now for the first time, fuel suppliers from the refineries through distribution hubs, to the final delivery of fuel into the aircraft can be sure that the fuel being delivered is clean and dry.
Please send all sales enquiries to:
Parker Hannifin - Racor Filter Division Europe, Shaw Cross Business
Park, Dewsbury, West Yorkshire,
WF12 7RD. Tel: 01924 487000, filtrationinfo@parker.com.
