In fuel systems

Compatibility and Corrosion. Gas turbine fuels must be compatible with the elastomeric materials and metals used in fuel systems. Elastomers are used for O-rings, seals, and hoses as well as pump parts and tank coatings. Polymers tend to swell and to improve their sealing abiUty when in contact with aromatics, but degree of swell is a function of both elastomer-type and aromatic molecular weight. Rubbers can also be attacked by peroxides that form in fuels that are not properly inhibited (see Elastomers, synthetic Rubber, natural). 

Oxygen pitting corrosion, in fuel systems Oxygen removal 686... 

The cloud point measurement is used to predict the temperature at which wax in fuel may begin causing operating problems such as filter plugging and blockage of lines in fuel systems. 

It is unique because of its powerful hydrogen bonding character and its distinct polarity. However, in fuel systems, these characteristics of water make it a source of a variety of problems. Corrosion of metal fuel system components, emulsification with fuel performance additives, and ice formation in fuel lines are some of the problems directly related to the presence of water in fuel. 

Described below are some of the more common problems caused by the presence of water in fuel systems ... 

The carryover of caustic into a finished fuel blend usually has minimal effect alone on the corrosion of ferrous metals. However, in fuel systems containing a conventional tall oil dimer-trimer fatty acid or partially esterifled corrosion inhibitor, caustic can react with and negate the effect of the corrosion inhibitor. As a calcium or sodium salt, these inhibitors will no longer function effectively as an oil-soluble, fuel corrosion inhibitor. 

In fuel systems containing water, certain microorganisms can survive. Typical species are the bacterial anaerobe Disulfovibrio and the fungal species Cladosporium resinae. These microorganisms are called hydrocarbon utilizing microbes and often referred to as HUM or HUM-bugs. They can initiate corrosion in fuel systems. 

The amount of carbon present in fuel components can be correlated with a tendency to form deposits in fuel systems. Although the use of various detergent and dispersant additives helps to minimize deposit formation, the carbon residue value is still quite useful. 

Mechanical components used in fuel systems such as pumps, valves, and bearings may contain copper or copper-containing alloys. As a fuel system component, copper is especially undesirable because it acts as a catalyst in promoting the oxidation of fuel paraffins to oxygen-rich, gumlike deposits. The following reaction sequence represents how copper ions can catalyze the oxidation and degradation of hydrocarbons. 

Copper can be present in fuel systems in the form of heating coils, cooling coils, brass fittings, or bronze parts. Copper is quite resistant to corrosion by water but can be attacked by ammonia and sulfur compounds. Finished fuels usually do not contain ammonia unless the ammonia somehow carries over from refining process operations. Sulfur compounds such as hydrogen sulfide and possibly elemental sulfur are more frequently the cause of copper corrosion problems in fuel systems. 

Although not common, fuel additives can cause problems in fuel systems. The problems often are due to the following ... 

Some stabilizer formulations can function as dispersants to prevent the settling and accumulation of deposits in fuel systems. If fuel containing a stabilizer with dispersant properties is stored or transported in a system having existing deposits, the dispersant would act to break loose and suspend the deposits into the fuel. The resulting fuel would appear dark in color. 

Sludge formation in fuel system filter plugging... 

Identify possible causes of ferrous and nonferrous metal corrosion in fuel systems. 

The primary considerations for the use of plastic materials in fuel and oil systems include resistance to swelling, softening, or embrittlement. Also important are flexibility and stability under a wide range of temperatures. Information on some common elastomers and plastics used in fuel systems is provided in TABLE 9-8. 

A typical fuel injection system is composed of the following components fuel tank, injection pump, mechanical or electronic governor, timing device, fuel supply pump, high-pressure fuel injection lines, and fuel injectors. The high-pressure fuel injection pump is the core of the fuel injection system. The in-line pump and distributor pump are the most common in fuel systems. 

Elastomer is a term used to describe a wide range of soft materials used in fuel systems. One of the best examples is the common O-ring—usually made from a soft, rubber-like material— that depends on its ability to deform under pressure to perform properly. The most common job for elastomers in fuel systems is to prevent leaks from fittings and joints. 

The metals recommended for use with ethanol include carbon steel, stainless steel, and bronze [3.10]. Like methanol, metals such as magnesium, zinc castings, brass, and copper are not recommended. Aluminum can be used if the ethanol is very pure, otherwise it should be nickel-plated or suitably protected from corrosion by another means. The metals compatible with ethanol represent a much wider range than those for methanol and represent most of the metals currently used in fuel systems, so few changes would be anticipated when using ethanol. 

Britton, L.G., and Hughes, J.F., Principles for Minimizing Electrostatic Hazards in Fuel Systems, Southampton University Applied Electrostatics Group, Progress Report No. 3 to Ministry of Defence Procurement Executive, Contract NCS 361/75737, June 30, 1980. 

The reactive species that initiate free-radical oxidation are present in trace amounts. Extensive studies (11) of the autoxidation mechanism have clearly established that the most reactive materials are thiols and disulfides, heterocyclic nitrogen compounds, diolefins, furans, and certain aromatic-olefin compounds. Because free-radical formation is accelerated by metal ions of copper, cobalt, and even iron (12), the presence of metals further complicates the control of oxidation. It is difficult to avoid some metals, particularly iron, in fuel systems. 

Is absorbed by cork carburetor, thus rendering them valueless. Loosens gummy or other materials deposited in fuel system and thereby clogs screens in the fuel lines. 

Various approaches have been suggested to reduce the number of fires at petrol filling stations caused by static electricity. One suggestion is metal door handles. Conducting additives are used to provide static dissipation in fuel systems, but there are difficulties in achieving adequate mechanical properties in polyethylene fuel tanks when carbon black is used as a filler. Doubts have also been raised in some quarters about whether some plastic fuel tanks will be able to meet the requirements for PZEVs , or partial zero emissions vehicles, required by California s new emission standards. Inergy Automotive recommends capless filler systems with locking mechanisms. Carbon nanotubes are likely to find a role in antistatic protection. 

Tests to determine microbial contamination in fuel systems... 

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