Deposits 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. 

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. 

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. 

Carbon number measurement serves as an indication of the tendency of fuel to form deposits in a system where the available air supply is limited. This value is less meaningful for home heating units burning distillate fuel. 

When water pH is <6, iron corrosion and the formation of corrosion products such as colloidal ferric hydroxide can result. Colloidal ferric hydroxide, however, is difficult to detect and difficult to remove through filtration. Fuel containing these particles appears bright and clear. Only about 1 micron in diameter, colloidal ferric hydroxide compounds can pass through fuel filters and deposit onto fuel system components. Further system corrosion can follow. 

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. 

Deposition and fouling can occur in the fuel system and in the hot section of the turbine. Deposition rates depend on the amounts of certain compounds contained in the fuel. Some compounds that cause deposits can be removed by fuel treating. 

Carbon residue, pour point, and viseosity are important properties in relation to deposition and fouling. Carbon residue is found by burning a fuel sample and weighing the amount of earbon left. The earbon residue property shows the tendeney of a fuel to deposit earbon on the fuel nozzles and eombustion liner. Pour point is the lowest temperature at whieh a fuel ean be poured by gravitational aetion. Viseosity is related to the pressure loss in pipe flow. Both pour point and viseosity measure the tendeney of a fuel to foul the fuel system. Sometimes, heating of the fuel system and piping is neeessary to assure a proper flow. 

The carbon residue is a measure of the carbon compounds left in a fuel after the volatile components have vaporized. Two different carbon residue tests are used, one for light distillates, and one for heavier fuels. For the light fuels, 90% of the fuel is vaporized, and the carbon residue is found in the remaining 10%. For heavier fuels, since the carbon residue is large, 100% of the sample can be used. These tests give a rough approximation of the tendency to form carbon deposits in the combustion system. The metallic compounds present in the ash are related to the corrosion properties of the fuel. 

Fuel system fouling is related to the amount of water and sediment in the fuel. A by-product of fuel washing is the desludging of the fuel. Washing rids the fuel of those undesirable constituents that cause clogging, deposition, and corrosion in the fuel system. The last part of treatment is filtration just prior to entering the turbine. Washed fuel should have less than. 025% bottom sediment and water. 

A fuel treatment system will effeetively eliminate eorrosion as a major problem, but the ash in the fuel plus the added magnesium does eause deposits in the turbine. Intermittent operation of 100 hours or less offers no problem, sinee the eharaeter of the deposit is sueh that most of it sheds upon refiring, and no speeial eleaning is required. However, the deposit does not reaeh a steady-state value with eontinuous operation and gradually plugs the first-stage nozzle area at a rate of between 5% and 12% per 100 hours. Thus, at present, residual oil use is limited to applieations where eontinuous operation of more than 1,000 hours is not required. 

Engine additives were required in all gasoline to prevent deposits in engines and fuel supply systems. 

Analysis of nitroaromatics found by treating diesel fuel with NO2 (column A) compared to nitroaromatics found in extracts of filters of exhaust from a diesel engine (column B) or in extracts of diesel soot deposited in a dilution tunnel of an animal exposure system (13). 

The problem of alkali deposition in biomass-fueled turbine systems can be a major problem with direct combustion... 

The PtRu bimetallic system has been the catalyst of choice for MeOH oxidation in acid elecfrolyfes since its discovery by workers at Shell in the early 1960s2 In practice, PtRu lowers the overpotential for MeOH oxidation by >200 mV compared to pure Pt. The MeOH oxidation reaction on Pt and PtRu is probably the most studied reaction in fuel cell electrocatalysis due to its ease of sfudy in liquid electrolytes and the many possible mechanistic pathways. In recent years, the deposition of PtRu particles onto novel carbon supports and the novel PtRu particle preparation routes have proved popular as a means to demonstrate superiority over conventional PtRu catalysts. 

Jet fuels are blended primarily from straight-run distillate components and contain virtually no olefins. Aromatics in jet fuel are also limited. High aromatic content can cause smoke to form during combustion and can lead to carbon deposition in engines. A total aromatic content >30% can cause deterioration of aircraft fuel system elastomers and lead to fuel leakage. 

This value helps predict the deposit-forming tendency of fuel. Deposits in oil burner systems can form hot spots on surfaces which can lead to stress, distortion, and even cracking of system components. 

Catalyst fines, metals, rust, sand, and other material can be contained in residual fuel. These compounds arise from the crude oil, processing catalysts, water contamination, transportation, and storage of the fuel. If the total ash content is >0.20 wt%, deposits can form in burner systems and corrosion in high-temperature burners can occur. 

Most of the deposits formed in fuel and oil systems are rich in oxygen content. Oxygen in these deposits is not naturally occurring in the petroleum product, but typically comes from atmospheric oxygen. 

Fuels such as diesel fuel and heating oil are sometimes stored in large tanks for extended periods of time. At temperatures below the cloud point of the fuel, wax can form and fall from solution. Accumulated wax within fuel systems can deposit onto component parts and settle into areas of low turbulence. Problems such as filter plugging and flow limitations can be due to accumulated wax. 

Other elements such as boron and silicon can be found in fuel and oil system deposits. They can originate from the following sources ... 

Paraffins function poorly as a solvent for some organic compounds. This fact can have various consequences. For example, gums, deposits, and fuel degradation products will not be dissolved or held in solution by high-paraffin-content fuels. As a result, gums and degradation products will fall from solution and settle onto fuel system parts such as storage tank bottoms and fuel system lines. The KB value for selected petroleum products is provided in TABLE 5-4. 

Also, additives which are used to enhance the performance of fuels and oils are usually highly polar organic compounds. Their solubility in paraffinic systems can be quite low unless formulated with paraffinic side chains or appropriate cosolvents. Additive dropout and deposition can occur unless paraffin solubility is maintained. 

High-carbon-residue values for marine diesel fuel, marine gas oil, and heavy marine bunker fuel can contribute significantly to exhaust system deposit problems. Deposit formation on exhaust ports and exhaust turbines have been linked directly to high carbon residue in fuel. 

Some distillate fuel stabilizers possess dispersant-like properties. By acting as a dispersant, any sludge or deposit-like component which may form can be suspended in the fuel and maintained as a soluble compound. As a result, deposits do not accumulate onto fuel system components, but remain dispersed in the fuel. However, due to this dispersing action, the fuel may appear dark in color. 

Corrosion inhibitors used to protect fuel system components such as storage tanks, pipelines, and combustion system equipment are typically dissolved in the fuel and delivered to the metal surface with the fuel. The inhibitor is deposited onto exposed metal surfaces as the fuel passes through the fuel distribution and handling system. 

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