Fuel filterability

Fuel systems can cause many problems, and fuel nozzles are especially susceptible to trouble. A gaseous fuel system consists of fuel filters, regulators, and gauges. Fuel is injected at a pressure of about 60 psi (4 Bar) above the compressor discharge pressure for which a gas compression system is needed. Knockout drums or centrifuges are recommended, and should be implemented to ensure no liquid carry-overs in the gaseous system. 

Cleanliness is a measure of the water and sediment and the partieulate eontent. Water and sediment are found primarily in liquid fuels, while partieulates are found in gaseous fuels. Partieulates and sediments eause elogging of fuel filters. Water leads to oxidation in the fuel system and poor eombustion. A fuel ean be eleaned by filtration. 

Table 12-4 is a summary of liquid fuel speeifieations set by manufaeturers for effieient maehine operations. The water and sediment limit is set at 1% by maximum volume to prevent fouling of the fuel system and obstruetion of the fuel filters. Viseosity is limited to 20 eentistokes at the fuel nozzles to prevent elogging of the fuel lines. Also, it is advisable that the pour point be 20 °F (11 °C) below the minimum ambient temperature. Failure to meet this speeifieation ean be eorreeted by heating the fuel lines. Carbon residue should be less than 1% by weight based on 100% of the sample. The hydrogen eontent is related to the smoking tendeney of a fuel. Lower... 

The pour point is an indication of the lowest temperature at which a fuel oil can be stored and still be capable of flowing under gravitational forces. Fuels with higher pour points are permissible where the piping has been heated. Water and sediment in the fuel lead to fouling of the fuel system and obstruction in fuel filters. 

Table (a) shows experimental data [24] for the initial charge density exiting a fuel filter Qq plus the charge density Q remaining 30 s downstream. At low conductivity the charge decays much faster than predicted by an exponential relaxation law [Eq. (2-3.7)] and instead follows a hyperbolic relaxation law [24] given by... 

This condition is of concern only when equipment operates in subzero ambient temperatures. Since diesel fuel extracted from crude oil contains a quantity of paraffin wax, at some low ambient temperatures this paraffin will precipitate and create wax crystals in the fuel. This can result in plugging of the fuel filters, resulting in a hard or no-start condition. Any moisture in the fuel can also form ice ciystals. Cloud point temperatures for various grades of diesel and other fuels should be at least 12°C (21.6°F) below the ambient temperature. In cases where cloud point becomes a problem, a fuel water separator and a heater are employed. 

All diesel fuels tend to contain trace water, expressed in parts per million (ppm). With the veiy high fuel injection pressures now used in electronically controlled diesel engine, fuel-filter/water separators are widely used, since water allowed to circulate freely through the injection system can result in seizure of components and erosion of injector orifice holes, and in extreme cases the high compressibility factor of water can blow the tip off of the fuel injector. 

Polyarylsulfones offer materials with good thermal-oxidative stability, solvent resistance, creep resistance, and good hydrolytic stability. Their low flammability and smoke evolution encourage their use in aircraft and transportation applications. They hold up to repeated steam sterilization cycles and are used in a wide variety of medical applications such as life support parts, autoclavable tray systems, and surgical and laboratory equipment. Blow-molded products include suction bottles, surgical hollow shapes, and tissue culture bottles. PPS has a number of automotive uses including as an injection-molded fuel line coimector and as part of the fuel filter system. 

To resolve the problem, personnel from the gasoline additive supplier worked with the customer to collect service station gasoline samples, customer fuel filters, and samples of gasoline from the retailer s local service stations and from the fuel distribition terminal. All of these samples were thoroughly analyzed. Also, January fuel delivery records were closely audited. 

Iron (rust), magnesium, silica, sodium and calcium were identified on customer fuel filters. 

Gasoline additive was not observed on customer fuel filters. 

Metal containments found on customer fuel filters are similar to those found in service station tank water. 

The fuel filters were then partially blocked by rust and corrosion products carried by the water. Below-freezing temperatures possibly initiated the formation of ice within fuel filters and in fuel lines containing water. The combination of ice and corrosion products blocked fuel flow through vehicle fuel lines and filters. Gasoline flow to the engine was halted and engine shutdown followed. 

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. 

Failure of sensitive filtration tests such as ASTM D-2276, Particulate Contamination in Aviation Fuel by Line Sampling, can be due to caustic neutralized corrosion inhibitor salts. Sodium or calcium salts of dimer-trimer fatty acid corrosion inhibitors are gel-like in character. Filtration of jet fuel containing gelled corrosion inhibitor will be impeded due to plugging of fuel filter media by the inhibitor gel. This slowdown of filtration can result in failure of jet fuel to pass this critical performance test. 

Also, the gel-like emulsion formed can be pumped with the fuel volume and accumulate on fuel filters. The result of this accumulation is usually filter plugging, pump sticking, and possible engine shutdown. 

This wax can accumulate on fuel filter media and can lead to plugging of small orifices and lines. This plugging temperature can be measured and is commonly referred to as the filter plugging temperature. Testing methods utilized to predict the filter plugging temperature and the low-temperature flow properties of distillate fuel are listed in TABLE 4-5. 

Diesel fuel pumped from storage tanks, through pipelines, and within internal combustion engines passes through various types of fuel filters. When cold fuel containing wax passes through these filters, the wax can be trapped on the filter media. Accumulated wax can slow the flow of fuel enough to shut down further fuel flow. 

Accumulation on fuel filter media to slow and eventually halt fuel flow... 

The different chemical compounds used as wax crystal modifiers do not all provide ideal performance under every circumstance. Various tests have been designed to help differentiate the performance of one wax crystal modifier over another. For example, a modifier may be quite effective at controlling wax crystal formation to enable a fuel to flow by gravity from a storage tank to a pump. However, once past the pump, the modifier may not effectively reduce the wax crystal size and shape to allow cold fuel to flow effectively through a line filter. The result is wax accumulation on the filter media, plugging of the fuel filter, and halting of fuel flow. A different wax crystal modifier or a product with wax dispersant properties may be required to permit effective fuel filtration. 

Problems caused by wax which has already formed in fuel cannot be reversed unless the fuel is warmed to temperatures above the fuel cloud point. Warming will dissolve wax crystals. Upon further cooling, the modifier will then function and inhibit wax-related problems such as wax deposition onto interior surfaces of cold fuel lines and plugging of fuel filters. 

The cloud point test is one of the most commonly used methods to evaluate the low-temperature characteristics of distillate fuel. The cloud point temperature identifies the point when wax begins to form into crystals large enough to become visible in the fuel. At this temperature, wax can settle from fuel, deposit onto fuel filters, and interfere with the flow of fuel through small tubes and pipes. During cold weather months, distillate fuels with lower cloud point values are refined and blended to minimize the low-temperature problems associated with wax. 

Additional low-temperature fuel filterability information is often required to confirm whether fuel will pass through fuel filters in cold environments. Two tests are commonly used to determine this performance value, ASTM D-4539 and IP 309. The method ASTM D-4539 is termed the Low-Temperature How Test (LIFT) and is used to determine the low-temperature filterability of diesel fuel. 

The CFPP was developed in 1965-66 to predict the low-temperature filterability performance of diesel fuels. This method is commonly used throughout the world to quickly determine low-temperature fuel filterability characteristics. In more recent... 

Passing value 20 mL of fuel filtered in 60 seconds 5 mL of fuel filtered in 60 seconds... 

After filtration through a 30-mesh filter at a nitrogen pressure of 15 psig, the amount of fuel filtered is recorded in 10-second intervals. After 60 seconds, the test is discontinued and the total amount of fuel filtered is recorded. Test results are rated as follows ... 

PROBLEM DIFFICULTY IN PUMPING DIESEL FUEL AT LOW TEMPERATURES / FUEL FILTER PLUGGING... 

Measuring the cloud point, pour point, CFPP, or LTFT will help to confirm whether pumpability problems are due to wax. Fuels at their cloud point, CFPP, or LTFT temperatures will eventually plug fuel filters when pumped. When a fuel is very near its pour point, pumping will be quite difficult. 

Water contamination in diesel fuel is common. When diesel fuel cools, ice crystals may form in the fuel well before the fuel reaches its pour point. These ice crystals will settle to the bottom of fuel tanks and may result in fuel filter plugging and pumpability problems. 

Although there is no worldwide standard under which fuel filters are manufactured, most contain a hydrophobic paper element with a porosity ranging from approximately 5 to 15 microns with an average porosity of about 8 microns. The porosity of filters used in distributor-type fuel pumps is smaller and generally ranges from 4 to 5 microns. 

Fuel filter throughput is reduced with increasing fuel viscosity. 

The high content of water and emulsifier in this fuel creates some differences in handling and application compared to conventional diesel fuel. The surfactant quality of the emulsification additive in the fuel can remove existing deposits from the internal surfaces of fuel handling and storage systems. Problems with fuel discoloration and fuel filter plugging may follow. Compared with conventional diesel, fuel economy ratings per tank of fuel will drop because the overall carbon content per unit volume of fuel is lower. This is due to carbon displacement by water. 

Mata, Zoila. 1994. (Internal report) Tank bottom and fuel filter analysis. 94/877. Sugar Land, Tex. Nalco/Exxon Energy Chemicals, L.P. 

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