Diesel fuel deposits

The reaction mechanism for these products is not clearly understood, but the introduction of organo-metallic compounds (barium or iron salts in colloidal suspension) has been shown to have a beneficiai action on the combustion of diesel fuel in engines and reduce smoke. However, these products cause deposits to form because they are used in relatively large proportions (on the order 0.6 to 0.8 weight %) to be effective. 

Detergent Additives. Diesel engine deposits ate most troublesome in the fuel dehvery system, ie, the fuel pump and both fuel side and combustion side of the injectors. Small clearances and high pressures mean that even small amounts of deposits have the potential to cause maldistribution and poor atomization in the combustion chamber. The same types of additives used in gasoline ate used in diesel fuel. Low molecular weight amines can also provide some corrosion inhibition as well as some color stabilization. Whereas detergents have been shown to be effective in certain tests, the benefit in widespread use is not fully agreed upon (77). 

Fuels and Lubricants. Rare-earth neodecanoates have been claimed as additives for diesel fuels that reduce the precipitation of particles and gum (108). Neodecanoic acid has also been used in the preparation of ashless detergent additives for fuels and lubricants that reduce engine deposits in internal combustion engines (109). 

The usual feed is a virgin gas oil that is, the part of crude oil boiling between about 60 °F. and 1050°F. Sometimes material below 600°F will be included into the cat feed but more often, it is put into diesel fuel or home heating oil. The heavy material above 1050°F is not normally used as cat feed because it often contains metallic compounds that contaminate the catalyst. Even if metals are not present, there are sometimes tarry materials that end up on the catalyst. This deposit increases the load on the regenerator, and, hence, the 1050 °F+ material is less desirable than lower boiling feeds. 

Diesel fuel may contain ash-forming materials in the form of abrasive solids or soluble metallic soaps. These solids cause wear of injection equipment, pistons, piston rings, and liners as well as increasing engine deposits. Ash content is expressed as a percentage of the weight of the original test sample of the fuel when burned to completion m an open container. 

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). 

In its commercial plants Sasol has to date used only iron based catalysts. (The preparation and properties of these catalysts have been reviewed elsewhere (2).) Not only is iron by far the cheapest of the metals (see Table I) but iron catalysts also produce large amounts of low molecular weight olefins which are important in the Sasol process. (These olefins are oligomerized to either gasoline or diesel fuel and this allows the production of these two liquid fuels to match the market requirement.) A major drawback of iron is that at high temperatures carbon deposition occurs which results in catalyst disintegration. 

Although hydroprocessing will remove most of the naturally occurring antioxidants contained in fuel, other less stable, more reactive components will also be reduced. As a whole, ultra-low sulfur diesel fuel will be much less prone to color degradation and deposit formation than earlier-era diesel fuels. 

Detergents added to gasoline and diesel fuel which help to control the formation and buildup of deposits within automobile and truck engines are highly polar oiganic compounds such as succinimides and polyethers. Water can have a strong affinity for many of these detergents. 

Degradation of diesel fuel color and accumulation of insoluble deposits... 

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. 

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. 

The addition of detergents and deposit control additives to fuels is a common practice today. Gasoline and diesel fuel may often contain significant levels of compounds formulated to prevent deposit formation on and within fuel intake system components. 

Detergents used in diesel fuel help to control deposit formation on fuel injector nozzles and act to prevent corrosion of the nozzle orifices. Diesel fuel detergents also aid in preventing deposit and gum formation on high-pressure fuel injector parts. 

High-pressure diesel fuel injection systems contain expensive and sophisticated components. The high-pressure pump and injector are the key components to ensuring proper fuel management within the diesel engine. Clearances and tolerances between moving parts of the fuel pump are quite fine. Even a small amount of deposit, contamination, or corrosion can significantly alter the efficient performance of the fuel injection system. 

Diesel fuel detergents are usually organic amines, imides, succinimides, polyalkyl amines, or other polyamine-type compounds. These compounds function by dispersing and solubilizing deposit-forming compounds into the fuel. Some detergents can also remove existing deposits from fuel injection system parts. 

Deposit control additives or detergents are added to diesel fuel to help prevent the formation and accumulation of deposits on fuel injection system parts. Detergents provide the following performance function in the diesel engine ... 

A common method used to evaluate the stability of diesel fuel is to heat the fuel at a temperature of 300°F (148.9°C) for 90 minutes. After that time period, the fuel is analyzed for color change and deposit formation. 

Fuel refiners will sometimes blend low levels of coker gas oil or vacuum gas oil into diesel fuel. These high-boiling-point fractions may contain high-molecular-weight polycyclic aromatic compounds which can eventually precipitate to form fuel-insoluble sludge and deposits. 

High-pressure diesel fuel pumps are not tolerant of dirt, debris, and organic deposits and can be seriously damaged by fuel contaminants. The barrel and plunger clearance is within a 1 to 2 micron tolerance. This tolerance is necessary to ensure that fuel injection pressures are maintained with minimal leakage past the plunger shaft. For this reason, thorough and complete filtration of fuel is required before the fuel reaches the injection pump. 

Very poor biodiesel and biodiesel blends do not shed water as effectively as conventional diesel fuel fuel haze, gelling, and low-temperature handling problems can develop if biodiesel is contaminated with water in storage and transport. Poor double bonds present in the methyl ester compounds are active sites for oxidation and condensation reactions peroxide values can increase fuel darkening and deposit formation in storage systems can occur the addition of oxidation inhibitors to biodiesel helps improve storage stability. 

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. 

The minimum fuel/air ratio for ignition is analogous to the lower limit of flammability. It is important in Diesel fuel combustion because partial oxidation will occur in local regions in which the concentration of fuel is less than the minimum or lower limit, but these regions will not ignite or inflame. Consequently, products of partial oxidation giving rise to odor, and possibly deposits, will appear in the exhaust. This is discussed in a subsequent section. 

CDDs are released into the air in emissions from municipal solid waste and industrial incinerators. Exhaust from vehicles powered with leaded and unleaded gasoline and diesel fuel also release CDDs to the air. Other sources of CDDs in air include emissions from oil- or coal-fired power plants, burning of chlorinated compounds such as PCBs, and cigarette smoke. CDDs formed during combustion processes are associated with small particles in the air, such as ash. The larger particles will be deposited close to the emission source, while very small particles may be... 

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