Diesel fuel corrosion

Sulfur. Sulfur in diesel fuel should be kept below set limits for both environmental and operational reasons. Operationally, high levels of sulfur can lead to high levels of corrosion and engine wear owing to emissions of SO that can react with condensed water during start-up to form sulfuric acids. From an environmental perspective, sulfur bums to SO2 and SO, the exact spHt being a function of temperature and time in the combustion chamber. 

Corrosion Inhibitors. The corrosion inhibitors used in diesel fuel ate generally similar to those used in gasoline and, like the latter, produce an effect primarily by surface action. If amine additives ate used for detergency, these may provide some corrosion protection as well. 

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). 

VFO works well in gas turbines. In a nine-month test program, the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to study the combustion characteristics of VFO, the erosive and corrosive effects of VFO, and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combustion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion tests showed the VFO to match natural gas in flame patterns, temperature profile, and flame color. The operation of the gas turbine revealed that the gas turbine not only operated well on VFO, but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for the vaporization process. Following the tests, a thorough inspection was made of materials in the combustion module and on the gas turbine, which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO. 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

There has been a recent revival in interest in the use of ethanol-diesel fuel blends (E-diesel) in heavy-duty vehicles as a means to reduce petroleum dependency, increase renewable fuels use, and reduce vehicle emissions [27]. E-diesel blends containing 10-15% ethanol could be prepared via the use of additives. However, several fuel properties that are essential to the proper operation of a diesel engine are affected by the addition of ethanol to diesel fuel - in particular, blend stability, viscosity and lubricity, energy content and cetane number (increasing concentrations of ethanol in diesel lower the cetane number proportionately) [28]. Materials compatibility and corrosiveness are also important factors that need to be considered. 

An extensive review has been conducted to identify potential oxygenates for blending into diesel fuels [55]. Over 70 molecules were identified and tested, taking into account numerous physical properties such as oxygen content, flash point, viscosity, cetane number, corrosivity, toxicity, and miscibility with diesel blends. Five key aspects were considered critical to develop commercially valuable diesel additives ... 

Calcium nitrate is used in explosives, matches and pyrotechnics. Other applications are in the manufacture of incandescent mantle and as an additive to diesel fuel for corrosion inhibition. 

Many new sugar based products present the advantage of being non-toxic and biodegradable. The products resulting from the telomerization of 1 with appropriate nucleophiles such as alcohols, amines, water, or carbon dioxide serve generally as useful intermediates in the synthesis of various natural products and fine chemicals [60-63], as precursors for plasticizer alcohols [56, 64], components of diesel fuels [65], surfactants [11, 66], corrosions inhibitors, and non-volatile herbicides [67]. 

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. 

In recent years, the concern over fuel lubricity has led to the use of a high concentration of corrosion inhibitors to improve diesel fuel lubricity performance. The film formed on the metal surface by fatty acid type corrosion inhibitors improves fuel lubricity. However, the result of this overtreatment may lead to sticking of injection pump parts. 

Although no ASTM ferrous metal corrosion specification exists now for gasoline, diesel fuel, and other fuels, many refiners and marketers have adopted the National Association of Corrosion Engineers (NACE) Corrosion Standard Method TM-01-72-93 as a specification. This method has also been utilized by most product pipeline companies and is an established requirement. The NACE corrosion method is summarized as follows ... 

Manufacturers of diesel engines generally recommend that fuels which contain less than 0.5 percent sulfur be used in order to minimize corrosion problems. A typical diesel fuel has approximately 0.15 percent sulfur though there is a wide variation in different fuels. The use of EDS fuel with a sulfur content of 0.4 percent could present a possible problem with regard to both SO2 and SO3 emissions. 

HSD Stabilizer (Diesel Stabilizer) additive is a multicomponent, oil soluble formulation, specially designed to maintain the total sediments level in diesel fuel within the specified limits, as per ISO 1460 1995. The additive will ensure that the diesel does not deteriorate on storage and the fuel system is protected from deposit formation and corrosion. The additive consists of three major components, namely ... 

Trace elemental analysis can also be used to indicate the level of contamination of middle distillate fuels, e.g. turbine fuels. Metal contamination can cause corrosion and deposition on turbine components at elevated temperatures. Some diesel fuels have specification limits to guard against engine deposits, however they sometimes employ Mo or Ni as a catalyst for the refining process which eventually ends up in the finished products. There are several sources of multi-elemental contamination in naval distillate fuels. Sea water is pumped into the diesel tanks as ballast to immerse ships and submarines. Some oil transport ships have dirty tanks and contamination and corrosive products can also come from piping, linings and heat exchangers. 

The copper strip test methods are used to determine the corrosiveness to copper of gasoline, diesel fuel, lubricating oil, or other hydrocarbons. Most sulfur compounds in petroleum are removed during refining. However, some residual sulfur compounds can have a corroding action on various metals. This effect is dependent on the types of sulfur compounds present. The copper strip corrosion test measures the relative degree of corrosivity of a petroleum product. 

The ash-forming constituents in diesel fuel (ASTM D-2880) are typically so low that they do not adversely affect gas turbine performance, unless such corrosive species as sodium, potassium, lead, or vanadium are present. However, there are recommendations for the storage and handling of these fuels (ASTM D-4418) to minimize potential contamination. 

The copper strip test methods are used to determine the corrosiveness to copper of diesel fuel and are a measure of the relative degree of corrosivity of diesel fuel. Most sulfur compounds in petroleum are removed during refining. However, some residual sulfur compounds can have a corroding action on various metals, and the effect is dependent on the types of sulfur compounds present. One method (ASTM D-130, IP 154) uses a polished copper strip immersed in a given quantity of sample and heated at a temperature for a time period characteristic of the material being tested. At the end of this period the copper strip is removed, washed, and compared with the copper strip corrosion standards (ASTM, 2000). This is a pass/fail test. In another method (ASTM D-849) a polished copper strip is immersed in 200 ml of specimen in a flask with a condenser and placed in boiling water for 30 min. At the end of this period, the copper strip is removed and compared with the ASTM copper strip corrosion standards. This is also a pass/fail test. 

Sulfur can cause wear, resulting from the corrosive nature of its combustion by -products and from an increase in the amount of deposits in the combustion chamber and on the pistons. The sulfur content of a diesel fuel (ASTM D-129, ASTM D-1266, ASTM D-1551, ASTM D-1552, ASTM D-2622, ASTM D-4294, IP 61, IP 63) depends on the origin of the crude oil from which it is made and on the refining methods. Sulfur can be present... 

Water can contribute to filter blocking and cause corrosion of the injection system components. In addition to clogging of the filters, sediment can cause wear and create deposits both in the injection system and in the engine itself. Thus one of the most important characteristics of a diesel fuel, the water and sediment content (ASTM D-1796, IP 75), is the result of handling and storage practices from the time the fuel leaves the refinery until the time it is delivered to the engine injection system. 

For engines using modern diesel fuels, with relatively low levels of sulphur, corrosive cylinder linear wear is not a problem, provided that adequate overbased detergents are present in the lubricant to neutralise the sulphur acids produced by combustion. The rate of formation of reacted films usually follows the Arrhenius Law, as in Equation (3.3) ... 

A basic guideline in a choice of corrosion environments during the test of RubCon specimens was their wide spreading into industrial production. Such environments were water, 30% and 70% solutions of sulfuric acid, 5% solutions of phosphoric and acetic acids, 3% solution of nitric acid, 3% and 30% solutions of hydrochloric acid, 10% solutions of lactic and lemon acids, caustic soda and caustic potash, diesel fuel, acetone, 25% water solution of ammonia, 30% solution of copper vitriol, and a saturated solution of sodium chloride. Chemical resistance of RubCon was estimated on test specimens measuring 4 x 4 x 16 cm [21-23],... 

FIGURE 2.57 Relationship between the RubCon coefficient of chemical resistance and time of corrosion medium exposition (1) water, (2) 30% solution of sulfuric acid, (3) 36% solution of hydrochloric acid, (4) 10% solution of caustic soda, (5) diesel fuel, (6) 5% solution of acetic acids. (Reprinted from Yu. Potapov, Yu. Borisov, V. Chmyhv, and D. Beilin, Research of Polymer Concrete Based on Low Molecular Polybutadiene, Part VIII Chemical Resistance of Polymer Concrete, J. Scientific Israel Technological Advantages 7, nos. 1-2 (2005) 72-78. With permission.)... 

Petroleum-based diesel fuel is commonly treated with a large number of additives to enhance cetane number, improve cold flow and oxidative stability, lessen corrosive-... 

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