Fuel stability

Combined Combustion Improver, Sludge Dispersant, and Fuel Stabilizer... 

Both -NH2 and -COOH groups are hydrophilic esterifying the -COOH group under acidic conditions would render surfactant properties to the final derivative (Figure 3). If both the -COOH and -NH2 functionalities of the amino acid are derivatized, making it a secondary amino compound, then it can be used as fuel stabilizer, although the exact mechanism of -NH- as free radical stabilizer is still uncertain. 

Some procedures for detection and determination of the damage caused by autoxidation are aimed at the determination of rather indefinite substances for example, the ASTM D-4625-92 standard test for fuel stability on storage consists of tracking the amount of insoluble gums formed by oxidation at a slightly elevated temperature . 

A variety of non-hydrocarbon species is found in crude oil. These compounds are found in all molecular weight ranges of crude oil components, but seem to concentrate in the heavier distillate and residual oil fractions. The effect of these materials on processing equipment, refining catalysts, and finished product quality can be dramatic. Corrosion, catalyst poisoning, and fuel stability problems can all be due to the effect of these nonhydrocarbon species. 

This value is a measure of the acidity or basicity of fuel. The presence of acidic compounds can indicate a fuel stability or oxidative degradation problem. 

Fuel stability is an indication of the sediment- and gum-forming tendency of fuel. Gums and sediment can cause filter plugging and combustion chamber deposits and result in sticking of pumping and injection system components. 

Compounds classified as distillate fuel stabilizers are often mixtures of various compounds having different performance enhancing capabilities. These mixtures are frequently added as a single package to a distillate fuel. Stabilizer packages can possess any combination or all of the following components ... 

Traditional hindered phenol and phenylenediamine free-radical scavenger type antioxidants do not usually provide the stability performance desired in distillate fuel. Stabilizer formulations containing components which provide a wider range of performance are often required. Some of the components commonly used in distillate fuel stabilizers are described as follows ... 

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-inhibiting properties of fuel stabilizers can be a secondary effect of the dispersing action of a fuel stabilizer. By functioning as a dispersant, sludge and water are held in suspension and prevented from initiating metal surface corrosion. Also, some stabilizer dispersants can form a thin film on the metal surfaces of fuel system components. This film-forming property enables the stabilizer-dispersant to function in corrosion control. A typical oil-soluble dispersant compound is shown in FIGURE 6-3. 

The structural design of a fuel stabilizer molecule can enable some compounds to function in metal ion chelation. Most stabilizers have nitrogen atoms within the structure of the compound. The electron pair on nitrogen can function in metal chelation if the nitrogen atoms are oriented in the appropriate conformation. 

The antioxidant and acid neutralization properties of most fuel stabilizer formulations help to prevent the initial formation of most acids. Compounds such as tertiary-alkyl primary amines, as shown by the example in FIGURE 6-5, are quite effective distillate fuel additives. These oil-soluble amines can be formulated into stabilizer formulations at relatively low concentrations and can provide a significant boost in overall performance of a fuel stabilizer. 

A diesel fuel stabilizer containing a blend of amines, polyamines, and alkyl ammonium alkyl phosphate as specified under MIL-S-53021 is recommended for federal diesel fuel oil. This stabilizer is to be used at a treat rate of 25 lb/1,000 barrels. It is not intended for use in routine applications, but for situations where increased stability protection is required. Typical applications include fueled equipment undergoing long-term storage in a warehouse or depot, prepositioned equipment or equipment maintained in a high-temperature environment. 

Also, some distillate fuel stabilizers contain metal chelating agents. The purpose of this is to help prevent the metal-catalyzed oxidation of fuel components. However, if a distillate fuel containing a chelating agent is stored in a tank or transferred through lines which are rusted, the stabilizer may act to chelate iron. As a result of this, the fuel containing the stabilizer appears dark. 

Fuel degradation by oxidation is a common cause of fuel stability problems. Gasoline, jet fuel, diesel fuel, and heating oil are all susceptible to oxidative degradation. The following methods can be used to help determine the oxidative stability of fuels ... 

USE Separately or together, these different distillate fuel stability methods can be used to help identify the following ... 

Some distillate fuel stabilizers possess the ability to perform as dispersants. By dispersing higher-molecular-weight compounds into fuel, their eventual deposition as fuel-insoluble compounds can be minimized. 

Potential fuel stability problems especially if sulfur exists in thiophene structure. 

Fuel acid number or neutralization number is a measure of the acidity or basicity of fuel. The presence of acidic compounds can indicate a fuel stability or oxidative degradation problem. Acidic organic compounds can react with other fuel components to initiate the formation of higher-molecular-weight, fuel-insoluble... 

Polymeric amines in deposit Indicates the presence of dispersant compounds gasoline detergents and IVD control additives fuel stabilizers... 

The addition of fuel stabilizers can help inhibit distillate fuel color degradation... 

Stavinoha, L. L., and C. P. Henry, Editors. 1981. Distillate Fuel Stability and Cleanliness. Philadelphia American Society for Testing and Materials. 

Jet Fuels (Grades JP-3, JP-4, JP-S JP-6). Specifications for early aircraft jet fuels were based primarily on manufg considerations, since it was believed that aircraft could burn almost anything of the nature of kerosene fuels (Ref 1). Later improvements in aircraft, particularly in high-speed jets, made it necessary to pay more attention to fuel characteristics and less attn to ease of manuf. The most important of these fuel characteristics is fuel stability at high temps. Other problems associated with jet aviation fuels, both for military civilian use, are minor compared to stability at high temps. Such problems include availability, handling physical property specifications... 

Although petroleum refiners are not unfamiliar with questions of thermal stability of petroleum products, jet fuel stability requirements (stable in the range 400—500°F) presented a new set of problems. One of the first things to be done was to define limits of acceptable stability. Such limits naturally would depend upon individual engine design and the environment to which the fuel is exposed. Fuels meeting one set of conditions could conceivably fail to meet another set. The solution devise some sort of laboratory test that would correlate with actual engine performance... 

More specifically, typical operating conditions are a flow rate of 4 pounds per hour, a fuel temperature from the heat exchanger of 400°F, a filter temperature of 500°F, and a fuel pressure of 150 pounds per square inch gage. Fuel stability is then determined by operating until a pressure drop of 25 inches of mercury is obtained across the filter or until 300 minutes have elapsed. No heater tube appearance requirements have been designated... 

Use of conventional treating processes was the logical starting point for improving thermal stability since refiners already have these facilities. One of the first treating processes considered was sulfur dioxide treatment, although current capacity would possibly be insufficient in an all-out war. In tests carried out at one petroleum laboratory, a JP-5 fuel stability was increased twofold Untreated fuel had a stability rating of 57 minutes. After sulfur dioxide extraction, the time was increased to 119 minutes. However, for all intent and purpose, this is not considered to offer any benefits since the test defines acceptable stability as 300 minutes... 

This is a process that is at present being integrated in the current models of spent fuel stability in repository conditions, but some work is still necessary in order to ascertain the reactions and mechanisms that control the reductive passivation of the U02 surface and the inhibition of the radiolytic production of oxidants. 

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