Fuel Instability

This will result in an increase in asphaltene agglomerations, polymerization and a dramatic loss of combustion efficiency. The chemistry of diesel fuel instability involves the chemical conversion of precursors to species of higher molecular weight with limited solubility. The conversion process often involves oxidation of the precursors. Fuel solvency plays a role, since the development of insolubles is always a function of both the presence of higher molecular weight species and the fuel s capacity to dissolve them. 

The diesel needs to be stabilized with diesel fuel additives that will inhibit diesel polymerization and inhibit oxidation, darkening and agglomeration of certain components of the diesel. One such effective stabilizing additive is Octel FOA-6. Octel FOA-6 and FOA-3 are amine-based antioxidants that are recommended for antioxidant protection of distillate fuels such as diesel. FOA-3 and FOA-6 together with AO-22, generally give then-best performance when added hot and early to the fuel, usually to a cracked component in the run-down from the cracker. 

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Identify possible causes of fuel instability or low induction time ratings. 

Mushrush, George W. 1992. Fuel instability 2 Organo-sulfur hydroperoxide reactions. Fuel Science and Technology International 10(10) 1563-1600. 

Research is likely to continue with a view to improving methods of sweetening and removing mercaptans from all middle distillates including heater oil. It is doubtful, however, that much effort will be applied specifically toward desulfurization of heater oils except in cases where fuel instability and poor performance of equipment are due to sulfur compounds or where the treatment for stability improvement simultaneously lowers sulfur content. 

The presence of reactive compounds of sulfur (e.g., thiophenes), nitrogen (pyrroles), and oxygen is also considered to contribute to fuel instability (Mushrush and Speight, 1995 Mushrush and Speight, 1998a Mushrush and Speight, 1998b Mushrush et al., 1999). 

Deposits sometimes block fuel nozzles and distort fuel spray patterns, leading to skewed temperature distribution with the possibility of burnout of turbine parts by a "hot streak" exhaust. These deposits are sometimes associated with metal-containing particulates, but in general are another manifestation of fuel instability. 

Introduction. While the solids-removal scheme discus.sed in Section G-1 will limit the amount of solids circulating through the reactor sj. s-tem, soluble elements will build up in the fuel solution. Nickel and manganese from the corrosion of. stainless. steel and fission-produced cesium will not precipitate from fuel solution under reactor conditions until concentrations have been reached which would result in fuel instability and loss of uranium by coprecipitation. Loss of neutrons to these poisons would seriously decrease the probability of the reactor producing more... 

The tendency to separate is expressed most often by the cloud point, the temperature at which the fuei-alcohol mixture loses its clarity, the first symptom of insolubility. Figure 5.17 gives an example of how the cloud-point temperature changes with the water content for different mixtures of gasoline and methanol. It appears that for a total water content of 500 ppm, that which can be easily observed considering the hydroscopic character of methanol, instability arrives when the temperature approaches 0°C. This situation is unacceptable and is the reason that incorporating methanol in a fuel implies that it be accompanied by a cosolvent. One of the most effective in this domain is tertiary butyl alcohol, TBA. Thus a mixture of 3% methanol and 2% TBA has been used for several years in Germany without noticeable incident. 

Combustion instability only used to be a problem with eonventional eombustors at very low engine powers. The phenomenon was ealled rumble. It was assoeiated with the fuel-lean zones of a eombustor, where the eonditions for burning are less attraetive. The eomplex 3D-flow strueture that exists in a eombustor will always have some zones that are suseeptible to the oseillatory burning. In a eonventional eombustor, the heat release from these oseillating zones was only a signifieant pereentage of the total eombustor heat release at low power eonditions. 

R.D. Gould, Combustion Instability of Solid Propellants Effect of Oxidizer Particle Size, Oxidizer/Fuel Ratio and Addition of Titanium Dioxide to Plastic Pro pell ants , Rept No RPE-TR-68/1, Westcott (Engl)... 

F.E.C. Culick. Combustion instabilities in liquid-fueled propulsion systems, an overview. AGARD Conference Proceedings Combustion Instabilities in Liquid Fuelled Propulsion Systems, 450, pp. 1.1-1.73. NATO, 1988. 

Fhosphoric acid does not have all the properties of an ideal fuel cell electrolyte. Because it is chemically stable, relatively nonvolatile at temperatures above 200 C, and rejects carbon dioxide, it is useful in electric utility fuel cell power plants that use fuel cell waste heat to raise steam for reforming natural gas and liquid fuels. Although phosphoric acid is the only common acid combining the above properties, it does exhibit a deleterious effect on air electrode kinetics when compared with other electrolytes ( ) including such materials as sulfuric and perchloric acids, whose chemical instability at T > 120 C render them unsuitable for utility fuel cell use. In the second part of this paper, we will review progress towards the development of new acid electrolytes for fuel cells. 

Ferreira PJ, La O GJ, Shao-Hom Y, Morgan D, Makharia R, Kocha S, Gasteiger HA. 2005. Instability of Pt/C electrocatalysts in proton exchange membrane fuel cells—A mechanistic investigation. J Electrochem Soc 152 A2256-A2271. 

A remaining crucial technological milestone to pass for an implanted device remains the stability of the biocatalytic fuel cell, which should be expressed in months or years rather than days or weeks. Recent reports on the use of BOD biocatalytic electrodes in serum have, for example, highlighted instabilities associated with the presence of 02, urate or metal ions [99, 100], and enzyme deactivation in its oxidized state [101]. Strategies to be considered include the use of new biocatalysts with improved thermal properties, or stability towards interferences and inhibitors, the use of nanostructured electrode surfaces and chemical coupling of films to such surfaces, to improve film stability, and the design of redox mediator libraries tailored towards both mediation and immobilization. 

MCFC Molten carbonate 650 48-56 High efficiency, internal fuel processing, high-grade waste heat Electrolyte instability, short operating life, C02 recycling Power production, cogeneration... 

Recently, Razumovskid441 studied the shape of drops, and satellite droplets formed by forced capillary breakup of a liquid jet. On the basis of an instability analysis, Teng et al.[442] derived a simple equation for the prediction of droplet size from the breakup of cylindrical liquid jets at low-velocities. The equation correlates droplet size to a modified Ohnesorge number, and is applicable to both liquid-in-liquid, and liquid-in-gas jets of Newtonian or non-Newtonian fluids. Yamane et al.[439] measured Sauter mean diameter, and air-entrainment characteristics of non-evaporating unsteady dense sprays by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on the Sauter mean diameter and air entrainment were investigated parametrically. An empirical equation for the Sauter mean diameter was proposed based on a dimensionless analysis of the experimental results. It was indicated that the Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It was also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory. 

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