Fuel Thermal Stability Research Articles

Effects of Oxygen and Additives on the Thermal Stability of Jet Fuels

A previously developed flowing single-pass heat-exchanger test rig (Phoenix rig) has been used to evaluate the effectiveness of various additives and the kinetic mechanism of both deposit formation and oxygen consumption. The Phoenix rig has been modified to include not just a heated single tube, but also a cooling test section and both hot and cold filters. The effects of flow conditions, antioxidants, and metal deactivator additives on the location and amount of the deposit are discussed. In general, antioxidants were effective at reducing the deposits on the hot test section, but almost invariably caused increased plugging of cool downstream filters. Downstream plugging of cool filters also increased with decreased temperatures in the heated section or with increased flow. Tests with both oxygen-saturated and oxygen-depleted fuels have shown that the solubility of oxygen is linearly related to the fraction of oxygen in a sparge gas, and that the amount of deposit is linearly related to the total quantity of dissolved oxygen passed. Finally, in contrast to initial modeling efforts, the consumption of oxygen is shown to be significantly more complex than a simple bimolecular, pseudo-first-order in oxygen, process. It is found to be much closer to pseudo-zero-order in the early stages, decaying to pseudo-first-order when the oxygen nears depletion.

Effect of Copper, MDA, and Accelerated Aging on Jet Fuel Thermal Stability As Measured by the Gravimetric JFTOT

Thermally unstable jet fuels pose operational problems. To adequately identify such fuels, factors that realistically impact on thermal stability were examined. Evaluation was based on a quantitative method of measuring thermal stability, viz., NRL's recently developed gravimetric JFTOT. This method gives a quantitative measurement of both the strip deposit and filterables formed. The pertinent factors examined included the individual and interactive effects of soluble copper, MDA (metal deactivator), and aging. Aging was accelerated to simulate field conditions of approximately 6 months storage at ambient temperature and pressure. The results indicate that the individual and interactive effects of copper, MDA, and accelerated aging appear to be fuel dependent. On the basis of the results, the three test fuels examined (one JP-8 and two JP-5s) were categorized as exhibiting very good, typical, and poor thermal stabilities, respectively. For both the very good and poor thermal stability fuels, copper in conjunction with aging did not significantly increase the total thermal deposits of the neat fuels. In contrast, for the typical thermal stability fuel, the combined effect of copper and accelerated aging did increase deposits. Furthermore, the addition of MDA prior to aging of the copper-doped, typical stability fuel significantly counteracted the adverse effect of copper and aging. No such beneficial effect of MDA was observed for the poor stability fuel. These findings focus attention on the compositional differences among fuels and the need to elucidate these differences (physical and chemical) for a better understanding and prediction of the fuels' performances

Studies of Jet Fuel Thermal Stability and Oxidation Using a Quartz Crystal Microbalance and Pressure Measurements

The thermal stability of aircraft jet fuels was measured in real time with a quartz crystal microbalance (QCM) at 140 C. Qualitative data on the oxidation of these fuels was also obtained by monitoring the system pressure during thermal stressing. The system was operated at relatively low oxygen availability (1 atm air) which more closely approximates the oxygen availability of flowing fuel tests and real fuel systems than previous work. The high sensitivity and good reproducibility of the QCM permitted deposition measurements under unaccelerated conditions (i.e., relatively low temperature and oxygen availability). Correlation of oxidation and deposition behavior provided insight into the deposition and oxidation processes.

Studies of Jet Fuel Thermal Stability in a Flowing System

A flowing, single-pass heat exchanger test rig, with a fuel capacity of 189 liters, has been developed to evaluate jet fuel thermal stability. This “Phoenix Rig” is capable of supplying jet fuel to a 2.15 mm i.d. tube at a pressure up to 3.45 MPa, fuel temperature up to 900 K, and a fuel-tube Reynolds number in the range 300–11,000. Using this test rig, fuel thermal stability (carbon deposition rate), dissolved oxygen consumption, and methane production were measured for three baseline jet fuels and three fuels blended with additives. Such measurement were performed under oxygen-saturation or oxygen-starved conditions. Tests with all of the blended fuel samples showed a noticeable improvement in fuel thermal stability. Both block temperature and test duration increased the total carbon deposits in a nonlinear fashion. Interestingly, those fuels that need a higher threshold temperature to force the consumption of oxygen exhibited greater carbon deposits than those that consume oxygen at a lower temperature. These observations suggested a complicated relationship between the formation of carbon deposits and the temperature-driven consumption of oxygen. A simple analysis, based on a bimolecular reaction rate, correctly accounted for the shape of the oxygen consumption curve for various fuels. This analysis yielded estimates of global bulk parameters of oxygen consumption. The test rig yielded quantitative results, which will be very useful in evaluating fuels additives, understanding the chemistry of deposit formation, and eventually developing a global chemistry model.

Closure to “Discussion of ‘Temperature Effects on Fuel Thermal Stability’” (1992, J. Eng. Gas Turbines Power, 114, p. 358)

Closure to “Discussion of ‘Temperature Effects on Fuel Thermal Stability’” (1992, J. Eng. Gas Turbines Power, 114, p. 358)

Temperature Effects on Fuel Thermal Stability

The thermal stability characteristics of four kerosine-type fuels are examined using a heated-tube apparatus that allows independent control of fuel pressure, fuel temperature, tube-wall temperature, and fuel flow rate. It is a closed loop system, and fuel flows through the heated tube for periods ranging from 6 to 22 h. The deposition rates of carbon on the tube walls are measured by weighing the tube before and after each test. The results obtained show that tube-wall and fuel temperatures both have a marked influence on deposition rates, the impact of fuel temperature being stronger than that of wall temperature. It is also found that deposition rates increase continuously with increases in tube-wall temperature. This finding contradicts the results of previous studies, which had led to the conclusion that deposition rates increase with increase in wall temperature up to a certain value, beyond which any further increase in wall temperature causes the deposition rate to decline.

A Computational Fluid Dynamics and Chemistry Model for Jet Fuel Thermal Stability

This paper describes the development of a model for predicting the thermal decomposition rates of aviation fuels. A thermal deposition model was incorporated into FLANELS-2D, an existing computational fluid dynamics (CFD) code that solves the Reynolds-averaged conservation equations of mass, momentum, and energy. The decomposition chemistry is modeled by three global Arrhenius expressions in which the fuel decomposition was assumed to be due to an autoxidation reaction with dissolved oxygen. The deposition process was modeled by assuming that all deposit-forming species transported to the wall adhered and formed a deposit. Calibration of the model required the determination of the following parameters for a given fuel: (1) the pre-exponential constant and activation energy for the wall reaction, (2) the pre-exponential constant and activation energy for the bulk autoxidation reaction, and (3) the pre-exponential constant and activation energy for the precursor decomposition reaction. Values for these parameters were estimated using experimental data from published heated-tube experiments. Results show that the FLANELS-2D code performed well in estimating the fuel temperatures and that the three-equation chemistry model performed reasonably well in accounting for both the rate of deposition and the amount of dissolved oxygen present in the fuel at the end of the heated tube.

Fuel thermal stability effects on spray characteristics

The propensity of a heated hydrocarbon fuel toward solids deposition within a fuel injector is investigated experimentally. Fuel is arranged to flow through the injector at constant temperature, pressure, and flow rate and the pressure drop across the nozzle is monitored to provide an indication of the amount of deposition. After deposits have formed, the nozzle is removed from the test rig and its spray performance is compared with its performance before deposition. The spray characteristics measured include mean drop size, drop-size distribution, and radial and circumferential fuel distribution. It is found that small amounts of deposition can produce severe distortion of the fuel spray pattern. More extensive deposition restores spray uniformity, but the nozzle flow rate is seriously curtailed.

The Thermal Stability of Al-USiAl Dispersion Fuels and Al-U Alloys

he stability of Al-USiAl dispersion fuels and Al-U alloys was examined at temperatures between 200 and 400°C for times up to 93 days.The Al-U alloys, which contained 21 to 37 wt% uranium, did not show any dimensional or metallurgical changes after 93 days at 400°C.After being heated at 200°C, the Al-USiAl fuel showed no dimensional or metallurgical changes. However, between 250 and 400°C, the USiAl particles reacted with the aluminum matrix to form UAl3 and UAl4. The amount of reaction increased with temperature and time. The aluminum diffuses into the USiAl particles along grain boundaries to form the new Al-U compounds.Although the Al-USiAl fuel showed thermal instability at 250°C and above, the in-reactor behavior under normal operation is expected to be satisfactory since fuel temperatures will generally be <200°C.

Thermal stability of fresh and long-stored jet propulsion fuels

1. TS-1 fuel-coming fresh from the plant is in accordance with the requirements of State Standard 10227-62 for thermal stability. A considerable portion of commercial T-1 fuel does not satisfy the State Standard. The main quantity of samples of this fuel has a thermal stability of not over 20 mg/100 ml. 2. The thermal stability as defined by State Standard 9144-59 does not deteriorate during the transport of T-1 and TS-1 to the storage sites. 3. When TS-1 fuel is stored up to six years its thermal stability changes almost insignificantly (by less than 1 mg/100 ml). The thermal stability of T-1 fuel stored for three to six years deteriorates by 2–4 mg/100 ml on the average. 4. A new standard for the thermal stability of fuels after long storage was established on the basis of these investigations: the permissible increment of sediment is 4 mg/100 ml in the case of T-1 and 2 mg/100 ml in the case of TS-1.

Effect of fractional composition and residual content of aromatic hydrocarbons on the stability of fuels

1. The effect of residual content of aromatic hydrocarbons in fuels with isoparaffinic-naphthenic base on their thermal stability during the oxidation process were studied. 2. During the determination of thermal stability of fuels in the presence of bronze, aromatic hydrocarbons did not exhibit any inhibiting effect. 3. It was shown that change in the aromatic hydrocarbon content from 0 to 9.5% exerted no effect on the process of sediment formation in the fuels. The amount of insoluble residues in all cases was less than 6.0 mg/100 ml. The amount of potential resins formed in the presence of bronze is almost twice as high. 4. It was shown that change in the end boiling point of the fuel from 260 to 330°C does not affect the sediment formation process. Raising the end boiling point temperature of the fuel to 360°C results in noticeable increase in the formation of sediment. However, in all cases, with change in the end boiling point of the fuels from 260 to 360°, the content of insoluble residue in the fuels did not exceed 6.0 mg/100 ml. The content of potential and actual resins increases with increase in the end boiling point of fuels. Sharp increase in the formation of potential resins from 72 to 231 mg/100 ml in the presence of bronze occurred when the end boiling point of the fuels was raised from 330 to 360°C.

Thermal Stability of Endothermic Heat-Sink Fuels

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal Stability of Endothermic Heat-Sink FuelsA. C. Nixon and H. T. HendersonCite this: Ind. Eng. Chem. Prod. Res. Dev. 1966, 5, 1, 87–92Publication Date (Print):March 1, 1966Publication History Published online1 May 2002Published inissue 1 March 1966https://doi.org/10.1021/i360017a018RIGHTS & PERMISSIONSArticle Views192Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts