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Two fluorocarbon lubricity additives were tested in the Minex heat exchanger to determine their effect upon the thermal stability of a highly refined jet fuel. The jet fuel without additives and the fuel with a standard metal deactivator additive were tested first to provide a base line for testing with the lubricity additives. The results show that the additive-free jet fuel would not degrade the heat transfer efficiency in a Minex heat exchanger at 680 F. The addition of the metal deactivator N, N' - disalicylidene - 1, 2 - propane diamine, had no effect upon the thermal stability of the fuel but the fluorocarbon lubricity additives would degrade thermal stability. Additive A changed thermal stability from greater than 680 F to 600 F, and Additive B decreased the break point to 650 F. Although there was an adverse effect upon thermal stability, the jet fuel with the fluorocarbon additive is still usable for modern high speed aircraft.
The effects of fuel additives and naturally occurring fuel components and impurities on the lubricity of JP-5 were determined. The ball-on-cylinder machine was used as a lubricity tester. Naturally occurring hydrocarbon compounds had very little effect on the lubricity of JP-5. Corrosion inhibitors, organic acids and nitrogen containing compounds were found to improve lubricity while sulfur compounds, non-acid oxygen containing compounds and anti-oxidants had little or no effect on lubricity. The compounds that were effective lubricity improvers did so by keeping dissolved oxygen from reaching the metal surface of the ball-on-cylinder machine and reacting there.
The two hydrocarbon structures exhibiting the most promise as candidate high temperature fuels are the alkyl-substituted monocyclics and the alkyl substituted condensed bicyclics. For specialized fuels, the isoparaffin structure best suits the requirements for a weight-limited fuel application whereas for an extreme high density fuel the condensed tricyclic structure exhibits the best compromise of properties. The preliminary results of a vapor fuels study indicate that the basic condensed bicyclic structure once again offers the most promise for an advanced vapor fuel. Research has indicated that a vapor fuel will extend the flight speed of advanced systems beyond mach 5. For greater speeds or for desirable additional cooling below Mach 5, a type of endothermic fuel will be required. The primary contribution of the endothermic fuels program is that the feasibility of conducting this type of reaction under conditions to be encountered in advanced air-breathing systems is established and that the reaction products will perform satisfactorily in the combustor.
NAVAIRSYSCOM has evaluated the individual benefits of 3 different thermal stability improving additives (TSIAs) in jet fuel using 2 separate, small-scale test devices - one laminar flow and the other turbulent. Both systems pump fuel at constant flowrate and use stainless steel tubes that are heated to maintain the bulk fuel at a constant, elevated test temperature. The laminar device has an inside diameter of 0.1 in. (0.262 cm) and an approximate Reynolds No. of 200, whereas the turbulent has an inside diameter of 0.01 in. (0.0254 cm) and a Reynolds No. of 13,000. The results have shown that all 3 TSIAs, when test at their maximum dose levels, reduce the amount of thermal deposits (measured via carbon burnoff) in both flow regimes for 3 different base fuels tested. Both units rank the level of thermal stability in the same order for the 3 baseline fuels tested. In addition, both devices show that Betz 8Q462. is the most effective additive of the 3 tested, with MDA demonstrating almost similar performance in controlling deposit formation. Furthermore, Betz 8Q406 was not as effective as the 2 other additives, but a change in its formulation by the addition of 2 mg/l MDA (to produce 8Q462) greatly improved its performance in both test devices, but most notably in the laminar unit. However, one exception had occurred when MDA was added to one of the test fuels (Tank 20122), which caused an increase in deposition compared to the neat fuel when tested in the turbulent unit. Overall, the combination of the accelerated test conditions in the turbulent unit of higher bulk fuel temperate, higher flowrate, turbulent flow (i.e., flatter temperature profile across the tub ID), and shorter residence time make this a more severe test when compared to the laminar device.
Various aspects of the thermal stability problem associated with the use of broadened-specification and nonpetroleum-derived turbine fuels are addressed. The state of the art is reviewed and the status of the research being conducted at various laboratories is presented. Discussions among representatives from universities, refineries, engine and airframe manufacturers, airlines, the Government, and others are presented along with conclusions and both broad and specific recommendations for future stability research and development. It is concluded that significant additional effort is required to cope with the fuel stability problems which will be associated with the potentially poorer quality fuels of the future such as broadened specification petroleum fuels or fuels produced from synthetic sources.
A literature survey was made on the lubricity of low-viscosity fluids and pump wear. Viscosity, volatility and purity data were obtained on commercial fuels and pure hydrocarbons. Four-ball tests showed the effect of load and speed on initial, steady-rate, and equilibrium wear regimes. Ball-and-cylinder tests uncovered advantages for certain commercial antiwear additives; in four-ball tests additives gave some improvement in wear at lower loads, but no improvement in scuff load. Two nitrogen compounds showed some antiwear effect but no anti-scuff activity. On the other hand, some of the sulfur compounds reduced scuffing in the four-ball test. Ryder gear tests confirmed the good performance of the antiwear additives in reducing gear-tooth scuffing. In the Vickers vane pump test, a commercial JP-5 fuel was clearly better than the reference Bayol 35 in spite of a lower viscosity. The addition of 1% bright stock to Bayol 35 gave somewhat better performance. Lubricity additives at 0.1% were considerably more effective.
A program to evaluate the effects of additives on JP-8 fuel lubricity at high temperatures is described. Operating temperatures to 163 C were examined, with a subsequent program goal of 315 C. Baseline data were obtained using the Ball-on-Cylinder Lubricity Evaluator (BOCLE). High-temperature data were obtained with an apparatus known as the Cameron-Plint High Frequency Reciprocating Machine. The most significant effect of variables observed was a consequence of a change in wear specimen material from 52100 steel to M-50 steel--the latter considered to be representative of advanced fuel system designs. Use of M-50 wear coupons resulted in considerably reduced wear levels with only slight separation between neat or additized fuels. M-50 specimen roughness was a major influence in wear level. At finalized test conditions, a dibasic acid ester, di(2-ethylhexyl) adipate, was found to give the lowest wear values when used as an additive in clay-treated JP-8, although distinctions between the various additized fuels were not large.
Investigation of the feasibility of using endothermic reactions to augment the latent and sensible heat of fuels for cooling engines operating under a high mach number regime is continuing. Studies in the literature continue to maintain the desirability and feasibility of producing vehicles with hypersonic flight speeds and suggest some areas of advantage of hydrocarbons. Laboratory studies on the dehydrogenation over Pt/Al2O3 of a number of mixtures of naphthenes have been made including methyl-Decalin and dicyclohexyl as well as the pure components, with additional studies on Decalin. About 220 dehydrogenation catalysts have been prepared using a variety of metals and supports. Propane and an advanced jet fuel were tested as possible heat sink fuels in our fuel system simulation test reactor under thermal cracking conditions. Our packed bed reactor program included herein, has been rewritten and simplified resulting in a considerable saving in both human and computer time. The thermal stability of MCH, Decalin and a naphthenic jet fuel were all critically, but uniquely, dependent on O2 concentration in the region below about 10 ppm. The ignition delay behavior of both ethane and ethylene was found to be considerably different from other hydrocarbons in the shock tube, the ignition delay reaching a minimum in the region of E/R = 0.5 with two different temperature coefficients which are dependent upon total reactives concentration.