Jet fuel stability

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... 

In aircraft jet fuels, for example, especially those for aircraft of the supersonic type, the chief problem so far encountered has been thermal stability prior to combustion. The fuel must be used as a cooling agent, and the resultant exposure to heat accelerates the formation of gum and sediment. These cause plugging of filters and fuel nozzles, and lacquering of heat-exchanger surfaces. Research to date has indicated that some additives are effective in improving jet-fuel stability (52), especially if the fuel has first been rigorously refined, but these additives are not combustion improvers in the sense discussed in this paper. 

Jet fuel stabilizer 1-Decene United States 3,034,876 1962 Socony Mobil ... 

Fuel passing through certain hot zones of an aircraft can attain high temperatures moreover it is used to cool lubricants, hydraulic fluids, or air conditioning. It is therefore necessary to control the thermal stability of jet fuels, more particularly during supersonic flight where friction heat increases temperatures in the fuel tanks. 

The most common technique for estimating thermal stability is called the Jet Fuel Thermal Oxidation Test (JFTOT). It shows the tendency of the fuel to form deposits on a metallic surface brought to high temperature. The sample passes under a pressure of 34.5 bar through a heated aluminum tube (260°C for Jet Al). After two and one-half hours, the pressure drop across a 17-micron filter placed at the outlet of the heater is measured (ASTM D 3241). 

ET Denisov, GI Kovalev. Oxidation and Stabilization of Jet Fuels. Moscow Khimiya, 1983 [in Russian],... 

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 ... 

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... 

The need for thermal stability of jet fuels is based on the following facts. In supersonic flight, the aircraft is subjected to high temperatures. This heat must be removed. Most convenient solution, in many types of jet aircraft, would be to use the fuel as a heat sink for cooling vital aircraft components, such as engine oil... 

Another possible solution to the problem of high temperature stability is the use of additives. Not exactly a stranger to petroleum people (as evidenced by use in gasoline and lubricants) they generally fall into two classes metallic and non-metallic. The former, for the most part are metal salts of sulfonates or naphthenates, whereas the latter are either amines or amine derivatives (later other organics may prove more effective) Use of additives in jet fuels, however, must of necessity be approached with caution. As surface active materials, many have a variety of uses and properties. Hence, they must not introduce new problems such as foaming at high altitudes, emulsification, or interference with low temperature flow. These could easily be severe limitations, but additives are under serious consideration thruout the industry... 

Studies have been made thruout the refining industry in an effort to utilize selected stocks for the production of jet fuels. Basically, this would amount to determining the stability of many stocks, for example, straight run gasolines, distillates, kerosines, alkylate bottoms, and whatever else is available from refinery streams. Those with best heat stability, by laboratory test, could then be blended into jet fuels meeting required... 

To meet military supply and demand it often becomes necessary to maintain large supplies of jet fuels at various locations thruout the world. This fuel must be stable so it can be available for immediate use. While fuel can be kept relatively new in some areas by means of stock rotation, this may not be possible in others. This brings up the problem of stability in standing storage... 

Jet fuels can be made from a very broad hydrocarbon range, in fact, anywhere from 150°F to 600°F depending upon specifications. Fuels consist of certain quantities of straight run, cata-lytically cracked, and thermal cracked material. Stability-wise, straight run is most stable thermal cracked least stable. Hence, most blends end up intermediate... 

The present status of jet fuel technology can be aptly described as being at the same point as motor fuel technology 25 years ago. Volatility and stability requirements have been recognized and current research activities are directed toward the solution of these problems. 

Hundred Milliters Thermal Stability, Jet Fuel Thermal D 1660 (See Text) No. 1 No. 1 ... 

For jet fuels, a visual rating of No. 1 or No. 2 is required at 260°C in the jet fuel thermal oxidation stability test (JFTOT-ASTM D 3241). Also, a pressure drop of less than 25 mm Hg is required in this test, As shown in Table XI, the 250°F+ product from hydrotreated Illinois H-Coal syncrude passes both parts of the JFTOT test, even when the jet fuel is not refined enough to pass three other specifications aromatic content, smoke point, and gum content. When jet fuels are prepared from coal-derived syncrudes, the smoke point appears to be the limiting specification. The gum content and end point specifications are met when the jet fuels are distilled at 600°F. 

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