EP0078998A2 - Liquid hydrocarbon fuel containing a polyisobutylene and its use in a gas turbine powered aircraft - Google Patents

Abstract

The invention relates to a liquid hydrocarbon mixture having a flash point of at least 32 DEG C and containing a polyisobutylene having a molecular weight greater than 10<6> according to the viscosity average, the concentration of the polyisobutylene being 0.0010 to 0.0099 and preferably 0.0050 to 0.0095 per cent by weight. The liquid fuel mixtures can be used for driving aircraft fitted with gas turbines.

Description

The invention relates to a liquid hydrocarbon fuel mixture with a flash point of at least 32 ° C, which contains a polyisobutylene with a molecular weight from the viscosity average greater than 10 ⁶ dissolved.

With hydrocarbon fuels of this type, an additive is required which on the one hand reduces the tendency of the liquid to particulate distribution or spreading when the surface of the fuel is subjected to shock, but on the other hand does not impair the use of such fuel mixtures for propelling aircraft with gas turbines. The shock can be such that part of the liquid is converted into a dispersion of fine liquid droplets in air, ie in a mist. This mist can be dangerous if it is flammable. One situation in which it is most important to keep the formation of such a mist to a minimum under shock conditions is, for example, the emergency landing of a flying machine, which results in damage to the tanks filled with combustible fuel. Although hydrocarbons currently used for aircraft gas turbine engines have a higher flash point than aviation gasoline used in piston engine machines, mists of hydrocarbons with flash points of 32 ° C or higher strongly speak of ignition by flame, electrical sparks or friction and the presence of hot metal in the aircraft, and there is therefore a significant fire hazard immediately after a flying machine collision.

There is also a risk of fire spreading to the bulk of the liquid hydrocarbon fuel by igniting the mist even if there is initially only a small defect.

From GB-PS 1 259 113 it is already known to obtain an improved liquid hydrocarbon fuel with a reduced tendency to particulate propagation when exposed to shock by adding a polymer with a molecular weight of greater than ₁ 0 ⁶ to the liquid. The proportion of the dissolved polymer should be 0.1 to 2 percent by weight, suitable polymers are polyisobutylene or an ethylene-propylene copolymer. According to known methods, the polymers are either dissolved directly in the liquid hydrocarbon or added to the fuel in the form of their aqueous dispersion, the water is removed and the polymer is simultaneously dissolved by appropriate heating.

However, such hydrocarbon fuel mixtures with the aforementioned additives have the disadvantage that they still contain residues of water and / or that a polymer degradation took place during the thermal dissolution process. In the first case, therefore, anti-jcing additives and in the other case higher polymer contents are required, which increases the viscosity of the liquid fuel and increases the precipitability of the polymer at low temperatures down to -40 ° C.

The same disadvantages listed above also occur in the processes known from the publications EP-A1 00 19 390, GB-PS 1 285 197, GB-PS 1 337 288 and GB-PS 1 384 536, in each of which a 0.1 to 2 percent by weight solution of a copolymer of tert-butylstyrene, polymers of 2-ethylhexyl acrylate, polymers of 2-ethylhexyl acrylic acid and others be used in hydrocarbon fuels.

The object of the invention was to find a liquid hydrocarbon fuel with flash points of at least 32 ° C. which does not have the disadvantages mentioned above and which has a relatively small particle-shaped spread when exposed to shock, i.e. The formation of fog, shows and the risk of explosion and burning properties when subjected to shock is therefore considerably reduced.

This task was solved according to the invention in that the concentration of the polyisobutylene is 0.0010 to 0.0099, preferably 0.0050 to 0.0095 percent by weight, based on the weight of the fuel mixture.

For use in accordance with the invention, the liquid hydrocarbon fuel should have a flash point of at least 32 ° C (determined according to the test method ASTM Standard D 93).

Suitable liquid hydrocarbon fuels with which the invention can be used include aircraft turbine fuels of the JP-8 quality (flash point at least 43 ° C., described in the "US Military Specification NIL-T-83 133"), the JP-5 quality ( Flash point min. 60 C, described in the "US Military Specification MIL-T-5 624 G"), the qualities Jet A and JetA-1 (flash point min. 43 ⁰ C, described in the "ASTM Specification DI 655/66 T ") and the quality AVTUR-NATO with the code No. F-35 (Flash point min. 38 ° C, described in the "UK Ministry of Aviation Specification", NO. D.Eng. RD 2494 (Issue 4).

• a) N,N'-Diisopropylparaphenylendiamin
• b) N,N^r-Disek.-butylparaphenylendiamin
• c) 2,6-Ditert.-butyl-4-methylphenol
• d) 2,4-Dimethyl-6-tert.-butylphenol
• e) 2,6-Ditert.-butylphenol
• f) min. 75 % 2,6-Ditert.-butylphenol max. 25 % Tert.-und Tritert-butylphenol
• g) min. 72 % 2,4-Dimethyl-6-tert.-butylphenol max. 28 % Monomethyl- und Dimethyltert.-butylphenol
• h) min. 65 % N,N'-Disek.-butylparaphenylendiamin max. 35 % N,N'-Disek.-butylorthophenylendiamin

The liquid hydrocarbon fuels that are suitable for use in an aircraft described with gas turbines can contain, for example, the following antioxidants:

• a) N, N'-Diisopropylparaphenylenediamine
• b) N, N ^r- Disek.-butylparaphenylenediamine
• c) 2,6-di-tert-butyl-4-methylphenol
• d) 2,4-dimethyl-6-tert-butylphenol
• e) 2,6-di-tert-butylphenol
• f) min. 75% 2,6-di-tert-butylphenol max. 25% Tert.- and Tritert-butylphenol
• g) min. 72% 2,4-dimethyl-6-tert-butylphenol max. 28% monomethyl and dimethyl tert-butylphenol
• h) min. 65% N, N'-Disek.-butylparaphenylenediamine max. 35% N, N'-dis-butylorthophenylenediamine

These materials are usually present in an amount of no more than 24 mg / l, and preferably at least 8.6 mg / l.

• - einen Metalldesaktivator wie N,N'-Disalicyliden-1,2-propandiamin, in einer 5,8 mg/l nicht überschreitenden Menge,
• - einen Korrosionsinhibitor (eine relevante "U.S. Military Specification" für kraftstofflösliche Korrosionsinhibitoren ist MIL-1-25 017), ein Frostschutzmittel, wie Ethylenglykol-oder Diethylenglykolmonomethylether oder eine Mischung desselben mit Glycerin (eine geeignete Menge beträgt 0,10 bis 0,15 Volumprozent des Kraftstoffs; eine relevante "U.S. Military Specification" für Kraftstoffsystem-Frostschutzmittel ist MIL-1-27-686), und
• - einen antistatischen Zusatz, wie Shell Antistatic Additive ASA-3, in einer Konzentration von nicht mehr als 1,0 Teile je Million. Durch Verwendung dieses Zusatzes kann die elektrische Leitfähigkeit des Kraftstoffs in den Bereich von 50 bis 300 Pico-Siemens/Meter eingestellt werden.

The fuel may also contain:

• a metal deactivator such as N, N'-disalicylidene-1,2-propanediamine, in an amount not exceeding 5.8 mg / l,
• a corrosion inhibitor (a relevant "US Military Specification" for fuel-soluble corrosion inhibitors is MIL-1-25 017), an antifreeze such as ethylene glycol or diethylene glycol monomethyl ether or a mixture thereof with glycerol (a suitable amount is 0.10 to 0.15 volume percent fuel; a relevant "US Military Specification" for fuel system antifreeze is MIL-1-27-686), and
• an antistatic additive, such as Shell Antistatic Additive ASA-3, in a concentration of not more than 1.0 part per million. By using this additive, the electrical conductivity of the fuel can be set in the range of 50 to 300 Pico-Siemens / meter.

The polyisobutylene used is a polymer of isobutylene with a molecular weight from the viscosity average greater than 10 ^6. Such polymers of isobutylene are known per se and, for example, in the reference "Chemical technology of plastics in individual representations of polyisobutylene" Springer-Verlag, Berlin / Göttingen / Heidelberg, 1959, pages 77 to 105. The polyisobutylene used in the above-cited GB-PS 1 259 133 can also be used in the process according to the invention. The molecular weight of the polyisobuylene viscosity agent, determined in isooctane solution at 20 ° C. and a concentration of 0.1 g / 100 ml) should suitably be between 2.5 to 7.0 · 10 ⁶ , preferably 3.5 to 6.0 · 10 ⁶ lie.

For the preparation of the claimed solutions of polyisobutene in fuels, all processes are suitable which work under conditions which ensure that the original molecular weight is maintained.

As a way of making a polyisobutylene solution. under gentle conditions the solid polymer can be e.g. Simply add 20 ° C to the fuel. The solution then occurs after 3 - 10 days without any further mechanical or thermal measure. Accelerating the dissolving process and therefore advantageous is a division of larger pieces into smaller parts, z.3. by cutting with a knife or scissors.

The polyisobutylene can also be dissolved directly in the intended application concentration or via a concentrate in the fuel, which is then further diluted.

It is an advantage of the hydrocarbon fuel mixture according to the invention that the viscosity of the liquid hydrocarbon fuel is increased only slightly by the small addition of polyisobutylene. Another advantage is that the polyisobutylene dissolved in the liquid hydrocarbon fuel remains in solution down to -40 ° C and does not fail.

To demonstrate the fog formation property (antimisting effect), the polyisobutylene Oppanol B 230 with a molecular weight from the solution viscosity of 5.7 · 10 ^{6 was dissolved} in aviation turbine fuel (JP-5). The solvent JP-5 (NATO Code F 44) used is a kerosene with a high flash point. The following physical properties are mentioned:

Die Versuche werden wie folgt ausgeführt:

The tests are carried out as follows:

A constantly lit pilot flame was attached to a rail and a holder for a spray can was attached at a distance of 15-20 cm on the same rail.

The spray can (type 60Z aluminum monoblock) was filled with 40 g Oppanol B 230 solution and 60 g propellant gas, consisting of a mixture of 50% fluorotrichloromethane and 50% difluorodichloromethane, for all tests.

The spray can was then attached to the rail so that the jet was directed horizontally across the pilot light. The drain valve was operated by hand and the volume of the flame was photographed. Experiments 1-5 with Oppanol B 230 additions of 0, 5, 10, 25 and 95 ppm by weight show the reduction in the burning intensity of the flame with increasing addition of Oppanol.

A reduction in the volume of the flame front can be estimated as follows:

This means that by adding 95 ppm by weight of Oppanol B 230, the fuel combustion and thus the relative flame volume can be reduced by approximately 80%, based on the non-additive JP-5 aviation fuel.

Claims (3)

_1st Liquid hydrocarbon fuel mixture with a flash point of at least 32 ° C, which contains a polyisobutylene with a molecular weight from the viscosity average greater than 10 ⁶ dissolved, characterized in that the concentration of the polyisobutylene 0.0010 to 0.0099 percent by weight, based on the weight of the fuel mixture , is. 2. Liquid hydrocarbon fuel mixture according to claim 1, characterized in that the concentration of polyisobutylene is 0.0050 to 0.0095 percent by weight. 3. Use of the liquid fuel mixture according to claim for driving aircraft with gas turbines.