US2945342A - Thermal stability additive in hydrocarbon jet fuels - Google Patents

Description

United States PatentOffice 2,945,342 Patented July 19, 1960 THERMAL STABILITY ADDITIVE IN HYDROCARBON JET FUELS Robert M. SchirmenBartlesville, kla., assignorto Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed May 9, 1958, Ser. No. 734,121

7 Claims. (Cl. 60--35.4)

This invention relates to an improved fuel. In another aspect it relates to a method of increasing the thermal stability of a jet or rocket fuel by incorporating an add tive therein. In still another aspect this invention relates to a method of operating a jet or rocket engine in which the fuel before combustion is subjected to high temperatures. 7

Jet engines including both the ram jet and turbo jet types operate on the thrust delivered when fuel is sprayed into a combustion chamber and burned continuously in a confined space. The hot products of combustion exhaust through a tube extending rearwardly from the engine. Many types of rocket engines operate on the same principle except that the required oxygen is supplied independently of the atmosphere. iln aircraft or missiles which achieve supersonic speeds the, fuel is subjected to relatively high temperatures as it passes through the conduits from the storage tanks to the combustion chamber. For example, at a speed of Mach 2 the air entering a jet engine is at a temperature of about 400 F. while at a speed of Mach 4 the ram air temperature would reach 1000" F. Also in some engines, jet fuel is used to cool the lubricant oil thereby adding more heat to the fuel. Some fuels are unstable at high temperatures and deposits form in the fuel lines tending to plug the nozzles in the combustion zone. 'At temperatures up to about 400 F. many of the usual detergent-disperant type additives are effective in alleviating the problems of deposits and 'filterability. However, at higher temperatures the usual detergent-dispersant type additives tend to promote deposit formation and plug fuel system filters.

I have discovered that the thermal stability of jet or rocket fuels can be' improved by incorporating therein an extract from an oily carbon black. By forming a furnace black having a photelometer reading less than 50, extracting the oily deposit with a suitable solvent and adding from 1 to 1000 parts per million of this extract to a jet type-fuel, the thermal stability of the fuel at temperatures above 400 F., can be improved. By practicing my invention a jet or rocket engine can be operated under conditions which subject the fuel in the fuel lines to temperatures above400 F. with the problems of filter plugging considerably reduced.

It is an object of my invention to provide an improved fuel. Another object is to provide 'an additive which can be incorporated into a jet or rocket fuel to improve its thermal stability. Still another object of my invention is to provide a method by which thermal stability of a jet fuel can be improved Another object is to provide a method of operating a jet 'or rocket engine under conditions which subject the fuel in the fuel lines to temperatures above 400 F. Other objects, advantages and features of my invention will be apparent to those skilled in the art from the following disclosure and claims,

A wide range of fuel compositions can be employed in jet engines. In general, the jet fuel should possess a low freezing point, burn With a stable flame, be non-corrosive, not form coke upon combustion, and have a high B.t.u. content per gallon. Jet fuels are generally hydrocarbons in the gasoline and kerosene boiling range and can be obtained from crude oil, gas oil, residual oils, shale oils, tars, or the like. My invention can be employed with both leaded and non-leaded fuels and the fuel can con tain other additives such as various phosphorus compounds to improve its stability or performance. A set of specifications which indicate the general properties of a typical jet fuel is as follows:

1. Freezing point -40 C. max. 2. Kinematic viscosity 6 centistokes max. 18 C. 3. Flash point 38 C. min. 4. Sulfur content 0.20% by Wt. max. 5. Corrosion Only slight discoloration of copper strip. 6. Gravity No specification. 7. Accelerated gum 20 mg./ ml. max. 8. Residue (air-jet method)". 10 mg./ 100 ml. max. 9. Aromatics content 20% max. 10. Water tolerance Substantially immiscible. ll. Distillation:

' Percent olf at 410 F 10% min.

Final B. Pt., F 550-600. Loss 1 /2% max. 12. Heat of combustion 18,300 B.t.u./1b., min.

The above specifications have been considered satisfactory by commercial airlines. Other specifications for jet aircraft fuels 7 include those of MIL-F-5624C and MIL-P-25656 (USAF). While some jet fuels are inherently more thermally stable than others, it is Within the scope of my invention to improve the thermal stability of any jet aircraft type fuel by adding thereto the carbon black extract described.

Rocket fuels for which my invention can be used are ofthe same general type as the jet fuels described above, being generally hydrocarbons of high B.t.u. content. Kerosene is a suitable rocket fuelwhen used with an oxidant such as liquid oxygen or hydrogen peroxide. The fuel and oxidant comprise what is known as -a bipropellant. To obtain the additive for my invention carbon black is formedin a furnace'with partial combustion so that a tarryor oilyblack is the product. Many different kinds of. fuels can be used to make such a carbon black. For example, adegraded recycle gas oil can be employed, or other oils, such as kerosene, gasoline boiling range hydrocarbons, light or heavy naphthas, or heavier oils are. satisfactory. Other hydrocarbon materials such as natural gas or refinery residue gas can be used. Broadly, any hydrocarbon can be used as the furnace feed and the charge stocks can contain saturated'or unsaturated hydrocarbons, parafiins, olefins, aromatics, naphthenes, or the like, I prefer to employ carbon black whichhas been formed from a highly. aromatic fuel, such as S0 extract oil oran aromatic cycle oil from catalytic cracking. Whatever the fuel that, is used, the conditions of furnace operation can be controlled by those skilled in thisart to produce a suitable black by partial combustion. The carbon black employed for my invention should have a photelometer reading less than 50 and preferably less than 20. Dily blacks having a photelometer reading. of about 10 are highly'satisfactory. A photelometer reading of a carbon black is an indica tion of the tar content of the black as determined by the amount of light which a standard sample of a chloroform extract transmits. The tar content of the carbon black is determined by mixing 2 grams of black with 50 cc. of chloroform, boiling the mixture, filtering out the carbon black, and determining the percentage of light transmittance of the filtrate as compared with the transmittance of a blank sample of chloroform. The comparison is preferably conducted with a photoelectric colorimeter. Thev photelometer reading is the percentage of light transmittance.

The fuel additive is obtained from the oily black by any suitable solvent, preferably using a solvent which can be added directly to the fuel without deleterious effects. Most hydrocarbon solvents are suitable and even chloroform can be used if the additive is recovered by distillation and redissolved in a solvent for adding to the fuel. Suitable solvents include kerosene, benzene, toluene, naphtha, cyclohexane, methylcyclohexane and the like.

Sufficient extract or solution should be added to the fuel in order to provide from 1 to 1000 parts of additive per million parts of fuel on a weight basis. Preferably, for best results in improved thermal stability and overall performance, the amount of additive in the fuel should be in the range of about 1 to 100 parts per million. The additive itself which is extracted from the carbon black is a brown, waxy material which boils above 600 F.

In the operation of a jet or rocket engine according to my invention a fuel is employed which contains the abovedescribed additive in the prescribed amount. This fuel can be subjected to temperatures above 400 F. and then passed through the filters and nozzle of the fuel system into the combustion chamber. In addition to improving the thermal stability of the fuel by reducing deposits and improving filterability, the additive of my invention has the added advantage over many other additives for this purpose in that it is insoluble in water and thus will not be leached out of the fuel when the fuel is stored over water, as is often done on aircraft carriers. Also, my additive increases the electrical conductivity of the fuel, thereby reducing the possibility of building up static charges of electricity in the fuel as it flows through the fuel lines.

Advantages of this invention are illustrated by the following examples. The reactants, and their proportions, and other specific conditions are presented as being typical and should not be construed to limit the invention unduly.

Example I Carbon black (a soft furnace black) produced from a highly aromatic heavy residuum and having a photelometer reading of 10 percent was extracted with kerosene to recover the tarry additive employed in this invention. One hundred (100) grams of the oily carbon black was extracted with 1600 milliliters of kerosene up to 600 F. A non-volatile residue which was a brown, dry, waxy material was recovered in an amount indicating a concentration of 700 milligrams of additive per liter of kirosene solution formed on extraction of the carbon blac Two hundred fifteen (215) milliliters of this solution was added to gallons of kerosene to give about p.p.m. of additive in the fuel. Three runs were made to determine the thermal stability of this kerosene, two runs without the additive (runs 2 and 3) and one run with the additive in the concentration of 10 ppm. (run 1). The test procedure was the Tentative Standard Method 3464-T (June 1, 1957), for Thermal Stability of Gas Turbine Fuels (part of Federal Test Method Standard No. 791 and described in the Coordinating Research Council, Inc. Manual No. 3). The manual operating procedure was used with the CFR Fuel .Coker. Results were as follows:

Filter Block Total Test Time (Minutes) Time to Pressure Drop (Minutes) Additive (pr- Preheater Rating Run Fuel Pressure (inches of Hg) Kerosene... do do CDO oro NNM more The above data show a marked improvement in the thermal stability of the fuel containing the carbon black extract. Pressure drop through the filter didnt approach the maximum for the full duration of the test for the fuel containing my additive while the preheater rating remained high. In contrast, fuel without the additive reached maximum pressure drop in less than half the run time.

The kerosene used had the following specifications:

Flash point, F. 142 Gravity, API 41.7 ASTM distillation, F.:

IBP 5% 10% 20% 40% 50% 0% End point 52,7 Recovery, percent 99 Sulfur, weight percent 0.024 Mercaptan sulfur, weight percent Neg. Copper strip corrosion Neg. Color ,+28 Smoke point, millimeters of flame height 19.5

Example II An oily carbon black was produced by passing a S0 extract oil into a porous combustor. The combustor can, which was 9 /2 inches long with an internal diameter of 2 inches, was constructed of porous stainless steel. The primary air inlet system consisted of four rows of A-inch holes, each row consisting of six holes equally spaced circumferentially around the can. The distance from the edge of the can to the center of the first row of holes was one inch, and subsequent rows were spaced at 1%- inch center to center. Quench air entered through two rows of holes, each consisting of six /2-iuch holes equally spaced circumferentially around the can, these rows continuing the 1 /z-inch center-to-center spacing of the primary air holes. Air, preheated to 500 F., was fed at a rate of one pound per second. Unpreheated oil was fed axially through a 29 gal/hour Monarch nozzle at a rate of 180 pounds per hour. The total air and oil feed to the reactor was fuel rich, and produced a carbon black having a photelometer reading of about 10.

Two grams of the above described oily black was extracted with cubic centimeters of kerosene using successive 10 cc. washings. The solution extract was then added to 5 gallons of kerosene and the resulting fuel was tested for thermal stability as described in Example I except that the recirculation method was used with a one quart sample. The fuel flow rate was 6 pounds per hour and the test time was 2 hours. The preheater temperature was 450 F. and the filter black temperature was 550 F. Two runs were made with the same fuel without the additive of my invention. The preheater rating of all runs was 4 on the Coordinating Research Council scale. Using a rating method which takes into account appearance, quantity and location of preheater deposits, the fuel containing my additive showed considerable improvement in this area. On a scale of zero to one hundred, zero being 100 percent coverage by black lacquer and one hundred being 100 percent clean, the preheater rating of the two fuels containing no additive was 58 and 58.3 while the rating of the fuel containing the carbon black extract was 71.5. This rating is made by evaluating each of four equal segments along the length of the preheater tube, multiplying each rating by a weighting factor, and adding the products to arrive at the final rating. The rating of each segment is obtained by multiplying the fraction of each segment covered by a particular deposit times a number assigned that deposit identity. These numerical ratings are as follows:

Deposit identity: Numerical rating Clean 10.0 Light amber lacquer 7.5 Medium amber lacquer 5.5 Dark amber lacquer 4.0 Light brown lacquer 2.8 Medium brown lacquer 1.9 Dark brown lacquer 1.2 Light black lacquer 0.7. Medium black lacquer 0.3 Black lacquer 0.0

The weighting factors for segments 1 through 4, segment 1 being nearest the fuel inlet and 4 being nearest the outlet, are as follows:

Segment 1 Segment 2 Segment 3 Segment 4 A pressure drop of 25 inches of mercury across the filter was reached in 29.3 and 29.8 minutes for the fuel without my additive. With the kerosene containingthe additive, a pressure drop of 25 inches of mercury across the filter was reached in 71.5 minutes. It is thus evident that the additive is responsible for a considerable improvement in filterability of the fuel.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope thereof.

I claim:

1. A method of operating a reaction engine in which the fuel is subjected to elevated temperatures before combustion which comprises supplying to said engine a hydrocarbon fuel containing as an additive from 1 to 1000 parts per million of the hydrocarbon soluble extract from an oily carbon black which before extraction had a photelometer reading less than 50, subjecting said fuel to a temperature in excess of 400 F. prior to combustion, and burning said fuel in the combustion chamber of said engine.

2. A method of operating a reaction engine in which the fuel is subjected to elevated temperatures before combustion which comprises supplying to said engine a hydrocarbon fuel containing from 1 to parts per million of the hydrocarbon soluble extract boiling above about 600 F. obtained from an oily carbon black which before extraction had a photelometer reading below 20, subjecting said fuel to a temperature in excess of 400 F.

prior to combustion, and burning said fuel in the combustion chamber of said engine.

3. A hydrocarbon jet fuel having improved thermal stability containing from 1 to 1000 parts per million of the hydrocarbon soluble extract from an oily carbon black which before extraction had a photelometer reading less than 50.

4. A hydrocarbon jet fuel having improved thermal stability containing from 1 to 100 parts per million of the hydrocarbon soluble extract from an oily carbon black which before extraction had a photelorneter reading less than 20, said extract being non-volatile, boiling above about 600 F.

5. A hydrocarbon jet fuel according to claim 4 wherein said carbon black is a furnace black prepared from a highly aromatic S0 extract oil.

6. A method of improving the thermal stability of a hydrocarbon jet 'fuel which comprises adding to said fuel from 1 to 1000 pants per million of the hydrocarbon soluble extract from an oily carbon black which before extraction had a photelometer reading less than 50.

7. A method of improving the thermal stability of a hydrocarbon jet fuel which comprises adding to said fuel from 1 to 100 parts per million of the hydrocarbon soluble extract of an oily carbon black which before extraction had a photelometer reading less than 20, said extract boiling above about 600 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,771,367 Thompson et a1 Nov. 20, 1956 2,771,368 Thompson et al. Nov. 20, 1956 2,82A,791 Osborg et al. Feb. 25, 1958 2,849,301 Gee Aug. 26, 1958

Claims (1)

1. A METHOD OF OPERATING A REACTION ENGINE IN WHICH THE FUEL IS SUBJECTED TO ELEVATED TEMPERATURES BEFORE COMBUSTION WHICH COMPRISES SUPPLYING TO SAID ENGINE A HYDROCARBON FUEL CONTAINING AS AN ADDITIVE FROM 1 TO 1000 PARTS PER MILLION OF THE HYDROCARBON SOLUBLE EXTRACT FROM AN OILY CARBON BLACK WHICH BEFORE EXTRACTION HAD A PHOTELOMETER READING LESS THAN 50, SUBJECTING SAID FUEL TO A TEMPERATURE IN EXCESS OF 400*F. PRIOR TO COMBUSTION, AND BURNING SAID FUEL IN THE COMBUSTION CHAMBER OF SAID ENGINE.